WO2016084311A1 - エピタキシャルウェーハ、半導体素子、エピタキシャルウェーハの製造方法、並びに、半導体素子の製造方法 - Google Patents
エピタキシャルウェーハ、半導体素子、エピタキシャルウェーハの製造方法、並びに、半導体素子の製造方法 Download PDFInfo
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- 239000004065 semiconductor Substances 0.000 title claims description 47
- 238000004519 manufacturing process Methods 0.000 title claims description 23
- 239000000203 mixture Substances 0.000 claims abstract description 70
- 238000003780 insertion Methods 0.000 claims abstract description 57
- 230000037431 insertion Effects 0.000 claims abstract description 57
- 239000000758 substrate Substances 0.000 claims abstract description 35
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 26
- 229910052710 silicon Inorganic materials 0.000 claims abstract description 26
- 239000010703 silicon Substances 0.000 claims abstract description 26
- 229910002601 GaN Inorganic materials 0.000 claims description 33
- 230000004888 barrier function Effects 0.000 claims description 13
- 238000000034 method Methods 0.000 claims description 13
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 claims description 6
- 229910016920 AlzGa1−z Inorganic materials 0.000 abstract 1
- 239000010410 layer Substances 0.000 description 315
- 229910002704 AlGaN Inorganic materials 0.000 description 15
- 150000004767 nitrides Chemical class 0.000 description 10
- 230000002093 peripheral effect Effects 0.000 description 9
- 239000002356 single layer Substances 0.000 description 8
- 238000010030 laminating Methods 0.000 description 4
- 238000002488 metal-organic chemical vapour deposition Methods 0.000 description 4
- 229910052782 aluminium Inorganic materials 0.000 description 3
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 229910052594 sapphire Inorganic materials 0.000 description 3
- 239000010980 sapphire Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 238000001000 micrograph Methods 0.000 description 2
- 230000002411 adverse Effects 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000005533 two-dimensional electron gas Effects 0.000 description 1
- 238000000927 vapour-phase epitaxy Methods 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
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Definitions
- the present invention relates to an epitaxial wafer, a semiconductor device, an epitaxial wafer manufacturing method, and a semiconductor device manufacturing method.
- the nitride semiconductor layer is generally formed on an inexpensive silicon substrate or sapphire substrate.
- the lattice constants of these substrates and the nitride semiconductor layers are greatly different, and the thermal expansion coefficients are also different. Therefore, large strain energy is generated in the nitride semiconductor layer formed by epitaxial growth on the substrate. As a result, the nitride semiconductor layer is likely to generate cracks and crystal quality.
- FIG. 6 A semiconductor wafer having a buffer layer of Patent Document 1 is shown in FIG.
- the buffer layer 3 is provided between the silicon substrate 2 and the active layer 4 (consisting of the electron transit layer 4a and the electron supply layer 4b).
- the second single layer structure buffer region 8 made of GaN provided on the first multilayer structure buffer region 5, and the second single layer structure buffer region 8 It has a second multilayer structure buffer region 5 '.
- the first multilayer structure buffer region 5 and the second multilayer structure buffer region 5 ′ are composed of a sub multilayer structure buffer region 6 and a first single layer structure made of GaN and thinner than the second single layer structure buffer region 8. It has a multilayer structure in which the buffer region 7 is repeatedly stacked.
- the sub-multilayer structure buffer region 6 has a multilayer structure in which a first layer made of AlN and a second layer made of GaN are repeatedly stacked.
- a first layer is formed of a nitride semiconductor containing aluminum at a first ratio
- a second layer, a first single-layer structure buffer region 7, and a second single-layer structure buffer are formed.
- the present inventors have found that the conventional buffer layer configuration has room for improvement in terms of wafer warpage and internal cracks.
- the present invention has been made in view of the above problems, and an object thereof is to provide an epitaxial wafer capable of reducing the warpage of the wafer and suppressing the occurrence of internal cracks.
- the present invention provides a silicon-based substrate, an Al x Ga 1-x N layer, an Al y Ga 1-y N layer (x> y) disposed on the silicon-based substrate, Are alternately arranged, and a first insertion layer made of an Al z Ga 1-z N layer (x> z) thicker than the Al y Ga 1-y N layer.
- the first multilayer buffer region and the first buffer layer in which the first insertion layers are alternately arranged, and the Al ⁇ Ga 1- ⁇ are arranged on the first buffer layer.
- a second insertion layer composed of an N layer ( ⁇ > ⁇ ), the second multilayer buffer region, and the second insertion layer. are alternately arranged, and a channel layer that is disposed on the second buffer layer and is thicker than the second insertion layer, and is an average of the second buffer layers.
