JP2002009003A - Semiconductor substrate, manufacturing method thereof, and light emitting element - Google Patents

Abstract

(57) Abstract: Provided is a high-quality, large-area, group III nitride semiconductor substrate having few crystal defects, a method for manufacturing the same, and a light-emitting element. A method of manufacturing a semiconductor substrate, comprising: forming an intermediate layer on an epitaxial growth substrate, forming a group III nitride epitaxial layer on the intermediate layer, and manufacturing a semiconductor substrate. After forming the group III nitride epitaxial layer 104, heat treatment is performed at a temperature equal to or higher than the thermal decomposition temperature of the intermediate layer 103.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate used for a semiconductor laser for optical communication and a light source for an optical disk, a method for manufacturing the same, and a light emitting device.

[0002]

2. Description of the Related Art Conventionally, a blue LED is a red or green LED.
Although the brightness was lower than that of the ED, there was a problem in practical use. However, in recent years, in a GaN-based compound semiconductor represented by the general formula InAlGaN, the crystal growth technology has been improved by using a low-temperature AlN buffer layer or a low-temperature GaN buffer layer. And a low-resistance p-type semiconductor layer doped with Mg were obtained, so that a high-brightness blue LED was put to practical use, and a semiconductor laser that did not reach practical use but continually oscillated at room temperature was realized. .

In general, when a high-quality semiconductor layer is epitaxially grown on a substrate, it is necessary that the substrate and the semiconductor layer have substantially the same lattice constant and thermal expansion coefficient. However, with respect to GaN-based semiconductors, there is no substrate in the world that satisfies these simultaneously.

[0004] At present, attempts have been made to produce bulk GaN single crystals, but only a few millimeters have been obtained, and they are still far from practical use.

[0005] Therefore, in the case of a GaN-based device, a crystal element is generally grown using a heterogeneous substrate having a lattice constant and a thermal expansion coefficient that are significantly different from those of a GaN-based semiconductor such as sapphire, MgAl ₂ O ₄ spinel, or SiC, thereby producing a laser device. are doing.

However, when a heterogeneous substrate is used, there are problems such as crystal defects, formation of an end face of an optical resonator, formation of an electrode, and heat dissipation, and a practical laser device has not yet been manufactured.

Hereinafter, these problems will be briefly described. Regarding crystal defects, when crystal growth is performed using a heterogeneous substrate having a lattice constant and a thermal expansion coefficient that are significantly different from those of GaN-based semiconductors such as sapphire, MgAl ₂ O ₄ spinel, and SiC, dislocations introduced by lattice mismatch Density of 10 ⁸ or more
It is very large at 10 ¹⁰ cm ^-2 and GaN
It is difficult to grow a crystal having a quality necessary for producing a practical semiconductor laser, such as generation of distortion and cracks due to a difference from a thermal expansion coefficient of the system semiconductor.

Further, regarding the formation of the optical resonator end face, since the cleavage planes of the heterosubstrate and the GaN-based compound semiconductor do not always coincide with each other, they are parallel and cleaved by a cleavage method like a conventional AlGaAs-based laser. It has been difficult to form a smooth optical resonator end face.

Therefore, in the case of the GaN system, the end face of the optical resonator is manufactured by a method such as cracking a GaN-based crystal by dry-etching or thinly polishing a substrate such as sapphire and cleaving the substrate.

Here, the method using dry etching is complicated because the manufacturing process requires steps such as formation of a dry etching mask, dry etching, and mask removal. Furthermore, since the dry etching technology of the GaN-based compound semiconductor has not been established yet, the formed resonator mirror has unevenness such as vertical streaks and is formed in a tapered shape.
Parallelism and perpendicularity were not yet enough. In addition, when the resonator mirror was formed by dry etching, the substrate remained as a terrace in front of the end face of the resonator mirror, so that light was reflected by the terrace, and the beam shape did not become a single peak.

Further, a substrate such as sapphire is polished thinly,
In the method of forming the optical resonator facet by cleaving the substrate to break the GaN-based crystal, the optical resonator facet has large irregularities due to a shift in the cleavage face between the GaN-based crystal and the substrate. Therefore, the threshold current of the laser was increased.

Further, regarding the formation of the electrodes, since the sapphire substrate generally used is insulative, the electrodes cannot be taken from the back surface of the substrate. Therefore, the electrodes are formed on the element surface, and the conventional AlGaAs
There is a problem that mounting such as forming an electrode on the back surface of a substrate and die bonding cannot be performed like a laser of an s type or the like, and further, a chip area is increased by a space of the electrode. In addition, since dry etching for exposing the n-type layer is required for forming the n-side electrode,
The manufacturing process of the laser element has been complicated.

As for heat dissipation, the life is extremely short in high-temperature operation or high-power operation due to the poor thermal conductivity of a sapphire substrate generally used.

In order to solve the above problems, a technique for manufacturing a GaN substrate with a high quality GaN thick film having a low defect density has been developed.

For example, JP-A-10-326912, JP-A-10-326751, and JP-A-10-3
JP-A-12971 and JP-A-11-4048 disclose:
A technique has been disclosed in which GaN is selectively grown on a heterogeneous substrate using a mask and crystal growth is continued to embed the mask to form a flat GaN thick film over the entire surface of the substrate.

FIG. 6 is a view for explaining a method of manufacturing a GaN thick film substrate disclosed in Japanese Patent Application Laid-Open No. 10-312971.

Referring to FIG. 6, first, a III-V compound semiconductor film 12 such as GaN is laminated on a heterogeneous substrate 11 such as sapphire, and a mask 14 having a width of several μm made of SiO ₂ or the like is formed thereon. Then, a growth region 13 for selectively growing a III-V compound semiconductor such as GaN is formed.
(A)).

Next, a III-
A facet structure 15 is manufactured by selectively growing a group V compound semiconductor (FIG. 6B).

When the growth of the group III-V compound semiconductor is further continued, the facet 15 grows laterally and the mask 14
Cover the top (FIG. 6 (c)).

