Semiconductor substrate, method of forming the same and light emitting device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a semiconductor substrate used for a semiconductor laser for optical communication, a light source for an optical disk, etc., a method for manufacturing the same, and a light emitting element.

【0002】

[Conventional technology]

Conventionally, blue LEDs have lower brightness than red and green LEDs and are difficult to put into practical use. However, in recent years, low-temperature AlN buffer layers or low-temperature GaN have been used in GaN-based compound semiconductors represented by the general formula InAlGaN. High-brightness blue LEDs have been put into practical use due to the improvement of crystal growth technology by using a buffer layer and the acquisition of a low-resistance p-type semiconductor layer doped with Mg, and further, it has not been put into practical use. A semiconductor laser that continuously oscillates at room temperature has been realized.

【0003】

Generally, when a high-quality semiconductor layer is epitaxially grown on a substrate, the lattice constant and the coefficient of thermal expansion of the substrate and the semiconductor layer need to be about the same. However, for GaN-based semiconductors, there is currently no substrate in the world that satisfies these requirements at the same time.

【0004】

At present, attempts are being made to fabricate a GaN bulk single crystal, but the reality is that only a few millimeters have been obtained, which is far from practical use.

【0005】

Therefore, in GaN systems, sapphire, MgAl is generally used.₂O₄Laser devices are manufactured by crystal growth using dissimilar substrates with significantly different lattice constants and coefficients of thermal expansion from GaN-based semiconductors such as spinel and SiC.

【0006】

However, when dissimilar substrates are used, there are problems such as crystal defects, optical resonator end face formation, electrode formation, and heat dissipation, and a practical laser element has not yet been realized.

【0007】

Hereinafter, these problems will be briefly described. For crystal defects, sapphire, MgAl₂O₄When crystal growth is performed using different substrates with significantly different lattice constants and coefficients of thermal expansion from GaN-based semiconductors such as spinel and SiC, the dislocation density introduced due to lattice mismatch is 10.⁸~10¹⁰cm^-2It is difficult to grow a crystal with the quality necessary for manufacturing a practical semiconductor laser, such as distortion and cracks due to the difference in the coefficient of thermal expansion between the dissimilar substrate and the GaN-based semiconductor. Met.

【0008】

Regarding the formation of the end face of the optical cavity, the cleavage planes of the dissimilar substrate and the GaN-based compound semiconductor do not always coincide with each other. It was difficult to form the end face of the resonator.

【0009】

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

【0010】

Here, in the method using dry etching, steps such as forming a mask for dry etching, dry etching, and removing the mask are required in the manufacturing process, which is complicated. Furthermore, since the dry etching technology for GaN-based compound semiconductors has not yet been established, the formed resonator mirror has vertical streaks and irregularities, and is formed in a tapered shape. Parallelism and verticality were not yet sufficient. Further, 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 the light was reflected by this terrace and the beam shape did not become a single peak.

【0011】

In addition, in the method of forming the end face of the optical cavity by cracking the GaN-based crystal by thinly polishing the substrate such as sapphire and cleaving the substrate, the gap between the cleavage surface between the GaN-based crystal and the substrate is used. Since the end face of the optical cavity has large irregularities and is not smooth, the threshold current of the laser is increased.

【0012】

Further, regarding the electrode formation, since the generally used sapphire substrate has an insulating property, the electrode could not be taken from the back surface of the substrate. Therefore, the electrodes are formed on the surface of the device, and unlike the conventional lasers such as AlGaAs, it is not possible to form the electrodes on the back surface of the substrate and perform die bonding. There was also a problem that the chip area became large. Further, in order to form the electrode on the n side, dry etching is required to expose the n-type layer, which complicates the manufacturing process of the laser element.

【0013】

Further, regarding heat dissipation, due to the poor thermal conductivity of a generally used sapphire substrate, the life was extremely short in high temperature operation or high output operation.

【0014】

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

【0015】

For example, in JP-A-10-326912, JP-A-10-326751, JP-A-10-312971, and JP-A-11-4048, GaN was selectively grown on a dissimilar substrate using a mask. Further, a technique of embedding a mask and forming a flat GaN thick film on the entire surface of a substrate by continuing crystal growth is disclosed.

【0016】

FIG. 5 is a diagram for explaining a method for producing a GaN thick film substrate shown in Japanese Patent Application Laid-Open No. 10-312971.

【0017】

Referring to FIG. 5, first, a III-V compound semiconductor film 12 such as GaN is laminated on a dissimilar substrate 11 such as sapphire, and SiO₂A mask 14 having a width of several μm made of the above is prepared to form a growth region 13 for selective growth of a group III-V compound semiconductor such as GaN (Fig. 5 (a)).

【0018】

Next, a III-V compound semiconductor such as GaN is selectively grown in the growth region 13 to prepare a facet structure 15 (Fig. 5 (b)).

【0019】

As the III-V compound semiconductor continues to grow, facets 15 grow laterally and cover the mask 14 (Fig. 5 (c)).

【0020】

As it continues to grow, the adjacent III-V compound semiconductor 15 coalesces and fills the groove (Fig. 5 (d)).

【0021】

As the growth continues, the surface of the III-V compound semiconductor 15 is flattened, and a flat III-V compound semiconductor thick film is formed on the entire surface of the substrate (Fig. 5 (e)).

