JP2006080497A - Compound semiconductor device and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound semiconductor device in which the occurrence of cracking is reduced, even when a plurality of semiconductor layers containing an AlGaN compound layer is made thicker, and to provide a method for manufacturing it. <P>SOLUTION: The compound semiconductor device 10 comprises a sapphire substrate 11, a GaN buffer layer 12 grown on the sapphire substrate 11, a GaN layer 13 grown on the GaN buffer layer 12 and has an irregular surface 13S, an AlN intermediate layer 14 grown on the irregular surface 13S of the GaN layer 13, a Al<SB>X1</SB>Ga<SB>Y1</SB>N compound layer 15 grown on the irregular surface 14S of the AlN intermediate layer 14, and an Al<SB>X2</SB>Ga<SB>Y2</SB>N compound layer 16, which is grown on the Al<SB>X1</SB>Ga<SB>Y1</SB>N compound layer 15 and satisfies the relational expression X1>X2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a compound semiconductor device including a plurality of layers grown on a sapphire substrate, and a method for manufacturing the compound semiconductor device.

As a crystal material for an ultraviolet semiconductor laser element, an AlGaN-based compound material is known. A single crystal sapphire substrate is usually used as the substrate of this material. For example, there is a method in which a semiconductor layer is formed by stacking a plurality of semiconductor layers made of Al _X Ga _Y In _1- XYN and having the composition changed stepwise between the substrate and the n contact layer. It has been reported (Patent Document 1).

As shown in FIG. 1, there is a method in which a GaN layer 13 is grown on the substrate 11 via a buffer layer 12 and an Al _X2 Ga _Y2 N-based compound layer 16 is grown thereon. As a result, the Al _X2 Ga _Y2 N-based compound layer 16 has an improved X-ray rocking curve half width (XRC FWHM), but there is a problem that cracks are generated due to tensile strain caused by lattice mismatch with the GaN layer 13. is there.

As a method for solving these problems, a method of growing an Al _X2 Ga _Y2 N-based compound layer 16 having a crack-free and good crystal quality has been reported (Non-Patent Documents 1 to 6). As shown in FIG. 2, a GaN layer 13 is grown on a sapphire substrate 11 via a buffer layer 12, an AlN intermediate layer 14 is grown thereon, and an Al _X2 Ga _Y2 N-based compound is further formed thereon. This is a method of growing the layer 16. As a result, the Al _X2 Ga _Y2 N-based compound layer 16 becomes crack-free, and a plurality of semiconductor layers can be further grown thereon.

In the structure shown in FIG. 2, in order to reduce the dislocation density, after etching the GaN layer 13 on the sapphire substrate 11 in the periodic stripes, the AlN intermediate layer 14 is grown and the Al thereon _X2 It has been reported that a Ga _Y2 N-based compound layer 16 is embedded and grown, whereby a reduction in dislocation density can be realized (see Patent Document 2).
JP 2001-230447 A JP 2002-16209 A M. Iwaya et al, 5th International Conference onNitride Semiconductor (ICNS-5), Technical Digest, Tu-P2.080 H. Amano et al., "IMPROVEMENT OF CRYSTALLINEQUALITY OF GROUP III NITRIDES ON SAPPHIRE USING LOW TEMPERATUREINTERLAYERS", MRS Internet J. Nitride Semicond. Res. 4S1, G10.1 (1999). M. Iwaya et al., "HIGH-QUALITYAlxGa1-xN USING LOW TEMPERATURE-INTERLAYER AND ITS APPLICATION TO UVDETECTOR", MRS Internet J. Nitride Semicond. Res. 5S1, W1.10 (2000). M. Iwaya et al., "High-EfficiencyGaN / AlxGaN1-xN Multi-Quantum Well Light Emitter Grown on Low-DislocationDensity AlxGa1-xN", IPAP Conf. Series, 1 (2000) 833. J. Han et al., "Control andelimination of cracking of AlGaNusinglow-temperature AlGaN containings", Appl. Phys. Lett. 78 (2001) 67. M. Iwaya et al., "Suppression of phase separation of AlGaN during lateral growth and fabrication of high-efficiency UV-LED on optimized AlGaN", J. Cryst. Growth 237-239 (2002) 951.

  However, when crystal growth for an ultraviolet semiconductor laser device was performed using the AlN intermediate layer technique described above, high-density cracks were generated in a plurality of semiconductor layers including an AlGaN-based compound layer. As described above, the AlN intermediate layer technology is not always effective, and as a result of the accumulation of tensile strain due to the increase in film thickness of a plurality of semiconductor layers including the AlGaN-based compound layer, cracks occur when the film thickness exceeds a certain film thickness, that is, the critical film thickness. There is a problem that occurs.