- the average Al composition at the upper part of the buffer layer is increased by increasing the average Al composition at the lower part of the buffer layer (a region below the upper part of the buffer layer), thereby reducing the warpage of the wafer.
- the generation of internal cracks can be suppressed while reducing peripheral cracks, and this makes it possible to improve electrical characteristics such as withstand voltage and reliability when manufacturing semiconductor elements. Can do.
- the second insertion layer is thinner than the first insertion layer.
- the number of repetitions of the Al ⁇ Ga 1- ⁇ N layer and the Al ⁇ Ga 1- ⁇ N layer in the second multilayer buffer region is equal to the Al x Ga 1 in the first multilayer buffer region.
- the number is preferably larger than the number of repetitions of the -xN layer and the Al y Ga 1-y N layer.
- the Al ⁇ Ga 1- ⁇ N layer of the second multilayer structure buffer region is thinner than the Al y Ga 1-y N layer of the first multilayer structure buffer region.
- the Al ⁇ Ga 1- ⁇ N layer in the second multilayer structure buffer region is thicker than the Al x Ga 1-x N layer in the first multilayer structure buffer region. Even with such a configuration, the average Al composition at the upper portion of the buffer layer can be made higher, the wafer warpage can be more effectively reduced, and the occurrence of internal cracks can be more effectively suppressed.
- the present invention provides the above-described epitaxial wafer, a barrier layer made of a gallium nitride based semiconductor disposed on the epitaxial wafer, a first electrode disposed on the barrier layer, a second electrode, and A semiconductor device comprising a control electrode is provided.
- the average Al composition at the top of the buffer layer can be increased, and the occurrence of internal cracks can be suppressed by reducing the warpage of the wafer.
- the semiconductor element can have excellent electrical characteristics and reliability.
- the present invention provides a step of preparing a silicon-based substrate, and Al x Ga 1-x N layers and Al y Ga 1-y N layers (x> y) are alternately arranged on the silicon-based substrate. And a first insertion layer made of an Al z Ga 1-z N layer (x> z) thicker than the Al y Ga 1-y N layer. Forming a first buffer layer in which one multilayer structure buffer region and the first insertion layer are alternately arranged by epitaxial growth; and Al ⁇ Ga 1- ⁇ on the first buffer layer.
- a second multi-layer buffer region having an N layer ( ⁇ > ⁇ ) and a second insertion layer Forming a second buffer layer alternately arranged with the second insertion layers by epitaxial growth, and epitaxially growing a channel layer thicker than the second insertion layer on the second buffer layer
- the average Al composition at the top of the buffer layer can be increased, and the generation of internal cracks can be suppressed while reducing peripheral cracks by reducing the warpage of the wafer.
- an epitaxial wafer can be manufactured that has good electrical characteristics such as breakdown voltage and reliability when a semiconductor element is manufactured.
- the second insertion layer is thinner than the first insertion layer so that the average Al composition of the second buffer layer is higher than the average Al composition of the first buffer layer. . If such an epitaxial wafer manufacturing method is used, the average Al composition at the upper portion of the buffer layer can be effectively increased.
- the present invention also includes a step of epitaxially growing a barrier layer made of a gallium nitride based semiconductor on the epitaxial wafer manufactured by the above method, and a first electrode, a second electrode, And a method of manufacturing a semiconductor element, comprising the step of forming a control electrode.
- the average Al composition at the top of the buffer layer can be increased, and the occurrence of internal cracks can be suppressed by reducing the warpage of the wafer.
- a semiconductor element with good electrical characteristics and reliability can be manufactured.
- the average Al composition of the upper portion of the buffer layer can be increased, and the occurrence of internal cracks can be suppressed by reducing the warpage of the wafer.
- electrical characteristics such as withstand voltage and reliability can be improved.
- the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.
- the conventional buffer layer has room for improvement in terms of wafer warpage and internal cracks.
- the present inventors have intensively studied an epitaxial wafer that can reduce the warpage of the wafer and suppress the occurrence of internal cracks.
- the average Al composition of the second buffer layer positioned above the buffer layer is higher than the average Al composition of the first buffer layer positioned below the buffer layer. It has been found that the average Al composition can be increased, thereby reducing the warpage of the wafer and suppressing the occurrence of internal cracks, and the present invention has been made.
- FIG. 7 shows an internal crack 9 generated in the sub multilayer buffer region 6 (the first layer 61 and the second layer 62 are alternately laminated) of the first multilayer buffer region 5 of FIG. Is shown.
