Graphite tray, preparation method of graphite tray and epitaxial growth equipment

Abstract

The embodiment of the invention provides a graphite tray, a preparation method of the graphite tray and epitaxial growth equipment, and relates to the technical field of semiconductors. The graphite tray is circular and is uniform in thickness; wherein the roughness of the upper surface of the graphite tray is gradually reduced from the circle center to the edge position; or the roughness of the upper surface of the graphite tray is gradually increased from the circle center to the edge position. According to the method, the heat transfer effect is controlled by controlling the roughness of the upper surface of the graphite tray, the temperature uniformity of the wafer substrate in the diameter direction is further adjusted in the epitaxial process, and finally the purposes of improving the distribution of the deposition temperature field in the surface of the wafer substrate, improving the doping concentration uniformity of the formed wafer epitaxial wafer and improving the yield of the wafer epitaxial wafer are achieved. And the problem of warping of the epitaxial wafer caused by thermal stress is solved.

Description

Technical Field

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

[0002] Wafer 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 wafer epitaxial wafers. At present, the mainstream method for preparing wafer epitaxial wafers is chemical vapor deposition (CVD).

[0003] At present, the preparation of wafer epitaxial wafers by chemical vapor deposition mainly involves placing the wafer substrate on a graphite tray, moving the wafer substrate and the graphite tray into an epitaxial furnace, introducing high-temperature reaction gas and high-temperature hydrogen as an ambient gas into the epitaxial furnace, and at the same time, radiating heat to the front and back of the wafer substrate through heating devices arranged above and below the graphite tray. In this way, the gas phase molecules in the silicon-containing reaction gas move to the surface of the wafer substrate, and under the action of high temperature, the gas phase molecules react with hydrogen, and the reaction products are deposited on the surface of the wafer substrate to form a wafer epitaxial wafer.

[0004] However, when a horizontal epitaxial furnace is used for epitaxial growth, the high-temperature reaction gases flow from one side of the epitaxial furnace to the other side. Therefore, due to the depletion mode of the reaction gases along the surface of the wafer substrate (the gas phase molecules in the reaction gas react with hydrogen in the process of moving to the substrate and causing consumption) and the low thermal conductivity of graphite (129W / (m·K)), the temperature of the high-temperature gas gradually decreases, resulting in a temperature unevenness problem in which the temperature of the wafer substrate surface gradually decreases along the gas flow direction.

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

[0006] In the related art, in order to solve the problem of uneven temperature, the graphite tray is rotated around the center of the tray during the heating process. This rotation method improves the temperature at the same radius, but still cannot improve the temperature difference at different diameters caused by the depletion mode.

[0007] That is to say, the wafer substrate on the graphite tray still has the problem of uneven temperature 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 embodiment 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 on a graphite tray in the radial direction from the center position to the edge position. The specific technical solution is as follows:

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

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

[0011] Alternatively, the surface roughness of the graphite tray gradually increases from the center of the circle 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 from the center of the circle to the edge; of two adjacent graphite rings, the minimum value of the upper surface roughness of the graphite ring close to the center of the circle is greater than the maximum value of the upper surface roughness of the other graphite ring away from the center of the circle; 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 close to the center is greater than the upper surface roughness of the other graphite ring far 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 of the roughness of the upper surface of the outermost graphite ring (Rq, Rq = ) is 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 to 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 close to the center of the circle is smaller than the minimum value of the upper surface roughness of the other graphite ring away 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 close to the center is smaller than the upper surface roughness of the other graphite ring far 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 100nm-500nm;

[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 to 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 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 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 disk;

[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 (micrometer) 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 of the upper surface.

[0037] The present application also provides a method for preparing a graphite tray, the specific steps of which are: providing a circular graphite substrate;

[0038] 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 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, so as to form a graphite tray.

