JPH10326912A - Production of non-dislocated gan substrate and gan base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-dislocation GaN substrate manufacturing method, capable of attaining the growth of a GaN semiconductor material of a thick film and excluding dislocation defects. SOLUTION: The surface of a base substrate 1 is partially covered with a 1st mask layer 2, consisting of a material substantially not to grow as crystal from its own surface and then a 1st GaN layer 3 is allowed to grow up to cover the surface of the layer 2 from the non-masked part 11 on the surface of the substrate 1 as a start point to obtain a GaN base material M. The surface of the GaN base material is regarded as the surface of the base substrate 1 in the process mentioned above, a 2nd mask layer 21 is similarly formed, and a 2nd GaN layer 31 is allowed to grow. The layer 21 is formed so as to cover the non-masked part 11. Consequently the 2nd GaN layer 31 can be formed as a non-dislocated semiconductor layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a dislocation-free GaN substrate and a GaN substrate suitable for producing, for example, a GaN-based light-emitting device.

[0002]

2. Description of the Related Art As a general means for growing a thick film of a GaN semiconductor material, there is a method of forming a buffer layer of ZnO or the like on a sapphire substrate and growing the GaN semiconductor material thereon by HVPE. In addition, as an improved technology, spinel, LGO, LAO, Zn
There are a method of using a substrate of O, SiC, or the like, a method of using an easily cleavable substrate, a method of providing a mask on the surface of the substrate, and performing selective growth thereon.

[0003]

SUMMARY OF THE INVENTION However, GaN
When a semiconductor material is grown in a thick film, a large stress is applied to an interface due to a difference in lattice constant and a thermal expansion coefficient between GaN and a sapphire substrate, and GaN is broken, and a large substrate cannot be obtained. Further, there is a problem that only a substrate having an extremely large dislocation density (1 × 10 ⁹ cm ⁻² to 1 × 10 ¹⁰ cm ⁻² ) can be obtained. Here, dislocations are defects that occur when a semiconductor layer is grown on a substrate in a state where lattice constants do not match (lattice mismatch), and these dislocations are crystal defects. When the GaN semiconductor material is used for a light-emitting element, it functions as a non-radiative recombination center or functions as a current path and causes a leakage current.

Accordingly, the present invention provides a method for growing a GaN semiconductor material having a large thickness, and having no dislocation-free G that does not include dislocation defects.
An object of the present invention is to provide a method of manufacturing an aN substrate and a GaN substrate.

[0005]

According to the method of manufacturing a dislocation-free GaN substrate of the present invention, a surface of a base substrate is partially covered with a mask layer made of a material that cannot substantially grow crystals from its own surface. Covering, and then growing a GaN layer to cover the mask layer from the non-mask portion of the base substrate surface as a starting point to obtain a GaN base material, and forming the GaN base material surface in the first step. The method is characterized by comprising a second step of similarly forming a mask layer and growing a GaN layer assuming the surface of the base substrate.

Further, the GaN substrate of the present invention comprises a base substrate, a first mask layer partially covering the surface of the base substrate, and a first mask layer grown on the base substrate and directly in contact with a non-mask portion on the surface of the base substrate. A GaN base material portion comprising a first GaN layer having a portion to be covered and covering the mask layer;
A second mask layer partially covering the surface of the N base material; and a second mask layer grown on the second mask layer and having a portion directly in contact with the non-mask portion of the GaN base material surface and covering the second mask layer. GaN
And a dislocation-free GaN portion comprising a layer.