- FIG. 8 shows a Nomarski image (differential interference microscope image) of the internal crack in the structure of FIG. Since the portion inside the internal crack generated by the generation of such an internal crack is buried during the subsequent epitaxial growth, the surface of the epitaxial layer after the epitaxial growth is flat. However, in the case of FIG. 7, since the substance of the first single-layer structure buffer region 7 is buried in the internal crack 9, it adversely affects electrical characteristics such as breakdown voltage and reliability.
- the GaN layer (or AlGaN layer having a small Al composition) I and the AlN layer (or AlGaN layer having a large Al composition) II are alternately stacked, the GaN layer (or the Al composition having a small Al composition is gradually decreased) as the distance from the silicon substrate increases. Since the AlGaN layer) I is lattice-relaxed, the strain on the GaN layer (or AlGaN layer with a small Al composition) I on the upper part of the buffer structure is increased by increasing the average Al composition especially on the upper part of the buffer structure. It is presumed that the effect of suppressing internal cracks is obtained by strengthening and weakening the strain on the AlN layer (or AlGaN layer having a large Al composition) II.
- a mechanism for reducing the warpage of the wafer will be described below.
- a strong compressive stress is also applied to the GaN layer (that is, the channel layer) formed thereon.
- the deformation to the negative side during epitaxial growth that is, the warpage of the negative side wafer
- the warpage of the wafer the warpage of the positive side wafer
- the wafer warpage is reduced, cracks generated on the outer periphery of the wafer (hereinafter referred to as outer peripheral cracks) are also suppressed.
- the epitaxial wafer 10 of the present invention shown in FIG. 1A has a silicon substrate 12, a buffer layer 25 provided on the silicon substrate 12, and a channel layer 26 provided on the buffer layer 25.
- the silicon-based substrate 12 is a substrate made of, for example, Si or SiC.
- the buffer layer 25 includes a first buffer layer 15 and a second buffer layer 16 provided on the first buffer layer 15.
- the first buffer layer 15 is formed by alternately stacking first multilayer structure buffer regions 19 and first insertion layers 20.
- the first multilayer buffer region 19 is formed by alternately laminating Al x Ga 1-x N layers 17 and Al y Ga 1-y N layers (x> y) 18, and the first insertion layer 20 Consists of an Al z Ga 1-z N layer (x> z) and is thicker than the Al y Ga 1-y N layer (x> y) 18.
- the second buffer layer 16 is formed by alternately stacking second multilayer structure buffer regions 23 and second insertion layers 24.
- the second multilayer buffer region 23 is formed by alternately laminating Al ⁇ Ga 1- ⁇ N layers 21 and Al ⁇ Ga 1- ⁇ N layers ( ⁇ > ⁇ ) 22. Consists of an Al ⁇ Ga 1- ⁇ N layer ( ⁇ > ⁇ ) and is thicker than the Al ⁇ Ga 1- ⁇ N layer 22.
- the second insertion layer 24 is configured to be thinner than the first insertion layer 20.
- the ⁇ Ga 1- ⁇ N layer 22 can be combined as shown in Table 1, for example.
- the channel layer 26 is composed of a GaN layer, an AlGaN layer, an InGaN layer, a composite layer including an InGaN layer on a thick GaN layer, or the like that is thicker than the second insertion layer 24.
- an AlN initial layer 13 may be provided between the silicon-based substrate 12 and the buffer layer 25 (see FIG. 1A).
- the average Al composition of the second buffer layer 16 is set to be higher than the average Al composition of the first buffer layer 15, the average Al composition at the top of the buffer layer 25 can be increased.
- the occurrence of internal cracks can be suppressed while reducing peripheral cracks by reducing the warpage of the wafer. Thereby, when a semiconductor element is manufactured, electrical characteristics such as withstand voltage and reliability can be improved.
- the second insertion layer 24 is preferably thinner than the first insertion layer 20.
- the average Al composition at the upper part of the buffer layer 25 can be effectively made higher than the average Al composition at the lower part of the buffer layer 25 below the upper part of the buffer layer 25. While reducing a curvature effectively, generation
- the number of repetitions of the Al ⁇ Ga 1- ⁇ N layer 21 and the Al ⁇ Ga 1- ⁇ N layer 22 in the second multilayer buffer region 23 is the same as that in the first multilayer buffer region 19.
- the number is preferably larger than the number of repetitions of the Al x Ga 1-x N layer 17 and the Al y Ga 1-y N layer 18.
- the Al ⁇ Ga 1- ⁇ N layer 22 in the second multilayer structure buffer region 23 is thinner than the Al y Ga 1-y N layer 18 in the first multilayer structure buffer region 19.
