JP2004193371A - Group-iii nitride independent substrate, semiconductor device using the same, and method for manufacturing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group-III nitride independent substrate having a low dislocation area of a large area. <P>SOLUTION: A GaN film 1002 is formed on a sapphire substrate 1000, and a plurality of masks 1003 having different mask widths are formed on it. A GaN layer 1004 of a thick film is grown via the opening of the mask 1003 from the surface of the GaN film 1002 to make a substrate for growing a crystal. The GaN layer 1004 comprises a small facet structure 1007 grown from the opening of the mask 1003, and a huge facet structure 1008 formed by being united with the small facet structure 1007. The GaN layer 1004 comprises a number of dislocations shown by arrows in the figure, and advancing directions of these dislocations are curved by the small facet structure 1007 and the huge facet structure 1008. As the result of this, dislocation 1006 reaching the surface of the GaN layer 1004 is largely reduced than dislocation existing near the surface of the GaN surface of the GaN film 1002. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a group III nitride free-standing substrate, a semiconductor device using the same, and a method for manufacturing the same.
[0002]
[Prior art]
Nitride semiconductor materials have a sufficiently large forbidden band width and a direct transition type transition between bands. Therefore, application to a short-wavelength light-emitting element has been actively studied. In addition, the application to electronic devices is also expected due to the high saturation drift velocity of electrons and the possibility of using a two-dimensional carrier gas by a heterojunction.
[0003]
The nitride semiconductor layers constituting these devices are formed by using a vapor phase growth method such as metal organic vapor phase epitaxy (MOVPE), molecular beam vapor phase epitaxy (MBE), or hydride vapor phase epitaxy (HVPE). It is obtained by performing epitaxial growth on a substrate. However, since there is no underlying substrate whose lattice constant matches that of the nitride semiconductor layer, it is difficult to obtain a high-quality growth layer, and the obtained nitride semiconductor layer contains many crystal defects. . Since this crystal defect becomes a factor that hinders the improvement of the device characteristics, techniques for reducing the crystal defect in the nitride semiconductor layer have been actively studied.
[0004]
As one of such techniques, a technique is known in which a thick GaN layer is used as a base layer for crystal growth, and a semiconductor multilayer film forming an element portion is formed thereon. ELO (Epitaxial Lateral Overgrowth) technology is known as a technique for forming a small GaN underlayer. ELO is a crystal growth method that covers a part of a base with a mask and prevents propagation of threading dislocations extending vertically from the base. In this method, the crystal grows laterally from the mask opening, and finally a continuous film covering the entire mask is formed. Japanese Patent Application Laid-Open No. H11-251253 (Patent Document 1) discloses that by using this ELO technique, crystal defects near the wafer surface are reduced to 1 × 10 ^Five Pieces / cm ^Two It is said that the following GaN substrate was obtained. However, when ELO is used, it has been difficult to reduce the crystal defect density over the entire surface of the wafer. In ELO, GaN selectively grows laterally from an opening in a mask. In the region where the mask is formed, the dislocation is prevented from proceeding upward, but in the opening, the dislocation is inherited from the underlying layer as it is, and the upper region has a structure including many threading dislocations. Therefore, in the crystal growth by ELO, a portion having few crystal defects is certainly formed, while a region having many threading dislocations is also formed at the same time, and it is difficult to reduce the crystal defect over the entire surface of the wafer. According to the examples of the above publication, the crystal defect density near the surface was observed by TEM to be 1 × 10 ^Four As described below, while such a region having a low crystal defect is formed, a region including a large number of crystal defects is also formed at the same time. Actually, “Applied Physics Letter Volume 71 1997 pp.2472-2474” (Non-Patent Document 1) includes SiO _Two Almost no dislocation is observed on the mask, but 10 ⁸ ~Ten ⁹ cm ^-2 Is reported to be observed.
[0005]
On the other hand, the present inventors have developed a FIELO (Facet-Initiated Epitaxial Lateral Overgrowth) technology that further develops the ELO method (Non-Patent Document 2: “Applied Physics” (Vol. 68, No. 7, 1999, pp. 774-779)). This technology uses SiO _Two It is common to ELO in that selective growth is performed using a mask, but is different in that a facet is formed in a mask opening. By forming facets, the direction of propagation of dislocations is changed, and threading dislocations reaching the upper part of the epitaxial growth layer are reduced. By using this method, a high-quality GaN substrate having relatively few crystal defects can be obtained by growing a thick GaN layer on an underlying substrate such as sapphire and then removing the underlying substrate. By using the element, it is possible to obtain an element having higher performance than the conventional one.
Japanese Patent Application Laid-Open No. 2002-33288 (Patent Document 2) describes a crystal growth method in which the ELO method is improved. This publication discloses a technique in which a semiconductor layer having an uneven portion in a mask opening is exposed and crystal growth is performed using this layer as a base to reduce dislocation density. This document discloses a method of forming crystal irregularities inside a mask opening, starting crystal growth from the irregularities, and growing the crystal laterally on a mask. It is said that in the uneven portion, the concave portion is left buried by growing laterally, and a void remains in that portion, causing discontinuity with the underlying crystal and reducing threading dislocation. FIG. 8 and paragraphs 0050 to 0051 of this publication describe a technique in which the entire mask opening is covered with an anti-surfactant that inhibits crystal growth, and crystal growth is performed from a pinhole portion. In this opening, a process is described in which growth starts in an island shape from the pinhole portion, and further progresses to spread the GaN layer so as to extend over the mask. According to this method, it is described that threading dislocations extending vertically are surely cut off and dislocations can be reduced.
[0006]
However, at present, a higher level of reduction of dislocations is desired from the viewpoint of improving the performance of the device, and the above-mentioned conventional technology has not sufficiently satisfied the demand.
The ELOs disclosed in Patent Documents 1 and 2 prevent the propagation of threading dislocations by covering a base with a mask, and high-density dislocations are generated above portions where no mask exists. Therefore, it is difficult to form a low dislocation region with a large area as an element formation region. In order to form a low dislocation region with a large area, it is conceivable to increase the mask width. However, in that case, the crystal axis (c axis) is disturbed, and it is difficult to obtain a crystal of good quality. It is well known that in mask growth, the c-axis orientation deteriorates as the mask width increases. 4. These prior arts are basically based on the idea of blocking the progress of dislocations with a mask, and include the concept of reducing dislocations reaching the surface by bending dislocations like FILEO. Absent.
[0007]
On the other hand, FIELO disclosed in Non-Patent Document 2 is effective in reducing dislocations, and can form a low dislocation region with a relatively large area as an element formation region. However, in order to realize a high level of crystal quality as currently desired, the crystal layer on the mask needs to be thick to some extent, and in response to a demand for a large area of a low dislocation region, it is not always necessary. It did not respond sufficiently and still had room for improvement.
[0008]
[Patent Document 1]
JP-A-11-251253
[Patent Document 2]
JP 2002-33288 A
[Non-patent document 1]
Applied Physics Letter Volume 71 1997 pp.2472-2474
[Non-patent document 2]
"Applied Physics" (Vol. 68, No. 7, 1999, pp. 774-779)
[Non-Patent Document 3]
2nd Intern. Symp. On Blue Laser and Light Emitting Diodes, Chiba, Japan, Sept. 29-Oct. 2, 1998, P488-491 (FIG. 4)
[0009]
[Problems to be solved by the invention]
In view of the above circumstances, an object of the present invention is to provide a group III nitride freestanding substrate in which dislocations are significantly reduced. Another object of the present invention is to form a low dislocation region with a large area. Another object of the present invention is to form such a large-area low-dislocation region without disturbing the crystal axis orientation. Another object of the present invention is to form such a large-area low-dislocation region without growing a thick semiconductor layer to reduce dislocations.
[0010]
[Means for Solving the Problems]
According to the present invention, there is provided a self-supporting substrate including a group II nitride semiconductor layer, wherein the group III nitride semiconductor layer includes a facet structure having a facet side face obliquely positioned with respect to a horizontal plane of the substrate, and covering the facet structure. A free-standing substrate provided with a nitride semiconductor layer is provided.
[0011]
In this free-standing substrate, dislocations propagating from the base are bent by a facet surface obliquely positioned with respect to the horizontal plane of the substrate, so that the dislocation density in the group III nitride semiconductor layer is significantly reduced. The “facet structure” refers to a polyhedral structure having a facet face obliquely positioned with respect to the horizontal plane of the substrate as a side face. The facet structure and the crystal layer outside the facet structure are usually formed in a continuous process to be semiconductor layers having the same composition, but they have different growth rates and accordingly different impurity concentrations. Therefore, the contour of the facet structure can be clearly grasped by a predetermined method. This point will be described later in an embodiment.
[0012]
Further, according to the present invention, a base material and a group III nitride semiconductor layer formed on the base material are provided, and the group III nitride semiconductor layer propagates upward from the base material in the group III nitride semiconductor layer. A free-standing substrate is provided, wherein the dislocation is bent a plurality of times in a direction substantially horizontal to the base material.