As the growth continues, the adjacent III-V
The group III compound semiconductors 15 are united and the grooves are filled (FIG. 6).
(D)).

As the growth is further continued, the surface of the group III-V compound semiconductor 15 is flattened, and
A group V compound semiconductor thick film is formed (FIG. 6E).

According to the techniques disclosed in each of the above publications, the density of threading dislocations generated at the substrate interface is high in the crystal layer of the portion selectively grown on the heterogeneous substrate, but the crystal layer extends laterally over the mask. In the laterally grown portion, the density of threading dislocations has been drastically reduced, resulting in a high-quality crystal. Furthermore, by repeating selective growth and lateral growth on this, over the entire surface of the wafer,
A high-quality GaN thick film with few dislocations can be formed. Further, according to this technology, a thick G of 100 μm or more is used.
Even if aN is grown, cracks due to a difference in thermal expansion coefficient do not occur, so that a GaN thick film having a thickness usable as a substrate can be grown even if a heterogeneous substrate is removed.

In the techniques disclosed in the above publications, finally, the GaN substrate is formed by removing the dissimilar substrate and the mask in order to solve the problems of the optical resonator end face, electrode formation, and heat dissipation. Removal of the dissimilar substrate and the mask material depends on a method utilizing polishing or thermal shock.

JP-A-10-312971 and JP-A-11-4048 disclose a GaN-based semiconductor laser produced by laminating a laser structure on a GaN substrate from which a different kind of substrate and a mask material have been removed. I have.

FIG. 7 is a view showing a semiconductor laser disclosed in JP-A-11-4048. In FIG.
As shown in FIG. 6, a nitride semiconductor substrate (GaN substrate) 40 is formed by thickly growing GaN doped with Si on a sapphire substrate via a selective growth mask, and then growing the sapphire substrate and the selective growth mask. By polishing to remove Si
It is manufactured using only a doped GaN substrate.

In the semiconductor laser shown in FIG.
On the aN substrate 40, a nitride semiconductor layer having a laser structure is grown. The lamination structure of the laser includes a second buffer layer 41 made of n-type GaN, n-type In _0.1 Ga _0.9 N
Crack prevention layer 42 of n-type Al _0.2 Ga _0.8 N /
N-side cladding layer 43 made of GaN superlattice, n-type GaN
N-side light guide layer 44 of In _0.05 Ga _0.95 N / I
Active layer 45 of n _0.2 Ga _0.8 N multiple quantum well structure, p-type A
The p-side cap layer 46 of l _0.3 Ga _0.7 N, p-type Ga
P-side light guide layer 47 made of N, p-type Al _0.2 Ga _0.8 N
-Side cladding layer 48 composed of / GaN superlattice, p-type Ga
It is formed by sequentially laminating p-side contact layers 49 made of N.

Then, the p-side contact layer 49 and a part of the p-side cladding layer 48 are dry-etched to form a ridge stripe having a width of 4 μm. The position where the ridge stripe is formed is the crystal portion immediately above the selective growth mask. Since the sapphire substrate and the selective growth mask have been removed, a mark serving as a starting point is placed on the GaN substrate before growing the nitride semiconductor device. A p-side electrode 51 made of Ni / Au is formed on the ridge stripe.
Is formed, and an n-side electrode 53 made of Ti / Al is formed on the back surface of the n-type GaN substrate. The end face of the laser resonator is formed by cleaving the M-plane of the n-type GaN substrate.

Other techniques for producing a GaN thick film substrate include, for example, Japanese Patent Application Laid-Open Nos. 7-202265 and
A technique disclosed in Japanese Patent Application Publication No. 165498 is known. In this technique, a buffer layer made of ZnO is formed on a sapphire substrate, a GaN-based semiconductor is grown thereon, and then the buffer layer is dissolved and removed. Then, the substrate and the GaN-based semiconductor are separately manufactured.

Japanese Unexamined Patent Publication No. 10-229218 discloses a first wafer having a GaN-based semiconductor formed on a first substrate and a second wafer having a GaN-based semiconductor formed on a second substrate. And bonding the first and second wafers so that the respective GaN-based semiconductors are in close contact with each other, and then polishing and removing the first substrate and the second substrate. I have.

[0030]

As described above, a high-quality GaN-based compound on a heterogeneous substrate such as sapphire can be obtained by the technology of a low-temperature buffer layer and the technology of manufacturing a low-defect substrate by a combination of selective growth and lateral growth. The semiconductor crystal can be grown, and the life of the GaN-based semiconductor laser is prolonged during low-power operation near room temperature. Moreover,
A GaN substrate is manufactured, and by using this substrate, G
Improvements in characteristics of aN-based semiconductor lasers are expected.

However, a large-area, high-quality GaN substrate that can be industrially used has not been realized yet. As a result, a practical laser that operates at a high output has not yet been realized.

Further, Japanese Patent Application Laid-Open No. 10-326912,
JP-A-10-326751, JP-A-10-312
In the method of manufacturing a GaN substrate disclosed in Japanese Patent Application Laid-Open No. 971 and Japanese Patent Application Laid-Open No. 11-4048, no crack occurs even when a thick GaN is grown. Warpage occurs. For this reason,
It is difficult to uniformly polish a heterogeneous substrate having a diameter of about 2 inches over the entire surface. Even if a high-quality GaN thick film is grown on a substrate having a diameter of about 2 inches, a 10 mm Large GaN
A substrate could not be made. That is, it is difficult to produce a large-area GaN substrate by the conventional method of polishing and removing the substrate. In addition, due to the warpage, defects are introduced into the GaN layer in the process of polishing a heterogeneous substrate, thereby deteriorating the crystallinity and increasing the threshold current density of the semiconductor laser fabricated thereon. Laser characteristics are not always good.

