Graphite tray, graphite tray preparation method and epitaxial growth equipment

Abstract

The embodiments of the present invention provide a graphite tray, a method for preparing a graphite tray, and an epitaxial growth device, which relate to the field of semiconductor technology. The graphite tray is circular and has a uniform thickness; wherein the surface roughness of the graphite tray gradually decreases from the center of the circle toward the edge; or, the surface roughness of the graphite tray gradually increases from the center of the circle toward the edge. The present application controls the heat transfer effect by controlling the surface roughness of the graphite tray, and further adjusts the temperature uniformity of the wafer substrate along the diameter direction during the epitaxial process, ultimately achieving the goal of improving the deposition temperature field distribution within the wafer substrate surface, improving the uniformity of the doping concentration of the formed wafer epitaxial wafer, and improving the warping problem of the wafer epitaxial wafer formed due to thermal stress.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, in particular to a graphite tray, a preparation method of the graphite tray and epitaxial growth equipment. Background Art

[0002] Epitaxial wafers have broad application prospects in the field of high-power devices. In practical applications, there are strict requirements for the thickness uniformity, doping concentration uniformity, and warpage of epitaxial wafers. Currently, the mainstream method for preparing epitaxial wafers is chemical vapor deposition (CVD).

[0003] Currently, the process of producing epitaxial wafers using chemical vapor deposition (CVD) involves placing a wafer substrate on a graphite tray and moving the wafer substrate and graphite tray into an epitaxial furnace. High-temperature reaction gases and high-temperature hydrogen, acting as an ambient gas, are introduced into the epitaxial furnace. Simultaneously, heating elements positioned above and below the graphite tray radiate heat to the front and back surfaces of the wafer substrate. This causes the gaseous molecules in the silicon-containing reaction gas to migrate to the surface of the wafer substrate. Under the influence of the high temperature, the gaseous molecules react with the hydrogen, and the reaction products are deposited on the surface of the wafer substrate, forming the epitaxial wafer.

[0004] However, when epitaxial growth is performed in a horizontal epitaxial furnace, the high-temperature reaction gases flow from one side of the furnace to the other. Consequently, due to the depletion pattern of the reaction gases along the wafer substrate surface (consumption caused by the gas-phase molecules in the reaction gases reacting with hydrogen during their migration to the substrate) and the low thermal conductivity of graphite (129 W / (m·K)), the high-temperature gas temperature gradually decreases, resulting in a temperature unevenness problem where the temperature of the wafer substrate surface gradually decreases along the direction of gas flow.

[0005] When a vertical epitaxial furnace is used for epitaxial growth, when a vertical cold wall is used for heating, the temperature at the center of the wafer substrate is higher than the temperature at the edge because the heating source is located below the graphite tray; when a vertical hot wall is used for heating, there is a risk that the temperature at the center of the wafer substrate is lower than the temperature at the edge because the heating source is located below and at the edge of the graphite tray.

[0006] To address this issue of uneven temperature, the graphite tray is rotated around its center during heating. This rotation improves the temperature at the same radius, but it still doesn't address the temperature differences across different diameters caused by the depletion mode.

[0007] That is, the wafer substrate on the graphite tray still has a temperature unevenness problem in which the temperature gradually decreases from the center position to the edge position in the radial direction. Summary of the Invention

[0008] The purpose of the present invention is to provide a graphite tray, a method for preparing a graphite tray, and an epitaxial growth device to improve the problem of uneven temperature of a wafer substrate radially from the center to the edge of the graphite tray. The specific technical solution is as follows:

[0009] The present application provides a graphite tray, which is circular and has a uniform thickness;

[0010] The roughness of the upper surface of the graphite tray gradually decreases from the center toward the edge;

[0011] Alternatively, the surface roughness of the graphite tray gradually increases from the center toward the edge.

[0012] In some embodiments of the present application, the graphite tray includes at least two graphite rings, and the at least two graphite rings are concentrically nested one by one around the center of the graphite tray;

[0013] An expansion gap is provided between two adjacent graphite rings.

[0014] In some embodiments of the present application, the upper surface roughness of the same graphite ring gradually decreases as it moves away from the center toward the edge; of two adjacent graphite rings, the minimum value of the upper surface roughness of the graphite ring closer to the center is greater than the maximum value of the upper surface roughness of the other graphite ring farther from the center; or,

[0015] The upper surface roughness of the same graphite ring is the same; among two adjacent graphite rings, the upper surface roughness of the graphite ring closer to the center is greater than the upper surface roughness of the other graphite ring farther from the center.

[0016] In some embodiments of the present application, the root mean square average value of the profile ordinate of the upper surface roughness of the innermost graphite ring is 1 μm-500 μm;

[0017] The root mean square average value (Rq, 100nm (nanometer)-500nm;

[0018] The root mean square average value of the profile ordinate of the upper surface roughness of the graphite ring located between the innermost graphite ring and the outermost graphite ring is 0.1 μm-100 μm.

[0019] In some embodiments of the present application, the upper surface roughness of the same graphite ring gradually increases from the center of the circle to the edge; of two adjacent graphite rings, the maximum value of the upper surface roughness of the graphite ring closer to the center of the circle is smaller than the minimum value of the upper surface roughness of the other graphite ring farther from the center of the circle; or,

[0020] The upper surface roughness of the same graphite ring is the same; among two adjacent graphite rings, the upper surface roughness of the graphite ring closer to the center is smaller than the upper surface roughness of the other graphite ring farther from the center.

[0021] In some embodiments of the present application, the root mean square average value of the profile ordinate of the upper surface roughness of the outermost graphite ring is 1 μm-500 μm;

[0022] The root mean square average value of the profile ordinate of the upper surface roughness of the innermost graphite ring is 100 nm to 500 nm;

[0023] The root mean square average value of the profile ordinate of the upper surface roughness of the graphite ring located between the innermost graphite ring and the outermost graphite ring is 0.1 μm-100 μm.

[0024] In some embodiments of the present application, the graphite tray also includes a limiting graphite ring, which is sleeved on the outer circumference of the outermost graphite ring; the top part of the limiting graphite ring extends toward the center of the circle, and the inner side wall of the extension is used to fix the wafer substrate.

[0025] In some embodiments of the present application, the difference between the inner diameter and the outer diameter of the graphite ring located on the inner side is equal to the difference between the inner diameter and the outer diameter of the graphite ring located on the outer side;

[0026] Or, the difference between the inner diameter and the outer diameter of the graphite ring located on the inner side is smaller than the difference between the inner diameter and the outer diameter of the graphite ring located on the outer side;

[0027] Alternatively, the difference between the inner diameter and the outer diameter of the graphite ring located on the inner side is greater than the difference between the inner diameter and the outer diameter of the graphite ring located on the outer side.

[0028] In some embodiments of the present application, the center of the graphite tray is a graphite disc;

[0029] Alternatively, the center of the graphite tray is the hollow area.

[0030] In some embodiments of the present application, the difference between the inner diameter and the outer diameter of the graphite ring ranges from 1 inch to 2 inches;

[0031] The outer diameter of the outermost graphite ring ranges from 4 inches to 12 inches;

[0032] The outer diameter of the limiting graphite ring ranges from 13 inches to 14 inches;

[0033] The number of the graphite rings is 2 to 10.

[0034] In some embodiments of the present application, the width of the expansion gap between two adjacent graphite rings ranges from 10 μm (micrometers) to 100 μm.

[0035] In some embodiments of the present application, the roughness of the lower surface of the graphite tray is uniformly set;

[0036] Alternatively, the roughness of the lower surface of the graphite tray is equal to the roughness of a corresponding position on the upper surface.

[0037] The present application also provides a method for preparing a graphite tray, which specifically comprises the following steps: providing a circular graphite substrate;

[0038] Performing a surface roughness treatment on the graphite substrate so that the surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge; or the surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge;

[0039] The lower surface of the graphite substrate is roughly ground or polished to keep the thickness of the graphite substrate uniform, thereby forming a graphite tray.