[0013]
The self-standing substrate is bent a plurality of times in a direction parallel to the base material. Since the number of dislocations propagating in the layer growth direction is reduced by changing the dislocation advancing direction, according to the present invention, a remarkable dislocation reduction effect can be obtained. In the FIELO described in the section of the related art, the dislocation is bent once, whereas the method of the present invention is bent a plurality of times, so that the dislocation reduction effect is significantly improved. In the above-mentioned FIELDO, as shown in the cross-sectional TEM image of FIG. 5 of Non-Patent Document 2, the dislocation is bent only once in the horizontal direction. On the other hand, in the present invention, remarkable reduction of dislocation is realized by bending a plurality of times.
[0014]
According to the present invention, there is provided a self-standing substrate including a group III nitride semiconductor layer, wherein the surface average dislocation density is 10%. ^-6 cm ^-2 The low dislocation density region is periodically formed in one direction in the horizontal plane of the substrate, the width of the low dislocation density region is 20 μm or more, and the tilt angle of the low dislocation density region is 1 degree or less. A free-standing substrate is provided.
[0015]
In this self-standing substrate, regions with low dislocations and good crystal orientation are formed periodically and in a large area. For this reason, the element formation region can be suitably formed on the self-standing substrate. The surface average dislocation density can be measured by observation of an etch pit or the like as described later. The surface average dislocation density in the low dislocation density region is preferably 10 ^-Five cm ^-2 Less than By doing so, it is possible to realize a light emitting element or an electronic element having excellent performance which has not been achieved conventionally.
[0016]
Further, according to the present invention, a base material, a mask pattern provided on a surface of the base material, having a predetermined opening, and a group III nitride formed to grow from the opening and cover the mask pattern. A plurality of first masks extending in a stripe shape, and a second mask located between the adjacent first masks and having a width smaller than the first mask. And a free-standing substrate is provided.
In this free-standing substrate, a small facet structure grown from the second mask and a facet structure formed between the adjacent first masks and including the small facet structure are stably formed. For this reason, a region with low dislocation and good crystal orientation is formed in a large area.
[0017]
Further, according to the present invention, there is provided a semiconductor device characterized in that any one of the above-mentioned free-standing substrates is used as a substrate, and an element structure is provided on the substrate. The element structure can be, for example, a laser structure including at least an active layer.
[0018]
Further, according to the present invention, a step of growing a group III nitride semiconductor on a base material and forming a small facet structure having a facet face located obliquely with respect to a horizontal plane of the base material, Forming a stripe-shaped facet structure including the small facet structure, further comprising: growing a semiconductor; and providing a method for growing a group III nitride semiconductor layer.
[0019]
In this growth method, a stripe-shaped facet structure including a small facet structure is formed. Therefore, the direction of the dislocation propagating in the vertical direction from the base material is changed by both the side surface of the small facet structure and the side surface of the stripe-shaped facet structure. Since the number of dislocations propagating in the layer growth direction is reduced by changing the dislocation advancing direction, according to the present invention, a remarkable dislocation reduction effect can be obtained. In the FIELO described in the section of the related art, the dislocation is bent once, whereas the method of the present invention is bent a plurality of times, so that the dislocation reduction effect is significantly improved.
[0020]
According to the present invention, a plurality of first masks extending in a stripe shape and a second mask located between the adjacent first masks and having a width smaller than the first mask are provided on the surface of the base material. A step of forming a mask pattern including, and a step of epitaxially growing a group III nitride semiconductor on the substrate while forming a facet surface forming an acute angle with respect to the substrate horizontal plane, with the opening of the mask pattern as a growth region. And a method for growing a group III nitride semiconductor layer.
[0021]
According to this growth method, a small facet structure is formed from the growth region of the second inter-mask opening, and then a striped facet structure including the small facet is formed between adjacent first masks. The direction of the dislocation propagating in the vertical direction from the base material is changed by the side face of the small facet structure, the side face of the stripe facet structure, and the like, so that a remarkable dislocation reduction effect is obtained.
[0022]
Further, according to the present invention, a step of forming a group III nitride semiconductor layer on a substrate by the above-described growth method, and further laminating a layer made of a group III nitride semiconductor on the group III nitride semiconductor layer Forming a device structure by performing the method described above.
According to this growth method, it is possible to obtain an element structure made of a high-quality crystal with few dislocations, and to realize excellent element performance.
[0023]
The self-standing substrate according to the present invention includes the group III nitride semiconductor layer having the above-described configuration, but may have a configuration in which another semiconductor layer is appropriately stacked.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
The facet structure in the present invention refers to a structure in which a crystal plane having a specific low plane index, which has the lowest growth rate during crystal growth, is left behind and has a shape peculiar to the crystal. In the case of GaN having a Wurtzite structure as in the present embodiment, when the stripe direction of the mask is the <11-20> direction of GaN, the growth rate of the {1-101} plane is the slowest in the opening, and this plane is A facet structure with a triangular cross section is formed to form a 62 ° angle with the (0001) plane parallel to the substrate plane. The growth rate of the plane differs depending on the growth method and growth conditions, in addition to the properties inherent to the crystal, and is not limited to the triangle composed of {1-101} as in the present embodiment, but the triangle having a different angle from this. A structure, a facet structure with a vertical side surface, or a shape such as a trapezoid may appear. As the growth continues, the facet structures coalesce to form a large triangular facet, and as the growth continues, a large triangular facet structure is formed between masks A. The process of forming such a facet can be observed, for example, with a fluorescence micrograph of a cross section shown in FIG. This fluorescence microscope uses ultraviolet light as a light source and captures light in the visible light band from the growth layer. The manner in which the impurities are incorporated differs depending on the plane orientation, and can be observed as a contrast corresponding to such a growth pattern. From this photograph, it can be seen that a small triangular facet structure is first formed in the opening, and finally a large facet structure is formed in the region between the wide masks.
[0025]
FIG. 12 schematically shows an example of a cross-sectional structure of a free-standing substrate according to the present invention and the movement of dislocations accompanying facet multiplexing. In this cross-sectional structure, a GaN film 1002 is provided on a sapphire substrate 1000, and a mask 1003 having a predetermined opening is formed thereon. As illustrated, the mask 1003 includes a narrow mask and a wide mask. A thick GaN layer 1004 is grown from the surface of the GaN film 1002 through the opening of the mask 1003.
[0026]
The facet structure grown from the opening of the mask 1003 and the facet structure obtained by combining these facet structures are shown as small facet structures 1007 in FIG. A large facet structure 1008 is formed by combining the larger small facet structure 1007 among them. This huge facet is formed stably due to the presence of a wide mask.
[0027]
The GaN layer 1004 contains many dislocations indicated by arrows in the figure. These dislocations have a dislocation traveling direction bent by the small facet structure 1007 and the giant facet structure 1008. As a result, the dislocation 1006 reaching the surface of the GaN layer 1004 is smaller than the dislocation existing near the surface of the GaN film 1002. It has been greatly reduced.
[0028]
By the formation of the facets, the edge dislocations occupying 70 to 80% of threading dislocations and the mixed dislocations of 20 to 30% change directions in a direction parallel to the substrate surface as described above. As a result, the density of threading dislocations is greatly reduced. However, at the meeting part between the facets, in particular, some of the mixed dislocations rise again toward the growth surface. In the above structure, the dislocation is reduced by bending the dislocation with the next facet structure or the next facet structure. The dislocations are driven to the edge of the finally formed giant facet.
[0029]
As described above, the example of the structure of the self-standing substrate according to the present invention has been described. However, in order to understand the dislocation reduction mechanism, a layer growth process using FIELO will be described in comparison. FIG. 13 is a process cross-sectional view showing a conventional layer growth process by FIELO. First, a base crystal film 202 containing GaN is grown on a sapphire substrate 201, and a stripe-shaped mask 204 is formed on the surface thereof by photolithography and wet etching to form a growth region 203 (FIG. 13 (a)). While growing a crystal on the facet plane 205 with the growth region 203 as a starting point (FIGS. 13B to 13D), a flat GaN layer is finally formed (FIG. 13E). In this process, the dislocation is only bent once by the facet surface 205 shown in FIG. The mask width is usually about 2 μm and the opening width is about 5 μm. In this case, it is difficult to obtain a large-area low-dislocation region. It is conceivable to increase the mask width in order to obtain a large-area low-dislocation region, but in that case, the crystal axis of the GaN layer tends to be disordered. The present invention solves these problems and realizes a free-standing substrate or crystal film of good quality.
[0030]
The “small facet structure” in the present invention refers to one having a smaller size than the “facet structure”. For example, in the case of using a mask pattern in which a second mask is provided between first masks, a facet structure formed from an opening of the second mask, or a plurality of facet structures formed integrally with each other. This is called a “small facet structure”, and a facet structure formed between adjacent first masks including the “small facet structure” is called a “facet structure”. The “small facet structure” can have any shape, but the “facet structure” preferably has a stripe shape. Since the upper portion of the facet structure is a low dislocation density region, a low dislocation density region having a shape and an area suitable for forming an element region can be obtained in this manner. When the facet structure has a stripe shape, the stripe width is preferably 20 μm or more. In this way, a large area low dislocation density region can be obtained. When both the “small facet structure” and the “facet structure” have a stripe shape, a large-area low-dislocation-density region can be more preferably formed.
[0031]
In the present invention, the facet structure preferably includes a plurality of small facet structures smaller than the facet structure. By doing so, the dislocation can be bent a plurality of times, and a more remarkable dislocation reduction effect can be obtained.
