Silicon carbide crystal ball and manufacturing method thereof

Abstract

The invention provides a silicon carbide crystal ball and a manufacturing method thereof, and the silicon carbide crystal ball comprises a flat surface, a truncated conical surface and an annular curved surface. The annular curved surface is connected with the flat surface and the truncated conical surface. And the width of the silicon carbide crystal ball is gradually reduced from the first end of the truncated conical surface connected with the annular curved surface to the second end opposite to the first end.

Description

Technical Field

[0001] The present invention relates to a silicon carbide crystal sphere and a manufacturing method thereof. Background Art

[0002] Silicon carbide (SiC) is a semiconductor material with unique and excellent properties. In recent years, it has received extensive attention and applications in the fields of high-power and high-frequency electronic devices. Compared with traditional silicon (Si) wafers, silicon carbide wafers have a higher breakdown electric field, a wider energy gap, a higher thermal conductivity, and better radiation resistance, making them have significant advantages in some extreme application environments.

[0003] The growth of silicon carbide crystals usually adopts the Physical Vapor Transport (PVT) method, which is a technology for growing crystals through vapor transport and deposition. In the PVT method, raw materials are placed in a high-temperature furnace and heated to sublimate them into a gas phase. Subsequently, by precisely controlling the temperature gradient, silicon carbide in the gas phase gradually deposits on the seed crystal to form a large single-crystal silicon carbide crystal, also known as a silicon carbide crystal sphere. However, the formed silicon carbide crystal spheres usually contain convex or concave surfaces. These surfaces need to be ground flat before cutting the silicon carbide crystal spheres to obtain silicon carbide wafers, resulting in material loss. In addition, the convex or concave surfaces of these surfaces will cause the problem of residual high stress in the silicon carbide crystal spheres, which is likely to cause different degrees of warping of the subsequent silicon carbide wafers. Summary of the Invention

[0004] The present invention provides a silicon carbide crystal sphere and a manufacturing method thereof, which can improve the problem of convex surfaces on the silicon carbide crystal sphere.

[0005] At least one embodiment of the present invention provides a method for manufacturing a silicon carbide crystal sphere, which includes the following steps. Provide a raw material containing carbon element and silicon element and a seed crystal located above the raw material in the furnace body of a crystal growth furnace system, wherein the first surface of the seed crystal faces the raw material. Heat the raw material, wherein a part of the raw material is vaporized and transferred to the first surface of the seed crystal and the side wall of the seed crystal and a silicon carbide material is formed on the seed crystal to form a growth body containing the seed crystal and the silicon carbide material. The growth body grows along the radial direction perpendicular to the side wall of the seed crystal and the axial direction perpendicular to the first surface of the seed crystal. During the growth process of the growth body, the growth body has an axial temperature gradient in the axial direction and a radial temperature gradient in the radial direction. The ratio of the axial temperature gradient to the radial temperature gradient is 0.3 to 0.8. Cool the raw material to obtain the grown growth body. The grown growth body is a silicon carbide crystal sphere. The silicon carbide crystal sphere includes a flat surface facing the raw material, a truncated conical surface located on the side, and an annular curved surface connecting the flat surface and the truncated conical surface. The width of the silicon carbide crystal sphere tapers from the first end where the truncated conical surface connects the annular curved surface to the second end opposite to the first end. The vertical distance between the plane where the first end is located and the flat surface is 1 millimeter to 5 millimeters.

[0006] At least one embodiment of the present invention provides a silicon carbide crystal sphere, which includes a flat surface, a truncated conical surface, and an annular curved surface. The annular curved surface connects the flat surface and the truncated conical surface. The width of the silicon carbide crystal sphere tapers from the first end where the truncated conical surface connects the annular curved surface to the second end opposite to the first end. The vertical distance between the plane where the first end is located and the flat surface is 1 millimeter to 5 millimeters. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1A and Figure 1B is a schematic diagram of manufacturing a silicon carbide crystal sphere using a crystal growth furnace system according to an embodiment of the present invention;

[0008] Figure 2A is a schematic cross-sectional view of a silicon carbide crystal sphere according to an embodiment of the present invention;

[0009] Figure 2B is a top view schematic diagram of a silicon carbide crystal sphere according to an embodiment of the present invention;

[0010] Figure 3 is a schematic cross-sectional view of a silicon carbide crystal bar according to an embodiment of the present invention;

[0011] Figure 4 is a schematic cross-sectional view of cutting a silicon carbide crystal bar into a plurality of silicon carbide wafers according to an embodiment of the present invention;

[0012] Figure 5 is a schematic diagram of the furnace body and an external heating module of a crystal growth furnace system according to an embodiment of the present invention. Detailed implementation mode

[0013] Figure 1A and Figure 1B is a schematic diagram of manufacturing a silicon carbide crystal ball using a crystal growth furnace system 100 according to an embodiment of the present invention. Please refer to Figure 1A , the crystal growth furnace system 100 includes a crucible 105, a furnace body 110, an external heating module 120, a power supply 140, a first driving device 150, a second driving device 160, a control device 170, a gas supply device 180, and a thermometer 190.