  The present invention has been made in view of such a problem, and a compound semiconductor device and a compound semiconductor device in which generation of cracks is reduced even if a plurality of semiconductor layers including an AlGaN-based compound layer are increased in thickness are provided. An object is to provide a manufacturing method.

In order to solve the above problems, a compound semiconductor device of the present invention includes a GaN layer, an AlN intermediate layer grown on the GaN layer, an Al _X1 Ga _Y1 N-based compound layer grown on the AlN intermediate layer, And an Al _X2 Ga _Y2 N-based compound layer that is grown on the Al _X1 Ga _Y1 N-based compound layer and satisfies a relational expression of X1> X2.

  The compound semiconductor device of the present invention can further include a sapphire substrate and a GaN buffer layer grown on the sapphire substrate and having a GaN layer grown thereon. The GaN buffer layer can relax the lattice mismatch between the sapphire substrate and the GaN layer, and can improve the crystallinity of the GaN layer formed on the sapphire substrate.

  In the compound semiconductor device of the present invention, the GaN layer can be a GaN substrate. In the case where the GaN layer is a GaN substrate, a sapphire substrate is not required, so that lattice mismatch does not occur and deterioration of crystallinity of each layer can be suppressed.

Here, an Al _X1 Ga _Y1 N-based compound layer is grown between the AlN intermediate layer and the Al _X2 Ga _Y2 N-based compound layer. In the Al _X2 Ga _Y2 N-based compound layer, the tensile strain is accumulated as the layer thickness increases. Here, since X1> X2, the Al _X2 Ga _Y2 N-based compound layer having a larger lattice constant than the Al _X1 Ga _Y1 N-based compound layer is subjected to compressive strain. Thereby, the tensile strain causing the generation of cracks is offset by the compressive strain. According to this arrangement, generation of cracks on the surface of Al X2 _Ga Y2 _N-based compound layer of the compound semiconductor device is reduced. Furthermore, even if a plurality of semiconductor layers grown on this layer are made thick, the generation of cracks is reduced.

Y1 and Y2 are 0 or more and 1 or less, and when the Al _X1 Ga _Y1 N-based compound layer and the Al _X2 Ga _Y2 N-based compound layer are ternary mixed crystals, Y1 and Y2 are 1-X1 and 1- X2. When the Al _X1 Ga _Y1 N-based compound layer and the Al _X2 Ga _Y2 N-based compound layer are quaternary mixed crystals, Y1 and Y2 have a sum of X1 and a sum of X2 smaller than 1, respectively.

Further, a structure in which the GaN layer has an uneven surface, the AlN intermediate layer grows on the uneven surface of the GaN layer, and the Al _X1 Ga _Y1 N-based compound layer grows on the uneven surface of the AlN intermediate layer is also preferable. This is because, in the concave portion, lateral growth occurs, and defects such as dislocations are bent in the lateral direction during the lateral growth process. As a result, the defect density in the region of the Al _X2 Ga _Y2 N-based compound layer can be reduced.

  It is also preferable that the irregularities on the irregular surface of the GaN layer are alternately arranged in stripes. Thereby, the area | region where a defect remains and the area | region where the defect was reduced are arrange | positioned alternately, and a defect density is further reduced.

The Al _X1 Ga _Y1 N-based compound layer is preferably made of Al _X1 Ga _Y1 N, and the Al _X2 Ga _Y2 N-based compound layer is preferably made of Al _X2 Ga _Y2 N satisfying the relational expression X1> X2. Thereby, even if the Al _X1 Ga _Y1 N-based compound layer and the Al _X2 Ga _Y2 N-based compound layer are composed of Al _X1 Ga _Y1 N and Al _X2 Ga _Y2 N, respectively, a plurality of semiconductors including the AlGaN-based compound layer Even if the layer is made thick, the generation of cracks can be reduced.

In addition, the method for manufacturing a compound semiconductor device of the present invention includes (1) a concavo-convex processing step for processing a GaN layer so as to have a concavo-convex surface, and (2) an AlN intermediate layer on the concavo-convex surface of the processed GaN layer. And (3) growing an Al _X1 Ga _Y1 N-based compound layer on the concavo-convex surface of the AlN intermediate layer and satisfying a relational expression X1> X2 on the Al _X1 Ga _Y1 N-based compound layer And a compound layer growth step of growing an Al _X2 Ga _Y2 N-based compound layer.