[0032]
The facet structure may have any cross-sectional shape, but may have a triangular or trapezoidal cross section with a base of 20 μm or more, for example. In the case of a triangular cross section, since there is no flat portion on the upper surface, propagation of dislocations from the base to the layer growth direction is further suppressed, which is preferable. Even in the case of a trapezoidal cross section, the propagation of dislocations can be significantly suppressed by reducing the width of the upper bottom. For example, when the facet structure is formed by mask growth, by making the width of the upper bottom smaller than the mask width, it is possible to more effectively reduce the dislocations that travel upward from the mask opening.
[0033]
The facet structure is preferably formed periodically in a direction perpendicular to the stripe direction. By doing so, a low dislocation density region in which an element region is to be formed can be formed stably, and the yield in the element formation process is improved.
[0034]
In the present invention, a configuration can be adopted in which 50% or more of the dislocations included in the low dislocation density region are mixed dislocations. There are edge dislocations and mixed dislocations as types of dislocations, but from the viewpoint of improving the characteristics of an element structure formed on a free-standing substrate, it is important to greatly reduce the edge dislocations in the upper facet forming region. . The reason will be described below with reference to an example of a semiconductor laser. As is well known in semiconductor lasers, a condition for obtaining an optical gain with respect to guided light in an active layer must be achieved. However, the edge dislocation is a cause of the generation of small-angle grain boundaries in the crystal, and light scattering is likely to occur at the small-angle grain boundaries. For these reasons, it is desired that the edge dislocation is reduced in the semiconductor laser.
[0035]
In the present invention, the first mask and the second mask each have a stripe shape extending in substantially the same direction, and the second mask is formed with a period smaller than the period of the first mask. Can be. In this manner, a small facet structure is formed from the growth region of the opening between the second masks, and a facet overlapping structure in which a striped facet structure including the small facet is formed between adjacent first masks is preferable. Can be formed. Thereby, a remarkable dislocation reduction effect can be obtained.
In the present invention, the width of the first mask is wider than the width of the second mask. The width of the first mask is larger than one time of the width of the second mask, preferably 1.2 times or more, and more preferably 1.5 times or more. By doing so, a large facet structure growing between the first masks can be formed more stably, and as a result, a more significant dislocation reduction effect can be obtained.
The first mask and the second mask need not all have the same mask width. For example, by using a plurality of types of widths of the second mask, multiplexing of the facet structure can be further promoted, and the dislocation reduction effect can be further enhanced.
[0036]
Here, the stripe direction of the first mask may be a [11-20] direction, a [1-100] direction, or a direction having a deviation angle within 30 degrees from these directions with respect to the crystal structure of the group III nitride semiconductor. It can be. By doing so, a facet structure exhibiting an excellent dislocation reduction effect is stably formed.
[0037]
The distance between the adjacent first masks is, for example, 20 μm or more, and preferably 30 μm or more. By doing so, a facet structure having a bottom width of 20 μm or more or 30 μm or more is formed, and a large-area low dislocation density region can be obtained.
[0038]
When the self-standing substrate of the present invention is used, an element structure having excellent crystal quality can be formed thereon. When a light emitting element is formed by forming an element structure including an active layer, an element having excellent light emitting characteristics can be obtained.
[0039]
In the method for manufacturing a self-supporting substrate of the present invention, the base material includes a heterogeneous material substrate made of a material different from the group III nitride semiconductor, and after the step of forming a group III nitride semiconductor layer, The configuration may be such that the step of removing is further performed. According to this configuration, a self-standing substrate made of a group III nitride semiconductor can be suitably formed.
[0040]
In the present invention, a substrate serving as a base for forming a facet structure can employ various forms. Examples of the substrate include sapphire, SiC, Si, GaAs, GaP, LGO, NGO, and ZrB. _Two , ZnO, MgAl _Two O _Three And the like, a group III nitride semiconductor substrate, and a substrate having a group III nitride semiconductor layer formed thereon. The surface shape of the underlayer is not particularly limited, and may be a flat surface or an uneven surface. Further, a groove may be formed in the base material, and a facet structure may be formed thereon. For example, it is also effective to use a combination of techniques such as PENDEO and LEPS to obtain a synergistic effect of the dislocation reduction effect of the facet structure and the dislocation reduction effect of PENDEO and the like.
[0041]
Next, a method for evaluating a self-standing substrate will be described.
[0042]
The simplest method of measuring the distribution of dislocation density on the surface of a free-standing substrate is to selectively etch the parts where dislocations protrude from the surface with a chemical solution, and measure the density of the formed pits (called etch pits) with an optical microscope. Alternatively, counting is performed using a scanning electron microscope. Thereby, the dislocation density and the distribution can be easily measured. In addition, it is possible to easily distinguish between mixed dislocations and edge dislocations based on the size and shape of the etch pit. The type of these dislocations can also be determined by TEM observation.
[0043]
In addition to the evaluation of the crystallinity, the half-width of the X-ray rocking curve by the two-crystal method can be used in addition to the observation of the etch pit. This half-value width is effective as a method for evaluating crystallinity because it is reduced by improving crystallinity, particularly, by reducing dislocations.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0044]
FIG. 1 is a process sectional view showing an example of a method for manufacturing a free-standing substrate according to the present invention. Here, an example of a manufacturing process of a GaN film on a (1000) plane sapphire substrate crystal will be described as an example. First, a first GaN film 12 including a low-temperature buffer layer as an example of a group III nitride is formed on a (1000) plane sapphire substrate 11 by MOVPE (Metal Organic Vapor Phase Epitaxy). Although GaN was used here, this layer contains at least one of Group III elements such as gallium (Ga), aluminum (Al), boron (B), and indium (In), and at least N as a Group V element. Including. For the MOVPE, any of normal pressure, reduced pressure, and pressurized methods can be used. Further, an HVPE (Hydride Vapor Phase Epitaxy) method using chloride as a raw material, a sublimation method formed by sublimating Ga, and the like can also be used.
Next, silicon oxide (SiO 2) is formed on the crystal film by a CVD (chemical vapor deposition) method. _Two ) And an insulating film made of silicon nitride. This insulating film is made of silicon oxide (SiO _Two ) And a silicon nitride film. Further, a high melting point metal such as titanium or tungsten can be used. Next, an opening is formed in the insulating film or the refractory metal film by a lithography technique and a wet etching technique. As an example, the mask material is SiO _Two Six masks B having a width of 5 μm were provided between the masks A having a width of 9 μm in the form of stripes, and a mask pattern having a period of 60 μm and having an opening having a width of 3 μm was formed between the masks. The stripe direction was the <11-20> direction of the GaN film 12. Here, the opening width is desirably 0.5 to 10 μm, but the opening width can be several nm to several hundred nm by using electron beam exposure or the like. The width of each of the masks A and B is preferably 0.5 to 20 μm. In this example, a mask having a width of 9 μm is used as the mask A and a mask having a width of 5 μm is used as the mask B. However, the width is not limited as long as the relationship of A> B can be satisfied. The stripe direction of the mask is preferably a direction within 30 degrees from the <11-20> direction or the <1-100> direction perpendicular to this direction, and more preferably the <11-20> direction or the <1-100> direction. . In particular, the growth method is preferably the <11-20> direction or <1-100> direction in the HVPE method, and the <11-20> direction in the MOVPE method.
[0045]
Next, the substrate crystal on which the mask pattern has been formed is set in a reaction tube of a HVPE growth apparatus, and GaN is grown. The growth of GaN starts from the surface of the GaN film 12 exposed at the opening 14. First, as shown in FIG. 1B, a GaN crystal having a facet structure having a triangular cross section with the (1-101) plane as a side face is formed in the opening.
[0046]
In the present embodiment, the period of the mask A is 60 μm, and the facets formed between the masks A have a giant facet structure that is finally formed. After the formation of the giant facet structure, further growth was performed by the HVPE method, and finally a flattened GaN crystal film having a thickness of 200 μm was produced. FIG. 7 shows the result of measuring the distribution of the dislocation density on the surface of the crystal film. A dislocation distribution with a period of 60 μm was observed, and 1.5 × 10 ^Five cm ^-2 That is a low value. Dislocation reduction can be realized in a wide area as compared with the conventional methods such as ELO and PENDEO. This is extremely convenient when fabricating an element structure such as a laser diode.
[0047]
By forming a crystal plane such as (1-101) in addition to the plane (0001) plane parallel to the substrate as in this embodiment mode, impurities such as silicon (Si) can be incorporated in a plane. Depends on Specifically, (1-100) is easier to take in impurities such as Si, and accordingly, when a facet structure is formed, the carrier concentration in this region increases and the resistance value decreases. Therefore, when the element structure is formed above the region where the facet is formed, the generation of heat is suppressed by low electric resistance, and the performance of the element can be improved.
[0048]
FIG. 6 is a diagram showing another embodiment. Here, a PENDEO type substrate is used. This substrate is obtained, for example, by etching the opening in FIG. 1 to the sapphire substrate. For this etching, for example, reactive etching using chlorine gas can be used. When GaN is grown using, for example, the HVPE method using this substrate, growth starts in the lateral direction only from the side wall of the GaN layer remaining on the pillar, and gradually merges with the adjacent growth layer, and at the same time, a facet structure is formed on the top. Is formed. As the growth continues, the facets coalesce and the larger facet structure gradually grows, eventually becoming a facet structure defined by the cycle of the widest mask, and dislocations similar to those shown in the first embodiment. A reduction effect is obtained. Further, in this case, since the initial growth is started only from the lateral growth, the influence of threading dislocations is reduced, and the dislocations can be further reduced.
