JP2005005723A - Nitride semiconductor epitaxial wafer manufacturing method and nitride semiconductor epitaxial wafer - Google Patents

Abstract

A method for manufacturing a nitride semiconductor epitaxial wafer and a nitride semiconductor epitaxial wafer with which a large-area nitride semiconductor epitaxial is obtained with few crystal defects, warpage, and cracks are provided.
An intermediate layer 2 obtained by implanting ions of hydrogen, nitrogen, oxygen or the like in the vicinity of the surface of a sapphire substrate 1 has an amorphous structure. To reduce. The intermediate layer 2 is heated during the growth of the nitride semiconductor layer 3 to generate voids. Voids have high strain absorption and relaxation effects, reduce cracks and warpage, and reduce crystal relaxation. Since the substrate surface is the heterogeneous substrate 1, the strain absorption effect of the void-containing intermediate layer 2 is increased, and a high-quality and large-diameter nitride semiconductor epitaxial wafer can be obtained.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a nitride semiconductor epitaxial wafer and a nitride semiconductor epitaxial wafer.

  In recent years, the band gap is large (3.4 eV), direct transition type, and the band gap is controlled over a wide range in order to increase the output and efficiency of light emitting diodes (LEDs) and laser diodes (LDs). For this reason, nitride semiconductors have been used.

  By the way, GaN or its mixed crystals such as AlGaN and InGaN do not have practically the same type of substrates, and therefore crystal growth is performed on different types of substrates such as sapphire and SiC. These dissimilar substrates have many crystal defects in the growth layer because the lattice constant is significantly different from that of the growth layer. Further, since the expansion coefficients are greatly different, warping and cracking occur during or after the thick film growth. These warpages and cracks are particularly serious problems when growing a nitride semiconductor thick film.

  Therefore, development of a GaN substrate has been underway in order to fundamentally solve such problems, and a high-temperature high-pressure method (S. Porowski et al, J. Cryst. Growth 178 ( 1997) p174) and a method of obtaining a GaN free-standing single crystal substrate by growing a thick film of about several hundreds μm on a sapphire substrate by HVPE method and then removing the sapphire substrate (Michael K. Kelly et al, Jpn. J. Appl.Phys.38 (1999) Pt.2, No.3A, pp.L217) and the like are typical.

  However, in the high-temperature and high-pressure method, since crystal growth is performed in an ultra-high pressure cell, the size of the obtained GaN single crystal cannot be increased so much, and currently only a diameter of about 10 mm is obtained. In addition, the manufacturing costs are very high and not practical. Although a method of growing a GaN thick film directly on a sapphire substrate by HVPE (hydride vapor phase epitaxy) is more realistic, there are still many crystal defects in this case, and practical removal of the sapphire substrate is practical. There is no way. Moreover, there is a problem that the GaN thick film remains warped after removal.

  During epitaxial growth of nitride semiconductors, warpage of the sapphire substrate causes non-uniform contact with a heated object such as a graphite susceptor during the epitaxial growth of nitride semiconductors, and the characteristics such as carrier concentration and composition of the growth layer are not uniform. Make uniform. In particular, this concentration non-uniformity is fatal in InGaN. Further, warping of the sapphire substrate after growth becomes a serious problem in exposure of a fine pattern in photolithography.

  In addition, the crystal defect deteriorates the light emission characteristics and reliability of the optical element, and causes leakage current, nonlinearity, and deterioration of reliability of the electronic device.

As countermeasures, the ELO method using lateral growth by selective growth (OH Nam et al, Appl. Phys. Lett. 71 (1997) 2472) or the FIELO method (A. Sakai et al, Appl. Phys. Lett. 71 (1997) 2259) and the like have been developed, but there are still crystal defects of about 10 ⁶ to 10 ⁷ cm ⁻³ , and the problem of warping has not been improved at all.

  On the other hand, with respect to a method for reducing the warpage, for example, as disclosed in JP-A-9-223819, a relaxation layer / peeling layer is formed by ion implantation of oxygen or nitrogen below the surface of the Si substrate. There is a method in which a nitride semiconductor is grown on a Si substrate that is carbonized to form SiC, and the Si substrate is removed by subsequent etching.

