JP5080429B2 - Nitride semiconductor multilayer structure and manufacturing method thereof - Google Patents

Description

  The present invention relates to a nitride semiconductor multilayer structure and a method for manufacturing the same.

Aluminum nitride (hereinafter also referred to as “AlN”), gallium nitride (hereinafter also referred to as “GaN”), indium nitride (hereinafter also referred to as “InN”), and aluminum nitride gallium indium Al which is a mixed crystal thereof. Nitride semiconductors such as _x Ga _1-xy In _y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) are used for the light emitting / receiving device and the electronic traveling device using the material characteristics thereof. A wide range of research has been conducted because it can be applied to. Nitride semiconductors have already been put into practical use as light-emitting diodes and laser diodes, but in recent years, further research has been conducted in order to expand the application fields of nitride semiconductors.

  Since it is difficult to grow a large bulk single crystal of a nitride semiconductor, a sapphire substrate is generally used as a substitute substrate, and nitride semiconductor is nitrided by heteroepitaxial growth on a sapphire substrate (0001). A physical semiconductor device is formed. When a sapphire substrate is used, a difference of 16% or more of the lattice constant existing between the sapphire substrate and the nitride semiconductor and the price of the sapphire substrate become a problem. A sapphire substrate having a large diameter of 3 to 4 inches or more is still expensive, and is a factor that hinders the price reduction of nitride semiconductor devices.

  On the other hand, since the silicon substrate is used in large-scale integrated circuits, the manufacturing technology is advanced. Therefore, the 4-inch substrate is about 1/10 the price of the sapphire substrate, and is cheaper than the sapphire substrate. Are better. In addition, the thermal conductivity of silicon is larger than that of sapphire and is excellent for forming a nitride semiconductor device having excellent heat dissipation. For this reason, development of a technique for epitaxially growing a high-quality nitride semiconductor layer on a silicon substrate is expected.

  However, when a nitride semiconductor layer is grown on a silicon substrate, there arises a problem that cracks occur in the nitride semiconductor layer. The maximum thickness of the nitride semiconductor layer that allows the nitride semiconductor layer to grow without cracking is referred to as a critical film thickness. Increasing the critical film thickness is necessary to expand the application range of nitride semiconductors. When gallium nitride (GaN) is directly grown on a silicon substrate, it is difficult to grow the gallium nitride (GaN) layer to a critical film thickness of 1 μm or more without generating cracks.

Hereinafter, a conventional technique for forming a nitride semiconductor layer on a silicon substrate will be described. Patent Document 1 (Japanese Patent Application Laid-Open No. 2003-059948) selects one of indium and boron as a material constituting a multilayer structure when a nitride semiconductor layer is grown on the silicon substrate via the multilayer structure. It is disclosed that Al _x M _y Ga _1-xy N (0 <x ≦ 1, 0 ≦ y <1, x + y ≦ 1) is used as the element to be M. Patent Document 1 describes the effect of suppressing cracks generated in the nitride semiconductor layer from the viewpoint of the thermal expansion coefficient (paragraph 0010) and the material robustness (paragraph 0041).

Patent Document 2 (Japanese Patent Laid-Open No. 2008-053399) discloses that when a nitride semiconductor layer is grown on a silicon substrate via a multilayer structure, In _x Al _1-x N / B _y Al _{1 is used} as the multilayer structure. _-Y N (0 <x ≦ 1, 0 <y ≦ 1) is disclosed. Further, in Patent Document 2, in a ternary mixed crystal, if the composition ratio of boron is 0.2 or more, the growth is performed by locally transitioning from a hexagonal system to a cubic system. It is disclosed that 0.2 or less is desirable (paragraph 0045).

  Non-Patent Document 1 (Tomoya Sugahara) has grown a gallium nitride (GaN) semiconductor layer of 1 μm or more on a silicon substrate via an aluminum nitride (AlN) / gallium nitride (GaN) multilayer structure, (GaN) semiconductor layer is evaluated and tensile stress and compressive stress are studied.