【0022】

According to the techniques shown in the above-mentioned publications, the crystal layer of the portion selectively grown on the dissimilar substrate has a high density of penetrating dislocations generated at the substrate interface, but laterally grows laterally on the mask. In the part, the density of penetrating dislocations is drastically reduced to obtain high quality crystals. Furthermore, by repeating selective growth and lateral growth on this, a high-quality GaN thick film with few dislocations can be formed on the entire surface of the wafer. Further, according to this technology, even if a thick GaN of 100 μm or more is grown, cracks due to the difference in thermal expansion coefficient do not occur, so that a GaN thick film having a thickness that can be used as a substrate even if a dissimilar substrate is removed can be obtained. Can grow.

【0023】

Then, in the techniques of the above-mentioned publications, in order to solve the problems of the end face of the optical cavity, the electrode formation, and the heat dissipation, the dissimilar substrate and the mask are finally removed to form the GaN substrate. The removal of dissimilar substrates and mask materials is by polishing or using thermal shock.

【0024】

Japanese Patent Application Laid-Open No. 10-312971 and Japanese Patent Application Laid-Open No. 11-4048 disclose a GaN-based semiconductor laser produced by laminating a laser structure on a GaN substrate from which a dissimilar substrate and a mask material have been removed.

【0025】

FIG. 6 is a diagram showing a semiconductor laser shown in Japanese Patent Application Laid-Open No. 11-4048. In FIG. 6, the nitride semiconductor substrate (GaN substrate) 40 is formed by thickly growing Si-doped GaN on the sapphire substrate via a selective growth mask in the same manner as in the process shown in FIG. 5, and then the sapphire substrate. The selective growth mask is polished and removed to make only a Si-doped GaN substrate.

【0026】

Then, in the semiconductor laser of FIG. 6, a nitride semiconductor layer having a laser structure is grown on the GaN substrate 40. The laminated structure of the laser consists of a second buffer layer 41 made of n-type GaN and n-type In._0.1Ga_0.9Crack prevention layer 42 consisting of N, n-type Al_0.2Ga_0.8N-side clad layer 43 made of N / GaN superlattice, n-side optical guide layer 44 made of n-type GaN, In_0.05Ga_0.95N / In_0.2Ga_0.8Active layer 45 of N multiple quantum well structure, p-type Al_0.3Ga_0.7P-side cap layer 46 made of N, p-side optical guide layer 47 made of p-type GaN, p-type Al_0.2Ga_0.8It is formed by sequentially laminating a p-side clad layer 48 made of N / GaN superlattice and a p-side contact layer 49 made of p-type GaN.

【0027】

Then, a part of the p-side contact layer 49 and the p-side clad layer 48 is 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 directly above the selective growth mask. Since the sapphire substrate and the selective growth mask have been removed, this alignment is performed by inserting a mark as a starting point on the GaN substrate side before the nitride semiconductor device grows. A p-side electrode 51 made of Ni / Au is formed on the ridge stripe, 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 cavity is formed by cleaving the M plane of the n-type GaN substrate.

【0028】

As other techniques for producing a GaN thick film substrate, for example, the techniques shown in JP-A-7-202265 and JP-A-7-165998 are known, and this technique is ZnO on a sapphire substrate. A buffer layer is formed, a GaN-based semiconductor is grown on the buffer layer, the buffer layer is melted and removed, and the substrate and the GaN-based semiconductor are separated and manufactured.

【0029】

Further, in Japanese Patent Application Laid-Open No. 10-229218, a first wafer in which a GaN-based semiconductor is formed on a first substrate and a second wafer in which a GaN-based semiconductor is formed on a second substrate are prepared. Then, a method is shown in which the first and second wafers are bonded to each other so that the GaN-based semiconductors are in close contact with each other, and then the first substrate and the second substrate are polished and removed.

【0030】

[Problems to be Solved by the Invention]

As described above, the low-temperature buffer layer technology and the technology for producing low-defect substrates by combining selective growth and lateral growth enable crystal growth of high-quality GaN-based compound semiconductors on dissimilar substrates such as sapphire, enabling GaN. The life of the system semiconductor laser is extended during low output operation near room temperature. Furthermore, a GaN substrate has been produced, and it is expected that the characteristics of the GaN-based semiconductor laser will be improved by using this substrate.

【0031】

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

【0032】

Further, in the method for producing a GaN substrate shown in JP-A No. 10-326912, JP-A-10-326751, JP-A-10-312971, and JP-A-11-4048, thick GaN is grown. However, cracks do not occur, but the wafer is warped due to the difference in the coefficient of thermal expansion between the GaN and the dissimilar substrate. For this reason, it is difficult to uniformly polish dissimilar substrates with a diameter of about 2 inches on the entire surface, and even if a high-quality GaN thick film is grown on a substrate with a diameter of about 2 inches, it is necessary to polish dissimilar substrates. Needed to be divided into about 10 mm, and a large GaN substrate could not be manufactured. 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 this warpage, defects are introduced into the GaN layer in the process of polishing dissimilar substrates, resulting in poor crystallinity and an increase in the threshold current density of the semiconductor laser manufactured on the semiconductor. The characteristics of the laser are not always good.

【0033】

Further, it is shown in Japanese Patent Application Laid-Open No. 10-229218, which removes the first substrate and the second substrate after adhering the first and second wafers so that the respective GaN-based semiconductors are in close contact with each other. In this method, the wafer warps when GaN is grown thick due to the difference in thermal expansion coefficient between the substrate and the GaN-based semiconductor. Therefore, in a large-area wafer, the GaN-based semiconductors may not completely adhere to each other on the entire surface of the wafer. is there. In addition, cracks may occur in the process of close contact. Further, since the first substrate and the second substrate are polished and removed, there is a problem that two expensive substrates are used to produce one GaN substrate, resulting in high cost.

