JP2016184663A - Semiconductor wafer, semiconductor device, and method of manufacturing semiconductor wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a semiconductor wafer with a smooth surface of a group-III nitride semiconductor layer while preventing a leakage current from flowing.SOLUTION: In a semiconductor wafer 1, a group-III nitride semiconductor layer 10 is provided on a substrate 2 via a buffer layer 8. A lattice constant of the buffer layer 8 is smaller than that of the group-III nitride semiconductor layer 10. The group-III nitride semiconductor layer 10 contains carbon. A peak of a carbon concentration of the group-III nitride semiconductor layer 10 is located away from both a front face and a rear face of the group-III nitride semiconductor layer 10.SELECTED DRAWING: Figure 1

Description

  The present specification discloses a semiconductor wafer, a semiconductor device, and a method for manufacturing a semiconductor wafer.

Research has been conducted on a technique for producing a semiconductor wafer by vapor-phase-growing a group III nitride semiconductor layer on a substrate. Patent Document 1 discloses a technique for growing a buffer layer on a silicon substrate and growing a group III nitride semiconductor layer (main functional layer) on the buffer layer. Patent Document 1 introduces high concentration (1 × 10 ¹⁸ cm ⁻³ ) carbon into the buffer layer and / or the buffer layer side of the group III nitride semiconductor layer. When a semiconductor device is manufactured using a semiconductor wafer into which carbon is introduced, leakage current can be prevented from flowing when the semiconductor device is turned off. If a material having a smaller thermal expansion coefficient than the group III nitride semiconductor is used as the substrate on which the group III nitride semiconductor layer is grown, the group III nitride semiconductor is heated from a high temperature (during vapor phase growth) to a low temperature (typically room temperature). It is known that a tensile strain is generated in a group III nitride semiconductor when cooled to a low temperature. Patent Document 1 cancels the tensile strain generated in the group III nitride semiconductor layer by growing the group III nitride semiconductor layer on the buffer layer having compressive strain.

JP 2010-287882 A

  However, when a high concentration of carbon is introduced into the buffer layer and / or the buffer layer side of the group III nitride semiconductor layer (main functional layer), the group III nitride semiconductor layer grows with inherent compression strain. As a result, strain-induced step bunching is likely to occur in the group III nitride semiconductor layer, and the surface of the group III nitride semiconductor layer cannot be smoothed. The present specification provides a technique that can prevent a leakage current from flowing and realize a semiconductor wafer having a smooth surface of a group III nitride semiconductor layer.

  In the semiconductor wafer disclosed in this specification, a group III nitride semiconductor layer is provided on a substrate via a buffer layer. The buffer layer has a smaller lattice constant than the group III nitride semiconductor layer. The group III nitride semiconductor layer contains carbon. In the semiconductor wafer disclosed in this specification, the peak of the carbon concentration of the group III nitride semiconductor layer is located away from both the front surface and the back surface of the group III nitride semiconductor layer.

  In the semiconductor wafer, since the group III nitride semiconductor layer contains carbon, leakage current of a semiconductor device manufactured using the semiconductor wafer can be prevented. In addition, by making the carbon concentration in the middle part of the group III nitride semiconductor layer (a position away from both the front surface and the back surface) the highest, the carbon concentration necessary to prevent leakage current is set to the group III nitride semiconductor layer. The carbon concentration of the group III nitride semiconductor layer can be lowered on the buffer layer side (the back side of the group III nitride semiconductor layer). By suppressing the carbon concentration on the buffer layer side, it is possible to suppress the occurrence of strain-induced step bunching in the group III nitride semiconductor layer. The semiconductor wafer described above can smooth the surface of the group III nitride semiconductor layer while preventing leakage current from flowing.

