JP7729038B2 - Wafer holder, chemical vapor deposition apparatus, and method for manufacturing SiC epitaxial wafer - Google Patents

Description

The present invention relates to a wafer holder, a chemical vapor deposition apparatus, and a method for manufacturing SiC epitaxial wafers.

Silicon carbide (SiC) has a breakdown field that is an order of magnitude larger than that of silicon (Si), a band gap that is three times larger, and a thermal conductivity that is approximately three times higher. Because of these properties, silicon carbide is expected to be used in power devices, high-frequency devices, high-temperature operating devices, and more. SiC semiconductor devices are fabricated using SiC epitaxial wafers.

SiC epitaxial wafers are manufactured by growing a SiC epitaxial film, which will become the active region of a SiC semiconductor device, on a SiC substrate. The SiC substrate is obtained by processing a bulk single crystal of SiC produced by a sublimation method or other method, and the SiC epitaxial film is formed by chemical vapor deposition (CVD). In this specification, a SiC epitaxial wafer refers to a wafer after the SiC epitaxial film has been formed, and a SiC substrate refers to a wafer before the SiC epitaxial film has been formed.

CVD is a technology for growing high-quality epitaxial films on the surface of a substrate, but this process can sometimes result in roughness on the backside. For example, Patent Documents 1 and 2 describe depositing an epitaxial film on a Si substrate placed on a susceptor. Film-forming gas and etching gas are supplied to the front side of the Si substrate, and purge gas is supplied to the backside. Supplying purge gas to the backside of the Si substrate prevents some of the gas supplied to the front side from flowing to the backside, thereby suppressing roughness and cloudiness on the backside of the Si epitaxial wafer.

Patent No. 3908112 Special Publication No. 2001-508599

However, when using a SiC substrate, simply supplying a purge gas to the backside may not sufficiently suppress the roughness and cloudiness of the backside of the SiC epitaxial wafer. SiC is more susceptible to backside roughness and cloudiness than Si. The reasons for this include the high deposition temperature for forming the epitaxial film, the fact that H ₂ used as a carrier gas also functions as an etching gas, the tendency for roughness (step bunching) to occur due to a discrepancy in the ratio (C/Si ratio) between the C-based source gas and the Si-based source gas, and the presence of many thermodynamically stable polytypes that are prone to the formation of mixed crystals. Furthermore, SiC substrates are susceptible to the influence of gas environments, temperature environments, and the like. Therefore, optimizing the growth conditions for the SiC epitaxial film is difficult, and there is also the problem of abnormal growth being prone to occur.

Roughness and abnormal growth on the backside of SiC epitaxial wafers can have adverse effects on the inspection process and device fabrication process. For example, roughness on the backside of SiC epitaxial wafers can be eliminated by backside polishing, but adding a backside polishing step increases the number of production processes, leading to increased costs and reduced throughput.

One way to prevent roughness on the back surface of a SiC substrate is to increase the efficiency of supplying purge gas to the back surface of the SiC substrate. However, if the amount of purge gas supplied to the back surface of the SiC substrate increases, the injection of purge gas can cause the SiC substrate to shift from its installed position during the film formation process. Misalignment of the SiC substrate creates a situation in which purge gas is more likely to be supplied to the front surface of the SiC substrate, causing deviations from the optimized film formation conditions, promoting abnormal growth, and being one of the causes of reduced quality in the formed epitaxial film.

The present invention was made in consideration of the above circumstances, and aims to provide a wafer holder, chemical vapor deposition apparatus, and method for manufacturing SiC epitaxial wafers that can produce high-quality SiC epitaxial wafers.

To solve the above problems, the present invention specifically provides the following means.

(1) The wafer holder according to the first aspect comprises a central portion facing the wafer placed thereon and a peripheral portion located outside the central portion, the peripheral portion having a first gas exhaust path extending outward from the central portion and a second gas exhaust path extending upward in the thickness direction from the first gas exhaust path.

(2) In the wafer holder according to the above aspect, a second end of the second gas exhaust path opposite to the first end that connects to the first gas exhaust path may be located outside the inner peripheral end of the outer peripheral portion.

(3) The wafer holder according to the above aspect may include a susceptor and a plurality of cover members that cover the susceptor at the outer periphery, and the first gas exhaust path may be formed between the susceptor and the plurality of cover members, and the second gas exhaust path may be formed between the plurality of cover members.