[0007]

In this specification, the lattice plane of a hexagonal lattice crystal such as a GaN-based crystal or a sapphire substrate has four Miller indices (hk
il), for convenience of description,
When an exponent is negative, the exponent is preceded by a minus sign, and the notation method for the negative exponent is the same as that of the general Miller index. Therefore, in the case of a GaN-based crystal, there are six prism surfaces (singular surfaces) parallel to the C-axis. For example, one of the surfaces is (1)
−100), and {1-100} when the six surfaces are grouped as equivalent surfaces. In addition, the above-mentioned Δ1-1
The planes perpendicular to the 00 plane and parallel to the C-axis are equivalently collectively denoted as {11-20}. The direction perpendicular to the (1-100) plane is [1-100], the set of equivalent directions is <1-100>, and the direction perpendicular to the (11-20) plane is [11-20]. The set of equivalent directions is <11
−20>. However, if there is a case where the Miller index is written in the drawing, if the index is negative, the index is indicated by adding a minus sign to the index, and all of the general Miller index notations are followed. The crystal orientations referred to in the present invention are all
The orientation is based on a GaN crystal grown on the base substrate with the C axis as the thickness direction.

[0008] The term "dislocation-free" as used herein means not only an ideal state in which dislocations do not exist at all (state theoretically present), but also a GaN-based layer on a sapphire substrate via a buffer layer. This means a state in which the dislocation density is sufficiently low so that the influence of the dislocation can be neglected industrially as compared with a normal dislocation density when a crystal is grown.

[0009] The inventors of the present invention have previously made GaN and sapphire substrates different in lattice constant and thermal expansion coefficient.
As a countermeasure against layer cracks, as shown in FIG. 5, a mask layer 2 patterned in a grid pattern is applied on a base substrate 1,
It has been proposed to grow a chip-sized GaN layer 30 intermittently on an exposed portion of the substrate (Japanese Patent Laid-Open No. 7-273667).
No.).

As a result of further studies conducted by the present inventors, when the GaN layer 30 which has been scattered is further grown, the GaN layer 30 is masked not only in the thickness direction as shown in FIG. It was confirmed that the growth was also performed in the lateral direction on the layer 2. In addition, it has been found that there is a crystal orientation dependency depending on the growth conditions.

Further, the dislocations existing in the above-mentioned crystal are:
It has the property of being inherited from a base including a substrate or being generated at any growth interface and growing together with crystal growth. When a GaN crystal is grown from the non-mask portion as a starting point to cover the mask layer, the thickness required to cover the mask layer and the location where the low dislocation region is formed are determined in the direction of the mask layer (the mask layer and the non-mask portion). Direction of the boundary line between the GaN crystal and the GaN crystal). Further, when the above-described lateral growth is further advanced, as shown in FIG. 2, the mask layer 2 is completely buried, and a flat, crack-free, large and thick GaN layer 3 with very few defects can be obtained. Was found. It is considered that the reason why cracks are not generated is that stress is reduced because the interface between the mask layer 2 and the GaN layer 3 is separated.

However, as shown in FIG. 2, in this state, although low dislocation regions are formed on the mask layer 2, dislocations are not reduced in other regions. Therefore, as shown in FIG. 3, the present invention uses such a laminate as a base material M, and forms a mask layer 21 thereon in the same manner to prevent dislocation lines from being stretched. By growing 22, a GaN substrate closer to a dislocation-free state is obtained.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are sectional views showing an example of a process of a method for manufacturing a dislocation-free GaN substrate according to the present invention. FIG. 4 schematically shows an example in which the dislocation propagates upward from the non-mask portion in a manner of propagating to the upper layer side. 1 and 2, 1 is a base substrate, 2 is a mask layer (first mask layer) that partially covers the surface of the base substrate 1, and 3 is a portion that directly contacts the non-mask portion 11 of the base substrate 1. A GaN layer (first GaN layer) having a mask and covering the mask layer 2
It is. The first GaN layer 3 is formed by further growing the dotted GaN layer 30 shown in FIG.

Then, using the laminate obtained above as a GaN base material M, a next-stage GaN layer is formed. That is, G
A similar process is performed by regarding the surface of the aN base material M as a base substrate in the previous process, that is, a second mask layer 21 that partially covers the surface is provided on the surface of the first GaN layer 3, and a second mask layer 21 is formed thereon. The second GaN layer 31 is grown.