  The “buffer layer” in the present specification does not mean a so-called “low-temperature buffer layer” for reducing the lattice constant difference between the substrate and the group III nitride semiconductor layer, but a group III nitride. This is to apply a surface force to the semiconductor layer to alleviate thermal strain generated in the group III nitride semiconductor layer when the group III nitride semiconductor layer changes from a high temperature to a low temperature after film formation. “Strain-induced step bunching” is a mechanism of step bunching generation discovered and proposed by Tersoff et al., And disclosed in “Physical Review Letters Volume 75 2730 (1995)”. The mechanism is that when a strain is generated on a semiconductor surface formed by periodic step terraces, an attractive force between steps is proportional to the square of the strain and inversely proportional to the distance between steps. The attractive force between steps forms a bundle of steps (step bunching) one after another, and a step is formed on the surface of the semiconductor wafer, so that the surface smoothness of the semiconductor wafer is lowered. Therefore, generation of step bunching can be suppressed by reducing the distortion of the semiconductor surface.

  Further, the strain-induced step bunching becomes more prominent in a wafer whose main axis is slightly inclined with respect to the normal of the growth surface (a wafer having a so-called off angle). For example, in the case of a group III nitride semiconductor, the c-axis is generally the main axis. Therefore, in the case of a group III nitride semiconductor, it can be said that the state where the c-axis is inclined with respect to the normal of the growth surface has an off angle. Typically, by providing an off-angle, the growth surface has a periodic structure in which step terraces are regularly repeated, and the flatness of the wafer surface can be improved. In addition, by providing an off-angle, it is possible to obtain advantages such as realizing a steep heterojunction and improving the interface characteristics of a semiconductor element formed on a wafer. However, the distance between steps on the wafer surface having an off angle is small under a situation where a strain-induced step attractive force is applied. Since the step-to-step attractive force cannot be ignored, step bunching is likely to occur under the situation where the strain-induced step-by-step attractive force is applied.

  Further, the strain-induced step bunching in the nitride semiconductor layer is more prominent in the group III nitride semiconductor mainly containing gallium as the group III element. Step bunching occurs in the process where group III atomic species on the terrace are diffused into the step edge. Therefore, step bunching is likely to occur in an environment that satisfies the condition of “average distance between steps × (1/2) ≦ surface diffusion length of group III atomic species”. In group III atomic species, gallium is known to have a longer surface diffusion length than aluminum and indium. Therefore, strain-induced step bunching is likely to occur in a group III nitride semiconductor mainly containing gallium, particularly gallium nitride. Note that “gallium nitride” as used in this specification includes gallium nitride containing impurities (Al, In, Mg, Si, Ge, C, Fe, etc.) less than 1%.

  In addition, “the buffer layer has a smaller lattice constant than the group III nitride semiconductor layer” means that the buffer layer has a lattice constant (average lattice constant) when the entire buffer layer and the entire group III nitride semiconductor layer are compared. ) Is smaller than the lattice constant (average lattice constant) of the group III nitride semiconductor layer. Therefore, when comparing a part of the buffer layer and a part of the group III nitride semiconductor layer, the lattice constant of a part of the buffer layer may be larger than the lattice constant of a part of the group III nitride semiconductor layer.

  In the semiconductor device disclosed in this specification, a group III nitride semiconductor layer is provided over a substrate via a buffer layer, and a semiconductor element is formed on the surface side of the group III nitride semiconductor layer. In this semiconductor device, the lattice constant (average lattice constant) of the buffer layer is smaller than the lattice constant (average lattice constant) of the group III nitride semiconductor layer. The group III nitride semiconductor layer contains carbon. The peak of the carbon concentration of the group III nitride semiconductor layer is located away from both the front surface and the back surface of the group III nitride semiconductor layer.

  The present specification also discloses a method for manufacturing a semiconductor wafer in which a group III nitride semiconductor layer is provided on a substrate. The manufacturing method includes a buffer layer forming step and a group III nitride semiconductor layer forming step. In the buffer layer forming step, a buffer layer having a lattice constant smaller than that of the group III nitride semiconductor layer is vapor-phase grown on the substrate. In the group III nitride semiconductor layer forming step, the group III nitride semiconductor layer is vapor-phase grown on the buffer layer. In the manufacturing method disclosed in this specification, the growth pressure of the group III nitride semiconductor layer is minimized during the group III nitride semiconductor layer forming step.