Non-Patent Document 2 (Shunsuke Watanabe), the molar fraction of viable boron quality crystal, aluminum (Al) does not include the ternary mixed crystal B _y Ga _{1-y N,} the mole fraction of boron y Is a ternary mixed crystal Al _x B _1-x N containing no gallium (Ga) and having a molar fraction x of boron of about 0.023 or less.

  FIG. 3 shows a cross section of a conventional nitride semiconductor multilayer structure. The conventional nitride semiconductor multilayer structure shown in FIG. 3 is disposed on the silicon substrate 10, the silicon substrate 10, the first layer 211, and the second layer disposed on the first layer 211. The multilayer structure layer 21 in which the layers 212 are alternately stacked, and the nitride semiconductor layer 22 disposed on the multilayer structure layer 21 are included. A conventional nitride semiconductor multilayer structure will be described using Non-Patent Document 1 and Patent Document 1 as examples.

  Non-Patent Document 1 is an example of a conventional nitride semiconductor multilayer structure. On a silicon substrate, the first layer 211 is made of aluminum nitride (AlN) and the second layer 212 is made of gallium nitride (GaN) alternately. The crystal growth is repeated to form an aluminum nitride (AlN) / gallium nitride (GaN) multilayer structure layer 21, and a gallium nitride (1 μm or more) via the aluminum nitride (AlN) / gallium nitride (GaN) multilayer structure layer 21. GaN) semiconductor layer is growing. However, the maximum critical film thickness of the gallium nitride (GaN) semiconductor layer was about 1.5 μm.

Patent Document 1 discloses that, on a silicon substrate, as the first layer 211 and the second layer 212, an element selected from either indium or boron is M, and Al _x M _y Ga _1-xy N (0 < The multilayer structure layer is formed by alternately stacking the composition ratios of x ≦ 1, 0 ≦ y <1, and x + y ≦ 1), and the nitride semiconductor layer is grown through the multilayer structure layer.

JP 2003-059948 A JP 2008-053399 A Tomoya Sugahara, Jeong-Sik Lee and Kohji Ohtsuka, Journal of Applied Physics, Vol. 43 (2004), p.L1595-L1597 Shunsuke Watanabe, Takayoshi Takano, Keisuke Jinen, Jun Yamamoto and Hideo Kawanishi, Phys. Stat. Sol. (C), Vol.0, No.7 (2003), p.2691-2694

  As one of the major problems that occur when a nitride semiconductor layer is epitaxially grown on a silicon substrate, it has been explained that cracks occur in the nitride semiconductor growth layer. This crack mainly occurs when a silicon substrate having a nitride semiconductor layer grown on the surface is cooled from a growth temperature of 1000 ° C. or higher to room temperature. It has been a problem to grow a nitride semiconductor layer by increasing the critical film thickness (size of 2 μm or more) without generating cracks.

  By laminating a multilayer structure layer made of a binary compound or a multi-element mixed crystal of a ternary mixed crystal or more on a silicon substrate, and growing a nitride semiconductor layer thereon, a crack is generated in the nitride semiconductor layer. Attempts have been made to suppress this and increase the critical thickness of the nitride semiconductor layer. However, since the molar fraction and growth rate of the compound constituting the mixed crystal change every moment depending on the state of the reaction furnace, it is particularly difficult to precisely control a multi-element mixed crystal higher than the ternary mixed crystal. It is a problem to form a multilayer structure layer with good reproducibility.

