JP2017122047A - SINGLE CRYSTAL 4H-SiC SUBSTRATE AND PRODUCTION METHOD THEREOF - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single crystal 4H-SiC substrate capable of reducing crystal defects, and to provide a production method thereof.SOLUTION: A 4H-SiC bulk single crystal 1 having surface smoothness, and having an off-angle of 2 degrees or more and 10 degrees or less is prepared. A first single crystal 4H-SiC layer 3 having a recess 2 is epitaxially grown on the 4H-SiC bulk single crystal 1. When expressing a film thickness of the first single crystal 4H-SiC layer 3 as X[μm], a diameter Y[μm] of the recess 2 is 0.2×X or more and 2×X or less, and a depth Z[μm] of the recess 2 is (0.95×X+0.5)×0.001 or more and 0.01×X or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a single crystal 4H—SiC substrate capable of reducing crystal defects and a method for manufacturing the same.

  In recent years, silicon carbide (hereinafter referred to as SiC), which has a relatively large band gap, dielectric breakdown field strength, saturation drift velocity, and thermal conductivity as compared with silicon, has been attracting attention as a power device material for power control. This power device using SiC can significantly reduce power loss and downsize, and can realize energy saving when converting power supply power. It will be a key device for realizing a low-carbon society such as functionalization.

  The doping density and film thickness are almost predetermined according to the specifications of the SiC power device, and usually higher accuracy than the bulk single crystal substrate is required. Therefore, the active region of the semiconductor device is epitaxially grown in advance on the 4H-SiC bulk single crystal substrate by a thermal CVD method (thermal chemical vapor deposition method) or the like. The active region here is a region in which the doping density and film thickness in the crystal are precisely controlled.

  In the 4H—SiC bulk single crystal substrate, screw dislocations propagating in the c-axis direction, edge dislocations, and dislocations propagating in the direction perpendicular to the c-axis (basal plane dislocations) are inherent. These dislocations propagate to the epitaxial film grown on the substrate. Furthermore, new dislocation loops and stacking faults are introduced during epitaxial growth. These crystal defects may deteriorate the withstand voltage characteristics, reliability, and yield of a device using this SiC substrate, and may be a practical problem.

  As a method for manufacturing a single crystal 3C-SiC substrate, there has been proposed a method for reducing crystal defects by forming a single crystal 3C-SiC layer so as to have a surface state in which surface pits are scattered on a flat surface. (For example, refer to Patent Document 1).

JP 2011-225421 A

  3C-SiC that is cubic and 4H-SiC that is hexagonal crystal have different crystal structures, that is, atomic arrangements, and therefore have greatly different growth conditions. For example, the growth temperature of 3C—SiC is 1000 to 1100 ° C., whereas the growth temperature of 4H—SiC is as high as 1600 to 1800 ° C. Therefore, a method for reducing crystal defects in a single crystal 3C—SiC substrate cannot be applied to a single crystal 4H—SiC substrate, and a method for reducing crystal defects in a single crystal 4H—SiC substrate has not been known.

  The present invention has been made to solve the above-described problems, and an object thereof is to obtain a single crystal 4H—SiC substrate capable of reducing crystal defects and a method for manufacturing the same.

  The method for manufacturing a single crystal 4H-SiC substrate according to the present invention includes a step of preparing a 4H-SiC bulk single crystal substrate having flatness and an off angle of 2 degrees to 10 degrees, and the 4H-SiC bulk. And a step of epitaxially growing a first single crystal 4H—SiC layer having a recess on a single crystal substrate, and the thickness of the first single crystal 4H—SiC layer is X [μm], the diameter of the recess Y [μm] is 0.2 × X or more and 2 × X or less, and the depth Z [μm] of the recess is (0.95 × X + 0.5) × 0.001 or more, 0.01 × X It is characterized by the following.

  According to the present invention, crystal defects can be reduced.

It is sectional drawing which shows the manufacturing method of the single crystal 4H-SiC substrate which concerns on Embodiment 1 of this invention. It is sectional drawing which shows the manufacturing method of the single crystal 4H-SiC substrate which concerns on Embodiment 1 of this invention. It is the microscope picture image which observed the recessed part formed in the growth surface of a single-crystal 4H-SiC layer with the optical microscope. It is a figure which shows the relationship between the diameter of a recessed part, and the film thickness of an epitaxial film. It is a figure which shows the relationship between the depth of a recessed part, and the film thickness of an epitaxial film. It is a figure which shows the relationship between the density of the recessed part of the surface of a single crystal 4H-SiC layer, and a defect density. It is sectional drawing which shows the manufacturing method of the single crystal 4H-SiC substrate which concerns on Embodiment 2 of this invention.