【0034】

Further, in the techniques shown in JP-A-7-202265 and JP-A-7-165488 for producing a GaN substrate that does not require polishing and removal of the substrate, the buffer layer made of ZnO in the thin film is dissolved and removed. It takes a very long time and is difficult to put into practical use.

【0035】

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

【0036】

The present invention solves the problems of these conventional methods for manufacturing GaN-based semiconductor substrates, and provides a high-quality, large-area group III nitride semiconductor substrate with few crystal defects, a method for producing the same, and a light emitting device. I am aiming.

【0037】

[Means for solving problems]

In order to achieve the above object, the invention according to claim 1 is formed by mixing a region in which the Group III nitride epitaxial layer selectively grows and a region in which the Group III nitride epitaxial layer does not selectively grow. A method for producing a semiconductor substrate by forming a group III nitride epitaxial layer on the epitaxial growth substrate, wherein the group III nitride epitaxial layer of the epitaxial growth substrate is selectively grown. It is characterized in that it is produced so that the Group III nitride epitaxial layer and the substrate for epitaxial growth are separated from each other.

【0038】

Further, in the invention according to claim 2, in the method for manufacturing a semiconductor substrate according to claim 1, the epitaxial growth substrate and the group III nitride epitaxial layer grown on the epitaxial growth substrate are lattice-mismatched, and the epitaxial growth substrate is lattice-mismatched. It is characterized in that the group III nitride epitaxial layer of the epitaxial growth substrate is produced so as to be separated by a super lattice structure on the region where the epitaxial growth substrate substrate and the group III nitride epitaxial layer are selectively grown. ..

【0039】

Further, the invention according to claim 3 is characterized in that, in the method for producing a semiconductor substrate according to claim 2, the film forming method until the superlattice structure is formed and the film forming method after the superlattice structure is formed are different. It is supposed to be.

【0040】

Further, in the invention according to claim 4, in the method for manufacturing a semiconductor substrate according to claim 1, claim 2 or claim 3, a semiconductor substrate in which a group III nitride epitaxial layer and an epitaxial growth substrate are integrated is used as a semiconductor substrate. This is a method for manufacturing a semiconductor substrate.

【0041】

Further, in the invention according to claim 5, in the method for manufacturing a semiconductor substrate according to claim 1, claim 2 or claim 3, the semiconductor substrate is obtained by removing the group III nitride epitaxial layer from the epitaxial growth substrate. This is a method for manufacturing a semiconductor substrate.

【0042】

Further, in the invention according to claim 6, in the method for producing a semiconductor substrate according to any one of claims 1 to 5, the group III nitride epitaxial layer is composed of a nitride containing at least Ga, and is super. The lattice structure is characterized in that it is composed of Ga, In, Al nitrides or mixed crystals thereof.

【0043】

The invention according to claim 7 is a semiconductor substrate manufactured by the method for manufacturing a semiconductor substrate according to any one of claims 1 to 6.

【0044】

The invention according to claim 8 is a light emitting device formed on the semiconductor substrate according to claim 7.

【0045】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

【0046】

In the embodiment of the present invention, epitaxial growth is formed in which a region in which the epitaxial layer of Group III nitride (for example, GaN) selectively grows and a region in which the epitaxial layer of Group III nitride does not selectively grow are mixed. A semiconductor substrate has been produced by forming an epitaxial layer of Group III nitride on the substrate. At this time, the Group III nitride epitaxial layer of the epitaxial growth substrate has grown into a region where it selectively grows. It is characterized in that a semiconductor substrate is manufactured so that the Group III nitride epitaxial layer and the epitaxial growth substrate are separated.

【0047】

In the embodiment of the present invention, the group III nitride epitaxial layer is formed by mixing a region in which the epitaxial layer of the group III nitride grows selectively and a region in which the epitaxial layer of the group III nitride does not selectively grow. A film is formed on the epitaxial growth substrate. Here, the region where the group III nitride selectively grows is determined by the atomic arrangement of the film based on the potential of the atomic arrangement of the epitaxial growth substrate, and the group III nitride epitaxial layer is perpendicular to the epitaxial growth substrate. It is a growing area. On the other hand, the region in which the group III nitride epitaxial layer does not selectively grow is a region in which 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.

【0048】

As described above, the group III nitride is formed on the epitaxial growth substrate formed by mixing the region in which the epitaxial layer of the group III nitride grows selectively and the region in which the epitaxial layer of the group III nitride does not selectively grow. When the epitaxial growth of the epitaxial layer is started, the group III nitride crystal grows in the region of selective growth on the epitaxial growth substrate in the direction perpendicular to the epitaxial growth substrate, and gradually grows laterally on the region where it does not grow selectively. It also begins to grow, and eventually covers the surface of the substrate for epitaxial growth. The part of the group III nitride epitaxial layer grown in the vertical direction has the same defect density as the crystal grown directly on the entire epitaxial growth substrate, but the part of the group III nitride epitaxial layer grown in the lateral direction has defects. Does not penetrate the crystal surface, and the defect density on the crystal surface is lower than that of the site of the group III nitride epitaxial layer growing in the vertical direction. However, when the epitaxial growth substrate and the group III nitride epitaxial layer are made of different materials, stress is generated between the epitaxial growth substrate and the group III nitride epitaxial layer due to the influence of the difference in the coefficient of thermal expansion and the like. ..

【0049】

In the embodiment of the present invention, this stress is relieved by separating the substrate for epitaxial growth and the group III nitride epitaxial layer. Note that the separation referred to here does not only mean physically dividing into two components (that is, removing the epitaxial layer of group III nitride from the substrate), but also mechanically such as stress relaxation by different interfaces. It includes separation in a certain sense, and does not depend on whether or not the substrate for epitaxial growth and the group III nitride epitaxial layer are integrated as a form. Further, the mechanism for separation may be expressed at any timing such as during growth, after growth, and during annealing.