[0049]
As a growth method in the above embodiment, it is preferable to use a method having a high growth rate such as the HVPE method. This is because in order to obtain a flat film by embedding the final facet structure, it is necessary to grow the film to a thickness of 100 μm to 1 mm. As a raw material of the HVPE method, a simple substance of a group III element B, Al, Ga, or In metal, a halide compound thereof, or an organic metal compound is used. When a group III metal alone is used, hydrogen chloride (HCl), hydrogen bromide (HBr), and hydrogen iodide (HI) are used to generate a halide compound of a group III element in a reaction tube. Further, ammonia, hydrazine-based raw materials, organic amines and the like are used as the nitrogen raw material. It is desirable to dope impurities to control conductivity. For example, as the n-type impurity, at least one element of C, Si, Ge, Sn, S, Se, and Te is used. Further, as the p-type impurity, at least one or more elements among C, Si, Ge, Sn, Be, Mg, Ca, Zn, and Cd are used. As these impurity raw materials, elemental elements, hydrides, halides such as chlorides, and organic metals can be used.
[0050]
In the above embodiment, the back surface of the sapphire substrate 11 may be irradiated with a laser to perform a substrate peeling process. By selecting the wavelength of this laser so that it passes through the sapphire substrate and is absorbed by the group III nitride semiconductor crystal film, a part of the group III nitride layer in contact with the sapphire substrate can be melted and only the sapphire substrate can be easily melted. Can be peeled off. Examples of such a laser include a KrF excimer laser having an oscillation wavelength of 248 nm and an Nd having an oscillation wavelength of 355 nm. ³⁺ : Third harmonic of YAG laser, etc. Also, only the group III nitride crystal film can be separated by dissolving only the substrate crystal by mechanical polishing or solution etching of the substrate.
[0051]
According to the method for manufacturing a group III nitride crystal film described in this embodiment, a gallium nitride substrate having a low dislocation density can be manufactured. Using this gallium nitride substrate, LEDs (Light Emitting Diodes), LDs (Laser Diodes), FETs (Field Effect Transistors), etc. can be fabricated, compared to those fabricated on conventional sapphire and SiC substrates. Thus, higher performance functions can be obtained.
[0052]
In the above embodiment, the shape of the mask can be variously changed. For example, in addition to the stripe pattern used in the present embodiment, a triangle, a quadrangle, various polygons, a circle, an ellipse, and the like can obtain similar results with respect to a reduction in dislocation density. However, for manufacturing a laser using a stripe-type active layer as in this embodiment, a crystal film in which a region having a low dislocation density exists in a stripe shape is more preferable.
[0053]
It is desirable that the width of the low dislocation density region is sufficiently large with respect to the laser stripe width. When the conventional PENDEO or ELO technology is used, the width of the low dislocation density region is about several μm, and the width of the low dislocation region cannot be sufficiently obtained with respect to the laser stripe width of about 2 μm. For this reason, the high dislocation regions existing on both sides of the low dislocation region may affect the laser structure and deteriorate device characteristics.
[0054]
【Example】
Example 1
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate.
[0055]
FIG. 1 is a schematic cross-sectional view showing a process of forming a GaN film on a (1000) plane sapphire substrate crystal. As the substrate 11, a (1000) plane sapphire substrate is used, and a group III nitride semiconductor layer is grown using the substrate as a base substrate for crystal growth to obtain a group III nitride free-standing substrate. To form the GaN film 12, trimethyl gallium (TMGa) is used as a group III material, and ammonia gas (NH) is used as a group V material. _Three ) Using a metal organic chemical vapor deposition method (MO-VPE method). In addition, SiO _Two The film 13 is made of disilane (SiH _Four ) And oxygen (O _Two The opening 14 is formed by a lithography technique. For the formation of the GaN film 15, gallium chloride (GaCl) which is a reaction product of gallium (Ga) and hydrogen chloride (HCl) is used as a group III material, and NH is used as a group V material. _Three A hydride vapor phase epitaxy (HVPE) using a gas was used.
[0056]
Details of the manufacturing process are as follows.
[0057]
First, the growth surface of the sapphire substrate 11 is cleaned and set in a reaction tube of an MO-VPE apparatus. Hydrogen (H _Two ) And nitrogen (N _Two ) Using a gas mixture, the sapphire substrate 11 is heated to a temperature of about 1050 ° C., heat-treated for about 10 minutes, and then the sapphire substrate 11 is cooled to a temperature of 500 ° C. After the temperature is stabilized, TMGa and NH _Three Is supplied to form a GaN film having a thickness of 350 nm, and the sapphire substrate 11 is heated again to a temperature of 1050 ° C. NH during heating _Three Supply gas. After the temperature was stabilized, TMG was supplied to form a planarized GaN film 12 having a thickness of about 2 μm. After the GaN film 12 is formed, supply of TMG is stopped, the temperature is lowered to room temperature, and the TMG is taken out of the growth apparatus. Next, the sapphire substrate 11 having the GaN film 12 formed thereon is _Two Set in the film forming apparatus. N _Two The temperature was raised to 450 ° C. in a gas atmosphere, and after the temperature was stabilized, the SiH _Four Gas and O _Two By supplying a gas, a 0.5 μm thick SiO 2 _Two The film 13 was formed. SiO _Two After forming the film 13, the SiH _Four Gas and O _Two The supply of gas is stopped, the temperature is lowered to room temperature, and the gas is removed from the forming apparatus. Next, patterning is performed using a lithography technique, and SiO 2 is formed by wet etching. _Two An opening 14 having a stripe shape is formed in the film 13. All opening widths are 3 μm. SiO between openings _Two This pattern was formed on the entire surface of the GaN crystal using a pattern consisting of six masks having a width of 5 μm as a film (called a mask) and two masks having a width of 9 μm on both sides of the mask as one cycle. The stripe direction of the opening 14 is the <1-100> direction of the GaN film 12 (FIG. 1A).
[0058]
Next, the sapphire substrate 11 having the opening 14 formed therein is set in a reaction tube of a HVPE growth apparatus. H for carrier gas _Two The sapphire substrate 11 was heated to a temperature of 1040 ° C. while supplying a flow rate of 3000 cc / min using gas. Sapphire substrate has a flow rate of 1500 cc / min from around 600 ° C. _Three The decomposition of the surface of the GaN film 12 exposed in the opening 14 was suppressed by adding a gas. The Ga source in the reaction tube was heated to a temperature of 850 ° C. After the temperature of the entire reaction tube is stabilized, HCl gas at a flow rate of 10 cc / min is supplied onto the Ga source, GaCl produced by the reaction is supplied to the growth region, and NH _Three It reacts with gas to grow GaN. The growth of GaN starts from the surface of the GaN film 12 exposed at the opening 14, and is grown for about 5 minutes. As shown in FIG. The GaN film 15 having the first facet structure is grown. When the growth is further continued, the adjacent facet structures are united by the growth for about 20 minutes, and the GaN film 15 having the second facet structure having a triangular cross section as shown in FIG. 1C grows. When the growth is further performed for about 120 minutes, the adjacent facet structures are united with each other, and a third facet structure (a giant facet structure) having a triangular cross section grows as shown in FIG. In the present embodiment, since a wide mask having a width of 9 μm is provided, the third facet structure is formed stably.
Thereafter, the growth is continued by increasing the flow rate of HCl supplied to the Ga source to 50 cc / min, and growing until the GaN film 15 having the third facet structure is united and the GaN film 15 having a flat surface appears. Was. The thickness of the flattened GaN film 15 is about 250 μm. After the growth of the GaN film 15, the HCl gas supplied on the Ga source was stopped, and the temperature of the reaction tube was lowered. NH _Three The substrate was cooled to room temperature while supplying gas, and the substrate was taken out.
[0059]
The following evaluation was performed on the group III nitride free-standing substrate obtained as described above.
[0060]
The surface of the formed GaN film 15 was etched with a mixed solution of phosphoric acid and sulfuric acid, and etch pits were measured. When the etch pit density was measured at 10 μm intervals in the <1-100> direction of the GaN film 15, a distribution as shown in FIG. 8 was shown. In the region where the facet structure is formed, the etch pit density is 1.2 × 10 ^Five / Cm ^Two And low values were obtained. In contrast, in the region of the junction of the GaN film 15 having the third facet structure having a triangular cross section, 1.5 × 10 ⁶ / Cm ^Two And the dislocation density increased. That is, in the region where the third facet structure (the giant facet structure) was formed, a defect density lower by at least one order of magnitude was obtained as compared with the joint portion of the facet. In addition, it was found that in a region having a small number of dislocations, 50% or more were mixed dislocations.
[0061]
Further, it was found that the tilt angle of the C-axis obtained from the (0002) reflection X-ray rocking curve measurement of the growth surface was as small as 80 seconds. Without using the technique of the present invention, the normal ELO pattern (mask width 40 μm, opening width 20 μm) shown in FIG. In a GaN film grown using the HVPE method for the thickness, the dislocation density is 5 × 10 5 at the surface above the opening. ⁷ cm ^-2 3 × 10 on the surface on the mask ⁸ cm ^-2 It was found that the tilt angle was as large as 10 degrees above the mask. Further, due to the inclination of the C axis, a film having a flat surface could not be obtained.