(4) In the wafer holder according to the above aspect, the first gas exhaust path may be inclined with respect to the radial direction so that the outer second end is located rearward of the inner first end in the direction of rotation, and the inclination angle of the first gas exhaust path with respect to the radial direction may be greater than 0° and less than 90°.

(5) In the wafer holder according to the above aspect, the first gas exhaust path may extend radially.

(6) In the wafer holder according to the above aspect, the second gas exhaust path may be inclined with respect to the in-plane direction in which the central portion extends so that the second end is positioned outward from the first end connected to the first gas exhaust path, and the inclination angle of the second gas exhaust path with respect to the in-plane direction may be greater than 0° and less than 90°.

(7) In the wafer holder according to the above aspect, the second gas exhaust path may extend vertically relative to the first gas exhaust path.

(8) In the wafer holder according to the above aspect, the central portion may have a gas inlet passage for supplying gas to the backside of the wafer.

(9) A chemical vapor deposition apparatus according to a second aspect includes a wafer holder according to the above aspect.

(10) The method for manufacturing a SiC epitaxial wafer according to the third aspect uses the wafer holder according to the above aspect.

The wafer holder, chemical vapor deposition apparatus, and SiC epitaxial wafer manufacturing method of the present invention can produce high-quality SiC epitaxial wafers.

1 is a cross-sectional view of a characteristic portion of a chemical vapor deposition apparatus according to a first embodiment. FIG. 2 is a cross-sectional view of the wafer holder according to the first embodiment. FIG. 2 is a plan view of the susceptor according to the first embodiment. FIG. 2 is a plan view of the cover member according to the first embodiment. FIG. 3 is a cross-sectional view of a characteristic portion of the wafer holder according to the first embodiment. FIG. 2 is a cross-sectional view of a first portion near a slit of the susceptor according to the first embodiment. FIG. 4 is a cross-sectional view of a second portion near the slit of the susceptor according to the first embodiment. FIG. 10 is a cross-sectional view of a wafer holder according to a second embodiment. FIG. 10 is a plan view of a susceptor according to a second embodiment. FIG. 10 is a plan view of a cover member according to a second embodiment. FIG. 11 is a cross-sectional view of a wafer holder according to a third embodiment. FIG. 11 is a plan view of a wafer holder according to a third embodiment. FIG. 11 is an enlarged cross-sectional view of the vicinity of a first gas exhaust path of a wafer holder according to a third embodiment. FIG. 10 is a cross-sectional view of a wafer holder according to a fourth embodiment. FIG. 10 is a plan view of a wafer holder according to a fourth embodiment. FIG. 10 is a plan view of a susceptor according to a first modified example. FIG. 10 is a plan view of a susceptor according to a second modified example. FIG. 10 is a cross-sectional view of a susceptor according to a third modified example. FIG. 10 is a plan view of a susceptor according to a fourth modified example. FIG. 10 is a cross-sectional view of a susceptor according to a fourth modified example.

The present embodiment will now be described in detail, with appropriate reference to the drawings. The drawings used in the following description may show enlarged portions of the characteristic parts of the present invention for the sake of clarity, and the dimensional proportions of the components may differ from the actual proportions. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them. Appropriate modifications can be made within the scope of the present invention's effectiveness.

First, let's define the directions. The thickness direction of the wafer holder is the z direction. The direction perpendicular to the z direction is called the in-plane direction, one of the in-plane directions is called the x direction, and the direction perpendicular to the x direction is called the y direction. Furthermore, the direction spreading outward from the center of the wafer holder is called the radial direction, and the direction along the circumference of the wafer holder with the center of the wafer holder as its axis is called the circumferential direction.

First Embodiment
1 is a cross-sectional view of a characteristic portion of a chemical vapor deposition apparatus 200 according to a first embodiment. The chemical vapor deposition apparatus 200 includes a wafer holder 100, a chamber 110, a support 120, and a heater H.

The chamber 110 forms the film formation space A1. The chamber 110 has, for example, a gas supply port, a gas exhaust port, a transfer port for transferring the SiC substrate W, etc. The chamber 110 is made of, for example, carbon, SiC, metal carbide, carbon coated with SiC or metal carbide, stainless steel, etc. Gas G is supplied to the film formation space A1 from the gas supply port. The gas G is, for example, a film formation gas or an etching gas. The gas G is supplied to the surface of the SiC substrate W placed on the wafer holder 100.