- the average Al composition at the upper part of the buffer layer 25 can be more effectively increased than the average Al composition at the lower part of the buffer layer 25 below the upper part of the buffer layer 25. Can be more effectively reduced, and the occurrence of internal cracks can be more effectively suppressed.
- the Al ⁇ Ga 1- ⁇ N layer 21 in the second multilayer structure buffer region 23 is thicker than the Al x Ga 1-x N layer 17 in the first multilayer structure buffer region 19. It is preferable.
- x ⁇ when the Al ⁇ Ga 1- ⁇ N layer 21 in the second multilayer buffer region 23 and the Al x Ga 1-x N layer 17 in the first multilayer buffer region 19 are compared, x ⁇ . It is preferable.
- the Al ⁇ Ga 1- ⁇ N layer 21 may be an Al 0.8 Ga 0.2 N layer, and the Al x Ga 1-x N layer 17 may be an Al 0.6 Ga 0.4 N layer.
- the Al ⁇ Ga 1- ⁇ N layer 22 in the second multilayer buffer region 23 and the Al y Ga 1-y N layer 18 in the first multilayer buffer region 19 are compared, y ⁇ .
- the Al ⁇ Ga 1- ⁇ N layer 22 may be an Al 0.3 Ga 0.7 N layer
- the Al y Ga 1-y N layer 18 may be an Al 0.1 Ga 0.9 N layer.
- the average Al composition at the upper portion of the buffer layer 25 can be more effectively increased than the average Al composition at the lower portion of the buffer layer 25 below the upper portion of the buffer layer 25.
- the method for increasing the average Al composition in the upper portion of the buffer layer 25 may be carried out simultaneously by a plurality of methods, whereby the average Al composition in the upper portion can be increased.
- a semiconductor element 11 of the present invention shown in FIG. 2A is provided with a barrier layer 27 made of a gallium nitride based semiconductor (for example, AlGaN) on the epitaxial wafer 10 described above with reference to FIG. 27, a first electrode (source electrode) 30, a second electrode (drain electrode) 31, and a control electrode 32 are provided.
- the semiconductor element 11 is, for example, a high electron mobility transistor (HEMT).
- the channel layer 26 and the barrier layer 27 constitute an active layer 29.
- the first electrode 30 and the second electrode 31 are arranged so that a current flows from the first electrode 30 to the second electrode 31 through the two-dimensional electron gas 28 formed in the channel layer 26. ing.
- the current flowing between the first electrode 30 and the second electrode 31 can be controlled by the potential applied to the control electrode 32.
- the average Al composition at the upper part of the buffer layer 25 is made higher than the average Al composition at the lower part of the buffer layer 25 below the upper part of the buffer layer 25, whereby the wafer By reducing the warpage, it is possible to suppress the generation of internal cracks while reducing peripheral cracks, and the devices fabricated using this wafer are semiconductor devices with good electrical characteristics such as withstand voltage and reliability. It can be.
- a silicon-based substrate 12 is prepared (see FIG. 3A).
- a silicon substrate or a SiC substrate is prepared as the silicon-based substrate 12.
- a silicon substrate or a SiC substrate is generally used as a growth substrate for a nitride semiconductor layer.
- the first buffer layer 15 is formed on the silicon-based substrate 12 by epitaxial growth (see FIG. 3B).
- the first buffer layer 15 constituting the buffer layer 25 is formed on the silicon substrate 12 by the MOVPE method (metal organic vapor phase epitaxy). As shown in FIG. 1B, the first buffer layer 15 is formed by alternately stacking the first multilayer structure buffer regions 19 and the first insertion layers 20.
- the first multilayer buffer region 19 is formed by alternately laminating Al x Ga 1-x N layers 17 and Al y Ga 1-y N layers (x> y) 18, and the first insertion layer 20 Consists of an Al z Ga 1-z N layer (x> z) and is thicker than the Al y Ga 1-y N layer (x> y) 18.
- AlN initial layer 13 may be formed before the first buffer layer 15 is formed.
- the second buffer layer 16 is formed on the first buffer layer 15 by epitaxial growth (see FIG. 3C).
- the second buffer layer 16 constituting the buffer layer 25 is formed on the first buffer layer 15 by the MOVPE method.
- the second buffer layer 16 is formed by alternately stacking second multilayer structure buffer regions 23 and second insertion layers 24.
- the second multilayer buffer region 23 is formed by alternately laminating Al ⁇ Ga 1- ⁇ N layers 21 and Al ⁇ Ga 1- ⁇ N layers ( ⁇ > ⁇ ) 22. Consists of an Al ⁇ Ga 1- ⁇ N layer ( ⁇ > ⁇ ) and is thicker than the Al ⁇ Ga 1- ⁇ N layer 22.