Thereby, the occurrence of cracks on the device surface is reduced, and a compound semiconductor device is provided in which the occurrence of cracks is reduced even when the plurality of semiconductor layers including the AlGaN-based compound layer is thickened. This is because, in the Al _X2 Ga _Y2 N-based compound layer, the tensile strain is accumulated as the layer thickness increases. On the other hand, since X1> X2, the lattice constant is higher than that of the Al _X1 Ga _Y1 N-based compound layer. This is because the large Al _X2 Ga _Y2 N-based compound layer is subjected to compressive strain, and as a result, the tensile strain that causes cracks is offset by the compressive strain.

  In addition, the manufacturing method of the compound semiconductor device of this invention can be further equipped with the GaN layer growth process which grows a GaN buffer layer on a sapphire substrate, and grows a GaN layer thicker than a GaN buffer layer on a GaN buffer layer. When a sapphire substrate is used, the GaN buffer layer is interposed between the sapphire substrate and the GaN layer, so that lattice mismatch can be alleviated and the crystallinity of the GaN layer can be improved.

  Moreover, the manufacturing method of the compound semiconductor device of this invention can further comprise the GaN substrate preparation process which uses a GaN substrate as a GaN layer. When a commercially available GaN substrate is prepared and used, since it is not necessary to use a sapphire substrate, the lattice mismatch as described above does not occur, and deterioration of crystallinity of each layer can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, even if it makes the several semiconductor layer containing an AlGaN-type compound layer thick, generation | occurrence | production of a crack can be provided, and the manufacturing method of a compound semiconductor device can be provided.

  Hereinafter, a compound semiconductor device and a method for manufacturing the compound semiconductor device according to an embodiment of the present invention will be described. In addition, the same code | symbol is used for the same element and the overlapping description is abbreviate | omitted. Further, the dimensional ratios in the drawings do not necessarily match those described. Furthermore, the present invention is not limited to this.

  The configuration of the compound semiconductor device 10 will be described.

  FIG. 3 is a cross-sectional view of the compound semiconductor device 10 according to the present embodiment.

This compound semiconductor device 10 has a sapphire substrate 11, a GaN buffer layer (hereinafter referred to as “buffer layer”) 12 grown on the sapphire substrate 11, and a concavo-convex surface 13 </ b> S grown on the buffer layer 12. GaN layer 13, AlN intermediate layer (hereinafter referred to as “intermediate layer”) 14 grown on uneven surface 13S of GaN layer 13, and Al _X1 Ga _Y1 grown on uneven surface 14S of intermediate layer 14 An N-based compound layer 15 and an Al _X2 Ga _Y2 N-based compound layer 16 grown on the Al _X1 Ga _Y1 N-based compound layer 15 are provided.

  A semiconductor structure in which a plurality of semiconductor layers made of an AlGaN compound are grown on the compound semiconductor device 10 is used as a crystal material for an ultraviolet semiconductor laser element, and is applied to devices such as a light emitting device, a light receiving device, and an electronic device. Is possible.

  The sapphire substrate 11 is made of sapphire and has a (0001) plane as a crystal growth surface.

  The buffer layer 12 is made of GaN, and the intermediate layer 14 is made of AlN.

  The GaN layer 13 is grown on the buffer layer 12 and has a concavo-convex surface 13S, thereby having a plurality of convex portions 13A and concave portions 13B. Here, the GaN layer 13 preferably has convex portions 13A and concave portions 13B arranged alternately in a stripe shape so as to have a stripe-like line and space with periodicity.

Furthermore, the intermediate layer 14 and the Al _X1 Ga _Y1 N-based compound layer 15 are grown on the uneven surface 13S of the GaN layer 13 and the uneven surface 14S of the intermediate layer 14, respectively. Further, the Al _X2 Ga _Y2 N-based compound layer 16 is grown on the Al _X1 Ga _Y1 N-based compound layer 15 so as to be buried and planarized with a periodic stripe structure.

The material of the Al _X1 Ga _Y1 N-based compound layer 15 includes a two-ternary compound represented by Al _X1 Ga _Y1 N (0 ≦ X1 ≦ 1, 0 ≦ Y1 ≦ 1, 0 <X1 + Y1 ≦ 1). Selected from compound semiconductors. For this reason, the material of the Al _X1 Ga _Y1 N-based compound layer 15 may contain other elements, for example, an Al _X1 Ga _Y1 In _Z1 N (Z1 = 1-X1-Y1) compound semiconductor, or an Al _X1 A semiconductor made of Ga _Y1 N may be used.