【0050】

According to the embodiment of the present invention, the epitaxial growth substrate and the group III nitride epitaxial layer are separated from each other, so that the epitaxial growth substrate and the group III nitride epitaxial layer are separated from each other due to the influence of the difference in the coefficient of thermal expansion and the like. The stress is released, and problems caused by stress such as warpage of the epitaxial growth substrate can be eliminated.

【0051】

FIG. 1 is a diagram showing a specific manufacturing process example of the semiconductor substrate according to the embodiment of the present invention. Referring to FIG. 1, first, Al₂O₃Prepare the substrate 101 (Fig. 1 (a)). Although the c-plane is used as the orientation of the substrate 101, other plane orientations may be used.

【0052】

Next, a GaN low-temperature barfer layer (not shown) is laminated on the substrate 101 by the MOCVD method, and then a Si-doped n-GaN film 102 (thickness: 1 μm) is formed (FIG. 1 (b)). Then, SiO on the n-GaN film 102₂A mask layer 103 (layer thickness 1.5 μm) is formed (Fig. 1 (c)).

【0053】

After that, a photoresist 104 is applied, and a desired pattern is patterned by photolithography (Fig. 1 (d)). Then, SiO is added with buffered hydrofluoric acid.₂The mask layer 103 is etched (Fig. 1 (e)).

【0054】

After that, SiO is used by the MOCVD method.₂A Si-doped n-GaN epitaxial layer 105 (layer thickness 1 μm) is selectively grown in the mask opening 110, and an InN layer 106 (layer thickness 200 nm) is subsequently formed (Fig. 1 (f)). In this way, a substrate for epitaxial growth is produced.

【0055】

After that, the Si-doped n-GaN epitaxial layer 107 is selectively grown by the MOCVD method to cover the mask opening surface, and the Si-doped n-GaN epitaxial layer 107 is grown in the lateral direction (Fig. 1 (g)).

【0056】

Further, by continuing the selective growth, the GaN epitaxial layers 107 of the entire substrate are coalesced, and the coalesced GaN epitaxial layers 107 form a single GaN substrate 108 (FIG. 1 (h)).

【0057】

After that, it is annealed at a temperature at which the InN layer 106 decomposes in a nitrogen atmosphere. GaN layer 108 / SiO due to thermal stress generated during cooling from annealing temperature₂Stress relaxation occurs selectively at the dissimilar interface of the mask layer 103, and a GaN substrate 108 grown on a dissimilar substrate without warpage is obtained (Fig. 1 (i)).

【0058】

As described above, in the production process example of FIG. 1, the group III nitride epitaxial layer grown in the region where the group III nitride epitaxial layer of the epitaxial growth substrate selectively grows and the epitaxial growth substrate are separated, and the epitaxial growth is performed. By providing a structure for separation between the substrate and the group III nitride epitaxial layer, it is possible to form the group III nitride epitaxial layer on the dissimilar material substrate between the dissimilar material substrates, which has been a problem in the past. It is possible to relax the stress due to the difference in the coefficient of thermal expansion of the above, reduce the strain due to the stress, and provide a high-quality and large-area group III nitride semiconductor substrate. That is, by reducing the residual strain, a large-area crystallized group III nitride semiconductor substrate without warpage or cracks can be obtained, and a high-quality group III nitride semiconductor substrate in which behaviors such as dislocation progress and proliferation are alleviated can be obtained. Is obtained.

【0059】

The details of the structure and process such as the layer structure and the composition of each layer are not limited to the above examples, and other structures and processes such as separation by a superlattice structure can be adopted as described later. is there.

【0060】

Further, in the above example, the GaN-based thin film was formed by the MOCVD method, but if the MBE method is used, not only the GaN-based thin film but also all layers and film configurations can be formed, and the HVPE method, By using the sublimation method, it is possible to form the composition of the layers and films after the InN layer 106. The material of the mask layer 103 is also SiO.₂Not limited to membranes, SiN_XA membrane or the like can be used.

【0061】

Further, the above-mentioned manufacturing process example is not limited to the GaN-based semiconductor substrate, and can be applied to all the fabrication of substrates in a system having a large difference in thermal expansion coefficient.

【0062】

Further, in the annealing steps of FIGS. 1 (h) and 1 (i), the GaN substrate 108 may not be separated after the annealing step depending on the annealing conditions, but even in this case, etching is performed on the mask layer 103. The GaN substrate 108 can be separated by the above method, and the present invention is also applicable in this case.

【0063】

Further, in the manufacturing method of the embodiment of the present invention described above, a superlattice structure can be used for separating the epitaxial growth substrate and the group III nitride epitaxial layer growing on the epitaxial growth substrate. The superlattice structure is constructed by superimposing different materials of thin films, and the different interfaces exhibit stress relaxation behavior for smaller shear stresses than in the same crystal. Therefore, the stress due to the lattice mismatch between the epitaxial growth substrate and the group III nitride epitaxial layer and the difference in the coefficient of thermal expansion is selectively relaxed at the heterogeneous interface between the mask material and the epitaxial layer and the heterogeneous interface of the superlattice structure. To do.

【0064】

FIG. 2 is a diagram showing an example of a manufacturing process of a semiconductor substrate when a superlattice structure is used for separating the epitaxial growth substrate and the group III nitride epitaxial layer growing on the epitaxial growth substrate. Referring to FIG. 2, first, Al₂O₃The board 201 is prepared (Fig. 2 (a)). Although the c-plane is used as the orientation of the substrate 201, other plane orientations may be used.

