Multilayer substrate

Abstract

To provide a multilayered substrate in which in-plane non-uniformity of a Si concentration distribution in a GaN layer is suppressed.SOLUTION: A multilayered substrate includes an underlying substrate, and a gallium nitride layer epitaxially grown above the underlying substrate and comprising gallium nitride containing silicon. The gallium nitride layer has a top surface with a radius of 50 mm or more, and the gallium nitride layer has a thickness of 4 μm or more. A silicon concentration on the top surface of the gallium nitride layer has a distribution in which an outer circumferential silicon concentration at a radial position 10 mm from an edge of the top surface is higher than a central silicon concentration at a center of the top surface, the central silicon concentration is 4×1015 cm-3 or more and less than 2×1016 cm-3, and an outer circumferential silicon contamination concentration, which is an excess of the outer circumferential silicon concentration from the central silicon concentration, is 1.2×1015 cm-3 or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This invention relates to a multilayer substrate. [Background technology]

[0002] Laminated substrates, in which gallium nitride (GaN) layers are epitaxially grown on various substrates, are used as materials for fabricating semiconductor devices (see, for example, Patent Document 1). To improve the production efficiency of semiconductor devices, efforts are being made to increase the diameter of the laminated substrates. Silicon (Si) is used as an n-type impurity added to the GaN layer.

[0003] As will be described in detail later, the inventors of this application investigated a multilayer substrate with a large diameter, a low added Si concentration, and a thick GaN layer, and found that in-plane non-uniformity of the Si concentration distribution in the GaN layer (specifically, non-uniformity where the Si concentration is higher on the outer periphery of the GaN layer) is likely to occur. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-199601 [Overview of the project] [Problems that the invention aims to solve]

[0005] One objective of the present invention is to provide a laminated substrate in which in-plane non-uniformity of the Si concentration distribution in the GaN layer is suppressed. [Means for solving the problem]

[0006] According to one aspect of the present invention Substrate and A gallium nitride layer, epitaxially grown above the aforementioned substrate and composed of silicon-containing gallium nitride, Equipped with, The gallium nitride layer has an upper surface with a radius of 50 mm or more. The thickness of the gallium nitride layer is 4 μm or more. The silicon concentration on the upper surface of the gallium nitride layer has a distribution where the outer peripheral silicon concentration at a radial position 10 mm from the edge of the upper surface is higher than the central silicon concentration at the center of the upper surface. The aforementioned central silicon concentration is 4 × 10 15 cm -3 The above 2 x 10 16 cm -3 It is less than, The peripheral silicon contamination concentration, which is the excess of the peripheral silicon concentration from the central silicon concentration, is 1.2 × 10⁻⁶ 15 cm -3 The following is: Multilayer substrate It will be provided. [Effects of the Invention]

[0007] A laminated substrate is provided in which in-plane non-uniformity of the Si concentration distribution in the GaN layer is suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic cross-sectional view illustrating a laminated substrate according to an embodiment. [Figure 2] Figure 2 is a top view of the GaN layer, illustrating how to measure the Si concentration in the GaN layer. [Figure 3] Figure 3 is a schematic side view showing a GaN layer manufacturing apparatus according to an embodiment. [Figure 4] Figure 4 is a graph showing an example of the Si concentration distribution on the upper surface of the GaN layer in the first example of the embodiment. [Figure 5] Figure 5 is a schematic graph showing the Si concentration distribution for the first example, similar to that in Figure 4. [Figure 6] Figure 6 is a graph showing an example of the Si concentration distribution on the upper surface of the GaN layer in the second example of the embodiment. [Figure 7]Figure 7 is a schematic graph showing the Si concentration distribution for a second example, similar to that in Figure 6. [Figure 8] Figure 8 is a schematic side view showing a GaN layer manufacturing apparatus in a comparative configuration. [Figure 9] Figure 9 is a graph showing an example of the Si concentration distribution on the upper surface of the GaN layer under different configurations. [Figure 10] Figure 10 is a schematic graph showing a Si concentration distribution in a comparative format similar to that of Figure 9. [Modes for carrying out the invention]

[0009] A laminated substrate 100 according to an embodiment of the present invention will be described. Figure 1 is a schematic cross-sectional view illustrating the laminated substrate 100. The laminated substrate 100 comprises at least a base structure 10 and a gallium nitride (GaN) layer 20 formed on the base structure 10.

[0010] The substrate structure 10 includes at least a substrate which is a crystalline substrate for epitaxial growth of the GaN layer 20. The substrate structure 10 may optionally have a buffer layer between the substrate and the GaN layer 20. The structure of the buffer layer may be appropriately selected as needed.

[0011] As the base substrate, a GaN substrate, sapphire substrate, silicon (Si) substrate, silicon carbide (SiC) substrate, etc., may be used as appropriate. For example, if the base substrate is a GaN substrate, the base structure 10 may be a GaN substrate. Also, for example, if the base substrate is a Si substrate, the base structure 10 may have a Si substrate and an aluminum nitride (AlN) layer provided as a nucleation layer.