[0040] In some embodiments of the present application, before the upper surface roughness treatment is performed 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 position; or the upper surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge position, 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 upper surface roughness treatment 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 includes:

[0043] The upper surface of each of the graphite rings is subjected to roughness treatment so that the upper surface roughness 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 close to the center of the circle is greater than the maximum value of the upper surface roughness of the other graphite ring far 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 close to the center is greater than the upper surface roughness of the other graphite ring far from the center.

[0045] In some embodiments of the present application, the upper surface roughness treatment 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 position includes:

[0046] The upper surface of each of the graphite rings is subjected to roughness treatment so that the upper surface roughness 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 close to the center of the circle is less than the minimum value of the upper surface roughness of the other graphite ring far 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 close to the center is smaller than the upper surface roughness of the other graphite ring far 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 comprises:

[0049] The lower surface of the graphite substrate is roughly ground or polished so that the lower surface roughness of the graphite tray is uniform and the thickness is kept 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 includes:

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

[0053] A limiting graphite ring is sleeved on the 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 arranged 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 placing platform is placed with the graphite tray described in any one of the above embodiments.

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

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

[0061] It can be understood 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 contacting 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 the epitaxial process, the hydrogen content in the typical ambient gas is 99%. At this time, the hydrogen content between the location with greater surface roughness on the graphite tray and the wafer substrate is higher, while the hydrogen content between the location with less surface roughness on the graphite tray and the wafer substrate is lower. Since the thermal conductivity of hydrogen is much lower than that of graphite, the heat transfer efficiency between the graphite tray and the wafer substrate at the location with greater surface roughness on the graphite tray is lower than that at the location with less surface roughness on the graphite tray, thereby 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 at the same time 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 drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description 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 diagram of the structure 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 shown;

[0067] Figure 3 A schematic diagram of the structure 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 shown;

[0069] Figure 5 A schematic diagram showing that the roughness at the center of the graphite tray provided in the present application is greater than the roughness at the edge;

[0070] Figure 6 A schematic diagram of the structure 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 diagram of the structure of a graphite tray provided in the third embodiment of the present application;

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

[0074] Fig.10 A flow chart of preparing the graphite tray of the first embodiment of the present application;

[0075] Fig.11 A flow chart of preparing a graphite tray according to the second embodiment of the present application;

[0076] Fig.12 A cross-sectional view of a horizontal epitaxial furnace is provided for the epitaxial growth equipment provided in the present application.

[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 device 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 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 described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field based on this application belong to 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 diagram of the structure of a graphite tray provided in the first embodiment of the present application; Figure 2 for Figure 1 The cross-sectional view of the graphite tray shown. The graphite tray 1 is circular and has a uniform thickness; wherein the surface roughness of the graphite tray 1 gradually decreases from the center of the circle toward the edge; or, the surface roughness of the graphite tray 1 gradually increases 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 position, or the roughness of the upper surface of the graphite tray 1 gradually increases from the center of the circle toward the edge position, and the thickness of the graphite tray 1 is uniformly set.

[0084] Specifically, when the graphite tray 1 is placed in a horizontal epitaxial furnace, the temperature of the high-temperature gas gradually decreases due to the depletion mode of the reaction gas along the surface of the wafer substrate, so that the temperature at the center of the wafer substrate 4 is higher than the temperature at the edge. At this time, a graphite tray 1 with a top surface roughness that gradually decreases from the center to the edge is used to improve the situation where the temperature at the center of the wafer substrate 4 is higher than the temperature at the edge.

[0085] When the graphite tray 1 is placed in a vertical epitaxial furnace and heated by a vertical cold wall, the temperature at the center of the wafer substrate 4 is higher than that at the edge because the heating source is located below the graphite tray 1. At this time, a graphite tray 1 with a top surface roughness that gradually decreases from the center to the edge is used to improve the situation in which the temperature at the center of the wafer substrate 4 is higher than that at the edge.