  When the growth pressure of the group III nitride semiconductor layer is reduced, the carbon concentration introduced into the group III nitride semiconductor layer is increased. Therefore, according to the manufacturing method described above, it is possible to manufacture a semiconductor wafer having the highest carbon concentration in the middle portion of the group III nitride semiconductor layer.

Sectional drawing of the semiconductor wafer of Example 1 is shown typically. The relationship between the position in a group III nitride semiconductor layer and carbon concentration is shown. The surface photograph of the semiconductor wafer of Example 1 is shown. The surface photograph of the semiconductor wafer of the comparative example 1 is shown. The relationship between the position in a group III nitride semiconductor layer and carbon concentration is shown.

  The technical features disclosed in this specification will be summarized below. The items described below have technical usefulness independently.

The semiconductor wafer includes a substrate, a buffer layer provided on the substrate, and a group III nitride semiconductor layer provided on the buffer layer. The substrate has a smaller coefficient of thermal expansion than the group III nitride semiconductor layer. Specifically, in the substrate, the temperature integral value of the linear expansion coefficient of 300 to 1300K is smaller than the temperature integral value of the linear expansion coefficient of 300 to 1300K in the a-axis direction of the material constituting the group III nitride semiconductor layer. More specifically, the material of the substrate is silicon (Si) or silicon carbide (SiC). The thickness of the substrate is 0.1 to 2 mm. Preferably, an interface layer and an aluminum nitride (AlN) layer are provided between the substrate and the buffer layer. Aluminum oxide (Al ₂ O ₃ ) can be used as the material for the interface layer. By providing the interface layer, the crystallinity of the buffer layer and the group III nitride semiconductor layer can be improved. The interface layer can be omitted. The thickness of the aluminum nitride layer is 10 to 500 nm. When the substrate is silicon, the aluminum nitride layer preferably has a thickness of 50 to 500 nm. When the substrate is silicon carbide, the thickness of the aluminum nitride layer is preferably 10 to 100 nm. Aluminum nitride has the smallest lattice constant among group III nitride semiconductors. Therefore, by providing the aluminum nitride layer, a necessary amount of compressive strain can be applied to the buffer layer. As described above, the interface layer and the aluminum nitride layer can be omitted, and the buffer layer can be formed directly on the surface of the substrate.

The buffer layer has a smaller lattice constant than the group III nitride semiconductor layer. Specifically, when comparing the entire buffer layer and the entire group III nitride semiconductor layer, the lattice constant (average lattice constant) of the buffer layer is the lattice constant (average lattice constant) of the group III nitride semiconductor layer. Smaller than. The buffer layer has a compressive strain. Preferably, the material of the buffer layer is Al _x Ga _1-x N (0 <x <1). As the buffer layer made of Al _x Ga _1-x N (0 <x <1), multilayer structures having different values of “x” can be used. Further, preferably, the value of “x” becomes smaller toward the surface (the group III nitride semiconductor layer side). That is, it is preferable that the buffer layer made of Al _x Ga _1-x N (0 <x <1) has a smaller Al composition toward the surface. As the buffer layer, a multilayer structure in which different materials are repeatedly stacked can be used. For example, the buffer layer may be repeatedly provided with a laminated structure of AlN and GaN. Alternatively, the buffer layer may be repeatedly provided with a laminated structure of AlN and AlGaN. The buffer layer can have a thickness of 0.5 to 10 μm. By providing the buffer layer, the tensile strain generated in the group III nitride semiconductor layer can be offset when the temperature of the group III nitride semiconductor layer changes from the growth temperature (high temperature) to room temperature (low temperature).