  However, in this method, in order to reduce the stress on the nitride semiconductor, the balance of the thickness of the Si substrate and the SiC layer, AlGaN buffer layer, and nitride semiconductor layer structure formed on the Si substrate must be precisely controlled. Don't be. In particular, when a nitride semiconductor layer formed by nitrogen implantation is used as a strain relaxation layer, a Si layer must be left between the SiC layer and the strain relaxation layer in order to remove the Si substrate by etching. Since the conditions are severe and the strain relaxation layer is far from the nitride semiconductor growth layer, the strain relaxation effect is reduced. In addition, it is difficult to carry out surface carbonization so as to completely cover the substrate surface in consideration of mass production.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems and provide a method for manufacturing a nitride semiconductor epitaxial wafer and a nitride semiconductor epitaxial wafer with less crystal defects and less warpage and cracks.

  Furthermore, an object of the present invention is to provide a nitride semiconductor epitaxial wafer manufacturing method and a nitride semiconductor epitaxial wafer that solve the above-mentioned problems and that can obtain a nitride semiconductor epitaxial having a large area with few crystal defects, warpage, and cracks. It is in.

  In order to achieve the above object, the nitride semiconductor epitaxial wafer manufacturing method of the present invention forms an intermediate layer having a lower mechanical strength than the sapphire substrate in the vicinity of the surface of the sapphire substrate, and on the sapphire substrate on which the intermediate layer is formed. A nitride semiconductor layer for devices is epitaxially grown.

  In the nitride semiconductor epitaxial wafer manufacturing method of the present invention in addition to the above configuration, the thickness of the nitride semiconductor layer for devices is preferably 10 μm or less.

  In addition to the above configuration, the method for manufacturing a nitride semiconductor epitaxial wafer of the present invention preferably forms the intermediate layer by implanting ions from the surface of the sapphire substrate to a depth at which the intermediate layer is to be formed.

  In addition to the above configuration, the method for producing a nitride semiconductor epitaxial wafer of the present invention preferably uses at least one of hydrogen ions, nitrogen ions and oxygen ions as ions.

In addition to the above-described configuration, the nitride semiconductor epitaxial wafer manufacturing method of the present invention has an ion implantation acceleration voltage of 1 keV to 1 MeV and an ion dose of 1 × 10 ¹⁵ cm ^{−2 to} 1 × 10 ¹⁹ cm. ^-2 or less is preferable.

  In addition to the above-described structure, the nitride semiconductor epitaxial wafer manufacturing method of the present invention performs ion treatment and then heat treatment to recover the damage caused by ion implantation of the surface crystal layer of the sapphire substrate, and also provides fine voids and The intermediate layer may be formed by generating an aggregate of voids.

In addition to the above-described configuration, the nitride semiconductor epitaxial wafer manufacturing method of the present invention preferably performs the heat treatment in H ₂ or NH ₃ or a mixed atmosphere of both.

  In addition to the above configuration, the method for producing a nitride semiconductor epitaxial wafer of the present invention preferably removes the portion from the intermediate layer to the sapphire substrate by peeling off the intermediate layer as a boundary.

  In addition to the above-described structure, the method for manufacturing a nitride semiconductor epitaxial wafer of the present invention peels off the portion from the intermediate layer to the sapphire substrate after attaching another substrate to the surface of the nitride semiconductor layer for devices. , May be removed.

  In addition to the above configuration, the nitride semiconductor epitaxial wafer manufacturing method of the present invention may use a semiconductor such as Si, a highly thermally conductive substrate such as AlN, or a metal such as Cu or Al as another substrate.

  In addition to the above configuration, in the method for manufacturing a nitride semiconductor epitaxial wafer of the present invention, a part of the sapphire substrate remaining on the device nitride semiconductor layer from which the sapphire substrate is removed may be removed by a method such as polishing.

Nitride semiconductor epitaxial wafer of the present invention has a composition of the produced by the method according to any _{one, In x Al y Ga 1-} xy N (x, y ≧ 1, x + y ≦ 1).