[0014] The external heating module 120 is electrically connected to the power supply 140. The external heating module 120 includes, for example, an induction coil. The crucible 105 is disposed inside the furnace body 110, and the furnace body 110 is movably disposed inside the external heating module 120 and is connected to the gas supply device 180 through a gas pipe. The first driving device 150 drives the furnace body 110 to move along the axis AL, and the second driving device 160 drives the furnace body 110 to rotate along the axis AL. The control device 170 is electrically connected to the power supply 140, the first driving device 150, the second driving device 160, the gas supply device 180, and the thermometer 190.

[0015] The furnace body 110 is movably disposed inside the external heating module 120. In some embodiments, the control device 170 can control the operations of the first driving device 150 and the second driving device 160 simultaneously or separately, so that the furnace body 110 moves and / or rotates inside the external heating module 120. The movement and rotation of the furnace body 110 can be operated simultaneously or separately.

[0016] In an embodiment of the present invention, the furnace body 110 of the crystal growth furnace system 100 can not only move up and down relative to the external heating module 120, but also rotate relative to the external heating module 120. Through such a design, the heating of the furnace body 110 can be more uniform, and thus the crystals inside the furnace body 110 are heated more evenly, thereby obtaining crystal balls with better quality.

[0017] In some embodiments, the external heating module 120 is a heating coil group. In some embodiments, the furnace body 110 includes a heat insulation layer, thereby enabling more precise control of the temperature inside the furnace body 110. A seed carrier 20 is provided in the furnace body 110 for fixing the seed crystal 30.

[0018] In the method for manufacturing a silicon carbide crystal ball, a raw material 10 containing carbon and silicon elements and a seed crystal 30 located above the raw material 10 are placed in a furnace body 110. For example, the raw material 10 can be silicon carbide powder, which is placed at the bottom of the furnace body 110 as a solid sublimation source, and the seed crystal 30 is disposed at the top of the furnace body 110. In some embodiments, the seed crystal 30 can be fixed to the seed crystal carrier 20 through an adhesive layer. The material of the seed crystal 30 includes silicon carbide. For example, the seed crystal 30 can be 6H silicon carbide or 4H silicon carbide. In other embodiments, the seed crystal 30 may contain both 6H silicon carbide and 4H silicon carbide.

[0019] The first surface 30B of the seed crystal 30 faces the raw material 10, and the side wall 30S of the seed crystal 30 faces the inner side wall 105S of the crucible 105.

[0020] Next, the furnace body 110 and the raw material 10 are heated by an external heating module 120. A silicon carbide material is formed on the seed crystal 30 by Physical Vapor Transport (PVT) to form a growth body 40 including the seed crystal 30 and the silicon carbide material, as Figure 1B shown. The seed crystal 30 will receive the raw material 10 that solidifies from the gas state and form a gradually growing growth body 40 until the growth body 40 grows to the expected size.

[0021] Please refer to Figure 1A and Figure 1B , in the heating process of the above physical vapor transport method, the growth body 40 grows along the radial direction DR perpendicular to the side wall 30S of the seed crystal 30 and the axial direction AR perpendicular to the first surface 30B of the seed crystal 30. During the growth process, the growth body 40 has an axial temperature gradient (ΔTz) in the axial direction AR and a radial temperature gradient (ΔTx) in the radial direction DR. In some embodiments, the axial temperature gradient (ΔTz) can also refer to the temperature gradient of the seed crystal 30 or the growth body 40 in the thickness direction; the radial temperature gradient (ΔTx) can also refer to the temperature gradient of the seed crystal 30 or the growth body 40 in the horizontal direction perpendicular to its thickness direction.

[0022] In the embodiments of the present disclosure, by adjusting the ratio (ΔTz / ΔTx) of the axial temperature gradient (ΔTz) to the radial temperature gradient (ΔTx) of the growth body 40, the problem of surface protrusions of the silicon carbide crystal ball is improved. In a preferred embodiment, the ratio (ΔTz / ΔTx) of the axial temperature gradient (ΔTz) to the radial temperature gradient (ΔTx) is 0.3 to 0.8. When the ratio (ΔTz / ΔTx) is less than 0.3, the growth rate of the growth body 40 becomes very slow, the finally obtained crystal ball size is too small, and the process is inefficient. When the ratio (ΔTz / ΔTx) is greater than 0.8, the growth rate of the growth body 40 is too fast, resulting in poor quality of the finally obtained crystal ball.