The material of the Al _X2 Ga _Y2 N-based compound layer 16 is a two-ternary compound represented by Al _X2 Ga _Y2 N (0 ≦ X2 ≦ 1, 0 ≦ Y2 ≦ 1, 0 <X2 + Y2 ≦ 1). For example, it may be an Al _X2 Ga _Y2 In _Z2 N (Z2 = 1-X2-Y2) compound semiconductor or a semiconductor composed of Al _X2 Ga _Y2 N. X2 satisfies the relational expression of X1> X2, thereby reducing the occurrence of cracks in the Al _X2 Ga _Y2 N-based compound layer 16 (the reason why the occurrence of cracks is reduced will be described later).

Thus, when the Al _X1 Ga _Y1 N-based compound layer 15 and the Al _X2 Ga _Y2 N-based compound layer 16 are ternary mixed crystals, Y1 and Y2 are 1-X1 and 1-X2, respectively. When the Al _X1 Ga _Y1 N-based compound layer and the Al _X2 Ga _Y2 N-based compound layer are quaternary mixed crystals, Y1 and Y2 have a sum of X1 and a sum of X2 smaller than 1, respectively.

Next, the reason why the generation of cracks in the device surface 10S of the Al _X2 Ga _Y2 N-based compound layer 16 is reduced will be described with reference to FIG.

  FIG. 4 is an explanatory diagram for explaining the reason why the occurrence of cracks is reduced.

A relational expression X1> X2 is established between the Al _X1 Ga _Y1 N-based compound layer 15 and the Al _X2 Ga _Y2 N-based compound layer 16. That is, the material of the Al _X2 Ga _Y2 N-based compound layer 16 has a smaller Al composition ratio than the material of the Al _X1 Ga _Y1 N-based compound layer 15. Thereby, the material of the Al _X2 Ga _Y2 N-based compound layer 16 has a larger lattice constant than the material of the Al _X1 Ga _Y1 N-based compound layer 15, and the Al _X1 Ga _Y1 N-based compound layer 15, which is a semiconductor layer immediately below. In order to match with the lattice constant, compression strain is applied.

On the other hand, the Al _X2 Ga _Y2 N-based compound layer 16 is subjected to tensile strain accumulated as the layer thickness increases.

As a result, the tensile strain is offset by the compressive strain, and the generation of cracks on the device surface 10S of the Al _X2 Ga _Y2 N-based compound layer 16 is reduced. Further, even if the plurality of semiconductor layers including the AlGaN-based compound layer grown on the Al _X2 Ga _Y2 N-based compound layer 16 is made thick, the generation of cracks is reduced.

Note that the difference between X1 and X2 is preferably at least 0.45. That is, it is preferable that the relational expression X1-X2 ≧ 0.45 is satisfied. If the lattice mismatch rate (lattice mismatch rate) between the Al _X1 Ga _Y1 N-based compound layer 15 and the Al _X2 Ga _Y2 N-based compound layer 16 is at least 1%, the Al _X1 Ga _Y1 N-based compound This is because the layer 15 is subjected to the above-described compressive strain, and the lattice mismatch rate of 1% corresponds to X1−X2 = 0.45 in terms of the difference in Al composition.

In addition, the GaN layer 13 has a plurality of convex portions 13A and concave portions 13B on the concave and convex surface 13S, so that the defect region 92 of the Al _X2 Ga _Y2 N-based compound layer 16 grown above the convex portions 13A has dislocations and the like. Many defects remain. This is caused by a lattice mismatch at the interface 90 between the Al _X1 Ga _Y1 N-based compound layer 15 and the Al _X2 Ga _Y2 N-based compound layer 16 in the defect region 92.

On the other hand, in the low defect region 94 of the Al _X2 Ga _Y2 N-based compound layer 16 grown above the recess 13B, lateral growth occurs, and defects such as dislocations occur in the lateral direction in the lateral growth process. Therefore, the defect density can be reduced.

Here, the plurality of convex portions 13A and concave portions 13B are also preferably arranged alternately in a stripe shape, and more preferably arranged alternately so as to have a periodic stripe-like line and space. As a result, defects are present in the plurality of defect regions 92 in the Al _X2 Ga _Y2 N-based compound layer 16 in a substantially uniform and non-uniform manner, and the defect regions 92 and the low defect regions 94 are alternately arranged. As a result, the density of defects is further reduced.

