CN115104175A - Large area III-nitride crystals and substrates, methods of making and methods of using - Google Patents

Large area III-nitride crystals and substrates, methods of making and methods of using Download PDF

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CN115104175A
CN115104175A CN202180013902.7A CN202180013902A CN115104175A CN 115104175 A CN115104175 A CN 115104175A CN 202180013902 A CN202180013902 A CN 202180013902A CN 115104175 A CN115104175 A CN 115104175A
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group iii
degrees
iii metal
metal nitride
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德鲁·卡德威尔
马克·P·德`伊夫林
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Slt Technology Co
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Slt Technology Co
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Abstract

Embodiments of the present disclosure include techniques related to processing materials used to fabricate group III metal nitrides and gallium-based substrates. More specifically, embodiments of the present disclosure include techniques for producing large area substrates using a combination of processing techniques. By way of example only, the present disclosure may be applied to growing crystals of GaN, AlN, InN, InGaN, AlGaN, AlInGaN, and the like to fabricate bulk or patterned substrates. Such bulk or patterned substrates can be used in a variety of applications including optoelectronic and electronic devices, lasers, light emitting diodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, and transistors, among others.

Description

Large area III-nitride crystals and substrates, methods of making and methods of using
Background
Technical Field
The present disclosure relates generally to techniques for processing materials to fabricate gallium-containing nitride substrates and the utilization of these substrates in optoelectronic and electronic devices. More specifically, embodiments of the present disclosure include techniques for producing large-area crystals and substrates using a combination of processing techniques.
Description of the related Art
Gallium nitride (GaN) based optoelectronic and electronic devices are of great commercial importance. However, the quality and reliability of these devices are affected by high defect levels, particularly threading dislocations, grain boundaries and strain in the semiconductor layers of the devices. Threading dislocations may be caused by lattice mismatch of the GaN-based semiconductor layer with a non-GaN substrate (such as sapphire or silicon carbide). The grain boundaries may be caused by a coalescence front of the epitaxially overgrown layer. Other defects may be caused by thermal expansion mismatch, impurities, and tilt boundaries, depending on the details of layer growth.
The presence of defects has a deleterious effect on the epitaxially grown layer. Such effects include compromising electronic device performance. To overcome these drawbacks, techniques have been proposed that require complex, cumbersome manufacturing processes to reduce the concentration and/or impact of the defects. Although a number of conventional growth methods for gallium nitride crystals have been proposed, limitations still exist. That is, conventional methods are still worth improvement to save cost and increase efficiency.
Progress has been made in the growth of large area gallium nitride crystals with significantly lower defect levels than heteroepitaxial GaN layers. However, most techniques for growing large area GaN substrates involve depositing GaN on non-GaN substrates such as sapphire or GaA. This method typically produces an average concentration of 10 on the surface of a thick ingot 5 -10 7 cm -2 Threading dislocations, and significant bending, stress and strain. For many applications, it is desirable to reduce the concentration of threading dislocations. When the boule is sliced into wafers, bow, stress and strain can result in low yield, make the wafers prone to cracking during downstream processing, and can also negatively impact device reliability and lifetime. Another consequence of bending, stress and strain is that during growth in the m-plane and semi-polar directions, significant concentrations of stacking faults may be generated even by near equilibrium techniques such as ammonothermal growth. Furthermore, the quality of c-plane growth may be unsatisfactory due to the formation of cracks, multiple crystalline domains, and the like. The ability to fabricate substrates larger than 2 inches is currently very limited, as is the ability to produce large area GaN substrates with nonpolar or semipolar crystallographic orientation. Most large area substrates are manufactured by vapor phase processes such as Hydride Vapor Phase Epitaxy (HVPE), which is relatively expensive. A less expensive process is desired while also achieving large areas and low threading dislocation densities as quickly as possible.
Ammonothermal crystal growth has many advantages over HVPE as a method of fabricating GaN boules. However, the performance of the ammonothermal GaN crystal growth process may depend significantly on the size and quality of the seed crystal. Seeds produced by HVPE may suffer from many of the limitations described above, and large area ammonothermally grown crystals are not widely available.
The conventional art has proposed a method of merging elemental GaN seed crystals into a larger composite crystal by a tiling method. Some conventional methods use a primary GaN seed crystal grown by Hydride Vapor Phase Epitaxy (HVPE) and involve polishing the edges of the primary crystal at an oblique angle to cause coalescence in the direction of rapid growth. Many or most conventional methods use HVPE as the crystal growth method to incorporate the seeds. However, such conventional techniques have limitations. In general, for example, conventional techniques do not specify the accuracy of crystallographic orientation (polarity and azimuth) between the merged elemental seeds, nor provide methods that can produce highly accurate crystallographic registration between the elemental seeds and minimize defects resulting from the merging of the elemental seeds. Ammonothermal GaN typically has a different, at least slightly different, lattice constant than HVPE GaN. Even a small mismatch in lattice constants can lead to stresses and cracks in the ammonothermally grown crystals on HVPE seeds, particularly when tiling and coalescence are involved. Additionally, cracks may develop during sawing or polishing of the ammonothermal grown crystals subsequently formed on one or more HVPE seeds.
Due at least to the above problems, there is a need for substrates having a lower defect density and formed by techniques that improve the crystal growth process. Moreover, as can be seen from the foregoing, techniques for improving crystal growth are highly desirable.
Disclosure of Invention
Embodiments of the present disclosure include a free-standing group III metal nitride crystal. The self-supporting crystal includes a wurtzite crystal structure having a first surface with a maximum dimension in a first direction of greater than 40 millimeters and less than 10 3 cm -1 Average stacking fault concentration of (a); between 10 1 cm -2 And 10 6 cm -2 Wherein the average threading dislocation concentration on the first surface varies periodically at least two times in a first direction with a period of variation between 5 microns and 20 millimeters, and a miscut angle that varies 0.1 degrees or less at a center 80% of the first surface of the crystal along the first direction and varies 0.1 degrees or less at the center 80% of the first surface of the crystal along a second direction orthogonal to the first direction. The first surface comprises a plurality of first regions, each of the plurality of first regions having a concentration of between 5cm -1 And 10 5 cm -1 A local approximately linear array of threading dislocations therebetween, the first surface further comprising a plurality of second regionsEach of the plurality of second regions disposed between adjacent pairs of the plurality of first regions and having a height of less than 10 5 cm -2 Has a threading dislocation concentration of less than 10 3 cm -1 And the first surface further comprises a plurality of third regions, each of the plurality of third regions disposed within one of the plurality of second regions or between adjacent pairs of the second regions and having a minimum dimension of between 10 microns and 500 microns and a concentration of between 10 microns 3 cm -2 And 10 8 cm -2 Threading dislocations in between.
Embodiments of the present disclosure include a free-standing group III metal nitride crystal comprising at least two crystal domains (domains). Each of the at least two domains comprises a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen. Each of the at least two domains has a wurtzite crystal structure and comprises a first surface having a maximum dimension greater than 10 millimeters in a first direction between 10 1 cm -2 And 1X10 6 cm -2 Average threading dislocation concentration of less than 10 3 cm -1 An average stacking fault concentration of less than 200 arcsec, a symmetric x-ray rocking curve full width at half maximum of greater than 10 17 cm -3 And an impurity concentration of H of more than 10 15 cm -3 As quantified by calibrated secondary ion mass spectrometry, impurity concentrations of at least one of Li, Na, K, F, Cl, Br, and I. The threading dislocation concentration within the first surface of the domains on the first surface may vary periodically at least two times in the first direction with a period of variation in the first direction between 5 microns and 5 millimeters. The first surface comprises a plurality of first regions, each of the plurality of first regions having a concentration of between 5cm -1 And 10 5 cm -1 A local approximately linear array of threading dislocations therebetween, the first surface may further comprise a plurality of second regions, each second region of the plurality of second regions being disposed between an adjacent pair of the plurality of first regions and having less than 10 angstroms 5 cm -2 Is worn onSum of threading dislocation density less than 10 3 cm -1 Stacking fault density of (a). The first surface further comprises a plurality of third regions, each of the plurality of third regions disposed within one of the plurality of second regions or between adjacent pairs of the second regions and having a minimum dimension of between 10 microns and 500 microns and a concentration of between 10 microns 1 cm -2 And 10 6 cm -2 Threading dislocations in between. The free-standing group III metal nitride crystal has a maximum dimension greater than 40 millimeters in a first direction, crystallographic miscut varies by 0.2 degrees or less in two orthogonal directions at a center 80% of the crystal along the first direction, and varies by 0.1 degrees or less in two orthogonal directions at the center 80% of the crystal along a second direction orthogonal to the first direction, and the at least two domains have a linear density of between about 50cm -1 And about 5X 10 5 cm -1 And the polar orientation difference angle gamma between the first and second domains is greater than about 0.005 degrees and less than about 0.2 degrees, and the orientation difference angles alpha and beta are greater than about 0.01 degrees and less than about 1 degree.
Embodiments of the present disclosure include a method for forming a composite group III metal nitride crystal, the method includes performing a bulk crystal (bulk crystal) growth process on a tiled array of at least two seeds in a crystal growth apparatus, wherein the bulk crystal growth process causes a bulk crystal layer grown from the first surface of the first seed and a bulk crystal layer grown from the first surface of the second seed to combine to form a composite crystal, a polar misorientation angle gamma between a crystalline orientation of the first surface of the first seed and a crystalline orientation of the first surface of the second seed is greater than about 0.005 degrees and less than about 0.2 degrees, and azimuthal orientation difference angles alpha and beta between the crystallographic orientations of the first surfaces of the first and second seed crystals are greater than about 0.01 degrees and less than about 1 degree, and each seed crystal contains nitrogen and at least one of gallium, aluminum, and indium and has a wurtzite crystal structure and a maximum dimension of at least 5 millimeters. In some embodiments, the bulk crystal growth process is performed at a first temperature, the tiled array of at least two seeds is positioned on a first surface of a mechanical fixture during the bulk crystal growth process, the mechanical fixture comprises at least a back plate member and a clamping member, each of the back plate member and the clamping member has a coefficient of thermal expansion that is between 80% and 99% of a coefficient of thermal expansion of the at least two seeds averaged over a range between room temperature and the first temperature, and the coefficient of thermal expansion is measured in a plane parallel to the first surface.
Embodiments of the present disclosure include a method for forming a composite group III metal nitride crystal, the method comprising placing at least two seeds each having a first surface on a mechanical fixture, placing the mechanical fixture into a crystal growth apparatus, and performing a bulk crystal growth process at a second temperature such that the first and second seeds are merged into a composite crystal, wherein each seed comprises nitrogen and at least one of gallium, aluminum, and indium and has a wurtzite crystal structure and a maximum dimension of at least 5 millimeters. The mechanical fixture includes at least a backing plate member and a clamping member, each of which has a coefficient of thermal expansion between 80% and 99% of the coefficient of thermal expansion of at least two seeds in the plane of the first surface averaged over a range between room temperature and a second temperature, and a polar orientation difference angle γ between the crystallographic orientation of the first surface of the first seed and the crystallographic orientation of the first surface of the second seed is greater than about 0.005 degrees and less than about 0.2 degrees, and azimuthal orientation difference angles α and β between the crystallographic orientations of the first surfaces of the first and second seeds are greater than about 0.01 degrees and less than about 1 degree.
Embodiments of the present disclosure include a method for forming a composite group III metal nitride crystal, the method comprising growing a polycrystalline group III metal nitride on a tiled array of at least two seeds, wherein the tiled array of at least two seeds comprises a first seed having a first surface and a second seed having a first surface and a second surface, and growing the polycrystalline group III metal nitride on the tiled array of at least two seeds such that layers of polycrystalline group III metal nitride grown from the second surfaces of the first seed and the second seed merge to form a tiled assembly; and performing a bulk crystal growth process on the tiled component in a crystal growth apparatus. The bulk crystal growth process causes a bulk crystal layer grown on the first surface of the first seed and a bulk crystal layer grown on the first surface of the second seed to merge to form a composite crystal, a polar orientation difference angle γ between the crystallographic orientations of the first surface of the first seed and the first surface of the second seed is greater than about 0.005 degrees and less than about 0.2 degrees, and azimuthal orientation difference angles α and β between the crystallographic orientations of the first surfaces of the first and second seeds are greater than about 0.01 degrees and less than about 1 degree, and each seed contains nitrogen and at least one of gallium, aluminum, and indium and has a wurtzite crystal structure and a maximum dimension of at least 5 millimeters.
Embodiments of the present disclosure include a method for forming a composite group III metal nitride crystal, the method comprising growing a polycrystalline group III metal nitride on a tiled array of at least two seed crystals, separating the tiled assembly from a base; and performing a bulk crystal growth process on the tiled component in a crystal growth apparatus. The tiled array of at least two seeds includes a first seed having a first surface and a second surface; and a second seed having a first surface and a second surface, a tiled array of at least two seeds disposed on the base, the process of growing the polycrystalline group III metal nitride on the tiled array of at least two seeds causing the layers of polycrystalline group III metal nitride deposited on the second surfaces of the first and second seeds to merge to form a tiled assembly. The bulk crystal growth process causes a layer of bulk crystal grown on the first surface of the first seed and a layer of bulk crystal grown on the first surface of the second seed to merge to form a composite crystal. A polar orientation difference angle γ between the crystallographic orientation of the first surface of the first seed and the crystallographic orientation of the first surface of the second seed is greater than about 0.005 degrees and less than about 0.2 degrees, and azimuthal orientation difference angles α and β between the crystallographic orientations of the first surfaces of the first seed and the second seed are greater than about 0.01 degrees and less than about 1 degree, and each seed comprises nitrogen and at least one of gallium, aluminum, and indium and has a wurtzite crystal structure and a maximum dimension of at least 5 millimeters.
Embodiments of the present disclosure include a method for forming a composite group III metal nitride crystal, the method comprising placing at least two seeds each having a first surface and a second surface opposite the first surface on a susceptor, placing the susceptor within a growth reactor and growing a polycrystalline group III metal nitride on the second surfaces of the at least two seeds to form a tiled assembly, separating the tiled assembly from the susceptor, and placing the tiled assembly into a crystal growth apparatus, and performing a bulk crystal growth process such that the first seeds and the second seeds merge into a composite crystal, wherein each seed comprises nitrogen and at least one of gallium, aluminum, and indium and has a wurtzite crystal structure and a maximum dimension of at least 5 millimeters. Each seed crystal contains nitrogen and at least one of gallium, aluminum and indium, and has a wurtzite crystal structure and a maximum dimension of at least 5 millimeters. A polar orientation difference angle γ between the crystallographic orientation of the first surface of the first seed and the crystallographic orientation of the first surface of the second seed is greater than about 0.005 degrees and less than about 0.2 degrees, and azimuthal orientation difference angles α and β between the crystallographic orientations of the first surfaces of the first and second seeds are greater than about 0.01 degrees and less than about 1 degree.
Embodiments of the present disclosure include a method for forming a composite group III metal nitride crystal, the method comprising growing a group III metal nitride crystal layer on an array of at least two first seeds, wherein each first seed of the array of at least two first seeds is arranged in an array extending along a first direction, and the process of growing the group III metal nitride crystal layer forms a first flat crystal; cutting the first flat crystal in a second direction orthogonal to the first direction, wherein cutting the first flat crystal forms at least two second seeds, and the at least two second seeds have a first surface; and growing a group III metal nitride crystal layer on the array of at least two second seeds, wherein each of the array of at least two second seeds is arranged in an array extending in the first direction, and the process of growing the group III metal nitride crystal layer on the array of at least two second seeds forms a second flat crystal. The method further includes cutting the second flat crystal in a second direction and the first direction to form at least two third seeds, and growing a group III metal nitride crystal layer on the at least two arrays of third seeds, wherein each third seed of the at least two arrays of third seeds is arranged in an array extending in the first direction, and growing the group III metal nitride crystal layer on the at least two arrays of second seeds forms a third flat crystal.
Embodiments of the present disclosure include a method for forming a composite group III metal nitride crystal, the method including placing at least two first seed crystals each having a first surface and a second surface opposite the first surface on a support structure in a first direction, performing a first bulk crystal growth operation to coalesce the at least two first seed crystals to form a first one-dimensional tiled crystal, cutting the first one-dimensional tiled crystal into at least two second seed crystals in a second direction orthogonal to the first direction, placing the at least two second seed crystals having a first surface and a second surface opposite the first surface on the support structure in a third direction orthogonal to the first direction and the second direction, performing a second bulk crystal growth operation to coalesce the at least two second seed crystals to form a second one-dimensional tiled crystal, cutting the second one-dimensional tiled crystal in the second direction and the first direction to form at least two third seed crystals, placing the at least two third seed crystals having a first surface and a second surface opposite the first surface on the support structure in a first direction, performing a third block-like crystal growth operation to coalesce the at least two third seed crystals to form third one-dimensional tiled crystals having a first surface and a second surface opposite the first surface and at least two domains. Each of the at least two domains within the third one-dimensional tiled crystal surrounds at least a portion of the at least two third seeds. A polar orientation difference angle γ between the crystalline orientation of the first surface of the first domain of the third one-dimensional tiled crystal and the crystalline orientation of the first surface of the second domain of the third one-dimensional tiled crystal is greater than about 0.005 degrees and less than about 0.2 degrees, and azimuthal orientation difference angles α and β between the crystalline orientations of the first surfaces of the first and second seed crystals are greater than about 0.01 degrees and less than about 1 degree. Each of the first seed crystal, the second seed crystal, and the third seed crystal includes nitrogen and at least one of gallium, aluminum, and indium, and has a wurtzite crystal structure. Each of the first, second, and third seeds includes a maximum dimension of at least 5 millimeters, and the crystallographic orientations of the first surface of each of the first, second, and third seeds are the same, with a difference within about 1 degree.
Embodiments of the present disclosure include a free-standing group III metal nitride substrate comprising at least two crystals, each of the at least two crystals comprising a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen. Each of the at least two crystals has a wurtzite crystal structure comprising a first surface having a maximum dimension greater than 10 millimeters in a first direction and a maximum dimension greater than 4 millimeters in a second direction orthogonal to the first direction, between 10 1 cm -2 And 1X10 6 cm -2 Average threading dislocation concentration in between, less than 10 3 cm -1 Average stacking fault concentration, symmetrical x-ray rocking curve full width at half maximum of less than 200 arc seconds. The free-standing group III metal nitride substrate has a maximum dimension in the first direction that is greater than 40 millimeters. The magnitude of crystallographic miscut of the first surface of each of the at least two crystals is equal, the difference being within 0.5 degrees, and the direction of crystallographic miscut of the first surface of each of the at least two crystals is the same, the difference being within 10 degrees. Each of the at least two crystals is bonded to a base member including polycrystalline GaN, and a difference angle γ in polarity orientation between the first domain and the second domain is greater than about 0.005 degrees and less than about 0.2 degrees, and difference angles α and β in orientation are greater than about 0.01 degrees and less than about 1 degree.
Embodiments of the present disclosure include a method for fabricating a free-standing group III metal nitride substrate including at least two domains, the method including depositing a layer of polycrystalline GaN on an array of at least two seeds disposed on a susceptor to form a tiled composite member, and separating the tiled composite member from the susceptor. The polycrystalline GaN layer forms a second surface of each of the at least two seed crystals opposite the first surface. Said toEach of the at least two seeds comprises a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen, and the at least two seeds having a wurtzite crystal structure comprise a first surface having a maximum dimension greater than 10 millimeters in a first direction and a maximum dimension greater than 4 millimeters in a second direction orthogonal to the first direction, less than about 2 x10 7 cm -2 Has an average threading dislocation concentration of less than 10 3 cm -1 And a symmetrical x-ray rocking curve full width at half maximum of less than 200 arc seconds.
Embodiments of the present disclosure include a method for fabricating a free-standing group III metal nitride substrate comprising at least two domains, the method comprising providing at least two seeds, each seed of the at least two seeds comprising a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen; placing the at least two seeds on a susceptor; depositing a polycrystalline GaN layer on a second surface of each of the at least two seed crystals opposite the first surface to form a tiled composite member; and removing the tiled composite member from the base. The at least two seeds having a wurtzite crystal structure comprise a first surface having a maximum dimension greater than 10 millimeters in a first direction and a maximum dimension greater than 4 millimeters in a second direction orthogonal to the first direction, less than about 2 x10 7 cm -2 Less than 10 3 cm -1 And a symmetric x-ray rocking curve full width at half maximum of less than 200 arc seconds. A polar orientation difference angle γ between the first surface of the first seed crystal and the first surface of the second seed crystal is greater than about 0.005 degrees and less than about 0.2 degrees, and orientation difference angles α and β are greater than about 0.01 degrees and less than about 1 degree.
Embodiments of the present disclosure include a free-standing group III metal nitride substrate comprising an array of seeds, wherein each seed in the array of seeds comprises a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen; and a polycrystalline GaN layer disposed over at least one surface of each seed within the array of seeds. With wurtzite crystal structureEach seed of the structure comprises a first surface having a thickness of between 10 1 cm -2 And 1x10 6 cm -2 Average threading dislocation concentration in between less than 10 3 cm -1 Average stacking fault concentration of (a). The magnitude of crystallographic miscut of the first surface of each seed is equal, the difference being within 0.5 degrees, and the direction of crystallographic miscut of the first surface of each seed is the same, the difference being within 10 degrees. A difference in polar orientation angle γ between a first seed of the array of seeds and a second seed of the array of seeds is greater than about 0.005 degrees and less than about 0.2 degrees, and difference in orientation angles α and β are greater than about 0.01 degrees and less than about 1 degree.
