DE102017102472A1 - Process for the preparation of a substrate based on nitride compound semiconductor material - Google Patents

Abstract

The invention relates to a method for producing a substrate (1) based on nidrid compound semiconductor material, in which at least one rod (3) based on nidride compound semiconductor material is formed on a starting substrate (2). A bulk material (5) based on nitride compound semiconductor material is formed from the rod and the starting substrate is separated from the bulk material.

Description

The present application relates to a method for producing a substrate based on nitride compound semiconductor material.

Producing nitride compound semiconductor material based bulk materials such as gallium nitride presents a major engineering challenge. Possible manufacturing processes include sublimation, HVPE, high pressure and ammonothermic processes, and sodium flow processes. Often, however, only a comparatively low material quality is achieved.

An object is to provide a method for producing a substrate based on nitride compound semiconductor material, with which a high crystal quality can be achieved in a simple and reliable manner.

This object is achieved by a method according to claim 1. Further embodiment and expediencies are the subject of the dependent claims.

A process for producing a substrate based on nitride compound semiconductor material is disclosed. The substrate is suitable, for example, as a growth substrate for the production of electronic or optoelectronic semiconductor components based on nitride compound semiconductor material, for example transistors or light-emitting diodes.

"On the basis of" nitride compound semiconductor material "in the present context means that the material, such as the substrate or at least a part thereof, a nitride compound semiconductor material, preferably Al _x In _y Ga _1-xy N comprises or consists of, wherein 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and x + y ≤ 1 holds. This material does not necessarily have to have a mathematically exact composition according to the above formula. Rather, it may, for example, have one or more dopants and additional constituents. For the sake of simplicity, however, the above formula contains only the essential constituents of the crystal lattice (Al, Ga, In, N), even if these can be partially replaced and / or supplemented by small amounts of further substances.

In accordance with at least one embodiment of the method, a starting substrate is provided. The starting substrate has, for example, a growth surface which is suitable for the deposition of nitride compound semiconductor material. For example, the growth surface is formed by a nitride compound semiconductor material.

For example, the starting substrate is a solid on the basis of nitride compound semiconductor material, such as GaN or AlN or a mixed crystal thereof. Alternatively, the starting substrate may comprise a substrate body and a growth layer disposed on the substrate body, wherein the growth layer forms the growth surface. The starting substrate may also be a composite substrate in which the growth layer is connected to the substrate body by means of a bonding layer, such as a dielectric layer, such as an oxide layer.

In accordance with at least one embodiment of the method, at least one rod based on nitride compound semiconductor material is formed on the starting substrate, in particular on the growth surface of the starting substrate. The preparation of the at least one rod is carried out for example by means of MOVPE. The at least one rod, in particular a main extension direction of the rod, can run perpendicular to the growth surface or obliquely to the growth surface, for example if the crystallographic direction <0001> of the starting substrate is not aligned perpendicular to the growth surface. Such substrates are also referred to as "off-axis" substrates. An angle between the main extension direction of the rod and a perpendicular to the growth surface is, for example, between 0.0 ° inclusive and 1.0 ° inclusive, in particular between 0.0 ° and 0.3 ° inclusive.

In particular, exactly one rod can be formed on the starting substrate. Alternatively, a plurality of bars are formed on the starting substrate, wherein the bars are spaced apart in the lateral direction, that is along a main extension plane of the starting substrate.

In accordance with at least one embodiment of the method, a volume material based on nitride compound semiconductor material is formed starting from the rod. In particular, the bulk material is formed starting from an end of the at least one rod facing away from the starting substrate. It has been found that the rods can have a particularly high crystal quality at the end remote from the starting substrate and can be defect-free or at least low in defects. The terms "defect-free" and "low-defect" here do not refer to point defects but to dislocation defects such as, in particular, screw dislocations. Starting from these ends, a defect-free or at least low-defect growth can take place. For example, a bulk material formed from a rod has defects between 0 and 10 inclusive.

The formation of the bulk material takes place for example by means of HVPE, a high-pressure and ammonothermic process or a sodium flow process. In the presence of more than one rod, the bulk material can be formed in the form of individual areas each starting from a rod, wherein the individual areas in plan view of the starting substrate cover the starting substrate between adjacent bars and the individual areas grow together to form a coherent volume material.