Further, after bonding the first and second wafers so that the respective GaN-based semiconductors are in close contact with each other, the first substrate and the second substrate are removed.
In the method disclosed in Japanese Patent No. 229218, the substrate and the G
Due to the difference in the coefficient of thermal expansion from the aN-based semiconductor, when the GaN is grown to a large thickness, the wafer warps. Therefore, in the case of a large-area wafer, the GaN-based semiconductor may not completely adhere to the entire surface of the wafer. In addition, cracks may occur in the process of close contact. In addition, since the first substrate and the second substrate are polished and removed, two expensive substrates are used for manufacturing one GaN substrate, resulting in a high cost.

In addition, Japanese Patent Application Laid-Open Nos. 7-202265 and 7-1995 produce a GaN substrate that does not require polishing and removal of the substrate.
In the technique disclosed in JP-A-165498, it takes a very long time to dissolve and remove the buffer layer made of ZnO as a thin film, and it is difficult to put it into practical use.

On the other hand, in the method of separating different kinds of substrates using thermal shock, the problem of introducing defects due to thermal shock is the same as in polishing, and it is difficult to produce a high-quality GaN substrate. .

The present invention solves the problems of the conventional method of manufacturing a GaN-based semiconductor substrate, and provides a high-quality and large-area group III nitride semiconductor substrate having few crystal defects, a method of manufacturing the same, and a light emitting device. It is intended to be.

[0037]

In order to achieve the above-mentioned object, according to the present invention, an intermediate layer is formed on an epitaxial growth substrate, and then a group III nitride epitaxial layer is formed on the intermediate layer. A method of manufacturing a semiconductor substrate, wherein a heat treatment is performed at a temperature equal to or higher than a thermal decomposition temperature of an intermediate layer after forming a group III nitride epitaxial layer.

According to a second aspect of the present invention, in the method of manufacturing a semiconductor substrate according to the first aspect, the heat treatment is performed by using II.
It is performed at a temperature lower than the temperature at which the group I nitride epitaxial layer deteriorates.

Further, according to a third aspect of the present invention, after forming an intermediate layer on the substrate for epitaxial growth, a region where the group III nitride epitaxial layer is selectively grown is formed on the intermediate layer. A method of manufacturing a semiconductor substrate, in which a region where a group III nitride epitaxial layer is selectively grown is formed, and a group III nitride epitaxial layer is grown in a region where a group III nitride epitaxial layer is selectively grown, thereby manufacturing a semiconductor substrate. Wherein a heat treatment is performed after growing the group III nitride epitaxial layer in a region where the group III nitride epitaxial layer is selectively grown.

According to a fourth aspect of the present invention, in the method of manufacturing a semiconductor substrate according to the first or third aspect, the intermediate layer is made of InN or a mixed crystal of InN.

The invention described in claim 5 is the first invention.
The method for manufacturing a semiconductor substrate according to any one of claims 3 and 4, wherein the intermediate layer is formed with a superlattice structure.

According to a sixth aspect of the present invention, in the method of manufacturing a semiconductor substrate according to the fourth aspect, when the intermediate layer is formed by a superlattice structure, the heat treatment is performed by using a group III nitride epitaxial layer. It is characterized in that, after being formed, the temperature is higher than the decomposition temperature of any of the layers constituting the superlattice structure of the intermediate layer.

According to a seventh aspect of the present invention, in the method of manufacturing a semiconductor substrate according to the fifth aspect, the film forming method up to forming the superlattice structure is different from the film forming method after forming the superlattice structure. It is characterized by

According to an eighth aspect of the present invention, in the method of manufacturing a semiconductor substrate according to any one of the first to sixth aspects, the group III nitride epitaxial layer and the substrate for epitaxial growth are integrated. It is characterized in that the substrate is a semiconductor substrate.

According to a ninth aspect of the present invention, there is provided the method of manufacturing a semiconductor substrate according to any one of the first to sixth aspects, wherein the group III nitride epitaxial layer is removed from the epitaxial growth substrate. It is characterized in that it is a semiconductor substrate.

The invention according to claim 10 is the first invention.
A semiconductor substrate manufactured by the method for manufacturing a semiconductor substrate according to claim 9.

The eleventh aspect of the present invention provides the first aspect of the present invention.
0 is a light emitting element formed on the semiconductor substrate described in FIG.

[0048]

Embodiments of the present invention will be described below with reference to the drawings.

In the first embodiment of the present invention, after forming an intermediate layer on a substrate for epitaxial growth,
A method of manufacturing a semiconductor substrate, comprising forming a group III nitride epitaxial layer and manufacturing a semiconductor substrate, wherein a heat treatment is performed at a temperature equal to or higher than a thermal decomposition temperature of the intermediate layer after forming the group III nitride epitaxial layer. And

That is, when the epitaxial growth substrate and the epitaxial layer are made of different materials, if the epitaxial layer is grown on the epitaxial growth substrate, the epitaxial growth substrate and the epitaxial layer may be affected by a difference in thermal expansion coefficient. A stress is generated between them. In the present invention, after forming an intermediate layer on the substrate for epitaxial growth, forming a Group III nitride epitaxial layer on the intermediate layer, after forming a Group III nitride epitaxial layer,
By subjecting the semiconductor substrate to heat treatment at a temperature equal to or higher than the thermal decomposition temperature of the intermediate layer, the epitaxial growth substrate and the epitaxial layer are separated from each other, and the stress generated between the epitaxial growth substrate and the epitaxial layer is relaxed. The term “separation” as used herein does not mean only physically dividing into two components (that is, removing the epitaxial layer from the substrate for epitaxial growth), but also has a mechanical meaning such as stress relaxation due to a heterogeneous interface. This does not depend on whether the epitaxial growth substrate and the epitaxial layer are integrated or not.

As described above, according to the present invention, by separating the epitaxial growth substrate and the epitaxial layer by interposing the intermediate layer, the stress generated between the epitaxial growth substrate and the epitaxial layer is reduced. Inconvenience caused by stress such as warpage can be solved.

FIG. 1 is a view showing a specific example of a manufacturing process of a semiconductor substrate according to the first embodiment of the present invention. Referring to FIG. 1, Al ₂ O _{3 is} first used as a substrate for epitaxial growth.
A substrate 101 is prepared (FIG. 1A). The substrate 10
The direction 1 uses the c-plane, but may be another plane direction.