[0012] The laminated substrate 100 may have an upper layer 30 formed on the GaN layer 20, if necessary. The structure of the upper layer 30 may be appropriately selected depending on the operation of the semiconductor device to be fabricated using the laminated substrate 100. The upper layer 30 may be, for example, a group III nitride layer epitaxially grown on the GaN layer 20.

[0013] The GaN layer 20 according to the embodiment has the following characteristics. The GaN layer 20 has an upper surface 25 with a radius of 50 mm or more (a diameter of 100 mm or more). That is, the laminated substrate 100 has a circular shape with a diameter of 100 mm or more. The laminated substrate 100 may have an orientation flat or a notch as required.

[0014] The GaN layer 20 contains silicon (Si) as an n-type impurity. The Si concentration on the upper surface 25 of the GaN layer 20 has a distribution in which the outer peripheral Si concentration C1 at the outer periphery of the upper surface 25 is higher than the central Si concentration C0 at the center of the upper surface 25.

[0015] The central Si concentration C0 is a low concentration with a concentration variation on the order of 10 15 cm -3 having an impact, specifically, 4×10 15 cm -3 or more and less than 2×10 16 cm -3 In an embodiment where the central Si concentration C0 is less than 1×10 16 cm -3 (that is, on the order of 10 15 cm -3 ), such an impact is more significant. The outer peripheral Si mixing concentration Δ, which is the excess of the outer peripheral Si concentration C1 over the central Si concentration C0 (that is, C1 - C0), is 1.2×10 15 cm -3 or less. That is, the outer peripheral Si concentration C1 is higher than the central Si concentration C0, but the outer peripheral Si mixing concentration Δ, which is the difference between the two, is suppressed to 1.2×10 15 cm -3 or less so as not to become excessively high. The thickness of the GaN layer 20 is 4 μm or more. Also, the thickness of the GaN layer 20 is, for example, 40 μm or less.

[0016] ]>In a semiconductor device including the laminated substrate 100, the GaN layer 20 is a layer that functions as at least part of an operating layer. Therefore, the GaN layer 20 preferably has both breakdown voltage characteristics and resistance characteristics in a balanced manner. From the perspective of improving the breakdown voltage, the central Si concentration C0 of the GaN layer 20 is 2×1016 cm -3 It is preferable that it be less than [a certain value]. Also, from the viewpoint of improving breakdown voltage, it is preferable that the thickness of the GaN layer 20 be 4 μm or more. From the viewpoint of reducing resistance, the central Si concentration C0 of the GaN layer 20 is 4 × 10 15 cm -3 The above is preferable. Furthermore, from the viewpoint of reducing resistance, the thickness of the GaN layer 20 is preferably 40 μm or less.

[0017] As will be explained in detail later, the peripheral Si contamination concentration Δ is the concentration of Si mixed into the outer periphery of the GaN layer 20 due to the Si-containing deposition 230. The central Si concentration C0 is approximately equal to the target addition concentration, which is the Si concentration that is intentionally added. The peripheral Si contamination concentration Δ is the excess Si at the outer periphery due to the Si mixed in from the central Si concentration C0. The GaN layer 20 according to this embodiment is characterized in that the peripheral Si contamination concentration Δ is suppressed compared to the comparative form.

[0018] In the following description, the radius of the GaN layer 20 is 50 mm, the thickness of the GaN layer 20 is 4 μm, and the target Si doping concentration in the GaN layer 20 is 9 × 10⁻¹⁶. 15 cm -3 Examples of such embodiments are provided. These conditions are common to both the embodiments and the comparative embodiments.

[0019] This section explains how to measure the Si concentration in the GaN layer 20. Figure 2 is a top view of the GaN layer 20, illustrating how to measure the Si concentration in the GaN layer 20. An XY Cartesian coordinate system is set up on the top surface 25 of the GaN layer 20, with the center of the top surface 25 as the origin.

[0020] First, let's explain the measurement positions within the plane. At least five measurement points are set on the top surface 25 to measure the Si concentration: a central measurement point and four outer circumference measurement points. The central measurement point is set at the center of the top surface 25. The four outer circumference measurement points are set at radial positions 10 mm from the edge of the top surface 25, for each of the X-positive, X-negative, Y-positive, and Y-negative directions (i.e., every 90° in the circumferential direction). Here, the radial positions 10 mm from the edge of the top surface 25 are set as representative positions on the outer circumference when defining the Si concentration on the outer circumference of the top surface 25.

[0021] The Si concentration at the central measurement point is the central Si concentration C0. The Si concentration obtained by averaging the Si concentrations at the outer circumference measurement points in the positive X direction (CX+), the outer circumference measurement points in the negative X direction (CX-), the outer circumference measurement points in the positive Y direction (CY+), and the outer circumference measurement points in the negative Y direction (CY-) is the outer circumference Si concentration C1. In other words, the outer circumference Si concentration C1 represents the circumferentially averaged Si concentration at the outer circumference. The excess of the outer circumference Si concentration C1 from the central Si concentration C0, i.e., C1-C0, is the outer circumference Si contamination concentration Δ.

[0022] In this example, the radius of the top surface 25 is 50 mm. The four outer circumference measurement points are set at radial positions 40 mm from the center in the positive X direction, negative X direction, positive Y direction, and negative Y direction, respectively.

