Crucible assembly and crucible for preparing silicon carbide crystals

Abstract

The utility model relates to the field of silicon carbide crystal preparation, and particularly discloses a crucible assembly and a crucible for preparing silicon carbide crystals. The shape and the size of the bottom surface of the crucible assembly are matched with those of the crucible cover; the crucible assembly is divided into a central area, a transition area and an outer edge area in the direction from the center to the outer edge; the thickness of the transition area is smaller than the thickness of the central area and the thickness of the outer edge area, and the transition area is in a thick-thin-thick state from the central area to the outer edge area. The utility model further provides a crucible assembled with the crucible assembly. According to the utility model, the temperature field and gas flow near the crucible wall can be effectively adjusted, the radial temperature gradient is reduced, the gas flow is improved, the temperature field distribution is homogenized, the thermal field stability is improved, and the process reproducibility is greatly improved, so that the quality of a large-size silicon carbide crystal is improved, and the resistivity unevenness of the wafer is only 1.23%.

Description

Technical Field

[0001] The utility model relates to the field of silicon carbide crystal preparation, and more specifically, to a crucible component and a crucible for preparing silicon carbide crystals. Background Art

[0002] Silicon carbide crystals have excellent physical and electrical properties, including wide band gap, high critical breakdown electric field, high thermal conductivity, high carrier saturation velocity, and excellent chemical stability. However, as the diameter of the crystal increases, the difficulty of controlling multiple physical fields increases greatly, especially the thermal field. As the size of the growth crucible increases, the thermal resistance increases from the outside to the inside. Therefore, the temperature at the center of the crystal and the raw material decreases, while the radial temperature gradient increases, resulting in an irregular crystal shape. Since the temperature at the edge of the raw material is relatively high, the decomposition rate is higher than that in the center, resulting in intense gas flow near the crucible wall. Therefore, during the crystal growth process, the growth rate of the outer edge of the crystal is accelerated, and the formation of the crystal is affected by the surrounding polycrystalline structure. Therefore, micro defects will increase during the growth of large-sized silicon carbide crystals.

[0003] Resistivity has a direct impact on the on-state of the device, so a conductive substrate with a uniform radial distribution of surface resistivity must be obtained to ensure high performance of power devices. However, at higher growth temperatures, nitrogen doping in silicon carbide decreases, resulting in increased resistance of silicon carbide. The radial temperature gradient on the surface of the crystal growth causes reduced nitrogen doping at the edge of the crystal and higher resistivity than in the center of the crystal. As the diameter of the crystal increases, the radial temperature gradient also increases. This makes the problem of nitrogen doping and non-uniform resistivity more obvious.

[0004] The prior art discloses a large-size high-purity silicon carbide single crystal, a single crystal substrate and a preparation method thereof. In the preparation method of the large-size high-purity silicon carbide single crystal and the single crystal substrate, crucibles with different wall thicknesses and insulation structures with different thicknesses are used to produce an axial temperature gradient, and the insulation structure on the upper side of the crucible is changed at the same time, thereby producing a thermal field with consistent radial temperature distribution.

[0005] The prior art discloses a thermal field structure for growing large-size silicon carbide single crystals by a PVT method. It includes a medium-frequency heating coil, a graphite felt insulation layer, an inner crucible, a seed crystal holder, an outer crucible, a gas cooling device and an outer crucible cover, wherein the medium-frequency heating coil is arranged on the outer ring of the graphite felt insulation layer, the graphite felt insulation layer is arranged on the outer ring of the outer crucible, the inner crucible and the outer crucible form a detachable nested crucible, the inner crucible is filled with silicon carbide raw materials, the seed crystal holder is arranged on the inner crucible cover, the crucible wall of the outer crucible is distributed in a gradient manner, and the diameter gradually decreases from bottom to top, and a uniform gas cooling device is arranged on the upper part of the outer crucible cover.