In each of the above-described embodiments, it is preferable to set the preferred thickness range of each layer as follows from the viewpoint of suppressing cracks by canceling out the above-described strain.
GaN layer 13 thickness range: 0.5 to 500 μm
The thickness range of the AlN layer 14: 5 to 100 nm
The thickness range of the AlGaN layer 15: 5 to 1000 nm
The thickness range of the AlGaN layer 16: 0.1 to 20 μm

  Next, a method of manufacturing the compound semiconductor device 10 and the semiconductor structure 30 in which a plurality of semiconductor layers made of an AlGaN compound are grown thereon will be described with reference to FIG. The compound semiconductor device 10 and the semiconductor structure 30 can be manufactured by sequentially performing the following steps (1) to (5).

  FIG. 5 is a cross-sectional view of the semiconductor structure 30 according to the present embodiment.

  In this embodiment, a metal organic chemical vapor deposition (MOCVD) method is used as a method for growing a crystal. However, the present invention is not limited to this, and a molecular beam growth (MBE) method, a hydride vapor phase epitaxy (HVPE). ) Method or other growth methods may be used.

In this embodiment, the gas containing ammonia (NH ₃ ) as the nitrogen source gas, the gas containing trimethylgallium (TMG) or trimethylaluminum (TMA) as the group III source gas, and silane ( The gas containing SiH ₄ ) includes a gas containing biscyclopentadienyl magnesium (Cp ₂ Mg) as a p-type doping source gas, but the present invention is not limited to this.

In the present embodiment, the Al _X1 Ga _Y1 N-based compound layer 15 is made of Al _X1 Ga _Y1 N, and the Al _X2 Ga _Y2 N-based compound layer 16 is made of Al _X2 Ga _Y2 N, but each of them is Al _X1 Ga _Y1. It may be composed of In _Z1 N and Al _X2 Ga _Y2 In _Z2 N.
Process (1) GaN layer growth process

  The sapphire substrate 11 is introduced and fixed in a space (MOCVD chamber) where crystal growth by MOCVD can be performed, and the MOCVD chamber is made a hydrogen atmosphere. Next, heat treatment is performed on the sapphire substrate 11 at 1050 ° C. for 5 minutes to clean the surface of the sapphire substrate 11. By performing the heat treatment under appropriate conditions in this manner, contaminants on the surface of the sapphire substrate 11 are removed and the flatness of the surface is improved.

Next, the temperature of the sapphire substrate 11 is lowered to 475 ° C., and a group III source gas containing trimethylgallium and a nitrogen source gas are supplied to grow a buffer layer 12 having a film thickness of 25 nm on the sapphire substrate 11. . Then, the temperature is raised to 1075 ° C., a group III source gas containing trimethylgallium, a nitrogen source gas, and the like are supplied to grow a 2.5 μm thick GaN layer 13 on the buffer layer 12. Let
Process (2) Concavity and convexity processing process

The substrate obtained in the step (1) is taken out from the MOCVD chamber, and introduced into a space (plasma CVD chamber) in which film formation by plasma CVD is possible and fixed. Next, a 300 nm thick SiO ₂ film is deposited on the substrate.

Next, when the SiO ₂ film is processed by a normal photolithography technique and the width is in the direction perpendicular to both the length and depth of the groove constituting the recess 13B, the width T2 of the recess 13B and the protrusion 13A A photoresist pattern having a line-and-space pattern with a width T1 of 14 μm and a periodic stripe shape is formed. When the width T1 = 5 to 25 μm and the width T2 = 5 to 25 μm, defects can be unevenly distributed as described above. The stripe direction is the GaN [1-100] direction.

Next, the GaN layer 13 is etched by 2 μm using parallel plate type reactive ion etching (RIE) using the SiO ₂ film formed in a periodic stripe shape as a mask. In the etching described above, 20 SCCM (cubic centimeter per minute) chlorine (Cl ₂ ) gas and 5 SCCM silicon tetrachloride (SiCl ₄ ) gas are used, the reactor pressure is set to 30 mTorr, and the RF power is set to 280 W. An etching rate of about 2 μm / min can be obtained.

Next, after the above etching, the SiO ₂ is removed by etching the SiO ₂ using buffered hydrofluoric acid (BHF), hydrofluoric acid (HF), or CF ₄ gas. Thereby, the GaN layer 13 has the uneven surface 13S. Next, the processed substrate is again introduced into the MOCVD growth chamber and fixed, and the MOCVD chamber is placed in an ammonia atmosphere and heat treatment is performed at 1075 ° C. for 5 minutes.