  In order to increase the critical thickness of the nitride semiconductor layer when growing the nitride semiconductor layer on the silicon substrate via the multilayer structure layer, the crack generation mechanism, thermal expansion coefficient, material robustness It has been studied from various viewpoints such as tensile stress and compressive stress. Under such circumstances, it has been studied to increase the critical film thickness of the nitride semiconductor layer formed on the multilayer structure layer by using a mixed crystal containing boron as a multilayer structure layer serving as a buffer layer. However, for mixed crystals containing boron, it is difficult to increase the boron ratio to make a good quality mixed crystal, so there are few experimental examples, how to increase the boron ratio, good reproducibility and good quality mixed crystals. The issue is whether to grow

  The present invention allows a nitride semiconductor layer to be thickly grown on a silicon substrate without causing cracks by crystallizing the multilayer structure layer as a buffer layer on the silicon substrate with good controllability. It is an object of the present invention to provide a multilayer structure that can be manufactured and a method for manufacturing the same.

In order to achieve the above object, a method for producing a nitride semiconductor multilayer structure of the present invention includes:
A step (a) of crystal growth of an aluminum nitride layer on a silicon substrate, and a boron nitride layer and a gallium nitride layer are alternately and repeatedly grown on the aluminum nitride layer, whereby the boron nitride layer and the gallium nitride are grown. The method includes a step (b) of forming a multilayer structure layer in which layers are alternately stacked, and a step (c) of growing a nitride semiconductor layer on the multilayer structure layer.

  The method for manufacturing a nitride semiconductor multilayer structure according to the present invention further includes a step (d) of crystal growing an aluminum gallium nitride layer on the aluminum nitride layer after the step (a), The multilayer structure layer may be formed on the layer by the step (b).

  Further, in the method for producing a nitride semiconductor multilayer structure of the present invention, the step (c) in which the lattice constant of the nitride semiconductor layer is larger than the lattice constant of the multilayer structure layer may be performed on the multilayer structure layer. This may be a step of growing a nitride semiconductor layer having a lattice constant larger than that of the multilayer structure layer.

  The nitride semiconductor multilayer structure according to the present invention includes a silicon substrate, an aluminum nitride layer disposed on the silicon substrate, and an aluminum nitride layer disposed on the aluminum nitride layer, wherein the boron nitride layer and the gallium nitride layer are alternately disposed. It has a multilayer structure layer to be laminated, and a nitride semiconductor layer disposed on the multilayer structure layer.

  The nitride semiconductor multilayer structure of the present invention has an aluminum gallium nitride layer, the aluminum gallium nitride layer is disposed on the aluminum nitride layer, and the multilayer structure layer is formed of the aluminum gallium nitride layer. It is good also as arrange | positioning above.

  The nitride semiconductor multilayer structure of the present invention may be characterized in that a lattice constant of the nitride semiconductor layer is larger than a lattice constant of the multilayer structure layer.

  According to the present invention, as a buffer layer on a silicon substrate, a boron nitride (BN) / gallium nitride (GaN) multilayer structure layer is crystal-grown with good controllability on the aluminum nitride layer and the aluminum nitride layer, thereby boron nitride (BN). / The nitride semiconductor layer can be grown thickly on the gallium nitride (GaN) multilayer structure layer without causing cracks.

  Further, even when the multilayer structure layer of the present invention is grown on the aluminum nitride layer and the aluminum gallium nitride layer as the buffer layer on the silicon substrate, the nitride semiconductor layer can be grown thick without causing cracks. it can. By providing the aluminum gallium nitride layer, the surface of the aluminum nitride layer can be planarized, which is preferable.

  Furthermore, by selecting a nitride semiconductor layer having a lattice constant larger than that of the multilayer structure layer as the nitride semiconductor layer grown on the multilayer structure layer, the compressive stress that the nitride semiconductor layer receives from the multilayer structure is reduced. The tensile stress generated in the cooling process after the growth can be offset, which is preferable.

  In addition, since the multilayer structure layer of this invention is comprised only with a binary compound, it can be manufactured with sufficient reproducibility.

  The best mode for carrying out the present invention will be described below with reference to the drawings. In addition, the same referential mark is attached | subjected to the same component and description is abbreviate | omitted.