  According to the present invention, the intermediate layer obtained by implanting ions of hydrogen, nitrogen, oxygen, or the like in the vicinity of the surface of the sapphire substrate different from the nitride semiconductor has an amorphous structure, so it absorbs and relaxes strain, Cracks and warpage are reduced. The intermediate layer into which hydrogen is implanted is heated during the growth of the nitride semiconductor layer, thereby generating voids. Voids have a high strain absorption and relaxation effect, reduce cracks and warpage, and reduce crystal defects. The substrate surface is a sapphire substrate, and the effect of strain absorption and strain relaxation of the intermediate layer with voids is large, so there is no need for cumbersome surface carbonization treatment and precise control of the film thickness balance of multiple layers, and high quality A large-diameter nitride semiconductor epitaxial wafer is obtained.

  As described above, according to the present invention, the following excellent effects are exhibited.

  It is possible to realize a nitride semiconductor epitaxial wafer manufacturing method and a nitride semiconductor epitaxial wafer with few crystal defects and no warpage or cracks.

  Embodiments of the present invention will be described below.

  In the method for producing a nitride semiconductor epitaxial wafer of the present invention, an intermediate layer having a mechanical strength lower than that of the sapphire substrate is formed near the surface of the sapphire substrate, and the nitride semiconductor layer for devices is formed on the sapphire substrate on which the intermediate layer is formed. Is epitaxially grown. The growing layer structure is an epitaxial structure of one or more layers, and may have a semiconductor structure such as a P / N junction or a heterojunction. A layer structure suitable for various semiconductor elements such as a light emitting diode, a laser, a light receiving element, a field effect transistor, HEMT, and HBT, or an epitaxial layer structure constituting a part thereof.

  The intermediate layer is a layer whose mechanical strength is made smaller than that of the sapphire substrate by implanting ions of hydrogen, nitrogen, oxygen, or the like near the surface of the sapphire substrate. By applying heat treatment to the sapphire substrate after ion implantation, a large number of fine voids can be generated in the intermediate layer, and the mechanical strength of the intermediate layer can be further reduced.

  Since this intermediate layer functions as a buffer layer that relieves the difference in thermal expansion between the nitride semiconductor crystal for devices and the sapphire substrate, the cracks and warpage that have been problems in the past are eliminated, and a high-quality nitride semiconductor epitaxial wafer is obtained. can get. Further, the portion up to the sapphire substrate with this intermediate layer as a boundary can be easily peeled off and removed.

  There are various peeling methods such as natural peeling by heating in the crystal film growth process of nitride semiconductor layer for devices, or peeling by subsequent heat treatment, peeling by nitrogen jet from the side, peeling by water jet, peeling by laser irradiation, etc. The method can be used.

  By removing a part of the sapphire substrate slightly remaining on the back surface of the device nitride semiconductor layer after peeling by polishing or the like, a large-diameter flat self-supporting nitride semiconductor epitaxial wafer can be easily obtained.

  The film thickness of the nitride semiconductor layer for devices is preferably 10 μm or less. This is to prevent warping of the sapphire substrate, and when the thickness exceeds this, the substrate warps due to a difference in thermal expansion between the nitride semiconductor and sapphire.

  The acceleration voltage for ion implantation is preferably 1 keV or more and 1 MeV or less. This is because the formation depth of the intermediate layer is made appropriate and the crystal state of the sapphire substrate surface is kept good. Below 1 keV, the position where the intermediate layer is formed is too shallow, which adversely affects the crystallinity of the sapphire substrate surface. On the other hand, at 1 MeV or higher, the damage given to the crystals on the substrate surface by the implanted ions cannot be ignored. In addition, the position where the intermediate layer is formed becomes too deep and the strain buffering effect by the intermediate layer becomes small, or the sapphire remaining on the back surface of the nitride semiconductor crystal for devices after the sapphire substrate peeling becomes thick and polished for removal This is because it takes time.

The dose is preferably 1 × 10 ¹⁵ cm ⁻² or more and 1 × 10 ¹⁹ cm ⁻² or less. This is because warping is relaxed while suppressing damage to crystals on the surface of the sapphire substrate to a negligible range, and voids sufficient for strain buffering and substrate peeling are generated. When the dose amount is 1 × 10 ¹⁵ cm ⁻² or less, the generation density of voids is small, so that the strain buffering effect is small, which is insufficient for peeling off the substrate. On the contrary, if the dose amount is 1 × 10 ¹⁹ cm ⁻² or more, the damage caused by the implanted ions to the crystal on the surface of the sapphire substrate cannot be ignored.