Next, after a low-temperature buffer layer (not shown) of GaN is laminated on the substrate 101 by MOCVD,
An i-doped n-GaN film 102 (having a thickness of 1 μm) is formed (FIG. 1B). Next, on the n-GaN film 102,
InGaN layer 103 (0.2 μm thick) as an intermediate layer
Is formed (FIG. 1C). Subsequently, the Si-doped n-GaN layer 104 is grown to a desired thickness (for example, a thickness of 5 μm) as an epitaxial layer by MOCVD (FIG. 1D).

After the epitaxial layer 104 is grown in this manner, the intermediate layer (InGaN layer) 1 is formed in a nitrogen atmosphere.
Temperature above the temperature at which 03 thermally decomposes (eg, 1050 ° C)
, The thermal decomposition of the InGaN layer 103 progresses quickly. The Al ₂ O ₃ substrate 101 side and n-GaN sandwiching the partially decomposed InGaN layer (intermediate layer) 103 due to thermal stress generated at the time of cooling from the annealing temperature
Stress relaxation occurs selectively at each heterogeneous interface on the epitaxial layer 104 side, and the GaN substrate 104 grown on a heterogeneous substrate (epitaxial growth substrate 101) without warpage is obtained.

In the method of manufacturing a semiconductor substrate according to the present invention, the heat treatment is preferably performed at a temperature lower than a temperature at which the group III nitride epitaxial layer deteriorates.

That is, if the thermal decomposition of the intermediate layer is higher than the decomposition temperature, the higher the temperature, the faster the thermal decomposition.
At a high temperature exceeding 00 ° C., the group III nitride (Ga
N) N vacancies are also generated in the epitaxial layer, and crystal deterioration occurs. Therefore, both the rapid stress relaxation and the suppression of the deterioration of the crystal surface can be achieved by the heat treatment at a temperature equal to or lower than the crystal deterioration temperature depending on the material of the group III nitride epitaxial layer.

In the above-described example of the manufacturing process, the intermediate layer 10
3 was made of InGaN, but the material of the intermediate layer 103 was
It is not limited to InGaN, and other crystals having a low decomposition temperature and mixed crystal materials thereof can be used.

For example, the intermediate layer can be made of InN or a mixed crystal of InN.

InN can be decomposed at a low temperature of about 750 ° C.
This temperature is lower than the temperature at which the group III nitride epitaxial layer deteriorates. Therefore, when InN is used for the intermediate layer, after forming the group III nitride epitaxial layer,
When performing heat treatment at a temperature higher than the thermal decomposition temperature of the intermediate layer,
This temperature can be set to a temperature equal to or lower than the temperature at which the group III nitride epitaxial layer deteriorates.

More specifically, in an example of the manufacturing process similar to the example of the manufacturing process shown in FIG. 1, an InN layer 103 (thickness: 0.2 μm) is formed as an intermediate layer, and is formed at 750 to 950 ° C. for about 30 minutes (typically). By applying a heat treatment at 800 ° C. for 30 minutes, stress was relaxed, and a GaN substrate grown on a non-warped heterogeneous substrate in which the deterioration of the substrate surface was suppressed was obtained.

In the present invention, a super lattice structure can be used for the intermediate layer. Then, when the intermediate layer is formed by a superlattice structure, the heat treatment is performed after the formation of the group III nitride epitaxial layer, at a temperature equal to or higher than the decomposition temperature of any of the layers constituting the superlattice structure of the intermediate layer. Good to be done in.

The superlattice structure is formed by laminating different materials of a thin film, and the different interfaces exhibit a stress relaxation behavior with respect to a smaller shear stress than in the same crystal. Further, any layer in the superlattice structure is decomposed by the heat treatment, and the shear stress is easily alleviated. Therefore, the stress due to the lattice mismatch between the substrate for epitaxial growth and the epitaxial layer and the difference in the coefficient of thermal expansion are selectively relaxed at the partially decomposed heterogeneous interface of the superlattice structure. In addition, the larger the substrate, the larger the absolute value of the stress, and the stress relaxation progresses effectively.

FIG. 2 is a view showing an example of a manufacturing process of a semiconductor substrate when a super lattice structure is used for an intermediate layer. Referring to FIG. 2, first, an Al ₂ O ₃ substrate 201 is prepared (FIG. 2).
(a)). Although the c-plane is used for the orientation of the substrate 201, another orientation may be used.

Next, a low-temperature GaN buffer layer (not shown) of GaN is laminated on the substrate 201 by MOCVD.
An i-doped n-GaN film 202 (1 μm in thickness) is formed (FIG. 2B).

Thus, the Si-doped n-GaN
After forming the film 202, InGaN (thickness 2
0 nm) / GaN (20 nm thick) superlattice structure 203
Is formed (FIG. 2C).

Next, a semiconductor substrate is manufactured by growing a Si-doped n-GaN layer 204 as an epitaxial layer by MOCVD (FIG. 2D).

After forming the semiconductor substrate in this manner, the semiconductor substrate is heated at 750-950 ° C., 3
By performing a heat treatment for about 0 minutes (typically, 800 ° C., 30 minutes), stress is selectively relaxed at a partially decomposed heterogeneous interface of the InGaN / GaN superlattice structure 204,
A warp-free substrate (epitaxial growth substrate 20)
1) An upper GaN substrate 204 is obtained.

Further, in the second embodiment of the present invention, after an intermediate layer is formed on an epitaxial growth substrate, a region where a group III nitride epitaxial layer is selectively grown is formed on the intermediate layer. A region where the epitaxial layer does not grow selectively is formed, and a group III nitride epitaxial layer is grown in a region where the group III nitride epitaxial layer grows selectively, thereby forming a semiconductor substrate. The method is characterized by performing a heat treatment after growing a group III nitride epitaxial layer in a region where a group III nitride epitaxial layer is selectively grown.