[0086] When a vertical hot wall is used for heating, since the heating source is located below the graphite tray 1 and at the edge of the graphite tray 1, there is a risk that the temperature at the center of the wafer substrate 4 is lower than the temperature at the edge. In this case, a graphite tray 1 with a gradually increasing upper surface roughness from the center to the edge is used to improve the situation where the temperature at the center of the wafer substrate 4 is lower than the temperature 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 in contact 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 process, the hydrogen content in the typical ambient gas is 99%. At this time, the hydrogen content between the position with greater surface roughness on the graphite tray 1 and the wafer substrate 4 is relatively high, while the hydrogen content between the position with less surface roughness on the graphite tray 1 and the wafer substrate 4 is relatively low. 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 position with greater surface roughness on the graphite tray 1 is lower than the heat transfer efficiency between the two at the position with less surface roughness on the graphite tray, thereby achieving temperature balance between the center position and the edge position of the wafer substrate 4.

[0089] Specifically, since the theoretical thermal conductivity of hydrogen is 0.1805 W / mK (watt / (meter·Kelvin)), which is much lower than the thermal conductivity of graphite 129 W / m·K, the heat transfer efficiency at the position with more hydrogen content between the graphite tray 1 and the wafer substrate 4 is lower than the heat transfer efficiency at the position with less hydrogen content between the graphite tray 1 and the wafer substrate 4, that is, when the graphite tray 1 whose upper surface roughness gradually decreases from the center of the circle to the edge position is used, the heat transfer efficiency at the position near the center of the circle between the graphite tray 1 and the wafer substrate 4 is lower than the heat transfer efficiency at the position near the edge between the two; when the graphite tray 1 whose surface roughness gradually increases from the center of the circle to the edge position is used, the heat transfer efficiency at the position near the center of the circle between the graphite tray 1 and the wafer substrate 4 is higher than the heat transfer efficiency at the position near the edge between the two. The uniform thickness of the graphite tray 1 avoids the introduction of excessive hydrogen due to the height difference between the graphite tray 1 and the wafer substrate 4, and ensures the overall heat transfer efficiency of the graphite tray 1. Therefore, during the heat transfer process, the temperature balance between the center position and the edge position of the graphite tray 1 is achieved.

[0090] This embodiment achieves 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 along the diameter direction during the epitaxial process, ultimately achieving the effect of improving the deposition temperature field distribution within the surface of the wafer substrate 4.

[0091] In the prior art, the doping concentration distribution of the formed epitaxial wafer is uneven due to the uneven temperature field of the wafer substrate 4. This embodiment makes the temperature field of the wafer substrate 4 uniform by adjusting the surface roughness of the graphite tray 1, thereby improving the uniformity of the doping concentration of the formed epitaxial wafer, improving the warpage of the formed epitaxial wafer due to thermal stress, and reducing the BOW (bending degree) value of the formed epitaxial wafer. BOW is usually used to describe the bending degree of the epitaxial wafer due to stress or other factors during the processing of the epitaxial wafer; it can also reduce the paired BPD (basal plane dislocation) 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 side wall of the portion of the extending portion of the limiting graphite tray that is higher than the graphite tray 1 is attached to the side wall 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 diagram of the structure of a graphite tray provided in the second embodiment of the present application; Figure 4 for Figure 3 The cross-sectional view of the graphite tray is shown. The graphite tray 1 comprises at least two graphite rings 11, which are concentrically nested one by one around the center of the graphite tray 1; and 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 to form a complete graphite tray 1 structure. Moreover, the thickness H of each graphite ring 1 is equal. After the graphite tray 1 is cut as a whole to form the graphite ring 11, an expansion gap 111 is formed between two adjacent graphite rings 11, so that when the graphite ring 11 is deformed by heat, the deformed part can be released through the expansion gap 111, preventing the graphite tray 1 from being damaged due to the deformation of the graphite ring 11 caused by high temperature, which leads to the breakage or deformation of the graphite tray 1 and the uneven heat transfer at 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 to affect the heat transfer effect.