[0040] In some embodiments of the present application, before performing the upper surface roughness treatment on the graphite substrate so that the upper surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge; or the upper surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge, the method further includes:

[0041] The graphite substrate is cut to form at least two graphite rings, so that an expansion gap exists between two adjacent graphite rings.

[0042] In some embodiments of the present application, the roughening treatment of the upper surface of the graphite substrate so that the roughness of the upper surface of the graphite substrate gradually decreases from the center of the circle toward the edge includes:

[0043] The upper surface of each graphite ring is subjected to roughening treatment so that the roughness of the upper surface of each graphite ring gradually decreases from the center of the circle to the edge; and, among two adjacent graphite rings, the minimum value of the upper surface roughness of the graphite ring closer to the center of the circle is greater than the maximum value of the upper surface roughness of the other graphite ring farther from the center of the circle; or,

[0044] The upper surface of each graphite ring is roughened so that the upper surface roughness of each graphite ring is the same; and, among two adjacent graphite rings, the upper surface roughness of the graphite ring closer to the center is greater than the upper surface roughness of the other graphite ring farther from the center.

[0045] In some embodiments of the present application, the roughening treatment of the upper surface of the graphite substrate so that the roughness of the upper surface of the graphite substrate gradually increases from the center of the circle toward the edge includes:

[0046] The upper surface of each graphite ring is subjected to roughening treatment so that the roughness of the upper surface of each graphite ring gradually increases from the center of the circle to the edge; and, among two adjacent graphite rings, the maximum value of the upper surface roughness of the graphite ring closer to the center of the circle is smaller than the minimum value of the upper surface roughness of the other graphite ring farther from the center of the circle; or,

[0047] The upper surface of each graphite ring is roughened so that the upper surface roughness of each graphite ring is the same; and, among two adjacent graphite rings, the upper surface roughness of the graphite ring closer to the center is smaller than the upper surface roughness of the other graphite ring farther from the center.

[0048] In some embodiments of the present application, the step of roughly grinding or polishing the lower surface of the graphite substrate to maintain a uniform thickness of the graphite substrate includes:

[0049] Roughly grinding or polishing the lower surface of the graphite substrate so that the lower surface roughness of the graphite tray is uniform and the thickness remains uniform; or,

[0050] The lower surface of the graphite substrate is roughly ground or polished, and the roughness of the lower surface of the graphite tray is equal to the roughness at the corresponding position of the upper surface and the thickness is kept uniform.

[0051] In some embodiments of the present application, after the lower surface of the graphite substrate is roughly ground or polished, the method further comprises:

[0052] Cleaning the graphite substrate to remove metal residues on the surface;

[0053] A limiting graphite ring is sleeved on the outer periphery of the graphite substrate; the top portion of the limiting graphite ring extends toward the center of the circle, and the inner side wall of the extension portion is used to fix the wafer.

[0054] The present application also provides an epitaxial growth device, which includes: a quartz cylinder;

[0055] Heating devices are provided above and below the quartz cylinder;

[0056] The quartz cylinder is provided with a reaction space inside which reaction gas and ambient gas can be introduced;

[0057] A rotatable graphite tray placement platform is provided in the reaction space;

[0058] The graphite tray placement platform is provided with the graphite tray described in any one of the above embodiments.

[0059] Beneficial effects of the embodiments of the present invention:

[0060] Embodiments of the present invention provide a graphite tray, a method for preparing a graphite tray, and an epitaxial growth device. The roughness of the upper surface of the graphite tray gradually decreases from the center of the circle toward the edge, or the roughness of the upper surface of the graphite tray gradually increases from the center of the circle toward the edge, and the thickness of the graphite tray is uniformly set.

[0061] It is understandable that there are tiny asperities on the surface of the graphite tray and the surface of the wafer substrate. When the wafer substrate is placed on the graphite tray, the contact between the two surfaces is incomplete. Even under great pressure, the actual contact area of ​​the two contact surfaces only accounts for a small part of the nominal contact area (the area that appears to be in contact macroscopically), and the uncontacted part is in a gas-occupied state.

[0062] During epitaxial growth, the typical ambient gas content is 99% hydrogen. At this point, the hydrogen content is higher between the wafer substrate and the graphite tray's surface roughness, while it is lower between the wafer substrate and the graphite tray's surface roughness. Since hydrogen's thermal conductivity is much lower than that of graphite, the heat transfer efficiency between the graphite tray and the wafer substrate at the roughest locations is lower than at the less rough locations, thus achieving temperature balance between the center and edge of the wafer substrate.

[0063] Of course, it is not necessary to achieve all of the advantages described above simultaneously in order to implement any product or method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0065] Figure 1 A schematic structural diagram of a graphite tray provided in the first embodiment of the present application;

[0066] Figure 2 for Figure 1 A cross-sectional view of the graphite tray is shown;

[0067] Figure 3 A schematic structural diagram of a graphite tray provided in the second embodiment of the present application;

[0068] Figure 4 for Figure 3 A cross-sectional view of the graphite tray is shown;

[0069] Figure 5 This is a schematic diagram of a graphite tray provided in the present application where the roughness at the center is greater than the roughness at the edge;

[0070] Figure 6 A schematic structural diagram of a limiting graphite ring of a graphite tray is provided for this application;

[0071] Figure 7 for Figure 6 A cross-sectional view of the limiting graphite ring shown;

[0072] Figure 8 A schematic structural diagram of a graphite tray provided in the third embodiment of the present application;

[0073] Figure 9 for Figure 8 A cross-sectional view of the graphite tray is shown;

[0074] Figure 10 Flowchart for preparing the graphite tray of the first embodiment of this application;

[0075] Figure 11 Flowchart for preparing the graphite tray of the second embodiment of this application;

[0076] Figure 12 The cross-sectional view of the epitaxial growth equipment provided in this application is a horizontal epitaxial furnace.

[0077] Reference numerals:

[0078] Graphite tray 1, reaction space 100, graphite ring 11, expansion gap 111, hollow area 112, limiting graphite ring 12, graphite disc 13;

[0079] Quartz cylinder 2, heating element 21, upper half-moon graphite piece 22, lower half-moon graphite piece 23, upper graphite cover plate 24, lower graphite cover plate 25, tray groove 251, graphite tray placement platform 26, rotating mechanism 261, sample injection door 27, tail exhaust door 28, air flow channel 29, upstream graphite piece 30, downstream graphite piece 31;

[0080] Wafer substrate 4. DETAILED DESCRIPTION

[0081] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of the present invention.

[0082] The first embodiment of the present application provides a graphite tray 1, such as Figure 1 and Figure 2 As shown, Figure 1 A schematic structural diagram of a graphite tray provided in the first embodiment of the present application; Figure 2 for Figure 1 The graphite tray 1 is a cross-sectional view of a graphite tray. The graphite tray 1 is circular and has a uniform thickness. The surface roughness of the graphite tray 1 decreases gradually from the center of the circle toward the edge. Alternatively, the surface roughness of the graphite tray 1 increases gradually from the center of the circle toward the edge.

[0083] In this embodiment, the upper surface of the graphite tray 1 is roughened so that the roughness of the upper surface of the graphite tray 1 gradually decreases from the center of the circle toward the edge, or the roughness of the upper surface of the graphite tray 1 gradually increases from the center of the circle toward the edge, and the thickness of the graphite tray 1 is uniformly set.

[0084] Specifically, when the graphite tray 1 is placed in a horizontal epitaxial growth furnace, the high-temperature gas gradually cools due to the depletion pattern of the reactant gas along the wafer substrate surface, causing the temperature at the center of the wafer substrate 4 to be higher than that at the edge. In this case, a graphite tray 1 with a top surface roughness that gradually decreases from the center toward the edge can be used to improve the situation where the center temperature of the wafer substrate 4 is higher than the edge temperature.