- the second buffer layer 16 is formed so that the average Al composition of the second buffer layer 16 is higher than the average Al composition of the first buffer layer 15.
- the channel layer 26 is formed on the second buffer layer 16 by epitaxial growth (see FIG. 3D).
- a channel layer 26 thicker than the second insertion layer 24 is formed on the second buffer layer 16 by the MOVPE method.
- the film thickness of the channel layer 26 is 1000 to 4000 nm, for example. In this way, the epitaxial wafer 10 of FIG. 1 can be manufactured.
- the average Al composition of the second buffer layer 16 higher than the average Al composition of the first buffer layer 15, the average Al composition at the top of the buffer layer 25 can be increased, and the warpage of the wafer is increased. It is possible to suppress the occurrence of internal cracks while reducing the outer peripheral cracks. Thereby, when a semiconductor element is produced, an epitaxial wafer having good electrical characteristics such as withstand voltage and reliability can be manufactured.
- the second insertion layer 24 is made thinner than the first insertion layer 20, and the average Al composition of the second buffer layer 16 is greater than the average Al composition of the first buffer layer 15. It is preferable to increase the height.
- the average Al composition at the upper part of the buffer layer 25 can be increased more effectively than the average Al composition at the lower part below the upper part of the buffer layer 25.
- a barrier layer 27 made of a gallium nitride-based semiconductor is formed by epitaxial growth on an epitaxial wafer 10 (see FIG. 3D) manufactured using the manufacturing method described with reference to FIG. )).
- a barrier layer 27 made of AlGaN is formed on the channel layer 26 by the MOVPE method.
- the film thickness of the barrier layer 27 is, for example, 10 to 50 nm.
- a first electrode (source electrode) 30, a second electrode (drain electrode) 31, and a control electrode 32 are formed on the barrier layer 27 (see FIG. 4B).
- the first electrode (source electrode) 30 and the second electrode (drain electrode) 31 can be formed of, for example, a laminated film of Ti / Al, and the control electrode 32 is, for example, a metal oxide such as SiO or SiN It is possible to form a laminated film of a lower layer film made of and an upper layer film made of a metal such as Ni, Au, Mo, Pt. In this way, the semiconductor element 11 of FIG. 2 can be manufactured.
- the average Al composition at the upper part of the buffer layer 25 is made higher than the average Al composition below the upper part of the buffer layer 25 to reduce the warpage of the wafer, thereby reducing peripheral cracks. It is possible to suppress the occurrence of internal cracks. Thereby, it is possible to manufacture a semiconductor element having good electrical characteristics such as breakdown voltage and reliability.
- the epitaxial wafer 10 shown in FIG. 1 was manufactured using the manufacturing method described with reference to FIG.
- the Al x Ga 1-x N layer 17 was an AlN layer
- the Al y Ga 1-y N (x> y) layer 18 was a GaN layer
- the first insertion layer 20 was a GaN layer.
- the Al ⁇ Ga 1- ⁇ N layer 21 was an AlN layer
- the Al ⁇ Ga 1- ⁇ N layer 22 was a GaN layer
- the second insertion layer 24 was a GaN layer.
- the first multilayer buffer area 19 and the second multilayer buffer area 23 have a repetition number of 8 pairs, and the repetition number of the second multilayer structure buffer area 23 and the second insertion layer 24 is 3 pairs. It was.
- the first insertion layer (GaN layer) 20 was 200 nm
- the second insertion layer (GaN layer) 24 was 160 nm.
- the manufactured epitaxial wafer 10 was examined for the amount of warpage of the wafer, the outer crack length, and the presence of internal cracks.
- the wafer warpage was measured based on the definition shown in FIG. The results are shown in Table 2.
- An epitaxial wafer 10 was produced in the same manner as in the example. However, the thickness of the second insertion layer (GaN layer) 24 was 200 nm.
- the produced epitaxial wafer 10 was examined for the amount of warpage of the wafer, the peripheral crack length, and the presence of internal cracks in the same manner as in the example. The results are shown in Table 2.
- the present invention is not limited to the above embodiment.
- the above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
- a thick GaN layer such as a pressure resistant layer may be provided between the buffer layer 25 and the channel layer 26.