[0006] However, the above-mentioned prior art only changes the axial temperature gradient during the crystal growth process by changing the thickness of the crucible wall. Not only can the radial temperature gradient not be adjusted according to the specific temperature field, but the thicker crucible wall means that more heat is lost when it is transferred to the inside of the crucible, resulting in reduced heating efficiency. In addition, the temperature response of the thick-walled crucible during heating and cooling will be slower, which may make temperature control difficult, making it more complicated to maintain suitable growth conditions, thereby affecting the crystal growth process. As the thickness of the crucible wall increases, the surface temperature of the seed crystal decreases, and the crystal growth rate will increase uncontrollably. Due to problems with temperature control and heat conduction efficiency, problems such as stress and increased defects may occur inside the crystal, thereby affecting the overall quality of the crystal. Summary of the invention

[0007] The utility model provides a crucible assembly to overcome the problems that the prior art cannot adjust the radial temperature according to the specific temperature field and the crucible wall is too thick.

[0008] Another object of the utility model is to provide a crucible for preparing silicon carbide crystals.

[0009] The technical solution of the utility model is as follows:

[0010] A crucible assembly for growing 8-inch and larger silicon carbide single crystals, wherein:

[0011] The bottom surface of the crucible assembly is adapted to the shape and size of the crucible cover and is used to be placed on the top of the crucible cover; the crucible assembly is divided into a central area, a transition area and an outer edge area from the center to the outer edge; the thickness of the transition area is smaller than that of the central area and the outer edge area, and it presents a thick-thin-thick pattern from the central area to the outer edge area.

[0012] Furthermore, the thickness of the central zone gradually decreases from the center to the edge, the thickness of the outer edge zone gradually increases from the center to the edge of the crucible cover, the thickness of the transition zone gradually increases from the center to the two sides, and the edges of the transition zone are smoothly connected to the central zone and the outer edge zone on both sides thereof.

[0013] Preferably, the central area of ​​the crucible assembly is conical, the bottom diameter of the crucible assembly is 260-340 mm, the central area diameter is 120-240 mm, and the thickness of the outer edge area and the central area is 8-18 mm.

[0014] The thickness described in this application is the thickness of the thickest part of the region.

[0015] Furthermore, the central area is a cylindrical structure, and the outer edge area and the transition area are annular structures.

[0016] Furthermore, the upper surface of the outer edge region is a step-shaped structure, and the thickness of the outermost step of the outer edge region is equal to that of the central region.

[0017] Preferably, the bottom diameter of the crucible assembly is 260-340 mm, the diameter of the central area is 20-140 mm, the inner diameter of the outer edge area is 120-240 mm, the inner diameter of the outermost step of the outer edge area is 220-320 mm, and the thickness of the outer edge area and the central area is 8-18 mm.

[0018] Furthermore, the thickness of the central area is equal to or approximately equal to the thickness of the outer edge area.

[0019] Preferably, the bottom diameter of the crucible assembly is 260-340 mm, the diameter of the central area is 20-140 mm, the inner diameter of the outer edge area is 120-300 mm, and the thickness of the outer edge area and the central area is 8-18 mm.

[0020] Furthermore, the crucible assembly is assembled on a crucible cover of the crucible, and the bottom diameter of the crucible assembly is not greater than the diameter of the crucible cover.

[0021] Furthermore, the bottom diameter of the crucible assembly is not less than the diameter of the prepared silicon carbide crystal.

[0022] Furthermore, the material of the crucible assembly includes carbon element material and carbon element-containing material.

[0023] Preferably, the carbon element material includes graphite material and carbon fiber material, and the carbon element-containing material includes tantalum-plated graphite material.

[0024] An application of the crucible assembly is to be mounted on a crucible for preparing silicon carbide crystals, wherein the size of the silicon carbide crystals ranges from 6 to 12 inches.

[0025] Preferably, the size of the silicon carbide crystal is 8 to 12 inches.

[0026] A crucible for preparing silicon carbide crystals comprises the crucible assembly.