[0062]
Example 2
In this example, a GaN substrate was used as a base substrate for crystal growth, and a group III nitride semiconductor layer was grown thereon to obtain a group III nitride free-standing substrate. The surface dislocation density of the GaN substrate used was 1 × 10 ⁷ / Cm ^Two It was about. Hereinafter, description will be made with reference to FIG.
[0063]
First, the surface of the GaN substrate 21 was treated with an organic solvent or an acid, and the SiO 2 used in Example 1 was used. _Two 1 μm thick SiO _Two A film 22 is formed. Next, the lithography technology and the wet etching technology _Two An opening 23 is formed by removing a part of the film 22. All the widths of the openings 23 are 5 μm. SiO between openings _Two This pattern was formed on the entire surface of the GaN crystal with one cycle consisting of four masks each having a width of 5 μm as a film (called a mask) and two masks each having a width of 15 μm on both sides thereof. The stripe direction of the opening was a direction inclined by 5 degrees from the <1-100> direction of the GaN film 12 (FIG. 2A).
[0064]
Next, the GaN substrate 21 having the opening 23 formed therein is set in the reaction tube of the HVPE growth apparatus used in the first embodiment. H at a flow rate of 3000 cc / min _Two Gas and N of 500cc / min _Two The GaN substrate 21 is heated while supplying the gas. When the substrate region of the reaction tube reaches a temperature of about 600 ° C., a flow rate of 2000 cc / min NH _Three Add gas and bring to a temperature of 1060 ° C. The temperature of the Ga source in the reaction tube rose to 850 ° C. After the temperature in the reaction tube becomes stable, HCl gas at a flow rate of 10 cc / min is supplied onto the Ga source to supply GaCl produced by the reaction to the growth region, _Three The GaN film 24 is grown by reacting with the gas.
[0065]
The GaN film 24 grows from the surface of the GaN substrate 21 in the opening 23. With the growth for about 6 minutes, as shown in FIG. 2B, the GaN film 24 having the first facet structure having a triangular cross section grows. When the growth is further continued, two or three adjacent first facet structures are united by growth for about 35 minutes, and as shown in FIG. 2C, a GaN film having a second facet structure having a triangular cross section as shown in FIG. 24 grow. Further growth is continued, and after growth for 100 minutes, the adjacent second facet structure has a width of 20 μm of SiO 2. _Two As a result, the third facet structure having a triangular cross section grows as shown in FIG. Further, the flow rate of HCl supplied on the Ga source was increased to 50 cc / min, _Three The flow rate is reduced to 1000 cc / min to continue the growth, and the adjacent third facet structure is united to form the GaN film 24 having a flat surface (FIG. 2E). The flattened GaN film 24 was formed to have a thickness of 300 μm. After the formation of the GaN film 24, the HCl gas supplied on the Ga source is stopped, and the temperature of the reaction tube is lowered. When the temperature of the reaction tube is around 500 ° C. and NH _Three The supply of gas was stopped, the temperature was cooled to room temperature, and the GaN substrate 21 was taken out of the reaction tube.
[0066]
The following evaluation was performed on the group III nitride free-standing substrate obtained as described above.
[0067]
The surface of the formed GaN film 24 was etched with a mixed solution of phosphoric acid and sulfuric acid in the same manner as in Example 1 to measure etch pits. Is 8 × 10 ^Four / Cm ^Two And low values were obtained.
[0068]
In the present embodiment, the direction of the opening is inclined by 5 degrees from the <11-00> direction. However, if the opening can be combined after the facet structure having the third triangular cross section is formed, the direction is limited to the above-described stripe direction. Instead, the same effect can be obtained even if the lens is inclined at an arbitrary angle.
[0069]
Example 3
In this embodiment, a SiC substrate 31 on which a GaN film 32 having a thickness of 5 μm is formed is used as a substrate crystal (FIG. 3), and a group III nitride semiconductor layer is grown using the SiC substrate 31 as a base substrate for crystal growth. A group nitride free-standing substrate was obtained. Hereinafter, description will be made with reference to FIG.
[0070]
First, the SiO 2 used in Example 1 was formed on the surface of the GaN film 32. _Two SiO 2 having a thickness of 0.2 μm using a film forming apparatus _Two A film 33 is formed. Next, the lithography technology and the wet etching technology _Two An opening 34 is formed in the film 33. The width of the opening 34 was 2 μm, and the mask width (interval between the openings) was formed to be 10 μm, 4 μm, 4 μm, 7 μm, 4 μm, 4 μm, 10 μm,. The stripe direction of the opening 54 was formed to be tilted twice in the <1-100> direction of the sapphire substrate 51 (FIG. 5A).
Next, the SiC substrate 31 having the opening 34 formed therein is set in the reaction tube of the HVPE growth apparatus used in the first embodiment. H at a flow rate of 3000 cc / min _Two The temperature of the GaN substrate 21 was raised while supplying gas, and the substrate region of the reaction tube was heated from a temperature of about 600 ° C. to a flow rate of 2000 cc / min. _Three The gas is added to reach a temperature of 1050 ° C. The temperature of the Ga source in the reaction tube rises to 800 ° C. After the temperature in the reaction tube is stabilized, HCl gas at a flow rate of 5 cc / min is supplied onto the Ga source to supply GaCl produced by the reaction to the growth region, _Three The gas reacts to grow GaN. The GaN is grown from the surface of the GaN film 32 in the opening 34, and is grown for about 10 minutes to form a GaN film 35 having a first facet structure having a triangular cross section as shown in FIG. grow up. When the growth is further continued, the GaN film 35 having the second facet structure having a triangular cross section grows as shown in FIG. Further, when the flow rate of HCl supplied on the Ga source is increased to 50 cc / min to continue the growth, the adjacent facet structures are united and flattened (FIG. 3D). The flattened GaN film 35 was formed to have a thickness of 270 μm. After the formation of the GaN film 35, the HCl gas supplied on the Ga source is stopped and the temperature of the reaction tube is lowered as in the above embodiment. When the temperature of the reaction tube is around 500 ° C. and NH _Three The gas supply was stopped and H _Two From gas to N _Two The gas was switched and cooled to room temperature, and the substrate was taken out of the reaction tube.
[0071]
As described above, a group III nitride free-standing substrate was obtained. The obtained substrate had good crystal quality with few dislocations.
[0072]
Example 4
In this example, a GaN substrate was used as a base substrate for crystal growth, and a group III nitride semiconductor layer was grown thereon to obtain a group III nitride free-standing substrate. The surface dislocation density of the GaN substrate used was 1 × 10 ⁷ / Cm ^Two It was about. Hereinafter, description will be made with reference to FIG.
[0073]
First, the surface of the GaN substrate 41 is cleaned, and then the SiO 2 shown in the above embodiment is used. _Two 1 μm thick SiO 2 _Two A film 42 is formed. Next, SiO 2 _Two An opening 43 is formed in the film 42. The opening 43 was formed by a lithography technique and a wet etching technique. The width of the opening 43 is set to 3 μm, and _Two The width of the film 42 was periodically changed from 4 μm, 6 μm, 4 μm, 8 μm, 4 μm, 6 μm, 4 μm, and 10 μm to form a mask pattern on the entire surface of the GaN substrate 41. The direction of the opening 43 was the <11-20> direction (FIG. 4A).
[0074]
Next, the GaN substrate 41 having the opening 43 formed therein is set in a reaction tube of a HVPE growth apparatus in the same manner as in the above embodiment. H at a flow rate of 2000 cc / min _Two And N of 1000cc / min _Two The GaN substrate 41 was heated while supplying gas, and the sapphire substrate was heated from around 600 ° C. to a flow rate of 1000 cc / min. _Three The temperature is increased to 1020 ° C. by adding gas. The temperature of the Ga source in the reaction tube was raised to 860 ° C. After the temperature in the reaction tube is stabilized, HCl gas at a flow rate of 20 cc / min is supplied onto the Ga source to cause GaCl produced by the reaction to be supplied to the growth region, and NH 3 _Three It reacts with gas to grow GaN. The growth of GaN occurs from the surface of the GaN substrate 41 in the opening 43. By the growth for about 3 minutes, the GaN film 44 having the first facet structure having a triangular cross section grows as shown in FIG. When the growth is further continued, the adjacent first facet structures are united by the growth for about 15 minutes, and the GaN film 44 having the second facet structure having a triangular cross section grows as shown in FIG. 4C. The growth is further continued, and the adjacent second facet structures are united by the growth for 40 minutes, and the GaN film 44 having the third facet structure having a triangular cross section grows as shown in FIG. 4D. Further, the growth is continued, and by the growth for 80 minutes, the adjacent third facet structure is united to grow the GaN film 44 having the fourth facet structure having a triangular cross section as shown in FIG. I do. Then, the flow rate of HCl supplied on the Ga source was increased to 70 cc / min to continue the growth, and the adjacent GaN film 44 having the fourth facet structure was united to form the GaN film 44 having a flat surface (FIG. 4). (F)). The flattened GaN film was formed to have a thickness of 350 μm. After the formation of the GaN film 44, the supply of HCl gas is stopped, and the temperature of the reaction tube is lowered. When the temperature of the reaction tube is around 500 ° C., NH _Three Gas is supplied and H _Two From gas to N _Two The gas was switched to a normal temperature, and the sapphire substrate 11 was taken out of the reaction tube.