[0023] In addition to the central measurement point and the four outer circumference measurement points, intermediate measurement points may be set at radial positions midway between the central measurement point and the outer circumference measurement points. In this example, intermediate measurement points are set at radial positions of 10 mm, 20 mm, and 30 mm from the center for each of the positive X, negative X, positive Y, and negative Y directions. In Figure 2, for ease of illustration, the central measurement point and outer circumference measurement points are shown as large black circles, and the intermediate measurement points are shown as small black circles.

[0024] Furthermore, even in embodiments where the radius of the upper surface 25 of the GaN layer 20 exceeds 50 mm, the four outer circumference measurement points are set at radial positions 10 mm from the edge of the upper surface 25. Also, even in embodiments where the radius of the upper surface 25 of the GaN layer 20 exceeds 50 mm, the intermediate measurement points may be set at radial positions 10 mm apart from the center in each of the positive X direction, negative X direction, positive Y direction, and negative Y direction.

[0025] The average Si concentration is calculated by averaging the Si concentrations at four measurement points set at equal radial positions from the center of the upper surface 25 in the positive X direction, negative X direction, positive Y direction, and negative Y direction. In other words, the Si concentration averaged circumferentially with respect to each radial position is called the average Si concentration. The outer perimeter Si concentration C1 is the average Si concentration at the outer perimeter.

[0026] As described later, the growth of the GaN layer 20 is carried out in such a way as to ensure uniformity in the circumferential direction. However, in reality, variations in Si concentration occur even between four measurement points set at equal radial positions. To reduce the effects of such variations, the radial distribution of Si concentration in the GaN layer 20 is evaluated using the average Si concentration, which is the Si concentration averaged in the circumferential direction. The concentration of impure Si is the excess of the average Si concentration from the central Si concentration C0 at each radial position.

[0027] Next, the measurement position in the height direction will be described. The Si concentration in the GaN layer 20 is measured by secondary ion mass spectrometry (SIMS) at the top surface 25. However, "Si concentration at the top surface 25" does not mean the Si concentration at the exact height of the top surface 25, but rather the Si concentration in the vicinity of the top surface 25, as will be explained below. In the embodiment where the upper layer 30 is not laminated, the top surface 25 is the uppermost surface of the laminated substrate 100, and in the embodiment where the upper layer 30 is laminated, it is the interface between the upper layer 30 and the GaN layer 20.

[0028] Generally, the reliability of SIMS measurements at the surface is not high. For this reason, it is preferable to perform SIMS measurements at a height slightly towards the substrate structure 10 from the top surface 25, that is, slightly inside the GaN layer 20. It is also preferable to use averaged measurements over a certain height range (depth range, thickness range). Here, for each measurement point in the plane, the average value of SIMS measurements in a depth range of 100 nm to 200 nm from the top surface 25 is defined as the Si concentration at the top surface 25. For example, in an embodiment where the thickness of the GaN layer 20 is 4 μm, the average value of Si concentration obtained by SIMS measurements in the range of 3.8 μm to 3.9 μm in height from the bottom surface of the GaN layer 20 is defined as the Si concentration at the top surface 25.

[0029] Before further describing the embodiments, a comparative configuration will be explained. Figure 8 is a schematic side view showing a GaN layer 20 manufacturing apparatus 200 according to the comparative configuration. The manufacturing apparatus 200 is an organometallic vapor deposition (MOVPE) apparatus and has a susceptor 210 on which a wafer 40 is placed. The wafer 40 is the object to be processed (an intermediate of the laminated substrate 100) at the stage in which the GaN layer 20 growth process is carried out by the manufacturing apparatus 200. Specifically, at the start of GaN layer 20 growth, it is the base structure 10, and after the start of GaN layer 20 growth, it is a laminate of the base structure 10 and the GaN layer 20.

[0030] The manufacturing apparatus 200 is a lateral flow type MOVPE apparatus in which the raw material gas 220 is supplied in a direction parallel to the upper surface of the wafer 40. The raw material gas 220 includes a GaN raw material gas for growing GaN constituting the GaN layer 20, and a Si doping raw material gas for supplying Si to be added to the GaN layer 20. The GaN raw material gas includes a gallium (Ga) raw material gas and a nitrogen (N) raw material gas. For example, trimethylgallium (TMG) gas is used as the Ga raw material gas, and for example, ammonia (NH3) gas is used as the N raw material gas. For example, silane (SiH4) gas is used as the Si doping raw material gas.

[0031] The growth temperature can be selected, for example, in the range of 900°C to 1400°C, and the V / III ratio, which is the flow rate ratio of Group V raw material gas to Group III raw material gas, can be selected, for example, in the range of 10 to 5000. The target doping concentration of the Si doping raw material gas in the GaN layer 20 is 4 × 10⁻¹⁰. 15 cm -3 The above 2 x 10 16 cm -3 A predetermined value within a range less than 9 × 10 15 cm -3 It is supplied in such a manner.