In the present embodiment, RIE is used for etching the GaN layer 13, but the GaN layer 13 is not limited to this. For example, an etching method such as reactive ion beam etching (RIBE), ECR-RIE, or ICP-RIE is used. Also good. Moreover, although chlorine gas and silicon tetrachloride gas were used for the gas used for etching, it is not limited to this, Chlorine gas, such as boron trichloride, methane gas, etc. may be used.
Process (3) Intermediate layer growth process

The temperature of the substrate obtained in the previous step is lowered to 550 ° C., and an intermediate layer 14 having a thickness of 10 nm is grown on the surface of the GaN layer 13.
Step (4) Compound layer growth step

The substrate obtained in step (3) is heated to 1125 ° C., and an Al _0.6 Ga _0.4 N layer (Al _X1 Ga _Y1 N-based compound having a film thickness of about 500 nm is formed on the uneven surface 14S of the intermediate layer 14. Layer 15) is grown. Next, an Al _0.15 Ga _0.85 N layer (Al _X2 Ga _Y2 N-based compound layer 16) having a thickness of 6 μm is grown. Thereby, the periodic stripe structure is embedded, the surface of the substrate is flattened, and the compound semiconductor device 10 is obtained. These film thicknesses are values converted into film thicknesses when grown on a flat substrate.
Process (5) Semiconductor structure 30 manufacturing process

On the substrate obtained in the previous step, a Si-doped Al _0.15 Ga _0.85 N layer (Si-doped cladding layer 17) is 3 μm and an Al _0.07 Ga _0.93 N layer (first guide layer). 18) 100 nm, AlGaN quantum well structure 19, Al _0.07 Ga _0.93 N layer (second guide layer 20) 100 nm, Al _0.35 Ga _0.65 N layer (block layer 21) 20 nm, Mg A _0.15 Ga _0.85 N layer (Mg-doped cladding layer 22) doped with Mg and a GaN layer (contact layer 23) doped with Mg are grown in order of 50 nm to obtain a semiconductor structure 30. It was.

  Moreover, it is also preferable that the manufacturing method of the compound semiconductor device 10 and the semiconductor structure 30 passes the following process (4-2) and the above-mentioned process (5) after passing through the above-mentioned processes (1) and (3). . Thereby, as shown in FIG. 6, the compound semiconductor device 10 and the semiconductor structure 30 provided with the GaN layer 13 having no uneven surface are obtained.

FIG. 6 is a cross-sectional view of another embodiment of a semiconductor structure.
Step (4-2) Another Embodiment of Compound Layer Growth Step

The substrate obtained in step (3) was heated to 1125 ° C., and an Al _0.6 Ga _0.4 N layer (Al _X1 Ga _Y1 N-based compound layer 15) having a film thickness of about 250 nm was grown. By growing an Al _0.15 Ga _0.85 N layer (Al _X2 Ga _Y2 N-based compound layer 16) having a film thickness of 3 μm doped with Si, the compound semiconductor device 10 having no uneven surface 13S is obtained. can get. Here, the addition amount of Si is 1 × 10 ¹⁸ cm ⁻³ .

  It is known that a gas containing trimethylaluminum, which is a group III source gas, and a gas containing ammonia, which is a nitrogen source gas, react in the gas phase. In order to suppress this reaction, the above AlGaN is used. The growth of the semiconductor layers 15 to 22 made of a system compound is preferably performed under reduced pressure, and is performed at 76 Torr in the present embodiment.

Next, the Al _X1 Ga _Y1 N-based compound layer 15 and the Al _X2 Ga _Y2 N-based compound layer 16 were obtained using Al _0.6 Ga _0.4 N and Al _0.15 Ga _0.85 N, respectively. A photograph of the surface of the compound semiconductor device 10 will be described.

  FIG. 7 is a photograph of the structure surface 30S of the semiconductor structure 30 obtained through the steps (1) to (5).

8 shows the structure surface of the semiconductor structure 30 obtained through steps (1) to (5) with the film thickness being about 250 nm with respect to the growth of the Al _X1 Ga _Y1 N-based compound layer 15 in step (4). It is a photograph of 30S.

Further, FIG. 9, as shown in Non-Patent Documents 1 to 6 which is in the _background, Al X1 _{Ga Y1} N-based compound layer 15 semiconductor structure 30 produced without growing the structure surface 30S It is a photograph.

  FIG. 10 is a photograph of the device surface 10S of the compound semiconductor device 10 in which the GaN layer 13 does not have an uneven surface, obtained through the steps (1), (3), and (4-2).