[0085] When graphite tray 1 is placed in a vertical epitaxial furnace and heated by a vertical cold wall, the heat source is located below the tray, causing the temperature at the center of wafer substrate 4 to be higher than at the edge. In this case, a graphite tray 1 with a top surface roughness that gradually decreases from the center toward the edge can be used to improve the problem of the wafer substrate 4 having a higher temperature at the center than at the edge.

[0086] When using a vertical hot wall for heating, because the heat source is located below and at the edge of the graphite tray 1, there is a risk that the temperature at the center of the wafer substrate 4 will be lower than that at the edge. In this case, a graphite tray 1 with a top surface roughness that gradually increases from the center toward the edge can be used to improve the problem of the center temperature of the wafer substrate 4 being lower than that at the edge.

[0087] It can be understood that there are tiny asperities on the surface of the graphite tray 1 and the surface of the wafer substrate 4. When the wafer substrate 4 is placed on the graphite tray 1, the contact between the two surfaces is incomplete. Even under great pressure, the actual contact area of ​​the two contact surfaces only accounts for a small part of the nominal contact area (the area that appears to be in contact macroscopically), and the uncontacted part is in a gas-occupied state.

[0088] During the epitaxial growth process, the hydrogen content of the ambient gas is typically 99%. At this point, the hydrogen content is higher between the graphite tray 1's surface roughness and the wafer substrate 4, while the hydrogen content is lower between the graphite tray 1's surface roughness and the wafer substrate 4. Since hydrogen's thermal conductivity is much lower than that of graphite, the heat transfer efficiency between the graphite tray 1 and the wafer substrate 4 at the roughest locations is lower than at the less rough locations, thus achieving temperature balance between the center and edge of the wafer substrate 4.

[0089] Specifically, because the theoretical thermal conductivity of hydrogen is 0.1805 W / mK (watts per meter Kelvin), far lower than graphite's thermal conductivity of 129 W / mK, the heat transfer efficiency between graphite tray 1 and wafer substrate 4 is lower at locations with higher hydrogen content than at locations with lower hydrogen content. Specifically, when using a graphite tray 1 with a surface roughness that gradually decreases from the center to the edge, the heat transfer efficiency near the center of the tray is lower than that near the edge. When using a graphite tray 1 with a surface roughness that gradually increases from the center to the edge, the heat transfer efficiency near the center of the tray is higher than that near the edge. The uniform thickness of graphite tray 1 prevents the introduction of excess hydrogen due to the height difference between the tray and wafer substrate 4, ensuring the overall heat transfer efficiency of the tray. Therefore, during the heat transfer process, temperature balance is achieved between the center position and the edge position of the graphite tray 1 .

[0090] This embodiment controls the heat transfer effect by controlling the surface roughness of the graphite tray 1. Furthermore, during the epitaxial growth process, the temperature uniformity of the wafer substrate 4 along the diameter direction is adjusted, thereby ultimately improving the deposition temperature field distribution within the surface of the wafer substrate 4.

[0091] In the prior art, the uneven temperature field of the wafer substrate 4 results in an uneven doping concentration distribution in the resulting epitaxial wafer. This embodiment adjusts the surface roughness of the graphite tray 1 to make the temperature field of the wafer substrate 4 uniform, thereby improving the uniformity of the doping concentration of the resulting epitaxial wafer. This also reduces the warpage of the resulting epitaxial wafer due to thermal stress and lowers the BOW (bow-of-warp) value of the resulting epitaxial wafer. BOW is typically used to describe the degree of curvature of the epitaxial wafer due to stress or other factors during processing. It also reduces paired BPDs (basal plane dislocations) caused by thermal stress.

[0092] like Figure 1 and Figure 2 As shown, the graphite tray 1 in this embodiment also includes a limiting graphite ring 12, which is sleeved on the outer circumference of the graphite tray 1; the top part of the limiting graphite ring 12 extends toward the center of the circle, and the inner side wall of the extension part is used to fix the wafer substrate 4.

[0093] When the wafer substrate 4 is placed on the graphite tray 1 , the inner sidewall of the portion of the extending portion of the limiting graphite tray that is higher than the graphite tray 1 is attached to the sidewall of the wafer substrate 4 , thereby fixing the wafer substrate 4 .

[0094] The second embodiment of the present application provides a graphite tray, such as Figure 3 and Figure 4 As shown, Figure 3 A schematic structural diagram of a graphite tray provided in the second embodiment of the present application; Figure 4 for Figure 3 The graphite tray 1 comprises at least two graphite rings 11 , which are concentrically nested around the center of the graphite tray 1 ; an expansion gap 111 is provided between two adjacent graphite rings 11 .

[0095] In this embodiment, the graphite tray 1 is cut into at least two graphite rings 11. Figure 3 , each graphite ring 11 is concentrically nested around the center of the graphite tray 1, forming a complete graphite tray 1 structure. Furthermore, the thickness H of each graphite ring 11 is equal. After the graphite tray 1 is cut to form the graphite rings 11, an expansion gap 111 is formed between two adjacent graphite rings 11. This allows the deformed portion of the graphite ring 11 to be released through the expansion gap 111 during the process of deformation caused by heat. This prevents damage to the graphite tray 1 caused by deformation of the graphite ring 11 due to high temperature, which could lead to breakage or deformation of the graphite tray 1 and the resulting uneven heat transfer on the back.

[0096] Furthermore, the thickness H of each graphite ring 11 is the same, so that there is no height difference between each graphite ring 11 , thereby preventing excessive hydrogen from entering between the wafer substrate 4 and the graphite tray 1 and affecting the heat transfer effect.

[0097] Also, see Figure 5 , Figure 5 This is a schematic diagram of a graphite tray provided in this application where the roughness at the center is greater than the roughness at the edge. Figure 5 The figure shows the distribution of the upper surface roughness of the same graphite ring 11 when the upper surface roughness of the same graphite ring 11 is the same. When the heating environment causes the temperature at the center of the graphite tray 1 to be higher than the temperature at the edge, the upper surface roughness of the same graphite ring 11 gradually decreases as it moves away from the center toward the edge. Of two adjacent graphite rings 11, the minimum upper surface roughness of the graphite ring 11 closer to the center is greater than the maximum upper surface roughness of the other graphite ring 11 farther from the center. Alternatively, the upper surface roughness of the same graphite ring 11 is the same, but of two adjacent graphite rings 11, the upper surface roughness of the graphite ring 11 closer to the center is greater than the upper surface roughness of the other graphite ring 11 farther from the center.

[0098] In this embodiment, the top surface roughness of the same graphite ring 11 is the same. Of two adjacent graphite rings 11, the minimum top surface roughness of the graphite ring 11 closer to the center is greater than the maximum top surface roughness of the graphite ring 11 farther from the center. Consequently, corresponding locations of each graphite ring 11 within the entire graphite tray 1 have the same heat transfer efficiency, resulting in more uniform heat transfer efficiency for the wafer substrate 4 across the corresponding regions of each graphite ring 11 within the graphite tray 1.

[0099] In some embodiments, the upper surface roughness of a single graphite ring 11 can gradually decrease as it moves away from the center toward the edge. Furthermore, of two adjacent graphite rings 11, the minimum upper surface roughness of the graphite ring 11 closer to the center is greater than the maximum upper surface roughness of the other graphite ring 11 farther from the center. Furthermore, the thickness H of each graphite ring 11 is equal. This allows the upper surface roughness of the graphite tray 1 composed of graphite rings 11 to gradually decrease as it moves away from the center toward the edge. Consequently, the hydrogen content between the graphite ring 11 near the center and the wafer substrate 4 is greater than the hydrogen content between the graphite ring 11 near the edge and the wafer substrate 4.

[0100] As previously mentioned, the thermal conductivity of hydrogen is much lower than that of graphite. During the heating process, the graphite ring 11 near the center of the circle heats the wafer substrate 4 more slowly due to the higher hydrogen content between the ring and wafer substrate 4. Conversely, the graphite ring 11 near the edge of the circle heats the wafer substrate 4 more quickly due to the lower hydrogen content. This achieves temperature balance between the center and the edge of the circle.