[0032] The susceptor 210 holds the wafer 40 so as to rotate the wafer 40 with its center as the center of rotation. By growing the GaN layer 20 while performing this rotation, the growth conditions of the GaN layer 20 can be made uniform in the circumferential direction of the wafer 40.

[0033] The inner peripheral edge 211 of the susceptor is the position on the susceptor 210 where the edge of the wafer 40 is located, in a plan view. The upper surface 213 of the susceptor edge is the upper surface of the susceptor 210 between the inner peripheral edge 211 and the outer peripheral edge 212 of the susceptor.

[0034] During the growth process of the GaN layer 20, a Si-containing deposition 230 adheres to the upper surface 213 of the susceptor edge, causing Si to be introduced into the GaN layer 20 from the Si-containing deposition 230. The Si-containing deposition 230 is a defective GaN and contains Si. It is speculated that the main source of Si in the Si-containing deposition 230 is either the Ga source gas or the Si doping source gas (one or both), but the details are unknown. Furthermore, it is not practical to prevent the Si-containing deposition 230 from adhering to the upper surface 213 of the susceptor edge. The introduction of Si from the Si-containing deposition 230 into the GaN layer 20 cannot be controlled with conventional technology.

[0035] The concentration of Si impregnated from the Si-containing deposition 230 is higher closer to the inner peripheral edge 211 of the susceptor, that is, closer to the outer edge of the wafer 40. The inclusion of Si in the GaN layer 20 due to the Si-containing deposition 230 is called "improper inclusion," and is distinguished from "addition," which is the intentional inclusion of Si in the GaN layer 20 using Si-doping raw material gas.

[0036] Ideally, the concentration of Si contained in the GaN layer 20 should be controlled to a target concentration, which is the concentration to be added by the Si doping source gas, across the entire upper surface 25. Therefore, as will be explained in the embodiments described later, it is preferable to minimize the amount of Si mixed in from the Si-containing deposition 230.

[0037] The concentration of Si mixed into the GaN layer 20 from the Si-containing deposition 230 is approximately the same during growth within the range of the growth conditions described above, and during growth within the range of the target doping concentration described above. Specifically, as described later, the concentration of mixed Si at the outer periphery (a radial position 10 mm from the edge of the wafer 40, and in the comparative configuration, a radial position 10 mm from the inner peripheral edge 211 of the susceptor) is 1.6 × 10⁻⁶. 15 cm -3 It will be to that extent.

[0038] Figure 9 is a graph showing an example of the Si concentration distribution on the upper surface 25 of the GaN layer 20 under comparative configuration. The horizontal axis shows the in-plane measurement position in mm, and the vertical axis shows the Si concentration in 10°C. 15 cm -3 The values ​​are shown in units. The Si concentration at each measurement point in the X direction is shown by a black circle, and the Si concentration at each measurement point in the Y direction is shown by a white square. The average Si concentration is shown by an "X". This method of display is the same as in the graphs in Figures 4 and 6 relating to the embodiment.

[0039] The central Si concentration C0 is the target addition concentration of 9 × 10⁻⁶. 15 cm -3 It is almost equal to that. Furthermore, the Si concentration is almost constant up to about 10 mm from the center. From this, it can be said that the contaminated Si has not reached the center of wafer 40.

[0040] At radial positions approximately 20 mm or more away from the center, the concentration of contaminated Si, which is the excess from the central Si concentration C0, is significantly higher. Furthermore, the concentration of contaminated Si increases towards the outer periphery.

[0041] In the comparative form, the central Si concentration C0 is 9.01 × 10⁻⁶. 15 cm -3 Therefore, the Si concentration C1 on the outer periphery is 10.65 × 10⁻⁶. 15 cm -3 Therefore, the Si contamination concentration Δ on the outer periphery is 1.64 × 10⁻⁶. 15 cm -3 That is the case.

[0042] Figure 10 is a schematic graph showing a comparative Si concentration distribution similar to that in Figure 9. For ease of understanding, Figure 10 also shows the wafer 40 and the inner periphery 211 of the susceptor along with the Si concentration distribution.

[0043] The doping distribution D0 is a constant Si concentration distribution across the entire surface of the wafer 40, equal to the central Si concentration C0, and schematically represents the Si concentration distribution due to Si added by the Si doping source gas. The contamination distribution D1 schematically represents the Si concentration distribution due to Si introduced from the Si-containing deposition 230. The overall Si concentration distribution is expressed as the sum of the doping distribution D0 and the contamination distribution D1.

[0044] The Si resulting from the Si-containing deposition 230 is mixed in radially from the edge of the wafer 40 to a width of approximately 40 mm. In a large-diameter wafer 40, such as the one in this example with a radius of 50 mm, Si mixing does not occur in the center. In contrast, if a smaller-diameter wafer, such as one with a radius of 25 mm, is used, Si mixing will occur even in the center of the wafer.

[0045] In small-diameter configurations where Si inclusion occurs at the center, the Si inclusions from both edges on either side of the center are superimposed at the center, resulting in a higher Si concentration at the center due to the inclusions. As a result, the Si concentration distribution due to the inclusions becomes more uniform across the plane.