The base substrate 1 used in the present invention is not particularly limited. For example, sapphire, quartz, SiC, etc., which have been conventionally used for growing a GaN layer, can be used. Above all, sapphire C side, A side, 6
An H-SiC substrate, particularly a C-plane sapphire substrate, is preferred.
In addition, ZnO, MgO or AlN for reducing the difference in lattice constant and thermal expansion coefficient from the GaN layer is formed on the surface of these materials.
And the like may be provided with a buffer layer.

In particular, selecting a GaN crystal having a lattice constant as close as possible to a GaN crystal to be grown later and having a thermal expansion coefficient as close as possible makes reduction of defects such as dislocations and generation of cracks more difficult. Desirable in point. Further, it is preferable to have excellent resistance to high heat and etching when forming a thin film of the mask layer 2 described later. As such a base substrate 1, at least the surface layer (the surface layer on the side on which the GaN layer 3 is grown) is made of In _x G
a _Y Al _Z N (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1,
X + Y + Z = 1). Specifically, on a relatively thick sapphire substrate, a buffer layer such as ZnO or AlN, and a GaN or G
The one in which a thin layer of aAlN is sequentially formed can be suitably used.

The first and second mask layers 2 and 21 are formed on the surface of the base substrate 1 where the first GaN layer 3 can be grown and on the surface of the first GaN layer 3 where the second GaN layer 30 is grown. Since the layer is intended to substantially limit the possible area, as a material constituting the mask layer,
It is necessary that crystals cannot grow substantially from its own surface. As such a material, for example, an amorphous body is exemplified, and further, as this amorphous body, Si,
Nitrides or oxides of Ti, Ta, Zr, etc., ie, Si
O ₂ , SiN _x , SiO _1-x N _x , TiO ₂ , ZrO ₂
Etc. are exemplified. In particular, SiO ₂ and Si which are excellent in heat resistance and relatively easy to form and remove by etching.
N _x and SiO _1-x N _x are suitable, and a multilayer structure of these materials may be used.

The mask layers 2 and 21 are, for example, MOVP
E, after being formed so as to cover the entire surface of the substrate by a method such as sputtering or CVD, the photosensitive resist is patterned by a normal photolithography technique, and is formed by means such as exposing a part of the substrate by etching. You.

The pattern for forming the mask layers 2 and 21 is not particularly limited, and may be a lattice shape, a stripe shape, a dot shape, or the like. The lattice shape is preferable because the surface area of the base substrate 1 can be effectively used. When lattice masking is employed, the shape of the exposed pattern of the base substrate 1 may be square, other polygonal, or circular. However, since the crystal growth rate in the lateral direction is higher in the <11-20> direction of the GaN layer than in the <1-100> direction of the GaN layer, as shown in FIG. > A and the lattice width B of the GaN layer in the <1-100> direction.
Is preferably in a relationship of 0 ≦ A ≦ B, and it is desirable to make the best use of the feature of good crystallinity on the mask.
The width of the grating is preferably about 1 μm to 2 mm, and the exposed pattern is preferably about 1 μm to 2 mm square in the case of a square.

In the present invention, a first GaN layer 3 is formed on a base substrate 1 partially covered with a mask layer 2 by crystal growth. In this case, the GaN crystal starts growing only from the non-mask portion of the base substrate 1. That is, the direct contact portion between the GaN layer 3 and the base substrate 1 is only the non-mask portion. As we continue to grow,
The non-mask portion cavity of the mask layer 2 is completely filled and swells on the mask layer 2 soon. In addition, when the growth is performed, Ga
The N crystal starts growing not only in the thickness direction but also in the lateral direction starting from the side surface of the bulging portion, and eventually merges with the growing crystal starting from the other non-mask portion, and finally the mask layer 2. The first GaN layer 3 is formed while completely covering the top and continuing to grow in the thickness direction.