[0075]
The surface of the formed GaN film 44 was etched with a mixed solution of phosphoric acid and sulfuric acid in the same manner as in Example 1 to measure etch pits. In the flat region on the GaN film 44 having the fourth facet structure, the etch pit density is 2 × 10 ^Four / Cm ^Two And low values were obtained.
[0076]
Example 5
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate. Hereinafter, description will be made with reference to FIG.
[0077]
In this embodiment, a (1000) plane sapphire substrate whose c-axis is inclined by 0.15 degrees is used as the substrate. In forming the GaN film, trimethyl gallium (TMGa) is used as a group III material, and ammonia gas (NH) is used as a group V material. _Three ) Was utilized. In addition, SiO _Two For the formation of the film 53, dichlorosilane (SiH _Four ) And oxygen (O _Two ), And the openings 54 were formed by using a lithography technique.
[0078]
Hereinafter, the details of the steps will be described. First, the growth surface of the sapphire substrate 51 is cleaned, and the sapphire substrate 51 is _Two Set in the film forming apparatus. Sapphire substrate 51 with N _Two The temperature is increased to 450 ° C. in a gas atmosphere. 0.04% SiH after temperature stabilizes _Four Gas and 0.4% O _Two By supplying a gas, a 0.5 μm thick SiO 2 is formed on the GaN film 52. _Two A film 53 is formed. SiO _Two After forming the film 53, the SiH _Four Gas and O _Two The supply of gas is stopped, the temperature is lowered to room temperature, and the gas is taken out from the growth apparatus.
[0079]
Next, SiO 2 _Two An opening 54 is formed in the film 53. The width of the opening 54 was set to 3 μm, and the mask width (interval between the openings) was formed to be 3 μm, 5 μm, 3 μm, 7 μm, 3 μm, 5 μm, 3 μm, and 9 μm, respectively. The stripe direction of the opening 54 was formed to be tilted twice in the <1-100> direction of the sapphire substrate 51 (FIG. 5A).
[0080]
Next, the sapphire substrate 51 having the opening 54 is set in a reaction tube of the MO-VPE apparatus. Hydrogen (H _Two ) And nitrogen (N _Two ) While supplying the gas mixture, the sapphire substrate 51 is heated to a temperature of about 1050 ° C., heat-treated for about 10 minutes, and the sapphire substrate 51 is cooled to a temperature of 520 ° C. After the temperature is stabilized, TMGa and NH _Three To form a 300 nm thick GaN film. Again, NH _Three The sapphire substrate 51 is heated to a temperature of 1050 ° C. while supplying gas. The heating time is about 12 minutes. In this heating step, SiO _Two The GaN on the film 53 evaporates. After the temperature is stabilized, TMG is supplied to form a GaN film 55 having a facet structure with the (1-101) plane as a side wall on the opening 54 (FIG. 5B).
[0081]
By continuing the growth, as shown in FIG. 5C, the adjacent GaN films 55 having a facet structure are united to form a GaN film 55 having a second facet structure. By continuing the growth, the adjacent second facet structure is united to form a GaN film 55 having a third facet structure (FIG. 5D).
[0082]
By continuing the growth, the adjacent third facet structure is united to form a GaN film 55 having a fourth facet structure having a flat surface 56 (FIG. 5E). Thereafter, the supply of TMG was stopped, the temperature was lowered to room temperature, and the TMG was taken out of the growth apparatus. Until the temperature during cooling is about 500 ° C. _Three Gas was supplied.
[0083]
The surface of the formed GaN film 55 was etched with a mixed solution of phosphoric acid and sulfuric acid in the same manner as in Example 1 to measure the etch pit. In the flat region of the GaN film 55 having the fourth facet structure, the etch pit density is 2 × 10 ^Five / Cm ^Two And low values were obtained.
[0084]
Example 6
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate. Hereinafter, description will be made with reference to FIG.
[0085]
Details of the manufacturing process are as follows. As the substrate, a (1000) plane sapphire substrate 61 inclined at 0.2 degrees was used, and trimethylgallium (TMGa) was used as a group III material, and ammonia gas (NH) was used as a group V material. _Three The GaN film 62 having a thickness of about 1 μm was formed on the surface by using a metal organic chemical vapor deposition method (MO-VPE method) using the method (1). Then dichlorosilane (SiH _Four ) And oxygen (O _Two 0.5 μm thick SiO 2 by a thermal CVD method using _Two The film 63 was formed. SiO by dry etching _Two After the opening 64 is provided in the film 63, _Two Using the film 63 as a mask, the GaN film 62 and the sapphire substrate 61 were dry-etched by 0.5 μm or more (FIG. 6A). Etching gas is Cl _Two Gas was used. Here, the width of the opening 64 was 4 μm, and the mask width (interval between the openings) was 6 μm, 6 μm, 6 μm, 10 μm, 6 μm, 6 μm, 6 μm, 10 μm,... That is, this pattern was formed on the entire surface of the GaN crystal using three patterns of 6 μm width and two patterns of 10 μm width on both sides as one cycle. The stripe direction of the opening 64 was formed in the <1-100> direction of the sapphire substrate 61.
[0086]
Next, the substrate that has been subjected to the above processing is set in a reaction tube of an HVPE growth apparatus. H at a flow rate of 2000 cc / min _Two And N of 1000cc / min _Two The temperature of the sapphire substrate 61 is increased while supplying gas, and the flow rate of 1000 cc / min. _Three The temperature is increased to 1020 ° C. by adding gas. The temperature of the Ga source in the reaction tube was raised to 860 ° C. After the temperature in the reaction tube is stabilized, HCl gas at a flow rate of 5 cc / min is supplied onto the Ga source to cause reaction, and GaCl produced by the reaction is supplied to the growth region, _Three It reacts with gas to grow GaN. The growth of GaN is performed from the side wall surface of the GaN film 62 in the groove 65, and the growth is performed for about 8 minutes, so that the first facet structure made of GaN is grown in the opening as shown in FIG. I do. Next, the flow rate of HCl supplied on the Ga source was increased to 50 cc / min, and the SiH _Two Cl _Two When the GaN growth is continued by supplying the gas, as shown in FIG. _Two A GaN film 66 having a second facet structure having a triangular cross section grows between the films 63. Further, the growth is continued, and the growth is continued until the adjacent GaN film 66 having a facet structure having a triangular cross section is united to form a GaN film 66 having a flat surface as shown in FIG. After forming the GaN film 66 having a flat surface, the supply of HCl gas is stopped and the temperature of the reaction tube is lowered. NH _Three The system was cooled to room temperature while supplying gas, and the sapphire substrate was taken out.
[0087]
The surface of the formed GaN film 66 was etched with the mixed solution of phosphoric acid and sulfuric acid used in Example 1 to measure the etch pit. In the <1-100> direction, in the central region where the GaN film 66 finally formed the facet structure, the etch pit density was 4 × 10 ^Five / Cm ^Two And a low value was obtained, and when the Hall measurement was performed, 2 × 10 ¹⁸ / Cm ^Three Was obtained.
[0088]
After the GaN film 66 is formed, the sapphire substrate 61 is removed, and the back surface of the GaN film 66 is flattened by polishing or the like, whereby a single GaN substrate 66 can be manufactured. The sapphire substrate 61 can be removed by a method such as polishing, laser peeling, and etching.
[0089]
Example 7
In this example, a GaN crystal was grown on a sapphire substrate to obtain a group III nitride free-standing substrate. Hereinafter, description will be made with reference to FIG.
[0090]
A (1000) plane sapphire substrate 71 inclined at 0.15 degrees was used as the substrate. A resist film 72 having a thickness of 4 μm or more was formed on the sapphire substrate 71, and an opening 73 was formed in the resist film 72 by lithography.
[0091]
Here, the width of the opening 73 was 4 μm, and the mask width (interval between the openings) was 6 μm, 6 μm, 6 μm, 6 μm, 8 μm, 6 μm, 6 μm, 6 μm, 6 μm, 8 μm,. That is, a mask pattern was prepared using four masks having a width of 6 μm and two masks having a width of 8 μm on both sides of the masks as one cycle. The stripe direction of the opening 73 was formed in the <1-100> direction of the sapphire substrate 71 (FIG. 7A).
[0092]
Next, Cl _Two The surface of the sapphire substrate 71 in the opening 73 was etched by a dry etching method using gas to form a groove 74 having a depth of 4 μm or more (FIG. 7B).
[0093]
Next, the resist film 72 is removed and set in a reaction tube of the MO-VPE apparatus. Hydrogen (H _Two ) And nitrogen (N _Two ) While supplying the gas mixture, the sapphire substrate 71 is heated to a temperature of about 1070 ° C., heat-treated for about 15 minutes, and the sapphire substrate 71 is cooled to a temperature of 520 ° C. After the temperature is stabilized, TMGa and NH _Three Is supplied to form a GaN film having a thickness of 250 nm. Again, NH _Three The sapphire substrate 71 is heated to a temperature of 1050 ° C. while supplying gas. After the temperature is stabilized, TMG is supplied to grow GaN. As shown in FIG. 7C, the GaN film 75 is formed on the surface of the sapphire substrate 71 and the GaN 76 grows on the bottom of the groove 74 as shown in FIG.