The bulk material is in particular at any point in the vertical direction spaced from the starting substrate. The volume material therefore does not directly adjoin the starting substrate at any point. For example, located between the bulk material and the starting substrate at locations laterally of the at least one rod, a cavity which is free of solid matter.

In accordance with at least one embodiment of the method, the starting substrate is separated from the bulk material. This can be done, for example, by mechanically or chemically severing or separating the at least one rod. In principle, however, it is also conceivable that the starting substrate remains on the bulk material.

In accordance with at least one embodiment of the method, the rod has an aspect ratio of between 3 and 1000 inclusive, in particular between 50 and 200 inclusive. It has been shown that the crystal quality of the bulk material can be improved by a sufficiently high aspect ratio. In this case, the aspect ratio denotes the ratio between the height, that is to say the vertical extent of the at least one rod perpendicular to the main extension plane of the starting substrate in relation to the diameter of the at least one rod. The term "diameter" here denotes the maximum extent of the rod in the lateral direction.

In accordance with at least one embodiment of the method, the at least one rod has a diameter of between 0.5 μm and 2 μm inclusive. It has been found that rods of this diameter can be made to be particularly reliable and of high crystal quality and are particularly suitable for the subsequent deposition of bulk material thereon.

In accordance with at least one embodiment of the method, the at least one bar has a height of between 2 μm and 1 mm inclusive, in particular between 20 μm and 1 mm inclusive.

By a height of the at least one rod of at least 2 microns ensures that the remote from the starting substrate end of the rod is defect-free or at least low in defects.

In addition, it has been found that a high height of the at least one rod of more than 2 μm, for example of 20 μm or more, can bring about an increased quality of the bulk material. This will be explained in more detail in connection with the embodiments.

In accordance with at least one embodiment of the method, at least one rod is twisted after the formation of the bulk material. That is, in plan view of the starting substrate, a cross section of the rod on the side remote from the starting substrate is rotated relative to a cross section on the side facing the starting substrate. This rotation takes place in particular during the merging of the individual regions of the volume material. By means of the rotation of the rods in the formation of new lattice defects due to a relative misorientation of adjacent bars in the growing together of the individual areas can be avoided or at least reduced.

In accordance with at least one embodiment of the method, the rod has, at an end facing away from the starting substrate, a facet which runs obliquely to a main extension plane of the starting substrate. For example, in the case of GaN, an angle between the facet and the main extension plane of the starting substrate is an angle of 61.9 ° for a (10-11) facet, 43.2 ° for a (10-12) facet, or 32.0 ° for a (10-13) facet.

It has been found that by growing from such a facet, a particularly high quality of crystal can be achieved for the bulk material, in particular compared to an end of the rod parallel to the main extension plane and compared to growth proceeding from a direction perpendicular to the main plane of extension Side surface of the rod.

In accordance with at least one embodiment of the method, the volume material is formed exclusively starting from the facet. For example, the production conditions, such as the temperature, in forming the bulk material are set such that crystal growth occurs only from the facet. In particular, no growth takes place on a side surface of the at least one rod which runs perpendicular to the main extension plane of the starting material.

In accordance with at least one embodiment of the method, a plurality of bars are formed, wherein when forming the bulk material, the bulk material formed from adjacent bars collides. Individual regions of the volume material, which respectively originate from a rod, thus grow together so that a closed surface of the volume material results in the lateral direction. In plan view of the starting substrate, the bulk material can completely cover the starting substrate at least between adjacent bars.

In accordance with at least one embodiment of the method, the bars are arranged at a center distance of at least 1 μm from each other. For example, a center distance is between 1 μm and 5 mm inclusive. The greater the center distance between the bars, the greater the individual areas formed when forming the bulk material from the respective bars. Furthermore, it has been shown that the larger the center distance between the bars, the faster the bars grow in the vertical direction, since the larger the center distance, the smaller the number of bars formed on the starting substrate. Consequently, with the same volume growth of the material of the bars, the vertical growth of the individual bars increases.

For example, a center distance between two bars is at least as large as a component to be produced on the formed volume material. A component produced in this way thus has no point at which individual areas of the volume material abut one another.