  A nitride semiconductor multilayer structure according to an embodiment of the present invention will be described with reference to FIG. A nitride semiconductor multilayer structure according to an embodiment of the present invention includes a silicon substrate 10, an aluminum nitride layer 11 disposed on the silicon substrate 10 by crystal growth, and an aluminum nitride layer 11. The multilayer structure layer 13 in which the boron layers 131 and the gallium nitride layers 132 are alternately stacked by crystal growth, and the nitride semiconductor layer 14 disposed by crystal growth on the multilayer structure layer 13 are included.

  In the nitride semiconductor multilayer structure according to the embodiment of the present invention, a boron nitride (BN) / gallium nitride (GaN) multilayer structure layer is formed with good controllability as a buffer layer on a silicon substrate. A nitride semiconductor layer can be formed thick (2 μm or more) on the (BN) / gallium nitride (GaN) multilayer structure layer without causing cracks.

  A nitride semiconductor multilayer structure according to an embodiment of the present invention includes an aluminum gallium nitride layer 12, and the aluminum gallium nitride layer 12 is disposed on the aluminum nitride layer 11 by crystal growth, and the multilayer structure layer 13 may be disposed on the aluminum gallium nitride layer.

  The reason why the aluminum gallium nitride layer 12 is provided is to planarize the surface of the aluminum nitride (AlN) layer 11. Accordingly, the aluminum gallium nitride layer 12 may be omitted if the surface of the aluminum nitride (AlN) layer 11 is sufficiently flat to form the multilayer structure layer 13.

  In the nitride semiconductor multilayer structure of the present invention, the lattice constant of the nitride semiconductor layer 14 is made larger than the lattice constant of the multilayer structure layer 13. Thereby, the nitride semiconductor layer 14 can be formed thick on the multilayer structure layer 13. This is because the compressive stress that the nitride semiconductor layer 14 receives from the multilayer structure layer 13 cancels out the tensile stress generated in the cooling process after the growth is completed. Since boron nitride has a smaller lattice constant than gallium nitride and aluminum nitride, the lattice constant of the multilayer structure layer including the boron nitride layer can be easily reduced, and the compressive stress exerted on the nitride semiconductor layer thereon is large. It is to become.

  Next, a method for manufacturing a nitride semiconductor multilayer structure according to an embodiment of the present invention will be described with reference to FIG. First, a silicon substrate 10 is prepared as a substrate for crystal growth of a nitride semiconductor multilayer structure. The silicon substrate 10 is preferably a plane orientation (111) substrate or a substrate in the range of −2 degrees to +2 degrees from this plane orientation. After this silicon substrate 10 is cleaned with a sulfuric acid-based cleaning solution, a treatment of immersing in a hydrofluoric acid-based solution is performed.

  Next, nitride semiconductor layers are sequentially grown on the silicon substrate 10 using a metal organic chemical vapor deposition (MOVPE) method. The use of metal organic vapor phase epitaxy is an example of the present invention, and molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE), or the like may be used.

Next, the silicon substrate 10 is heated to, for example, a substrate temperature of 1100 ° C., and held for 10 minutes in a hydrogen atmosphere for cleaning. Then, trimethylaluminum (TMA) is used as a group III material, and ammonia (NH ₃ ) is used as a group V material, and an aluminum nitride (AlN) layer 11 is epitaxially grown in a thickness range of 20 to 200 nm. The aluminum nitride (AlN) layer 11 is stacked on the silicon substrate 10 because when a layer containing gallium (Ga) is directly stacked on the silicon substrate 10, silicon (Si) and gallium (Ga) react. This is to prevent the silicon substrate 10 from being etched (eroded).

Next, an aluminum gallium nitride Al _x Ga _1-x N layer 12 is grown in a thickness range of 10 to 100 nm as necessary. Trimethylgallium (TMG) is used in addition to trimethylaluminum (TMA) as a group III material, and ammonia (NH ₃ ) is used as a group V material. The supply ratio of trimethylaluminum (TMA) and trimethylgallium (TMG) is controlled so that the molar fraction x of AlN becomes a preferable value of x <1. The reason why the aluminum nitride gallium Al _x Ga _1-x N layer 12 is grown is to bury the uneven shape on the surface of the aluminum nitride (AlN) layer 11 and planarize it.