The support 120 is located below the chamber 110. The support 120 supports the wafer holder 100. The support 120 may rotate the wafer holder 100. The support 120 and the wafer holder 100 surround a purge space A2. A heater H is located within the purge space A2. The heater H is located, for example, below the wafer holder 100. The heater H heats the wafer holder 100. The purge space A2 is filled with an inert gas to protect the heater H. The inert gas is, for example, nitrogen or argon. The inert gas is an example of a purge gas P. The purge gas P is supplied from the purge space A2 to the back side of the SiC substrate W through through holes (e.g., vertical hole VH, slit SL) in the susceptor 10, which will be described later. The purge gas P supplied to the backside of the wafer passes through the first gas exhaust path C1 and second gas exhaust path C2, which will be described later, and escapes into the film formation space A1.

Figure 2 is a cross-sectional view of the wafer holder 100 according to the first embodiment. The wafer holder 100 includes, for example, a susceptor 10 and a cover member 20. Figure 2 also illustrates a SiC substrate W held by the wafer holder 100.

The wafer holder 100 has a central portion 30 and an outer peripheral portion 31. The central portion 30 is the portion of the wafer holder 100 that faces the SiC substrate W, and the outer peripheral portion 31 is the portion radially outward from the central portion 30. In the wafer holder 100 shown in FIG. 2, the central portion 30 consists of a portion of the susceptor 10, and the outer peripheral portion 31 consists of a portion of the susceptor 10 and a cover member 20. The cover member 20 is placed on the susceptor 10 at the outer peripheral portion 31. The outer peripheral portion 31 has a first gas exhaust path C1 and a second gas exhaust path C2.

Figure 3 is a plan view of the susceptor 10 according to the first embodiment. Figure 4 is a plan view of the cover member 20 according to the first embodiment. Figure 4 also shows the SiC substrate W. The cross section taken along line A-A in Figures 3 and 4 corresponds to Figure 2.

The susceptor 10 has a main body portion 15 and a support portion 16. The susceptor 10 rotates, for example, in either circumferential direction. Hereinafter, the direction in which the susceptor 10 rotates will be referred to as the rotation direction R. The support portion 16 protrudes from the main body portion 15 in the z direction and supports the SiC substrate W. For example, the support portion 16 shown in Figure 3 supports the SiC substrate W at a position that does not interfere with the exhaust port. There are no particular restrictions on the shape or position of the support portion 16, as long as it does not result in a structure that prevents the purge gas P from being exhausted.

The central portion 30 of the susceptor 10 has, for example, a vertical hole VH and a slit SL. Both the vertical hole VH and the slit SL are holes that penetrate the susceptor 10. Purge gas is supplied to the backside of the SiC substrate W through the vertical hole VH and the slit SL.

A groove 17 is formed in the outer peripheral portion 31 of the susceptor 10. The thickness of the susceptor 10 where the groove 17 is formed is preferably 0.3 mm or more. The groove 17 is formed radially outward from the central portion 30. The space between the groove 17 and the cover member 20 is the first gas exhaust channel C1. The first gas exhaust channel C1 is formed between the susceptor 10 and the cover member 20, and extends outward from the central portion 30.

There are, for example, multiple cover members 20. Each cover member 20 is, for example, a ring-shaped member connected in the circumferential direction. The cover members 20 are, for example, arranged concentrically. There are gaps between the cover members 20. The gaps between the cover members 20 form the second gas exhaust channels C2. The second gas exhaust channels C2 extend in the z direction from the first gas exhaust channel C1.

The first gas exhaust path C1 and the second gas exhaust path C2 are paths through which the purge gas P supplied to the back surface of the SiC substrate W is exhausted.

The first gas discharge channel C1 has a first end e1 and a second end e2. The first end e1 is located radially inward from the second end e2. The first end e1 is located, for example, at the boundary between the central portion 30 and the outer peripheral portion 31. The first end e1 may be located inward from the boundary between the central portion 30 and the outer peripheral portion 31. In other words, a portion of the first gas discharge channel C1 may extend to the central portion 30. The second end e2 is located, for example, at the outer peripheral edge of the outer peripheral portion 31. The second end e2 of the first gas discharge channel C1 is located rearward from the first end e1 in the rotational direction R.

The first gas exhaust passage C1 is inclined relative to the radial direction. The first gas exhaust passage C1 is inclined relative to the radial direction so that the second end e2 is located further rearward in the rotational direction R than the first end e1. The inclination angle θ1 of the first gas exhaust passage C1 relative to the radial direction is, for example, greater than 0° and less than 90°.