Embodiments of the present disclosure include a free standing group III metal nitride crystal comprising a wurtzite crystal structure, at least two domains, each of the at least two domains comprising a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen; a first surface having a maximum dimension in a first direction of more than 40 millimeters, the first surface comprising a domain surface of each of the at least two domains, wherein the domain surface of each of the at least two domains has a dimension in the first direction of at least 10 millimeters, less than 10 3 cm -1 And an average stacking fault concentration of between 10 1 cm -2 And 10 6 cm -2 Average threading dislocation concentration in between. An average threading dislocation concentration on a domain surface of each of the at least two domains periodically varies by at least two times in a first direction with a period of variation in the first direction between 5 microns and 20 millimeters. A domain surface of each of the at least two domains comprises a plurality of first regions, each of the plurality of first regions having a concentration between 5cm -1 And 10 5 cm -1 In between, locally approximate a linear array of threading dislocations. The domain surface of each of the at least two domains further comprises a plurality of second regions, each of the plurality of second regions being disposed between an adjacent pair of the plurality of first regions and having a thickness of less than 10 5 cm -2 Has a threading dislocation concentration of less than 10 3 cm -1 Stacking fault concentration of (a). The domain surface of each of the at least two domains further comprises a plurality of third regions, each of the plurality of third regions disposed within one of the plurality of second regions or between adjacent pairs of the second regions and having a minimum dimension of between 10 microns and 500 microns and a concentration of between 10 microns 3 cm -2 And 10 8 cm -2 Threading dislocations in between. The free-standing group III metal nitride crystal has crystallographic miscut that varies by 0.5 degrees or less in two orthogonal directions at a center 80% of the crystal along a first direction and varies by 0.5 degrees or less in two orthogonal directions at the center 80% of the crystal along a second direction orthogonal to the first direction. The at least two crystal domains have a linear density of between about 50cm -1 And about 5X 10 5 cm -1 And the polar orientation difference angle gamma between the first and second domains is greater than about 0.005 degrees and less than about 0.3 degrees, and the orientation difference angles alpha and beta are greater than about 0.01 degrees and less than about 1 degree.
Drawings
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, for other equivalent embodiments may be permissible.
Fig. 1A, 1B and 1C are simplified diagrams illustrating different stages of a method of forming a patterned photoresist layer on a seed or substrate according to an embodiment of the present disclosure.
Fig. 1D and 1E are simplified diagrams illustrating a method of forming a patterned mask layer on a seed or substrate according to an embodiment of the present disclosure.
Fig. 1F, 1G, 1H, 1I, and 1J are top views of an arrangement of openings in a patterned mask layer on a seed or substrate according to an embodiment of the present disclosure.
Fig. 1K and 1L are top views of an arrangement of openings in a patterned mask layer on a seed or substrate according to an embodiment of the present disclosure.
Fig. 1M and 1N are simplified diagrams illustrating different stages of a method of forming a patterned photoresist layer on a seed or substrate according to an alternative embodiment of the present disclosure.
Fig. 1O and 1P are simplified diagrams illustrating a method of forming a patterned mask layer on a seed or substrate according to an alternative embodiment of the present disclosure.
Fig. 1Q is a simplified diagram illustrating a method of forming a patterned trench within a seed or substrate according to an embodiment of the present disclosure.
Fig. 1R, 1S, and 1T are simplified diagrams illustrating an alternative method of forming patterned trenches within a seed or substrate according to embodiments of the present disclosure.
Fig. 2A, 2B, and 2C are simplified diagrams illustrating an epitaxial lateral overgrowth process for forming a large-area group III-metal nitride crystal according to an embodiment of the present disclosure.
Fig. 3A, 3B, and 3C are simplified diagrams illustrating an improved epitaxial lateral overgrowth process for forming large-area group III metal nitride crystals, according to embodiments of the present disclosure.
Fig. 3D and 3E are simplified diagrams illustrating an improved epitaxial lateral overgrowth process for forming large-area group III metal nitride crystals, according to an embodiment of the present disclosure.
Fig. 4A, 4B, and 4C are simplified diagrams illustrating methods of forming a free-standing ammonothermal group III metal nitride boule and a free-standing ammonothermal group III metal nitride wafer.
Fig. 5A-5E are simplified diagrams illustrating a first threading dislocation pattern and region on individual grains or domains of a self-supporting merged ammonothermal group III metal nitride boule or wafer according to an embodiment of the present disclosure.
Fig. 6A-6F are simplified diagrams illustrating a second threading dislocation pattern and region of a free-standing merged ammonothermal group III metal nitride boule or wafer according to an embodiment of the present disclosure.
Fig. 6G shows a free-standing consolidated ammonothermal group III nitride boule or wafer, according to an embodiment of the disclosure, characterized by a square pattern and formed by performing a crystal growth process on a tiled seed array configured as shown in fig. 1G.
Fig. 7A-7D are cross-sectional views illustrating methods and resulting optical and electronic devices according to embodiments of the present disclosure.
Fig. 8 is a top view (plan view) of a self-supporting laterally grown GaN boule or wafer formed by ammonothermal lateral epitaxial growth using a mask layer having openings arranged in a two-dimensional square array.
Fig. 9A, 9B, and 9C are top views of device structures, such as LEDs, according to embodiments of the present disclosure.
FIG. 10 is an optical micrograph of a polished cross section of a trench in a c-plane GaN substrate made according to an embodiment of the disclosure.
Fig. 11A and 11B are optical micrographs of a cross section of a c-plane ammonothermal GaN layer formed according to an embodiment of the disclosure, and close-up images from the same cross section.
Fig. 12A and 12B are plan view optical micrographs of a c-plane ammonothermal GaN layer that has been subjected to defect selective etching, showing a low concentration of etch pits in the window region above the slit-shaped mask opening oriented in the <10-10> direction and a linear array of etch pits (threading dislocations) at the coalescence front formed approximately midway between the two window regions, according to two embodiments of the present disclosure.
Figure 13 is a summary of x-ray diffraction measurements comparing the variation in miscut for a 50mm wafer manufactured according to one embodiment of the present disclosure with that of a commercially available 50mm wafer.
Figure 14 is a summary of x-ray rocking curve measurements comparing the full width at half maximum values of two reflections for a 50mm wafer made according to one embodiment of the present disclosure with the full width at half maximum values of two reflections for a commercially available 50mm wafer.
Fig. 15 is an optical micrograph of a laser cut profile of a trench in a c-plane GaN substrate made according to an embodiment of the present disclosure.
Fig. 16 is a plan view optical micrograph of a c-plane ammonothermal GaN layer that has been subjected to defect selective etching showing a low concentration of etch pits in the window regions above the slit-shaped mask openings oriented in the <10-10> direction and a linear array of etch pits (threading dislocations) at the coalescence front formed approximately midway between the two window regions, according to an embodiment of the present disclosure.
Fig. 17A to 17F are plan views of a seed crystal array according to an embodiment of the present invention.
Fig. 18A to 18D are schematic views of a fixture for holding a seed array during a substrate bulk crystal growth process according to an embodiment of the present invention.
Fig. 19A to 19D are schematic diagrams of seed arrays in various states in a process for forming a tiled composite substrate according to an embodiment of the present invention.
Figure 19E is a close-up view of a portion of a seed within the array of seeds shown in figure 19B, in accordance with an embodiment of the present invention.
FIG. 19F is a top cross-sectional view of a portion of a structure including the porous member and the polycrystalline GaN layer, as shown in FIG. 19B, according to an embodiment of the invention.
Fig. 19G is a top view of a tiled composite substrate according to an embodiment of the invention.
Fig. 20A is a schematic illustration of a seed suitable for use in a seed array, in accordance with an embodiment of the present invention.
Fig. 20B is a top view of a one-dimensional array of seeds including the seeds shown in fig. 20A, according to an embodiment of the invention.
Figure 20C is an end view of the one-dimensional seed array shown in figure 20B, in accordance with embodiments of the present invention.
Fig. 20D is a top view of the one-dimensional seed array shown in fig. 20B after a crystal layer is grown thereon, according to an embodiment of the present invention.
Figure 20E is an end view of the one-dimensional seed array shown in figure 20D, according to an embodiment of the present invention.
Fig. 21A illustrates a lateral portion formed in the one-dimensional seed array illustrated in fig. 20E by a desired manufacturing process according to an embodiment of the present invention.
Fig. 21B is a top view of a one-dimensional seed array formed using the lateral portion shown in fig. 21A, according to an embodiment of the present invention.
Fig. 21C is an end view of a transverse portion of the seed crystal shown in fig. 21B, in accordance with embodiments of the present invention.
Fig. 21D is a top view of the one-dimensional seed crystal array shown in fig. 21B after a crystal layer is grown thereon, according to an embodiment of the present invention.
Fig. 21E is a side view of the one-dimensional seed array shown in fig. 21D, in accordance with an embodiment of the present invention.
Fig. 22A illustrates a lateral portion formed in the one-dimensional seed array illustrated in fig. 21E by a desired manufacturing process according to an embodiment of the present invention.
Fig. 22B is a top view of the one-dimensional array of seeds of fig. 22A showing cuts along the coalescence front, in accordance with an embodiment of the present invention.
Fig. 22C is a top view of a one-dimensional array of seeds formed using a portion of the lateral portion formed by one or more of the fabrication processes described in conjunction with fig. 22A and 22B, in accordance with an embodiment of the present invention.
Figure 22D is an end view of the one-dimensional seed array shown in figure 22C, in accordance with an embodiment of the present invention.
Fig. 22E is a top view of the one-dimensional seed array shown in fig. 22C after a crystal layer is grown thereon, according to an embodiment of the present invention.
Fig. 22F is an end view of the one-dimensional seed array shown in fig. 22E, in accordance with an embodiment of the present invention.
Fig. 23A to 23C are schematic views of a composite substrate in various states in a process for forming an electronic device and recovering the composite substrate according to an embodiment of the present invention.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
Detailed Description
According to the present disclosure, techniques related to techniques for processing materials used to fabricate group III metal nitrides and gallium-based substrates are provided. More specifically, embodiments of the present disclosure include techniques for producing large area substrates using a combination of processing techniques. In some embodiments of the present disclosure, the large area substrate is referred to herein as a free-standing group III metal nitride wafer. Furthermore, in some embodiments, the formed or grown component configured to be further processed to form one or more free-standing group III metal nitride wafers is referred to herein as a free-standing group III metal nitride boule (boule). By way of example only, the present disclosure may be applied to growing crystals of GaN, AlN, InN, InGaN, AlGaN, AlInGaN, and the like to fabricate bulk substrates (bulk substrates) or patterned substrates. Such bulk or patterned substrates can be used in a variety of applications including photovoltaic devices, laser diodes, light emitting diodes, photodiodes, solar cells, photoelectrochemical water splitting and hydrogen generation, photodetectors, integrated circuits, transistors, and the like.
Threading dislocations in GaN are known to act as strong non-radiative recombination centers, which can severely limit the efficiency of GaN-based LEDs and laser diodes. Non-radiative recombination can produce localized heating that can lead to faster device degradation (Cao et al, Microelectronics Reliabilities, 2003,43(12), 1987-1991). In high power applications, the efficiency of GaN-based devices decreases with increasing current density, referred to as voltage drop. There is evidence for a correlation between dislocation density and magnitude of the voltage drop in LEDs (Schubert et al, Applied Physics Letters,2007,91(23), 231114). For GaN-based laser diodes, there is a significant negative correlation between dislocation density and Mean Time To Failure (MTTF) (Tomiya et al, IEEE Journal of Selected topocs in Quantum Electronics,2004,10(6), 1277-material 1286), which appears to be due to diffusion of impurities along dislocations (Orita et al, IEEE International Reliability Physics Symposium Proceedings,2009, 736-material 740). For electronic devices, dislocations have been shown to significantly increase leakage current in HEMT structures (Kaun et al, Applied Physics Express,2011,4(2),024101) and shorten device lifetime (Tapajna et al, Applied Physics Letters,2011,99(22), 223501-. One of the main advantages of using bulk GaN as a substrate material for epitaxial thin film growth is the greatly reduced concentration of threading dislocations in the thin film. Therefore, the dislocation density in bulk GaN substrates will have a significant impact on device efficiency and reliability.
Lateral Epitaxial Overgrowth (LEO) is a method that has been widely used to improve the crystalline quality of films grown by the vapor phase method. For example, a method has been reported in which a GaN layer is nucleated on a sapphire substrate, and SiO having a periodic array of openings is deposited on the GaN layer 2 A mask, then a Metal Organic Chemical Vapor Deposition (MOCVD) through the SiO 2 The openings in the mask layer allow GaN to grow, laterally grow on the mask and coalesce. The dislocation density in the region above the opening in the mask is very high, similar to the layer below the mask, but the dislocation density in the lateral overgrowth region is orders of magnitude smaller. This approach is attractive because it can be applied to large area substrates, significantly reducing their dislocation density. Similar methods with variations have been applied to the vapor phase growth of GaN layers by multiple groups. These methods are variously referred to as LEO, epitaxial lateral overgrowth (ELO or ELOG), Selective Area Growth (SAG), and dislocation elimination by epitaxial growth with reverse pyramidal pits (DEEP), and the like. For substantially all variations of this method, it is believed that a thin heteroepitaxial GaN layer is grown on a non-GaN substrate, a patterned mask is deposited on the GaN layer, and growth is resumed in a one-or two-dimensional array of openings in the mask. The period or pitch of the growth sites defined by the openings in the mask is typically between 2 and 100 microns, typically between about 5 and 20 microns. Individual GaN crystallites or regions grow and then coalesce. Epitaxial growth may then continue on top of the coalesced GaN material to produce a thick film or "ingot". A relatively thick GaN layer may be deposited on the coalesced GaN material by HVPE. The LEO process can greatly reduce the dislocation concentration, particularly in the region above the mask, typically to about 10 5 -10 7 cm -2 The level of (c). However, the laterally grown wings of the formed LEO layer are typically crystallographically tilted ("wing tilt") up to several degrees from the underlying substrate, which may be acceptable for thin film processes, but may be unacceptable for bulk crystal growth processes because it may produce stress and cracking and unacceptable variations in surface crystallographic orientation.
As conventionally practiced, there are several factors that limit the LEO process from reducing the mean dislocation density to less than about 10 5 To 10 7 cm -2 Or the ability to reduce the variation in miscut from 50 or 100mm wafers to less than about 0.1 degrees. First, the pitch of the pattern of openings formed in the mask layer tends to be moderate, but a larger pitch may be desirable for some applications. Second, c-plane LEO growth is typically performed in the (0001) or Ga-plane direction, which creates at least two limitations. One limitation is that the growth rate in the M-direction tends to be lower than that in the (0001) direction and semi-polar (10-11) crystal planes are typically formed, with the result that the overall crystal diameter decreases with increasing thickness and coalescence of large pitch patterns becomes difficult. Furthermore, another limitation is that growth in the (0001) direction tends to exclude oxygen, in contrast to growth in other crystallographic directions. Thus, there may be a significant lattice mismatch between the (0001) grown HVPE crystal used as a seed crystal and the crystal grown on it by another technique. Furthermore, if semi-polar crystal planes are formed during the LEO process, oxygen (or other dopant) levels may vary significantly, resulting in lateral variations in lattice constant and stress, which may lead to cracks (growth on the latter) in the LEO crystal itself or in the crystal used as a seed.
In addition to HVPE, variations of the LEO method have been disclosed for other group III metal nitride growth techniques. In a first example, Jiang et al (u.s.no.2014/0147650, now u.s.no.9,589,792) discloses a method for ammonothermal LEO growth of group III metal nitrides by replacing the mask layer (SiO) in a typical vapor phase LEO type process by a combination of adhesion, diffusion barrier and inert layers 2 Or SiN x ). In a second exampleMori et al (U.S. Pat. No. 2014/0328742, now U.S. Pat. No.9,834,859) disclose a method for LEO growth of group III metal nitrides in a sodium-gallium flux. However, in this approach, the coalesced crystallites typically have prominent semi-polar crystal planes, resulting in significant lateral variation in impurity content of the polycrystals, and thermal expansion mismatch between the coalesced nitride layer and the foreign substrate, which comprises a different material than the coalesced nitride layer, may result in uncontrolled cracking.
Several authors such as Linthicum et al (Applied Physics Letters,75,196, (1999)), Chen et al (Applied Physics Letters 75,2062(1999)), and Wang et al (U.S. patent No. 6,500,257) have noted that threading dislocations in growing GaN generally propagate primarily in the growth direction, and demonstrate that dislocation density can be reduced more than in conventional LEO methods by growing from the sidewalls of trenches in thin, highly defective c-plane GaN layers rather than vertically through windows in patterned masks. These methods have been extended by other authors to nonpolar and semipolar oriented GaN films, such as Chen et al (japan Journal of Applied Physics 42, L818(2003)) and Imer et al (U.S. patent No. 7,361,576). However, to the best of the inventors' knowledge, the sidewall LEO method has not been extended to the growth of bulk GaN, nor to the growth of N-sector GaN. In particular, we have found that the different methods used in thin film research are most effective in forming trenches hundreds of microns deep with a millimeter-scale pitch, and yield some unexpected benefits.
Fig. 1A-1T are schematic cross-sectional views of a seed or substrate during various stages of a method of forming a patterned mask seed layer for ammonia thermal sidewall lateral epitaxial overgrowth. Referring to fig. 1A, a substrate 101 has a photoresist layer 103 disposed thereon. The substrate 101 and subsequently formed layers described in connection with fig. 1A-1T may be used in subsequent tiling operations, as further discussed in connection with fig. 2A-2C, 3A-3E, and 17A-22F. In some embodiments, some of the layer formation process steps described in connection with fig. 1A-1T are performed after some of the process steps in the tiling operation, e.g., as discussed further in connection with fig. 17A-F. In certain embodiments, the substrate 101 is composed of or comprises a substrate material that is a single crystal group III metal nitride, a gallium-containing nitride, or gallium nitride. The substrate 101 may be grown by HVPE, ammonothermal or flux methods. One or both large area surfaces of the substrate 101 may be polished and/or chemically-mechanically polished. The large area surface 102 of the substrate 101 may have a crystalline orientation within 5 degrees, within 2 degrees, within 1 degree, or within 0.5 degrees of (0001) + c-plane, (000-1) -c-plane, {10-10} m-plane, {11-2 + -2 }, {60-6 + -1 }, {50-5 + -1 }, {40-4 + -1 }, {30-3 + -1 }, {50-5 + -2 }, {70-7 + -3 }, {20-2 + -1 }, {30-3 + -2 }, {40-4 + -3 }, {50-5 + -4}, {10-1 + -1 }, {10-1 + -2 }, {10-1 + -3 }, { 21-3 + -1 }, or {30-3 + -4 }. It should be understood that the planes 30-3 + -4 refer to the planes 30-34 and 30-3-4. The large area surface 102 may have an (hki l) semipolar orientation, where i ═ h + k, and at least one of l and h and k are nonzero. The large area surface 102 may have a maximum lateral dimension of between about 5 millimeters and about 600 millimeters and a minimum lateral dimension of between about 1 millimeter and about 600 millimeters, and the substrate 101 may have a thickness of between about 10 microns and about 10 millimeters or between about 100 microns and about 2 millimeters.
The surface threading dislocation density of the substrate 101 may be less than about 10 7 cm -2 Less than about 10 6 cm -2 Less than about 10 5 cm -2 Less than about 10 4 cm -2 Less than about 10 3 cm -2 Or less than about 10 2 cm -2 . The stacking fault density of the substrate 101 may be less than about 10 4 cm -1 Less than about 10 3 cm -1 Less than about 10 2 cm -1 Less than about 10cm -1 Or less than about 1cm -1 . The symmetric x-ray rocking curve (e.g., (002) in terms of c-plane) full width at half maximum (FWHM) of the substrate 101 can be less than about 500 arc-seconds, less than about 300 arc-seconds, less than about 200 arc-seconds, less than about 100 arc-seconds, less than about 50 arc-seconds, less than about 35 arc-seconds, less than about 25 arc-seconds, or less than about 15 arc-seconds. The asymmetric x-ray rocking curve (e.g., in terms of c-plane, (201)) full width at half maximum (FWHM) of the substrate 101 may be less than about 500 arc-seconds, less than about 300 arc-seconds, smallAt about 200 arcseconds, less than about 100 arcseconds, less than about 50 arcseconds, less than about 35 arcseconds, less than about 25 arcseconds, or less than about 15 arcseconds. The substrate 101 may have a radius of crystalline curvature in at least one, at least two, or three independent or orthogonal directions of greater than 0.1 meter, greater than 1 meter, greater than 10 meters, greater than 100 meters, or greater than 1000 meters.
The substrate 101 may include regions having a relatively high concentration of threading dislocations separated by regions having a relatively low concentration of threading dislocations. The threading dislocation concentration in the relatively high concentration region may be greater than about 10 5 cm -2 Greater than about 10 6 cm -2 Greater than about 10 7 cm -2 Or greater than about 10 8 cm -2 . The threading dislocation concentration in the relatively low concentration region may be less than about 10 6 cm -2 Less than about 10 5 cm -2 Or less than about 10 4 cm -2 . The substrate 101 may include regions of relatively high conductivity separated by regions of relatively low conductivity. The thickness of the substrate 101 may be between about 10 microns and about 100 millimeters, or between about 0.1 millimeters and about 10 millimeters. The largest dimension of the substrate 101 may include a diameter of at least about 5 millimeters, at least about 10 millimeters, at least about 25 millimeters, at least about 50 millimeters, at least about 75 millimeters, at least about 100 millimeters, at least about 150 millimeters, at least about 200 millimeters, at least about 300 millimeters, at least about 400 millimeters, or at least about 600 millimeters.