Here, the region where the group III nitride epitaxial layer selectively grows is a region where the atomic arrangement of the film is determined based on the potential due to the atomic arrangement of the substrate and grows perpendicularly to the epitaxial growth substrate. . Also,
The region where the group III nitride epitaxial layer is not selectively grown is a region where the group III nitride epitaxial layer does not grow at all or grows three-dimensionally regardless of the potential due to the atomic arrangement of the substrate for epitaxial growth.

In the second embodiment, when the group III nitride epitaxial layer starts epitaxial growth, the group III nitride epitaxial layer grows in a region on the substrate where it is selectively grown, in a direction perpendicular to the substrate, and gradually grows selectively. It begins to grow laterally on the region that does not grow, and eventually covers the substrate surface. The portion grown vertically has the same defect density as the crystal grown directly on the entire substrate, but the portion grown vertically does not penetrate the crystal surface and grows vertically. Thus, the defect density on the crystal surface is reduced.

However, when the substrate for epitaxial growth and the epitaxial layer are made of different materials, a stress is generated between the substrate for epitaxial growth and the epitaxial layer due to a difference in thermal expansion coefficient and the like. In the second embodiment, it is possible to obtain a low defect density and stress-free epitaxial layer as a semiconductor substrate by thermally decomposing an intermediate layer between the epitaxial growth substrate and the epitaxial layer and relaxing the stress. it can.

FIG. 3 is a view showing a specific example of a manufacturing process of a semiconductor substrate according to the second embodiment of the present invention. Referring to FIG. 3, first, an Al ₂ O ₃ substrate 301 is prepared (FIG.
(A)). Although the c-plane is used for the orientation of the substrate 301, other orientations may be used.

Then, after a low-temperature GaN buffer layer (not shown) of GaN is laminated on the substrate 301 by MOCVD,
An i-doped n-GaN film 302 (having a thickness of 1 μm) is formed (FIG. 3B).

Thus, the Si-doped n-GaN
After the film 202 is formed, InGaN (thickness 1) is used as an intermediate layer.
0 nm) / GaN (20 nm thick) superlattice structure 303
Is formed (FIG. 3C).

Next, the Si-doped n
A GaN film (n-GaN epitaxial layer) 304 is grown (FIG. 3D).

Thereafter, the SiO 2 is deposited on the n-GaN film 304.
( _{2) A} mask layer 305 (thickness: 1.5 μm) is formed, a photoresist is applied, and a desired pattern is formed by photolithography.
Etching the iO ₂ mask layer 305 (FIG. 3)
(E)).

Next, the Si-doped n
-The GaN epitaxial layer 306 is selectively grown, covers the opening surface of the mask layer 305, and is further grown in the lateral direction (FIG. 3 (f)). Further, by continuing to selectively grow the Si-doped n-GaN epitaxial layer 306,
Si-doped n-GaN epitaxial layer 30 over entire substrate
6 are united to form a single n-GaN substrate 307 (FIG. 3 (g)).

After growing the Si-doped n-GaN epitaxial layer in this way, in a chamber at 750 to 950 ° C. for about 30 minutes (typically 80 ° C.) in a nitrogen atmosphere.
(0 ° C., 30 minutes).
At the heterogeneous interface in which the aN superlattice structure 303 is partially decomposed, stress relaxation occurs selectively, and a GaN substrate 308 on a heterogeneous substrate without warpage is obtained (FIG. 3 (h)).

In the above-described method for manufacturing a semiconductor substrate in which separation is performed using a superlattice structure, a film forming method up to forming a superlattice structure (intermediate layer) and a film forming method after forming a superlattice structure (intermediate layer) The method can be different. That is, in the above-described manufacturing process, in the manufacturing process up to the superlattice structure, it is considered that a method in which the growth conditions are relatively slow and the thickness of each layer is easily controlled, for example, the MOCVD method or the MBE method is suitable. By creating a superlattice structure by a method in which the growth conditions are relatively slow and the thickness of each layer is easily controlled, the effect of stress relaxation can be obtained effectively. However, after the superlattice structure is manufactured, a semiconductor substrate can be manufactured at a lower cost by adopting an inexpensive film forming method with a high film forming speed. As described above, by adopting different growth methods before the intermediate layer is grown and after the intermediate layer is grown, high-quality crystals can be obtained while using a low-cost process.

FIG. 4 shows an example of a manufacturing process of a semiconductor substrate in the case where the film forming method up to forming the superlattice structure (intermediate layer) is different from the film forming method after forming the superlattice structure (intermediate layer). FIG.

Referring to FIG. 4, first, the Al ₂ O ₃ substrate 4
01 is prepared (FIG. 4A). Although the c-plane is used for the orientation of the substrate 401, other orientations may be used. Next, after stacking a low-temperature burfer layer of GaN on the substrate 401 by MOCVD, the Si-doped n-GaN film 402 is formed.
(FIG. 4 (b)).

Thus, the Si-doped n-GaN film 4
02 after growing InGaN (20 nm thick) / GaN
A superlattice structure 403 having a thickness of 20 nm is formed (FIG. 4).
(C)).

Next, the Si-doped n
-The GaN film 404 is selectively grown (FIG. 4D).

Thereafter, the SiN film is formed on the n-GaN film 404.
_{An x} mask layer 405 (thickness: 1.5 μm) is formed, a photoresist is applied, patterning is performed to a desired pattern by photolithography, and S is formed by CF ₄ using RIE.
Etching the iN _x mask layer 405 (FIG. 4)
(E)).

After that, 100 μm /
The Si-doped n-GaN epitaxial layer 406 is selectively grown at a speed of about h at a high speed to cover the mask opening surface and grow laterally (FIG. 4 (f)). Further, by continuing selective growth of the Si-doped n-GaN epitaxial layer 406, the Si-doped n-GaN epitaxial layer 406 of the entire substrate is united to form a single GaN substrate 407 (FIG. 4 (g)).

After growing the Si-doped n-GaN epitaxial layer in this way, in a nitrogen atmosphere in a chamber at 750-950 ° C. for about 30 minutes (typically 80 ° C.).
(0 ° C., 30 minutes).
At the heterogeneous interface where the aN superlattice structure 403 is partially decomposed, stress relaxation occurs selectively, and a GaN substrate 408 on a heterogeneous substrate without warpage is obtained (FIG. 4 (h)).