When the tilt angle θ1 is greater than 0°, a flow of purge gas P is formed from the central portion 30 toward the outside, and the purge gas P is efficiently discharged from the back surface side of the SiC substrate W. Furthermore, when the tilt angle θ1 is less than 90°, the gas vector does not deviate significantly from the direction in which the first gas discharge path C1 extends. The gas vector is the flow direction of the purge gas P, and is a direction that spreads radially from the central portion 30. In other words, when the tilt angle θ1 is within the above range, the purge gas P is efficiently discharged.

The preferred range of the inclination angle θ1 is determined by the rotation speed of the susceptor 10, the discharge speed of the purge gas P, etc. For example, if the circumferential speed at the first end e1 is V _R and the discharge speed of the purge gas P at the first end e1 is V _p , it is preferable that θ1=sin ⁻¹ (V _R /V _p ) be satisfied.

Figure 5 is a cross-sectional view of a characteristic portion of the wafer holder 100 according to the first embodiment. The second gas exhaust path C2 has a first end e3 and a second end e4. The first end e3 is the end that connects to the first gas exhaust path C1. The second end e4 is the end opposite the first end e3. The second end e4 is exposed on the upper surface of the cover member 20. The second end e4 is located outside the first end e3 and outside the inner peripheral end of the outer peripheral portion 31. By separating the second end e4, from which the purge gas P is exhausted, from the edge of the SiC substrate W, it is possible to prevent the film formation conditions near the edge of the SiC substrate W from deviating from the optimal conditions.

The second gas exhaust path C2 is, for example, inclined with respect to the in-plane direction. The inclination angle θ2 of the second gas exhaust path C2 with respect to the in-plane direction is preferably, for example, greater than 0° and less than 90°. The purge gas P passing through the second gas exhaust path C2 acts to press the susceptor 10 downward, preventing misalignment of the susceptor 10 itself. Furthermore, the inclination angle θ2 is preferably greater than or equal to 30° and less than or equal to 60°. The purge gas P passing through the second gas exhaust path C2 acts to press the cover member 20 downward, preventing misalignment of the susceptor 10 and the cover member 20.

The vertical hole VH and slit SL are gas inlet channels that supply purge gas P to the back side of the SiC substrate W.

The vertical hole VH penetrates the susceptor 10 in the z direction and extends in the z direction. The vertical hole VH is, for example, located at the center of the susceptor 10 when viewed from above in the z direction. The slit SL penetrates the susceptor 10 at an angle in the circumferential direction with respect to the z direction. The slit SL is, for example, located outside the susceptor 10 relative to the vertical hole VH. The slit SL extends from the center outward.

As shown in Figure 3, the slit SL is inclined relative to the radial direction of the susceptor 10. The first inner end of the slit SL is located further forward in the rotation direction R than the second outer end. The inclination angle φ1 of the slit SL relative to the radial direction of the susceptor 10 is, for example, greater than 0° and less than 90°. When the inclination angle φ1 is greater than 0°, it is easy to form a flow of purge gas P from the center of the susceptor 10 toward the outside. Furthermore, when the inclination angle φ1 is less than 90°, there is little deviation between the gas vector and the opening direction of the slit SL. The gas vector is the flow direction of the purge gas P passing through the slit SL. The opening direction of the slit SL is from the end on the back side of the slit SL toward the end on the front side.

Figures 6 and 7 are cross-sectional views of the vicinity of the slit SL of the susceptor 10. Figure 6 is a cross-section taken along line B-B in Figure 3, and Figure 7 is a cross-section taken along line CC in Figure 3. The first portion shown in Figure 6 is located radially inward of the susceptor 10 relative to the second portion shown in Figure 7.

The slits SL are inclined circumferentially with respect to the z direction. The end of the slits SL on the back surface bs side is located forward in the rotation direction R from the end of the slits SL on the front surface fs side. The slits SL are inclined in the opposite direction to the rotation direction R from the end on the back surface bs side.

The inclination angle φ3 of the slit SL in the second portion relative to the z direction is greater than the inclination angle φ2 of the slit SL in the first portion relative to the z direction. The inclination angle of the slit SL in the z direction increases, for example, toward the outside of the susceptor 10.

The inclination angles φ2 and φ3 of the slit SL satisfy, for example, the relationship tanφ=V _R1 /V _p1 , where V _p1 is the vertical component of the relative velocity of the purge gas P with respect to the main body portion 15 at the position of the slit SL when viewed from the rotating coordinate system of the susceptor 10, and V _R1 is the horizontal component of the relative velocity of the purge gas P with respect to the main body portion 15 at the position of the slit SL when viewed from the rotating coordinate system of the susceptor 10.