[0027] The crucible assembly of the utility model has heat preservation and heat insulation properties. The heat preservation and heat insulation performance is better in the thicker area, so that the axial temperature gradient in this area becomes smaller and the crystal thickness is reduced. On the contrary, the heat preservation performance of the thinner area is slightly worse, and the inhibitory effect on the crystal thickness is relatively small. The crucible assembly with uneven thickness adjusts the temperature field shape on the crystal. In addition, the crucible assembly can also effectively adjust the temperature field and gas flow near the crucible wall.

[0028] The radial temperature gradient in the growth chamber without the crucible assembly is large, the gas flow is uneven, and the gas phase components mainly flow out of the raw material area near the crucible wall, resulting in a greater supersaturation around the crystal growth interface than the center of the interface, and the crystal surface grows into an "M" shape. By adding the crucible assembly, the radial temperature gradient in the entire growth chamber is smaller, the gas flow is more uniform, and the crystal morphology is smoother. In addition, the almost flat micro-convex surface reduces the step height of the non-facet area, thereby reducing impurity incorporation, resulting in an increase in carrier concentration and improved resistivity uniformity of the crystal.

[0029] Compared with the prior art, the beneficial effects of the technical solution of the utility model are:

[0030] The utility model innovatively provides a crucible assembly, which can effectively adjust the temperature field and gas flow near the crucible wall, and obtain a thermal field with a small radial temperature gradient by changing the assembly conditions. On the basis of this thermal field, the surface morphology of the crystal is improved, forming a nearly flat micro-convex crystal, reducing the step height of the non-facet area, thereby reducing impurity incorporation, resulting in an increase in carrier concentration, thereby improving the uniformity of resistivity. The crystal is cut, ground and polished to obtain a silicon carbide wafer, so that the resistivity non-uniformity is only 1.23%. The utility model provides a simple and feasible method for improving the resistivity uniformity of large-sized silicon carbide crystals grown by the PVT method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of crucible assembly A; a is a top view, b is a cross-sectional view; 1-central area, 2-transition area, 3-outer edge area;

[0032] Figure 2 Schematic diagram of crucible assembly B; a is a top view, b is a cross-sectional view; 1-central area, 2-transition area, 3-outer edge area;

[0033] Figure 3 Schematic diagram of crucible assembly C; a is a top view, b is a cross-sectional view; 1-central area, 2-transition area, 3-outer edge area;

[0034] Figure 4 Schematic diagram of preparing crystal in Example 1, a is the crucible assembly structure after adding crucible assembly A, b is the temperature field distribution of the growth unit, and c is the temperature field of the silicon carbide crystal; wherein 4-crucible assembly A, 6-seed crystal, 7-crucible, 8-SiC raw material, 9-growth furnace;

[0035] Figure 5 Schematic diagram of preparing a wafer in Example 1; a is an image of a polished wafer, and b is the resistivity of the polished wafer;

[0036] Figure 6Schematic diagram of preparing crystals in Example 7, a is the crucible assembly structure after adding the crucible assembly B, b is the temperature field distribution of the growth unit, and c is the temperature field of the silicon carbide crystal; wherein 5 is the crucible assembly B, 6 is the seed crystal, 7 is the crucible, 8 is the SiC raw material, and 9 is the growth furnace;

[0037] Figure 7 Schematic diagram of preparing a wafer in Example 7; a is an image of the polished wafer, and b is the resistivity of the polished wafer. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0039] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0040] The utility model discloses a crucible assembly for growing 8-inch and above silicon carbide single crystals, wherein:

[0041] The bottom surface of the crucible assembly is adapted to the shape and size of the crucible cover and is used to be placed on the top of the crucible cover; the crucible assembly is divided into a central area, a transition area and an outer edge area from the center to the outer edge; the thickness of the transition area is smaller than that of the central area and the outer edge area, and it presents a thick-thin-thick pattern from the central area to the outer edge area.

[0042] like Figure 1 As shown, the crucible assembly includes a central area 1, a transition area 2, and an outer edge area 3. The central area is a cylindrical structure, the outer edge area and the transition area are annular structures, the upper surface of the outer edge area is a step-shaped structure, and the thickness of the outermost step of the outer edge area is equal to that of the central area, which is a crucible assembly A.