  The group III nitride semiconductor layer contains carbon. The peak of the carbon concentration of the group III nitride semiconductor layer is located away from both the front surface and the back surface (surface in contact with the buffer layer) of the group III nitride semiconductor layer. Further, the carbon concentration on the surface of the group III nitride semiconductor layer is preferably lower than the carbon concentration on the back surface. Specifically, when the carbon concentration peak of the group III nitride semiconductor layer is an intermediate part, the surface side is the front part from the intermediate part, and the back side is the back part from the intermediate part. Preferably satisfies the relationship of intermediate portion> back surface portion> front surface portion. For example, a functional layer through which a current flows may be formed on the surface portion. When the carbon concentration of the surface (surface portion) of the group III nitride semiconductor layer is lowered, the carbon concentration of the functional layer can be kept low, and a semiconductor element with a small loss (resistance) can be obtained. Note that if the functional layer contains a large amount of carbon, the current flow may be hindered by the presence of carbon.

  The group III nitride semiconductor layer preferably includes a plurality of layers having different concentrations of contained carbon. Specifically, the nitride semiconductor layer has a stacked structure in which the first layer, the second layer, and the third layer are stacked in this order from the buffer layer side, and the average value of the carbon concentration is second layer> first layer. It is preferable to satisfy the relationship. It is particularly preferable that the average value of the carbon concentration of each layer satisfies the relationship of second layer> first layer> third layer. Note that at least the first layer and the second layer preferably have a larger lattice constant than the buffer layer.

  The material of the first layer and the second layer is preferably a group III nitride semiconductor mainly composed of gallium (Ga). The “group III nitride semiconductor mainly composed of gallium” typically means gallium nitride (GaN), and as an impurity, B, Al, In, on the order of atomic percent of less than 1% with respect to GaN. Those containing elements such as S, As, and Sb are also “group III nitride semiconductors mainly composed of gallium”. By using a group III nitride semiconductor mainly composed of gallium as the material of the first layer, strain relaxation can be efficiently caused between the buffer layer and the second layer using the thin first layer. For example, when the group III nitride semiconductor constituting the first layer contains a large amount of aluminum, the difference in lattice constant between the buffer layer and the first layer is small, and the thin first layer is sufficient between the buffer layer and the second layer. Distortion is less likely to occur. Further, by using a group III nitride semiconductor mainly composed of gallium as the material of the second layer, it is possible to suppress the occurrence of new strain between the first layer and the second layer. That is, since a material close to the lattice constant of the first layer is laminated as the second layer, new strain is unlikely to occur between the first layer and the second layer.

The thickness of the first layer is preferably 0.05 to 0.5 μm. When the thickness of the first layer is less than 0.05 μm, strain relaxation is not easily caused. Further, when the thickness of the first layer is thicker than 0.5 μm, the effect of suppressing the leakage current cannot be sufficiently obtained. More preferably, the thickness of the first layer is less than 0.05 to 0.2 μm from the viewpoint of suppressing leakage current. If the first layer is sufficiently thinner than the second layer, it is possible to prevent the leakage current suppressing effect from being lowered. The carbon concentration of the first layer is preferably 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ . More preferably, the carbon concentration of the first layer is 1 × 10 ^{16 to} 5 × 10 ¹⁷ cm ⁻³ . By making the carbon concentration of the first layer lower than that of the second layer, the compressive strain inherent in the buffer layer can be relaxed.