【0065】

Next, a GaN low-temperature barfer layer (not shown) is laminated on the substrate 201 by the MOCVD method, and then a Si-doped n-GaN film 202 (thickness: 1 μm) is formed (FIG. 2 (b)). Then, SiO on the n-GaN film 202₂A mask layer 203 (layer thickness 1.5 μm) is formed (Fig. 2 (c)).

【0066】

After that, the photoresist 204 is applied, and the desired pattern is patterned by photolithography (Fig. 2 (d)). Then, SiO is added with buffered hydrofluoric acid.₂The mask layer 203 is etched (Fig. 2 (e)).

【0067】

After that, SiO is used by the MOCVD method.₂A Si-doped n-GaN epitaxial layer 205 (layer thickness: 1 μm) is selectively grown in the mask opening 210, whereby a substrate for epitaxial growth is produced.

【0068】

After that, a superlattice structure 206 of InGaN (thickness 20 nm) / GaN (thickness 20 nm) is formed (Fig. 2 (f)).

【0069】

After that, the Si-doped n-GaN epitaxial layer 207 is selectively grown by the MOCVD method to cover the mask opening surface, and the Si-doped n-GaN epitaxial layer 207 is grown in the lateral direction (Fig. 2 (g)).

【0070】

Further, by continuing the selective growth, the GaN epitaxial layer 207 of the entire substrate is coalesced, and the coalesced GaN epitaxial layer 207 forms a single GaN substrate 208 (FIG. 2 (h)).

【0071】

In this case, the thermal stress generated during cooling from the growth temperature causes the GaN layer 208 / SiO.₂Stress relaxation occurs selectively at the interface with the mask layer 203 and at the heterogeneous interface of the InGaN / GaN superlattice structure 206, and a GaN substrate 208 on a heterogeneous substrate without warpage can be obtained.

【0072】

As described above, in the production process example of FIG. 2, the epitaxial growth substrate and the group III nitride epitaxial layer (207,208) growing on the epitaxial growth substrate are lattice-mismatched, and the epitaxial growth substrate and the group III nitride are formed. Since the epitaxial layer (207,208) is separated by the super lattice structure 206, a high-quality and large-area group III nitride semiconductor substrate can be provided. That is, when manufacturing a substrate with a lattice strain type material, high-density dislocations caused by lattice strain are reduced by selective growth, and the stress due to the difference in the coefficient of thermal expansion from the epitaxial growth substrate is reduced between the epitaxial growth substrate and Group III. It can be reduced by selective lattice relaxation between different materials of the super lattice structure provided between the nitride epitaxial layer. The lattice relaxation by the superlattice structure works to relieve the shear stress parallel to the layer surface of the superlattice structure during and after the growth. This direction is the direction in which the stress generated by the lattice strain acts, and also the direction in which the stress acts due to the difference in the coefficient of thermal expansion. Therefore, by designing the superlattice structure so that it exhibits lattice relaxation behavior with respect to smaller shear stress, it is possible to obtain a high-quality and large-area semiconductor crystal with smaller residual strain, that is, a group III nitride semiconductor substrate. it can.

【0073】

The details of the structure and the process such as the layer structure and the composition of each layer are not limited to the above examples, and other structures and processes can be adopted.

【0074】

Further, in the above example, the GaN-based thin film was formed by the MOCVD method, but if the MBE method is used, not only the GaN-based thin film but all the layers and film configurations can be formed, and the HVPE method and the sublimation method can be used. Can be used to form layers and films after the superlattice structure 206. The material of the mask layer 203 is also SiO.₂Not limited to membranes, SiN_XA membrane or the like can be used.

【0075】

Further, the above-mentioned manufacturing process example is not limited to the GaN-based semiconductor substrate, and can be applied to the general fabrication of a lattice-mismatched substrate.

【0076】

Further, in the above-mentioned method for producing a semiconductor substrate for separation by a superlattice structure, the film forming method until the superlattice structure is produced and the film forming method after the superlattice structure is produced can be different. That is, in the above-mentioned manufacturing process, it is considered that the MOCVD method and the MBE method, in which the growth conditions are relatively slow in the manufacturing process up to the superlattice structure and the thickness of each layer can be easily controlled, are suitable. However, after the superlattice structure is produced, a semiconductor substrate can be produced at a lower cost by adopting an inexpensive film forming method having a high film forming speed.

【0077】

FIG. 3 is a diagram showing an example of a semiconductor substrate manufacturing process in which the film forming method until the superlattice structure is manufactured and the film forming method after the superlattice structure is manufactured are different.

【0078】

Referring to FIG. 3, first, Al₂O₃Prepare the substrate 301 (Fig. 3 (a)). Although the c-plane is used as the orientation of the substrate 301, other plane orientations may be used. Next, a GaN low-temperature barfer layer (not shown) is laminated on the substrate 301 by the MOCVD method, and then a Si-doped n-GaN film 302 (thickness is 1 μm) is formed (FIG. 3 (b)). Then SiN on the n-GaN film 302_xA mask layer 303 (thickness 1.5 μm) is formed (Fig. 3 (c)).

【0079】

After that, photoresist 304 is applied and the desired pattern is patterned by photolithography (Fig. 3 (d)). Then CF using RIE₄By SiN_xThe mask layer 303 is etched (Fig. 3 (e)).

【0080】

After that, SiO is used by the MOCVD method.₂A Si-doped n-GaN epitaxial layer 305 (1 μm) is selectively grown in the mask opening 310, whereby a substrate for epitaxial growth is produced.