The large area surface 102 (fig. 1A) may have a crystallographic orientation within about 5 degrees of the (000-1) N-plane, c-plane orientation, may have an x-ray diffraction ω -scan rocking curve full width at half maximum (FWHM) for (002) and/or (102) and/or (201) reflections of less than about 200 arcseconds, less than about 100 arcseconds, less than about 50 arcseconds, or less than about 30 arcseconds, and may have an x-ray diffraction ω -scan rocking curve full width at half maximum (FWHM) of less than about 10 arcseconds 7 cm -2 Less than about 10 6 cm -2 Less than about 10 5 cm -2 Or less than about 10 4 cm -2 Average dislocation density of (a). In some embodiments, the threading dislocations in the large area surface 102 are substantially uniformly distributed. In other embodiments, threading dislocations in the large area surface 102 are non-uniformly arranged as regions of relatively high and relatively low concentrationA one-dimensional array of rows or a two-dimensional array of high dislocation density regions within a matrix of low dislocation density regions. The crystallographic orientation of the large area surface 102 may be constant at less than about 1 degree, less than about 0.5 degrees, less than about 0.2 degrees, less than about 0.1 degrees, or less than about 0.05 degrees, less than about 0.02 degrees, or less than about 0.01 degrees. In certain embodiments, the large area surface 102 is roughened, for example by wet etching, to enhance adhesion of the mask layer to form a frosted finish.
Referring again to fig. 1A, a photoresist layer 103 may be deposited on the large area surface 102 by methods known in the art. For example, in a particular embodiment of the lift-off process, a liquid solution of a negative photoresist is first applied to the large area surface 102. The substrate 101 is then spun at high speed (e.g., between 1000 to 6000 revolutions per minute for 30 to 60 seconds) to produce a uniform photoresist layer 103 over the large area surface 102. The photoresist layer 103 may then be baked (e.g., between about 90 degrees celsius and about 120 degrees celsius) to remove excess photoresist solvent. After baking, the photoresist layer 103 may then be exposed to UV light through a photomask (not shown) to form a patterned photoresist layer 104 (fig. 1B) having a predetermined pattern of cross-linked photoresist formed within the unexposed regions 104B, such as regions 104A. The regions 104B of patterned photoresist may form stripes or dots having a feature width or diameter W and a pitch L. The patterned photoresist layer 104 may then be developed to remove the uncrosslinked material found in regions 104B and leave regions 104A, such as shown in fig. 1C.
Referring to fig. 1D, one or more patterned masking layers 111 may be deposited over the large area surface 102 and the regions 104A of the patterned photoresist layer 104. The one or more patterned masking layers 111 may include an adhesion layer 105 deposited on the large area surface 102, a diffusion barrier layer 107 deposited on the adhesion layer 105, and an inert layer 109 deposited on the diffusion barrier layer 107. Adhesion layer 105 may comprise Ti, TiN y 、TiSi 2 、Ta、TaN y 、Al、Ge、Al x Ge y 、Cu、Si、Cr、V、Ni、W、TiW x 、TiW x N y Etc., and may have a thickness between about 1 nanometer and about 1 micrometer. The diffusion barrier layer 107 may comprise TiN, TiN y 、TiSi 2 、W、TiW x 、TiN y 、WN y 、TaN y 、TiW x N y 、TiW x Si z N y One or more of TiC, TiCN, Pd, Rh, Cr, etc., and has a thickness between about 1 nanometer and about 10 micrometers. Inert layer 109 may comprise one or more of Au, Ag, Pt, Pd, Rh, Ru, Ir, Ni, Cr, V, Ti, or Ta, and may have a thickness between about 10 nanometers and about 100 micrometers. The patterned mask layer or layers 111 may be deposited by sputter deposition, thermal evaporation, e-beam evaporation, or the like. After depositing the patterned mask layer 111, the portion of the patterned mask layer 111 over the region 104A of the patterned photoresist layer 104 is not in direct contact with the substrate 101, as shown in fig. 1D. The regions 104A and portions of the patterned masking layer 111 disposed thereon are then stripped by methods known in the art to form openings 112 in the patterned masking layer 111, as shown in fig. 1E. In some embodiments, a relatively thin inert layer, for example 10 to 500 nanometers thick, is deposited prior to the lift-off process. After performing the lift-off process, an additional thicker inert layer, such as 5 to 100 microns thick, may be deposited on the already patterned inert layer by electroplating, electroless deposition, or the like.
Other methods besides the lift-off process described above may be used to form patterned mask layer 111, including shadow masking, positive resist reactive ion etching, wet chemical etching, ion milling, and nanoimprint lithography, as well as variations of the negative resist lift-off process described above.
In some embodiments, a patterned masking layer 111 is deposited on the front and back surfaces of the substrate 101.
Fig. 1F-1L are top views of arrangements of exposed regions 120 on the substrate 101 formed by one or more of the processes described above. The exposed regions 120 (or also referred to herein as growth centers), such as shown in fig. 1F-1L, can be defined by the openings 112 formed in the patterned mask layer 111 shown in fig. 1E. In some embodiments, the storm is performed by a computerThe exposed areas 120 are arranged in a one-dimensional (1D) array in the y-direction, such as a single column of exposed areas 120 shown in fig. 1I. In certain embodiments, the exposed regions 120 are arranged in a two-dimensional (2D) array in the x-and y-directions, such as shown in FIGS. 1F-1H and 1J-1L. Opening 112, and thus exposed region 120, may be circular, square, rectangular, triangular, hexagonal, etc., and may have an opening size or diameter W of between about 1 micron and about 5 millimeters, or between about 10 microns and about 500 microns, such as shown in fig. 1F-1L. The exposed regions 120 may be arranged in a 2D hexagonal or square array with a pitch dimension L of between about 5 microns and about 20 millimeters, between about 200 microns and about 15 millimeters, or between about 500 microns and about 10 millimeters, or between about 0.8 millimeters and about 5 millimeters, such as shown in fig. 1F and 1G. The exposed regions 120 may be arranged in a 2D array with a pitch dimension L in the y-direction 1 And a pitch dimension L in the x-direction 2 May be different from each other as shown in fig. 1H and 1J to 1L. The exposed regions 120 may be arranged in a rectangular, parallelogram, hexagonal, or trapezoidal array (not shown) with a pitch dimension L in the y-direction 1 And a pitch dimension L in the x-direction 2 May be different from each other as shown in fig. 1H and 1J to 1L. The array of exposed areas 120 may also be linear or irregularly shaped. The exposed regions 120 in the patterned masking layer 111 may be placed in alignment with the structure of the substrate 101. For example, in certain embodiments, the large area surface 102 is hexagonal, e.g., (0001) or (000-1) crystallographic orientation, and the openings in the patterned mask layer 111 comprise a 2D hexagonal array such that the spacing between nearest neighbor openings is parallel to the spacing in the large area surface 102<11-20>Or<10-10>And (4) direction. In certain embodiments, the large area surface 102 of the substrate is non-polar or semi-polar, and the exposed regions 120 comprise a 2D square or rectangular array such that the spacing between nearest neighbor openings is parallel to the projection of two of the c-axis, m-axis, and a-axis onto the large area surface 102 of the substrate 101. In some embodiments, the pattern of exposed regions 120 is oriented obliquely with respect to the structure of the substrate 101, e.g., where the exposed regions 120 are oriented with respect to a high symmetry axis of the substrate (such as of the substrate 101)A projection of the c-axis, m-axis, or a-axis on the large area surface 102 having a hexagonal crystal structure, such as Wurtzite crystal structure, from about 1 degree to about 44 degrees). In some embodiments, the exposed region 120 is substantially linear rather than substantially circular. In some embodiments, the exposed region 120 is a slit having a width W and a period L that spans the entire length of the substrate 101, as shown in fig. 1I. In some embodiments, the exposed region 120 is a region having a width W in the y-direction 1 And has a predetermined length W in the x-direction that is less than the length of the substrate 101 2 And may be arranged to have a period L in the y-direction 1 And a period L in the x-direction 2 As shown in fig. 1J to 1L. In some embodiments, adjacent rows of exposed regions 120 (e.g., slits) may be offset from each other in the x-direction, rather than being arranged directly adjacent, as shown in fig. 1K. In some embodiments, adjacent rows of exposed areas 120 (e.g., slits) may be offset from each other in the longitudinal y-direction. In some embodiments, the exposed region 120 includes slits that extend in two or more different directions (e.g., x-direction and y-direction), as shown in FIG. 1L. In some embodiments, the exposed regions 120 (e.g., slits) may be arranged in a manner that reflects the hexagonal symmetry of the substrate. In some embodiments, the exposed region 120 (e.g., a slit) may extend to an edge of the substrate 101.
In some embodiments, the pattern of openings terminates at a predetermined distance from the edge of the substrate, for example, a distance between 10 microns and 5 millimeters, between 20 microns and 2 millimeters, between 50 microns and 1 millimeter, or between 100 microns and 500 microns. The termination of the pattern forms a rim around the edge of the substrate. The edge may have a width equal to the predetermined distance, which may be used, for example, to improve the integrity and robustness of the edge of the patterned mask layer. The edges, as well as the edges of the substrate, may be covered by a patterned masking layer 111.
In an alternative embodiment, as shown in fig. 1M, the large area surface 102 of the substrate 101 is covered with a blanket mask 116 comprising one, two, or more of the adhesion layer 105, the diffusion barrier layer 107, and the inert layer 109, followed by a positive photoresist layer 113. The photoresist layer is exposed to UV light through a photomask (not shown) to form soluble exposed regions 106B and unexposed regions 106A, as shown in fig. 1N (which is essentially a negative of the pattern shown in fig. 1B). The exposed region 106B is then removed by development. As shown in fig. 1O, an opening 112 in a blanket mask 116 (including adhesion layer 105, diffusion barrier layer 107, and inert layer 109) may then be formed by wet or dry etching through the opening in patterned photoresist layer 113A to form a patterned mask layer 111. After forming the opening 112, the photoresist layer 113 is removed, as shown in fig. 1P, resulting in a structure similar or identical to that shown in fig. 1E.
A trench 115 is then formed in the exposed region 120 of the substrate 101 through an opening 112 (or "window") formed in the patterned masking layer 111, as shown in fig. 1Q. In some embodiments, the depth of the grooves 115 is between 50 microns and about 1 millimeter or between about 100 microns and about 300 microns. In some embodiments, the trench 115 penetrates through the entire thickness of the substrate 101, forming a patterned hole or slit extending from the backside 118 of the substrate 101 and through the opening 112 of the patterned mask layer 111. The width of a single trench may be between about 10 microns and about 500 microns or between about 20 microns and about 200 microns. Each groove 115 may be linear or curved, and may have a length in the X-direction and/or the Y-direction of between about 100 microns and about 50 millimeters, or between about 200 microns and about 10 millimeters, or between about 500 microns and about 5 millimeters. In one embodiment, the large area surface 102 of the substrate 101 has a (000-1) N-face orientation and the trench 115 is formed by wet etching. In one embodiment, the etchant composition or solution comprises 85% phosphoric acid (H) 3 PO 4 ) And sulfuric acid (H) 2 SO 4 ) In which H is 2 SO 4 /H 3 PO 4 The ratio is between 0 and about 1: 1. In certain embodiments, the phosphoric acid solution is adjusted to form polyphosphoric acid, thereby increasing its boiling point. For example, reagent grade (85%) H 3 PO 4 By heating at a temperature between about 200 degrees Celsius and about 450 degrees CelsiusIs stirred and heated in a beaker for about 5 minutes to about five hours. In one embodiment, the trench 115 is formed by heating the masked substrate 101 in one of the above described etching solutions at a temperature between about 200 degrees celsius and about 350 degrees celsius for a time between about 15 minutes and about 6 hours. In another embodiment, trench 115 is formed by electrochemical wet etching.
Fig. 1R-1T illustrate an alternative method of forming an array of patterned masking trenches in a substrate 101. A blanket mask 116 (comprising adhesion layer 105, diffusion barrier layer 107, and inert layer 109) may be deposited over the large area surface 102 of the substrate 101 as shown in fig. 1R. The nascent trench 114 may be formed by laser ablation, as shown in fig. 1S, to form the patterned mask layer 111. The laser ablation process is also referred to or referred to as a laser machining or laser beam machining process. Laser ablation may be performed by a watt-level laser, such as a neodymium-doped yttrium aluminum garnet (Nd: YAG) laser, CO 2 Lasers, excimer lasers, Ti: sapphire lasers, and the like. The laser may emit pulses with pulse lengths in the nanosecond, picosecond, or femtosecond range. In some embodiments, suitable nonlinear optics may be used to double, triple or quadruple the frequency of the output light of the laser. The beam width, power, and scan rate of the laser on the surface of the substrate 101 with the patterned mask layer 111 can be varied to adjust the width, depth, and aspect ratio of the nascent trenches 114. The laser may be repetitively scanned over a single trench or an entire trench array.
The surface and sidewalls of the nascent trench 114 may contain damage left by the laser ablation process. In some embodiments, the substrate 101 including the nascent trenches 114 is further processed by wet etching, dry etching or photoelectrochemical etching to remove residual damage in the nascent trenches 114, as shown in fig. 1T. In one embodiment, the large area surface 102 of the substrate 101 has a (000-1) N-face orientation, and the trench 115 is formed from the nascent trench 114 by wet etching. In one embodiment, the etchant composition or solution comprises 85% phosphoric acid (H) 3 PO 4 ) And sulfuric acid (H) 2 SO 4 ) In which H is 2 SO 4 /H 3 PO 4 The ratio is between 0 and about 1: 1. In certain embodiments, the phosphoric acid solution is adjusted to form polyphosphoric acid, thereby increasing its boiling point. For example, reagent grade (85%) H 3 PO 4 Can be adjusted by stirring and heating in a beaker at a temperature between about 200 degrees celsius and about 450 degrees celsius for about 5 minutes to about five hours. In one embodiment, the trench 115 is formed by heating the substrate 101 in one of the above described etching solutions at a temperature between about 200 degrees celsius and about 350 degrees celsius for a time between about 15 minutes and about 6 hours.
After one or more of the above-described processes are performed on the substrate 101, a crystal growth process may be performed on a single substrate 101 or simultaneously on an array of substrates 101. During the crystal growth process, a single substrate 101 or an array of substrates 101, respectively, serves as one or more seeds. Fig. 17A-17F illustrate some examples of various arrays of seeds 370, such as substrate 101, that may be used during a crystal growth process. Referring to fig. 17A-17F, at least some edges 395 of two or more seeds 370 are prepared for tessellation to form a one-or two-dimensional array of tiled crystals. The seeds 370 may each be prepared in a square shape (fig. 17A), a rectangular shape (fig. 17B), a hexagonal shape (fig. 17C), a mixture of diamonds and triangles (fig. 17D), a mixture of hexagons and pentagons (fig. 17E), a mixture of hexagons and diamonds (fig. 17F), or other shapes, or combinations thereof. A square or rectangular shape may be preferred when surface 102 has a non-polar or semi-polar orientation. When surface 102 has a (000 ± 1) c-plane orientation, a hexagonal, rhomboid, triangular, rhomboid, pentagonal, or trapezoidal shape may be preferred. A triangle, quadrilateral or pentagon may be used to define the outer perimeter of the seed array. In certain embodiments, some or all of the edges 395 of the seed 370 are prepared such that the intersection of the edge with the large area surface 102 is parallel to a plane selected from the group consisting of the {11-20} a-plane, (000 + -1) c-plane, the {10-10} m-plane, the {10-1 + -1 } plane, or a plane defined by a perpendicular to the large area surface 102 and an axis selected from the group consisting of the c-axis, the m-axis, or the a-axis, within a difference of 0.5 degrees, 0.2 degrees, 0.1 degrees, 0.05 degrees, 0.02 degrees, or 0.01 degrees. In certain embodiments, the edge 395 is prepared to have a root mean square surface roughness of less than 10 microns, less than 5 microns, less than 2 microns, or less than 1 micron. In certain embodiments, the edge 395 is prepared prior to pattern deposition and patterning, as described above and in fig. 1A-1T, such that the patterned mask layer 111 extends from the large area surface 102 over at least a portion of the edge. In certain embodiments, the edge 395 is prepared by at least one of a dicing saw, a wire saw, and a laser. In certain embodiments, the edge 395 further includes orientation flats (such as missing corners) or orientation notches to simplify the tracking of the crystallographic orientation of each seed crystal 370.
In certain embodiments, many, most, or all of the seeds 370 positioned in the array are prepared such that they are exactly the same size and shape. For example, the X-direction dimension 380 of each nominally identical seed 370 in the array may be equal, with a variance within 0.5 millimeters, 0.2 millimeters, 0.1 millimeters, 50 micrometers, 20 micrometers, 10 micrometers, 5 micrometers, 2 micrometers, or 1 micrometer. In some embodiments, the X-direction dimension 380 is between 4 millimeters and 10 millimeters, between 10 millimeters and 15 millimeters, between 15 millimeters and 25 millimeters, between 25 millimeters and 50 millimeters, between 50 millimeters and 100 millimeters, or between 100 millimeters and 150 millimeters. Similarly, the Y-direction dimension 390 of each nominally identical seed in the array can be equal, with a variance within 0.5 millimeters, 0.2 millimeters, 0.1 millimeters, 50 micrometers, 20 micrometers, 10 micrometers, 5 micrometers, 2 micrometers, or 1 micrometer. Similarly, the Y-direction dimension 390 of each nominally identical seed in the array can be equal, with a variance within 0.5 millimeters, 0.2 millimeters, 0.1 millimeters, 50 micrometers, 20 micrometers, 10 micrometers, 5 micrometers, 2 micrometers, or 1 micrometer. In some embodiments, the Y-direction dimension 390 is between 8 millimeters and 10 millimeters, between 10 millimeters and 15 millimeters, between 15 millimeters and 25 millimeters, between 25 millimeters and 50 millimeters, between 50 millimeters and 100 millimeters, or between 100 millimeters and 150 millimeters. In some embodiments, some edges 395, particularly the outward facing edges in the seed array, may be cut into a circular or elliptical cross-section, rather than straight lines, in order to achieve a curved or near circular or elliptical perimeter of the seed array 370, as shown in fig. 19G. In some embodiments, the starting point for seed 370 is a wafer, which has a mainly circular perimeter, and a portion of the original edge is retained while the other edge is prepared for tessellation as described above.
In certain embodiments, the back and optionally one or more edges and/or front faces of one or more seeds are coated with a mechanically compliant coating or interface layer 1921 (fig. 19E) configured to accommodate any extrinsic or intrinsic stresses formed between the seed 370 and a deposited layer or structure disposed thereon without the seed 370 or deposited layer or structure experiencing cracking or other failure. The mechanically compliant coating may comprise or consist of one or more of graphite, pyrolytic graphite, boron nitride, pyrolytic boron nitride, molybdenum disulfide, and tungsten disulfide. In certain embodiments, the mechanically compliant coating is deposited by at least one of sputtering, chemical vapor deposition, plasma enhanced chemical vapor deposition, high density plasma chemical vapor deposition, and electron beam evaporation. In certain embodiments, the mechanically compliant coating is not fully dense and is deposited by one or more of spraying particles suspended in a slurry, screen printing of particles suspended in a slurry, painting of particles suspended in a slurry, plasma spraying, and the like. In certain embodiments, the mechanically compliant coating is subjected to a heat treatment process to partially or fully sinter the particles in the mechanically compliant coating.
In some embodiments, each seed 370 is equal in thickness, with a variance within 50 microns, within 25 microns, within 10 microns (μm), within 5 microns, within 2 microns, or within 1 micron. In certain embodiments, a uniform seed thickness will improve the mechanical integrity of the seed-holding array. In certain embodiments, a uniform seed thickness will enhance the coplanarity of the top surfaces of the seeds. In certain embodiments, uniform seed thickness may enhance the mechanical integrity and thermal uniformity of the fabricated composite structure. The crystallographic miscut of each large area surface 102 of seed 370 has a magnitude and direction 397. For example, if a particular c-plane seed crystal is miscut 0.50 degrees in the m-direction and 0.06 degrees in the orthogonal a-direction, the magnitude of the miscut is about 0.504 degrees and its direction is 6.8 degrees from the particular m-direction. In some embodiments, each crystal miscut of seed crystal 370 is of equal magnitude, differing by within 0.2 degrees, within 0.1 degrees, within 0.05 degrees, within 0.02 degrees, or within 0.01 degrees. In some embodiments, the directions 397 of crystallographic miscut for each seed are aligned within 10 degrees, within 5 degrees, within 2 degrees, within 1 degree, within 0.5 degrees, within 0.2 degrees, or within 0.1 degrees.
In certain embodiments, an array of seeds 370 is placed in a mechanical fixture, as schematically illustrated in fig. 18A-18D. This embodiment may be suitable when there are a small number of seeds, or when each seed may be held in place by clamping a portion of the perimeter of each seed in the array of seeds. For example, this technique can be used for the seed arrays shown in fig. 17E and 17F, but not for the seed arrays shown in fig. 17A-D. Seed 370 may be placed on back plate 1810 (fig. 18A), retainer ring 1830 (fig. 18B) may be placed around the perimeter of the array of seed 370, and gripper ring 1840 (fig. 18C) may be placed on top of retainer ring 1830. Each of the back plate 1810, the retainer ring 1830, and the clamp ring 1840 may have three or more through holes 1820, 1825 for attachment by a set of fasteners such as screws, bolts, or threaded rods. In some embodiments, the through-hole 1820 is tapped while the through-hole 1825 is drilled through. In a preferred embodiment, each of the back plate 1810, the retainer ring 1830 and the clamp ring 1840 is made of a material, such as molybdenum, having a Coefficient of Thermal Expansion (CTE) slightly less than that of the seed crystal 370. In some embodiments, the through-holes 1820 are located at the periphery of the seed crystal 370. In some embodiments, at least one seed crystal 370 is penetrated by a through hole aligned with at least one through hole 1820 or 1825 in the back plate 1810. In certain embodiments, one or more of the backplate 1810, the retention ring 1830, and the clamp ring 1840 may be coated with a release coating to simplify removal of the incorporated crystals from the fixture component. In certain embodiments, the release coating inhibits deposition or adhesion of GaN on the mechanical component. In certain embodiments, the release coating provides mechanical compliance between the seed and the fixture components to accommodate stresses due to residual CTE mismatch without cracking or failure. The release coating may comprise or consist of one or more of graphite, boron nitride, molybdenum disulfide or tungsten disulfide. In certain embodiments, the release coating is not fully dense and is deposited by one or more of spraying particles suspended in a slurry, screen printing of particles suspended in a slurry, painting of particles suspended in a slurry, and the like.