FIG. 11 is a photograph of the device surface 10S of the compound semiconductor device 10 that does not have the Al _X1 Ga _Y1 N-based compound layer 15 and the GaN layer 13 does not have an uneven surface.

  When the semiconductor structure 30 was obtained through the steps (1) to (5), no crack was observed on the structure surface 30S as shown in FIG. In addition, the horizontal stripe in a photograph originates in the periodic stripe-shaped GaN layer 13 processed in process (2), and is not a crack.

Also, when the semiconductor structure 30 is obtained by growing the Al _X1 Ga _Y1 N-based compound layer 15 grown in the step (4) by about 250 nm, cracks are observed on the structure surface 30S as shown in FIG. Was not.

On the other hand, the semiconductor structure 30 manufactured without growing the Al _X1 Ga _Y1 N-based compound layer 15 has cracks (two vertical stripes in the photograph indicated by white arrows) on the structure surface 30S, as shown in FIG. ) Was observed at high density.

  As shown in FIG. 10, cracks are present on the device surface 10 </ b> S of the compound semiconductor device 10 in which the GaN layer 13 does not have an uneven surface obtained through the steps (1), (3), and (4-2). Not observed.

Further, as shown in FIG. 11, cracks were observed on the device surface 10S of the compound semiconductor device 10 that does not have the Al _X1 Ga _Y1 N-based compound layer 15 and the GaN layer 13 does not have an uneven surface.

  Next, functions and effects of the compound semiconductor device 10 according to the present embodiment will be described.

When the compound semiconductor device 10 does not include the Al _X1 Ga _Y1 N-based compound layer 15 and the Al _X2 Ga _Y2 N-based compound layer 16 is grown on the intermediate layer 14 so as to increase the thickness, a certain thickness (critical) Cracks occur when the film thickness is greater.

On the other hand, when the compound semiconductor device 10 includes the Al _X1 Ga _Y1 N-based compound layer 15, the Al _X2 Ga _Y2 N-based compound layer 16 has a lattice constant larger than that of the Al _X1 Ga _Y1 N-based compound layer 15, and thus compressive strain is generated. receive. Here, the tensile strain accumulated with the increase in the film thickness of the Al _X2 Ga _Y2 N-based compound layer 16 is offset by this compressive strain, and the occurrence of cracks on the device surface 10S is suppressed. Further, even if a plurality of semiconductor layers including an AlGaN-based compound layer are grown thick on the compound semiconductor device 10, the generation of cracks is reduced.

Further, when the GaN layer 13 has a concavo-convex surface, the Al _X2 Ga _Y2 N-based compound layer 16 grown above the recess 13B grows in the lateral direction, which causes the defects to be bent in the lateral direction. Is formed.

  FIG. 12 is a cross-sectional view of a semiconductor device 10 according to another embodiment.

  This compound semiconductor device 10 differs from that shown in FIG. 3 only in that it does not include the sapphire substrate 11 and the buffer layer 12. The GaN layer 13 is a GaN substrate having a thickness capable of holding its own weight alone. That is, the GaN layer 13 of the compound semiconductor device 10 can be the GaN substrate 13. When the commercially available GaN substrate 13 is prepared and used, the above-described sapphire substrate is not necessary, so that lattice mismatch does not occur and deterioration of crystallinity of each layer can be suppressed. Further, when the GaN substrate 13 is used, the above-described GaN layer forming step (1) becomes unnecessary. A GaN layer 13 that is epitaxially grown on the GaN substrate 13 may be newly formed, and the whole may be a GaN substrate.

  The GaN substrate 13 has a thickness of 50 μm to 500 μm.

  FIG. 13 is a cross-sectional view of a semiconductor device 10 according to yet another embodiment.

  This compound semiconductor device 10 differs from that shown in FIG. 3 only in that the recess 13B of the GaN layer 13 is etched to a depth at which the AlN layer 14 contacts the sapphire substrate 11. The AlN layer 14 on the sapphire substrate 11 is located on the side of the GaN buffer layer 12. The concave portion 13 </ b> B on the concave and convex surface of the GaN layer 13 is constituted by the side wall of the GaN layer 13 and the surface of the sapphire substrate 11.

  In the case of this example, the AlN layer 14 in the recess 13B grows on the sapphire substrate 11, not on the GaN layer. In this case, the effect of relaxing the lattice mismatch between the sapphire and the AlGaN layer is achieved.