  A single crystal 4H—SiC substrate and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to the drawings. The same or corresponding components are denoted by the same reference numerals, and repeated description may be omitted.

Embodiment 1 FIG.
Hereinafter, a method for manufacturing a single crystal 4H—SiC substrate according to Embodiment 1 of the present invention will be described. 1 and 2 are cross-sectional views showing a method for manufacturing a single crystal 4H-SiC substrate according to Embodiment 1 of the present invention.

  First, as shown in FIG. 1, a 4H—SiC bulk single crystal substrate 1 having an off angle of 4 degrees in the <11-20> direction with respect to the (0001) plane (C plane) serving as the main surface is prepared. Here, the off angle is not limited to 4 degrees, and may be in the range of 2 degrees to 10 degrees.

  Specifically, the 4H—SiC bulk single crystal substrate 1 is planarized by mechanical polishing and chemical mechanical polishing using a chemical solution exhibiting acidity or alkalinity. Furthermore, ultrasonic cleaning is performed using acetone to remove organic substances. Next, so-called RCA cleaning is performed on the 4H—SiC bulk single crystal substrate 1. That is, after immersing in a mixed solution (1: 9) of ammonia water and hydrogen peroxide solution heated to 75 ° C. (± 5 ° C.) for 10 minutes, hydrochloric acid and hydrogen peroxide solution heated to 75 ° C. (± 5 ° C.) Immerse in (1: 9). Further, the 4H—SiC bulk single crystal substrate 1 is cleaned by immersing it in an aqueous solution containing about 5% hydrofluoric acid by volume ratio and further performing substitution treatment with pure water.

Next, the 4H—SiC bulk single crystal substrate 1 is introduced into a CVD apparatus. Vacuuming is performed to about 1 × 10 ⁻⁷ kPa. Then, it heats to about 1400 degreeC-1700 degreeC, and implements the annealing process in a reducing gas atmosphere. Next, as shown in FIG. 2, a source gas is supplied and a single crystal 4H− having a recess 2 having a diameter of 2 to 20 μm and a depth of 10 to 100 nm on the 4H—SiC bulk single crystal substrate 1. The SiC layer 3 is epitaxially grown. As the source gas, for example, silane gas (SiH ₄ ) is used as a supply source of Si atoms, propane gas (C ₃ H ₈ ) is used as a supply source of C atoms, and nitrogen gas is used as N-type doping. Here, SiH ₄ gas is supplied at a flow rate of 500 sccm and C ₃ H ₈ gas is supplied at a flow rate of 200 sccm to form a single crystal 4H—SiC layer 3 having a thickness of 10 μm. Nitrogen gas was supplied as N-type doping so that the carrier concentration was 1 × 10 ¹⁷ / cm ³ at the substrate interface and the carrier concentration was 8 × 10 ¹⁵ / cm ^{3 in} the active region. Thereafter, the supply of the source gas is stopped and the temperature is lowered to room temperature.

Here, when the inventor forms the single crystal 4H-SiC layer 3, the pressure and temperature in the growth furnace are appropriately set, so that the growth surface of the single crystal 4H-SiC layer 3 is very small. It has been found that the recess 2 is formed. FIG. 3 is a photomicrograph image obtained by observing a recess formed on the growth surface of the single crystal 4H—SiC layer with an optical microscope. When the density of the recesses 2 was calculated using an optical microscope, the density was about 600 / cm ² . When the surface shape of the concave portion 2 was measured by an atomic force microscope, the shape was an asymmetrical elliptical cone shape, the diameter was 2 to 20 μm, and the depth of the deepest portion was 10 to 100 nm. As a result of repeating further detailed experiments, it was found that the size of the recess differs depending on the film thickness of the epitaxial film to be formed, and that the thicker the film, the larger the diameter and depth of the recess. FIG. 4 is a diagram showing the relationship between the diameter of the recess and the film thickness of the epitaxial film. FIG. 5 is a diagram showing the relationship between the depth of the recess and the film thickness of the epitaxial film. As a result of the experiment, assuming that the film thickness of the epitaxial film is X [μm], the diameter Y [μm] of the recess is 0.2 × X [μm] or more and 2 × X [μm] or less, and the depth of the recess It was found that Z [nm] was 0.95 × X [μm] +0.5 [nm] or more and 10 × X [μm] or less.

FIG. 6 is a diagram showing the relationship between the density of the recesses on the surface of the single crystal 4H—SiC layer and the defect density. The defect density was observed by a photoluminescence topography method (PL-TOPO method). Here, the defect density is defined as an abnormal emission region observed by the PL-TOPO method. In the case of a conventional substrate on which a single crystal 4H—SiC layer is formed using general growth conditions, the concave portion is hardly observed with an optical microscope, and the density thereof is less than 10 pieces / cm ² . In this case, the defect density is 60 pieces / cm ² or more. Some device electrodes have a large area of 1 to 2 mm square or more. If a conventional single crystal 4H-SiC substrate is used, one or more defects will exist under the electrodes, and the device withstand voltage characteristics will deteriorate. To do.