Therefore, if the surface of the aluminum nitride (AlN) layer 11 is flat enough to grow the boron nitride / gallium nitride (BN / GaN) multilayer structure 13 later, the Al _x Ga _1-x N layer There are no particular restrictions on 12 x, and for example, x may be about 0.25. The growth temperature of the Al _x Ga _1-x N layer 12 may be 1100 ° C. or a temperature different from 1100 ° C. If the surface of the aluminum nitride (AlN) layer 11 is sufficiently flat, the growth of the Al _x Ga _1-x N layer 12 may be omitted.

Next, a boron nitride layer as the first layer 131 and a gallium nitride layer as the second layer 132 are alternately and repeatedly grown to form a boron nitride / gallium nitride (BN / GaN) multilayer structure 13. . When a boron nitride layer is grown as the first layer 131, triethylboron (TEB) is used as a group III material, and ammonia (NH ₃ ) is used as a group V material. Further, when a gallium nitride layer is grown as the second layer 132, trimethylgallium (TMG) is used as a group III material and ammonia (NH ₃ ) is used as a group V material. In FIG. 1, only four cycles of the multilayer structure 13 are illustrated, but actually, the multilayer structure 13 has a large number of cycles of four cycles or more, not four cycles.

  The boron nitride layer as the first layer 131 is grown at a high temperature of 1400 ° C., for example, so that the quality of the boron nitride layer is improved. Actually, since the silicon substrate is used in the present invention, when the boron nitride layer is grown at a temperature around 1414 ° C. which is the melting point of silicon, the quality of the boron nitride layer is improved, but the silicon substrate is melted, May reduce performance. Therefore, it is preferable to set the growth temperature of the boron nitride layer so that the temperature of the silicon substrate is about 1350 ° C.

  When boron nitride is stacked on a hexagonal semiconductor layer, it can be formed as a hexagonal semiconductor layer by controlling the growth conditions, but if the growth conditions cannot be controlled well, a cubic layer is formed. Occurs and the film quality deteriorates. In the present invention, by using a high temperature process, growth conditions suitable for hexagonal crystal growth can be easily realized, and a uniform and excellent quality boron nitride layer can be grown.

As described above, in order to grow a high-quality boron nitride (BN) layer, for example, Al _x In _y Ga _1-xy N containing no boron (0 ≦ x ≦ 1, 0 ≦ y ≦ It is necessary to raise the growth temperature as compared with the case of growing 1, 0 ≦ x + y ≦ 1). A graphite heater whose surface is coated with silicon carbide, which is usually used for growing an Al _x In _y Ga _1-xy N layer, is inferior in atmospheric resistance at high temperatures. In practice, defects such as pinholes are generated during use, and graphite is deteriorated. It is difficult to grow a BN layer having desired characteristics by growing a BN layer at a high temperature using a graphite heater whose surface is coated with silicon carbide.

  Therefore, for example, a graphite heater whose surface is coated with tantalum carbide (TaC) is used. A graphite heater whose surface is coated with tantalum carbide (TaC) has excellent atmospheric resistance to ammonia at a high temperature and does not deteriorate at a temperature of about 1400 ° C. Therefore, by using a graphite heater whose surface is coated with tantalum carbide (TaC), the temperature of the silicon substrate is set to about 1350 ° C., and a boron nitride layer is grown to obtain a high-quality boron nitride layer. The quality of the boron nitride / gallium nitride (BN / GaN) multilayer structure 13 can be improved.