In some embodiments, it is desirable to form at least some portions of the mechanical fixation device from molybdenum (Mo), as Mo is known to have about 5.8 x10 when averaged over a temperature range of 20 degrees celsius to 1000 degrees celsius -6 CTE of/K. In some embodiments, the alloy of Mo is selected such that its recrystallization temperature exceeds the highest temperature that the mechanical fixture will reach during the crystal growth process. If the recrystallization temperature is exceeded during processing, grain growth may occur in the Mo substrate, resulting in a change in the stress state of the material, which may lead to embrittlement of the material after its subsequent cooling. It is known to dope Mo with titanium and zirconium to produce a material commercially known as a titanium-zirconium-molybdenum (TZM) alloy that increases the recrystallization temperature relative to Mo to a range of 1200 to 1400 degrees celsius above the recrystallization temperature of elemental Mo by 200 to 300 degrees celsius and 100 to 600 degrees celsius above the epitaxial growth temperature. TZM is a low alloy of Mo (greater than 98%, preferably at least 99%), Ti (between 0.2% and 1.0%), Zr (between 0% and 0.3%) and C (between 0% and 0.1%). Other alloys are also possible. For example, the CTE of a MoW alloy averaged over a temperature range of 20-1000 degrees Celsius may be engineered to fall within 4.9 × 10 -6 K to 5.8X 10 -6 In the range of/K. The CTE of the mechanical fixture component material may be engineered to be between 80% and 99%, 85% and 98%, 90% and 97%, or 94% and 96% of the CTE of the crystal in the plane of the first surface.
The flatness of the mechanical fixture components is such that the amount of warping in their diameter should not exceed 0.1%, preferably not 0.02%, of their diameter. Warpage is defined herein as the sum of the maximum positive and negative deviations of the top surface of the fixture component from an imaginary plane selected as the plane that intersects the top surface of the fixture component and minimizes the magnitude of warpage.
The gap between the retaining ring and the array of seeds 370 may be selected such that the gap shrinks to near zero at a predetermined temperature for bulk crystal growth, such that each seed 370 is positioned such that there is little or no gap between adjacent edges of adjacent seeds, thereby ensuring accurate crystallographic alignment of the seeds 370. In one example, the gap 1711 (fig. 17A-17F) between adjacent edges of the seed 370 is between zero and 200 microns, between 0.1 microns and 50 microns, or between 0.2 microns and 50 microns. In certain embodiments, each of the back plate 1810, the retention ring 1830, and the grip ring 1840 is made of molybdenum or a molybdenum alloy, such as MoW or TZM or silver-clad Mo, W, or Ni. In certain embodiments, the material used to make at least one of the back plate 1810, the retainer ring 1830, and the clamp ring 1840 is annealed to remove residual stresses prior to machining. In certain embodiments, mesa structures are incorporated into the back plate 1810 at the intersection of two, three, or more seeds. In some embodiments, the top of the mesa is ground to be precisely flat and coplanar in order to improve the alignment accuracy or planarity of the surface of the seed 370 that is parallel to the flat or coplanar surface of the mesa. In certain embodiments, additional components are incorporated into the mechanical fixture, such as spacers or springs. The additional component may be made of a material compatible with the ammonothermal crystal growth environment, such as at least one of molybdenum, tungsten, tantalum, niobium, silver, gold, platinum, or iridium.
After assembling the seed array in the fixture, the fixture may be fastened together using at least three screws, bolts, threaded rods and nuts, or similar fasteners 1855 to form a tiled array 1860 (fig. 18D).
Mechanically fixing the apparatus so that each of the group III nitride crystals positioned on or in the apparatusAre designed and fabricated in substantially the same manner. Referring again to FIG. 18D, a first coordinate system 1821 (x) 1 y 1 z 1 ) Denotes the crystal orientation of first group III nitride crystal 1801, wherein z 1 Is a negative surface normal to the nominal orientation of surface 1811 of first group III-nitride crystal 1801, and x 1 And y 1 Is a reaction of 1 Orthogonal vectors. For example, if surface 1801 has a (0001) orientation, then z 1 Is along [ 000-1 ]]Unit vector of (a), and x 1 And y 1 Can be selected along [ 10-10 ] respectively]And [ 1-210 ]]. If surface 1811 has a (10-10) orientation, then z 1 Is along [ -1010 ]]Unit vector of (a), and x 1 And y 1 Can be selected to be respectively along [ 1-210 ]]And [0001 ]]. Similarly, a second coordinate system 1822 (x) 2 y 2 z 2 ) Represents the crystallographic orientation of the second nitride crystal 1802, wherein z 2 Is the negative surface normal of the nominal orientation of the surface 1812 of the second nitride crystal 1802, and x 2 And y 2 Is a reaction of 2 Orthogonal vectors, wherein for a vector corresponding to (x) 2 y 2 z 2 ) The crystal orientation of (a) and (x) 1 y 1 z 1 ) The same convention applies. The difference in crystal orientation between the surface of the first nitride crystal and the surface of the second nitride crystal may be specified by three angles α, β, and γ, where α is x 1 And x 2 Is an angle between, β is y 1 And y 2 Angle between, and gamma is z 1 And z 2 The angle therebetween. Since the surface orientations of the first nitride crystal and the second nitride crystal are almost the same, the polar orientation difference angle γ is very small, for example, less than 0.5 degrees, less than 0.2 degrees, less than 0.15 degrees, less than 0.1 degrees, less than 0.05 degrees, less than 0.02 degrees, or less than 0.01 degrees. Due to the precise control of the nitride crystal orientation during placement, the orientation difference angles α and β are also very small, e.g., less than 1 degree, less than 0.5 degrees, less than 0.2 degrees, less than 0.1 degrees, less than 0.05 degrees, less than 0.02 degrees, or less than 0.01 degrees. Typically, γ will be less than or equal to α and β. The difference in crystal orientation between the additional adjacent nitride crystals is also very small. However, the crystal orientation is at a different angleAlpha, beta, and gamma are detectable by x-ray measurements and can be greater than about 0.005 degrees, greater than about 0.01 degrees, greater than about 0.02 degrees, greater than about 0.05 degrees, greater than about 0.1 degrees, or greater than about 0.2 degrees.
In the above embodiments, the mechanical fixture supporting the seed array may have a CTE similar to but slightly less than the CTE of the seed itself. In another embodiment, a polycrystalline group III nitride-containing support structure is used in place of the molybdenum material in the mechanical fixture. The polycrystalline group III nitride may be textured or highly textured. For example, because the CTE of GaN differs by about 12% between the a-and c-directions, polycrystalline GaN will not have an exact CTE match with the single crystal GaN seed. However, the mismatch is small and the temperature dependence of the CTE in the a-direction and the c-direction is similar. Furthermore, the lateral CTE of the polycrystalline GaN material will be very close to the CTE of single crystal GaN in the a-direction, subject to the limitation of high texturing of the material in the c-direction. Exemplary methods for producing textured polycrystalline group III metal nitrides are described in U.S. patent 8,039,4128,461,071, RE47114, 10,094,017, and 10,619,239, each of which is incorporated by reference in its entirety.
In some embodiments for supporting an array of seeds 370 during processing, the array of seeds 370 is placed on a support surface 1915 of a susceptor 1910, as shown in fig. 19A. This embodiment may be applied to each of the seed arrays schematically shown in fig. 17A-F. In some embodiments, spacers (not shown) of a desired size are disposed between adjacent edges of each seed 370 such that a defined and regular spacing may be maintained in at least one direction, such as the X-direction or even the X-direction and the Y-direction. The spacer may comprise a machined block or wire of a desired diameter. The spacing between adjacent edges of each seed 370 may be set such that the spacing is less than 2 millimeters (mm), such as between 0.1 micrometers (μm) and 1 millimeter (mm), or between 0.1 micrometers and 200 micrometers, between 0.1 micrometers and 50 micrometers, or between 0.2 micrometers and 50 micrometers.
The pedestal 1910 may comprise SiO 2 One or more of graphite, Pyrolytic Boron Nitride (PBN), SiC coated graphite, PBN coated graphite, TaC coated graphite, molybdenum or molybdenum alloyConsisting of one or more of them. In certain embodiments, the surface 1915 of the base 1910 facing the one or more seeds may be coated with a release coating 1923. The release coating 1923 may comprise or consist of one or more of graphite, boron nitride, molybdenum disulfide, or tungsten disulfide. In certain embodiments, the release coating 1923 is not fully dense and is deposited by one or more of spraying particles suspended in a slurry, screen printing of particles suspended in a slurry, painting of particles suspended in a slurry, and the like. In some embodiments, the array of seeds 370 is surrounded by a retaining ring 1930 disposed above the support surface 1915. In certain embodiments, the retention ring 1930 comprises or consists of a material having a CTE slightly less than GaN, such as molybdenum or a molybdenum alloy. In some embodiments, the susceptor 1910 is machined to have a hollow region or shaped recess formed in the support surface 1915 in the shape of the seed crystal 370 to facilitate the precise alignment of the seed crystal and crystal planes formed therein with one another. In certain embodiments, the retention ring 1930 comprises or consists of a wire. In certain embodiments, a large area surface of one or more seeds having a mechanically compliant coating formed therebetween (e.g., interface layer 1921 in fig. 19E) is placed in contact with the support surface 1915 of the susceptor 1910. In certain embodiments, a large area surface of one or more seeds having a mechanically compliant coating (e.g., the interface layer 1921) is positioned on a side opposite the support surface 1915 of the base 1910. The mechanically compliant coating serves to relieve some of the extrinsic and intrinsic stresses formed between the seed crystal 370 and the base 1910 and/or the seed crystal 370 and the porous member 1940 and/or the polycrystalline GaN layer 1950 disposed on opposing sides, as will be discussed below.
In certain embodiments, the porous member 1940 is placed on one or more seeds 370 and is configured to minimize extrinsic stresses induced in the seeds 370 due to CTE mismatch created between the seeds 370 and the porous member 1940. The porous member 1940 may also serve to reduce stress induced in the seed crystal 370 due to a CTE mismatch created between the seed crystal 370 and a subsequently deposited polycrystalline GaN layer 1950 formed thereon. In certain embodiments, porous member 1940 has a honeycomb structure, as shown in fig. 19F. Porous member 1940 may comprise or consist of one or more of graphite, carbon fiber, silica fiber, aluminosilicate fiber, borosilicate fiber, silicon carbide coating, pyrolytic boron nitride coating, pyrolytic graphite coating, or polymer.
As part of the method for forming the support for the array of seeds 370, the susceptor 1910 with the array of seeds 370 precisely positioned thereon may be placed into a reactor capable of polycrystalline GaN synthesis. The polycrystalline GaN reactor may then be closed, evacuated, and backfilled with nitrogen. The temperature of the susceptor 1910 in the reactor may be raised to about 900 ℃ and may be at 5% H 2 /N 2 Is baked for about 24 hours to remove oxygen and moisture from the oven. After the nitrogen bake, for example, 1.2 standard liters per minute of Cl can be used 2 Flows through the gallium-containing source chamber at a temperature of 850 degrees Celsius, and the effluent may be contacted with 15 standard liters per minute of NH 3 Gas flow mixing of nitrogen carrier gas. The process may run for about 30 hours, the reactive gases may be stopped, and the reactor may be cooled. A textured polycrystalline GaN layer 1950 of about 1mm thickness may be deposited on the array of seed crystals 370, resulting in a structure similar to that schematically shown in fig. 19B. The openings, gaps 1941, or pores (if present) within porous member 1940 are partially or completely filled with polycrystalline GaN. In certain embodiments, porous member 1940 is completely encapsulated (not shown) within polycrystalline GaN. In certain embodiments, one or more components of porous member 1940 (e.g., a polymer disposed within the material used to form porous member 1940) undergo partial or complete decomposition during deposition of polycrystalline GaN layer 1950, and thus allow the material within porous member 1940 to develop one or more desired mechanical properties.
After forming the polycrystalline GaN layer 1950, the tiled composite structure 1960 including the seed crystals 370 bonded together by the polycrystalline GaN layer 1950 may then be separated from the susceptor 1910 as schematically shown in fig. 19C. As part of a tiled composite structure 1960 that also includes at least an array of seed crystals 370, the polycrystalline GaN layer 1950 is generally referred to herein as a base member. Although the tiled composite structure 1960 and the polycrystalline GaN layer or substrate member 1950 shown in fig. 19C-19F include the porous member 1940, this configuration is not intended to limit the scope of the disclosure provided herein. In some embodiments, the base member may optionally include a porous member 1940. In certain embodiments, base 1910 is separated from tiled composite structure 1960 by using a mechanical process for breaking any bonds formed between base 1910 and components within tiled composite structure 1960. In one example, a mechanical shear force is applied between base 1910 and tiled composite 1960 to cause a portion of release coating 1923 or interface layer 1921 disposed therebetween to rupture and fail, thereby allowing base 1910 and tiled composite 1960 to separate. In other embodiments, base 1910 is dissolved in, for example, an inorganic acid or base.
In certain embodiments of a tiled composite structure 1960, gaps 1970 are formed between adjacent tiled seeds 370, as schematically illustrated in fig. 19D. The formed gap 1970 helps to inhibit growth of the polycrystalline GaN layer 1950 from interfering with lateral growth of the seed 370 during subsequent process steps, such as a merge process. Gap 1970 may have a width of between about 1 micron and about 5 millimeters, between about 5 microns and about 1 millimeter, between about 10 microns and about 500 microns, or between about 20 microns and about 200 microns. Gap 1970 may have a depth of between about 1 micron and about 1 millimeter, between about 5 microns and about 300 microns, or between about 10 microns and about 100 microns. Gap 1970 may be formed by laser machining such as dicing saws and the like. In some embodiments, the gap formation process includes a masking operation, either in lieu of or in addition to etching, such that formation of polycrystalline group III-nitride material between adjacent seeds 370 is prevented. In some embodiments, the patterning and etching of the seed 370, as schematically illustrated in fig. 1A-1T, is performed after the formation of the tiled composite structure 1960, rather than in advance.
The tiled array 1860 and/or tiled composite structure 1960 including the array of precisely oriented seeds 370 may then be used as a substrate for bulk crystal growth including, for example, ammonothermal growth, HVPE growth, or flux growth. Under the circumstancesIn the discussion of the planes, the grown GaN layer will be referred to as an ammonia thermal layer, but other bulk growth methods, such as HVPE or flux growth, may also be used. In certain embodiments involving ammonia thermal block growth, one or more tiled arrays 1860 and/or tiled composite structures 1960 may then be hung on a seed rack and placed in a liner within a sealable container, such as a capsule, autoclave, or autoclave. In certain embodiments, one or more pairs of tiled arrays are suspended back-to-back with the open and/or patterned large area surface facing outward. A group III metal source, such as a polycrystalline group III metal nitride, at least one mineralizer composition, and ammonia (or other nitrogen-containing solvent) are then added to and sealed within the sealable container. The mineralizer composition may comprise an alkali metal such as Li, Na, K, Rb or Cs, an alkaline earth metal such as Mg, Ca, Sr or Ba, or an alkali or alkaline earth metal hydride, amide, imide, amido-imide, nitride or azide. The mineralizer may comprise an ammonium halide such as NH 4 F、NH 4 Cl、NH 4 Br or NH 4 I, gallium halides such as GaF 3 、GaCl 3 、GaBr 3 、GaI 3 Or by F, Cl, Br, I, HF, HCl, HBr, HI, Ga, GaN and NH 3 Any compound formed by the reaction of one or more of (a). The mineralizer may comprise other alkali metal, alkaline earth metal or ammonium salts, other halides, urea, sulfur or sulfide salts, or phosphorus-containing salts. The sealable container (e.g., capsule) can then be placed in a high pressure apparatus, such as an internally heated high pressure apparatus or autoclave, and the high pressure apparatus sealed. The sealable container containing the tiled arrays 1860 and/or tiled composite structure 1960 is then heated to a temperature above about 400 degrees celsius and pressurized above about 50 megapascals for ammonothermal crystal growth.
Fig. 2A-2C illustrate different steps in a bulk crystal growth process performed on an adjacent tiled seed array, where patterned seeds are formed by a LEO process and there are no trenches under the mask openings. During the bulk crystal growth process, group III metal nitride layer 213 grows through openings 112 of patterned mask layer 111, grows outward through the openings, as shown in fig. 2B, grows laterally over patterned mask layer 111, and coalesces first between adjacent mask openings (fig. 2C) and second between adjacent tiles or seeds. After coalescence, group III metal nitride layer 213 includes a window region 215 grown vertically with respect to the opening in patterned mask layer 111, a wing region 217 grown laterally over patterned mask layer 111, and a coalescence front 219 formed at the boundary between wings grown from adjacent openings in patterned mask layer 111, and a second coalescence front 235 formed at the boundary between wings grown from adjacent tiles or seeds. Threading dislocations 214 may be present in window region 215, which originate from threading dislocations present at the surface of substrate 101.
Fig. 3A-3C illustrate a bulk III-nitride sidewall LEO process. Fig. 3D-3E illustrate bulk crystal growth on adjacent tiled seeds, where patterned seeds are formed by a sidewall LEO process. Fig. 3A shows a substrate including patterned masking trenches 115 formed by one of the processes described herein. In the sidewall LEO process, a group III metal nitride material 221 is grown on the sides and bottom of patterned masking trench 115, as shown in fig. 3B. As the group III metal nitride material 221 on the sidewalls of the trench 115 grows inward, the group III nitride nutrient material becomes progressively more difficult to reach the bottom of the trench, whether the nutrient material contains an ammonothermal complex of a group III metal (in the case of ammonothermal growth), a group III metal halide (in the case of HVPE), or a group III metal alloy or inorganic complex (in the case of flux growth). Eventually, the group III metal nitride material 221 pinches off the lower region of the trench, forming a void 225, as shown in fig. 3C. It has been found that the threading dislocation concentration in the laterally grown group III metal nitride material 221 is lower than the threading dislocation concentration in the substrate 101. Many threading dislocations 223 originating from the substrate 101 terminate on the surface of the void 225. Concomitantly, the group III metal nitride layer 213 grows up through the opening 112 (or window) in the patterned mask layer 111. However, since the laterally grown group III metal nitride material 221 has a lower threading dislocation concentration than the substrate 101, and many dislocations from the substrate 101 have terminated at the surface of the voids 225, the dislocation density in the vertically grown group III metal nitride layer 213 is significantly reduced relative to conventional LEO processes, as described above in connection with fig. 2A-2C.
Fig. 3D-3E illustrate continuation of the sidewall LEO growth process and fusion between adjacent tiling or seeds. As in conventional LEO processes (fig. 2A-2C), the group III metal nitride layer 213 grows within the openings 112 of the patterned mask layer 111, grows outward through the openings, as shown in fig. 3D, grows laterally over the patterned mask layer 111, and coalesces first between adjacent mask openings (fig. 3E) and second between adjacent tiles or seeds. After coalescence, group III metal nitride layer 213 includes a window region 215 grown vertically with respect to the opening in patterned mask layer 111, a wing region 217 grown laterally over patterned mask layer 111, and a first coalescence front 219 formed at the boundary between wings grown from adjacent openings in patterned mask layer 111, as shown in fig. 3E, and a second coalescence front 235 formed at the boundary between wings grown from adjacent tiling or seeding. Since the laterally grown group III metal nitride material 221 has a lower threading dislocation concentration than the substrate 101, and many threading dislocations from the substrate 101 terminate in the voids 225, the threading dislocation concentration in the window region 215 is significantly lower than in the case of conventional LEO.
The thickness of the ammonothermal group III metal nitride layer 213 may be between about 10 microns and about 100 millimeters, or between about 100 microns and about 20 millimeters.
In certain embodiments, the ammonothermal group III metal nitride layer 213 is subjected to one or more processes, such as at least one of sawing, lapping, grinding, polishing, chemical mechanical polishing, or etching.
In certain embodiments, the concentration of extension defects (such as threading dislocations and stacking faults) in the ammonothermal group III metal nitride layer 213 may be quantified by defect selective etching. Defect selective etching can be performed, for example, using a mask comprising H 3 PO 4 And H 2 SO 4 Or a molten flux comprising one or more of NaOH and KOH, H 3 PO 4 Has passed through the elongationThe heat treatment conditions to form polyphosphoric acid. The defect-selective etch may be performed at a temperature between about 100 degrees celsius and about 500 degrees celsius for a time between about 5 minutes and about 5 hours, with the process temperature and time selected so as to form etch pits between about 1 micron and about 25 microns in diameter, and then removing the ammonothermal group III metal nitride layer, crystal, or wafer from the etchant solution.