The thickness and low dislocation region required for the GaN layer to grow from the non-mask portion as a starting point for crystal growth and to cover the mask layer are determined in the direction of the mask layer (the mask layer and the non-mask portion). (The direction of the boundary line between the two) changes depending on the gas atmosphere when the GaN crystal is grown. When the longitudinal direction of the mask layer is set to the <11-20> direction, the growth rate in the C-axis direction is higher than the growth rate in the lateral direction.
Oblique facets such as the 101 ° plane are easily formed. Therefore, the pyramid shape is first formed and then flattened. For this reason, a certain thickness is required for flat embedding. On the other hand, when the longitudinal direction of the mask layer is set to the <1-100> direction, the growth rate in the lateral direction is increased, and therefore, {1-1}.
It is difficult to form oblique facets such as the 01 ° plane. As a result, flat embedding can be made thinner than <11-20>.

The growth atmosphere gas for growing the GaN layer so as to cover the mask layer from the non-mask portion as a starting point is as follows:
Examples thereof include hydrogen, nitrogen, argon, and helium, and hydrogen and nitrogen are preferable for controlling the shape and the like. Since the speed ratio of hydrogen and nitrogen changes in the C-axis direction and in the lateral direction, if they are used properly according to the purpose, the range of element design can be widened. Substrate
Dislocation lines propagating upward from the growth layer interface (threading dislocations)
Is formed on the opening of the mask layer by {1-10}.
When an oblique facet such as a 1｝ plane appears, the plane is bent at this plane, and dislocations are formed on the mask layer.
Above the non-mask portion (opening) is a low dislocation region. On the other hand, when the lateral growth rate is high and an oblique facet such as the {1-101} plane is difficult to form, the dislocation line propagates in the C-axis direction. In this case, a region above the mask layer is a low dislocation region. As described above, by changing the growth conditions, the thickness and the position of the low dislocation region required for embedding the mask layer can be controlled, so that the degree of freedom in device design increases. In addition, the direct contact portion between the GaN layer and the base substrate is only the non-mask portion and the contact area is small, and the GaN layer and the base substrate are not significantly affected by the difference in the thermal expansion coefficient between the two, so that a thick GaN layer can be easily grown. There is also an advantage.

However, as described above, since defects such as dislocations may be inherited from the non-mask portion 11 into the first GaN layer 3, the first GaN layer 3 is completely dislocation-free. Not a crystal. Therefore, a second mask layer 21 is provided on the first GaN layer 3 to stop dislocation lines (remaining dislocation lines) propagating in the first GaN layer 3 by the second mask layer 21. The GaN crystal closer to a dislocation-free crystal is obtained by growing the second GaN layer 31 thereon while keeping the dislocation lines from being stretched. Therefore, as the steps of forming a mask layer and a GaN layer on the second GaN layer 31 in the same manner are further repeated, a GaN crystal closer to a completely dislocation-free crystal can be obtained.

When dislocation lines propagate linearly in the first GaN layer 3 above the non-mask portion, the second mask layer 21 is used as the non-mask portion 11 in the first step. If it is formed on the surface portion of the GaN base material M so as to cover the portion directly above the portion that has been set, the residual dislocation lines can be effectively cut off. There is an advantage that a high-quality GaN crystal can be obtained without repeating the operation.

The material for forming the GaN layers 3 and 31 is G
aN well, can be used GaN-based semiconductor material, such as those of the formula _{In X Ga Y Al Z N (} 0 ≦ X ≦ 1,0 ≦ Y ≦ 1,
A material represented by 0 ≦ Z ≦ 1, X + Y + Z = 1) can be used. There is no limitation on the method of growing the GaN layer 3, and an HVPE method, a MOCVD method, an MBE method, or the like is preferable. The HVPE method is preferable for forming a thick film by growing at a high speed in the C-axis direction.
The VD method is preferred.

A dislocation-free GaN substrate obtained by the present invention,
That is, a light emitting element such as an LED or an LD is manufactured by forming a light emitting portion or the like including a clad layer and an active layer and an electrode on the second GaN layer 31 grown thickly as a substrate. Can be.