(Example 1)
1A to 1E are process diagrams showing an example of the method for manufacturing a nitride semiconductor substrate of the present invention.

  As a substrate, a sapphire substrate (diameter: about 50 mm, thickness: about 0.33 mm) is prepared (FIG. 1 (a)).

Hydrogen ions are implanted into the sapphire substrate 1. The condition is that the dose is 1 × 10 ¹⁷ cm ⁻² , the acceleration voltage is 100 keV, and the intermediate layer 2 having a thickness of 0.1 μm is formed to a depth of 0.5 μm from the surface of the sapphire substrate 1. A single crystal layer is maintained near the surface 1a of the sapphire substrate 1 into which hydrogen is implanted, and a hydrogen implantation layer, that is, an intermediate layer 2 exists under the single crystal layer 1a (FIG. 1B).

  A GaN single crystal serving as the device nitride semiconductor layer 3 was epitaxially grown by 2 μm on the surface of the sapphire substrate 1a by metal organic vapor phase epitaxy (MOVPE). As the growth furnace, a horizontal normal pressure MOVPE furnace was used, ammonia gas and trimethyl gallium were used as raw materials, and a mixed gas of hydrogen and nitrogen was used as a carrier gas.

  First, the substrate is heated to 1100 ° C. in a hydrogen atmosphere to clean the surface oxide and the like. Subsequently, the substrate temperature is lowered to 550 ° C. to grow GaN by 20 nm, and the substrate temperature is further raised to 1050 ° C. to grow GaN by 2 μm.

  When one of the GaN epitaxial growth substrates taken out from the MOVPE furnace was divided and the cross section was observed with a scanning electron microscope, it was observed that many fine voids were generated in the intermediate layer.

  A GaN single crystal is epitaxially grown 300 μm on the produced GaN epitaxial growth substrate 4 by using the HVPE method. The apparatus uses a horizontal atmospheric HVPE furnace. GaCl obtained by reacting ammonia gas, metal Ga, and HCl gas at 850 ° C. is used as a raw material, and hydrogen gas is used as a carrier gas. The growth temperature is set to 1050 ° C., and the growth rate is set to 80 μm / h (FIG. 1C).

  After the epitaxial growth is completed, a portion from the intermediate layer 2 to the sapphire substrate 1b is naturally separated from the intermediate layer (void layer) 2 in the cooling process from the growth temperature to room temperature (FIG. 1D).

  By polishing and removing the thin sapphire layer 1a remaining on the back surface of the device nitride semiconductor layer 3 made of GaN single crystal, a GaN free-standing single crystal substrate having a diameter of about 50 mm and a thickness of about 300 μm is obtained. It was. This substrate was colorless and transparent and had no cracks or warpage (FIG. 1 (e)).

  In the above-described embodiments, the case where a sapphire substrate is used as a substrate and hydrogen is used as ions to be implanted has been described. However, a substrate other than a sapphire substrate or ions other than hydrogen ions may be used.

  As a method for epitaxial growth of nitride semiconductor, there are various known methods such as MOVPE method, HVPE method, MBE method and the like, which can be used. In addition, a two-stage growth method using a low-temperature buffer layer such as gallium nitride or aluminum nitride, a method of growing directly at a high temperature, an ELO method or a FIELO method for reducing dislocation by lateral growth using microfabrication and regrowth during the growth Various known methods such as these can be used.

  The void layer can be used as the void layer during the temperature rise before the growth of the other nitride semiconductor layers, during the cooling, after the growth, in the whole process, or in several processes. Alternatively, heat treatment may be performed after ion implantation and before the start of growth of another nitride semiconductor layer.

  The method of peeling the sapphire substrate with the intermediate layer as a boundary can be implemented by various methods such as peeling by heat treatment after growth, peeling by nitrogen jet from the side, peeling by water jet, peeling by laser irradiation, and the like.