【0081】

After that, a superlattice structure 306 of InGaN (thickness 20 nm) / GaN (thickness 20 nm) is formed (Fig. 3 (f)).

【0082】

After that, the Si-doped n-GaN epitaxial layer 307 is selectively grown by the MOCVD method, the mask opening surface is covered, and the Si-doped n-GaN epitaxial layer 307 is grown in the lateral direction (Fig. 3 (g)).

【0083】

After that, the Si-doped n-GaN epitaxial layer 307 is grown at high speed by the HVPE method at a rate of about 100 μm / h to form a single GaN substrate 308 (Fig. 3 (h)).

【0084】

As described above, in the production process example of FIG. 3, the film formation method until the superlattice structure is produced is different from the film formation method after the superlattice structure is produced (the process until the superlattice structure is produced). By a method that has a slow growth rate and easy control of the film thickness, and by forming a superlattice structure after the film is formed by an inexpensive film formation method that has a faster film formation rate), high quality. Moreover, a large-area semiconductor crystal, that is, a group III nitride semiconductor substrate can be obtained at a lower cost.

【0085】

The details of the structure and the process such as the layer structure and the composition of each layer are not limited to the above examples, and other structures and processes can be adopted. For example, in the flux method, the morphology of the crystal can be controlled by controlling the growth conditions, and a plate-shaped crystal can be obtained. Therefore, the density of the mask opening 310 per unit area is reduced as in the above example. As a result, a GaN-based substrate 308 on a dissimilar substrate with easier stress relaxation can be obtained.

【0086】

Further, as a film forming method after producing the superlattice structure 306, it is also possible to use another growth method having a high crystal growth rate.

【0087】

Further, in the above example, the GaN-based thin film was formed by the MOCVD method, but it can also be formed by the MBE method.

【0088】

In the semiconductor substrate of the present invention, as described above, the epitaxial growth substrate and the group III nitride epitaxial layer grown on the epitaxial growth substrate are separated. Here, the separation represents a separation in a mechanical sense such as stress relaxation due to a different interface. That is, the stress between the epitaxial growth substrate and the group III nitride epitaxial layer is relaxed, and the introduction of dislocations due to warpage and stress is eliminated. However, since the group III nitride epitaxial layer is not removed from the substrate, the group III nitride epitaxial layer and the epitaxial growth substrate can be handled as one, and in this case, the entire epitaxial growth substrate is used. It is possible to secure the strength of.

【0089】

That is, when the group III nitride epitaxial layer and the epitaxial growth substrate are integrated, the semiconductor substrate can be easily handled in the crystal growth step and the device manufacturing step, and a large-area, low-cost semiconductor without warpage. A substrate can be provided. That is, after the group III nitride epitaxial layer is grown, the group III nitride epitaxial layer in a state where the lattice is relaxed and the strain is reduced and the epitaxial growth substrate are left as one, so that a large-area substrate without warpage can be obtained. At the same time, the substrate for epitaxial growth can be used as a support substrate for the group III nitride epitaxial layer during the device forming process, which facilitates handling. Further, the presence of the support substrate makes it possible to reduce the thickness of the group III nitride epitaxial layer, and a lower cost semiconductor substrate can be obtained.

【0090】

On the contrary, the group III nitride epitaxial layer can be removed from the epitaxial growth substrate to form a semiconductor substrate. In this case, the semiconductor substrate has a configuration in which a thick group III nitride epitaxial layer is selectively grown on the epitaxial growth substrate, and the epitaxial growth substrate and the group III nitride epitaxial layer are separated. In this case, the term "separation" means, in addition to the above-mentioned separation for stress relaxation at different interfaces, due to the rigidity of the thick film group III nitride epitaxial layer itself after being removed from the epitaxial growth substrate. This means that the nitride epitaxial layer alone is used as a semiconductor substrate.

【0091】

By removing the group III nitride epitaxial layer from the epitaxial growth substrate to form a semiconductor substrate in this way, the epitaxial growth substrate and the group III nitride epitaxial layer are physically separated, stress is relaxed, and a large area is obtained. Group III nitride semiconductor substrate is obtained. Further, since the lattice relaxation progresses in the entire epitaxial growth substrate and the group III nitride epitaxial layer, the group III nitride epitaxial layer can be easily removed from the epitaxial growth substrate. This makes it possible to provide a high-quality, large-area GaN-based semiconductor substrate.

【0092】

In the semiconductor substrates of each of the above examples, the group III nitride epitaxial layer can be composed of group III nitride containing at least Ga, and the superlattice structure is composed of Ga, In, Al nitrides or mixed crystals thereof. it can.

【0093】

FIG. 4 shows a manufacturing process of a semiconductor substrate when the group III nitride epitaxial layer is composed of a group III nitride containing at least Ga and the superlattice structure is composed of Ga, In, Al nitrides or a mixed crystal thereof. It is a figure which shows an example.

【0094】

Referring to FIG. 4, first, Al₂O₃Prepare the board 401 (Fig. 4 (a)). Although the c-plane is used as the orientation of the substrate 401, other plane orientations may be used.

【0095】

Next, a GaN low-temperature barfer layer (not shown) is laminated on the substrate 401 by the MOCVD method, and then a Si-doped n-GaN film 402 (thickness: 1 μm) is formed (FIG. 4 (b)). Then, SiO on the n-GaN film 402₂A mask layer 403 (layer thickness 1.5 μm) is formed (Fig. 4 (c)).