[0043] like Figure 2 As shown, the crucible assembly includes a central area 1, a transition area 2, and an outer edge area 3. The thickness of the central area gradually decreases from the center to the edge, the thickness of the outer edge area gradually increases from the center to the edge of the crucible cover, the thickness of the transition area gradually increases from the center to the sides, and the edges of the transition area are smoothly connected to the central area and the outer edge area on both sides thereof, which is a crucible assembly B.

[0044] like Figure 3 As shown, the crucible assembly includes a central area 1, a transition area 2, and an outer edge area 3. The central area is a cylindrical structure, the outer edge area and the transition area are annular structures, and the thickness of the central area is equal or approximately equal to the thickness of the outer edge area, which is a crucible assembly C.

[0045] like Figure 4As shown in FIG. 1 , the assembly structure of the crucible includes a crucible assembly A 4, a seed crystal 6, a crucible 7, a SiC raw material 8, and a growth furnace 9. The bottom diameter of the crucible assembly is not greater than the diameter of the crucible cover, and the bottom diameter of the crucible assembly is not less than the diameter of the growing silicon carbide crystal.

[0046] like Figure 6 As shown in FIG. 1 , the assembly structure of the crucible includes a crucible assembly C5, a seed crystal 6, a crucible 7, a SiC raw material 8, and a growth furnace 9. The bottom diameter of the crucible assembly is not greater than the diameter of the crucible cover, and the bottom diameter of the crucible assembly is not less than the diameter of the growing silicon carbide crystal.

[0047] Example 1

[0048] This embodiment uses a crucible assembly A made of graphite, with a bottom diameter of 300 mm, a center diameter of 80 mm, a transition zone thickness of 4 mm, a transition zone step inner diameter of 180 mm, an outer edge inner diameter of 240 mm, and a thickness of 10 mm between the outer edge and the center.

[0049] A 4H-SiC seed crystal with an eccentricity of 4° was fixed on the top of the graphite crucible, SiC powder was placed as a raw material at the bottom of the crucible, and the crucible assembly was assembled on the crucible cover. The crucible was heated using an induction coil, the growth pressure was maintained at 1-5 mbar, and the carrier gas was argon. Temperature measurements were performed at the top cover using a color pyrometer. During the growth process, nitrogen was introduced as a donor dopant by flowing N2 gas. After 50 hours of short-term growth, the macroscopic surface morphology of the 4H-SiC crystal was observed using an optical microscope. After cutting, grinding and polishing, the 4H-SiC single crystal was made into an 8-inch silicon carbide substrate, and the resistivity test was performed. The resistivity of the wafer was tested using a non-contact resistivity measuring instrument.

[0050] Embodiments 2 to 9

[0051] The technical solutions of Examples 2 to 9 are similar to those of Example 1, except for the crucible assembly used and the diameter of the prepared crystals. The specific differences are shown in Table 1.

[0052] Table 1 Crucible components used in Examples 2 to 9 and diameters of crystals prepared

[0053]

[0054]

[0055] According to Example 1, Figure 4 As shown in a, the crucible assembly A is assembled on the crucible cover. Figure 4 b and Figure 4c shows that the temperature field distribution in the growth unit is more uniform, the temperature field distribution of the crystal is flatter, and the radial temperature gradient is smaller. The nitrogen doping concentration in the dark small surface area is higher, resulting in a decrease in resistivity, which in turn leads to poor resistivity uniformity across the wafer. Figure 5 As can be seen from a, the wafer only has dark surface areas at the edge, and the color is lighter, reflecting good resistivity uniformity. The resistivity test results show that the resistivity uniformity of the entire wafer is excellent, with the maximum resistivity recorded being 0.02308Ω·cm and the minimum resistivity being 0.02060Ω·cm, meeting the industry requirement of 0.015 to 0.025Ω·cm. The resistivity change rate is only 1.44% ( Figure 5 b).