In the manufacturing process examples shown in FIGS. 1, 2, 3 and 4, the details of the structure and process such as the layer structure and the composition of each layer are not limited to those described above. ， It is also possible to take a process.

In the manufacturing process examples shown in FIGS. 1, 2, 3 and 4, a GaN-based thin film is formed by the MOCVD method. However, when the MBE method is used, not only the GaN-based thin film but also all the GaN-based thin films are used. Layer and film configurations can be formed.
If the sublimation method or the sublimation method is used, it is possible to form the structure of layers and films after the intermediate layer.

The manufacturing process examples shown in FIGS. 1, 2, 3 and 4 are not limited to the GaN-based semiconductor substrate, but are generally used for manufacturing a substrate having a large difference in thermal expansion coefficient. The present invention is applicable to general substrate fabrication.

The heat treatment conditions given in the example of the manufacturing process shown in FIGS. 1, 2, 3 and 4 are examples of the conditions for the GaN substrate, and can be applied to a substrate made of another material. In this case, the heat treatment conditions are not limited to the conditions described in the example of the manufacturing process in FIGS. 1, 2, 3, and 4.

In the semiconductor substrate of the present invention, as described above, the substrate for epitaxial growth and the group III nitride epitaxial layer grown on the substrate for epitaxial growth are separated. Here, separation refers to separation in a mechanical sense such as relaxation of stress due to a heterogeneous interface. That is, the stress between the epitaxial growth substrate and the group III nitride epitaxial layer is relaxed, and the introduction of dislocation due to warpage or stress is eliminated. But III
Since the group III nitride epitaxial layer has not been removed from the substrate (see the example of the manufacturing process in FIG. 2), the group III nitride epitaxial layer and the substrate for epitaxial growth can be handled as an integral body. Can secure the entire strength by the epitaxial growth substrate.

That is, when the group III nitride epitaxial layer and the substrate for epitaxial growth are integrated,
In a crystal growth step or a device manufacturing step, a semiconductor substrate can be easily handled, and a large-area, low-cost semiconductor substrate without warpage can be provided. In other words, after growing the group III nitride epitaxial layer, by leaving the group III nitride epitaxial layer and the substrate for epitaxial growth in a state where the lattice is relaxed and the strain is reduced, a large-area substrate without warpage is obtained. During the device formation process, the substrate for epitaxial growth can be used as a support substrate for the group III nitride epitaxial layer,
Handling becomes easy. Also, with the support substrate,
The thickness of the group III nitride epitaxial layer can be reduced, and a semiconductor substrate with lower cost can be obtained.

On the contrary, the group III nitride epitaxial layer can be removed from the substrate for epitaxial growth and used as a semiconductor substrate (see a manufacturing process example in FIG. 3). In this case, the semiconductor substrate selectively grows a thick group III nitride epitaxial layer on the substrate for epitaxial growth, and
The structure is separated from the group I nitride epitaxial layer.
In this case, the term “separation” means not only the above-described separation for relaxing stress at the heterogeneous interface, but also the group III nitride epitaxial layer itself after removal from the substrate for epitaxial growth. This means that the nitride epitaxial layer alone is used as a semiconductor substrate.

As described above, by removing the group III nitride epitaxial layer from the substrate for epitaxial growth and forming a semiconductor substrate, the substrate for epitaxial growth and the III
A group III nitride semiconductor layer is physically separated from the group III nitride epitaxial layer, stress is relieved, and a large-area group III nitride semiconductor substrate is obtained. In addition, since lattice relaxation progresses on the entire substrate for epitaxial growth and the group III nitride epitaxial layer,
The group III nitride epitaxial layer can be easily removed from the substrate for epitaxial growth. Thereby, a high-quality and large-area GaN-based semiconductor substrate can be provided.

Then, a light emitting element can be formed on the above-described semiconductor substrate of the present invention.

FIG. 5 is a view showing an example of a light emitting element formed on a semiconductor substrate of the present invention. In the example of FIG. 5,
The light emitting device is configured as a semiconductor laser device, III
A semiconductor substrate (GaN free-standing substrate) obtained by removing the group III nitride epitaxial layer from the substrate for epitaxial growth is used.

That is, the light emitting device shown in FIG.
The n-GaN semiconductor substrate (self-supporting substrate) 502 is separated by an n-GaN buffer layer 503 into n-In
_0.1 Ga _0.9 N crack prevention layer 504, n-Al _0.1 Ga
_0.9 N cladding layer 505, n-GaN guide layer 506,
DQW structure 507 composed of two periods of In _0.15 Ga _0.85 N / GaN as active layers, p-GaN guide layer 508, p
-Al _0.1 Ga _0.9 N clad layer 509 and p-GaN contact layer 510 are formed in this order, and p-electrode metal 512 is formed.
Is formed via an SiO ₂ insulating layer 511 for current confinement. The n-electrode metal 501 is connected to the conductive substrate 5.
5, since it can be formed on the back surface of the substrate 502 as shown in FIG. 5, face-down mounting is possible. In addition, since the substrate itself has cleavage properties and the crystal orientation matches the epitaxial layer forming the element, the end face of the light emitting element is easily formed by cleavage.

FIG. 5 shows an example of the light emitting device, and the present invention is not limited to the structure and the manufacturing method of the light emitting device.

[0099]

As described above, according to the first and second aspects of the present invention, after forming an intermediate layer on an epitaxial growth substrate, a group III nitride epitaxial layer is formed on the intermediate layer. Then, in a method of manufacturing a semiconductor substrate to manufacture a semiconductor substrate, after forming a Group III nitride epitaxial layer, heat treatment is performed at a temperature equal to or higher than the thermal decomposition temperature of the intermediate layer, so that stress is relaxed, The residual strain is reduced, large-area crystallization free of warpage and cracks can be obtained, and a high-quality substrate in which the behavior such as dislocation development and multiplication can be reduced.