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Abstract
Description
図6の半導体ウェーハ1において、バッファ層3は、シリコン基板2と能動層4(電子走行層4aと電子供給層4bからなる)との間に設けられており、バッファ層3は、第一の多層構造バッファ領域5と、第一の多層構造バッファ領域5の上に設けられたGaNからなる第二の単層構造バッファ領域8と、第二の単層構造バッファ領域8の上に設けられた第二の多層構造バッファ領域5’を有している。
さらに、第一の多層構造バッファ領域5及び第二の多層構造バッファ領域5’は、サブ多層構造バッファ領域6と、GaNからなり第二の単層構造バッファ領域8より薄い第一の単層構造バッファ領域7とが繰り返し積層された多層構造を有している。
また、サブ多層構造バッファ領域6は、AlNからなる第一の層と、GaNからなる第二の層とが繰り返し積層された多層構造を有している。
このような構成により、バッファ層の上部の平均Al組成を効果的に高くすることができ、ウェーハの反りを効果的に低減させるとともに、内部クラックの発生を効果的に抑制することができる。
このような構成により、バッファ層の上部の平均Al組成をより高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
このような構成により、バッファ層の上部の平均Al組成をより高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
このような構成によっても、バッファ層の上部の平均Al組成をより高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
このような構成によっても、バッファ層の上部の平均Al組成をより高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
このような構成によっても、バッファ層の上部の平均Al組成をより高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
このようなエピタキシャルウェーハの製造方法を用いれば、バッファ層の上部の平均Al組成を効果的に高くすることができる。
前述のように、シリコン基板上やサファイア基板上に形成された窒化物半導体層の特性を改善するために、バッファ層を設けること、及び、バッファ層の構成を最適化することが行われてきたが、従来のバッファ層においては、ウェーハの反りや内部クラックの発生の点で改善の余地があった。
その結果、バッファ層の上部に位置する第2のバッファ層の平均Al組成がバッファ層の下部に位置する第1のバッファ層の平均Al組成よりも高い構成とすることによって、バッファ層の上部の平均Al組成を高くすることができ、これによってウェーハの反りを低減させるとともに、内部クラックの発生を抑制することができることを見出し、本発明をなすに至った。
GaN層(又はAl組成の少ないAlGaN層)IとAlN層(又はAl組成の多いAlGaN層)IIが交互に積層された構造において、内部クラックはGaN層(又はAl組成の少ないAlGaN層)Iに引っ張られることによりAlN層(又はAl組成の多いAlGaN層)IIが割れることにより生じるため、内部クラックの発生を抑制するには、AlN層(又はAl組成の多いAlGaN層)IIに加えられる引っ張り応力を低減させることが必要となる。GaN層(又はAl組成の少ないAlGaN層)IとAlN層(又はAl組成の多いAlGaN層)IIが交互に積層されたバッファ構造中でシリコン基板から離れるにつれて徐々にGaN層(又はAl組成の少ないAlGaN層)Iが格子緩和していくため、特にバッファ構造の上部で平均Al組成を高めることで、従来に比べてバッファ構造上部のGaN層(又はAl組成の少ないAlGaN層)Iへの歪を強め、AlN層(又はAl組成の多いAlGaN層)IIへの歪を弱めることで内部クラックの抑制効果を得ているものと推定される。
バッファ層の上部の平均Al組成が高くなることにより、この上に形成されるGaN層(すなわち、チャネル層)にも強い圧縮応力がかかる。これによりエピタキシャル成長中の負側への変形(すなわち、負側のウェーハの反り)が強くなり、エピタキシャル成長終了後に室温に戻した際のウェーハの反り(正側のウェーハの反り)が小さくなると推定される。なお、ウェーハの反りが小さくなることで、ウェーハの外周に発生するクラック(以下、外周クラックと称する)も抑制される。
図1(a)に示す本発明のエピタキシャルウェーハ10は、シリコン系基板12と、シリコン系基板12上に設けられたバッファ層25と、バッファ層25上に設けられたチャネル層26を有している。
ここで、シリコン系基板12は、例えば、SiまたはSiCからなる基板である。
バッファ層25は、第1のバッファ層15と第1のバッファ層15上に設けられた第2のバッファ層16を有している。