[0023] In some embodiments, in order to better control the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), the distance D2 between the top end of the external heating module 120 and the second surface 30T of the seed crystal 30 opposite to the first surface 30B is less than 80 millimeters. If the distance D2 is too large (for example, greater than 80 millimeters), the edge of the crucible 105 is likely to be affected by the external heating module 120, and the excessively high temperature will make it difficult for the silicon carbide material to deposit on the side wall of the growth body 40 close to the crucible 105, resulting in a convex structure with a thick middle and a thin periphery in the growth body 40.

[0024] In some embodiments, during the execution of the physical vapor transport method (i.e., during the growth process of the growth body 40), the doping amount of nitrogen concentration in the growth body 40 is increased to optimize the uniformity of the resistivity of the produced silicon carbide crystal sphere.

[0025] After the growth body 40 grows to the expected size, the raw material 10 is cooled to obtain the grown growth body 40. The grown growth body 40 is the desired silicon carbide crystal sphere 50, as Figure 2A shown in Figure 2B In some embodiments, the silicon carbide crystal sphere may have different crystal structures depending on the crystal orientation of the single crystal seed used. For example, the silicon carbide crystal sphere 50 includes 4H-silicon carbide, 6H-silicon carbide, etc. Both 4H-silicon carbide and 6H-silicon carbide belong to the hexagonal crystal system.

[0026] Please refer to Figure 1B and Figure 2A and Figure 2B As shown, the silicon carbide crystal sphere 50 includes a flat surface 40B facing the raw material, a truncated conical surface 40S on the side, an annular curved surface 40R connecting the flat surface 40B and the truncated conical surface 40S, and a bottom surface 40T opposite to the flat surface 40B. The width of the silicon carbide crystal sphere tapers from the first end E1 where the truncated conical surface 40S connects the annular curved surface 40R to the second end E2 opposite to the first end E1. The maximum distance between the plane where the first end E1 is located (a virtual plane, shown as a dotted line in the figure) and the flat surface 40B is the vertical distance D3. There is an angle θ between the plane where the first end E1 is located and the annular curved surface 40R. Generally, the larger the vertical distance D3, the larger the angle θ. In some embodiments, the angle θ is from 1 degree to 8 degrees.

[0027] In some embodiments, by adjusting the ratio (ΔTz / ΔTx) of the axial temperature gradient (ΔTz) to the radial temperature gradient (ΔTx) of the growth body 40, the vertical distance D3 between the plane where the first end E1 is located and the flat surface 40B can be reduced. For example, when the ratio (ΔTz / ΔTx) is from 0.3 to 0.8, the vertical distance D3 is from 1 millimeter to 5 millimeters.

[0028] In addition, the width WD1 of the flat surface 40B and the width WD2 of the annular curved surface 40R are also affected by the ratio (△Tz / △Tx). Generally speaking, when the diameter of the silicon carbide crystal sphere 50 is fixed, the larger the width WD1 of the flat surface 40B, the flatter the surface of the silicon carbide crystal sphere 50, and the less material is lost when the uneven surface of the silicon carbide crystal sphere 50 is removed by the grinding process subsequently. In some embodiments, the width WD1 of the flat surface 40B is 6.5 inches to 8 inches. Taking the diameter of the silicon carbide crystal sphere 50 being 200 mm as an example, when the width WD1 of the flat surface 40B is 150 mm, the width WD2 of the annular curved surface 40R is about 25 mm; when the width WD1 of the flat surface 40B is 190 mm, the width WD2 of the annular curved surface 40R is about 5 mm.

[0029] Table 1 presents the vertical distance D3, the angle θ, and the width WD1 of the silicon carbide crystal sphere 50 obtained after adjusting the ratio (△Tz / △Tx) of the axial temperature gradient (△Tz) to the radial temperature gradient (△Tx) in some embodiments of the present disclosure.

[0030] Table 1

[0031]

[0032] It can be seen from Table 1 that reducing the ratio (△Tz / △Tx) is beneficial to reducing the vertical distance D3. In the present disclosure, setting the ratio (△Tz / △Tx) within the range of 0.3 to 0.8 can balance the manufacturing efficiency of the silicon carbide crystal sphere 50 and the quality of the silicon carbide crystal sphere 50. In a preferred embodiment, the ratio (△Tz / △Tx) is set within the range of 0.3 to 0.6, and the vertical distance D3 is 1 mm to 4 mm.

[0033] In addition, please refer to Figure 1A and Figure 2A , the distance D2 between the top end of the external heating module 120 and the second surface 30T of the seed crystal 30 opposite to the first surface 30B also affects the growth quality of the silicon carbide crystal sphere 50. Table 2 presents the vertical distance D3 of the silicon carbide crystal sphere 50 obtained after adjusting the distance D2 in some embodiments of the present disclosure. In Table 2, a negative value of the distance D2 indicates the distance that the top end of the external heating module 120 is higher than the second surface 30T, and a positive value of the distance D2 indicates the distance that the top end of the external heating module 120 is lower than the second surface 30T.