In particular, according to the second aspect of the present invention, in the method of manufacturing a semiconductor substrate according to the first aspect, the heat treatment is performed at a temperature equal to or lower than a temperature at which the group III nitride epitaxial layer deteriorates. In addition to the effect of claim 1, it is possible to obtain a high-quality group III nitride semiconductor substrate having reduced distortion, a large-area crystal free from warpage and cracks, and having a reduced behavior such as propagation and propagation of dislocations. Thus, it is possible to obtain a group III nitride semiconductor substrate in which the deterioration of the substrate surface is reduced.

According to the third aspect of the present invention, after forming the intermediate layer on the substrate for epitaxial growth, the region where the group III nitride epitaxial layer is selectively grown is formed on the intermediate layer. A region where the epitaxial layer does not grow selectively is formed, and a group III nitride epitaxial layer is grown in a region where the group III nitride epitaxial layer grows selectively, thereby forming a semiconductor substrate. A manufacturing method in which a group III nitride epitaxial layer is grown selectively in a region where the group III nitride epitaxial layer is selectively grown, and then subjected to a heat treatment, so that residual strain is reduced, and a large area without warpage or cracks is formed. It is possible to obtain a high-quality group III nitride semiconductor substrate in which the behavior of crystal and dislocation propagation / proliferation is alleviated, and to achieve high density due to lattice strain in lattice strain materials. It is possible to reduce the dislocation. Therefore, by reducing the residual strain, a large-area, high-quality semiconductor substrate free of warpage and cracks can be obtained, and the dislocation density due to the lattice strain is low, and the behavior of the dislocation progression and proliferation, etc., has been reduced. A semiconductor substrate having a low defect density can be obtained.

According to a fourth aspect of the present invention, in the method of manufacturing a semiconductor substrate according to the first or third aspect, the intermediate layer is made of InN or a mixed crystal of InN, so that the residual strain is reduced. In addition to the effects of claim 1 and claim 3, a large-area crystallization free of warpage and cracks can be obtained, and a high-quality substrate with reduced behavior such as the development and propagation of dislocations can be obtained. Is further reduced, thereby obtaining a group III nitride semiconductor substrate. That is, in order to thermally decompose the intermediate layer and release the stress between both interfaces, the heat treatment temperature must be raised to a temperature at which the intermediate layer is thermally decomposed. In order to suppress crystal defects caused by the generation of N vacancies on the surface of the epitaxial film due to the heat treatment, it is necessary to perform the heat treatment at a temperature as low as possible and promptly. According to the fourth aspect of the present invention, InN decomposable at a low temperature of about 750 ° C
By using for the intermediate layer, a group III nitride semiconductor substrate with further reduced deterioration of the substrate surface can be obtained.

According to the fifth and sixth aspects of the present invention, since the intermediate layer is formed by a super lattice structure,
A high-quality and large-area semiconductor substrate with smaller residual distortion can be obtained. That is, in producing a substrate using a lattice-strain-based material, by thermally decomposing one of the layers of the superlattice structure by heat treatment after epitaxial growth, the stress due to the lattice distortion and the difference in the coefficient of thermal expansion between the substrate and the superlattice is reduced. It can be reduced by selective stress relaxation between interfaces of dissimilar materials of partially decomposed structure. Then, the stress relaxation by the superlattice structure acts to relieve the shear stress parallel to the layer surface of the superlattice structure. This direction is the direction in which the stress caused by the lattice strain acts.
This is also the direction in which stress acts due to the difference in the coefficient of thermal expansion. Therefore,
First, by using a material that decomposes at low temperature, secondly, it shows lattice relaxation behavior for small shear stress,
By designing a superlattice structure, a high-quality and large-area semiconductor substrate with smaller residual distortion can be obtained.
In addition, by setting each layer constituting the superlattice structure to be equal to or less than the critical film thickness, it is possible to use a material having a significantly different lattice constant, and to select a wider material system satisfying the above two guidelines. .

According to a seventh aspect of the present invention, in the method of manufacturing a semiconductor substrate according to the fifth aspect, a film forming method up to forming a superlattice structure, a film forming method after forming a superlattice structure, Therefore, a high-quality and large-area semiconductor substrate can be obtained at lower cost. That is, in order to manufacture a semiconductor substrate at a low cost, it is necessary to adopt a film forming method with a high film forming speed and a low cost. However, the growth method with a high film-forming rate has difficulty in controlling the film thickness and controlling the composition ratio of the mixed crystal in forming the superlattice, and cannot provide a sufficient stress relaxation effect. Therefore, the process up to the formation of the superlattice structure is formed using a method with a low growth rate and easy control of the film thickness. Even if is used, a high-quality crystal can be obtained, and a high-quality and large-area semiconductor substrate can be obtained at lower cost.

According to an eighth aspect of the present invention, in the method of manufacturing a semiconductor substrate according to any one of the first to sixth aspects, the group III nitride epitaxial layer and the substrate for epitaxial growth are integrated. After the epitaxial layer growth, by leaving the epitaxial layer and the substrate for epitaxial growth in a state where the lattice is relaxed and the strain is reduced,
A semiconductor substrate having a large area without warpage can be obtained, and a substrate for epitaxial growth can be used as a substrate for supporting an epitaxial layer in a crystal growth step or a step of forming a device (for example, a light emitting element such as a semiconductor laser). In addition, the handling of the semiconductor substrate becomes easy. In addition, the presence of the supporting substrate also enables the thickness of the epitaxial layer to be reduced, so that a lower-cost semiconductor substrate can be obtained.

According to a ninth aspect of the present invention, in the method of manufacturing a semiconductor substrate according to any one of the first to sixth aspects, the group III nitride epitaxial layer is removed from the epitaxial growth substrate. Since the semiconductor substrate is used as a semiconductor substrate, the cleavage property for forming the cavity end face necessary for forming a device (for example, a light emitting element such as a semiconductor laser) is secured, and the formation of a back electrode (conductive layer) for face-down mounting is ensured. Substrate), and the defect density in the device is reduced by homoepitaxial growth, thereby achieving a long life and high output of the device. Since the lattice relaxation progresses in the epitaxial growth substrate and the entire epitaxial layer, the epitaxial layer can be easily removed from the epitaxial growth substrate.