[0101] At the same time, the heat transfer efficiency of the graphite tray 1 as a whole gradually increases from the center to the edge, so that the heat transfer efficiency of the wafer substrate 4 on the graphite tray 1 changes more continuously.

[0102] The present application realizes the control of the heat transfer effect by controlling the surface roughness of the graphite tray 1, and further adjusts the temperature uniformity of the wafer substrate 4 in the radial direction from the center position to the edge position during the epitaxial process, thereby improving the deposition temperature field distribution within the surface of the wafer substrate 4, improving the uniformity of the doping concentration of the formed wafer epitaxial wafer, improving the warping of the wafer epitaxial wafer caused by thermal stress, reducing the BOW value of the formed wafer epitaxial wafer and reducing the paired BPD caused by thermal stress.

[0103] In some embodiments of the present application, when a graphite tray 1 is used in which the upper surface roughness gradually decreases from the center toward the edge, and the diameter of the graphite tray 1 is 6 inches to 8 inches, the root mean square average value (Rq, ) is 1 μm-500 μm; the root mean square average value of the vertical coordinate of the profile of the upper surface roughness of the outermost graphite ring 11 is 100 nm (nanometer)-500 nm; the root mean square average value of the vertical coordinate of the profile of the upper surface roughness of the graphite ring 11 located between the innermost graphite ring 11 and the outermost graphite ring 11 is 0.1 μm-100 μm.

[0104] In this embodiment, the graphite ring 11 with the largest diameter is finely polished on one side, so that the root mean square average value of the vertical coordinate of the profile of its upper surface roughness is on the order of nm; the graphite ring 11 with the smallest diameter is coarsely ground on one side, so that the root mean square average value of the vertical coordinate of the profile of its upper surface roughness is on the order of μm; for the graphite rings 11 with diameters between the maximum and minimum values, the upper surface roughness is adjusted by adjusting the coarseness of the abrasive for fine grinding and rough polishing, and the typical value of the upper surface roughness is 0.1μm-100μm. Ultimately, the upper surface roughness of the graphite tray 1 formed by the concentric nesting of the graphite rings 11 is such that it gradually decreases from the center position toward the edge position, so that the heat transfer efficiency of the graphite rings 11 to the wafer substrate 4 gradually increases from the center position toward the edge position, achieving a uniform temperature field effect on the wafer substrate 4.

[0105] In some embodiments of the present application, when the heating environment causes the temperature at the edge of the graphite tray 1 to be higher than the temperature at the center, the upper surface roughness of the same graphite ring 11 gradually increases from the center to the edge; of two adjacent graphite rings 11, the maximum value of the upper surface roughness of the graphite ring 11 close to the center is less than the minimum value of the upper surface roughness of the other graphite ring 11 away from the center; or, the upper surface roughness of the same graphite ring 11 is the same; of two adjacent graphite rings 11, the upper surface roughness of the graphite ring 11 close to the center is less than the upper surface roughness of the other graphite ring 11 away from the center.

[0106] In this embodiment, the upper surface roughness of the same graphite ring 11 is the same. Of two adjacent graphite rings 11, the maximum upper surface roughness of the graphite ring 11 closer to the center is less than the minimum upper surface roughness of the other graphite ring 11 farther from the center. Consequently, corresponding locations of each graphite ring 11 within the entire graphite tray 1 have the same heat transfer efficiency, resulting in more uniform heat transfer efficiency for the wafer substrate 4 across the corresponding regions of each graphite ring 11 within the graphite tray 1.

[0107] In some embodiments, the upper surface roughness of a single graphite ring 11 can gradually increase from the center toward the edge, and, of two adjacent graphite rings 11, the maximum upper surface roughness of the graphite ring 11 closer to the center is less than the minimum upper surface roughness of the other graphite ring 11 farther from the center. Furthermore, the thickness H of each graphite ring 11 is equal. This allows the upper surface roughness of the graphite tray 1 composed of graphite rings 11 to gradually increase from the center toward the edge. Consequently, the hydrogen content between the graphite ring 11 near the center and the wafer substrate 4 is less than the hydrogen content between the graphite ring 11 near the edge.

[0108] As previously mentioned, the thermal conductivity of hydrogen is much lower than that of graphite. During the heating process, the graphite ring 11 near the center of the circle heats the wafer substrate 4 faster due to the lower hydrogen content between the ring and wafer substrate 4. Conversely, the graphite ring 11 near the edge of the circle heats the wafer substrate 4 more slowly due to the higher hydrogen content between the ring and wafer substrate 4. This achieves temperature balance between the center and edge of the circle.

[0109] At the same time, the heat transfer efficiency of the graphite tray 1 as a whole gradually decreases from the center toward the edge, so that the heat transfer efficiency of the wafer substrate 4 on the graphite tray 1 changes more continuously.

[0110] The present application realizes the control of the heat transfer effect by controlling the surface roughness of the graphite tray 1, and further adjusts the temperature uniformity of the wafer substrate 4 in the radial direction from the center position to the edge position during the epitaxial process, thereby improving the deposition temperature field distribution within the surface of the wafer substrate 4, improving the uniformity of the doping concentration of the formed wafer epitaxial wafer, improving the warping of the wafer epitaxial wafer caused by thermal stress, reducing the BOW value of the formed wafer epitaxial wafer and reducing the paired BPD caused by thermal stress.

[0111] In some embodiments of the present application, when a graphite tray 1 is used whose upper surface roughness gradually increases from the center to the edge, and the diameter of the graphite tray 1 is 6 inches to 8 inches, the root mean square average value of the vertical coordinate of the profile of the upper surface roughness of the outermost graphite ring 11 is 1 μm-500 μm; the root mean square average value of the vertical coordinate of the profile of the upper surface roughness of the innermost graphite ring 11 is 100 nm-500 nm; and the root mean square average value of the vertical coordinate of the profile of the upper surface roughness of the graphite ring 11 between the innermost graphite ring 11 and the outermost graphite ring 11 is 0.1 μm-100 μm.

[0112] In this embodiment, the graphite ring 11 with the smallest diameter is finely polished on one side, so that the root mean square average value of the vertical coordinate of the profile of its upper surface roughness is on the order of nm. The graphite ring 11 with the largest diameter is coarsely ground on one side, so that the root mean square average value of the vertical coordinate of the profile of its upper surface roughness is on the order of μm. For graphite rings 11 with diameters between the maximum and minimum values, the upper surface roughness is adjusted by adjusting the coarseness of the abrasive for fine grinding and rough polishing, and the typical value of the upper surface roughness is 0.1μm-100μm. Ultimately, the upper surface roughness of the graphite tray 1 formed by the concentric nesting of the graphite rings 11 is such that it gradually increases from the center position toward the edge position, so that the heat transfer efficiency of the graphite rings 11 to the wafer substrate 4 gradually decreases from the center position toward the edge position, achieving a uniform temperature field effect on the wafer substrate 4.

[0113] The following description will be made by taking as an example a solution in which the minimum value of the upper surface roughness of the graphite ring 11 close to the center of the circle is greater than the maximum value of the upper surface roughness of another graphite ring 11 far from the center of the circle.

[0114] like Figure 3 and Figure 4 As shown, the graphite tray 1 in this embodiment also includes a limiting graphite ring 12, which is nested on the outer periphery of the outermost graphite ring 11; the top part of the limiting graphite ring 12 extends toward the center of the circle, and the inner side wall of the extension part is used to fix the wafer substrate 4.

[0115] In this embodiment, a limiting graphite ring 12 is provided on the outer periphery of the outermost graphite ring 11, and the top portion of the limiting graphite ring 12 extends toward the center of the circle. Figure 6 and Figure 7 As shown, Figure 6 A schematic diagram of the structure of the limiting graphite ring provided in this application; Figure 7 for Figure 6 A cross-sectional view of the graphite ring is shown. The graphite ring 12 has a groove structure that secures it to the outer circumference of the graphite ring 11. When the wafer substrate 4 is placed on the graphite tray 1, the inner sidewall of the extended portion of the graphite tray, which extends above the portion of the graphite ring 11, abuts against the sidewall of the wafer substrate 4, securing the wafer substrate 4.