【0096】

After that, photoresist 404 is applied, and the desired pattern is patterned by photolithography (Fig. 4 (d)). Then, SiO is added with buffered hydrofluoric acid.₂The mask layer 403 is etched (Fig. 4 (e)).

【0097】

After that, SiO is used by the MOCVD method.₂A Si-doped n-GaN epitaxial layer 405 (layer thickness: 1 μm) is selectively grown in the mask opening 410, whereby a substrate for epitaxial growth is produced.

【0098】

After that, a superlattice structure 406 of AlGaN (thickness 10 nm) / GaN (thickness 20 nm) is formed (Fig. 4 (f)).

【0099】

After that, the Si-doped n-GaN epitaxial layer 407 is selectively grown by the MOCVD method, the mask opening surface is covered, and the Si-doped n-GaN epitaxial layer 407 is grown in the lateral direction (Fig. 4 (g)).

【0100】

Further, by continuing the selective growth, the GaN epitaxial layers 407 of the entire substrate are coalesced, and the coalesced GaN epitaxial layers 407 form a single GaN substrate 408 (Fig. 4 (h)).

【0101】

In this case, the thermal stress generated during cooling from the growth temperature causes the GaN layer 408 / SiO.₂Stress relaxation occurs selectively at the interface with the mask layer 403 and at the heterogeneous interface of the AlGaN / GaN superlattice structure 406, and a GaN substrate 408 on a heterogeneous substrate without warpage can be obtained.

【0102】

As described above, the group III nitride epitaxial layer may be composed of a nitride containing at least Ga, and the superlattice structure may be composed of Ga, In, Al nitrides or a mixed crystal thereof. In this case, a GaN-based material. High quality and large area substrate can be obtained. That is, by changing the layer structure including the composition of the superlattice structure, a high-quality and large-area substrate can be obtained even for a substrate containing Al.

【0103】

The details of the structure and the process such as the layer structure and the composition of each layer are not limited to the above examples, and other structures and processes can be adopted.

【0104】

Further, in the above example, the GaN-based thin film was formed by the MOCVD method, but if the MBE method is used, not only the GaN-based thin film but also all layers and film configurations can be formed, and the HVPE method and sublimation can be formed. By using the method, it is possible to form the structure of layers and films after the superlattice structure. The material of the mask layer is also SiO₂Not limited to membranes, SiN_XA membrane or the like can be used.

【0105】

The present invention is applicable to all GaN-based substrates. Regarding the configuration of the AlGaN / GaN superlattice, by increasing the Al composition and increasing the strain, lattice relaxation can be promoted with a smaller shear stress.

【0106】

Further, the light emitting element can be formed on the semiconductor substrate of the present invention produced by each of the above-mentioned production process examples. In this case, the present invention is not limited to the structure and manufacturing method of the light emitting device.

【0107】

In the light emitting element manufactured on the semiconductor substrate, the life of the light emitting element can be extended and the cost can be reduced by the large area semiconductor substrate having a low crystal defect density and no warp. Further, when a group III nitride epitaxial layer removed from the epitaxial growth substrate is used as a semiconductor substrate, since this semiconductor substrate has conductivity, an electrode can be formed on the back surface, and face-down mounting is performed. Therefore, it is possible to provide a semiconductor laser having excellent heat dissipation and a long life at low cost.

【0108】

[Effect of the invention]

As described above, according to the inventions of claims 1 to 7, there are a region in which the group III nitride epitaxial layer selectively grows and a region in which the group III nitride epitaxial layer does not selectively grow. A method for producing a semiconductor substrate by forming a Group III nitride epitaxial layer on a mixedly formed substrate for epitaxial growth, and the Group III nitride epitaxial layer of the epitaxial growth substrate is selected. The Group III nitride epitaxial layer and the epitaxial growth substrate that have grown in the region of growth are separated, and by providing a structure for separation between the epitaxial growth substrate and the Group III nitride epitaxial layer, different types are provided. It is possible to alleviate the stress due to the difference in thermal expansion coefficient between the material substrate and the dissimilar material substrate, which has been a problem in the past when forming the Group III nitride epitaxial layer on the material substrate, and reduce the strain due to the stress. As a result, a high-quality, large-area Group III nitride semiconductor substrate can be provided. That is, by reducing the residual strain, a large-area crystallized group III nitride semiconductor substrate without warpage or cracks can be obtained, and a high-quality group III nitride semiconductor substrate in which behaviors such as dislocation progress and proliferation are alleviated can be obtained. Is obtained.

【0109】

In particular, according to the invention of claim 2, in the method for manufacturing a semiconductor substrate according to claim 1, the epitaxial growth substrate and the group III nitride epitaxial layer growing on the epitaxial growth substrate are lattice-mismatched. In addition, the epitaxial growth substrate substrate and the group III nitride epitaxial layer are produced so as to be separated by a superlattice structure in the region where the group III nitride epitaxial layer of the epitaxial growth substrate is selectively grown. It is possible to provide a high-quality and large-area group III nitride semiconductor substrate. That is, when manufacturing a substrate with a lattice strain type material, high-density dislocations caused by lattice strain are reduced by selective growth, and the stress due to the difference in the coefficient of thermal expansion from the epitaxial growth substrate is reduced between the epitaxial growth substrate and Group III. It can be reduced by selective lattice relaxation between different materials of the super lattice structure provided between the nitride epitaxial layers. The lattice relaxation by the superlattice structure works to relieve the shear stress parallel to the layer surface of the superlattice structure during and after the growth. This direction is the direction in which the stress generated by the lattice strain acts, and also the direction in which the stress acts due to the difference in the coefficient of thermal expansion. Therefore, by designing the superlattice structure so that it exhibits lattice relaxation behavior with respect to smaller shear stress, it is possible to obtain a high-quality and large-area semiconductor crystal with smaller residual strain, that is, a group III nitride semiconductor substrate. it can.