  Since the gallium nitride layer to be the second layer 132 has high volatility when grown at 1350 ° C., the growth rate is lower than that when grown at 1100 ° C., which is a normal growth temperature. Therefore, when the growth temperature of the gallium nitride layer is set to a high temperature in accordance with the growth temperature of the boron nitride layer, the desired amount of gallium nitride is controlled by increasing the supply amount of trimethylgallium TMG and controlling the amount of gallium. It is possible to grow layers.

  For example, when the film thickness of the boron nitride layer as the first layer 131 is in the range of 0.1 to 2.0 nm, and the film thickness of the gallium nitride layer as the second layer 132 is in the range of 3.0 to 5.0 nm, The boron nitride / gallium nitride (BN / GaN) multilayer structure 13 can be grown with good periodicity and coherently. The boron nitride / gallium nitride (BN / GaN) multilayer structure 13 grown under this condition makes it possible to effectively apply compressive stress to the nitride semiconductor layer 14 grown later on the multilayer structure 13. The tensile stress generated in the physical semiconductor layer 14 can be offset. Thereby, the nitride semiconductor layer 14 can be formed thick (2 μm or more).

The boron nitride / gallium nitride (BN / GaN) multilayer structure 13 is composed of a binary compound for both boron nitride (BN) and gallium nitride (GaN). Multi-layer mixed crystal Al _x B _z Ga _1-x-yz In _y N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ x + y + z ≦ 1) is used to form a multilayer structure Compared to the case where a multilayer structure is formed using a binary compound, the molar fraction of boron (B) in the multilayer structure layer is increased, and the periodicity of the multilayer structure layer is significantly improved. It becomes possible.

Thereafter, the growth temperature is lowered to about 1100 ° C., and the nitride semiconductor is controlled by controlling the growth time using one or more of trimethylaluminum (TMA), trimethylgallium (TMG), and trimethylindium (TMI) as a raw material. Grow layers. After the growth is completed, the nitride semiconductor multilayer structure is taken out by cooling to room temperature. The nitride semiconductor layer grown on the multilayer structure layer needs to have a lattice constant larger than that of the multilayer structure layer. Examples of such a nitride semiconductor layer include GaN, Ga _1-x In _x N (0 <x ≦ 1), and B _x Ga _1-x N, Al _x Ga if the molar fraction is appropriately selected. _1-xN can be used.

  Next, the following experiment was performed in order to investigate the critical film thickness of the nitride semiconductor layer 14. For example, by changing the thickness of the boron nitride (BN) layer that is the first layer 131 and the thickness of the gallium nitride (GaN) layer that is the second layer 132, boron nitride / gallium nitride (BN / GaN) The multilayer structure layer 13 was grown, and the growth was stopped up to the multilayer structure layer 13 to prepare a sample. About the produced sample, the generation | occurrence | production state of the crack to a multilayer structure was observed with the optical microscope, and the periodicity of the multilayer structure was evaluated by the X ray diffraction method.

  Next, a nitride semiconductor layer 14 made of gallium nitride (GaN) was grown on the multilayer structure 13 grown under each condition as a sample while changing the film thickness. Each sample was observed using an optical microscope, and the critical film thickness of the nitride semiconductor layer 14 in which cracks occurred in the nitride semiconductor layer 14 was evaluated.

  FIG. 2 shows the thickness of the boron nitride (BN) layer as the first layer 131 and the gallium nitride (GaN) layer as the second layer 132, with each sample as Experimental Examples 1 to 13 and Comparative Example 1. The table shows the thickness of the film, the occurrence and periodicity of cracks in the boron nitride / gallium nitride (BN / GaN) multilayer structure 13, and the critical film thickness of the nitride semiconductor layer 14. In FIG. 2, a circle is indicated when no crack is generated in the multilayer structure 13, and an X is indicated when a crack is generated. Moreover, it is marked with ◯ when the periodicity of the crack 13 is good and marked with x when the periodicity is inferior.