[0046] In contrast, in the case of a large-diameter wafer, as in this example, where Si contamination does not occur in the center, the Si concentration distribution due to the contaminated Si becomes non-uniform, with a large difference between the center and the outer edge. Thus, in large-diameter wafers, specifically those with a radius of 50 mm or more, the in-plane non-uniformity of the Si concentration distribution due to the contaminated Si becomes pronounced.

[0047] Although the example shows a configuration with a radius of 50 mm, even in wafers 40 with a radius greater than 50 mm, the concentration of Si in the outer periphery (a radial position 10 mm from the edge of the wafer 40, and in the comparative configuration, a radial position 10 mm from the inner peripheral edge 211 of the susceptor) is about the same as in the case of a 50 mm radius.

[0048] In the comparative form, the Si contamination concentration Δ at the outer edge, which is the difference in Si concentration between the center and the outer edge, is 1.64 × 10⁻⁶. 15 cm -3 On the other hand, the target Si addition concentration, that is, the central Si concentration C0, is 10 15 cm -3 The concentration is so low that even a concentration fluctuation of the order of magnitude can have an effect. Therefore, the influence of the Si contamination concentration Δ on the outer edge of the plane becomes significant in the Si concentration distribution.

[0049] Thus, the radius of the upper surface 25 is 50 mm or more, and the central Si concentration C0 is 4 × 10 15 cm -3 The above 2 x 10 16 cm -3 Less than (and even 1 x 10) 16 cm -3 In GaN layers 20 (less than ), a significant difference in Si concentration between the center and the outer periphery occurs due to the inclusion of Si. As described below, the embodiment proposes a technique that can suppress such in-plane non-uniformity of Si concentration compared to the comparative form, that is, a technique that can suppress the outer Si inclusion concentration Δ compared to the comparative form.

[0050] Furthermore, the Si contamination concentration Δ on the outer edge generally increases as the GaN layer 20 becomes thicker. This is because the amount of Si-containing deposition 230 adhering to the upper surface 213 of the susceptor edge increases as the growth time of the GaN layer 20 lengthens.

[0051] The comparative form (and embodiment) exemplifies the peripheral Si contamination concentration Δ in a GaN layer 20 with a thickness of 4 μm. If the thickness of the GaN layer 20 is sufficiently thin, the Si contamination due to Si-containing deposition 230 may not be sufficient to cause the in-plane non-uniformity described above. However, when growing a GaN layer 20 with a thickness of 4 μm (or more), the in-plane non-uniformity described above will occur. As described below, the embodiment proposes a technique that can reduce the peripheral Si contamination concentration Δ in a GaN layer 20 with a thickness of 4 μm compared to the comparative form, and further proposes a technique that can similarly reduce the peripheral Si contamination concentration Δ even in a GaN layer 20 thicker than 4 μm.

[0052] The embodiments will be described further. Figure 3 is a schematic side view showing a GaN layer 20 manufacturing apparatus 200 according to the embodiment. The manufacturing apparatus 200 according to the embodiment is a horizontal flow type MOVPE apparatus, similar to the comparative embodiment.

[0053] In this embodiment, the GaN layer 20 is grown with an annular dummy wafer 50 placed on the outside of the wafer 40 in a plan view. The dummy wafer 50 has a radial width WD and the same thickness as the wafer 40. As the material of the dummy wafer 50 (dummy substrate) at the start of GaN layer growth, a substrate material for epitaxial growth of GaN is used, such as GaN, or such as sapphire. After the start of GaN layer growth, the dummy wafer 50 becomes a structure in which the grown GaN layer is stacked on the dummy substrate.

[0054] The entire wafer 60 is a structure formed by combining the wafer 40 and the dummy wafer 50. In this embodiment, the object processed by the manufacturing apparatus 200 is the entire wafer 60. The edge of the entire wafer 60, that is, the position where the outer peripheral edge of the dummy wafer 50 is located, becomes the inner peripheral edge 211 of the susceptor.

[0055] In this embodiment, the dummy wafer 50 is positioned outside the wafer 40, so that the Si released from the Si-containing deposition 230 is preferentially mixed into the GaN grown on the dummy wafer 50. The Si released from the Si-containing deposition 230 that exceeds the width WD of the dummy wafer 50 is mixed into the GaN layer 20 of the wafer 40. In this way, by using the dummy wafer 50, the amount of Si mixed into the GaN layer 20 from the Si-containing deposition 230 can be reduced compared to the comparative embodiment.

[0056] Next, a first example of the embodiment will be described. In the first example of the embodiment, a configuration in which the width WD of the dummy wafer 50 is 10 mm is illustrated. The growth conditions for the GaN layer 20 in the first example of the embodiment are the same as those for the comparative configuration described above.

[0057] Figure 4 is a graph showing an example of the Si concentration distribution on the upper surface 25 of the GaN layer 20 in the first example of the embodiment. Si inclusion on the outer periphery is observed in the first example of the embodiment, as in the comparative embodiment, but it is more suppressed than in the comparative embodiment.