【0110】

Further, according to the invention of claim 3, the film forming method until the superlattice structure is produced and the film forming method after the superlattice structure is produced are different (the process until the superlattice structure is produced is grown). The film is formed by a method that is slow and the film thickness can be easily controlled, and the film formation after the superlattice structure is formed is formed by an inexpensive film formation method that has a faster film formation rate), and is of high quality and large. A semiconductor crystal having an area, that is, a group III nitride semiconductor substrate can be obtained at a lower cost.

【0111】

Further, according to the invention of claim 4, since the group III nitride epitaxial layer and the epitaxial growth substrate are integrated, the semiconductor substrate can be easily handled in the crystal growth step and the device manufacturing step, and the semiconductor substrate is warped. It is possible to provide a low-cost semiconductor substrate having a large area. That is, after the group III nitride epitaxial layer is grown, the group III nitride epitaxial layer in a state where the lattice is relaxed and the strain is reduced and the epitaxial growth substrate are left as one, so that a large-area substrate without warpage can be obtained. At the same time, the substrate for epitaxial growth can be used as a support substrate for the group III nitride epitaxial layer during the device forming process, which facilitates handling. Further, the presence of the support substrate makes it possible to reduce the thickness of the group III nitride epitaxial layer, and a lower cost semiconductor substrate can be obtained.

【0112】

Further, according to the invention of claim 5, by removing the group III nitride epitaxial layer from the epitaxial growth substrate to form a semiconductor substrate, the epitaxial growth substrate and the group III nitride epitaxial layer are physically separated. The stress is relaxed and a large area III-nitride semiconductor substrate is obtained. Further, since the lattice relaxation progresses in the entire epitaxial growth substrate and the group III nitride epitaxial layer, the group III nitride epitaxial layer can be easily removed from the epitaxial growth substrate. This makes it possible to provide a high-quality, large-area group III nitride semiconductor substrate.

【0113】

Further, according to the invention of claim 6, the group III nitride epitaxial layer is composed of a nitride containing at least Ga, and the superlattice structure is composed of Ga, In, Al nitrides or a mixed crystal thereof. , A high-quality, large-area substrate made of GaN-based material can be obtained. Further, by changing the layer structure including the composition of the superlattice structure, a high-quality and large-area substrate can be obtained for the substrate containing Al.

【0114】

Further, according to the invention of claim 8, since the light emitting element is formed on the semiconductor substrate of claim 7, it is possible to provide a light emitting element having excellent heat dissipation and a long life (for example, a semiconductor laser) at low cost. can do. That is, in the semiconductor substrate used, the dislocation density due to selective growth is reduced, and the stress caused by the difference in thermal expansion rate between the epitaxial growth substrate and the group III nitride epitaxial layer is stressed by the epitaxial growth substrate and group III nitride. By separating the material epitaxial layer, the residual stress is relaxed, crystal defects generated by the stress are reduced, and the area of the semiconductor substrate can be increased. In the light emitting element manufactured on the semiconductor substrate, the life of the light emitting element can be extended and the cost can be reduced by the large area semiconductor substrate having a low crystal defect density and no warp. Further, when a group III nitride epitaxial layer removed from the epitaxial growth substrate is used as the semiconductor substrate, the semiconductor substrate can form electrodes on the back surface and can be face-down mounted, so that heat can be dissipated. It is possible to provide a semiconductor light emitting device having excellent properties and a long life at low cost.

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the example of the manufacturing process of the semiconductor substrate which concerns on this invention.

[Figure 2]

It is a figure which shows the example of the manufacturing process of the semiconductor substrate when the superlattice structure is used for the separation of the substrate for epitaxial growth and the group III nitride epitaxial layer which grows on the substrate for epitaxial growth.

[Fig. 3]

It is a figure which shows the example of the manufacturing process of the semiconductor substrate in the case where the film forming method until the superlattice structure is manufactured and the film forming method after the superlattice structure are manufactured are different.

[Fig. 4]

It is a figure which shows the example of the manufacturing process of the semiconductor substrate when the superlattice structure is used for the separation of the substrate for epitaxial growth and the group III nitride epitaxial layer which grows on the substrate for epitaxial growth.

[Fig. 5]

It is a figure for demonstrating the manufacturing method of the conventional semiconductor substrate.

[Fig. 6]

It is a figure which shows the conventional semiconductor laser.

[Explanation of symbols]

101 Al₂O₃substrate 102 Si-doped n-GaN film 103 SiO₂Mask layer 104 Photoresist 105 Si-doped n-GaN epitaxial layer 106 In N layer 107 Si-doped n-GaN epitaxial layer 108 GaN substrate 201 Al₂O₃substrate 202 Si-doped n-GaN film 203 SiO₂Mask layer 204 photoresist 205 Si-doped n-GaN epitaxial layer 206 Superlattice structure 207 Si-doped n-GaN epitaxial layer 208 GaN substrate 301 Al₂O₃substrate 302 Si-doped n-GaN film 303SiO_xMask layer 304 photoresist 305 Si-doped n-GaN epitaxial layer 306 Superlattice structure 307 Si-doped n-GaN epitaxial layer 308 GaN substrate 401 Al₂O₃substrate 402 Si-doped n-GaN film 403 SiO₂Mask layer 404 photoresist 405 Si-doped n-GaN epitaxial layer 406 Superlattice structure 407 Si-doped n-GaN epitaxial layer 408 GaN substrate