According to at least one embodiment of the method, the at least one bar is formed with Ga polarity. This polarity is also called Ga-face. In this polarity, the gallium and / or optionally another group III material is respectively arranged on the side facing away from the starting substrate, while the nitrogen side faces the starting substrate.

According to at least one embodiment of the method, a side surface of the at least one rod is locally provided with a cover layer prior to forming the bulk material. In particular, the cover layer may cover the entire rod apart from the facet. By means of the cover layer can be achieved in a simplified manner that the growth of the volume material takes place exclusively starting from the facet.

According to at least one embodiment of the method, prior to forming the at least one bar on the starting substrate, a masking layer having at least one opening is formed, wherein the bar is formed in the opening. For example, the masking layer contains an oxide, such as silicon oxide. In a plurality of rods to be produced, a plurality of openings is accordingly provided, wherein the openings and thus the rods to be produced can be arranged, for example, in a regular grid, for example a regular hexagonal grid or a triangular grid.

Further embodiments and expediencies will become apparent from the following description of the embodiments in conjunction with the figures.

• die 1A bis 1D ein Ausführungsbeispiel für ein Verfahren anhand von jeweils in schematischer Schnittansicht dargestellten Zwischenschritten;
• 2A eine perspektivische Darstellung eines Zwischenstadiums gemäß einem Ausführungsbeispiel des Verfahrens;
• 2B eine Rasterelektronenmikroskopieaufnahme von Stäben;
• die 2C und 2D Rasterelektronenmiskroskopieaufnahmen eines Stabs an einem einem Ausgangssubstrat abgewandten Ende (2C) und an einem Übergang zum Ausgangssubstrat (2D);
• 2E eine perspektivische Darstellung eines Zwischenstadiums eines Verfahrens gemäß einem Ausführungsbeispiel mit einer zugehörigen schematischen Darstellung in Schnittansicht;
• die 3A und 3B schematische Darstellungen der relativen Orientierungen einzelner Stäbe und daraus resultierender Einzelbereiche zueinander;
• 4 ein Ausführungsbeispiel für ein Verfahren anhand eines in perspektivischer Darstellung gezeigten Zwischenstadiums und einer zugehörigen schematischen Schnittansicht;
• die 5 und 6 jeweils ein Ausführungsbeispiel für ein Verfahren anhand eines jeweils in perspektivischer Darstellung gezeigten Zwischenstadiums; und
• 7 ein Ausführungsbeispiel für ein Substrat in schematischer Draufsicht.

Show it:

• the 1A to 1D an exemplary embodiment of a method based on intermediate steps respectively shown in a schematic sectional view;
• 2A a perspective view of an intermediate stage according to an embodiment of the method;
• 2 B a scanning electron micrograph of rods;
• the 2C and 2D Scanning electron micrographs of a rod on an end facing away from a starting substrate ( 2C ) and at a transition to the starting substrate ( 2D );
• 2E a perspective view of an intermediate stage of a method according to an embodiment with an associated schematic representation in sectional view;
• the 3A and 3B schematic representations of the relative orientations of individual bars and resulting individual areas to each other;
• 4 an embodiment of a method based on an intermediate stage shown in perspective and an associated schematic sectional view;
• the 5 and 6 in each case an exemplary embodiment of a method on the basis of an intermediate stage respectively shown in perspective; and
• 7 an embodiment of a substrate in a schematic plan view.

The same, similar or equivalent elements are provided in the figures with the same reference numerals.

The figures are each schematic representations and therefore not necessarily scale. Rather, comparatively small elements and in particular layer thicknesses may be exaggerated for clarity.

In the 1A to 1D an embodiment of a method for producing a substrate is shown.

As in 1A is shown, becomes a starting substrate 2 provided for the subsequent epitaxial deposition of nitride compound semiconductor material. An intended for the deposition growth surface 20 is formed by a nitride compound semiconductor material, for example Al _x In _y Ga _1-xy , in particular with y = 0, such as x = 1 (ie AlN) or x = 0 (ie GaN).