  Here, conventionally, epitaxial growth of nitride semiconductors has been performed on a substrate such as sapphire having a significantly different thermal expansion coefficient, so that there are many crystal defects, and warping and cracking occur when a thick film is grown. there were. In order to fundamentally solve this problem, a nitride semiconductor substrate has been developed. However, since the production of the nitride semiconductor substrate was performed under an ultra-high pressure, the cost is very high, and only about 10 mm is required. It was not obtained. Further, it is more realistic than a method of obtaining a GaN free-standing substrate by removing a sapphire substrate after a GaN thick film of about several hundred μm is grown on a sapphire substrate by the HVPE method. There have been problems such as warpage and cracks due to the difference in thermal expansion coefficient between the two, and a large number of crystal defects, no practical method for removing the sapphire substrate, and warping remaining after removal.

  However, according to the present invention, since the intermediate layer formed in the substrate by hydrogen implantation and heat treatment functions as a buffer layer that alleviates the difference in thermal expansion coefficient, crystal defects that have been a problem in the past are significantly reduced, A high-quality nitride semiconductor epitaxial wafer in which warpage and cracks are eliminated can be easily obtained. In addition, the nitride semiconductor layer is peeled off from the substrate with the intermediate layer as a boundary, and a large-area and flat self-supporting epitaxial wafer of the nitride semiconductor can be easily obtained.

(A)-(e) is process drawing which shows an example of the manufacturing method of the nitride semiconductor epitaxial wafer of this invention.

Explanation of symbols

1, 1a, 1b Sapphire substrate 2 Intermediate layer 3 Nitride semiconductor layer for device

Claims (12)

A nitride semiconductor epitaxial characterized by forming an intermediate layer having a lower mechanical strength than the sapphire substrate near the surface of the sapphire substrate and epitaxially growing a nitride semiconductor layer for devices on the sapphire substrate on which the intermediate layer is formed. Wafer manufacturing method. The method for producing a nitride semiconductor epitaxial wafer according to claim 1, wherein a thickness of the nitride semiconductor layer for devices is 10 μm or less. The method for producing a nitride semiconductor epitaxial wafer according to claim 1 or 2, wherein the intermediate layer is formed by implanting ions from a surface of the sapphire substrate to a depth at which the intermediate layer is to be formed. The method for producing a nitride semiconductor epitaxial wafer according to claim 3, wherein at least one of hydrogen ions, nitrogen ions, and oxygen ions is used as the ions. The nitride semiconductor epitaxial according to claim 4, wherein an acceleration voltage of the ion implantation is 1 keV or more and 1 MeV or less, and a dose amount of the ions is 1 x 10 ¹⁵ cm ^-2 or more and 1 x 10 ¹⁹ cm ^-2 or less. Wafer manufacturing method. After implanting the ions, heat treatment is performed to recover the damage caused by the ion implantation of the surface crystal layer of the sapphire substrate, and the intermediate layer is formed by generating fine voids and aggregates of voids near the surface. The method for producing a nitride semiconductor epitaxial wafer according to claim 3. The method for producing a nitride semiconductor epitaxial wafer according to claim 6, wherein the heat treatment is performed in an atmosphere of H ₂ or NH ₃ or a mixture of both. The method for producing a nitride semiconductor epitaxial wafer according to any one of claims 1 to 7, wherein a portion from the intermediate layer to the sapphire substrate is removed by peeling off the intermediate layer as a boundary. The nitride semiconductor epitaxial according to claim 8, wherein a part from the intermediate layer to the sapphire substrate is peeled and removed at the boundary of the intermediate layer after another substrate is attached to the surface of the nitride semiconductor layer for devices. Wafer manufacturing method. 10. The method for producing a nitride semiconductor epitaxial wafer according to claim 9, wherein a semiconductor such as Si, a high thermal conductivity substrate such as AlN, or a metal such as Cu or Al is used as the other substrate. 11. The method for producing a nitride semiconductor epitaxial wafer according to claim 8, wherein a part of the sapphire substrate remaining on the device nitride semiconductor layer from which the sapphire substrate has been removed is removed by a method such as polishing. Manufactured by the method according to any one of claims 1 to 11,
_{In x Al y Ga 1-xy} N (x, y ≧ 1, x + y ≦ 1) nitride semiconductor epitaxial wafer characterized by having a composition.

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