  As described above, according to the present invention, the AlGaN compound layer 15 is grown between the AlN intermediate layer 14 and the AlGaN compound layer 16, and cracks are generated by canceling out the tensile strain and the compressive strain. Can be suppressed.

It is sectional drawing of the device which grew the AlGaN layer on the GaN layer. It is sectional drawing of the device which made the AlN intermediate layer grow on the GaN layer, and made the AlGaN layer grow on it. It is sectional drawing of the compound semiconductor device which concerns on this embodiment. It is explanatory drawing explaining the reason that generation | occurrence | production of a crack is reduced. It is sectional drawing of a semiconductor structure. FIG. 6 is a cross-sectional view of another embodiment of a semiconductor structure. It is a photograph of the structure surface of the semiconductor structure obtained through steps (1) to (5). It is a photograph of the structure surface of the semiconductor structure obtained through steps (1) to (5) with the film thickness of the Al _X1 Ga _Y1 N-based compound layer being about 250 nm in step (4). Al X1 _Ga Y1 _N-based compound layer semiconductor structure manufactured without growth is a photograph of the structure surface. It is a photograph of the device surface of the compound semiconductor device in which a GaN layer does not have an uneven surface. Has no Al _X1 Ga _Y1 N-based compound layer, GaN layer is a photograph of the device surface of the compound semiconductor device having no uneven surface. It is sectional drawing of the semiconductor device 10 which concerns on another embodiment. It is sectional drawing of the semiconductor device 10 which concerns on another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Compound semiconductor device, 10S ... Device surface, 11 ... Sapphire substrate, 12 ... Buffer layer, 13 ... GaN layer, 13A ... Convex part, 13B ... Concave part, 13S ... Concave surface of GaN layer, 14 ... Intermediate layer, 14S ... irregular surface of the intermediate layer, _{15 ...} Al X1 _{Ga Y1} N-based compound layer, _{16 ...} Al X2 _{Ga Y2} N-based compound layer, 17 ... Si-doped cladding layer, 18 ... first guide layer, 19 ... AlGaN quantum well structure, 20 2nd guide layer, 21 Block layer, 22 Mg doped cladding layer, 23 Contact layer, 30 Semiconductor structure, 30S Structure surface, 90 Interface, 92 Defect region, 94 Low defect region

Claims (9)

A GaN layer;
An AlN intermediate layer grown on the GaN layer;
An Al _X1 Ga _Y1 N-based compound layer grown on the AlN intermediate layer;
An Al _X2 Ga _Y2 N-based compound layer grown on the Al _X1 Ga _Y1 N-based compound layer and satisfying a relational expression of X1>X2;
A compound semiconductor device comprising: A sapphire substrate,
A GaN buffer layer grown on the sapphire substrate and having the GaN layer grown thereon;
The compound semiconductor device according to claim 1, further comprising:   The compound semiconductor device according to claim 1, wherein the GaN layer is a GaN substrate. The GaN layer has an uneven surface,
The AlN intermediate layer grows on the uneven surface of the GaN layer,
The Al _X1 Ga _Y1 N-based compound layer has grown on the uneven surface of the AlN intermediate layer,
The compound semiconductor device according to claim 1, wherein:   5. The compound semiconductor device according to claim 4, wherein the irregularities on the irregular surface of the GaN layer are alternately arranged in a stripe shape. The Al _X1 Ga _Y1 N-based compound layer is made of Al _X1 Ga _Y1 N,
The Al _X2 Ga _Y2 N-based compound layer is made of Al _X2 Ga _Y2 N satisfying a relational expression of X1> X2.
The compound semiconductor device according to claim 1, wherein the compound semiconductor device is a device. A concavo-convex processing step for processing the GaN layer to have a concavo-convex surface;
An intermediate layer growth step of growing an AlN intermediate layer on the irregular surface of the processed GaN layer;
An Al _X1 Ga _Y1 N-based compound layer is grown on the uneven surface of the AlN intermediate layer, and an Al _X2 Ga _Y2 N-based compound layer satisfying the relational expression X1> X2 is formed on the Al _X1 Ga _Y1 N-based compound layer. A compound layer growth step to grow,
The manufacturing method of the compound semiconductor device characterized by the above-mentioned.   8. The compound semiconductor device according to claim 7, further comprising a GaN layer growth step of growing a GaN buffer layer on the sapphire substrate and growing the GaN layer thicker than the GaN buffer layer on the GaN buffer layer. Manufacturing method.   The method of manufacturing a compound semiconductor device according to claim 7, further comprising a GaN substrate preparation step using a GaN substrate as the GaN layer.

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