[0058] In the first example of the embodiment, specifically, the central Si concentration C0 is 9.00 × 10⁻⁶. 15 cm -3 Therefore, the Si concentration C1 on the outer periphery is 10.05 × 10⁻⁶. 15 cm -3 Therefore, the Si contamination concentration Δ on the outer periphery is 1.05 × 10⁻⁶. 15 cm -3 Therefore, the Si contamination concentration on the outer periphery in the comparative form is Δ1.64 × 10⁻⁴. 15 cm -3 It is suppressed compared to [another factor].

[0059] Peripheral Si contamination concentration in comparative form Δ1.64 × 1015 cm -3 As a reference value for a Si concentration lower than , the first concentration reference value is 1.2 × 10⁻⁶. 15 cm -3 The outer Si contamination concentration Δ of the first example of the embodiment is the first concentration reference value of 1.2 × 10⁻⁶. 15 cm -3 The following suppression is observed. In Figure 4 (and Figure 9), the first concentration reference value is shown as Δ1.2.

[0060] Figure 5 is a schematic graph showing the Si concentration distribution of a first example of an embodiment similar to that in Figure 4. For ease of understanding, Figure 5 also shows the wafer 40, dummy wafer 50, and the inner periphery 211 of the susceptor along with the Si concentration distribution.

[0061] The contamination distribution D1 in the comparative configuration is shown on the central side of the wafer 40, and the contamination distribution D1 in the first example of the embodiment is shown on the outer periphery side of the wafer 40. The dummy wafer 50 has the function of moving the inner periphery 211 of the susceptor further outward from the wafer 40 compared to the comparative configuration. As a result, the contamination distribution D1 can be moved 10 mm in width from the dummy wafer 50 towards the outer periphery of the wafer 40 compared to the comparative configuration. In this way, in the first example of the embodiment, the contamination Si concentration can be suppressed to a lower level at the base of the contamination distribution D1 compared to the comparative configuration.

[0062] Next, a second example of the embodiment will be described. In the second example of the embodiment, a configuration in which the width WD of the dummy wafer 50 is 20 mm is illustrated. The growth conditions for the GaN layer 20 in the second example of the embodiment are the same as those in the comparative configuration described above (or the first example of the embodiment).

[0063] Figure 6 is a graph showing an example of the Si concentration distribution on the upper surface 25 of the GaN layer 20 in the second example of the embodiment. Si contamination on the outer periphery is observed in the second example of the embodiment, as in the comparative form and the first example of the embodiment, but it is even more suppressed than in the first example of the embodiment.

[0064] In the second example of the embodiment, specifically, the central Si concentration C0 is 8.91 × 10⁻⁶ 15 cm -3 Therefore, the Si concentration C1 on the outer periphery is 9.44 × 10⁻⁶. 15 cm -3 Therefore, the Si contamination concentration Δ on the outer periphery is 0.53 × 10⁻⁶. 15 cm -3 The outer Si contamination concentration in the first example of the embodiment is Δ1.05 × 10 15 cm -3 It is even more suppressed than that.

[0065] First concentration standard value: 1.2 × 10 15 cm -3 Lower second and third concentration reference values ​​are set at 0.9 × 10⁻⁶, respectively. 15 cm -3 and 0.6 × 10 15 cm -3 The outer Si contamination concentration Δ in the second example of the embodiment is the same as in the first example of the embodiment, the first concentration reference value 1.2 × 10 15 cm -3 The following is suppressed: In the second example of the embodiment, the outer Si contamination concentration Δ is preferably the second concentration reference value of 0.9 × 10 15 cm -3 The following is suppressed, and more preferably, a third concentration reference value of 0.6 × 10 15 cm -3 The following suppression is observed. In Figure 6, the third concentration reference value is shown as Δ0.6.

[0066] Figure 7 is a schematic graph showing the Si concentration distribution of a second example of an embodiment similar to that in Figure 6. For ease of understanding, Figure 7 also shows the wafer 40, dummy wafer 50, and the inner periphery 211 of the susceptor along with the Si concentration distribution.

[0067] On the central side of the wafer 40, the contamination distribution D1 in the comparative form is shown, and on the outer peripheral side of the wafer 40, the contamination distribution D1 in the second example of the embodiment is shown. In the second example of the embodiment, the contamination distribution D1 can be moved 20 mm in the width of the dummy wafer 50 to the outer peripheral side of the wafer 40 as compared with the comparative form. In this way, in the second example of the embodiment, the contamination Si concentration can be suppressed to a lower level on the further trailing side of the contamination distribution D1 as compared with the first example of the embodiment.

[0068] As in the second example, by increasing the width WD of the dummy wafer 50, the incorporation of Si on the outer peripheral side of the wafer 40 can be further suppressed. However, increasing the width WD of the dummy wafer 50 increases the area of the entire wafer 60, that is, increases the area of the GaN layer to be grown.

[0069] The horizontal flow type MOVPE apparatus has the characteristic that the raw material efficiency (the ratio of the raw material contributing to growth) decreases as the area of the GaN layer to be grown increases. In the embodiment, in order to grow the thick GaN layer 20 with a thickness of 4 μm or more, the decrease in the raw material efficiency causes deterioration of the production efficiency and an increase in the cost. Also, as the growth area increases, the problem of raw material depletion on the downstream side is more likely to occur.