ここで、AlxGa1-xN層17はAlN層(すなわち、x=1)又はAlGaN層とすることができ、AlyGa1-yN層18はGaN層(すなわち、y=0)とすることができ、第1の挿入層20はGaN層(すなわち、z=0)とすることができる。
ここで、AlαGa1-αN層21はAlN層(すなわち、α=1)又はAlGaN層とすることができ、AlβGa1-βN層22はGaN層(すなわち、β=0)とすることができ、第2の挿入層24はGaN層(すなわち、γ=0)とすることができる。
このような構成により、バッファ層25の上部の平均Al組成をバッファ層25の上部よりも下側のバッファ層25の下部の平均Al組成と比較して効果的に高くすることができ、ウェーハの反りを効果的に低減させるとともに、内部クラックの発生を効果的に抑制することができる。
このような構成により、バッファ層25の上部の平均Al組成をバッファ層25の上部よりも下側のバッファ層25の下部の平均Al組成と比較してより効果的に高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
このような構成により、バッファ層25の上部の平均Al組成をバッファ層25の上部よりも下側のバッファ層25の下部の平均Al組成と比較してより効果的に高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
又、第2の多層構造バッファ領域23のAlαGa1-αN層21と、第1の多層構造バッファ領域19のAlxGa1-xN層17を比較した時、x<αであることが好ましい。例えば、AlαGa1-αN層21をAl0.8Ga0.2N層とし、AlxGa1-xN層17をAl0.6Ga0.4N層としてもよい。
さらに、第2の多層構造バッファ領域23のAlβGa1-βN層22と、第1の多層構造バッファ領域19のAlyGa1-yN層18を比較した時、y<βであることが好ましい。例えば、AlβGa1-βN層22をAl0.3Ga0.7N層とし、AlyGa1-yN層18をAl0.1Ga0.9N層としてもよい。
これらのような構成によっても、バッファ層25の上部の平均Al組成をバッファ層25の上部よりも下側のバッファ層25の下部の平均Al組成と比較してより効果的に高くすることができ、ウェーハの反りをより効果的に低減させるとともに、内部クラックの発生をより効果的に抑制することができる。
上記バッファ層25の上部の平均Al組成を高くする方法は、同時に複数の方法を行ってもよく、それにより、より上部の平均Al組成を高くすることができる。
図2(a)に示す本発明の半導体素子11は、図1を用いて上記で説明したエピタキシャルウェーハ10の上に、窒化ガリウム系半導体(例えば、AlGaN)からなるバリア層27を設け、バリア層27上に第1の電極(ソース電極)30、第2の電極(ドレイン電極)31、及び、制御電極32を設けたものである。半導体素子11は、例えば、高電子移動度トランジスタ(HEMT)である。
チャンネル層26とバリア層27は、能動層29を構成している。
第1の電極30及び第2の電極31は、第一の電極30から、チャネル層26内に形成された二次元電子ガス28を介して、第2の電極31に電流が流れるように配置されている。第1の電極30と第2の電極31との間に流れる電流は、制御電極32に印可される電位によってコントロールすることができる。
まず、シリコン系基板12を準備する(図3(a)を参照)。
ここで、AlxGa1-xN層17はAlN層(すなわち、x=1)とすることができ、AlyGa1-yN(x>y)層18はGaN層(すなわち、y=0)とすることができ、第1の挿入層20はGaN層(すなわち、z=0)とすることができる。
ここで、AlαGa1-αN層21はAlN層(すなわち、α=1)とすることができ、AlβGa1-βN層22はGaN層(すなわち、β=0)とすることができ、第2の挿入層24はGaN層(すなわち、γ=0)とすることができる。
このようにして、図1のエピタキシャルウェーハ10を製造することができる。
このようなエピタキシャルウェーハの製造方法を用いれば、バッファ層25の上部の平均Al組成をバッファ層25の上部より下側の下部の平均Al組成と比較してより効果的に高くすることができる。
まず、図3を用いて説明した製造方法を用いて作製したエピタキシャルウェーハ10(図3(d)を参照)上に、窒化ガリウム系半導体からなるバリア層27をエピタキシャル成長により形成する(図4(a)を参照)。
このようにして、図2の半導体素子11を製造することができる。
図3を用いて説明した製造方法を用いて、図1のエピタキシャルウェーハ10を作製した。ただし、AlxGa1-xN層17はAlN層とし、AlyGa1-yN(x>y)層18はGaN層とし、第1の挿入層20はGaN層とした。また、AlαGa1-αN層21はAlN層とし、AlβGa1-βN層22はGaN層とし、第2の挿入層24はGaN層とした。また、第1の多層構造バッファ領域19、第2の多層構造バッファ領域23は、繰り返し数を8ペアとし、第2の多層構造バッファ領域23と第2の挿入層24の繰り返し数は、3ペアとした。