[0094]
After forming the GaN film 75 having a facet structure, the supply of TMG is stopped, the temperature is lowered to room temperature, and the substrate is taken out of the growth apparatus. When the temperature during cooling is around 500 ° C, NH _Three Supply gas.
[0095]
Next, it is set in the reaction tube of the HVPE growth apparatus used in the above embodiment. H for carrier gas _Two And N _Two The sapphire substrate 71 is heated to a temperature of 1060 ° C. while supplying a flow rate of 4000 cc / min by using the mixed gas (flow rate ratio 1: 2). After the sapphire substrate 71 reaches a temperature of about 600 ° C. _Three Supply gas. The Ga source in the reaction tube was heated to a temperature of 840 ° C. After the temperature of the entire reaction tube is stabilized, HCl gas at a flow rate of 50 cc / min is supplied onto the Ga source, GaCl produced by the reaction is supplied to the growth region, and NH _Three It reacts with gas to grow GaN. Further, in order to dope Si impurities, SiH _Two Cl _Two The gas was supplied at a flow rate of 0.015 cc / min. GaN growth occurs from the surface of the GaN film 75. The growth of the GaN film at the bottom of the groove 74 is delayed, and the state shown in FIG.
[0096]
When the growth is further continued, a GaN film 75 having a giant facet structure is formed (FIG. 7D), and when the growth is continued for 200 minutes, a GaN film 75 having a flat surface is formed (FIG. 7E). ). The GaN film 75 was flattened to a thickness of 320 μm. After the formation of the GaN film 75, the HCl gas supplied on the Ga source is stopped, and the temperature of the reaction tube is lowered. When the temperature of the reaction tube is around 500 ° C., NH _Three Gas is supplied and H _Two From gas to N _Two The gas was switched to a normal temperature, and the substrate was taken out.
[0097]
It is assumed that the surface of the formed GaN film 75 was etched with the mixed solution of phosphoric acid and sulfuric acid used in Example 1 to measure etch pits. The measurement was performed at 10 μm intervals in the <1-100> direction. The GaN film 65 has a density of 2 × 10 ^Five / Cm ^Two And low values were obtained.
[0098]
In the present embodiment, dry etching is used to form the grooves in the sapphire substrate 71. However, similar effects can be obtained by using a phosphoric acid-based mixed solution.
[0099]
Example 8
In this example, a semiconductor laser structure was manufactured using the group III nitride free-standing substrate manufactured in Example 1. Hereinafter, description will be made with reference to FIG.
[0100]
For the fabrication of the laser structure, metal organic chemical vapor deposition (MO-VPE) using an organic metal as a group III raw material was used. The group III nitride free-standing substrate produced in Example 1 was set in an MO-CVD apparatus. H _Two Gas and NH _Three The temperature was raised to 1050 ° C. while supplying gas. After the temperature was stabilized, an n-type GaN layer 91 having a thickness of 1 μm to which Si was added was formed. Further, 0.4 μm-thick n-type Al _0.15 Ga _0.85 An N-cladding layer 92 and an n-type GaN optical guide layer 93 having a thickness of 0.1 μm to which Si was added were formed. Subsequently, at a temperature of 790 ° C., an undoped In _0.2 Ga _0.8 N quantum well layer and undoped In 5 nm thick _0.05 Ga _0.95 An active layer 94 having a three-period multiple quantum well structure made of an N barrier layer was formed. Then, at a temperature of 1000 ° C.
A 0.1 μm-thick p-type GaN optical guide layer 95 to which Mg is added,
0.4 μm thick p-type Al with Mg added _0.1 Ga _0.9 N cladding layer 96,
A 0.5 μm-thick p-type GaN contact layer 97 doped with Mg,
Were sequentially formed to form a laser element structure (FIG. 9A).
[0101]
After fabrication of the laser structure, the NH _Three Cooling to a temperature of 500 ° C. while supplying gas, _Two It cooled to room temperature while supplying gas.
[0102]
After cooling, the substrate on which the laser structure was formed was taken out of the apparatus, and a 0.5 μm thick SiO _Two A film 98 was formed. Further, an opening 99 having a width of 1.8 μm was formed in a region where the facet structure was formed by lithography. Further, a p-type electrode 100 of palladium (Pd) having a thickness of 50 nm and gold (Au) having a thickness of 0.3 μm is formed on the p-type GaN contact layer 97 in the opening 99, and N _Two The heat treatment was performed at a temperature of 450 ° C. in a gas atmosphere.
[0103]
Next, the sapphire substrate 11, the GaN film 12, and the GaN film 15 were polished from the back surface so that the total film thickness was about 100 μm. The polished backside GaN film 15 is etched with a phosphoric acid-based solution to form an n-electrode 101 made of 50 nm thick Ti and 0.3 μm thick aluminum (Al) (FIG. 9B). Subsequently, the GaN film 15 was cleaved on the M plane, which is the cleavage direction, to form a resonator mirror surface having a laser structure.
[0104]
The semiconductor laser manufactured as described above is oscillated at room temperature (25 ° C.). The threshold was measured. The threshold current of the obtained laser was 20 mA (current density: ~ 3.5 KA / cm ^Two ) Good values before and after. The laser life exceeded 5000 hours at 60 ° C. and 30 mW output, and was confirmed to be a practical level as a light source for pickup of an optical disk.
[0105]
It is considered that the reason why excellent light emitting performance was obtained in the present example is that dislocations introduced into the laser element structure including the active layer were significantly reduced. In particular, the fact that the edge dislocation has been reduced is also considered to be one of the causes of the improvement of the characteristics. As described above, the edge dislocation is a cause of generation of a small-angle grain boundary in a crystal, and light scattering is likely to occur at the small-angle grain boundary. In this embodiment, it is considered that the laser characteristics are significantly improved because such edge dislocations are significantly reduced in the active layer.
[0106]
Example 9
In this example, a GaN substrate was used as a base substrate for crystal growth, and a group III nitride semiconductor layer was grown thereon using various mask patterns to obtain a group III nitride free-standing substrate. The surface dislocation density of the GaN substrate used was 1 × 10 ⁷ / Cm ^Two It was about.
[0107]
FIG. 10 is a schematic diagram of the mask pattern used in this embodiment. All masks are SiO _Two A film having a thickness of 0.5 μm was formed.
[0108]
In FIG. _Two The width of the film 110 is set to 10 μm, and other SiO _Two The films 112, 113, 114, 115, 116 and 117 were formed so as to be wider than the widths. SiO _Two The interval between the films 110 was 20 μm or more. The width of the opening 111 exposing the substrate surface was set to 1.5 μm or more. SiO _Two The direction of the film 110 was the <1-100> direction of the underlying GaN substrate.
[0109]
In the mask pattern of FIG. _Two SiO between the films 110 _Two A film 112 is formed. SiO _Two The size of the film 112 is 5 μm in width and 5 μm to 50 μm in length.
[0110]
In the mask pattern of FIG. _Two SiO between the films 110 _Two A film 113 is formed. SiO in horizontal plane of substrate _Two The shape of the film 113 is a triangle and a rhombus.
[0111]
In the mask pattern of FIG. _Two SiO between the films 110 _Two A film 114 is formed. SiO in horizontal plane of substrate _Two The shape of the film 114 is a rectangle including a hollow portion. The width (short side) of the rectangle was about 1 μm.
[0112]
In the mask pattern of FIG. _Two SiO between the films 110 _Two A film 115 is formed. SiO in horizontal plane of substrate _Two The film 115 is a parallelogram having a width of 5 μm and a length of 20 μm.
[0113]
In the mask pattern of FIG. _Two SiO between the films 110 _Two A film 116 is formed. SiO in horizontal plane of substrate _Two The film 116 is a triangle having one side of about 7 μm.
[0114]
In the mask pattern of FIG. _Two SiO between the films 110 _Two A film 117 is formed. SiO in horizontal plane of substrate _Two The film 117 has a circular shape with a diameter of about 10 μm.
[0115]
Next, a GaN film was epitaxially grown by the HVPE method or the MOVPE method using the substrate on which the mask patterns having the shapes shown in FIGS.
[0116]
In the growth process, a GaN film is grown from the opening 111 to form a facet structure, as in the above embodiment. By continuing the growth, the coalescence of the adjacent facet structures is repeated, and SiO 2 is deposited on the substrate crystal. _Two A GaN film having a giant triangular facet structure is formed between the films 110. When the growth is further continued, the GaN film having a giant triangular facet structure is also combined to form a GaN film having a flat surface region.
[0117]
Defects on the surface of the GaN film formed using each of the above mask patterns were measured. In each case, the etch pit density was 2 × 10 in the area where the huge facet structure was formed. ^Five / Cm ^Two Was reduced to
[0118]
The present invention has been described based on the embodiments. Each of the free-standing substrates obtained in Examples 1 to 8 has a large facet structure including a plurality of small facet structures. The facet structure has a triangular or trapezoidal cross section with a base of 20 μm or more, and dislocations propagating from the base to the top in the formed group III nitride semiconductor layer are substantially horizontal to the base. In multiple directions.
The self-standing substrates obtained in Examples 1 to 8 were all observed by observation of etch pits.
(i) Surface average dislocation density is 10 ^-6 cm ^-2 The low dislocation density region below is periodically formed in one direction in the horizontal plane of the substrate
(ii) The width of the low dislocation density region is 20 μm or more
(iii) It was confirmed that 50% or more of the dislocations contained in the low dislocation density region consisted of mixed dislocations.