The thickness of the second layer is preferably 0.2 to 3.0 μm. The carbon concentration of the second layer is preferably 5 × 10 ¹⁷ to 1 × 10 ²⁰ cm ⁻³ . More preferably, the carbon concentration of the second layer is 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ from the viewpoint of suppressing the leakage current. If the thickness of the second layer is sufficiently thicker than that of the first layer, the leakage current suppressing effect can be sufficiently exerted. Gallium nitride can be used as the material for the third layer. The third layer can be used as a functional layer (a layer constituting a semiconductor element). The carbon concentration of the third layer is preferably less than 1 × 10 ¹⁷ cm ⁻³ . More preferably, the third layer is substantially free of carbon. The thickness of the third layer can be appropriately adjusted according to the target semiconductor device. A plurality of layers (fourth layer, fifth layer, etc.) can be further provided on the surface of the third layer. For example, an HEMT (High Electron Mobility Transistor) including a heterojunction can be manufactured by forming an AlGaN layer (fourth layer) on the surface of a gallium nitride layer (third layer).

(First embodiment)
The semiconductor wafer 1 will be described with reference to FIGS. The semiconductor wafer 1 includes a silicon substrate 2, an interface layer 4 formed on the silicon substrate 2, an AlN layer 6 formed on the interface layer 4, a buffer layer 8 formed on the AlN layer 6, a buffer A group III nitride semiconductor layer 10 formed on the layer 8 is provided. The thickness T2 of the silicon substrate 2 is 675 μm. The material of the interface layer 4 is aluminum oxide. The thickness T4 of the interface layer 4 is adjusted to be less than 3 nm. The thickness T6 of the AlN layer 6 is adjusted to 0.3 μm. The material of the buffer layer 8 is Al _x Ga _1-x N. The thickness T8 of the buffer layer 8 is adjusted to 2.5 μm. The buffer layer 8 has a multilayer structure, and a layer having a larger value of “x” is formed toward the AlN layer 6 side.

The group III nitride semiconductor layer 10 includes a first GaN layer 10a, a second GaN layer 10b, and a third GaN layer 10c. The material of the group III nitride semiconductor layer 10 is gallium nitride (GaN). The first GaN layer 10a contains 2 × 10 ¹⁶ cm ^{−3 of} carbon. The second GaN layer 10b contains 4 × 10 ¹⁸ cm ^{−3 of} carbon. The third GaN layer 10c does not substantially contain carbon (may contain inevitable carbon). The group III nitride semiconductor layer 10 is formed using a metal organic chemical vapor deposition method. The thickness T10a of the first GaN layer 10a is adjusted to 0.1 μm, the thickness T10b of the second GaN layer 10b is adjusted to 0.5 μm, and the thickness T10c of the third GaN layer 10c is adjusted to 0.4 μm. . Further, another nitride semiconductor layer may be formed on the surface of the third GaN layer 10c. The third GaN layer 10c may contain n-type impurities (Si or the like) and p-type impurities (Mg or the like). The first GaN layer 10a, the second GaN layer 10b, and the third GaN layer 10c are examples of the first layer, the second layer, and the third layer, respectively.

  As an example, a nitride stack (typically AlGaN) having a heterojunction is formed on the surface of the group III nitride semiconductor layer 10 (the surface of the third GaN layer 10c). Thereby, a semiconductor device having a HEMT structure that operates as a heterojunction two-dimensional electron gas and a channel can be manufactured.

  A method for manufacturing the semiconductor wafer 1 will be described. First, the interface layer 4 is formed on the silicon substrate 2 using an atomic layer deposition method (ALD method). Thereafter, an AlN layer 6 and a buffer layer 8 are formed in this order on the interface layer 4 using a metal organic chemical vapor deposition method (MOCVD method) (buffer layer forming step). In the buffer layer forming step, trimethylaluminum is used as the Al material, trimethylgallium is used as the Ga material, and ammonia is used as the N material. The growth temperature is about 1000 ° C.

Next, the first GaN layer 10a is formed on the buffer layer 8 at a growth pressure of 300 Torr. Thereafter, the second GaN layer 10b is formed on the first GaN layer 10a at a growth pressure of 50 Torr. Thereby, the carbon concentration (4 × 10 ¹⁸ cm ⁻³ ) of the second GaN layer 10 b is higher than the carbon concentration (2 × 10 ¹⁶ cm ⁻³ ) of the first GaN layer 10 a. Next, the third GaN layer 10c is formed on the second GaN layer 10b at a growth pressure of 300 Torr. The carbon concentration of the third GaN layer 10c (substantially does not contain carbon) is adjusted to be lower than the carbon concentrations of the first GaN layer 10a and the second GaN layer 10b using parameters other than the growth pressure.