A growth layer 22 forms the growth area 20 , The growth layer is epitaxially deposited, for example, on a substrate body 21. For example, the substrate body 21 Sapphire or silicon carbide on. The starting substrate may also be formed as a composite substrate in which the growth layer 22 by means of a bonding layer (not explicitly shown), such as an oxide layer on the substrate body 21 connected is. In this case, the substrate body, for example, also comprise another semiconductor material, such as silicon or germanium, or a metal or consist of such a material.

Furthermore, the starting substrate 2 two are themselves based on a nitride compound semiconductor material, such as GaN or AlN.

On the growth surface 20 is a mask layer 4 arranged. The mask layer 4 has a plurality of openings 40 on. The openings 40 are arranged in a regular grid, for example a regular rectangular or hexagonal grid. For the mask layer, for example, silicon oxide or another material is suitable, on which no or at least no significant growth of semiconductor material takes place.

From the growth area 20 proceeding, the formation of a plurality of rods takes place 3 , where in each opening 40 exactly one rod each 3 is trained ( 1B ). Deviating from the illustration shown, only one rod can be used on the starting substrate 2 be formed. Of course, a larger number of rods can be used.

The separation of the rods is carried out, for example, by means of MOVPE, wherein the deposition conditions are selected such that only growth in the vertical direction takes place. The growth of rods is for GaN micro rods in the article of J. Hartmann et al. in phys. Status Solidi A, Vol. 212, no. 12, 2830 to 2836 (2015 ). The entire disclosure content of this document with respect to the growth of such rods is hereby explicitly incorporated by reference into the present application.

At one of the starting substrate 2 opposite end have the rods 3 one facet each 31 which extends obliquely to a main extension plane of the starting substrate. For example, in the case of GaN, a facet angle is 310 61.9 ° for a (10-11) facet, 43.2 ° for a (10-12) facet, or 32.0 ° for a (10-13) facet. It has been shown that a bulk material can be deposited particularly efficiently from such a facet.

In 1B The bars are perpendicular to the growth surface 20. This is the case when the crystallographic direction <0001> of the starting substrate is aligned exactly perpendicular to the growth surface. Alternatively, an angle between a main extension direction of the rods and a perpendicular to the growth surface 20 for example, between 0.0 ° inclusive and 1.0 ° inclusive, especially between 0.0 ° and 0.3 ° inclusive, such as when using an off-axis substrate as the starting substrate.

From the bars 3 Each case is based on a single area 55 a volume material 5 educated.

In 1C a stage is shown in which the bulk material starting from the rods 3 has already grown together in the lateral direction, so that a coherent volume material 5 results. Between adjacent individual areas 55 is in each case an interface 51, at which the individual areas abut each other, drawn for illustration.

In the vertical direction is the volume material 5 at any point from the starting substrate 2 spaced. Between the volume material 5 and the starting substrate thus arises laterally of the rods 3 a cavity 5 which is free of solid matter. For example, the cavity 5 filled with a gas, say with air.

The bars 3 and the bulk material 5 are each based on a nitride compound semiconductor material, in particular on the same nitride compound semiconductor material. The deposition of the nitride compound semiconductor material is preferably carried out with gallium polarity, so that the gallium atoms in each case on the starting substrate 2 opposite side of the associated nitrogen atoms are.

In the vertical direction is the expansion of the bulk material 5 so large that the bulk material is self-supporting. A mechanical stabilization of the bulk material 5 through the starting substrate 2 is not required. The starting substrate 2 can therefore be removed. The removal can be accomplished, for example, by mechanically or chemically removing the rods 3 respectively.

In 1D is the volume material 5 in the form of a substrate 1 after removal of the starting substrate 2 shown.

The deposition of the bulk material 5 for example by means of HVPE, a high pressure and ammonothermic process or a sodium flow process.

An HVPE method is for example in the article of H. Morkoc in Materials Science and Engineering R 33, 135-207 (2001) whose entire disclosure content is hereby explicitly incorporated by reference into the present application.

A high pressure and ammonothermic process is for example in the article of S. Porowski in Journal of Crystal Growth, Vol. 166, 583-589 (1996) whose entire disclosure content is hereby explicitly incorporated by reference into the present application.

For example, a sodium flow method is described in the article of M. Aoki et al. in Journal of Crystal Growth, Vol. 242, 70-76 (2002) whose entire disclosure content is hereby explicitly incorporated by reference into the present application.