The threading dislocation concentration in the surface of the window region 215 may be about 10 to about 10 less than the threading dislocation concentration in the underlying substrate 101 4 And (4) multiplying. The threading dislocation concentration in the surface of window region 215 may be less than about 10 8 cm -2 Less than about 10 7 cm -2 Less than about 10 6 cm -2 Less than about 10 5 cm -2 Or less than about 10 4 cm -2 . The threading dislocation concentration in the surface of wing region 217 may be about one to about three orders of magnitude lower than the threading dislocation concentration in the surface of window region 215, and may be less than about 10 5 cm -2 Less than about 10 4 cm -2 Less than about 10 3 cm -2 Less than about 10 2 cm -2 Or less than about 10cm -2 . Some stacking faults, e.g. at a concentration of about 1cm -1 And about 10 4 cm -1 May be present at the surface of the window region 215. The stacking fault concentration in the surface of wing region 217 may be about one to about three orders of magnitude lower than the stacking fault concentration in the surface of window region 215, and may be less than about 10 2 cm -1 Less than about 10cm -1 Less than about 1cm -1 Or less than about 0.1cm -1 Or may be undetectable. Threading dislocations (e.g., edge dislocations) may be present at the coalescence front regions 219 and 235, e.g., with a linear density of less than about 1 × 10 5 cm -1 Less than about 3X 10 4 cm -1 Less than about 1X10 4 cm -1 Less than about 3X 10 3 cm -1 Less than about 1X10 3 cm -1 Less than about 3X 10 2 cm -1 Or less than 1X10 2 cm -1 . The density of dislocations along the coalescence front may be greater than 5cm -1 Greater than 10cm -1 More than 20cm -1 Greater than 50cm -1 Greater than 100cm -1 Greater than 200cm -1 Or more than 500cm -1 。
In certain embodiments, the process of masking and bulk group III-nitride crystal growth is repeated one, two, three, or more times. In some embodiments, these operations are performed while the first bulk group III metal nitride layer remains coupled to the substrate 101. In other embodiments, the substrate 101 is removed, for example by sawing, lapping, grinding and/or etching, prior to subsequent masking and bulk crystal growth operations.
Fig. 4A, 4B, and 4C are simplified diagrams illustrating methods of forming a free-standing group III metal nitride boule and a free-standing group III metal nitride wafer. In certain embodiments, the substrate 101 is removed from the ammonothermal group III metal nitride layer 213 (fig. 4A, which is similar to the configuration of fig. 3E) or the last deposited such layer to form a free-standing merged ammonothermal group III metal nitride boule 413 comprising at least a portion of the ammonothermal group III metal nitride layer 213. Removal of the substrate 101 may be accomplished by one or more of sawing, grinding, lapping, polishing, laser lift-off, self-separation, and etching to form a treated free-standing laterally-grown group III metal nitride boule 413. The treated free-standing laterally-grown group III metal nitride boule 413 may comprise a composition similar or substantially the same as the ammonothermal group III metal nitride layer and may be etched under conditions where the etch rate of the backside of the substrate 101 is much faster than the etch rate of the front surface of the ammonothermal group III metal nitride layer. In certain embodiments, a portion of the ammonothermal group III metal nitride layer 213, or a last deposited such layer, may be protected from the etchant by depositing a mask layer, wrapping the portion of the layer with teflon, sandwiching the portion of the layer over teflon, painting with teflon paint, and the like. In one embodiment, the substrate 101 comprises single crystal gallium nitride, the large area surface 102 of the substrate 101 has a crystallographic orientation within about 5 degrees of the (0001) crystallographic orientation, and is formed by including H at a temperature between about 150 degrees celsius and about 500 degrees celsius 3 PO 4 H which has been conditioned by prolonged heat treatment to form polyphosphoric acid 3 PO 4 And H 2 SO 4 For a time between about 30 minutes and about 5 hours or by heating in a molten flux comprising one or more of NaOH and KOH to preferentially etch the substrate 101. Surprisingly, the patterned masking layer 111 can facilitate preferential removal of the substrate 101 by acting as an etch stop layer. The processed free-standing merged ammonothermal group III metal nitride crystal block 413 may comprise one or more window regions 415 formed over exposed regions 120 on the substrate 101, such as openings 112 in the patterned mask layer 111. The processed free-standing merged laterally grown group III-metal nitride boule 413 may further include one or more wing regions 417 formed over the non-open regions in the patterned masking layer 111, as well as a pattern of threading dislocations that locally approximate a linear array 419, as shown in fig. 4B, and one or more second condensation fronts 435. One or more of the front surface 421 and the back surface 423 of the free-standing consolidated ammonothermal group III metal nitride boule 413 may be ground, polished, etched, and chemically-mechanically polished. As similarly discussed above, the pattern of local approximate linear array 419 and one or more second junction fronts 435 may include a coalescence front region including a "sharp boundary" having a width of less than about 25 microns or less than about 10 microns disposed between adjacent wing regions 417, or an "extended boundary" having a width of between about 25 microns and about 1000 microns or between about 30 microns and about 250 microns disposed between adjacent wing regions 417, depending on growth conditions.
In certain embodiments, the edges of the free-standing consolidated ammonothermal group III metal nitride boule 413 are ground to form a cylindrical ammonothermal group III metal nitride boule. In some embodiments, one or more of the planar surfaces are ground to the sides of the freestanding combined ammonothermal group III metal nitride boule 413. In certain embodiments, the free-standing combined ammonothermal group III metal nitride boule 413 is sliced into one or more free-standing combined ammonothermal group III metal nitride wafers 431, as shown in fig. 4C. Dicing may be performed by multi-wire sawing, multi-wire slurry sawing, dicing, inside diameter sawing, outside diameter sawing, cleaving, ion implantation followed by stripping, spalling, laser cutting, and the like. One or more large area surfaces of the self-supporting merged ammonothermal group III metal nitride wafer 431 may be ground, polished, etched, electrochemically polished, photoelectrochemically polished, reactive ion etched, and/or chemically mechanically polished according to methods known in the art. In certain embodiments, the chamfer, bevel or rounded edge is ground to the edge of the free-standing merged ammonothermal group III metal nitride wafer 431. The self-supporting merged ammonothermal group III metal nitride wafer may have a diameter of at least about 10 millimeters, at least about 25 millimeters, at least about 50 millimeters, at least about 75 millimeters, at least about 100 millimeters, at least about 150 millimeters, at least about 200 millimeters, at least about 300 millimeters, at least about 400 millimeters, or at least about 600 millimeters, and may have a thickness between about 50 micrometers and about 20 millimeters, or between about 150 micrometers and about 5 millimeters. One or more large area surfaces of the free-standing merged ammonothermal group III metal nitride wafer 431 may be used as a substrate for group III metal nitride growth by chemical vapor deposition, metalorganic chemical vapor deposition, hydride vapor phase epitaxy, molecular beam epitaxy, flux growth, solution growth, ammonothermal growth, and the like.
Tiled seed array configuration examples
In some embodiments of the present disclosure, a tiled array of seeds used during a crystal growth process or in one or more steps in a multi-step crystal growth process may include the use and arrangement of seeds having desirable crystalline and structural properties such that a crystal layer grown from the formed tiled array of seeds has a reduced number of crystal defects (particularly at the coalescence front), and reduced misalignment between adjacent grains or seeds. In certain embodiments, the array of seeds 370 is arranged, oriented, and positioned in a one-dimensional array, as shown in fig. 20B-20C, rather than a two-dimensional array, as shown in fig. 17A-19G. Tiling in one dimension at a time may provide certain advantages over tiling in two dimensions at the same time, as described in more detail below. Generally, a fixture or handle substrate supporting two or more seeds positioned in an array is approximately CTE matched to the seeds. However, with respect to tiling of non-polar or semi-polar GaN crystals, where the CTEs in the c-direction and a-direction are different, due to the wurtzite crystal structure, the handle substrate cannot be CTE matched in both directions unless the handle substrate is also single crystal GaN with the same crystallographic orientation. An advantage of forming and coalescing a one-dimensional array of seeds is that it is more difficult to poly-crystallize in both directions at the same time than it is to poly-crystallize in only one growth direction at a time. Furthermore, the defect level at the coalescence boundary and the orientation difference angle tiled to tiling are strictly dependent on the accuracy of the polishing and alignment operations, and therefore the one-dimensional seed crystal array can be more easily aligned and structured, so that very high-quality coalesced GaN crystals can be formed in subsequent operations.
In certain embodiments of the present disclosure, a plurality of first GaN tiles or seeds 2001 are provided to be tiled in a first direction to form a one-dimensional seed array, as shown in fig. 20A to 20C. In certain embodiments, each of the tiled crystals 2001 that may include or consist of seed crystals 370 is prepared from a common single crystal, such as by multi-wire sawing, grinding, polishing, and chemical-mechanical polishing. The resulting tiled crystals 2001 can be tiled in one dimension, for example, along the C-direction of the m-plane seed, coalesced, and grown to an approximately equilibrium shape, as shown in fig. 20A-20C. In another embodiment, c-plane seeds may be tiled in the a-direction and grown to an approximately equilibrium shape. The original seed crystals may have been grown by the ammonothermal method or by HVPE.
In forming the one-dimensional array of seeds, after the seeds are positioned and aligned in the desired orientation, a coalescing step is used to join the seeds disposed in the one-dimensional array together (Y-direction). During the coalescence process, the gaps 2011 (fig. 20B, similar to the gaps 1711 in fig. 17A-17F) between adjacent tiled crystals 2001 may fill, forming a coalescence front 2015 in the same location as the gaps 2011 (fig. 20B and 20D). The coalescing step may be performed in a separate step, for example, using a mechanical fixture as shown in fig. 18A-18D, by bonding using a polycrystalline group III nitride layer as shown in fig. 19A-19C, or by bonding to a handle substrate as described below. The coalesced seed array may then be removed from the handle substrate and used as a seed for a subsequent ammonothermal crystal growth run. During subsequent ammonothermal crystal growth, the grown crystal layer 2045 formed on the coalesced seed array may grow to a near equilibrium shape to form a grown tiled seed 2050, as shown in fig. 20D-20E.
In some embodiments, the coalescing step is performed using a handle substrate composed of or including support members formed of one or more of molybdenum, a molybdenum alloy, a single or polycrystalline group III metal nitride, or another material having a close CTE match with the seed and compatible with the crystal growth environment, rather than using a mechanical fixture (fig. 18A-18D) or a polycrystalline group III nitride bonding layer (fig. 19A-19C). An adhesion layer may be deposited on the front side of the handle substrate and the back side of the seed. The adhesion layer may comprise SiO 2 、GeO 2 SiNx, AlNx, or B, Al, Si, P, Zn, Ga, Si, Ge, Au, Ag, Ni, Ti, Cr, Zn, Cd, In, Sn, Sb, Tl, W, In, Cu, or Pb, or an oxide, nitride, or oxynitride thereof. In certain embodiments, the composition of the adhesion layer on at least one of the handle substrate and the seed may have a melting point that may be selected so as to undergo incipient melting at a temperature of less than about 300 degrees celsius, less than about 400 degrees celsius, or less than about 500 degrees celsius. In certain embodiments, the composition of the adhesion layer on the other of the at least one of the handle substrate and the seed may have a melting point that may be selected so as to undergo incipient melting at a temperature of less than about 300 degrees celsius, less than about 400 degrees celsius, or less than about 500 degrees celsius, and may be selected so as to have a melting point of greater than about 600 degrees celsius, greater than about 700 degrees celsius, greater than about 800 degrees celsius, or greater than about 900 degrees celsius. The composition and structure of the adhesion layer may be selected to undergo incipient melting at a temperature of less than about 300 degrees celsius, less than about 400 degrees celsius, less than about 500 degrees celsius, or less than about 600 degrees celsius, and then, after bonding to the formulationThe adhesive layer remains unmelted or has a melt volume fraction of less than about 20%, less than about 10%, or less than about 5% at a temperature greater than about 600 degrees celsius, greater than about 700 degrees celsius, greater than about 800 degrees celsius, or greater than about 900 degrees celsius after being combined and heat treated at a temperature below the solidus temperature. The seed crystal may be bonded to the handle substrate at a first temperature at which the at least one adhesion layer composition may melt, and then thermally treated so as to remain unmelted at a second, higher temperature at which a crystal growth process is performed to coalesce the seed crystal into a consolidated crystal. Further details are described in us patent 10,400,352, which is hereby incorporated by reference in its entirety.
In some embodiments of the crystal formation process, the grown tiled seed 2050 is then cut, as schematically shown in fig. 21A. In one example, the slices are taken parallel to the m-plane and parallel to the original seed surface, forming long and narrow portions of the grown tiled seed 2050, such as crystals 2101, 2102, 2103, 2104, 2105, 2106, 2107, and 2108. The grown, tiled seed crystals 2050 are then tiled side-by-side, as shown in fig. 21B. Since adjacent stripes are formed of crystals above or below each other, the crystallographic orientation along the rows will be quite precise, e.g., better than 0.3 °, better than 0.1 °, better than 0.05 °, better than 0.02 °, or better than 0.01 °, even though the original one-dimensional tiling process shown in fig. 20A-20E is not as accurate.
In the process of forming the seed array, as shown in fig. 21B to 21C, after the narrow portions of the grown tiled seed are positioned and aligned in a desired orientation, the narrow portions of the grown tiled seed are coupled together (X direction) using a coalescence step. During the coalescence process, the gaps 2112 between adjacent tiled crystals 2001 (fig. 21B) may fill, forming a coalescence front 2115 at the same location as the gaps 2112 (fig. 21B and 21D). After coalescence, the first two-dimensional tiled crystal can be debonded from the fixture or processing substrate and regrown to a near-equilibrium shape, enclosing the regrown crystal layer 2145, as shown in fig. 21D-21E. Regrown crystal 2150 will include a growing crystal layer 2145 that includes a coalescence front 2115 formed within or over the gap 2112 (fig. 21B) present in the crystal array, similar to second coalescence front 435 described above, and a coalescence front 2015 formed by the extension of the pre-existing coalescence front 2015 in seed 2101, 2102, etc. Inaccuracies in the original tiling can manifest as grain boundaries in the Y-direction or axial direction (i.e., the coalescence front 2015; c-direction in the particular example shown), but differences in orientation in the X-direction (i.e., the coalescence front 2115; a-direction in the particular example shown) should be minimal.
Regrown crystal 2150 may then be cut in the X-Y plane (parallel to the m-plane in the particular example shown), as schematically illustrated in fig. 22A, forming, for example, slices 2201, 2202, 2203, 2204, 2205, 2206, 2207, and 2208. Further, as shown in fig. 22B, regrown crystals 2150 or slices 2201-2208 may then be cut at location 2220, corresponding to the defect grain boundaries present at the coalescence front 2015, which in the particular example shown (fig. 21D) is parallel to the C-plane, forming, for example, slabs 2201A, 2201B, 2201C, …, 2202A, 2202B, 2202C, … 2208C, 2208D, and 2208E (e.g., 40 slabs in total). After the slices 2201-2208 are formed and cut at location 2220, the resulting slabs 2201A-2208E may then be tiled again in a direction orthogonal to the previous tiling operation, as shown in FIG. 22C. In this configuration, slabs adjacent to each other in the Z direction are placed side by side to form a one-dimensional array in the Y direction, and edges prepared at position 2220 are placed adjacent to each other. This formed array of slabs 2201A-2208A (fig. 22C-22D) will allow the very small orientation differences present in regrown crystal 2150 to be replicated throughout the subsequently formed damascene crystal 2250.
In forming the array of slabs 2201A-2208A, as shown in fig. 22B-22C, after the slabs 2201A-2208A are positioned and aligned in a desired orientation, the array of slabs 2201A-2208A are coupled together (Y-direction) using a coalescing step. During coalescence, the gaps 2212 between adjacent slabs 2201A-2208A (fig. 22C) may fill, forming a coalescence front 2215 at the same location as the gaps 2212 (fig. 22C and 22E). Each slab 2201A-2208A disposed in an array is coupled together by at least one coalescing front 2215 (fig. 22C). Once the array of slabs 2201A-2208A are re-coalesced, they can be de-bonded from the fixture or process substrate and re-grown to form an equilibrium shape with a growing crystal layer 2245 that includes a greatly reduced defect concentration associated with the coalescence front 2215, as shown in fig. 22E. Similar processes may be followed for coalescence and growth on slabs 2201B-2208B, 2201C-2208C … and 2201E-2208E.
The process schematically illustrated in FIGS. 20A-22F can be used to fabricate large area, low defect m-plane GaN crystals suitable for use as seeds in subsequent ammonothermal crystal growth of m-plane ingots or in subsequent bulk crystal growth by another method such as HVPE or flux growth. Similarly, the continuous 1-D tiling operation can be used to produce large area, low defect c-plane or semi-polar GaN crystals suitable for use as seed crystals in subsequent bulk crystal growth or as substrates for electronic or optoelectronic device fabrication.
In certain embodiments, the inlaid crystal 2250 is cut along a short dimension or at an oblique angle, for example to form a seed suitable for use as a seed in a subsequent ammonothermal crystal growth or in a subsequent bulk crystal growth by another method such as HVPE or flux growth, for further one-or two-dimensional tiling processes, or as a substrate for electronic or optoelectronic device fabrication.
In an alternative embodiment, for example, for c-plane or semi-polar crystal growth, the initial one-dimensional tiling operation (fig. 20A-20D) is omitted and the separated m-plane crystals are grown only to near-equilibrium shapes. The formed crystals can be cut and tiled parallel to the m-plane as shown in fig. 21A-21E to form regrown crystals 2150. Alternatively, the crystals formed may be cut parallel to the c-plane or semi-polar direction to prepare seeds for one-dimensional tiling operations. From at + c [0001 ]]Directionally grown boule region-sliced crystals having substantially reduced dislocation density and are particularly suitable for dislocation densities below 10 6 cm -2 Less than 10 5 cm -2 Less than 10 4 cm -2 Or less than 10 3 cm -2 And/or semi-polar crystals.
Relative to a two-dimensional one-step tiling process as schematically illustrated in fig. 17A-19F, the sequential 1-D tiling approach may have several advantages, including the ability to more easily perform tile selection, preparation, and stacking; more accurately arranging single crystal domains; reducing CTE mismatch with the handle substrate or fixture, thereby reducing the risk of cracking; and reduces the risk of each tile misdirecting beyond a target specification (e.g., 0.1 deg.).
Growing and self-supporting Crystal examples
Fig. 5A to 5E are simplified diagrams illustrating threading dislocation patterns formed over respective tiled crystals formed by the patterned growth method outlined in fig. 1A to 4C. Each of the tiled crystals shown in fig. 5A-5E can form a portion of a free-standing merged group III-metal nitride boule 413 or wafer 431 as described in connection with fig. 4A-4C, or a portion of a free-standing merged ammonothermal group III-nitride boule or wafer as shown in fig. 6A-6G, as described further below. The large-area surface of the free-standing merged ammonothermal group III metal nitride boule 413 or wafer 431 may be characterized by a pattern of threading dislocations that propagate from a locally approximately linear array 419 of coalescence fronts 219 formed during the epitaxial lateral overgrowth process, as discussed above in connection with fig. 3A-3E. The pattern of threading dislocations of the local approximately linear array may be 2D hexagonal, square, rectangular, trapezoidal, triangular, 1D linear, or an irregular pattern formed at least in part due to the pattern of exposed regions 120 (fig. 1F-1L) used during the process of forming the free-standing laterally-grown group III-metal nitride boule 413. One or more window regions 415 are formed over the exposed regions 120 (fig. 1F-1L), and one or more wing regions 417 are formed on portions not over the exposed regions 120, i.e., by lateral growth. As discussed above, the pattern of the formed coalescence fronts 219 or local approximately linear array 419 may include coalescence front regions having lateral widths (i.e., measured parallel to the surface of the page containing fig. 5A-5E) that may vary depending on growth conditions.
More complex patterns are also possible and may be advantageous, for example, being more resistant to cracking or splitting. The pattern 502 may be elongated in one direction as compared to the other orthogonal direction, for example, due to the free-standing merged laterally grown group III metal nitride boule 413 being cut at an oblique angle relative to the large area surface of the free-standing merged ammonothermal group III metal nitride boule 413. The pattern 502 of local approximate linear arrays of threading dislocations may be characterized by a linear array of threading dislocations (fig. 5D) having a pitch dimension L between about 5 microns and about 20 millimeters or between about 200 microns and about 5 millimeters. The pattern 502 of threading dislocations in a local approximately linear array may be characterized by a pitch dimension L (fig. 5A, 5B) or a pitch dimension L in two orthogonal directions 1 And L 2 (fig. 5C and 5E), the pitch dimension being between about 5 microns and about 20 millimeters, or between about 200 microns and about 5 millimeters, or between about 500 microns and about 2 millimeters. In some embodiments, the local approximately linear array of threading dislocation patterns 502 is approximately aligned with the underlying crystalline structure of the group III metal nitride, e.g., the local approximately linear array is located<1 0 -1 0>、<1 1 -2 0>Or [ 000. + -. 1%]Within about 5 degrees, within about 2 degrees, or within about 1 degree of a projection in the plane of the surface of the free-standing merged ammonothermal group III metal nitride boule 413 or group III metal nitride wafer 431. The linear concentration of threading dislocations in the pattern may be less than about 1x10 5 cm -1 Less than about 3X 10 4 cm -1 Less than about 1X10 4 cm -1 Less than about 3X 10 3 cm -1 Less than about 1X10 3 cm -1 Less than about 3X 10 2 cm -1 Or less than about 1X10 2 cm -1 . The linear concentration of threading dislocations in the pattern 502 may be greater than 5cm -1 Greater than 10cm -1 Greater than 20cm -1 Greater than 50cm -1 Greater than 100cm -1 Greater than 200cm -1 Or more than 500cm -1 。
Referring again to FIGS. 5A-5E, self-supporting consolidationThe large area surface of individual grains or domains within an ammonothermal group III metal nitride boule or wafer may also be characterized by an array of wing regions 417 and an array of window regions 415. Each domain (or sometimes referred to herein as a grain) may be formed by growing over a single tiled crystal (e.g., seed 370). The crystalline domains will typically include wing regions, window regions, coalescence fronts and local approximately linear arrays of dislocations, and are typically bounded by coalescence fronts. Each wing region 417 may be positioned between threading dislocations of adjacent local approximately linear arrays 419. Each window region 415 may be positioned within a single wing region 417, or may be positioned between two adjacent wing regions 417, and may have a minimum dimension of between 10 microns and 500 microns, and be characterized by a minimum dimension of between 10 microns and 500 microns 3 cm -2 And 10 8 cm -2 A concentration of threading dislocations therebetween, the threading dislocations resulting from residual threading dislocations vertically propagating from the window region during the bulk crystal growth process, and less than 10 3 cm -1 Stacking fault concentration of (a). In some embodiments, the boundary between the window region and the wing region may be decorated with dislocations, for example, having a linear density of between about 5cm -1 And 10 5 cm -1 In the meantime.