The susceptor 10 rotates in a rotation direction R. The circumferential velocity (peripheral velocity) at each point on the susceptor 10 is expressed as the product of the distance between the corresponding point and the center and the angular velocity of the susceptor. With the susceptor 10 as the reference, the purge gas moves at a relative velocity V _R1 in the direction opposite to the rotation direction relative to the slit SL. The absolute value of the relative velocity V _R1 is the same as the absolute value of the circumferential velocity. The relative velocity V _R1 is referred to as the first vector. Furthermore, the purge gas P is supplied in the z direction from below the susceptor 10 at a flow velocity V _p1 . The flow velocity V _p1 is referred to as the second vector.

When each point on the susceptor 10 is considered as the reference point, the purge gas P is supplied to each point on the susceptor 10 from the direction of the resultant vector of the first and second vectors. When the inclination angles φ2 and φ3 at each point on the slit SL satisfy the above relationship, the inflow direction of the purge gas into the slit SL coincides with the inclination direction of the slit SL, allowing the purge gas to flow smoothly into the slit SL.

The wafer holder 100 according to the first embodiment has a first gas exhaust path C1 and a second gas exhaust path C2, which allows it to efficiently exhaust purge gas P from the backside of the SiC substrate W. As a result, the purge gas P prevents the SiC substrate W from floating up during the film formation process, thereby preventing misalignment of the SiC substrate W. Furthermore, efficient exhaust of purge gas P from the backside of the SiC substrate W allows the amount of purge gas supplied to the backside of the SiC substrate W to be increased. Increasing the amount of purge gas supplied to the backside of the SiC substrate prevents roughening of the backside of the SiC substrate.

Furthermore, by discharging the purge gas P from a position away from the edge of the SiC substrate W using the first gas exhaust path C1 and the second gas exhaust path C2, it is possible to prevent a decrease in the concentration ratio of the film formation gas near the outer peripheral edge of the SiC substrate W. In other words, it is possible to reduce variation in film formation conditions near the outer peripheral edge of the SiC substrate W and suppress abnormal growth.

Furthermore, the purge gas P discharged from the second end e4 of the second gas discharge path C2 flows over the top surface of the wafer holder 100, thereby pressing the entire wafer holder 100 downward and preventing the wafer holder 100 itself from shifting position. Furthermore, the purge gas P flows over the top and bottom surfaces of the cover member 20, preventing a temperature difference from occurring between the top and bottom surfaces of the cover member 20. A temperature difference occurring between the top and bottom surfaces of the cover member 20 could cause the cover member 20 and susceptor 10 to crack.

Second Embodiment
FIG. 8 is a cross-sectional view of a wafer holder 101 according to the second embodiment. The wafer holder 101 has, for example, a susceptor 40 and a cover member 21. FIG. 8 also illustrates a SiC substrate W held by the wafer holder 101. FIG. 9 is a plan view of the susceptor 40 according to the second embodiment. FIG. 10 is a plan view of the cover member 21 according to the second embodiment. FIG. 10 also illustrates the SiC substrate W. The cross sections taken along line A-A in FIGS. 9 and 10 correspond to FIG. 8.

The susceptor 40 has a main body portion 45 and a support portion 46. The susceptor 40 differs from the susceptor 10 shown in Figure 2 in that the groove 17 is not formed in the outer peripheral portion 31. A description of the same configuration as in Figure 2 will be omitted.

There are, for example, multiple cover members 21. Each cover member 21 is, for example, a ring-shaped member connected in the circumferential direction. The cover members 21 are, for example, arranged concentrically. A groove 25 is formed on the underside of the cover member 21. The space between the groove 25 of the cover member 21 and the main body portion 45 of the susceptor 40 is the first gas exhaust channel C3. The specific configuration of the first gas exhaust channel C3 is the same as the first gas exhaust channel C1 shown in FIG. 1. The gaps between the multiple cover members 21 are second gas exhaust channels C2.

The wafer holder 101 according to the second embodiment achieves the same effects as the wafer holder 100 according to the first embodiment, except that the relationship between the groove and the lid that form the first gas exhaust path C3 is the opposite of that of the first gas exhaust path C1 according to the first embodiment.