A staff 3 preferably each has an aspect ratio of between 3 and 1000 inclusive, in particular between 50 and 200 inclusive. It has been shown that the use of rods with a high aspect ratio, a particularly high crystal quality can be achieved. This is based on the 3A and 3B illustrated. So can neighboring bars 3 have on their side facing the starting substrate relative to each other a rotation, as the left part of 3A shows. When growing together of the individual sectors emanating from these bars 55 of the bulk material could cause crystal defects. However, this torsion may occur with rods having a sufficiently high aspect ratio on the starting substrate 2 opposite end of the bars 3 be corrected, as the right part of 3A shows.

In the right part of the 3B is a misoriented staff with a dashed line 3 shown an orientation angle 35 compared to neighboring bars 3 would, if this angle would not be corrected.

In the left part of the 3B is a height L of the bars, a diameter D of the bars, a pitch P of the bars and a distance R = P / 2 between the bars and an interface 51 between adjacent individual areas 55 of the bulk material 5 shown.

For a correctable orientation angle θ provided with reference numerals 35 , the proportionality relation θ ~ (F * R * L) / r ⁴ = (F * P * AR) / r ³ , where r = D / 2 and AR are the aspect ratio. The correctable orientation angle is therefore in particular proportional to the aspect ratio of the rods. By means of a high aspect ratio, therefore, the correctability of misorientations at the level of the volume material to be produced is simplified and the risk of newly arising crystal defects at the interfaces 51 between adjacent individual areas 55 reduced. During the production of the substrate, therefore, mis-oriented rods can be used 3 undergo a rotation, so that the end remote from the starting substrate of a rod is rotated relative to the starting substrate facing the end.

The diameter D of the bars 3 is, for example, between 0.5 μm inclusive and 2 μm inclusive. The height L of the bars is for example between 2 μm and 1 mm inclusive, in particular between 20 μm and 1 mm inclusive.

As 2 B shows, the bars can be grown with a high aspect ratio, for example in a hexagonal grid, wherein the bars have a hexagonal basic shape. Out 2C It can be seen that no defects in the form of dislocations occur at the end of the rods facing away from the starting substrate. Only on the side facing the starting substrate are individual defects present, such as 2D shows. In 2D Furthermore, an opening in the dark-appearing mask layer can be seen, from which the growth proceeds. However, the defects resulting in particular from the starting substrate bend in lateral directions within the rods, so that the rods are free of defects with a sufficient distance from the starting substrate.

In 2E is the process stage where the bulk material 5 starting from the bars 3 already grown together, shown in perspective view. At the in 2E As shown, adjacent bars are at a comparatively small distance from each other arranged. However, the distance between adjacent bars can also be increased.

This is in the 5 and 6 illustrated. According to 5 are the bars 3 at a pitch of, for example, 100 μm or more. In particular, a center distance can be so large that one from a rod 3 single region is so great that a later to be made of the bulk material semiconductor device comprises only semiconductor material which is deposited on a single area. In other words, no boundary surface of adjacent individual regions runs through the semiconductor component thus produced. The semiconductor device is characterized by a particularly high crystal quality.

In 7 is a substrate 1 shown in plan view, with the individual areas 55 each have a hexagonal basic shape. The greater the distance between adjacent bars 3, the greater the lateral extent of the resulting individual areas 55 , For example, a center distance is between 1 μm and 5 mm inclusive. Typically, the larger the pitch, the larger the aspect ratio. In particular, the individual regions can be so large that a semiconductor component to be produced or even a plurality of semiconductor components to be produced, for example in a matrix-like arrangement, is formed by means of a single region.

The achievable defect density in defects per cm ² depends in particular on the center distance of the bars and the number of defects per single area. The larger the center distance, the lower the achievable defect density.

For example, a defect density with a defect number between a defect and ten defects per single region for a center distance of 1 μm is approximately between 1.2 * 10 ⁸ / cm ² and 1.2 * 10 ⁹ / cm ² , for a center distance of 10 μm approximately between 1.2 * 10 ⁶ / cm ² and 1.2 * 10 ⁷ / cm ² , for a center distance of 100 μm approximately between 1.2 * 10 ⁴ / cm ² and 1.2 * 10 ⁵ / cm ² , for a center distance of 1 mm approximately between 1.2 * 10 ² / cm ² and 1.2 * 10 ³ / cm ² and for a center distance of 10 mm approximately between 1.2 / cm ² and 12 / cm ² .