[0027]

【Example】

(Example 1) On a C-plane sapphire substrate having a diameter of 2 inches and a thickness of 330 μm, using a MOVPE apparatus, a thickness of 20 n was used.
m AlN buffer layer was grown at low temperature followed by 1.5 μm
A m-GaN thin layer was grown and used as a base substrate. A SiO ₂ thin film was formed as a mask material on the surface of the base substrate by a sputtering method, and was further etched to form a mask layer having a lattice pattern with a line width of 100 μm and a pitch of 200 μm. That is, a 100 μm square exposed portion is arranged at 100 μm intervals. This is loaded into the HVPE apparatus as a new substrate, and the first n of 300 μm is set.
A type GaN layer was grown. The mask layer is completely buried, the surface flatness is good, and n-type Ga
An N base material was obtained.

On the surface of the n-type GaN base material, a SiO ₂ thin film is formed as a mask material by sputtering using the same machine, and the mask material is left in a lattice pattern having a line width of 100 μm and a pitch of 200 μm to form a second mask layer. Formed. Note that this mask patterning covers the area immediately above the non-mask portion in the previous step. Then, this is loaded into an HVPE apparatus, and a second n-type G
An aN layer was grown. As a result of evaluating the second n-type GaN layer of the obtained n-type GaN base material by TEM, the dislocation density was 1 ×
It was 10 ² cm ^-2 or less.

Example 2 A 500-nm-thick SiO ₂ film was used as a mask material on the surface of the base substrate fabricated in Example 1.
A thin film was formed by a sputtering method, and the mask material was left as a mask layer in a striped pattern in which linear patterns having a line width of 200 μm were arranged at a pitch of 400 μm. That is, 2
The exposed portions of a straight line having a width of 00 μm are arranged at intervals of 200 μm. The direction of the stripe is <1-10 of the GaN layer.
0> direction. This was loaded into an HVPE apparatus as a new substrate, and a 300 μm n-type GaN layer was grown. The mask material was completely embedded, no cracks were observed, and a 2-inch diameter n-type GaN base material having good surface flatness was obtained.

An SiO ₂ thin film was similarly formed as a mask material on the surface of the n-type GaN base material by a sputtering method, and a second mask layer was formed while leaving the mask material in the same pattern. Note that this mask patterning covers the area immediately above the non-mask portion in the previous step. Then, this was loaded into an HVPE apparatus, and a second n-type GaN layer having a thickness of 300 μm was grown to obtain a GaN base material.

Example 3 Si having a crystal structure of 6H type
On a C substrate (0001), a mask material having a thickness of 150
A SiO ₂ thin film having a thickness of 10 nm was formed by a thermal CVD method, and the mask material was left as a mask layer in a dot pattern in which circular exposed portions having a diameter of 10 μm were arranged at a pitch of 100 μm. That is, 1
The circular exposed portions are arranged on the grid points at intervals of 00 μm. This was loaded into an HVPE apparatus as a new substrate, and a 300 μm n-type GaN layer was grown. The mask material is completely embedded, no cracks are seen,
A 2-inch diameter n-type GaN base material having good surface flatness was obtained.

On the surface of the n-type GaN base material, an SiO ₂ thin film was similarly formed as a mask material by a sputtering method, and a second mask layer was formed while leaving the mask material in the same pattern. Note that this mask patterning covers the area immediately above the non-mask portion in the previous step. Then, this was loaded into an HVPE apparatus, and a second n-type GaN layer of 350 μm was grown to obtain a GaN base material.

Example 4 Specification of Mask Layer and GaN
A first n-type GaN layer was grown in the same manner as in Example 1 except that the method of forming the layer was as follows. The mask layer is
The material was SiO ₂ , and the formed pattern was a stripe shape. The stripe has a longitudinal direction of <1-10 of the GaN layer.
0> direction, and the width of the strip-shaped mask layer and the width of the non-mask portion (gap between the mask layers) were both 4 μm. The GaN layer was grown by MOCVD, and the atmosphere gas was hydrogen.