"Third embodiment"
FIG. 11 is a cross-sectional view of a wafer holder 102 according to the third embodiment. The wafer holder 102 is made of, for example, a susceptor 50. The wafer holder 102 differs from the first and second embodiments in that it does not have a cover member. FIG. 11 also shows a SiC substrate W held by the wafer holder 102. FIG. 12 is a plan view of the wafer holder 102 according to the third embodiment. The cross section taken along line A-A in FIG. 12 corresponds to FIG. 11.

The susceptor 50 has a main body portion 55, a support portion 56, and a sidewall 57. The sidewall 57 is located to the side of the SiC substrate W and prevents the SiC substrate W from protruding in the radial direction. The susceptor 50 differs from the susceptor 10 shown in Figure 2 in that the outer peripheral portion 31 consists of a part of the main body portion 55 and the sidewall 57. A description of the same configuration as in Figure 2 will be omitted.

A hole 58 is formed in the main body portion 55. The hole 58 is formed from the central portion 30 toward the outside. The hole 58 may be formed by hollowing out a portion of the main body portion 55 as shown in FIG. 13(a), or may be formed by a recess 55A and a lid 55B covering the recess 55A as shown in FIG. 13(b). The lid 55B may be provided with a protrusion 55C to prevent misalignment. The inside of the hole 58 serves as the first gas exhaust channel C4.

A hole 59 is also formed in the side wall 57. Hole 59 is connected to hole 58 and extends in the z direction. The interior of hole 59 forms the second gas exhaust channel C5.

The wafer holder 102 according to the third embodiment has a first gas exhaust path C4 and a second gas exhaust path C5, and provides the same effects as the wafer holder 100 according to the first embodiment.

Fourth Embodiment
Fig. 14 is a cross-sectional view of a wafer holder 103 according to the fourth embodiment. The wafer holder 103 has, for example, a susceptor 60 and a cover member 22. Fig. 14 also shows a SiC substrate W held by the wafer holder 103. Fig. 15 is a plan view of the wafer holder 103 according to the fourth embodiment. The cross section taken along line A-A in Fig. 15 corresponds to Fig. 14.

The susceptor 60 has a main body portion 65, a support portion 66, and a sidewall 67. The sidewall 67 is located to the side of the SiC substrate W. The susceptor 60 differs from the susceptor 10 shown in Figure 2 in that it has a sidewall 67 and the groove 68 does not extend all the way to the outer periphery. A description of the same configuration as in Figure 2 will be omitted.

A groove 68 is formed in the main body portion 65 at the outer peripheral portion 31. The groove 68 is formed from the central portion 30 outward. The groove 68 does not reach the outer peripheral edge, but extends to the side wall 67. The space between the groove 68 and the cover member 22 is the first gas discharge channel C6.

The cover member 22 is located between the SiC substrate W and the side wall 67. The cover member 22 is, for example, a ring-shaped member. There is a gap between the cover member 22 and the side wall 67. The gap between the cover member 22 and the side wall 67 is the second gas exhaust channel C7. The second gas exhaust channel C7 extends in the z direction from the first gas exhaust channel C6.

The wafer holder 103 according to the fourth embodiment has a first gas exhaust path C6 and a second gas exhaust path C7, and provides the same effects as the wafer holder 100 according to the first embodiment.

As mentioned above, specific examples of wafer holders have been described in detail in the first to fourth embodiments, but the wafer holders can be modified and changed in various ways within the scope of the present invention.

For example, in the first to fourth embodiments, examples have been shown in which the gas inlet passage is composed of vertical holes VH and slits SL, but the shape and position of the gas inlet passage are not important. For example, it may be composed of only vertical holes VH, as shown in Figure 16.

For example, in the first to fourth embodiments, examples were shown in which the first gas inlet channels C1, C3, and C4 were inclined relative to the radial direction. However, as shown in FIG. 17, the first gas inlet channel C1' may extend in the radial direction. That is, the inclination angle θ1 of the first gas inlet channel C1' relative to the radial direction may be 0°. While FIG. 17 illustrates a modified example of the first embodiment (FIG. 3), the same applies to the second to fourth embodiments. If the inclination angle θ1 is 0°, the flow of the purge gas P from the central portion 30 toward the outside is not impeded, and the purge gas P is efficiently discharged from the back surface side of the SiC substrate W.

Furthermore, for example, in the first to fourth embodiments, examples were shown in which the second gas inlet channels C2, C5, and C7 were inclined relative to the in-plane direction, but as shown in FIG. 18, the second gas inlet channel C2' may extend vertically relative to the first gas inlet channel C1. Even in this case, a portion of the purge gas P discharged from the second end e4 of the second gas inlet channel C2' flows along the upper surface of the cover member 20, thereby pressing the entire wafer holder 100 downward.