Compared to conventional methods, extremely low defect densities can be achieved.

In extreme cases, only a single rod 3 be provided as in 6 is shown. The entire volume material 5 So grows from just one rod. The volume mateiral thus has no interfaces between adjacent individual areas.

In 4 another embodiment of a method for producing a substrate is shown. This embodiment corresponds essentially to that in connection with 1A to 1D described embodiment.

In contrast, this is on side surfaces 32 of the bars 3 a cover layer 6 applied before the bulk material 5 is trained. By means of the cover layer 6 Simplified ensures that on the vertical side surfaces 32 no or at least only greatly reduced growth takes place in the lateral direction. The cover layer 6 may in particular also be designed so that the vertically extending side surfaces 32 are completely covered and only the facets 31 exposed. Deviating from this, one can also turn to the facets 31 adjacent part of the vertical side surfaces 32 free from the cover layer 6 be.

With the described method, a bulk material based on nitride compound semiconductor material can be produced efficiently and with a particularly high crystal quality. In particular, the formation of the volume material takes place starting from the defect-free or at least largely defect-free material of the at least one rod 3 ,

The invention is not limited by the description with reference to the embodiments. Rather, the invention encompasses any novel feature as well as any combination of features, which in particular includes any combination of features in the patent claims, even if this feature or combination itself is not explicitly stated in the patent claims or the exemplary embodiments.

LIST OF REFERENCE NUMBERS

1

substratum

2

starting substrate

20

growth surface

21

substrate body

22

growth layer

3

Rod

31

facet

310

facet angle

32

side surface

35

orientation angle

4

mask layer

40

opening

5

bulk material

51

interface

55

Single area

6

covering

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• J. Hartmann et al. in phys. Status Solidi A, Vol. 212, no. 12, 2830-2836 (2015) [0040]
• H. Morkoc in Materials Science and Engineering R 33, 135-207 (2001) [0050]
• S. Porowski in Journal of Crystal Growth, Vol. 166, 583-589 (1996) [0051]
• M. Aoki et al. in Journal of Crystal Growth, Vol. 242, 70-76 (2002) [0052]

Claims (15)

Process for producing a substrate (1) based on nitride compound semiconductor material, comprising the steps: a) providing a starting substrate (2); b) forming at least one rod (3) based on nidride compound semiconductor material on the starting substrate; c) forming a bulk material (5) based on nitride compound semiconductor material from the rod; and d) separating the starting substrate from the bulk material. Method according to Claim 1 in which the bar has an aspect ratio of between 3 and 1000 inclusive. Method according to Claim 1 in which the bar has an aspect ratio of between 50 and 200 inclusive. Method according to one of the preceding claims, wherein the at least one rod has a diameter of between 0.5 microns inclusive and including 2 microns. Method according to one of the preceding claims, in which the at least one rod has a height of between 2 μm and 1 mm inclusive. Method according to one of the preceding claims, in which the at least one bar has a height of between 20 μm and 1 mm inclusive. Method according to one of the preceding claims, in which the rod has, at an end remote from the starting substrate, a facet (31) which runs obliquely to a main extension plane of the starting substrate. Method according to Claim 7 in which the bulk material is formed exclusively from the facet. Method according to one of the preceding claims, in which in step b) a plurality of bars is formed, in step c) the bulk material is formed from the bars, and collides the volume material formed from adjacent bars. Method according to Claim 9 , wherein after step c) at least one rod is twisted in itself. Method according to Claim 9 or 10 in which the bars are arranged at a center distance of at least 1 μm from one another. Method according to one of Claims 9 to 11 in which the bars are arranged at a center distance of at least 100 μm from one another. Method according to one of the preceding claims, wherein the at least one bar is formed with Ga polarity. Method according to one of the preceding claims, wherein before step c) a side surface (32) of the rod is provided in places with a covering layer (6). Method according to one of the preceding claims, wherein prior to step b) on the starting substrate, a masking layer (4) with at least one opening (40) is formed and the rod is formed in the opening.

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