[0116] In addition, in the actual production process, the limiting graphite ring 12 can also be set as follows Figure 5 In the structure shown, the limiting graphite ring 12 is entirely sleeved on the outermost graphite ring 11. The thickness of the limiting graphite ring 12 is greater than the thickness H of the graphite ring 11. Moreover, the lower surfaces of the limiting graphite ring 12 and the graphite ring 11 are both located in the same plane, ensuring that the upper surface of the limiting graphite ring 12 is higher than the upper surface of the graphite ring 11. During the epitaxial growth process, the inner sidewall of the portion of the limiting graphite ring 12 that is higher than the graphite ring 11 is in close contact with the sidewall of the wafer substrate 4, thereby fixing the wafer substrate 4.

[0117] In some embodiments of the present application, the difference between the inner diameter and the outer diameter of the graphite ring 11 located on the inside is equal to the difference between the inner diameter and the outer diameter of the graphite ring 11 located on the outside; or, the difference between the inner diameter and the outer diameter of the graphite ring 11 located on the inside is smaller than the difference between the inner diameter and the outer diameter of the graphite ring 11 located on the outside; or, the difference between the inner diameter and the outer diameter of the graphite ring 11 located on the inside is greater than the difference between the inner diameter and the outer diameter of the graphite ring 11 located on the outside.

[0118] In this embodiment, the difference between the inner and outer diameters of each graphite ring 11 is adjusted to meet the thermal conductivity requirements of the wafer substrate 4 under different ambient temperatures. The following example illustrates the case where the temperature at the center of the wafer substrate 4 is higher than that at the edge. In some embodiments, the difference between the inner and outer diameters of each graphite ring 11 remains consistent. In this case, the overall surface roughness change rate of the graphite tray 1 is uniform, and the thermal conductivity change rate at each location on the wafer substrate 4 is uniform.

[0119] In some embodiments, the difference between the inner and outer diameters of the inner graphite ring 11 is smaller than that of the outer graphite ring 11. In this case, the rate of change in the upper surface roughness at the center of the graphite tray 1 is greater than that at the edges, causing the heat transfer efficiency at the center to decrease rapidly, effectively resolving the issue of higher temperatures at the center than at the edges.

[0120] In some embodiments, the difference between the inner and outer diameters of the inner graphite ring 11 is greater than that of the outer graphite ring 11. In this case, the rate of change in the upper surface roughness at the edges of the graphite tray 1 is greater than that at the center, causing the heat transfer efficiency at the edges to decrease rapidly, effectively balancing the temperature uniformity at the edges.

[0121] In actual production, the difference between the inner and outer diameters of the graphite ring 11 can be set to other ranges as needed, for example: Figure 5 As shown in the figure, the difference between the inner and outer diameters of the graphite ring 11 in the range of φ1 to φ3 is equal, and the difference between the inner and outer diameters of the graphite ring 11 in the range of φ3 to φ5 is equal, and the difference between the inner and outer diameters of the graphite ring 11 in the range of φ1 to φ3 is smaller than the difference between the inner and outer diameters of the graphite ring 11 in the range of φ3 to φ5. At this time, the change rate of the upper surface roughness of the graphite tray 1 as a whole in the range of φ1 to φ3 is greater than the change rate of the upper surface roughness in the range of φ3 to φ5, so that the heat transfer efficiency at the center position is rapidly reduced, effectively improving the problem that the temperature at the center position is higher than that at the edge position.

[0122] Or, the difference between the inner and outer diameters of the graphite ring 11 in the range of φ1 to φ3 in the figure is equal, the difference between the inner and outer diameters of the graphite ring 11 in the range of φ3 to φ5 is equal, and the difference between the inner and outer diameters of the graphite ring 11 in the range of φ1 to φ3 is greater than the difference between the inner and outer diameters of the graphite ring 11 in the range of φ3 to φ5. At this time, the change rate of the upper surface roughness at the edge position of the entire graphite tray 1 is greater than the change rate of the upper surface roughness at the center position, so that the heat transfer efficiency at the edge position is rapidly reduced, effectively balancing the temperature field uniformity at the edge position.

[0123] like Figure 3 、 Figure 4 and Figure 5As shown, in the graphite tray 1 provided in the second embodiment of the present application, the center position of the graphite tray 1 is a graphite disc 13 .

[0124] See also Figure 3 and Figure 4 A graphite disc 13 is provided at the center of the graphite tray 1. An expansion gap 111 is provided between the graphite disc 13 and the adjacent graphite ring 11. This prevents the graphite tray 1 from being damaged or deformed due to the thermal expansion of the graphite ring 11 and the graphite disc 13 during heating, and prevents the uneven heat transfer problem on the back thereof.

[0125] In the third embodiment of the present application, Figure 8 and Figure 9 As shown, Figure 8 A schematic structural diagram of a graphite tray provided in the third embodiment of the present application; Figure 9 for Figure 8 In this embodiment, the center of the graphite tray 1 is a hollow area 112 .

[0126] See also Figure 8 and Figure 9 At this time, the center of the graphite tray 1 is a hollow area 112. On the one hand, this hollow area 112 provides space for the innermost graphite ring to release deformation caused by heat, preventing damage or deformation of the graphite tray 1 caused by the thermal expansion of the innermost graphite ring 11 and the resulting uneven heat transfer problem on the back. On the other hand, the center of the graphite tray 1 is completely in contact with hydrogen, which greatly reduces the heat conduction capacity of the center of the wafer substrate 4, thereby balancing the temperature field uniformity of the wafer substrate 4 at different diameters.

[0127] In some embodiments of the present application, the difference between the inner diameter and the outer diameter of the graphite ring 11 ranges from 1 inch to 2 inches; the outer diameter of the outermost graphite ring 11 ranges from 4 inches to 12 inches; the outer diameter of the limiting graphite ring 12 ranges from 13 inches to 14 inches; and the number of graphite rings 11 ranges from 2 to 10. Figure 3 、 Figure 4 、 Figure 8 and Figure 9 As shown, in the second embodiment and the third embodiment of the present application, the number of graphite rings 11 is 7.

[0128] In this embodiment, the number of graphite rings 11 is a subdivided integer value greater than 2, that is, the minimum number of graphite rings 11 cut from the graphite tray 1 is 2. When the outer diameter of the outermost graphite ring 11 ranges from 4 inches to 12 inches, the number of graphite rings 11 is set to 5 to 10, which can effectively avoid the problem of breakage caused by the graphite ring 11 being too thin.

[0129] In some implementations of the present application, the width of the expansion gap 111 between two adjacent graphite rings 11 ranges from 10 μm (micrometers) to 100 μm.

[0130] In this embodiment, the width of the expansion gap 111 between two adjacent graphite rings 11 is in the range of 10 μm to 100 μm, which can prevent the graphite rings 11 from being deformed and broken due to local stress concentration caused by thermal expansion during heating.

[0131] In addition, in the above embodiment, the roughness of the lower surface of the graphite tray 1 can be set uniformly; or, the roughness of the lower surface of the graphite tray 1 can be equal to the roughness at the corresponding position of the upper surface.

[0132] In this embodiment, the lower surface of the graphite tray 1 as a whole or the graphite tray 1 assembled by the graphite rings 11 is uniformly rough ground or polished so that the thickness H of the graphite tray 1 or the graphite rings 11 is consistent, and it is ensured that the lower surface of each graphite ring 11 has the same roughness and heat transfer efficiency.

[0133] Alternatively, the lower surface of each graphite ring 11 is roughened separately, or different areas of the lower surface of the entire graphite tray 1 are roughened, so that the roughness of the lower surface of the entire graphite tray or each graphite ring 11 is equal to the roughness at the corresponding position on its upper surface, thereby making its ability to adjust the temperature field more significant.