  In the experiment in which the thickness of the second layer made of GaN is constant at 10 nm and the thickness of the first layer made of BN is changed, cracks are generated in the multilayer structure 13 in Experimental Example 7. This is presumably because the multilayer structure 13 itself contains tensile stress. In Experimental Examples 1 to 6, no crack was detected in the multilayer film structure, and sharp satellite peaks were observed even in X-ray diffraction, and it was evaluated that their periodicity was good. Furthermore, the GaN layer is grown on the multilayer structure 3 by 1 μm or more without cracking, but the critical film thickness is 2 μm or more because the first film made of BN shown in Experimental Examples 4 to 6 is used. This is the case when the layer thickness is 0.5 to 2.0 nm.

  In the experiment in which the thickness of the first layer made of BN is constant at 1 nm and the thickness of the second layer made of GaN is changed, in Experimental Examples 8 and 9, the entire multilayer structure 13 is averaged. Since the mole fraction of BN is increased, in Experimental Example 13, the mole fraction of GaN when the entire multilayer structure 13 is averaged is increased, so that the periodicity is disturbed, thereby sharpening the X-ray diffraction pattern. Satellite peaks are not detected. The reason why the GaN layer is grown on the multilayer structure 3 by 1 μm or more without cracking is when the thickness of the second layer made of GaN in Examples 10 to 13 is 3.0 to 5.0 nm. . The critical film thickness of the GaN layer is 2 μm or more in the case of Experimental Example 12 in which the film thickness of the second layer made of GaN is 5.0 nm. Regarding the entire experimental example shown in FIG. 2, the critical film thickness is 2 μm or more in the cases shown in Experimental Examples 4 to 6 and 12.

  According to the present invention, if a hexagonal boron nitride (BN) layer / gallium nitride (GaN) multilayer structure layer 13 can be grown as a buffer layer with good controllability on a silicon substrate, boron nitride (BN) / nitride is possible. The nitride semiconductor layer 14 can be thickly grown on the gallium (GaN) multilayer structure layer 13 without causing cracks.

  In accordance with the present invention, a boron nitride layer 131 and a gallium nitride layer 132 are alternately and repeatedly stacked on a silicon substrate to grow a multilayer structure layer, and a nitride semiconductor layer is grown on the multilayer structure layer, It is possible to grow a GaN layer having a critical film thickness of 2 μm or more without cracks. The mechanism will be discussed below.

  In recent years, AlN layers and GaN layers can be alternately and periodically grown on a silicon substrate to laminate an AlN / GaN multilayer structure, and a GaN layer having a critical thickness of 1 μm or more can be grown thereon. It has become. Here, the in-plane lattice constants a of hexagonal AlN, GaN, and InN oriented in the c-axis are 3.112Å, 3.189Å, and 3.548Å, respectively. Accordingly, the lattice constant a when the AlN / GaN multilayer structure is distorted and coherently grown is a value between AlN and GaN. As a result, the lattice constant a of the AlN / GaN multilayer structure is smaller than the lattice constant a of the GaN layer grown on the AlN / GaN multilayer structure, which is considered to apply compressive stress to the GaN layer on the multilayer structure. Can do. However, also in this case, the critical thickness of the GaN layer is about 1.5 μm.

  In forming a semiconductor device, the film thickness of the GaN layer is preferably 2 μm or more, and it is necessary to further increase the critical film thickness. For this purpose, in the present invention, it is considered to apply a larger compressive stress to the GaN layer by the multilayer structure layer to cancel the tensile stress of the GaN layer generated in the cooling process.

When a nitride semiconductor layer is grown on a silicon substrate via a multilayer structure, an element selected from either indium or boron is used as a material constituting the multilayer structure, and M is a quaternary mixed crystal Al _x M _y Attempts have been made to use Ga _1-xy N (0 <x ≦ 1, 0 ≦ y <1, x + y ≦ 1). From the viewpoint of explaining the effect of suppressing cracks generated in the nitride semiconductor layer from the viewpoint of the thermal expansion coefficient (and the robustness of the material), it is conceivable to use indium. However, the lattice constant a of InN is 3.548Å. Therefore, when In is used, the lattice constant a of Al _x In _y Ga _1-xy N is increased by increasing the molar fraction y of InN, and therefore Al _x In _y Ga _1-x. The lattice constant a of the multilayer structure layer containing _-yN becomes close to the lattice constant a of the GaN layer, and reduces the compressive stress applied to the GaN layer. It is counterproductive in terms of suppression.