[0034] Table 2

[0035]

[0036] It can be seen from Table 2 that when the distance D2 is smaller, it is beneficial to reduce the vertical distance D3.

[0037] After the silicon carbide crystal sphere 50 is formed, the silicon carbide crystal sphere 50 is taken out from the crystal growth furnace system 100. Then, the top surface, bottom surface, and side surfaces of the silicon carbide crystal sphere 50 are ground to obtain a silicon carbide crystal bar 50' with a uniform width, as Figure 3 shown. Then, the silicon carbide crystal bar 50' is cut into a plurality of silicon carbide wafers 60, as Figure 4 shown.

[0038] Figure 5 FIG. Figure 5 is a schematic diagram of a furnace body and an external heating module of a crystal growth furnace system according to an embodiment of the present invention. For example, Figure 1A and Figure 1B the furnace body 110 and the external heating module 120 in Figure 5 can be as

[0039] shown. Figure 5 Please refer to Figure 1A and Figure 5 . In some embodiments, the distance D2 between the top end of the uppermost one of the heating rings 122 and the second surface 30T of the seed crystal 30 is less than 80 millimeters in the vertical direction VD.

[0040] With such a coil design, it is beneficial to control the axial temperature gradient (ΔTz) and the radial temperature gradient (ΔTx), thereby obtaining a silicon carbide crystal sphere with better quality.

Claims

1. A manufacturing method of a silicon carbide crystal ball, comprising: Providing a raw material containing carbon element and silicon element and a seed crystal above the raw material in a furnace body of a crystal growth furnace system, wherein a first surface of the seed crystal faces the raw material; Heating the raw material, wherein a part of the raw material is vaporized and transferred to the first surface of the seed crystal and the side wall of the seed crystal to form a silicon carbide material on the seed crystal, so as to form a growth body containing the seed crystal and the silicon carbide material, wherein the growth body grows along a radial direction perpendicular to the side wall of the seed crystal and an axial direction perpendicular to the first surface of the seed crystal. During the growth process of the growth body, the growth body has an axial temperature gradient in the axial direction and a radial temperature gradient in the radial direction, wherein a ratio of the axial temperature gradient to the radial temperature gradient is 0.3 to 0.8; and Cooling the raw material to obtain the grown growth body, wherein the grown growth body is the silicon carbide crystal ball, wherein the silicon carbide crystal ball includes a flat surface facing the raw material, a truncated conical surface located on a side surface of the silicon carbide crystal ball, and an annular curved surface connecting the flat surface and the truncated conical surface, wherein a width of the silicon carbide crystal ball tapers from a first end where the truncated conical surface connects the annular curved surface to a second end opposite to the first end, and a vertical distance between a plane where the first end is located and the flat surface is 1 mm to 5 mm.

2. The manufacturing method according to claim 1, wherein the crystal growth furnace system comprises: An external heating module, comprising a plurality of heating rings stacked along a vertical direction, wherein each heating ring is respectively located at a different horizontal plane.

3. The manufacturing method according to claim 2, wherein each of the heating rings is a coil, and coil axes of the coils are parallel to each other.

4. The manufacturing method according to claim 1, wherein the crystal growth furnace system comprises: An external heating module, wherein the furnace body is movably disposed within the external heating module, and a distance between a top end of the external heating module and a second surface of the seed crystal opposite to the first surface is less than 80 mm.

5. The manufacturing method according to claim 4, wherein the external heating module comprises a plurality of heating rings stacked along a vertical direction, and a distance between a top end of the topmost one of the heating rings and the second surface is less than 80 mm in the vertical direction.

6. The manufacturing method according to claim 1, wherein an included angle between the plane where the first end is located and the annular curved surface is 1 degree to 8 degrees.

7. The manufacturing method according to claim 1, wherein a ratio of the axial temperature gradient to the radial temperature gradient is 0.3 to 0.6, and a vertical distance between the plane where the first end is located and the flat surface is 1 mm to 4 mm.

8. A silicon carbide crystal ball, comprising: A flat surface; A truncated conical surface; And An annular curved surface connects the flat surface and the truncated conical surface, wherein the width of the silicon carbide crystal sphere tapers from a first end where the truncated conical surface connects the annular curved surface to a second end opposite to the first end, and the vertical distance between the plane where the first end is located and the flat surface is 1 millimeter to 5 millimeters.

9. The silicon carbide crystal sphere according to claim 8, wherein the angle between the plane where the first end is located and the annular curved surface is 1 degree to 8 degrees.

10. The silicon carbide crystal sphere according to claim 8, wherein the width of the flat surface is 6.5 inches to 8 inches.

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