The array may be elongated in one direction as compared to another orthogonal direction, for example, due to the boule being cut at an oblique angle relative to the large area surface of the self-supporting merged ammonothermal group III metal nitride boule. The pattern of threading dislocations that locally approximate the linear array 419 may be characterized by a pitch dimension L or pitch dimensions L in two orthogonal directions 1 And L 2 The pitch dimension is between about 5 microns and about 20 millimeters, or between about 200 microns and about 2 millimeters. In some embodiments, the first pattern of threading dislocations of the local approximately linear array 419 are approximately aligned with the underlying crystalline structure of the group III metal nitride, e.g., the local approximately linear array is located<1 0 -1 0>、<1 1 -2 0>Or [ 000. + -. 1%]Or within about 5 degrees, within about 2 degrees, or within about 1 degree of a projection of the one or more of in the plane of the surface of the free-standing ammonothermal group III nitride boule or wafer. Penetration in patternsThe linear concentration of dislocations may be less than about 1x10 5 cm -1 Less than about 3X 10 4 cm -1 Less than about 1X10 4 cm -1 Less than about 3X 10 3 cm -1 Less than about 1X10 3 cm -1 Less than about 3X 10 2 cm -1 Or less than about 1X10 2 cm -1 . The linear concentration of threading dislocations in the pattern may be greater than 5cm -1 Greater than 10cm -1 Greater than 20cm -1 Greater than 50cm -1 More than 100cm -1 Greater than 200cm -1 Or more than 500cm -1 。
The threading dislocation concentration in the wing regions 417 between the local approximately linear array of threading dislocations may be less than about 10 5 cm -2 Less than about 10 4 cm -2 Less than about 10 3 cm -2 Less than about 10 2 cm -1 Or less than about 10cm -2 . The threading dislocation concentration in the surface of window region 415 may be less than about 10 8 cm -2 Less than about 10 7 cm -2 Less than about 10 6 cm -2 Less than about 10 5 cm -2 Or less than about 10 4 cm -2 . The concentration of threading dislocations in the surface of the window region may be at least two times, at least three times, at least ten times, at least 30 times, or at least 100 times higher than the concentration of threading dislocations in the surface of the wing region. The concentration of threading dislocations in the surface of the window region may be less than 10 higher than the concentration of threading dislocations in the surface of the wing region 4 Multiple, less than 3000 times, less than 1000 times, less than 300 times, less than 100 times, or less than 30 times. In some embodiments, the boundary between the window region 415 and the wing region 417 may be decorated with a misalignment, for example, having a linear density of between about 5cm -1 And 10 5 cm -1 In the meantime. The average threading dislocation concentration on the large area surface of a free-standing ammonothermal group III nitride boule or wafer may be less than about 10 7 cm -2 Less than about 10 6 cm -2 Less than about 10 5 cm -2 Less than about 10 4 cm -2 Less than about 10 3 cm -2 Or less than about 10 2 cm -2 . In self-supportingThe average stacking fault concentration on a large area surface of an ammonothermal group III nitride boule or wafer may be less than about 10 3 cm -1 Less than about 10 2 cm -1 Less than about 10cm -1 Less than about 1cm -1 Or less than about 0.1cm -1 Or may be undetectable. In some embodiments, for example, after repeated regrowth and/or growth to a thickness greater than 2 millimeters, greater than 3 millimeters, greater than 5 millimeters, or greater than 10 millimeters on a seed having a patterned dislocation array, the location of the threading dislocations may be shifted laterally to some extent relative to the pattern on the seed. In this case, the regions having higher threading dislocation concentrations may be more dispersed than the relatively sharp lines schematically shown in fig. 5A to 5E. However, the threading dislocation concentration as a function of lateral position along a line on the surface will vary periodically with a period between about 5 microns and about 20 millimeters, or between about 200 microns and about 5 millimeters. The concentration of threading dislocations within the periodically varying region may vary by a factor of at least 2, at least 5, at least 10, at least 30, at least 100, at least 300, or at least 1000.
Referring to fig. 6A-6F, a free-standing consolidated ammonothermal group III nitride boule or wafer may be formed by using one or more tiling processes described in conjunction with fig. 3A-4C and 17A-22F, as described above. A self-supporting merged ammonothermal group III nitride boule or wafer may include two or more domains or grains separated by one or more second dislocation lines 635 resulting from a second condensation front 235 or 2215 formed during lateral growth of the ammonothermal group III metal nitride material from one seed to its neighboring seed, as schematically illustrated in fig. 2C, 3E, and 22E. Depending on the geometry of the original nitride crystal, the pattern of domains may be, for example, (a) squares (fig. 6A and 17A), (B) rectangles (fig. 6B and 17B), (C) hexagons (fig. 6C and 17C), (D) diamonds (fig. 6D and 17D), (E) a mixture of hexagons and pentagons (fig. 6E and 17E); or (F) a mixture of hexagons and diamonds (fig. 6F and 17F). Other patterns are also possible. FIG. 6G illustrates the use of multiple tiled seed crystals (e.g., crystalline) as shown in FIG. 1G during a crystal growth processSeed 370), wherein each domain created by a single tiled crystal (e.g., seed 370) includes a window region and wing regions and a coalescence front. The crystal domains may have a first lateral tiling dimension 680 and a second lateral tiling dimension 690 that approximately correspond to the original tiled crystal dimensions 380 and 390, respectively (see fig. 17A-17F), the lateral dimensions defining a plane perpendicular to the thickness, wherein each of the first lateral tiling dimension 680 and the second lateral tiling dimension 690 may be at least about 5 millimeters, 10 millimeters, 15 millimeters, 20 millimeters, 25 millimeters, 35 millimeters, 50 millimeters, 75 millimeters, 100 millimeters, 150 millimeters, or at least about 200 millimeters. The difference angle of polar orientation γ between adjacent domains may be less than 0.5 degrees, less than 0.2 degrees, less than 0.1 degrees, less than 0.05 degrees, less than 0.02 degrees, or less than 0.01 degrees. The first lateral tiling dimension 680 may be approximately the same as the first lateral seed dimension (i.e., the X-direction dimension 380). Similarly, the second lateral tiling dimension 690 can be approximately equal to the second lateral seed dimension (i.e., the Y-direction dimension 390). The orientation difference angles α and β between adjacent domains may be less than 0.5 degrees, less than 0.2 degrees, less than 0.1 degrees, less than 0.05 degrees, less than 0.02 degrees, or less than 0.01 degrees. Typically, γ will be less than or equal to α and β. The crystallographic orientation difference angles α, β, and γ may be greater than about 0.01 degrees, greater than about 0.02 degrees, greater than about 0.05 degrees, or greater than about 0.1 degrees. The dislocation density along lines between adjacent domains may be less than about 5 x10 5 cm -1 Less than about 2X 10 5 cm -1 Less than about 1X10 5 cm -1 Less than about 5X 10 4 cm -1 Less than about 2X 10 4 cm -1 Less than about 1X10 3 cm -1 Less than about 5X 10 3 cm -1 Less than about 2X 10 3 cm -1 Or less than about 1X10 3 cm -1 . The dislocation density along lines between adjacent domains may be greater than 50cm -1 Greater than 100cm -1 Greater than 200cm -1 Greater than 500cm -1 Greater than 1,000cm -1 Greater than 2000cm -1 Or more than 5000cm -1 。
A symmetric x-ray rocking curve (e.g., (002) in terms of c-plane) full width at half maximum (FWHM) of a self-supporting merged ammonothermal group III nitride boule or wafer may be less than about 300 arcseconds, less than about 200 arcseconds, less than about 100 arcseconds, less than about 50 arcseconds, less than about 35 arcseconds, less than about 25 arcseconds, or less than about 15 arcseconds. An asymmetric x-ray rocking curve (e.g., (201) or (102) in terms of c-plane) of a free-standing merged ammonothermal group III nitride ingot or wafer may have a full width at half maximum (FWHM) of less than about 300 arcseconds, less than about 200 arcseconds, less than about 100 arcseconds, less than about 50 arcseconds, less than about 35 arcseconds, less than about 25 arcseconds, or less than about 15 arcseconds. The free-standing consolidated ammonothermal group III nitride boules or wafers may have a thickness between about 100 microns and about 100 millimeters, or between about 1 millimeter and about 10 millimeters. The self-supporting consolidated ammonothermal group III nitride boule or wafer may have a diameter of at least about 15 millimeters, at least about 20 millimeters, at least about 25 millimeters, at least about 35 millimeters, at least about 50 millimeters, at least about 75 millimeters, at least about 100 millimeters, at least about 150 millimeters, at least about 200 millimeters, or at least about 400 millimeters. The surface of the free-standing merged ammonothermal group III nitride boule or wafer may have a crystallographic orientation within 10 degrees, within 5 degrees, within 2 degrees, within 1 degree, within 0.5 degrees, within 0.2 degrees, within 0.1 degrees, within 0.05 degrees, within 0.02 degrees, or within 0.01 degrees of (0001) Ga-polar, (000-1) N-polar, {10-10} nonpolar, or {11-20} nonpolar a-plane. The surface of the free-standing consolidated ammonothermal group III nitride boule or wafer may have an (hki) semipolar orientation, where i ═ h + k, and at least one of i and h and k are non-zero. In one embodiment, the crystalline orientation of the self-supporting consolidated ammonothermal group III nitride boule or wafer is within {11-2 + -2 }, {60-6 + -1 }, {50-5 + -1 }, {40-4 + -1 }, {30-3 + -1 }, {50-5 + -2 }, {70-7 + -3 }, {20-2 + -1 }, {30-3 + -2 }, {40-4 + -3 }, {50-5 + -4}, {10-1 + -1 }, {10-1 + -2 }, {10-1 + -3 }, { 21-3 + -1 } or {30-3 + -4} within 10 degrees, 5 degrees, 2 degrees, 1 degree, 0.5 degrees, 0.2 degrees, 0.1 degrees, 0.05 degrees, 0.02 degrees or 0.01 degrees. The free-standing consolidated ammonothermal group III nitride boules or wafers have a minimum lateral dimension of at least ten millimeters. In some embodiments, the combined nitride crystal has a minimum lateral dimension of at least two centimeters, at least three centimeters, at least four centimeters, at least five centimeters, at least six centimeters, at least eight centimeters, at least ten centimeters, or at least twenty centimeters.
In some embodiments, a free-standing consolidated ammonothermal group III nitride boule or wafer is used as a substrate for epitaxy to form a semiconductor structure. The free-standing consolidated ammonothermal group III nitride boule may be sawed, lapped, polished, dry etched, and/or chemically mechanically polished by methods known in the art. One or more edges of the free-standing consolidated ammonothermal group III nitride boule or wafer may be ground. The self-supporting consolidated ammonothermal group III nitride boules or wafers may be placed in a suitable reactor and epitaxial layers grown by MOCVD, MBE, HVPE, or the like. In one embodiment, the epitaxial layer comprises GaN or Al x In y Ga (1-x-y) N, wherein x is more than or equal to 0 and y is less than or equal to 1. The morphology of the epitaxial layer is uniform from one domain to another on the surface because the surface orientations are nearly the same.
In some embodiments, a free-standing consolidated ammonothermal group III nitride boule or wafer is used as a substrate for further tiling. For example, referring to fig. 17A through 19D, the seed crystal 370 itself may be selected to be a free-standing consolidated ammonothermal group III metal nitride boule or wafer. The tiling, coalescing, and re-tiling operations may be repeated more than two times, more than 4 times, more than 8 times, or more than 16 times. In this way, by successive tiling operations, a combined nitride crystal having excellent crystalline quality and an extremely large diameter can be produced.
The self-supporting merged aminothermal group III nitride boule or wafer may be used as a substrate for the fabrication of optoelectronic devices and electronic devices such as light emitting diodes, laser diodes, photodetectors, avalanche photodiodes, transistors, rectifiers, Schottky rectifiers, thyristors, p-i-n diodes, metal-semiconductor-metal diodes, high electron mobility transistors, metal semiconductor field effect transistors, metal oxide field effect transistors, power metal oxide semiconductor field effect transistors, power metal insulator semiconductor field effect transistors, bipolar junction transistors, metal insulator field effect transistors, heterojunction bipolar transistors, power insulated gate bipolar transistors, power vertical junction field effect transistors, cascode switches, internal sub-band emitters, photovoltaic devices, quantum well infrared photodetectors, quantum dot infrared photodetectors, solar cells, or diodes for photoelectrochemical water splitting and hydrogen generation devices. In some embodiments, the position of the devices relative to the domain structures in the self-supporting merged ammonothermal group III nitride boule or wafer is selected such that the active regions of the individual devices are located within a single domain or grain of the self-supporting merged ammonothermal group III nitride boule or wafer.
The self-supporting merged ammonothermal group III metal nitride boule or wafer may have a grain size within 5 degrees, within 2 degrees, within 1 degree, within 0.5 degrees, within (0001) + c-plane, (000-1) -c-plane, {10-10} m-plane, {11-20} a-plane, {11-2 + -2 }, {60-6 + -1 }, {50-5 + -1 }, {40-4 + -1 }, {30-3 + -1 }, {50-5 + -2 }, {70-7 + -3 }, {20-2 + -1 }, {30-3 + -2 }, {40-4 + -3 }, {50-5 + -4}, {10-1 + -1 }, {10-1 + -2 }, {10-1 + -3 + -1 }, or {30-3 + -4}, of { 10-3 + -4}, or { 1-1 degree, Large area crystallographic orientation within 0.2 degrees, within 0.1 degrees, within 0.05 degrees, within 0.02 degrees, or within 0.01 degrees. The free-standing ammonothermal group III metal nitride boule or wafer may have a (hkil) semipolar large area surface orientation, where i ═ h + k, and at least one of l and h and k is nonzero.
In certain embodiments, the large-area surface of a self-supporting ammonothermal group III metal nitride crystal or wafer has a surface from {10-10} m-plane to [0001 [ ]]About-60 degrees to about +60 degrees miscut in + c-direction and orthogonal in direction<1-210>The a-direction is miscut to a crystallographic orientation of up to about 10 degrees. In certain embodiments, the large-area surface of a self-supporting ammonothermal group III metal nitride crystal or wafer has a surface from {10-10} m-plane to [0001 [ ]]About-30 degrees to about +30 degrees miscut in the + c-direction and orthogonal in the direction<1-210>The a-direction is miscut with a crystallographic orientation of up to about 5 degrees. In certain embodiments, the large-area surface of a self-supporting ammonothermal group III metal nitride crystal or wafer has a surface from {10-10} m-plane to [0001 [ ]]About-5 degrees to about +5 degrees miscut in the + c-direction and orthogonal in the direction<1-210>The a-direction is miscut with a crystallographic orientation of up to about 1 degree. The free-standing ammonothermal group III metal nitride crystal or wafer may have less than 1 on one or both of the two large area surfaces0 2 cm -1 Less than 10cm -1 Or less than 1cm -1 A stacking fault density of less than about 10 5 cm -2 Less than about 10 4 cm -2 Less than about 10 3 cm -2 Less than about 10 2 cm -2 Or less than about 10cm -2 Very low dislocation density.
The self-supporting merged ammonothermal group III metal nitride boule or wafer may have a symmetric x-ray rocking curve full width at half maximum (FWHM) of less than about 200 arc seconds, less than about 100 arc seconds, less than about 50 arc seconds, less than about 35 arc seconds, less than about 25 arc seconds, or less than about 15 arc seconds. The free-standing consolidated ammonothermal group III metal nitride boule or wafer may have a radius of crystalline curvature in at least one, at least two, or three independent or orthogonal directions of greater than 0.1 meter, greater than 1 meter, greater than 10 meters, greater than 100 meters, or greater than 1000 meters.
In certain embodiments, the atomic impurity concentration of at least one of oxygen (O) and hydrogen (H) of at least one surface of the free-standing consolidated ammonothermal group III metal nitride boule or wafer is greater than about 1x10 16 cm -3 Above about 1 × 10 17 cm -3 Or greater than about 1X10 18 cm -3 . In certain embodiments, the ratio of the atomic impurity concentration of H to the atomic impurity concentration of O is between about 0.3 and about 1000, between about 0.4 and about 10, or between about 10 and about 100. In certain embodiments, the impurity concentration of at least one of lithium (Li), sodium (Na), potassium (K), fluorine (F), chlorine (Cl), bromine (Br), or iodine (I) of at least one surface of the self-supporting consolidated ammonothermal group III metal nitride boule or wafer is greater than about 1x10 15 cm -3 Above about 1 × 10 16 cm -3 Or greater than about 1X10 17 cm -3 Above about 1 × 10 18 cm -3 . In certain embodiments, the impurity concentrations of O, H, carbon (C), Na, and K for the top and bottom surfaces of the free-standing combined ammonothermal group III metal nitride boule or wafer, respectively, may be between about 1x10 16 cm -3 And 1X10 19 cm -3 Between about 1X10 16 cm -3 And 2X 10 19 cm -3 A middle part of the upper part,Less than 1X10 17 cm -3 Less than 1X10 16 cm -3 And less than 1X10 16 cm -3 As quantified by calibrated Secondary Ion Mass Spectrometry (SIMS). In another embodiment, the impurity concentrations of O, H, C and at least one of Na and K for the top and bottom surfaces of the free-standing combined ammonothermal group III metal nitride boule or wafer, respectively, may be between about 1X10 16 cm -3 And 1X10 19 cm -3 Between about 1X10 16 cm -3 And 2X 10 19 cm -3 Middle, lower than 1X10 17 cm -3 And between about 3X 10 15 cm -3 And 1X10 18 cm -3 As quantified by calibrated Secondary Ion Mass Spectrometry (SIMS). In another embodiment, the impurity concentrations of O, H, C and at least one of F and Cl for the top and bottom surfaces of the free-standing combined ammonothermal group III metal nitride boule or wafer, respectively, may be between about 1X10 16 cm -3 And 1X10 19 cm -3 Between about 1X10 16 cm -3 And 2X 10 19 cm -3 Middle, lower than 1X10 17 cm -3 And between about 1 × 10 15 cm -3 And 1X10 19 cm -3 As quantified by calibrated Secondary Ion Mass Spectrometry (SIMS). In some embodiments, the impurity concentration of H for the top and bottom surfaces of the free-standing combined ammonothermal group III metal nitride boule or wafer may be between about 5 x10 17 cm -3 And 1X10 19 cm -3 As quantified by calibrated Secondary Ion Mass Spectrometry (SIMS). In certain embodiments, the impurity concentration of copper (Cu), manganese (Mn), and iron (Fe) at least one surface of the free-standing consolidated ammonothermal group III metal nitride boule or wafer is between about 1x10 16 cm -3 And 1X10 19 cm -3 In the meantime. In one embodiment, the free-standing consolidated ammonothermal group III metal nitride boule or wafer is at about 3175cm -1 Has an infrared absorption peak and an absorbance per unit thickness of greater than about 0.01cm -1 。
The self-supporting merged ammonothermal group III metal nitride crystals or wafers may be characterized by a wurtzite structure being substantially free of any cubic entities or other crystal structures, the other structures being less than about 0.1% by volume relative to the volume of the substantially wurtzite structure.
Surprisingly, in view of the lattice mismatch between HVPE GaN and ammonothermal GaN, the results of the use of the techniques disclosed herein indicate that ammonothermal lateral epitaxial overgrowth can produce thick large-area GaN layers without cracks. In certain embodiments, the free-standing, consolidated ammonothermal group III metal nitride crystal or wafer has a diameter greater than about 25 millimeters, greater than about 50 millimeters, greater than about 75 millimeters, greater than about 100 millimeters, greater than about 150 millimeters, greater than about 200 millimeters, greater than about 300 millimeters, or greater than about 600 millimeters, and a thickness greater than about 0.1 millimeters, greater than about 0.2 millimeters, greater than about 0.3 millimeters, greater than about 0.5 millimeters, greater than about 1 millimeter, greater than about 2 millimeters, greater than about 3 millimeters, greater than about 5 millimeters, greater than about 10 millimeters, or greater than about 20 millimeters, and is substantially free of cracks. In contrast, we found that ammonothermal growth on large area, unpatterned HVPE GaN seeds can lead to cracking if the layer is thicker than a few hundred microns, even if patterning processes have been used to form HVPE GaN seeds.