[0070] Therefore, from the viewpoint of favorably growing the GaN layer 20 in the wafer 40, the area of the entire wafer 60, that is, the width WD of the dummy wafer 50, is preferably small within a range where the Si incorporation suppressing effect can be appropriately obtained.

[0071] For this reason, the width WD of the dummy wafer 50 is not increased excessively so that the outer peripheral Si incorporation concentration Δ becomes zero. Specifically, with the fourth concentration reference value being 0.3×10[[ID=***]] 15 cm -3 as, the width WD of the dummy wafer 50 is limited to a size such that the outer peripheral Si incorporation concentration Δ becomes 0.3×10 15 cm -3 or more.

[0072] Thus, in the embodiment, by using the dummy wafer 50, the concentration Δ of the peripheral Si incorporation is suppressed, but the concentration Δ of the peripheral Si incorporation is not reduced to zero. That is, the feature that the peripheral Si concentration C1 is higher than the central Si concentration C0 remains. Specifically, the concentration Δ of the peripheral Si incorporation is suppressed to be less than or equal to the first concentration reference value of 1.2×10 15 cm -3 or less, preferably suppressed to be less than or equal to the second concentration reference value of 0.9×10 15 cm -3 or less, more preferably suppressed to be less than or equal to the third concentration reference value of 0.6×10 15 cm -3 or less. However, the concentration Δ of the peripheral Si incorporation is 0.3×10 15 cm -3 or more.

[0073] In addition, when defining that "the peripheral Si concentration C1 is higher than the central Si concentration C0", it is assumed that not only the first condition that the value of the peripheral Si concentration C1 is greater than the value of the central Si concentration C0 is satisfied, but also the second condition described below is satisfied.

[0074] [[ID=2,3]] The peripheral Si concentration C1 is the average value of the four peripheral measurement points. If only the average value is considered, for example (virtually), the Si concentration at three peripheral measurement points is lower than the central Si concentration C0, but there is a variation such that the Si concentration at one peripheral measurement point is extremely high, so the average value, that is, the peripheral Si concentration C1, may be higher than the central Si concentration C0, including an inappropriate situation like this.

[0075] In the embodiment, as described above, the growth of the GaN layer 20 is performed while rotating so as to achieve uniformity in the circumferential direction. Therefore, a definition that takes into account the uniformity in the circumferential direction is preferable. Here, when defining that "the peripheral Si concentration C1 is higher than the central Si concentration C0", as an additional second condition, it is assumed that the Si concentration at at least three (preferably four) of the four peripheral measurement points is higher than the central Si concentration C0.

[0076] The above explanation illustrates an embodiment in which the thickness of the GaN layer 20 is 4 μm. As mentioned above, the longer the growth time of the GaN layer 20, that is, the thicker the GaN layer 20, the greater the Si-containing deposition 230 tends to be. As a result, when the width WD of the dummy wafer 50 is kept constant, the Si contamination concentration Δ on the outer edge increases as the thickness of the GaN layer 20 increases.

[0077] Therefore, in embodiments where the thickness of the GaN layer 20 is greater than 4 μm, it is preferable to appropriately increase the width WD of the dummy wafer 50 in accordance with the thickness of the GaN layer 20, compared to the embodiment where the thickness of the GaN layer 20 is 4 μm, so that the peripheral Si contamination concentration Δ is reduced to a predetermined value. In this way, by appropriately increasing the width WD of the dummy wafer 50 in accordance with the thickness of the GaN layer 20, the peripheral Si contamination concentration Δ can be reduced to a predetermined value even in embodiments where the thickness of the GaN layer 20 is greater than 4 μm.

[0078] The characteristics of the GaN layer 20 according to this embodiment will be described below. As described above, in this embodiment, the Si contamination concentration Δ at the outer edge is suppressed by using a dummy wafer 50. This makes it possible to expand the region with a low concentration of Si contamination on the central side of the upper surface 25 of the GaN layer 20 towards the outer edge compared to the comparative embodiment. In other words, the width of the region with a high concentration of Si contamination on the outer edge of the upper surface 25 of the GaN layer 20 can be made smaller than in the comparative embodiment.

[0079] The concentration of added Si is 4 × 10, which is the lower limit of the target addition concentration, i.e., the lower limit of the central Si concentration C0. 15 cm -3 A Si concentration of 0.4 × 10⁻⁶ is 10% higher than the limit. 15 cm -3 The region exceeding this is called the high Si concentration region. In Figure 4, etc., the Si concentration is (0.4 × 10⁻⁶). 15 cm -3This region is denoted as ΔSi. The high-concentration Si region is the annular region on the edge of the upper surface 25 of the GaN layer 20. The entire circular region inside the annular region which is the high-concentration Si region is the low-concentration Si region. The width of the annular region which is the high-concentration Si region from the edge of the upper surface 25 is W1, and the diameter of the circular region which is the low-concentration Si region is W0.