In addition, for example, in the first to fourth embodiments, examples were shown in which the support portions 16, 46, 56, and 66 did not overlap the first gas inlet channel C1 in the radial direction. However, as shown in FIG. 19, the support portion 76 may be located in a position where it overlaps the first gas inlet channel C1 in the radial direction over the entire circumferential direction. In this case, as shown in FIG. 20, a groove extending radially is formed below the support portion 76, thereby connecting the central portion 30 and the first gas inlet channel C1.

Furthermore, for example, in the first to fourth embodiments, the arrangement of the first and second gas exhaust channels does not have to be regular. When symmetry is present, as in the first to fourth embodiments, it is preferable to regularly arrange the gas exhaust channels so as to achieve N-fold symmetry, where N=3 or more, with the center of the wafer holder 100 as the center of rotation. For example, if the flow velocity of the purge gas P at the second end e4 is _Vc2 , _Vc2 becomes faster where the exhaust port of the second end e4 is narrow, and a relatively strong force acts to move inward. That is, the cover member 20 is subjected to a vector force directed toward the center of the wafer holder 100. As a result, the position of the cover member 20 is stabilized at a position where _Vc2 is the same at each exhaust port of the second end e4, making it easier to design optimal film formation conditions and suppressing abnormal growth. Furthermore, for example, in the first to fourth embodiments, the shapes of the first and second gas exhaust channels may be different.

Example 1
A susceptor 10 having the configuration shown in FIG. 3 was prepared. The susceptor 10 had grooves 17 in its outer peripheral portion 31. The area of the grooves 17 occupying 50% of the outer peripheral portion 31 was set. The depth of the grooves 17 was set to 1 mm. Three concentrically arranged ring-shaped members were placed on the outer peripheral portion 31 of the susceptor 10 as cover members 20. The area surrounded by the grooves 17 and the cover members 20 functions as a first gas exhaust channel C1. The spaces between the multiple cover members 20 function as second gas exhaust channels C2. The inclination angle θ1 of the first gas exhaust channel C1 with respect to the radial direction was set to 45°. The inclination angle θ2 of the second gas exhaust channel C2 with respect to the in-plane direction was set to 45°.

A SiC substrate with a diameter of 150 mm was placed on the susceptor 10, and film formation was performed. During film formation, the susceptor 10 was rotated at a rotation speed of 100 rpm. Purge gas was supplied to the backside of the SiC substrate W at a rate of 25 sccm. The surface roughness (Rq: root mean square height) of the backside after film formation was then measured. In Example 1, the area of the region with a surface roughness (Rq) of 10 μm or more was 3.7% of the total area.

Example 2
Example 2 differs from Example 1 in that the amount of purge gas supplied to the back surface side of the SiC substrate W was 100 sccm. The surface roughness (Rq) was measured under the same conditions as in Example 1. In Example 2, the area of the region having a surface roughness (Rq) of 10 μm or more was 0.5% of the total area.

(Comparative Example 1)
Comparative Example 1 differs from Example 1 in that no grooves 17 were formed. That is, the susceptor of Comparative Example 1 does not have the first gas exhaust channel C1. The surface roughness (Rq) was measured under the same conditions as in Example 1. In Comparative Example 1, the area of the region where the surface roughness (Rq) was 10 μm or more was 29.8% of the total area.

(Comparative Example 2)
Comparative Example 2 differs from Example 2 in that grooves 17 were not formed. That is, the susceptor of Comparative Example 2 does not have first gas exhaust channels C1. The surface roughness (Rq) was measured under the same conditions as in Example 2. In Comparative Example 2, the area of the region where the surface roughness (Rq) was 10 μm or more was 25.4% of the total area.

In Examples 1 and 2, where the susceptor has the first gas exhaust channel C1, roughening of the back surface of the SiC substrate was prevented compared to Comparative Examples 1 and 2, where the susceptor does not have the first gas exhaust channel C1.