The free-standing consolidated ammonothermal group III metal nitride wafer may be characterized by a Total Thickness Variation (TTV) of less than about 25 microns, less than about 10 microns, less than about 5 microns, less than about 2 microns, or less than about 1 micron, and by a macrobow of less than about 200 microns, less than about 100 microns, less than about 50 microns, less than about 25 microns, or less than about 10 microns. The large area surface of the self-supporting merged ammonothermal group III metal nitride wafer may have less than about 2cm -2 Less than about 1cm -2 Less than about 0.5cm -2 Less than about 0.25cm -2 Or less than about 0.1cm -2 Has a diameter or feature size greater than about 100 microns. The variation in the miscut angle across the large area surface of a free-standing ammonothermal group III metal nitride crystal or wafer may be less than about 1 degree, less than about 0.5 degree, less than about 0.2 degree, less than about 0.1 degree, less than about 0.05 degree, or less than about 0 in each of the two orthogonal crystallographic directions.025 degrees. The root mean square surface roughness of the large area surface of the self-supporting merged ammonothermal group III metal nitride wafer, as measured over an area of at least 10 μm x10 μm, may be less than about 0.5 nanometers, less than about 0.2 nanometers, less than about 0.15 nanometers, less than about 0.1 nanometers, or less than about 0.10 nanometers. The free-standing combined ammonothermal group III metal nitride wafer may be characterized by n-type conductivity with a carrier concentration between about 1x10 17 cm -3 And about 3X 10 19 cm -3 And carrier mobility greater than about 100cm 2 V-s. In an alternative embodiment, the self-supporting merged ammonothermal group III metal nitride wafer is characterized by p-type conductivity with a carrier concentration between about 1x10 15 cm -3 And about 1X10 19 cm -3 In the meantime. In other embodiments, the free-standing, consolidated ammonothermal group III metal nitride wafers are characterized by semi-insulating electrical properties, room temperature resistivity greater than about 10 7 Ohm-cm, greater than about 10 8 Ohm-cm, greater than about 10 9 Ohm-cm, greater than about 10 10 Ohm-cm or greater than about 10 11 Ohm-cm. In certain embodiments, the self-supporting merged ammonothermal group III metal nitride wafer is highly transparent and has an optical absorption coefficient of less than about 10cm at a wavelength of 400 nanometers -1 Less than about 5cm -1 Less than about 2cm -1 Less than about 1cm -1 Less than about 0.5cm -1 Less than about 0.2cm -1 Or less than about 0.1cm -1 。
In some embodiments, a self-supporting merged ammonothermal group III metal nitride crystal or wafer is used as a seed for further bulk growth. In one embodiment, the further bulk growth comprises a combined ammonothermal bulk crystal growth. In another embodiment, the further bulk growth comprises high temperature liquid crystal growth, also known as flux crystal growth. In another embodiment, the further bulk growth comprises HVPE. The further grown crystal may be cut, lapped, polished, etched and/or chemically mechanically polished into wafers by methods known in the art. The wafer surface may be characterized by a root mean square surface roughness of less than about 1 nanometer or less than about 0.2 nanometers measured over a 10 micron by 10 micron area.
The wafer may be incorporated into a semiconductor structure. The semiconductor structure may include at least one Al x In y Ga (1-x-y) And the N epitaxial layer, wherein x is more than or equal to 0, y is more than or equal to 1, and x + y is less than or equal to x. Epitaxial layers may be deposited on the wafer, for example, by Metal Organic Chemical Vapor Deposition (MOCVD) or by Molecular Beam Epitaxy (MBE), according to methods known in the art. At least a portion of the semiconductor structure may form part of a gallium nitride-based electronic or optoelectronic device, such as a light emitting diode, a laser diode, a power conversion photodiode, a photodetector, an avalanche photodiode, a photovoltaic cell, a solar cell, a cell for photoelectrochemical decomposition of water, a transistor, a rectifier and a thyristor; one of a transistor, a rectifier, a schottky rectifier, a thyristor, a p-i-n diode, a metal-semiconductor-metal diode, a high electron mobility transistor, a metal semiconductor field effect transistor, a metal oxide field effect transistor, a power metal oxide semiconductor field effect transistor, a power metal insulator semiconductor field effect transistor, a bipolar junction transistor, a metal insulator field effect transistor, a heterojunction bipolar transistor, a power insulated gate bipolar transistor, a power vertical junction field effect transistor, a cascode switch, an internal sub-band emitter, a quantum well infrared photodetector, a quantum dot infrared photodetector, and combinations thereof. Gallium nitride-based electronic or optoelectronic devices may be incorporated into lamps or fixtures such as illuminators. The gallium nitride-based electronic or optoelectronic device may have lateral dimensions of at least 0.1mm x 0.1mm after singulation. The gallium nitride-based electronic or optoelectronic device may have a maximum dimension of at least 8 millimeters and may comprise, for example, a laser diode. Gallium nitride-based electronic or optoelectronic devices may be completely free of dislocations throughout their volume. For example, at 10 4 cm -2 At a dislocation density of (2), most of 0.1X 0.1mm can be expected 2 The device of (a) has no dislocations. At 10 2 cm -2 At a dislocation density of (2), most of 1X 1mm can be expected 2 The device of (a) has no dislocations. The gallium nitride-based electronic or optoelectronic device may be completely free of stacking faults throughout its volume. E.g. at 1cm -1 At a stacking fault density of (2), a large part of 10X 1mm can be expected 2 Stripe-shaped devices, such as laser diodes with non-polar or semi-polar large area surfaces and c-plane facets, are free of stacking faults.
Fig. 7A-7D are cross-sectional views illustrating a method and resulting optoelectronic and electronic devices according to embodiments of the present disclosure. A two-or three-terminal device such as an optoelectronic device or an electronic device may be formed by a series of steps including a step of epitaxial layer deposition on a self-supporting merged ammonothermal group III metal nitride wafer 431 or substrate having a pattern of threading dislocations locally approximating a linear array 419 and including at least one AlInGaN active layer or GaN drift layer 631, for example by MOCVD, as shown in fig. 7B. In some embodiments, the deposited layers include an n-type or n + layer 633, a doped or unintentionally doped Single Quantum Well (SQW), Multiple Quantum Well (MQW) structure, double heterostructure (DH structure), or n-drift layer, and a p-type layer 636, as shown. The device structure may be vertical, as schematically shown in fig. 7B and 7D, or lateral, as schematically shown in fig. 7C. The device may be electrically connected to external circuitry to provide a potential between n-type contact 639 and p-type contact 637. Additional layers may be deposited such as a Separate Confinement Heterostructure (SCH) layer, cladding layers, AlGaN electron blocking layers, and p + contact layers, among others. In many cases, threading dislocations in the substrate, such as the pattern of the local approximately linear array 419, will propagate into the deposited layer and potentially affect device performance.
In one embodiment, the method also deposits n-type contact 639 and p-type contact 637, as shown in fig. 7B and 7C. In some embodiments, at least one contact of the set of n-type and p-type contacts is placed in a particular arrangement relative to the coalescence front, the wing region, and/or the window region. The light-emitting portion may be centered above or between the coalescence fronts. In one embodiment, transparent p-type contacts are deposited and placed in a manner that avoids contact with a coalescence front that may have an increased threading dislocation concentration. Thus, canA light emitting structure or photodiode structure is formed having a relatively low concentration of threading dislocations. In this way, a light emitting structure, a PN diode, a photodiode, or a schottky barrier diode, having a relatively low concentration of threading dislocations can be formed. In a preferred embodiment, the areas of light emission and/or maximum electric field are designed to cover the wing areas 417 and avoid locally approximating the pattern of the linear array 419. In some embodiments, the defect region associated with the coalescence front or window region is used as a shunt path for reducing series resistance. In some embodiments, an n-type contact is placed over a coalescence front or window region with an edge dislocation density greater than 10 3 cm -1 And/or a threading dislocation density greater than about 10 5 cm -2 。
Referring now to fig. 7C, in some embodiments, such as a laser diode, PN diode, photodiode, or schottky barrier diode, the p-contact may be placed in a region substantially free of a coalescence front. In some embodiments, such as a laser diode, the laser ridge or stripe structure 740 may be placed in an area that is substantially free of a coalescence front. The mesa may be formed by conventional lithography and an n-type contact placed in electrical contact with the n-type layer and/or the substrate. Additional structures may be placed in line with the coalescence front, such as sidewall passivation, ion implantation regions, field plates, etc.
Referring now to fig. 7D, in some embodiments, such as a Current Aperture Vertical Electron Transistor (CAVET), an n-drift layer 731 is deposited over an n + contact layer 730, which in turn is deposited on the self-supporting merged ammonothermal group III metal nitride boule 413. A p-type layer 636 is formed over the n-layer 731 with the hole 736. After the remaining regrowth of the n-layer 731, an AlGaN 2D electron gas layer 738 is deposited. Finally, source contact 737, drain contact 739, dielectric layer 741, and gate contact 743 are deposited. In a preferred embodiment, the holes 736 are located away from the first 419 and second 435 coalescing fronts. In a preferred embodiment, the aperture 736 is located away from the window region 415. In a preferred embodiment, the aperture 736 is positioned above the wing region 417. Other types of three-terminal devices such as trench CAVETs, MOSFETs, etc. are positioned such that the region of maximum electric field is located within the wing region 417.
Fig. 8 shows a top view (plan view) of a free-standing GaN substrate formed by ammonothermal lateral epitaxial growth using a mask in the form of a two-dimensional array. The GaN layer is grown through the two-dimensional array of openings in the original mask layer to form window region 415. The coalescence of the GaN layers may form a two-dimensional grid of patterns of threading dislocations that locally approximate the linear array 419.
Fig. 9A illustrates a top view of a device structure, such as an LED, in which transparent p-contact 970 has been aligned with respect to and placed out of contact with the pattern of threading dislocations of the window region 415 or the local approximate linear array 419. Fig. 9B shows a top view of an alternative embodiment of a device structure, such as an LED, in which electrical contacts 980 are again aligned with respect to the window region 415 and the pattern of threading dislocations of the local approximate linear array 419, but are now positioned over the pattern of threading dislocations of the local approximate linear array 419. Fig. 9C shows a top view of an alternative embodiment of a device structure, such as a flip-chip LED, in which n-type electrical contacts 990 are arranged with respect to window regions 415 and p-type electrical contacts 995 are arranged between window regions 415.
Individual dies, such as light emitting diodes or laser diodes, may be formed by sawing, cleaving, cutting, singulating, etc., between adjacent sets of electrical contacts. Referring again to fig. 9A, the cuts may be made along the pattern of threading dislocations of the local approximately linear array 419. Dicing may also be performed through window region 415. Referring now to fig. 9B, in some embodiments, the cutting may be performed through window region 415 rather than along the pattern of threading dislocations of the locally approximately linear array 419. Referring again to fig. 9C, in some embodiments, the cut is made neither through the seed region nor along all of the coalescence fronts. The singulated die may have three corners, four corners, or six corners depending on the arrangement of the one-dimensional or two-dimensional array of seed regions.
The methods described herein provide a means for fabricating large area group III metal nitride substrates despite having some potential defect regions. The methods described herein provide means for fabricating high performance light emitting diodes and/or laser diodes that avoid potential problems associated with defective regions in large area group III metal nitride substrates.
Tiled crystalline array substrate examples
Referring again to fig. 19D and 19G, rather than using the tiled composite structure 1960 as a seed for further bulk crystal growth, in some embodiments, the tiled composite structure 1960 is further processed to form a tiled composite substrate 1980 and used directly as a substrate for optical or electronic device fabrication. The resulting tiled composite substrate 1980 includes an array of seed crystals 370 bonded together by a layer of polycrystalline GaN 1950, which may also be referred to as a base member. In some embodiments, the array of seeds 370 is positioned such that the surface 1975 of each seed is parallel to a first plane, such as the X-Y plane shown in fig. 19G. The array of seeds 370 may be positioned such that gaps 1986 (fig. 19G) are formed between adjacent edges of the seeds 370. In one example, gap 1986 is less than 2 millimeters (mm), such as between 0.1 micrometers (μm) and 1 millimeter (mm), or between 0.1 micrometers and 200 micrometers, between 0.1 micrometers and 50 micrometers, or between 0.2 micrometers and 50 micrometers. In certain embodiments, the gap 1986 is completely filled with the matrix member material 1950. In certain embodiments, the top surface of the base member material 1950 is below the top surface of the seed surface 1975, as shown in fig. 19D. In certain embodiments, the matrix member material 1950 is not present within the gap 1986 such that the seed crystal 370 is held in place only by bonding from its back side to the matrix member 1950. In certain embodiments, the surface 1975 of the seeds 370 within the array is planarized by grinding, lapping, polishing, or the like. In certain embodiments, surface 1975 is chemically-mechanically polished and subjected to a final cleaning operation in a clean room environment. In certain embodiments, the back side of the tiled composite structure 1960 is thinned and planarized, for example by grinding, buffing, and/or polishing, during the process used to form the tiled composite substrate 1980. In certain embodiments, the thickness of the tiled composite substrate 1980 is the same as the thickness of the seed 370, such that the matrix member 1950 is only present within the gap 1986. In other embodiments, the thickness of the tiled composite substrate 1980 is greater than the thickness of the seed crystal 370, in which case the matrix member 1950 is bonded to the back side of the seed crystal 370. The perimeter of the tiled composite structure 1960 can be ground to form the outer edge 1990 of the tiled composite substrate 1980. In some embodiments, a chamfer, bevel, or rounded edge is ground to edge 1990 of the tiled composite substrate 1980. In some embodiments, the outer edge 1990 around the array of seeds 370 is circular in shape. In certain embodiments, one or more orientation planes 1995 can be ground to lay flat the edges 1990 of the composite substrate 1980. In some embodiments, the tiled composite substrate 1980 has a diameter of between 20 and 210 millimeters, between 20 and 30 millimeters, between 45 and 55 millimeters, between 90 and 110 millimeters, between 140 and 160 millimeters, or between 190 and 210 millimeters, and a thickness of between 150 microns and about 5 millimeters, between about 200 microns and about 2 millimeters, or between about 250 microns and about 1.5 millimeters.
In some embodiments, each seed 370 within tiled composite substrate 1980 is equal in thickness, with a variance within 50 microns, within 25 microns, within 10 microns, within 5 microns, within 2 microns, or within 1 micron. In certain embodiments, the surfaces 1975 of each seed 370 are coplanar, with a difference of within 10 microns, within 5 microns, within 2 microns, or within 1 micron. The crystallographic miscut of each surface 1975 of seed crystal 370 is of equal magnitude, differing by within 0.5 degrees, within 0.3 degrees, within 0.2 degrees, within 0.1 degrees, within 0.05 degrees, within 0.02 degrees, or within 0.01 degrees. In a preferred embodiment, the crystals of each seed crystal 370 are arranged in a miscut direction with a difference of within 10 degrees, within 5 degrees, within 2 degrees, within 1 degree, within 0.5 degrees, within 0.2 degrees, or within 0.1 degrees. In a particular embodiment, each surface 1975 of seed crystal 370 has an orientation within 5 degrees, within 2 degrees, within 1 degree, or within 0.5 degrees of an orientation selected from {20-2 ± 1}, {30-3 ± 1}, and {10-10}, and a miscut in the a-direction of less than 0.5 degrees, less than 0.2 degrees, less than 0.1 degrees, or less than 0.05 degrees.
The tiled composite substrate 1980 may be characterized by a thickness of less than about 25 microns,A Total Thickness Variation (TTV) of less than about 10 microns, less than about 5 microns, less than about 2 microns, or less than about 1 micron, and is characterized by a macrobend of less than about 200 microns, less than about 100 microns, less than about 50 microns, less than about 25 microns, or less than about 10 microns. The small values of TTV and macrobending are useful for electronic device fabrication because they enable the deposition of epitaxial layers with uniform properties and high device yield. At least one surface 1975 (fig. 19D) of tiled composite substrate 1980 can have less than about 2cm -2 Less than about 1cm -2 Less than about 0.5cm -2 Less than about 0.25cm -2 Or less than about 0.1cm -2 Has a diameter or feature size greater than about 100 microns. The variation in the miscut angle across the surface 1975 of the seed crystal 370 may be less than about 1 degree, less than about 0.5 degrees, less than about 0.2 degrees, less than about 0.1 degrees, less than about 0.05 degrees, or less than about 0.025 degrees in each of the two orthogonal crystallographic directions. The average root mean square surface roughness of at least one surface 1975 of the tiled composite substrate 1980, as measured over an area of at least 10 μm x10 μm, may be less than about 0.5 nanometers, less than about 0.2 nanometers, less than about 0.15 nanometers, less than about 0.1 nanometers, or less than about 0.10 nanometers. At least one seed 370 in tiled composite substrate 1980 may be characterized by n-type conductivity with a carrier concentration between about 1x10 17 cm -3 And about 3X 10 19 cm -3 And carrier mobility greater than about 100cm 2 V-s. In an alternative embodiment, at least one seed 370 in tiled composite substrate 1980 is characterized by p-type conductivity with a carrier concentration between about 1 × 10 15 cm -3 And about 1X10 19 cm -3 In the meantime. In other embodiments, at least one seed 370 in a tiled composite substrate 1980 wafer is characterized by semi-insulating electrical properties, room temperature resistivity greater than about 10 7 Ohm-cm, greater than about 10 8 Ohm-cm, greater than about 10 9 Ohm-cm, greater than about 10 10 Ohm-cm or greater than about 10 11 Ohm-cm.
One or more device structures may be grown or deposited on one or more of the seeds 370 within tiled composite substrate 1980, as schematically illustrated in fig. 23A. In certain embodiments, after first layer 2310 is deposited, for example by MOCVD, MBE, or HVPE, release layer 2320 may be deposited thereon. In some embodiments, the first layer 2310 may include a layer doped with an n-type dopant. The lift-off layer 2320 may comprise or consist of InGaN. The exfoliation layer 2320 may include or consist of a multiple quantum well or strained layer superlattice.
In some embodiments, a device layer 2340 is then deposited, covering the lift-off layer 2320. Device layer 2340 may include one or more low GaN drift layers, one or more AlInGaN active layers, one or more AlInGaN cladding layers, p-type layers, and p-type electrical contacts. Other layers may also be present in the device layer 2340, as may be suitable for fabricating devices such as light emitting diodes, laser diodes, photodiodes, diodes, transistors, and the like. In some embodiments, an adhesion layer 2350 may be deposited so as to cover the device layer 2340. In some embodiments, the trench 2355 is formed through the adhesion layer 2350, the device layer 2340, and into or through the release layer 2320. As schematically shown in fig. 23B, the handle substrate 2360 is then bonded to the adhesion layer 2350. Bonding of the handle substrate 2360 to the adhesion layer 2350 can be accomplished by one or more of thermocompression bonding, soldering, unsintered silver bonding, or adhesive bonding. In some embodiments, the lift-off layer 2320 is then removed, separating one or more device layers 2340 bonded to the handle substrate 2360 from one or more seed crystals 370, as schematically illustrated in fig. 23C. In certain embodiments, the lift-off layer 2320 is removed by photoelectrochemical etching. In some embodiments, the order of the operations is changed. In a particular embodiment, some or all of release layer 2320 is removed prior to bonding handle substrate 2360 to adhesion layer 2350.
In certain embodiments, surface 2370 of seed 370 (which may also have portions of first layer 2310 or other layers present) may be re-planarized by one or more of grinding, lapping and polishing. Surface 2370 may also be prepared by chemical mechanical polishing and final cleaning in a clean room environment. After device layer 2340 is removed from tiled composite substrate 1980 and surface 2370 of seed 370 is re-prepared within tiled composite substrate 1980, the tiled composite substrate is again used directly as a substrate for optical or electronic device manufacturing. Tiled composite substrate 1980 may be reused at least once, at least twice, at least three times, at least five times, or at least ten times as a substrate for forming an optical or electronic device. Although fig. 19A-19E and 23A-23C show configurations in which the polycrystalline GaN layer 1950 of the tiled composite substrate 1980 extends over a surface of the seed crystal 370 (e.g., the lower surface in fig. 23A-23C), this configuration is not intended to limit the scope of the disclosure herein, as in some configurations, the polycrystalline GaN layer 1950 is positioned only between the edges of the seed crystal 370, and not on any of the major surfaces (e.g., the upper and lower surfaces in fig. 23A-23B) of the seed crystal 370.
The above sequence of steps provides a method according to an embodiment of the present disclosure. In a specific embodiment, the present disclosure provides a method and resulting crystalline material provided by a high voltage apparatus having a structured support member. Other alternatives may also be provided in which steps are added, one or more steps are removed, or one or more steps are provided in a different order without departing from the scope of the claims herein.
Examples
Embodiments provided by the present disclosure are further illustrated by reference to the following examples. It will be apparent to those skilled in the art that many modifications, both to materials and methods, may be practiced without departing from the scope of the disclosure.
Example 1
An approximately 0.3 mm thick bulk c-plane oriented GaN crystal grown by HVPE was provided for use as the substrate 101 for patterning and ammonothermal crystal growth. A 100 nm thick layer of TiW was sputter deposited as an adhesion layer on the (000-1) N-face of the substrate followed by a 780 nm thick inert layer comprising Au. A 6 micron thick Au layer is then electroplated over the sputtered layer, thereby increasing the thickness of the inert layer (e.g., blanket mask 116). Using AZ-4300 as the photoresist (e.g., photoresist layer 103), a slit (e.g., open) is defined that includes a width of 3 micrometers by a length of 1 centimeterPort 112) with a pitch diameter of 1200 microns. As schematically shown in fig. 1M to 1P, a wet etching process is performed at room temperature using a commercial TFA gold etching solution to obtain a substrate having a patterned mask layer 111. The mask pattern includes m-stripe domains having an orientation of about 30-40 microns wide and parallel to<10-10>Is used to form the linear opening. The substrate with patterned mask layer 111 is then placed in a chamber containing concentrated H 3 PO 4 In a stirred beaker. The beaker was heated to about 280 degrees celsius over about 30 minutes, held at that temperature for about 90 minutes, and cooled. The profile of the trench 115 formed by this process is shown in fig. 10, having a depth of about 162 microns and a top width of about 105 microns. The sidewalls of the trench 115 are obviously almost vertical.