On the other hand, in the case of the single crystal 4H—SiC substrate according to the present embodiment in which the density of the recesses 2 is 10 pieces / cm ² or more, the defect density can be greatly reduced to 2 pieces / cm ² . When the density of the recesses 2 was 1500 / cm ² , the defect density was as low as 1 / cm ² .

  As described above, in the present embodiment, the diameter Y [μm] is 0.2 × X [μm] or more and 2 × X [μm] or less, and the depth Z [nm] is 0.95 ×. The single crystal 4H—SiC layer 3 having a recess that is X [μm] +0.5 [nm] or more and 10 × X [μm] or less is epitaxially grown. Thereby, crystal defects can be reduced. Furthermore, the withstand voltage characteristics, reliability, and yield of a device using this high-quality single crystal 4H—SiC substrate can be improved.

  Note that when forming the single crystal 4H—SiC layer 3, an organometallic material containing Al, B, and Be may be supplied for P-type doping as necessary. In order to increase the growth speed, a gas containing chlorine may be used in combination. In addition, the growth rate of the single crystal 4H—SiC layer 3 can be changed by changing the raw material gas flow rate, and the same effect can be obtained regardless of whether the growth rate is 1 μm / h or 10 μm / h. confirmed.

  Moreover, it discovered that the density of the recessed part 2 could be adjusted by setting the pressure and temperature in a growth furnace appropriately. However, the conditions are not uniquely determined, and are considered to largely depend on the internal structure and structure of the CVD apparatus, and suitable conditions are determined in each case.

Embodiment 2. FIG.
Hereinafter, a method for manufacturing a single crystal 4H—SiC substrate according to Embodiment 2 of the present invention will be described. FIG. 7 is a cross-sectional view showing a method for manufacturing a single crystal 4H—SiC substrate according to Embodiment 2 of the present invention.

  First, similarly to the first embodiment, a single crystal 4H—SiC layer 3 having a recess 2 on the growth surface is formed by epitaxial growth with a film thickness of 300 nm. Note that the film thickness of the single crystal 4H—SiC layer 3 is not limited to 300 nm and may be in the range of 50 nm to 10 μm. Next, as shown in FIG. 7, the single crystal 4H—SiC layer 4 is formed on the single crystal 4H—SiC layer 3 to a thickness of 10 μm by epitaxial growth so as to fill the recess 2.

At this time, SiH ₄ gas is supplied at a flow rate of 900 sccm and C ₃ H ₈ gas is supplied at a flow rate of 360 sccm, and nitrogen gas is supplied so that the carrier concentration is 8 × 10 ¹⁵ / cm ³ as N-type doping. Thereafter, the supply of the source gas is stopped and the temperature is lowered to room temperature. Other configurations and manufacturing steps are the same as those in the first embodiment.

  Here, if the single crystal 4H—SiC layer 4 is grown under a growth condition in which a growth mode called step flow growth is dominant by appropriately setting the growth temperature and the like, the recess 2 of the single crystal 4H—SiC layer 3 is formed. Can be embedded.

When the density of the concave portions 2 on the surface of the single crystal 4H—SiC substrate according to the present embodiment was calculated by an optical microscope, it was very low as about 1 piece / cm ² . Furthermore, when the 10 μm square region was evaluated with an atomic force microscope, no abnormal growth called step bunching occurred, and the average roughness (Ra) was very good at 0.3 nm or less. Further, as a result of observation by the PL-TOPO method, it was confirmed that the defect density was as low as 2 pieces / cm ² and the low defect density obtained at the time of forming the single crystal 4H—SiC layer 3 could be maintained. .

  In the present embodiment, single crystal 4H—SiC layer 4 is formed so as to fill recess 2 of single crystal 4H—SiC layer 3. Thereby, crystal defects can be reduced and the flatness of the single crystal 4H—SiC substrate can be improved.

  Note that even when the single crystal 4H—SiC layer has a two-layer structure as in the second embodiment, the relationship between the density of the recesses and the defect density shown in FIG. 6 can be obtained. In addition, the single crystal 4H—SiC layer 3 in which the recesses are formed is not necessarily in contact with the 4H—SiC bulk single crystal substrate 1. can do. Therefore, the layer position of the single crystal 4H—SiC layer 3 can be freely changed according to the required device specifications. As a result, it is possible to simultaneously control the defect density while precisely controlling the carrier concentration and film thickness of the active region.