さらに、第1の挿入層(GaN層)20を200nmとし、第2の挿入層(GaN層)24を160nmとした。
実施例と同様にしてエピタキシャルウェーハ10を作製した。ただし、第2の挿入層(GaN層)24の膜厚を200nmとした。
例えば、上記実施形態において、バッファ層25とチャネル層26との間に耐圧層等の厚いGaN層を設けてもよい。
Claims (11)
- シリコン系基板と、
該シリコン系基板の上に配置され、AlxGa1-xN層とAlyGa1-yN層(x>y)とが交互に配置された第1の多層構造バッファ領域と、前記AlyGa1-yN層よりも厚いAlzGa1-zN層(x>z)からなる第1の挿入層とを有し、前記第1の多層構造バッファ領域と、前記第1の挿入層とが交互に配置された第1のバッファ層と、
前記第1のバッファ層の上に配置され、AlαGa1-αN層とAlβGa1-βN層(α>β)とが交互に配置された第2の多層構造バッファ領域と、前記AlβGa1-βN層よりも厚いAlγGa1-γN層(α>γ)からなる第2の挿入層とを有し、前記第2の多層構造バッファ領域と、前記第2の挿入層とが交互に配置された第2のバッファ層と、
前記第2のバッファ層の上に配置され、前記第2の挿入層よりも厚いチャネル層と
を有し、
前記第2のバッファ層の平均Al組成が前記第1のバッファ層の平均Al組成よりも高いことを特徴とするエピタキシャルウェーハ。 - 前記第2の挿入層が前記第1の挿入層よりも薄いことを特徴とする請求項1に記載のエピタキシャルウェーハ。
- 前記第2の多層構造バッファ領域の前記AlαGa1-αN層と前記AlβGa1-βN層の繰り返し数が、前記第1の多層構造バッファ領域の前記AlxGa1-xN層と前記AlyGa1-yN層の繰り返し数よりも多いことを特徴とする請求項1又は請求項2に記載のエピタキシャルウェーハ。
- 前記第2の多層構造バッファ領域の前記AlβGa1-βN層が、前記第1の多層構造バッファ領域の前記AlyGa1-yN層より薄いことを特徴とする請求項1から請求項3のいずれか一項に記載のエピタキシャルウェーハ。
- 前記第2の多層構造バッファ領域の前記AlαGa1-αN層が、前記第1の多層構造バッファ領域の前記AlxGa1-xN層より厚いことを特徴とする請求項1から請求項4のいずれか一項に記載のエピタキシャルウェーハ。
- 前記第2の多層構造バッファ領域の前記AlαGa1-αN層と、前記第1の多層構造バッファ領域の前記AlxGa1-xN層とにおいて、x<αであることを特徴とする請求項1から請求項5のいずれか一項に記載のエピタキシャルウェーハ。
- 前記第2の多層構造バッファ領域の前記AlβGa1-βN層と、前記第1の多層構造バッファ領域の前記AlyGa1-yN層とにおいて、y<βであることを特徴とする請求項1から請求項6のいずれか一項に記載のエピタキシャルウェーハ。
- 請求項1から請求項7のいずれか一項に記載のエピタキシャルウェーハと、
前記エピタキシャルウェーハ上に配置された窒化ガリウム系半導体からなるバリア層と、
前記バリア層上に配置された第1の電極、第2の電極、及び、制御電極と
を有することを特徴とする半導体素子。 - シリコン系基板を準備する工程と、
該シリコン系基板の上に、AlxGa1-xN層とAlyGa1-yN層(x>y)とが交互に配置された第1の多層構造バッファ領域と、前記AlyGa1-yN層よりも厚いAlzGa1-zN層(x>z)からなる第1の挿入層とを有し、前記第1の多層構造バッファ領域と、前記第1の挿入層とが交互に配置された第1のバッファ層をエピタキシャル成長により形成する工程と、
前記第1のバッファ層の上に、AlαGa1-αN層とAlβGa1-βN層(α>β)とが交互に配置された第2の多層構造バッファ領域と、前記AlβGa1-βN層よりも厚いAlγGa1-γN層(α>γ)からなる第2の挿入層とを有し、前記第2の多層構造バッファ領域と、前記第2の挿入層とが交互に配置された第2のバッファ層をエピタキシャル成長により形成する工程と、
前記第2のバッファ層の上に、前記第2の挿入層よりも厚いチャネル層をエピタキシャル成長により形成する工程と
を含み、
前記第2のバッファ層の平均Al組成を前記第1のバッファ層の平均Al組成よりも高くすることを特徴とするエピタキシャルウェーハの製造方法。 - 前記第2の挿入層を前記第1の挿入層よりも薄くすることで、前記第2のバッファ層の平均Al組成を前記第1のバッファ層の平均Al組成よりも高くすることを特徴とする請求項9に記載のエピタキシャルウェーハの製造方法。
- 請求項9又は請求項10に記載の方法により製造されたエピタキシャルウェーハ上に、窒化ガリウム系半導体からなるバリア層をエピタキシャル成長により形成する工程と、
前記バリア層上に、第1の電極、第2の電極、及び、制御電極を形成する工程と
を含むことを特徴とする半導体素子の製造方法。
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