Using the non-mask portion as a starting point for crystal growth, GaN was grown until the upper surface became flat covering the mask layer. When the upper surface became flat, the thickness of the GaN layer was 3 μm. Was. At this time, the low dislocation region was located above the mask layer. In addition, the flatness of the surface of the GaN layer was good, and a GaN substrate having a diameter of 2 inches was obtained.

The obtained GaN base material is used as a new substrate, and its surface is formed on the surface of the GaN layer in the form of a stripe having a longitudinal direction in the <1-100> direction and on the lower non-mask portion. A second mask layer was formed such that the mask layer was located.

Using the non-mask portion as a starting point for crystal growth, the second GaN layer is covered with the second mask layer until the upper surface becomes flat.
When the layer is grown, G at the point where the upper surface becomes flat
The thickness of the aN layer was 3 μm. Dislocation lines propagating from the first substrate are blocked by the second mask layer,
As a result, the growth of the GaN layer having a total thickness of 6 μm yielded a GaN substrate having low dislocations on the entire surface.

[0037]

As described above, the dislocation-free Ga of the present invention is used.
According to the method of manufacturing the N substrate and the GaN substrate,
N semiconductor material can be grown, and dislocation defects are substantially eliminated.
It is possible to create a dislocation-free GaN substrate that is not included in the GaN substrate. Therefore, when the GaN substrate obtained by the present invention is used as a constituent material of a light-emitting element, since there is no dislocation, there is no problem of generation of a non-radiative recombination center or generation of a leakage current, An excellent effect is obtained in that the life characteristics are not reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a state in which a GaN substrate according to the present invention is growing.

FIG. 2 is a cross-sectional view showing a state in which a GaN substrate according to the present invention is being grown in the next stage.

FIG. 3 is a sectional view showing a GaN substrate according to the present invention.

FIG. 4 is a top view showing an example of a mask layer pattern according to the present invention.

FIG. 5 is a sectional view showing a conventional GaN substrate.

[Explanation of symbols]

 Reference Signs List 1 base substrate 11 non-mask portion 2 first mask layer 21 second mask layer 3 first GaN layer 31 second GaN layer M GaN base material

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoichiro Ouchi 4-3 Ikejiri, Itami-shi, Hyogo Mitsubishi Electric Cable Industry Co., Ltd. Itami Works

Claims (6)

[Claims] 1. A method according to claim 1, wherein the surface of the base substrate is partially covered with a mask layer made of a material that cannot substantially grow crystals from the surface of the base substrate. A first step of growing a GaN layer to cover the layer to obtain a GaN preform; and treating the GaN preform surface as a base substrate surface in the first step, similarly forming a mask layer and forming a GaN layer. A method for producing a dislocation-free GaN substrate, comprising a second step of growing. 2. The method of manufacturing a dislocation-free GaN substrate according to claim 1, wherein the same step is repeated a required number of times after the completion of the second step. 3. The method according to claim 1, wherein the mask layer formed in the second step is formed on a surface portion of the GaN base material corresponding to the non-masked portion in the first step. 2. The method for producing a dislocation-free GaN substrate according to 1. 4. The method according to claim 1, wherein the GaN layer is grown by HVPE or MOC.
The method for producing a dislocation-free GaN substrate according to claim 1, wherein the method is performed by one of a VD method and an MBE method. 5. A mask substrate having a base substrate, a first mask layer partially covering the surface of the base substrate, a portion grown thereon and in direct contact with a non-mask portion of the base substrate surface, and A GaN base material portion including a first GaN layer covering the top, a second mask layer partially covering a surface of the GaN base material,
A dislocation-free GaN portion comprising a second GaN layer grown thereon and having a portion directly in contact with the non-mask portion of the GaN base material surface and covering the second mask layer. GaN base material. 6. The GaN substrate according to claim 5, wherein the dislocation-free GaN portion is formed in a plurality of layers.