  As described above, the lattice constant (lattice constant in the a-plane direction) of the buffer layer 8 is smaller than the lattice constant of the group III nitride semiconductor layer (lattice constant in the a-plane direction of GaN) 10. Therefore, the buffer layer 8 applies compressive strain to the group III nitride semiconductor layer 10. The group III nitride semiconductor layer 10 tends to undergo tensile strain in the process of temperature drop after growth. The buffer layer 8 cancels the tensile strain generated in the group III nitride semiconductor layer 10 and suppresses the group III nitride semiconductor layer 10 from warping and generating cracks and the like.

Advantages of the semiconductor wafer 1 will be described. FIG. 2 shows the carbon concentration of the group III nitride semiconductor layer 10. The horizontal axis of the graph indicates the carbon concentration (cm ⁻³ ), and the vertical axis indicates each layer (the first GaN layer 10a to the third GaN layer 10c). In addition, the carbon concentration shown in FIG. 2 has shown the average value of each layer. As described above, the carbon concentration of the second GaN layer 10b is 4 × 10 ¹⁸ cm ⁻³ . When the concentration of carbon contained in the GaN layer is higher than 1 × 10 ¹⁸ cm ⁻³ , the leakage current can be suppressed. Therefore, when a semiconductor device is manufactured using the semiconductor wafer 1, it is possible to suppress a leak current from flowing between the group III nitride semiconductor layer 10 and the silicon substrate 2. Further, as described above, the thickness T10a of the first GaN layer 10a is thinner than the thickness T10b of the second GaN layer 10b. When the thickness T10a is increased, the effect of suppressing leakage current may be reduced. By making the thickness T10a thinner than the thickness T10b, the effect of suppressing leakage current can be improved.

As shown in FIG. 2, the carbon concentration (2 × 10 ¹⁶ cm ⁻³ ) of the first GaN layer 10a is lower than the carbon concentration (4 × 10 ¹⁸ cm ⁻³ ) of the second GaN layer 10b. That is, the first GaN layer 10a does not contain carbon at a concentration sufficient to suppress leakage current. When the first GaN layer 10a having a low carbon concentration is formed on the buffer layer 8, effective strain relaxation occurs. Note that, if the carbon concentration of the first GaN layer 10a is high (for example, 1 × 10 ¹⁸ cm ⁻³ or more that is effective in suppressing leakage current), the group III nitride semiconductor layer remains with the compressive strain of the buffer layer 8 inside. 10 grows. As a result, distortion-induced step bunching occurs and the surface of the semiconductor wafer 1 cannot be smoothed. When a semiconductor device is manufactured using a semiconductor wafer having poor surface smoothness, the characteristics of the semiconductor device may deteriorate.

  In the semiconductor wafer 1, the compressive strain of the buffer layer 8 is reduced in the first GaN layer 10a by making the carbon concentration of the first GaN layer 10a lower than the carbon concentration of the second GaN layer 10b. By reducing the compressive strain of the buffer layer 8 in the first GaN layer 10a, it is possible to suppress the occurrence of strain-induced step bunching even if the second GaN layer 10b contains a high concentration of carbon. The surface of the semiconductor wafer 1 can be smoothed, and a semiconductor device exhibiting good characteristics can be manufactured.

  As described above, the concentration of carbon in the group III nitride semiconductor layer 10 can be controlled by the growth pressure of the group III nitride semiconductor layer. When other growth conditions are the same, the carbon concentration of the group III nitride semiconductor layer increases as the growth pressure decreases. The carbon concentration of the second GaN layer 10b can be increased by adjusting the growth pressure low after crystal growth of the first GaN layer 10a.