1 4H-SiC bulk single crystal substrate, 2 recesses, 3 single crystal 4H-SiC layer (first single crystal 4H-SiC layer), 4 single crystal 4H-SiC layer (second single crystal 4H-SiC layer)

Claims (19)

Preparing a 4H-SiC bulk single crystal substrate having flatness and an off angle of 2 degrees or more and 10 degrees or less;
Epitaxially growing a first single crystal 4H-SiC layer having a recess on the 4H-SiC bulk single crystal substrate,
When the film thickness of the first single crystal 4H—SiC layer is X [μm], the diameter Y [μm] of the recess is 0.2 × X or more and 2 × X or less, and the depth of the recess Z [μm] is (0.95 × X + 0.5) × 0.001 or more and 0.01 × X or less, and a method for producing a single crystal 4H—SiC substrate. ^{2. The} method for producing a single crystal 4H—SiC substrate according to claim 1, wherein the density of the recesses on the surface of the first single crystal 4H—SiC layer is 1 piece / cm ² or more.   When forming the first single crystal 4H—SiC layer, the pressure and temperature in the growth furnace are set so that the recess is formed on the growth surface of the first single crystal 4H—SiC layer. The manufacturing method of the single-crystal 4H-SiC substrate of Claim 1 or 2 characterized by the above-mentioned.   The diameter Y [μm] of the recess is 2 μm or more and 20 μm or less, and the depth Z [μm] of the recess is 0.01 μm or more and 0.1 μm or less. The manufacturing method of the single-crystal 4H-SiC board | substrate as described in a term.   5. The single-crystal 4H—SiC substrate according to claim 1, wherein a film thickness X [μm] of the first single-crystal 4H—SiC layer is 0.3 μm or more and 10 μm or less. Manufacturing method. The method for producing a single crystal 4H-SiC substrate according to any one of claims 1 to 5, wherein the defect density of the first single crystal 4H-SiC layer is 2 pieces / cm ² or less.   The method for manufacturing a single crystal 4H-SiC substrate according to any one of claims 1 to 6, wherein the first single crystal 4H-SiC layer is doped with an N-type impurity.   8. The method according to claim 1, further comprising a step of epitaxially growing a second single crystal 4H—SiC layer on the first single crystal 4H—SiC layer so as to fill the recess. The manufacturing method of the single-crystal 4H-SiC board | substrate as described in 2 ..   The method for manufacturing a single crystal 4H-SiC substrate according to claim 8, wherein the second single crystal 4H-SiC layer is doped with an N-type impurity.   The method for producing a single crystal 4H-SiC substrate according to claim 8 or 9, wherein the second single crystal 4H-SiC layer has a surface average roughness of 0.3 nm or less. A 4H-SiC bulk single crystal substrate having flatness and an off angle of 2 degrees or more and 10 degrees or less;
A first single crystal 4H-SiC layer formed on the 4H-SiC bulk single crystal substrate and having a recess;
When the film thickness of the first single crystal 4H—SiC layer is X [μm], the diameter Y [μm] of the recess is 0.2 × X or more and 2 × X or less, and the depth of the recess Z [μm] is (0.95 × X + 0.5) × 0.001 or more and 0.01 × X or less, a single crystal 4H—SiC substrate. The single crystal 4H-SiC substrate according to claim 11, wherein the density of the concave portions on the surface of the first single crystal 4H-SiC layer is 1 piece / cm ² or more.   The diameter Y [μm] of the recess is 2 μm or more and 20 μm or less, and the depth Z [μm] of the recess is 0.01 μm or more and 0.1 μm or less. Crystal 4H-SiC substrate.   14. The single-crystal 4H—SiC substrate according to claim 11, wherein a film thickness X [μm] of the first single-crystal 4H—SiC layer is 0.3 μm or more and 10 μm or less. . The single crystal 4H-SiC substrate according to any one of claims 11 to 14, wherein a defect density of the first single crystal 4H-SiC layer is 2 pieces / cm ² or less.   The single crystal 4H-SiC substrate according to any one of claims 11 to 15, wherein the first single crystal 4H-SiC layer is doped with an N-type impurity. A second single crystal 4H-SiC layer formed on the first single crystal 4H-SiC layer;
The single crystal 4H-SiC substrate according to any one of claims 11 to 16, wherein the recess is embedded in the second single crystal 4H-SiC layer.   The single crystal 4H-SiC substrate according to claim 17, wherein the second single crystal 4H-SiC layer is doped with an N-type impurity.   The single-crystal 4H-SiC substrate according to claim 17, wherein the surface average roughness of the second single-crystal 4H-SiC layer is 0.3 nm or less.

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