[0080] The width W1 of the high-concentration Si-containing region is approximately 30 mm in the comparative form (Figure 9), but is smaller, approximately 20 mm, in the first example (Figure 4) and the second example (Figure 6) of the embodiment. The width W1 in the second example is even smaller than the width W1 in the first example. The width W1 of the high-concentration Si-containing region in the first and second examples of the embodiment is suppressed to 20 mm or less.

[0081] Thus, in the GaN layer 20 of the embodiment, the concentration of mixed Si (the excess of the average Si concentration from the central Si concentration C0) in the circular region (the entire region) inside the annular region with a width of 20 mm from the edge of the upper surface 25 is 0.4 × 10⁻¹⁴. 15 cm -3 It has the following characteristics:

[0082] In the embodiment (and comparative embodiment), the concentration of mixed Si decreases schematically monotonically from the outer periphery to the center of the GaN layer 20. Therefore, the GaN layer 20 of the embodiment has the characteristic that the intermediate Si concentration C2 at a radial position midway between the center and the outer periphery is higher than the central Si concentration C0 and lower than the outer periphery Si concentration C1.

[0083] The intermediate Si concentration C2 is defined, for example, as the average Si concentration at a radial position 30 mm from the center. In the first example of the embodiment shown in Figure 4, the intermediate Si concentration C2 (9.40 × 10) 15 cm -3 ) is the central Si concentration C0 (9.00 × 10 15 cm -3 ) is higher than the peripheral Si concentration C1 (10.05 × 10 15 cm -3It is lower than ). Also, in the second example of the embodiment shown in Figure 6, the intermediate Si concentration C2 (9.25 × 10 15 cm -3 ) is the central Si concentration C0 (8.91 × 10⁻¹⁰ 15 cm -3 ) is higher than the peripheral Si concentration C1 (9.44 × 10 15 cm -3 It is lower than ).

[0084] <Preferred Embodiments of the Invention> Preferred embodiments of the present invention are described below.

[0085] (Note 1) Substrate and A gallium nitride layer, epitaxially grown above the aforementioned substrate and composed of silicon-containing gallium nitride, Equipped with, The gallium nitride layer has an upper surface with a radius of 50 mm or more. The thickness of the gallium nitride layer is 4 μm or more. The silicon concentration on the upper surface of the gallium nitride layer has a distribution where the outer peripheral silicon concentration at a radial position 10 mm from the edge of the upper surface is higher than the central silicon concentration at the center of the upper surface. The aforementioned central silicon concentration is 4 × 10 15 cm -3 The above 2 x 10 16 cm -3 It is less than, The peripheral silicon contamination concentration, which is the excess of the peripheral silicon concentration from the central silicon concentration, is 1.2 × 10⁻⁶ 15 cm -3 The following (preferably 0.9 × 10) 15 cm -3 The following is more preferable: 0.6 × 10 15 cm -3 The following is: Multilayer substrate.

[0086] (Note 2) In the circular region inside the annular region with a width of 20 mm from the edge of the upper surface, the excess of the silicon concentration on the upper surface of the gallium nitride layer from the central silicon concentration is 0.4 × 10 15 cm -3 The following is: The laminated substrate described in Appendix 1.

[0087] (Note 3) The silicon concentration on the upper surface of the gallium nitride layer has a distribution in which the intermediate silicon concentration at a radial position 30 mm from the center of the upper surface is higher than the central silicon concentration and lower than the outer peripheral silicon concentration. A laminated substrate as described in Appendix 1 or 2. [Explanation of Symbols]

[0088] 10…Underlying structure, 20…GaN layer, 25…Top surface (of GaN layer), 30…Upper layer, 40…Wafer, 50…Dummy wafer, 60…Full wafer, 100…Laminated substrate, 200…Manufacturing equipment, 210…Susceptor, 211…Inner edge of susceptor, 212…Outer edge of susceptor, 213…Top surface of susceptor edge, 220…Raw material gas, 230…Si-containing deposition

Claims

1. Substrate and A gallium nitride layer, epitaxially grown above the aforementioned substrate and composed of silicon-containing gallium nitride, Equipped with, The gallium nitride layer has an upper surface with a radius of 50 mm or more. The thickness of the gallium nitride layer is 4 μm or more. The silicon concentration on the upper surface of the gallium nitride layer has a distribution in which the outer peripheral silicon concentration at a radial position 10 mm from the edge of the upper surface is higher than the central silicon concentration at the center of the upper surface. The central silicon concentration is 4 × 10 １５ cm －３ The above 2 x 10 １６ cm －３ It is less than, The peripheral silicon contamination concentration, which is the excess of the peripheral silicon concentration from the central silicon concentration, is 1.2 × 10⁻⁶ １５ cm －３ The following is: Multilayer substrate.

2. In the circular region inside the annular region with a width of 20 mm from the edge of the upper surface, the excess of the silicon concentration on the upper surface of the gallium nitride layer from the central silicon concentration is 0.4 × 10 １５ cm －３ The following is: The laminated substrate according to claim 1.

3. The silicon concentration on the upper surface of the gallium nitride layer has a distribution in which the intermediate silicon concentration at a radial position 30 mm from the center of the upper surface is higher than the central silicon concentration and lower than the outer peripheral silicon concentration. A laminated substrate according to claim 1 or 2.

Images