On the other hand, since the in-plane lattice constant a of hexagonal boron nitride (BN) is 2.504Å, when B is used, Al _x ByGa _1-xy N is increased by increasing the molar fraction y of BN. The lattice constant a becomes smaller. _Thus, if it is possible to use _{Al x B y Ga 1-x} -y N, it can be expected to further increase the critical thickness of the GaN layer. _{However, Al x B y Ga 1-} x-y N (0 <x ≦ 1,0 ≦ y <1, x + y ≦ 1) is, _Al-plane lattice constant a large _{x Ga 1-x N (y} = 0 ) Except in the case of (4), it is very difficult to actually grow group III elements with good controllability.

  According to the present invention, a multilayer structure layer in which a boron nitride layer 131 and a gallium nitride layer 132 are stacked is grown on a silicon substrate, and a nitride semiconductor layer is grown on the multilayer structure layer. By using a multilayer structure of binary compounds, the controllability of the reaction is improved. Moreover, by improving the heater and adopting a high temperature process, the transition from hexagonal to cubic is suppressed, and a multilayer structure layer including a high-quality boron nitride layer is formed. By optimizing the conditions, a GaN layer having a critical film thickness of 2 μm or more can be grown.

1 is a cross-sectional view showing a nitride semiconductor multilayer structure according to an embodiment of the present invention. It is a figure which shows an experiment example and an evaluation result as a table | surface. It is sectional drawing which shows the conventional nitride semiconductor multilayer structure.

Explanation of symbols

10: silicon substrate, 11: AlN layer, 12: AlGaN layer, 13: BN / GaN multilayer structure, 131: BN layer, 132: GaN layer, 14: nitride semiconductor layer,
21: Multilayer structure 211: First layer 212: Second layer 22: Nitride semiconductor layer

Claims (6)

A step (a) of crystal growth of an aluminum nitride layer on a silicon substrate;
(B) forming a multilayer structure layer in which a boron nitride layer and a gallium nitride layer are alternately and repeatedly grown on the aluminum nitride layer to alternately laminate the boron nitride layer and the gallium nitride layer; ,
A step (c) of growing a nitride semiconductor layer on the multilayer structure layer;
A method for producing a nitride semiconductor multilayer structure comprising: After the step (a), the method includes a step (d) of crystal-growing an aluminum gallium nitride layer on the aluminum nitride layer,
The method for producing a nitride semiconductor multilayer structure according to claim 1, wherein the multilayer structure layer is formed on the aluminum gallium nitride layer by the step (b).   The nitriding according to claim 1 or 2, wherein the step (c) is a step of growing a nitride semiconductor layer having a lattice constant larger than that of the multilayer structure layer on the multilayer structure layer. For manufacturing a semiconductor multilayer structure. A silicon substrate;
An aluminum nitride layer disposed on the silicon substrate;
A multilayer structure layer disposed on the aluminum nitride layer, wherein a boron nitride layer and a gallium nitride layer are alternately stacked;
A nitride semiconductor layer disposed on the multilayer structure layer;
A nitride semiconductor multilayer structure comprising: Having an aluminum gallium nitride layer;
5. The nitride semiconductor multilayer structure according to claim 4, wherein the aluminum gallium nitride layer is disposed on the aluminum nitride layer, and the multilayer structure layer is disposed on the aluminum gallium nitride layer. .   6. The nitride semiconductor multilayer structure according to claim 4, wherein a lattice constant of the nitride semiconductor layer is larger than a lattice constant of the multilayer structure layer.

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