10, 40, 50, 60... susceptor, 15, 45, 55, 65... main body portion, 16, 46, 56, 66... support portion, 17, 25, 68... groove, 20, 21, 22... cover member, 30... central portion, 31... outer peripheral portion, 55A... recess, 55B... lid, 55C... protrusion, 57, 67... side wall, 58, 59... hole, 100, 101, 102, 103... wafer holder, 110 ...Chamber, 120...Support, 200...Chemical vapor deposition apparatus, A1...Deposition space, A2...Purge space, C1, C3, C4, C6...First gas exhaust path, C2, C5, C7...Second gas exhaust path, e1, e3...First end, e2, e4...Second end, G...Gas, P...Purge gas, R...Rotation direction, VH...Vertical hole, SL...Slit, W...SiC substrate, fs...Front surface, bs...Back surface

Claims (9)

The wafer support includes a central portion facing the wafer to be placed thereon, and an outer peripheral portion located outside the central portion,
the central portion has a gas inlet passage for supplying a purge gas to the backside of the wafer;
the central portion has a support portion, and by supporting the wafer with the support portion, the center of the wafer is spaced apart from the central portion, and a space into which a purge gas is supplied is formed between the central portion and the wafer;
the outer peripheral portion has a first gas discharge path extending outward from the central portion and a second gas discharge path extending upward in a thickness direction from the first gas discharge path,
the first gas discharge path is connected to the space,
a second end of the second gas discharge path opposite to a first end connected to the first gas discharge path is positioned outside the outer peripheral edge of the wafer, and the second end is located at the same position as the first end or outside the first end in the radial direction. The wafer support includes a central portion facing the wafer to be placed thereon, and an outer peripheral portion located outside the central portion,
the central portion has a gas inlet passage for supplying a purge gas to the backside of the wafer;
a space to which a purge gas is supplied is provided between the central portion and the wafer;
the outer peripheral portion has a first gas discharge path extending outward from the central portion and a second gas discharge path extending upward in a thickness direction from the first gas discharge path,
the first gas discharge path is connected to the space,
a second end of the second gas discharge path opposite to a first end connected to the first gas discharge path is disposed outside an outer peripheral edge of the wafer, and the second end is located at the same position as the first end or outside the first end in a radial direction;
the second end of the second gas exhaust path is located outside an inner peripheral end of the outer circumferential portion. The wafer support includes a central portion facing the wafer to be placed thereon, and an outer peripheral portion located outside the central portion,
the central portion has a gas inlet passage for supplying a purge gas to the backside of the wafer;
a space to which a purge gas is supplied is provided between the central portion and the wafer;
the outer peripheral portion has a first gas discharge path extending outward from the central portion and a second gas discharge path extending upward in a thickness direction from the first gas discharge path,
the first gas discharge path is connected to the space,
a second end of the second gas discharge path opposite to a first end connected to the first gas discharge path is disposed outside an outer peripheral edge of the wafer, and the second end is located at the same position as the first end or outside the first end in a radial direction;
a susceptor; and a plurality of cover members that cover the susceptor at the outer periphery,
the first gas discharge path is formed between the susceptor and the plurality of cover members,
The second gas exhaust path is formed between the plurality of cover members. the first gas discharge passage is inclined with respect to the radial direction so that an outer second end is located rearward of an inner first end in the rotation direction;
4. The wafer holder of claim 1, wherein an inclination angle of the first gas discharge path with respect to the radial direction is greater than 0° and less than 90°. The wafer holder according to any one of claims 1 to 3, wherein the first gas exhaust path extends radially. The wafer support includes a central portion facing the wafer to be placed thereon, and an outer peripheral portion located outside the central portion,
the central portion has a gas inlet passage for supplying a purge gas to the backside of the wafer;
a space to which a purge gas is supplied is provided between the central portion and the wafer;
the outer peripheral portion has a first gas discharge path extending outward from the central portion and a second gas discharge path extending upward in a thickness direction from the first gas discharge path,
the first gas discharge path is connected to the space,
a second end of the second gas discharge path opposite to a first end connected to the first gas discharge path is disposed outside an outer peripheral edge of the wafer, and the second end is located at the same position as the first end or outside the first end in a radial direction;
the second gas discharge path is inclined with respect to an in-plane direction in which the central portion extends so that a second end thereof is positioned outward from a first end thereof connected to the first gas discharge path;
a tilt angle of the second gas exhaust path with respect to the in-plane direction being greater than 0° and less than 90° ; The wafer holder according to any one of claims 1 to 5, wherein the second gas exhaust path extends vertically relative to the first gas exhaust path. A chemical vapor deposition apparatus equipped with the wafer holder according to any one of claims 1 to 7. A method for manufacturing SiC epitaxial wafers using the wafer holder described in any one of claims 1 to 7.