[0056] According to Example 7, Figure 6 As shown in a, the crucible assembly C is assembled on the crucible cover. Figure 6 b and Figure 6 c shows that the temperature field distribution in the growth unit is relatively uniform, and the temperature field distribution of the crystal is relatively flat. Figure 7 As can be seen from a, a small dark surface area also appears on the edge of the wafer. The resistivity test results show that the maximum resistivity recorded is 0.02338Ω·cm, the minimum resistivity is 0.01944Ω·cm, and the resistivity change rate is only 2.25% ( Figure 7 b).

[0057] Table 2 Wafer resistivity test results of Examples 2 to 9

[0058]

[0059] Comparative Examples 1 to 4

[0060] The technical solutions of Comparative Examples 1 to 4 are similar to those of Example 1, except for the total height of the crucible assembly, as specifically shown in Table 3.

[0061] Table 3 Crucible components used in Comparative Examples 1 to 4

[0062] type Bottom diameter Material Crystal diameter Comparative Example 1 Crucible Assembly A 200mm graphite 8 inches Comparative Example 2 Crucible Assembly A 300mm graphite 12 inches Comparative Example 3 Crucible Assembly A 350mm graphite 6 inches Comparative Example 4 Crucible assembly B 300mm Tantalum 8 inches

[0063] According to the test results of the chip resistivity in Table 4, crucible components A, B and C can all play a role in homogenizing the temperature field, thereby improving the uniformity of resistivity. As can be seen from Table 4, when the crucible component used does not match the diameter of the crucible cover, or the bottom diameter of the crucible component is too large or too small for the inner diameter of the crucible, the effect of homogenizing the temperature field becomes worse, and the resistivity non-uniformity can reach 3.37%. This is because when the crucible component with thermal insulation properties does not match the crucible, it will lead to difficulty in temperature control and large temperature field changes, making it more complicated to maintain suitable growth conditions, thereby affecting the crystal growth process. In addition, it will also lead to a decrease in the crystal growth rate and affect production capacity. In addition, compared with materials containing carbon elements, tantalum materials have worse thermal insulation properties, resulting in poor control of the temperature field and worse resistivity uniformity of the prepared chips.

[0064] Table 4 Wafer resistivity test results of Comparative Examples 1 to 4

[0065]

[0066] Obviously, the above embodiments of the utility model are only examples for clearly explaining the utility model, and are not intended to limit the implementation methods of the utility model. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to list all the implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the utility model should be included in the protection scope of the claims of the utility model.

Claims

1. A crucible assembly, characterized in that: Used for the growth of 8-inch and above silicon carbide single crystals, including: The bottom surface of the crucible assembly is adapted to the shape and size of the crucible cover and is used to be placed on the top of the crucible cover; The crucible assembly is divided into a central area, a transition area and an outer edge area from the center to the outer edge; the thickness of the transition area is smaller than that of the central area and the outer edge area, and it presents a thick-thin-thick pattern from the central area to the outer edge area.

2. The crucible assembly according to claim 1, characterized in that: The thickness of the central zone gradually decreases from the center to the edge, the thickness of the outer edge zone gradually increases from the center to the edge of the crucible cover, the thickness of the transition zone gradually increases from the center to the two sides, and the edges of the transition zone are smoothly connected to the central zone and the outer edge zone on both sides thereof.

3. The crucible assembly according to claim 1, characterized in that: The central area is a cylindrical structure, and the outer edge area and the transition area are annular structures.

4. The crucible assembly according to claim 3, characterized in that: The upper surface of the outer edge area is a step-shaped structure, and the thickness of the outermost step of the outer edge area is equal to that of the central area.

5. The crucible assembly according to claim 3, characterized in that: The thickness of the central area is equal to or approximately equal to the thickness of the outer edge area.

6. The crucible assembly according to claim 1, characterized in that: The crucible assembly is assembled on the crucible cover of the crucible, and the bottom diameter of the crucible assembly is not greater than the diameter of the crucible cover.

7. The crucible assembly according to claim 6, characterized in that: The bottom diameter of the crucible assembly is not less than the diameter of the growing silicon carbide crystal.

8. A crucible for preparing silicon carbide crystals, characterized in that: Assemble the crucible assembly according to any one of claims 1 to 7.

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