Example 2
A patterned trenched c-plane oriented bulk GaN substrate 101 was prepared by a similar procedure as described in example 1. Patterning the substrate with a 15% open area baffle, polycrystalline GaN nutrient, NH 4 The mineralizer F was placed in a silver capsule with ammonia and the capsule was sealed. GaN nutrient and NH 4 The weight ratio of F mineralizer to ammonia was about 1.69 and 0.099, respectively. The capsules were placed in an internally heated high pressure apparatus and heated to a temperature of about 666 degrees celsius in the upper nutrient zone and about 681 degrees celsius in the lower crystal growth zone, held at these temperatures for about 215 hours, then cooled and removed. The ammonia-heated GaN filled in the bulk of the trench grows through the linear openings in the patterned mask on the HVPE GaN substrate, grows laterally and coalesces completely, forming an approximately 1200 micron thick ammonia-heated GaN layer with a smooth top surface. Two parallel cuts were made in the ammonothermal GaN layer perpendicular to the surface and pattern, resulting in a bar sample with an m-plane surface. One m-plane of the sample was polished and examined by optical microscopy as shown in fig. 11A and 11B. An interface can be seen between the substrate 101 and the laterally grown group III metal nitride material 221, as shown by the dashed line in the enlarged view on the right side of fig. 11B. The patterned mask layer 111 and the voids 225 both appear black in the image and are located below the ammonothermal group III metal nitride layer 213.
Example 3
A patterned trenched c-plane oriented bulk GaN substrate was prepared by a similar process to that described in examples 1 and 2, and the final group III metal nitride layer 213 is shown in fig. 12B (i.e., right side view). A second patterned substrate is prepared by a similar process except that no trench is prepared under the mask opening and the final group III metal nitride layer is shown in fig. 12A (i.e., left side view). Patterning the substrate with a 15% open area baffle, polycrystalline GaN nutrients, NH 4 The mineralizer F was placed in a silver capsule with ammonia and the capsule was sealed. GaN nutrient and NH 4 The weight ratio of F mineralizer to ammonia was about 2.05 and 0.099, respectively. The capsules were placed in an internally heated high pressure apparatus and heated to a temperature of about 666 degrees celsius in the upper nutrient zone and about 678 degrees celsius in the lower crystal growth zone, held at these temperatures for about 427 hours, then cooled and removed. The ammonothermal GaN filled in most of the volume of the trench substrate (fig. 12B) grows through the linear openings in the patterned mask on the HVPE GaN substrate, grows laterally and coalesces completely, forming an approximately 2100 micron thick ammonothermal GaN layer with a smooth top surface. The ammonothermal GaN layer was similarly grown through linear openings in a patterned mask on a patterned ungrooved HVPE GaN substrate (fig. 12A), grown laterally and coalesced completely, forming an approximately 2100 micron thick ammonothermal GaN layer with a smooth top surface. The surfaces of the two ammonothermal GaN layers were slightly etched and examined by optical microscopy. Differential interference difference (Nomarski) micrographs and transmission micrographs of the two layers are shown in fig. 12A to 12B. The average etch pit density (which is believed to accurately represent threading dislocation density) of an ammonothermal GaN layer grown on a patterned substrate without trenches (fig. 12A) was about 1.0 x10 5 cm -2 . The average etch pit density of the ammonothermal GaN layer grown on the patterned trench substrate (FIG. 12B) was about 1.0X 10 4 cm -2 This is a complete order of magnitude improvement.
Example 4
Patterned trenched c-plane oriented bulk GaN substrates were prepared by a similar procedure as described in examples 1 and 2, but with a pitch of 800 μmAnd (4) rice. Patterning the trench substrate with a 15% open area baffle, polycrystalline GaN nutrients, NH 4 The mineralizer F was placed in a silver capsule with ammonia and the capsule was sealed. GaN nutrient and NH 4 The weight ratio of F mineralizer to ammonia was about 1.71 and 0.099, respectively. The capsules were placed in an internally heated high pressure apparatus and heated to a temperature of about 668 degrees celsius for the upper nutrient zone and about 678 degrees celsius for the lower crystal growth zone, held at these temperatures for about 485 hours, then cooled and removed. The ammonothermal GaN filled in the bulk of the trench substrate grows through the linear openings in the patterned mask on the HVPE GaN substrate, grows laterally and coalesces completely, forming an approximately 980 micron thick ammonothermal GaN layer with a smooth top surface. The HVPE GaN substrate was removed by grinding, and the resulting free-standing ammonia-thermal GaN substrate was polished and chemically-mechanically polished. The self-supporting ammonia-heated GaN substrate was then characterized by X-ray diffraction at nine different locations on the substrate using a PANALYtic X' Pert PRO diffractometer using electron energy of 45kV and a line focus of 40mA, a step size of 0.0002 degrees, a dwell time of 1 second, a Ge (220) mirror, a slit height of 1.0mm, and a slit width of 1.0 mm. The analysis results of the formed GaN substrate are summarized in fig. 13. Along [1-100 ]]Is measured at 0.078 degrees at the center 80% of the large area surface of the crystal and is along [11-20 ]]The miscut range of (a) is measured as 0.063 degrees at the central 80% of the large area surface of the crystal. Thus, in some embodiments, a free-standing crystal has a miscut angle that varies by 0.1 degrees or less at the central 80% of the large area surface of the crystal along a first direction and a miscut angle that varies by 0.1 degrees or less at the central 80% of the large area surface of the crystal along a second direction orthogonal to the first direction. In contrast, the same measurements performed on commercial HVPE wafers resulted in edges [1-100 ]]0.224 degree miscut range and edge [11-20 ]]0.236 degrees. (002) The full width at half maximum of the reflected rocking curve was measured as 36 arcseconds, while the full width at half maximum of the (201) reflected rocking curve was measured as 32 arcseconds, as summarized in the table and graph shown in fig. 14. In contrast, the same measurements made on a 50mm diameter commercial HVPE substrate yielded values of 48 and 53 arc seconds, respectively, and on a 10 mm diameter commercial HVPE substrateThe same measurements made on a 0mm diameter commercial HVPE substrate yielded values of 78 and 93 arc seconds, respectively.
Example 5
An approximately 0.3 mm thick bulk c-plane oriented GaN crystal grown by HVPE was provided for use as a substrate for patterning and ammonothermal crystal growth. A 100 nm thick layer of TiW was sputter deposited as an adhesion layer on the (000-1) N-face of the substrate followed by a 780 nm thick inert layer containing Au. A 6 micron thick Au layer was then electroplated over the sputtered layer to increase the thickness of the inert layer. A frequency doubled YAG laser with nanosecond pulses was used to pattern the N-face of the substrate. The pattern includes m-trench domains having an orientation of about 50-60 microns wide and parallel to<10-10>With a pitch of 1200 microns. The patterned substrate is then placed in a chamber containing concentrated H 3 PO 4 In a stirred beaker. The beaker was heated to about 280 degrees celsius over about 30 minutes, held at that temperature for about 60 minutes, and cooled. The profile of the trench formed by this process is shown in fig. 15, which has a depth of about 200 microns and a top width of about 80 microns. The sidewalls of the trenches are obviously almost vertical.
Example 6
A patterned trenched c-plane oriented bulk GaN substrate was prepared by a similar process to that described in example 5, except that the laser used higher power so that trenches were formed that penetrated completely through the substrate. Using concentrated H at about 280 deg.C 3 PO 4 After about 30 minutes of etching, the width of the trench was about 115 microns. Patterning the substrate with a 15% open area baffle, polycrystalline GaN nutrients, NH 4 The mineralizer F was placed in a silver capsule with ammonia and the capsule was sealed. GaN nutrient and NH 4 The weight ratio of F mineralizer to ammonia was about 1.74 and 0.099, respectively. The capsules were placed in an internally heated high pressure apparatus and heated to a temperature of about 667 degrees celsius in the upper nutrient zone and about 681 degrees celsius in the lower crystal growth zone, held at these temperatures for about 500 hours, then cooled and removed. The ammonothermal GaN filled in most of the volume of the trench substrate grows through the linear opening in the patterned mask on the HVPE GaN substrate, grows laterally and finishesFully coalesced to form an ammonia-hot GaN layer about 2010 microns thick with a smooth top surface. The surface of the ammonothermal GaN layer was slightly etched and examined by optical microscopy. An optical micrograph of this layer is shown in fig. 16. The etch pits in rectangles A, B, C, D, E, F and G shown in FIG. 16 were counted to determine that the average etch pit density for the ammonothermal GaN layer grown on the patterned laser trench substrate was about 6.0X 10 3 cm -2 The average etch pit density is believed to accurately represent the threading dislocation density.
Example 7
Four c-plane oriented bulk GaN seeds were laser cut from three 100mm diameter bulk GaN wafers such that the linear cut edges were approximately a-plane, similar to the configuration shown in fig. 17E. A 100 nm thick layer of TiW was sputter deposited as an adhesion layer on the (000-1) N face of the seed followed by a 2.6 micron thick layer containing Ag. A frequency doubled YAG laser with nanosecond pulses was used to pattern the N-face of the seed. The pattern includes m-trench domains having parallel to<10-10>Linear openings oriented to form a triangular pattern. Four tiled seed crystals are placed on a flat Mo backplane within the Mo array ring such that the linear tiled edges and scrap directions are aligned. An Ag ring washer and a Mo ring clip were placed on the seed and clamped to the back plate using four Mo bolts, thereby fixing the seed, similar to the configuration shown in fig. 18D. Four additional Mo bolts were installed through holes in two larger seeds to secure the latter to the backplate and reduce the tiling bow. The assembled fixture had an exposed circular flat area of about 5.3 inches in diameter. The assembled fixture was combined with 7% open area baffle, polycrystalline GaN nutrient, NH 4 The mineralizer F was placed in a silver capsule with ammonia and the capsule was sealed. GaN nutrient and NH 4 The weight ratios of F mineralizer to ammonia were about 2.53 and 0.094, respectively. The capsules were placed in an internally heated high pressure apparatus and heated to a temperature of about 667 degrees celsius in the upper nutrient zone and about 680 degrees celsius in the lower crystal growth zone, held at these temperatures for about 500 hours, then cooled and removed. Ammonothermal GaN growth through linear openings in a patterned mask on a seedGrown and coalesced between the patterned trenches and between the seeds to form an ammonothermal GaN layer about 2600 microns thick with a circular diameter of about 5.3 inches and including four crystalline domains. X-ray diffraction measurements performed on the tiled interface after growth showed a crystalline orientation difference of about 0.2 degrees between adjacent tiled domains.
Example 8
Four c-plane oriented bulk GaN seeds were laser cut from three 100mm diameter bulk GaN wafers such that the linear cut edges were approximated as a-planes, similar to the configuration shown in fig. 17E. A 200 nm thick layer of AlN was sputtered on the (0001) Ga face of the seed. A Mo base comprising a backing plate and an alignment ring was sprayed with very fine BN particles suspended in a volatile organic carrier to form a release layer. Four seeds were placed (000-1) N face down on a flat Mo base inside the Mo alignment ring, allowing for accurate alignment of linear tiling edges and trim directions. The susceptor was placed horizontally in a poly-GaN reactor and a conformal polycrystalline GaN layer of about 1mm thickness was grown to form a continuous polycrystalline GaN handle layer on the (0001) Ga face of the four seeds. After the growth of the polycrystalline GaN was completed and the reactor cooled, the susceptor was removed from the poly-GaN reactor, where the seed and the polycrystalline GaN were intact. The seed crystals embedded in the polycrystalline GaN matrix are then separated from the Mo back plate by separation at the exfoliation layer. A frequency-doubled YAG laser with nanosecond pulses trimmed the edges of the tiled composite structure to form a circular tiled composite structure with a diameter of about 5.3 inches. The large area exposed poly-GaN handle layer and (000-1) N-face surface were subjected to lapping, polishing and chemical mechanical polishing. A 100 nm thick layer of TiW was sputter deposited as an adhesion layer on the (000-1) N-face of the seed followed by a 1.3 micron thick layer containing Ag. A six micron thick Au layer was then electroplated on the (000-1) N-face of the seed and the exposed polycrystalline GaN treated surface. A frequency-doubled YAG laser with nanosecond pulses was used to pattern the N-face of the tile. The pattern includes m-trench domains having parallel to<10-10>Linear openings oriented to form a triangular pattern. Then the patterned tiled composite structure is combined with 15% open area baffle, poly-crystalline GaN nutrients, NH 4 Placing the mineralizer F in a silver capsule together with ammonia, and sealing the silver capsuleAnd (4) making capsules. GaN nutrient and NH 4 The weight ratio of F mineralizer to ammonia was about 1.74 and 0.099, respectively. The capsules were placed in an internally heated high pressure apparatus and heated to a temperature of about 667 degrees celsius in the upper nutrient zone and about 681 degrees celsius in the lower crystal growth zone, held at these temperatures for about 500 hours, then cooled and removed. The ammonothermal GaN grows through linear openings in the patterned mask on the seed, grows laterally, and coalesces between patterned trenches and between tiles, forming an ammonothermal GaN layer of about 3000 microns thick.
Example 9
A tiled composite structure similar to that described in example 8 was prepared, except that 38 seeds having (30-3-1) orientation, a dimension of 10 mm in the direction projected parallel to the c-axis, a dimension of 20 mm in the m-direction, and a thickness of 300 microns were used. Before placing the seed (30-3-1) side down on the Mo susceptor, the edges of the seed constituting the periphery of the array were laser trimmed to a 95 mm diameter circle. After deposition of a 1mm thick polycrystalline GaN matrix on the (30-31) side of the seed and susceptor, the tiled composite structure was removed from the susceptor by separation at the lift-off layer. The perimeter of the tiled composite structure was ground to a diameter of 100mm and a plane parallel to the m-plane of the seed crystal was ground on one edge. The back side of the tiled composite structure was then ground using a 1000 mesh grinding wheel followed by a 4800 mesh grinding wheel to form a flat surface exactly parallel to the front surface. The front side of the tiled composite structure was then chemically mechanically polished to remove approximately 15 microns of material, resulting in a tiled composite substrate having a thickness of 600 microns, similar to the substrate shown in fig. 19G.
The tiled composite substrate was then placed on a susceptor in a commercial MOCVD reactor. An n-type GaN layer is deposited, followed by an InGaN strained layer superlattice lift-off layer, followed by another n-type GaN layer, followed by an n-type InGaN cladding layer, followed by an undoped InGaN multiple quantum well, followed by a p-type cladding layer, followed by a p-type layer and a p-contact layer. Trenches were then formed by conventional photolithography to form mesas that were approximately 1200 microns long in projection in the c-direction and 100 microns wide in the orthogonal m-direction in the (30-3-1) surface. Approximately 95% of the release layer was etched away by a photoelectrochemical process using KOH solution and 405 nm illumination. A gold-containing adhesion layer is then deposited on the p-contact layer and the mesa structure is transferred to a silicon carbide handle substrate by means of thermocompression bonding by a sequential process, followed by breaking the unremoved lift-off layer. After the mesa structure is removed, the surface of the tiled composite substrate is re-prepared by chemical mechanical polishing.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims (24)

1. A free-standing group III metal nitride substrate comprising at least two crystals, each crystal of the at least two crystals comprising:
a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen, wherein:
each of the at least two crystals has a wurtzite crystal structure comprising a first surface having: a maximum dimension greater than 10 mm in a first direction and greater than 4 mm in a second direction orthogonal to the first direction, between 10 2 cm -2 And 1X10 6 cm -2 Average threading dislocation concentration in between, less than 10 3 cm -1 Average stacking fault concentration, symmetrical x-ray rocking curve full width at half maximum of less than 200 arc seconds,
the magnitude of crystallographic miscut of the first surface of each of the at least two crystals is equal, differing by within 0.5 degrees,
the crystallographic miscut direction of the first surface of each of the at least two crystals is the same, within a difference of 10 degrees,
each of the at least two kinds of crystals is bonded to a base member comprising polycrystalline GaN, and
a polar orientation difference angle γ between a first surface of a first crystal of the at least two crystals and a first surface of a second crystal of the at least two crystals is greater than about 0.005 degrees and less than about 0.2 degrees, and orientation difference angles α and β are greater than about 0.01 degrees and less than about 1 degree.
2. The free-standing group III metal nitride substrate of claim 1 wherein the free-standing group III metal nitride substrate has a maximum dimension in the first direction that is greater than 40 millimeters.
3. The free-standing group III metal nitride substrate of claim 2, wherein the crystallographic miscut of the first surface of each of the at least two crystals is equal in magnitude, within 0.2 degrees of difference, and the crystallographic miscut of the first surface of each of the at least two crystals is the same in direction, within 2 degrees of difference.
4. A free-standing group III metal nitride substrate according to claim 2, wherein each of the first surfaces has a crystallographic orientation within 5 degrees of an orientation selected from the group consisting of {20-2 ± 1}, {30-3 ± 1}, and {10-10}, and a miscut in the a-direction of less than 0.5 degrees.
5. A free-standing group III metal nitride substrate according to claim 4, wherein each of the first surfaces has a crystallographic orientation within 1 degree of an orientation selected from the group consisting of {20-2 ± 1}, {30-3 ± 1}, and {10-10}, and a miscut in the a-direction of less than 0.1 degree.
6. A free-standing group III metal nitride substrate according to claim 2 wherein the largest dimension in the first direction is between 45 and 110 millimeters.
7. The free-standing group III metal nitride substrate of claim 2, wherein the free-standing group III metal nitride substrate further comprises:
a thickness between about 150 microns and about 2 millimeters,
a total thickness variation of less than about 25 microns, an
A macrobend of less than about 50 microns.
8. A self-supporting group III metal nitride crystal according to claim 1, wherein a gap is formed between adjacent edges of each of the at least two crystals, the gap being at least partially filled by the base member.
9. A free-standing group III metal nitride crystal according to claim 1, wherein the first surface of each of the at least two crystals has a crystallographic orientation within 5 degrees of a {10 "10 } m-plane.
10. A free-standing group III metal nitride crystal according to claim 1, wherein the first surface of each of the at least two crystals has a crystalline orientation within 5 degrees of the (0001) + c-plane or within 5 degrees of the (000-1) -c-plane.
11. A self-supporting group III metal nitride crystal according to claim 1, wherein the first surface of each of the at least two crystals has a crystalline orientation within 5 degrees of a semipolar orientation selected from the group consisting of {60-6 ± 1}, {50-5 ± 1}, {40-4 ± 1}, {30-3 ± 1}, {50-5 ± 2}, {70-7 ± 3}, {20-2 ± 1}, {30-3 ± 2}, {40-4 ± 3}, {50-5 ± 4}, {10-1 ± 1}, {10-1 ± 2}, {10-1 ± 3}, { 21-3 ± 1} and {30-3 ± 4 }.
12. A free-standing group III metal nitride crystal according to claim 1, wherein the first surface has the following impurity concentrations:
between 1X10 16 cm -3 And 1X10 19 cm -3 With the presence of oxygen (O) therebetween,
between 1X10 16 cm -3 And 2X 10 19 cm -3 Hydrogen (H) in between, and
between 1X10 15 cm -3 And 1X10 19 cm -3 Fluorine (F) and chlorine (C) in betweenl) is used.
13. A free-standing group III metal nitride crystal according to claim 1, wherein the first surface has the following impurity concentrations:
between 1X10 16 cm -3 And 1X10 19 cm -3 With the presence of oxygen (O) therebetween,
between 1X10 16 cm -3 And 2X 10 19 cm -3 Hydrogen (H) in between, and
between 3X 10 15 cm -3 And 1X10 18 cm -3 Sodium (Na) and potassium (K).
14. A free-standing group III metal nitride crystal according to claim 1, further comprising an interface layer at an interface between at least one of the at least two crystals and the base member.
15. A free-standing group III metal nitride crystal according to claim 14, wherein the interface layer comprises at least one of graphite, boron nitride, molybdenum disulfide, and tungsten disulfide.
16. A free-standing group III metal nitride crystal according to claim 1, wherein the first surface of each of the at least two crystals is substantially parallel to a first plane.
17. A self-supporting group III metal nitride crystal according to claim 1, wherein the base member has a diameter greater than 40 mm.
18. A self-supporting group III metal nitride crystal according to claim 1, wherein the base member further includes a porous member.
19. The self-supporting group III metal nitride crystal of claim 18, wherein the porous member comprises at least one of graphite, carbon fiber, silica fiber, aluminosilicate fiber, borosilicate fiber, silicon carbide coating, pyrolytic boron nitride coating, or pyrolytic graphite coating.
20. A free-standing group III metal nitride substrate, comprising:
an array of seeds, wherein each seed in the array of seeds comprises a group III metal selected from gallium, aluminum, and indium, or a combination thereof, and nitrogen; and
a polycrystalline GaN layer disposed over at least one surface of each seed within the array of seeds,
wherein:
each of the seeds having a wurtzite crystal structure comprising a first surface having between 10 2 cm -2 And 1X10 6 cm -2 Average threading dislocation concentration in between less than 10 3 cm -1 The average stacking fault concentration of (a) is,
the magnitude of crystallographic miscut of the first surface of each of the seeds is equal, the difference being within 0.5 degrees,
the direction of crystallographic miscut of the first surface of each of the seeds is the same, the difference is within 10 degrees, and
a polar misorientation angle γ between a first seed of the array of seeds and a second seed of the array of seeds is greater than about 0.005 degrees and less than about 0.2 degrees, and misorientation angles α and β are greater than about 0.01 degrees and less than about 1 degree.
21. A free-standing group III metal nitride crystal according to claim 20 wherein each of the seed crystals further comprises:
a symmetric x-ray rocking curve full width at half maximum of less than 200 arcsec, an
A maximum dimension greater than 10 millimeters in the first direction, and a maximum dimension greater than 4 millimeters in the second direction orthogonal to the first direction.
22. A self-supporting group III metal nitride crystal according to claim 20, wherein the base member has a diameter greater than 40 mm.
23. A free-standing group III metal nitride substrate according to claim 20 wherein each of the first surfaces has a crystallographic orientation within 5 degrees of an orientation selected from the group consisting of {20 "2 ± 1}, { 30" 3 ± 1}, and {10 "10 }, and a miscut in the a-direction of less than 0.5 degrees.
24. The free-standing group III metal nitride substrate of claim 20, wherein the free-standing group III metal nitride substrate further comprises:
a thickness between about 150 microns and about 2 millimeters,
a total thickness variation of less than about 25 microns, an
A macrobend of less than about 50 microns.
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