  For example, even if the second GaN layer 10b is grown thick without forming the first GaN layer 10a on the buffer layer 8, the compressive strain of the buffer layer 8 is reduced as the thickness of the second GaN layer 10b increases. Can do. However, the warpage of the semiconductor wafer varies depending on the product of the group III nitride semiconductor layer 10 “strain” and “film thickness”. That is, when the second GaN layer 10b is formed directly on the buffer layer 8, since the “strain” is large, the amount of warpage of the semiconductor wafer greatly changes due to a slight change in the “film thickness”. For this reason, it is difficult to control the amount of warpage of the semiconductor wafer in the method of forming the second GaN layer 10b containing high-concentration carbon thickly. As described above, in the semiconductor wafer 1, after the compressive strain of the buffer layer 8 is relaxed by the first GaN layer 10a, the second GaN layer 10b containing a high concentration of carbon is crystal-grown. Therefore, even if an error occurs in the film thickness of the group III nitride semiconductor layer 10, variation in the amount of warpage between batches can be suppressed. The semiconductor wafer 1 can also improve the robustness of warpage control.

(Experimental example)
FIG. 3 is an optical micrograph of the surface of a semiconductor wafer in which an interface layer, an AlN layer, a buffer layer, a first GaN layer, and a second GaN layer are grown in this order on a silicon substrate (Experimental Example 1). The carbon concentration of the first GaN layer is 2 × 10 ¹⁶ cm ⁻³ (growth pressure 300 Torr), and the carbon concentration of the second GaN layer is 4 × 10 ¹⁸ cm ⁻³ (growth pressure 50 Torr). By setting the carbon concentration to the first GaN layer <the second GaN layer, step flow growth was confirmed, and it was confirmed that a semiconductor wafer having a smooth surface was obtained. As a result of the X-ray reciprocal lattice map measurement, the residual strain in the a-axis direction of the GaN layer was 0.11%. The c-axis of the first GaN layer 10a was inclined 0.26 degrees in the m-axis direction with respect to the normal to the growth surface.

  FIG. 4 is an optical micrograph of the surface of a semiconductor wafer in which an interface layer, an AlN layer, a buffer layer, a second GaN layer, and a first GaN layer are grown in this order on a silicon substrate (Experimental Example 2). The order of growing the first GaN layer and the second GaN layer is opposite to that of the semiconductor wafer of Experimental Example 1. That is, in the semiconductor wafer of Experimental Example 2, the second GaN layer containing a high concentration of carbon is grown on the surface of the buffer layer. As is apparent from FIG. 4, when the second GaN layer and the first GaN layer are grown in this order, a striped pattern is formed on the surface, and it can be confirmed that a bundle of steps (step bunching) is formed. As a result of measurement with an atomic force microscope with a viewing angle of 100 μm, the step difference in the bundle of steps was 80 nm at the maximum. The residual strain in the a-axis direction of the GaN layer measured by X-ray reciprocal lattice map was 0.42%. The c-axis of the first GaN layer 10a was inclined 0.26 degrees in the m-axis direction with respect to the normal to the growth surface.

  From the results of the above experimental examples 1 and 2, in a semiconductor wafer having a carbon-containing GaN layer, by reducing the carbon concentration of the GaN layer at the portion in contact with the buffer layer, the distortion of the GaN layer is suppressed, and the surface of the semiconductor wafer It was confirmed that strain-induced step bunching can be suppressed.

  In the above embodiment, the example in which the group III nitride semiconductor layer includes the first GaN layer 10a, the second GaN layer 10b, and the third GaN layer 10c has been described. However, the technique disclosed in this specification can also be applied to a semiconductor wafer in which another nitride semiconductor layer is formed on the surface of the third GaN layer 10c. The first GaN layer 10a, the second GaN layer 10b, and the third GaN layer 10c are examples of a group III nitride semiconductor layer, and the first GaN layer 10a, the second GaN layer 10b, and the third GaN layer 10c are a group III mainly composed of GaN. It can also be made of a nitride semiconductor.