[0134] The present application also provides a method for preparing a graphite tray 1, which is used to prepare the graphite tray 1 in the first embodiment. Figure 10 As shown, Figure 10 This is a flow chart for preparing the graphite tray of the first embodiment of this application. The specific steps are:

[0135] S101, providing a circular graphite substrate;

[0136] S102, performing a surface roughness treatment on the graphite substrate so that the surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge; or the surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge;

[0137] S103 , roughly grinding or polishing the lower surface of the graphite substrate to keep the thickness of the graphite substrate uniform, thereby forming a graphite tray.

[0138] In this embodiment, the upper surface of the graphite substrate is roughened by grinding and polishing, surface plating, surface sandblasting, acid washing and alkali washing, etc., so that the upper surface roughness of the graphite substrate gradually decreases or increases from the center to the edge.

[0139] It can be understood that there are tiny asperities on the surface of the graphite tray 1 and the surface of the wafer substrate 4. When the wafer substrate 4 is placed on the graphite tray, the contact between the two surfaces is incomplete. Even under great pressure, the actual contact area of ​​the two contact surfaces only accounts for a small part of the nominal contact area (the area that appears to be in contact macroscopically), and the uncontacted part is in a gas-occupied state.

[0140] During the epitaxial growth process, the hydrogen content of the ambient gas is typically 99%. At this point, the hydrogen content is higher between the graphite tray 1 where the surface roughness is greater and the wafer substrate 4, while the hydrogen content is lower between the graphite tray 1 where the surface roughness is less. Since the thermal conductivity of hydrogen is much lower than that of graphite, the heat transfer efficiency between the graphite tray 1 and the wafer substrate 4 at the locations where the surface roughness is greater is lower than at the locations where the surface roughness is less, thus achieving temperature balance between the center and edge of the wafer substrate 4.

[0141] Specifically, because the theoretical thermal conductivity of hydrogen is 0.1805 W / mK (watts per meter Kelvin), far lower than graphite's thermal conductivity of 129 W / mK, the heat transfer efficiency between graphite tray 1 and wafer substrate 4 is lower at locations with higher hydrogen content than at locations with lower hydrogen content. Specifically, when using a graphite tray 1 with a surface roughness that gradually decreases from the center to the edge, the heat transfer efficiency near the center of the tray is lower than that near the edge. When using a graphite tray 1 with a surface roughness that gradually increases from the center to the edge, the heat transfer efficiency near the center of the tray is higher than that near the edge. The uniform thickness of graphite tray 1 prevents the introduction of excess hydrogen due to the height difference between the tray and wafer substrate 4, ensuring the overall heat transfer efficiency of the tray. Therefore, during the heat transfer process, temperature balance is achieved between the center position and the edge position of the graphite tray 1 .

[0142] This embodiment controls the heat transfer effect by controlling the surface roughness of the graphite tray 1. Furthermore, during the epitaxial growth process, the temperature uniformity of the wafer substrate 4 along the diameter direction is adjusted, thereby ultimately improving the deposition temperature field distribution within the surface of the wafer substrate 4.

[0143] Furthermore, the lower surface of the graphite substrate is roughened to ensure that the thickness of the graphite substrate is uniform at all locations. Therefore, during heat transfer, temperature balance is achieved at the center and edge of the graphite tray 1.

[0144] In the prior art, the uneven temperature field of the wafer substrate 4 results in an uneven doping concentration distribution in the resulting epitaxial wafer. This embodiment adjusts the surface roughness of the graphite tray 1 to make the temperature field of the wafer substrate 4 uniform, thereby improving the uniformity of the doping concentration in the resulting epitaxial wafer. This also reduces the warpage of the resulting epitaxial wafer caused by thermal stress and lowers the bow-of-wave (BOW) value of the resulting epitaxial wafer. BOW is typically used to describe the degree of curvature of a wafer caused by stress or other factors during processing. It also reduces paired basal plane dislocations (BPDs) caused by thermal stress.

[0145] In some implementations of this application, such as Figure 11 As shown, Figure 11 This is a flow chart for preparing the graphite tray of the second embodiment of this application. When preparing the graphite tray 1 of the second embodiment, at S102, the graphite substrate is subjected to a surface roughness treatment so that the surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge; or, before the surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge, the process further includes:

[0146] S104 , cutting the graphite substrate to form at least two graphite rings 11 , such that an expansion gap 111 is formed between two adjacent graphite rings 11 .

[0147] Thus, when a graphite tray 1 having a surface roughness that gradually decreases from the center of the circle toward the edge is used, step S102 performs a roughening treatment on the upper surface of the graphite substrate so that the upper surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge. This may include: performing a roughening treatment on the upper surface of each graphite ring 11 so that the upper surface roughness of each graphite ring 11 gradually decreases away from the center of the circle toward the edge; and, of two adjacent graphite rings 11, the minimum value of the upper surface roughness of the graphite ring 11 closer to the center of the circle is greater than the maximum value of the upper surface roughness of the other graphite ring 11 farther from the center of the circle.

[0148] Alternatively, performing a roughening treatment on the upper surface of the graphite substrate so that the upper surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge position, which may include: performing a roughening treatment on the upper surface of each graphite ring 11 so that the upper surface roughness of each graphite ring 11 is the same; and, among two adjacent graphite rings 11, the upper surface roughness of the graphite ring 11 closer to the center of the circle is greater than the upper surface roughness of the other graphite ring 11 farther from the center of the circle.

[0149] When a graphite tray 1 having a surface roughness that gradually increases from the center of the circle toward the edge is used, step S102 performs a roughening treatment on the upper surface of the graphite substrate so that the upper surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge. The step S102 may also include: performing a roughening treatment on the upper surface of each graphite ring 11 so that the upper surface roughness of each graphite ring 11 gradually increases from the center of the circle toward the edge; and, of two adjacent graphite rings 11, the maximum value of the upper surface roughness of the graphite ring 11 closer to the center of the circle is smaller than the minimum value of the upper surface roughness of the other graphite ring 11 farther from the center of the circle;

[0150] Alternatively, the upper surface of each graphite ring 11 is roughened so that the upper surface roughness of each graphite ring 11 is the same; and, among two adjacent graphite rings 11, the upper surface roughness of the graphite ring 11 closer to the center is smaller than the upper surface roughness of the other graphite ring 11 farther from the center.

[0151] The technical effects achieved in this embodiment are the same as those in the aforementioned embodiments and will not be described in detail here.

[0152] In some embodiments of the present application, the lower surface of the graphite substrate is roughly ground or polished to maintain a uniform thickness of the graphite substrate, including: roughly grinding or polishing the lower surface of the graphite substrate so that the roughness of the lower surface of the graphite tray 1 is uniform and the thickness is maintained uniform; or roughly grinding or polishing the lower surface of the graphite substrate so that the roughness of the lower surface of the graphite tray 1 is equal to the roughness at the corresponding position of the upper surface and the thickness is maintained uniform.

[0153] The lower surface of the graphite rings 11 is subjected to roughening treatment. If the lower surface roughness of each graphite ring 11 needs to be consistent, the individual graphite rings 11 are assembled before the lower surface roughness treatment. The assembly method is to concentrically nest the graphite rings 11 with a specific upper surface roughness. The assembled graphite tray 1 is then subjected to lower surface roughening treatment, i.e., rough grinding or polishing, to uniformly set the thickness H at each position of the graphite substrate and ensure that the lower surface of each graphite ring 11 has the same roughness. The technical effects achieved are the same as those in the aforementioned embodiment and will not be repeated here.

[0154] like Figure 11 As shown, in this embodiment, after the lower surface of the graphite substrate is roughly ground or polished in step S103, the following steps are further included:

[0155] S105, cleaning the graphite substrate to remove metal residues on the surface;

[0156] S106 , sleeve a limiting graphite ring 12 on the periphery of the graphite substrate; the top portion of the limiting graphite ring 12 extends toward the center of the circle, and the inner sidewall of the extension portion is used to fix the wafer.