[0119]
Further, when the tilt angle in the low dislocation density region was measured by the method described in Example 1, it was confirmed that each was less than 1 degree.
[0120]
As described above, the present invention has been described based on the embodiments. However, the present invention is not limited to these, and various configurations can be changed.
[0121]
For example, in the above embodiment, a 0.5 μm thick SiO _Two A film was used, but SiO _Two Any thickness may be used as long as a facet structure can be formed without depositing GaN on the film by epitaxial growth. As for the mask material, SiO _Two SiN (x) film other than film, Al _Two O _Three A film or the like can be used. Also, the mask opening width and the stripe direction can be changed as appropriate.
[0122]
Further, as the base substrate, it is also possible to use a substrate other than those described in the above embodiment.
[0123]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a group III nitride free-standing substrate in which dislocations are significantly reduced. The low dislocation density region formed on the self-standing substrate has a large area, and the element structure can be suitably formed thereon.
[Brief description of the drawings]
FIG. 1 is a process cross-sectional view illustrating an example of a method for manufacturing a free-standing substrate according to the present invention.
FIG. 2 is a process sectional view illustrating an example of a method for manufacturing a free-standing substrate according to the present invention.
FIG. 3 is a process sectional view illustrating an example of a method for manufacturing a free-standing substrate according to the present invention.
FIG. 4 is a process sectional view illustrating an example of a method for manufacturing a free-standing substrate according to the present invention.
FIG. 5 is a process sectional view illustrating an example of a method for manufacturing a free-standing substrate according to the present invention.
FIG. 6 is a process sectional view illustrating an example of the method for manufacturing a free-standing substrate according to the present invention.
FIG. 7 is a process sectional view illustrating an example of the method for manufacturing a free-standing substrate according to the present invention.
FIG. 8 is a diagram showing a measurement result of an etch pit density in Example 1.
FIG. 9 is a process sectional view of the method for manufacturing the semiconductor laser shown in the example.
FIG. 10 is a diagram illustrating an example of a mask pattern used in the example.
FIG. 11 is a diagram showing a facet multiplex structure observed by an electron microscope.
FIG. 12 is a schematic view showing a state of dislocation bending due to a facet structure.
FIG. 13 is a view showing a process of crystal growth by FIELD.
[Explanation of symbols]
11 Sapphire substrate
12 GaN film
13 SiO _Two film
14 Opening
15 GaN film
21 GaN substrate
22 SiO _Two film
23 opening
24 GaN film
31 SiC substrate
32 GaN film
33 SiO _Two film
34 opening
35 GaN film
41 GaN substrate
42 SiO _Two film
43 opening
44 GaN film
51 Sapphire substrate
52 GaN film
53 SiO _Two film
54 opening
55 GaN film
56 flat surface
61 Sapphire substrate
62 GaN film
63 SiO _Two film
64 opening
65 grooves
66 GaN film
71 Sapphire substrate
72 resist film
72 grooves
73 opening
74 grooves
75 GaN film
91 GaN layer
92 cladding layer
93 n-type GaN optical guide layer
94 Multiple Quantum Well Structure Active Layer
95 p-type GaN optical guide layer
96 cladding layer
97 Contact Layer
98 SiO _Two film
99 opening
100 p-type electrode
101 n-type electrode
110 SiO _Two film
111 opening
112 SiO _Two film
113 SiO _Two film
114 SiO _Two film
115 SiO _Two film
116 SiO _Two film
117 SiO _Two film
201 Sapphire substrate
202 Base crystal film
203 growth area
204 mask
205 facet surface
1000 sapphire substrate
1002 GaN film
1003 mask
1004 GaN layer
1006 dislocation
1007 Small facet structure
1008 giant facet structure

Claims (27)

A self-supporting substrate including a group III nitride semiconductor layer, including a facet structure having a side facet face obliquely positioned with respect to a horizontal plane of the substrate, wherein the group III nitride semiconductor layer is formed so as to cover the facet structure. A self-supporting substrate characterized by being made. The self-standing substrate according to claim 1,
A free-standing substrate, wherein the facet structure has a stripe shape. The self-standing substrate according to claim 1 or 2,
A free-standing substrate, characterized in that the facet structure has a stripe width of 20 μm or more. The self-standing substrate according to any one of claims 1 to 3,
The self-standing substrate according to claim 1, wherein the facet structure includes a plurality of small facet structures smaller than the facet structure. The self-standing substrate according to any one of claims 1 to 4,
The self-standing substrate according to claim 1, wherein the facet structure has a triangular or trapezoidal cross section having a base of 20 μm or more. The self-standing substrate according to any one of claims 1 to 5,
A self-supporting substrate, wherein the plurality of facet structures are periodically formed in a direction perpendicular to the stripe direction. A base material, and a group III nitride semiconductor layer formed on the base material, comprising, in the group III nitride semiconductor layer, dislocations propagating upward from the base material, the base material and A self-supporting substrate characterized by being bent several times in a substantially horizontal direction. A free-standing substrate including a group III nitride semiconductor layer,
A low dislocation density region having a surface average dislocation density of less than 10 ⁻⁶ cm ⁻² is periodically formed in one direction in a horizontal plane of the substrate,
A free-standing substrate, wherein the width of the low dislocation density region is 20 μm or more, and the tilt angle of the low dislocation density region is 1 degree or less. The self-standing substrate according to claim 8,
A free-standing substrate, wherein 50% or more of the dislocations contained in the low dislocation density region are composed of mixed dislocations. A substrate, provided on the surface of the substrate, a mask pattern having a predetermined opening, and a group III nitride semiconductor layer grown from the opening and formed to cover the mask pattern. ,
The mask pattern includes a plurality of first masks extending in a stripe shape and a second mask located between the adjacent first masks and having a width smaller than the first mask. Freestanding substrate. The self-standing substrate according to claim 10,
Each of the first mask and the second mask has a stripe shape extending in substantially the same direction, and the second mask is formed with a period smaller than the period of the first mask. Freestanding substrate. The self-standing substrate according to claim 10,
The stripe direction of the first mask is a [11-20] direction, a [1-100] direction, or a direction forming a deviation angle within 30 degrees from these directions with respect to the crystal structure of the group III nitride semiconductor. A free-standing substrate, characterized in that: 13. The self-standing substrate according to claim 10, wherein an interval between adjacent first masks is 20 μm or more. 14. The self-supporting substrate according to claim 10, further comprising a stripe-shaped facet structure having a base defined by an area defined by the adjacent first mask. The self-standing substrate according to claim 14,
The self-standing substrate according to claim 1, wherein the facet structure includes a plurality of small facet structures smaller than the facet structure. A semiconductor device comprising the self-standing substrate according to claim 1 as a substrate, and an element structure provided on the substrate. The semiconductor device according to claim 16,
A semiconductor device, wherein the device structure is a laser structure including at least an active layer. Growing a group III nitride semiconductor on the base material, forming a small facet structure with the facet surface located obliquely to the horizontal surface of the base material,
Further growing the group III nitride semiconductor, forming a stripe-shaped facet structure including the small facet structure,
A method for growing a group III nitride semiconductor layer, comprising: The growth method according to claim 18,
The method of growing a group III nitride semiconductor layer, wherein the stripe width of the stripe-shaped facet structure is 20 μm or more. The growth method according to claim 18 or 19,
The method of growing a group III nitride semiconductor layer, wherein the stripe-shaped facet structure has a triangular or trapezoidal cross section having a base of 20 μm or more. 21. The group III nitride semiconductor layer according to claim 18, wherein the plurality of stripe-shaped facet structures are periodically formed in a direction perpendicular to a stripe direction. Growth method. Forming a mask pattern including a plurality of first masks extending in a stripe pattern on the surface of the base material and a second mask located between the adjacent first masks and having a width smaller than the first mask; When,
A step of epitaxially growing a group III nitride semiconductor on the substrate while forming a facet surface forming an acute angle with respect to the substrate horizontal plane, with the opening of the mask pattern as a growth region;
A method for growing a group III nitride semiconductor layer, comprising: The growth method according to claim 22,
The first mask and the second mask each have a stripe shape, and the second mask is formed with a period smaller than the period of the first mask. Method. The growth method according to claim 22 or 23,
The stripe direction of the first mask is a [11-20] direction, a [1-100] direction, or a direction forming a deviation angle within 30 degrees from these directions with respect to the crystal structure of the group III nitride semiconductor. A method for growing a group III nitride semiconductor layer, comprising: A method for manufacturing a free-standing substrate including a step of forming a group III nitride semiconductor layer on a base material,
25. A method for manufacturing a free-standing substrate, wherein the step of forming a group III nitride semiconductor layer is performed by the growth method according to claim 18. The manufacturing method according to claim 25,
The base material includes a heterogeneous material substrate made of a material different from the group III nitride semiconductor,
A method for manufacturing a free-standing substrate, further comprising, after the step of forming a group III nitride semiconductor layer, a step of removing the heterogeneous material substrate. Forming a group III nitride semiconductor layer on a substrate by the growth method according to any one of claims 18 to 24;
Forming a device structure by further laminating a layer made of a group III nitride semiconductor on the group III nitride semiconductor layer;
A method for manufacturing a semiconductor device, comprising:

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