  Further, as shown in FIG. 5, the group III nitride semiconductor layer may have a structure in which the carbon concentration continuously changes from the back surface (buffer layer side) to the front surface. In this case, the group III nitride semiconductor layer may not form a clear layer structure. Even in such a case, the peak of the carbon concentration of the group III nitride semiconductor layer is located away from both the front surface and the back surface of the group III nitride semiconductor layer. The surface of the wafer can be smoothed.

  In the above embodiment, the semiconductor wafer 1 in which the group III nitride semiconductor layer 10 has the carbon concentration of the second GaN layer 10b> the first GaN layer 10a> the third GaN layer 10c has been described. However, the technique disclosed in this specification is effective if the peak of the carbon concentration of the group III nitride semiconductor layer is located away from both the front surface and the back surface. That is, if the condition that the carbon concentration of the second GaN layer 10b is the highest among the group III nitride semiconductor layers 10 is satisfied, the carbon concentration is: second GaN layer 10b> third GaN layer 10c> first GaN layer 10a. Even if there is an effect. If the peak of the carbon concentration of the group III nitride semiconductor layer is at a position away from both the front surface and the back surface, distortion-induced step bunching can be suppressed while suppressing leakage current.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above. The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of objects at the same time, and has technical usefulness by achieving one of the objects.

1: Semiconductor wafer 2: Substrate 8: Buffer layer 10: Group III nitride semiconductor layer

Claims (9)

A semiconductor wafer in which a group III nitride semiconductor layer is provided on a substrate via a buffer layer,
The buffer layer has a smaller lattice constant than the group III nitride semiconductor layer,
The group III nitride semiconductor layer contains carbon,
A semiconductor wafer in which a peak of the carbon concentration of the group III nitride semiconductor layer is located away from both the front surface and the back surface of the group III nitride semiconductor layer.   The semiconductor wafer according to claim 1, wherein a carbon concentration on a surface of the group III nitride semiconductor layer is lower than a carbon concentration on the back surface. The group III nitride semiconductor layer includes, in order from the buffer layer side, a first layer, a second layer, and a third layer,
3. The semiconductor wafer according to claim 1, wherein an average value of carbon concentration of the second layer is higher than both of an average value of carbon concentration of the first layer and an average value of carbon concentration of the third layer.   The semiconductor wafer according to claim 3, wherein an average value of the carbon concentration of the third layer is lower than an average value of the carbon concentration of the first layer.   The semiconductor wafer according to claim 3, wherein the material of the first layer is gallium nitride.   6. The semiconductor wafer according to claim 1, wherein a c-axis of the group III nitride semiconductor layer is inclined with respect to a normal to a growth surface.   The semiconductor wafer according to claim 1, wherein a material of the substrate is silicon. A semiconductor device in which a group III nitride semiconductor layer is provided on a substrate via a buffer layer, and a semiconductor element is formed on the surface side of the group III nitride semiconductor layer,
The buffer layer has a smaller lattice constant than the group III nitride semiconductor layer,
The group III nitride semiconductor layer contains carbon,
A semiconductor device in which the peak of the carbon concentration of the group III nitride semiconductor layer is located away from both the front surface and the back surface of the group III nitride semiconductor layer. A method for producing a semiconductor wafer in which a group III nitride semiconductor layer is provided on a substrate,
A buffer layer forming step in which a buffer layer having a lattice constant smaller than that of the group III nitride semiconductor layer is vapor-phase grown on the substrate;
A group III nitride semiconductor layer forming step of vapor-phase-growing the group III nitride semiconductor layer on the buffer layer;
With
A method of manufacturing a semiconductor wafer, wherein the growth pressure of the group III nitride semiconductor layer is minimized during the group III nitride semiconductor formation step.