[0157] In this embodiment, the graphite ring 11 after the roughening treatment is subjected to ultrasonic cleaning and hydrochloric acid pickling to remove metal residues and surface damage generated during the grinding and polishing process.

[0158] A limiting graphite ring 12 is sleeved on the outer side of the outermost graphite ring 11 of the assembled graphite ring 11. When the wafer substrate 4 is placed on the graphite tray, the inner side wall of the extended part of the limiting graphite ring 12 is attached to the side wall of the wafer substrate 4, thereby fixing the wafer substrate 4.

[0159] This application also provides an epitaxial growth device, see Figure 12 , Figure 12 The cross-sectional view of the epitaxial growth equipment provided in this application is a horizontal epitaxial furnace. Figure 12 The figure shows the internal structure of the epitaxial furnace when the graphite tray 1 is placed in the horizontal epitaxial furnace.

[0160] like Figure 12 As shown, the epitaxial growth equipment includes: a quartz cylinder 2; heating devices 21 are provided above and below the quartz cylinder 2; a reaction space 100 is provided inside the quartz cylinder 2, into which reaction gas and ambient gas can be introduced; a rotatable graphite tray placement platform 26 is provided in the reaction space 100; and the graphite tray 1 of any of the aforementioned embodiments is placed on the graphite tray placement platform 26.

[0161] like Figure 12 As shown, the epitaxial growth apparatus further comprises: an upper half-moon graphite member 22, a lower half-moon graphite member 23, an upper graphite cover plate 24, and a lower graphite cover plate 25. The lower graphite cover plate is provided with a tray groove 251, within which a graphite tray placement platform 26 is disposed. A rotating mechanism 261 is also provided below the graphite tray placement platform 26, which is used to drive the graphite tray placement platform 26 to rotate the graphite tray 1 placed thereon along the center of the graphite tray 1. Furthermore, the area between the upper graphite cover plate 24 and the lower graphite cover plate 25 forms a reaction space 100. The epitaxial growth apparatus further comprises: an injection gate 27, a tail exhaust gate 28, and an airflow channel 29. An upstream graphite member 30 is provided on the outer side of the graphite tray 1 near the injection gate 27, and a downstream graphite member 31 is provided on the outer side of the graphite tray 1 near the tail exhaust gate 28. The upstream graphite member 30 is higher than the downstream graphite member 31.

[0162] In the epitaxial growth apparatus of this embodiment, before chemical vapor deposition (CVD), a quartz tube 2 is filled with ambient hydrogen. Once the quartz tube 2 is filled with ambient gas, a reaction gas is introduced. When wafers are formed from silicon-containing materials, the reaction gas can be a silicon-containing reaction gas; when wafers are formed from gallium nitride or gallium arsenide, the reaction gas can also be a silicon-free reaction gas. Heating devices 21 located above and below the quartz tube 2 heat the interior of the quartz tube 2. Heat from the heating devices 21 is transferred to the upper and lower graphite meniscus 22 and 23. The upper and lower graphite meniscus 22 and 23 transfer the heat to the reaction space 100 formed between the upper and lower graphite cover plates 24 and 25. The ambient gas is heated, and the reaction gas is continuously heated during its flow. The reaction gas, ambient gas, and graphite tray 1 collectively heat the wafer substrate 4 placed on the upper surface of the graphite tray. Finally, the reaction gas reacts with hydrogen at high temperature, and the reactants are deposited on the upper surface of the wafer substrate 4 to form an epitaxial wafer. The typical growth temperature is 1500°C (Celsius) to 1700°C.

[0163] For details, see Figure 12 The reaction gas enters the quartz cylinder 2 through the injection door 27, and then enters the reaction space 100 formed between the upper graphite cover plate 24 and the lower graphite cover plate 25 through the air flow channel 29. An expansion gap 111 is provided between the air flow channel 29 and the upper graphite cover plate 24 to prevent the air flow channel 29 from being damaged due to thermal expansion and inability to release deformation.

[0164] The reaction gas flows in the accommodation space through the upstream graphite member 30 to the wafer substrate 4 located on the upper surface of the graphite tray 1. Figure 12 As shown, the upstream graphite member 30 is used to adjust the gas flow field of the reaction gas passing through the upstream graphite member 30 so that the reaction gas is more uniform.

[0165] When the reaction gas passes over the surface of the wafer substrate 4, it reacts with hydrogen at high temperature, and the reactants are deposited on the upper surface of the wafer substrate 4, forming a wafer epitaxial wafer on the upper surface of the wafer substrate 4. During this process, the rotating mechanism 261 located below the graphite tray placement platform 26 drives the graphite tray placement platform 26 located in the tray groove 251 of the lower graphite cover plate 25 to rotate along the center of the graphite tray placement platform 26. The graphite tray placement platform 26 drives the graphite tray 1 placed thereon to rotate along the center of the graphite tray 1, so that the temperature field at the same diameter position on the graphite tray 1 is uniform. The graphite tray 1 drives the wafer substrate 4 placed thereon to rotate along the center of the wafer substrate 4, so that the temperature field at the same diameter position on the wafer substrate 4 is uniform.

[0166] At the same time, graphite tray 1 heats wafer substrate 4. Because the roughness of the upper surface of graphite tray 1 gradually decreases from the center toward the edge, or increases from the center toward the edge, the heat transfer efficiency at locations on graphite tray 1 with higher hydrogen content is lower than at locations with lower hydrogen content. That is, the heat transfer efficiency between graphite tray 1 and wafer substrate 4 near the center is lower than that near the edge, or vice versa. The uniform thickness H of graphite tray 1 prevents the introduction of excess hydrogen due to the height difference between graphite tray 1 and wafer substrate 4, ensuring the overall heat transfer efficiency of graphite tray 1. Therefore, during the heat transfer process, the heating rate of the wafer substrate 4 at the center position is lower than the heating rate at the edge position, or the heating rate of the wafer substrate 4 at the center position is higher than the heating rate at the edge position, thereby achieving temperature balance between the center position and the edge position.

[0167] The reacted gas passes through the downstream graphite member 31 and is discharged from the quartz cylinder 2 through the tail exhaust door 28 through the air flow channel 29 close to the tail exhaust door 28 .

[0168] In this embodiment, the graphite tray 1 can be placed into the quartz cylinder 2 through the injection door 27 by a clamp.

[0169] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0170] Each embodiment in this specification is described in a related manner. Similar parts between the various embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences between the other embodiments. In particular, the system embodiment is generally similar to the method embodiment, so the description is relatively simple. For related parts, refer to the description of the method embodiment.

[0171] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A graphite tray, characterized in that: The graphite tray (1) is circular and has a uniform thickness; The graphite tray (1) comprises at least two graphite rings (11), and the at least two graphite rings (11) are concentrically nested one by one around the center of the graphite tray (1); The wafer substrate (4) on the graphite tray (1) is heated at a high temperature at its center and at a low temperature at its edge, and the surface roughness of the graphite tray (1) gradually decreases from the center toward the edge. The root mean square average value of the profile ordinate of the upper surface roughness of the innermost graphite ring (11) is 1 μm to 500 μm; The root mean square average value of the profile ordinate of the upper surface roughness of the outermost graphite ring (11) is 100 nm to 500 nm; The root mean square average value of the profile ordinate of the upper surface roughness of the graphite ring (11) located between the innermost graphite ring (11) and the outermost graphite ring (11) is 0.1 μm-100 μm; Alternatively, during the heating process, the center of the wafer substrate (4) on the graphite tray (1) is at a low temperature, while the edge is at a high temperature, and the surface roughness of the graphite tray (1) gradually increases from the center toward the edge; The root mean square average value of the profile ordinate of the upper surface roughness of the outermost graphite ring (11) is 1 μm-500 μm; The root mean square average value of the profile ordinate of the upper surface roughness of the innermost graphite ring (11) is 100 nm to 500 nm; The root mean square average value of the profile ordinate of the upper surface roughness of the graphite ring (11) located between the innermost graphite ring (11) and the outermost graphite ring (11) is 0.1 μm-100 μm.