According to a tenth aspect of the present invention, there is provided a semiconductor substrate manufactured by the method of manufacturing a semiconductor substrate according to any one of the first to ninth aspects.
High quality III with reduced residual strain, large area crystal without warpage and cracks, and reduced dislocation growth / growth behavior III
A group nitride semiconductor substrate can be provided.

According to the eleventh aspect of the present invention, since the light emitting element is formed on the semiconductor substrate according to the tenth aspect, a large-area semiconductor substrate having a low density of crystal defects and no warpage can be provided. A long-life light-emitting element can be provided at low cost. In addition, when a conductive epitaxial layer removed from a substrate for epitaxial growth is used as a semiconductor substrate, a conventional light-emitting element structure in which an electrode is formed on the back surface can be used, and face-down mounting is possible. A light-emitting element having excellent properties can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a manufacturing process of a semiconductor substrate according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a manufacturing process of a semiconductor substrate when a superlattice structure is used for an intermediate layer.

FIG. 3 is a diagram illustrating an example of a manufacturing process of a semiconductor substrate according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a manufacturing process of a semiconductor substrate in a case where a film formation method until a superlattice structure (intermediate layer) is manufactured is different from a film formation method after the superlattice structure (intermediate layer) is manufactured. is there.

FIG. 5 is a diagram showing an example of a light emitting element formed on a semiconductor substrate of the present invention.

FIG. 6 is a view for explaining a conventional method for manufacturing a semiconductor substrate.

FIG. 7 is a diagram showing a conventional semiconductor laser.

[Explanation of symbols]

Reference Signs List 101 Al ₂ O ₃ substrate 102 n-GaN film 103 InGaN layer 104 n-GaN epitaxial layer 201 Al ₂ O ₃ substrate 202 n-GaN film 203 Superlattice structure 204 n-GaN epitaxial layer 301 Al ₂ O ₃ substrate 302 n- GaN film 303 super lattice structure 304 n-GaN epitaxial layer 305 SiO ₂ mask layer 306 n-GaN epitaxial layer 307 n-GaN substrate 308 n-GaN substrate 401 Al ₂ O ₃ substrate 402 n-GaN film 403 super lattice structure 404 n -GaN layer 405 SiN _x mask layer 406 n-GaN epitaxial layer 407 GaN substrate 408 GaN substrate 501 n-electrode metal 502 n-GaN semiconductor substrate 503 n-GaN buffer layer 504 n-InGaN crack preventing layer 505 n-A GaN clad layer 506 n-GaN guide layer 507 DQW active layer 508 p-GaN guide layer 509 p-AlGaN cladding layer 510 p-GaN contact layer 511 SiO ₂ insulating layer 512 p-electrode metal

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F041 AA40 CA05 CA34 CA40 CA46 CA73 5F045 AA04 AB09 AB14 AB17 AB32 AB33 AF04 AF09 AF13 AF20 BB12 CA09 CB02 DA54 DA69 DB02 GB05 HA16 5F073 AA71 AA74 AA89 BA01 BA06 CA07 CB05 CB07

Claims (11)

[Claims] 1. A method of manufacturing a semiconductor substrate, comprising: forming an intermediate layer on an epitaxial growth substrate, forming a group III nitride epitaxial layer on the intermediate layer, and manufacturing a semiconductor substrate. After forming the epitaxial layer,
A method for manufacturing a semiconductor substrate, comprising performing heat treatment at a temperature equal to or higher than a thermal decomposition temperature of an intermediate layer. 2. The method of manufacturing a semiconductor substrate according to claim 1, wherein the heat treatment is performed at a temperature equal to or lower than a temperature at which the group III nitride epitaxial layer deteriorates. 3. After forming an intermediate layer on the substrate for epitaxial growth, a region where the group III nitride epitaxial layer selectively grows and a region where the group III nitride epitaxial layer does not grow selectively are formed on the intermediate layer. Are formed together,
A method of manufacturing a semiconductor substrate, comprising: growing a group III nitride epitaxial layer in a region where a group III nitride epitaxial layer is selectively grown, and manufacturing a semiconductor substrate, wherein the group III nitride epitaxial layer is selectively grown. III
A method for manufacturing a semiconductor substrate, comprising performing a heat treatment after growing a group III nitride epitaxial layer. 4. The method for manufacturing a semiconductor substrate according to claim 1, wherein said intermediate layer is made of InN or IN.
A method for manufacturing a semiconductor substrate, comprising a mixed crystal of nN. 5. The method of manufacturing a semiconductor substrate according to claim 1, wherein said intermediate layer is formed by a superlattice structure. Method of manufacturing. 6. The method of manufacturing a semiconductor substrate according to claim 4, wherein when the intermediate layer is formed with a superlattice structure, the heat treatment is performed after forming a group III nitride epitaxial layer. A method for manufacturing a semiconductor substrate, which is performed at a temperature equal to or higher than a decomposition temperature of any one of layers constituting a superlattice structure. 7. The method for manufacturing a semiconductor substrate according to claim 5, wherein a film forming method before forming a superlattice structure is different from a film forming method after forming a superlattice structure. Method of manufacturing. 8. The method for manufacturing a semiconductor substrate according to claim 1, wherein a semiconductor substrate is obtained by integrating a group III nitride epitaxial layer and a substrate for epitaxial growth. A method for manufacturing a semiconductor substrate. 9. The method of manufacturing a semiconductor substrate according to claim 1, wherein the semiconductor substrate is obtained by removing the group III nitride epitaxial layer from the epitaxial growth substrate. Of manufacturing a semiconductor substrate. 10. A semiconductor substrate manufactured by the method for manufacturing a semiconductor substrate according to claim 1. 11. A light emitting device formed on the semiconductor substrate according to claim 10.