2. The graphite tray according to claim 1, characterized in that An expansion gap (111) is provided between two adjacent graphite rings (11).

3. The graphite tray according to claim 2, characterized in that The upper surface roughness of the same graphite ring (11) gradually decreases away from the center toward the edge; of two adjacent graphite rings (11), the minimum value of the upper surface roughness of the graphite ring (11) closer to the center is greater than the maximum value of the upper surface roughness of the other graphite ring (11) farther from the center; or, The upper surface roughness of the same graphite ring (11) is the same; among two adjacent graphite rings (11), the upper surface roughness of the graphite ring (11) closer to the center is greater than the upper surface roughness of the other graphite ring (11) farther from the center.

4. The graphite tray according to claim 2, characterized in that The upper surface roughness of the same graphite ring (11) gradually increases from the center of the circle toward the edge; of two adjacent graphite rings (11), the maximum value of the upper surface roughness of the graphite ring (11) closer to the center of the circle is smaller than the minimum value of the upper surface roughness of the other graphite ring (11) farther from the center of the circle; or, The upper surface roughness of the same graphite ring (11) is the same; among two adjacent graphite rings (11), the upper surface roughness of the graphite ring (11) closer to the center is smaller than the upper surface roughness of the other graphite ring (11) farther from the center.

5. The graphite tray according to claim 2, characterized in that The graphite tray (1) further comprises a limiting graphite ring (12), wherein the limiting graphite ring (12) is sleeved on the outer circumference of the outermost graphite ring (11); the top portion of the limiting graphite ring (12) extends toward the center of the circle, and the inner side wall of the extension portion is used to fix the wafer substrate (4).

6. The graphite tray according to claim 2, characterized in that The difference between the inner diameter and the outer diameter of the graphite ring (11) located on the inner side is equal to the difference between the inner diameter and the outer diameter of the graphite ring (11) located on the outer side; Or, the difference between the inner diameter and the outer diameter of the graphite ring (11) located on the inner side is smaller than the difference between the inner diameter and the outer diameter of the graphite ring (11) located on the outer side; Alternatively, the difference between the inner diameter and the outer diameter of the graphite ring (11) located on the inner side is greater than the difference between the inner diameter and the outer diameter of the graphite ring (11) located on the outer side.

7. The graphite tray according to claim 2, characterized in that The center of the graphite tray (1) is a graphite disc (13); Alternatively, the center of the graphite tray (1) is a hollow area (112).

8. The graphite tray according to claim 5, characterized in that The difference between the inner diameter and the outer diameter of the graphite ring (11) ranges from 1 inch to 2 inches; The outer diameter of the outermost graphite ring (11) ranges from 4 inches to 12 inches; The outer diameter of the limiting graphite ring (12) ranges from 13 inches to 14 inches; The number of the graphite rings (11) is 2 to 10.

9. The graphite tray according to claim 2, characterized in that The width of the expansion gap (111) between two adjacent graphite rings (11) ranges from 10 μm to 100 μm.

10. The graphite tray according to any one of claims 1 to 9, characterized in that: The roughness of the lower surface of the graphite tray (1) is uniformly set; Alternatively, the roughness of the lower surface of the graphite tray (1) is equal to the roughness at a corresponding position on the upper surface.

11. A method for preparing a graphite tray, characterized in that: Used to prepare the graphite tray according to any one of claims 1 to 10; Providing a circular graphite substrate; Performing a surface roughness treatment on the graphite substrate so that the surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge; or the surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge; Roughly grinding or polishing the lower surface of the graphite substrate to maintain a uniform thickness of the graphite substrate to form a graphite tray; After the wafer substrate (4) is mounted on the graphite tray (1), during the heating process, the center of the wafer substrate (4) on the graphite tray (1) is at a high temperature and the edge is at a low temperature, and the surface roughness of the graphite tray (1) gradually decreases from the center toward the edge; Alternatively, after the wafer substrate (4) is mounted on the graphite tray (1), during the heating process, the center of the wafer substrate (4) on the graphite tray (1) is at a low temperature and the edge is at a high temperature, and the surface roughness of the graphite tray (1) gradually increases from the center toward the edge.

12. The preparation method according to claim 11, characterized in that Before performing the upper surface roughness treatment on the graphite substrate so that the upper surface roughness of the graphite substrate gradually decreases from the center of the circle toward the edge; or before gradually increasing the upper surface roughness of the graphite substrate from the center of the circle toward the edge, the method further includes: The graphite substrate is cut to form at least two graphite rings (11), so that an expansion gap (111) is provided between two adjacent graphite rings (11).

13. The preparation method according to claim 11, characterized in that The step of performing roughness treatment on the upper surface of the graphite substrate so that the roughness of the upper surface of the graphite substrate gradually decreases from the center of the circle toward the edge includes: The upper surface of each graphite ring (11) is subjected to roughness treatment so that the upper surface roughness of each graphite ring (11) gradually decreases from the center of the circle toward the edge; and, among two adjacent graphite rings (11), the minimum value of the upper surface roughness of the graphite ring (11) closer to the center of the circle is greater than the maximum value of the upper surface roughness of the other graphite ring (11) farther from the center of the circle; or, The upper surface of each graphite ring (11) is subjected to roughness treatment so that the upper surface roughness of each graphite ring (11) is the same; and, among two adjacent graphite rings (11), the upper surface roughness of the graphite ring (11) closer to the center is greater than the upper surface roughness of the other graphite ring (11) farther from the center.

14. The preparation method according to claim 11, characterized in that The step of performing roughness treatment on the upper surface of the graphite substrate so that the roughness of the upper surface of the graphite substrate gradually increases from the center of the circle toward the edge includes: The upper surface of each graphite ring (11) is subjected to roughness treatment so that the upper surface roughness of each graphite ring (11) gradually increases from the center of the circle toward the edge; and, among two adjacent graphite rings (11), the maximum value of the upper surface roughness of the graphite ring (11) closer to the center of the circle is smaller than the minimum value of the upper surface roughness of the other graphite ring (11) farther from the center of the circle; or, The upper surface of each graphite ring (11) is subjected to roughness treatment so that the upper surface roughness of each graphite ring (11) is the same; and, among two adjacent graphite rings (11), the upper surface roughness of the graphite ring (11) closer to the center is smaller than the upper surface roughness of the other graphite ring (11) farther from the center.

15. The preparation method according to claim 11, characterized in that The step of roughly grinding or polishing the lower surface of the graphite substrate to maintain a uniform thickness of the graphite substrate comprises: The lower surface of the graphite substrate is roughly ground or polished so that the lower surface roughness of the graphite tray (1) is uniform and the thickness is kept uniform; or, The lower surface of the graphite substrate is roughly ground or polished, and the roughness of the lower surface of the graphite tray (1) is equal to the roughness at the corresponding position of the upper surface, and the thickness is kept uniform.

16. The preparation method according to claim 15, characterized in that After the lower surface of the graphite substrate is roughly ground or polished, the method further comprises: Cleaning the graphite substrate to remove metal residues on the surface; A limiting graphite ring (12) is sleeved on the outer periphery of the graphite substrate; the top portion of the limiting graphite ring (12) extends toward the center of the circle, and the inner side wall of the extension portion is used to fix the wafer.

17. An epitaxial growth device, characterized in that: include: Quartz tube (2); Heating devices (21) are provided above and below the quartz cylinder (2); A reaction space (100) is provided inside the quartz cylinder (2) for allowing the introduction of reaction gas and ambient gas; A rotatable graphite tray placement platform (26) is provided in the reaction space (100); The graphite tray placement platform (26) is provided with the graphite tray (1) according to any one of claims 1 to 10.

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