[0097] Also, see Figure 5 , 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. Figure 5 The figure shows the distribution of the upper surface roughness of the 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 from the center to the edge; of two adjacent graphite rings 11, the minimum value of the upper surface roughness of the graphite ring 11 close to the center is greater than the maximum 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 greater than the upper surface roughness of the other graphite ring 11 away from the center.

[0098] In this embodiment, the upper surface roughness of the same graphite ring 11 is the same, and the minimum value of the upper surface roughness of the graphite ring 11 close to the center of the circle of two adjacent graphite rings 11 is greater than the maximum value of the upper surface roughness of the other graphite ring 11 away from the center of the circle. At this time, the corresponding positions of each graphite ring 11 in the entire graphite tray 1 have the same heat transfer efficiency, so that the heat transfer efficiency of the wafer substrate 4 in the corresponding area of ​​each graphite ring 11 in the graphite tray 1 is more uniform.

[0099] In some embodiments, the upper surface roughness of the same graphite ring 11 can gradually decrease in the direction away from the center of the circle toward the edge position, and, of two adjacent graphite rings 11, 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 the other graphite ring 11 away from the center of the circle. Moreover, the thickness H of each graphite ring 11 is equal. The upper surface roughness of the graphite tray 1 composed of graphite rings 11 gradually decreases in the direction away from the center of the circle toward the edge position, so that the hydrogen content between the graphite ring 11 near the center of the circle and the wafer substrate 4 is greater than the hydrogen content between the graphite ring 11 near the edge position and the wafer substrate 4.

[0100] As mentioned above, the thermal conductivity of hydrogen is much lower than that of graphite. During the heating process, since the hydrogen content between the graphite ring 11 and the wafer substrate 4 near the center is relatively high, the heating rate of the graphite ring 11 at this position to the wafer substrate 4 is relatively slow; while the hydrogen content between the graphite ring 11 and the wafer substrate 4 near the edge is relatively low, and the heating rate of the graphite ring 11 at this position to the wafer substrate 4 is relatively fast. Thus, the temperature balance of the wafer substrate 4 at the center and the edge is achieved.

[0101] At the same time, the heat transfer efficiency of the graphite tray 1 as a whole gradually increases from the center of the circle toward 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 finally 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 formed due to thermal stress, reducing the BOW value of the formed wafer epitaxial wafer and reducing the paired BPD caused by thermal stress.

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

[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 contour of the upper surface roughness is in 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 contour of the upper surface roughness is in the order of μm; for the graphite ring 11 with a diameter between the maximum and minimum values, the upper surface roughness is adjusted by means of fine grinding and rough polishing by adjusting the coarseness of the abrasive, and the typical value of the upper surface roughness is 0.1μm-100μm. Finally, the upper surface roughness of the entire graphite tray 1 formed by the concentric nesting of each graphite ring 11 is gradually reduced from the center position to the edge position, so that the heat transfer efficiency of the graphite ring 11 to the wafer substrate 4 gradually increases from the center position to the edge position, achieving a uniform temperature field effect of 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, and the maximum value of the upper surface roughness of the graphite ring 11 close to the center of the circle of two adjacent graphite rings 11 is smaller than the minimum value of the upper surface roughness of the other graphite ring 11 away from the center of the circle. At this time, the corresponding positions of each graphite ring 11 in the entire graphite tray 1 have the same heat transfer efficiency, so that the heat transfer efficiency of the wafer substrate 4 in the corresponding area of ​​each graphite ring 11 in the graphite tray 1 is more uniform.

[0107] In some embodiments, the upper surface roughness of the same graphite ring 11 can gradually increase in the direction away from the center of the circle toward the edge position, and, of two adjacent graphite rings 11, the maximum value of the upper surface roughness of the graphite ring 11 close to the center of the circle is less than the minimum value of the upper surface roughness of the other graphite ring 11 away from the center of the circle. Moreover, the thickness H of each graphite ring 11 is equal. The upper surface roughness of the graphite tray 1 composed of graphite rings 11 gradually increases in the direction away from the center of the circle toward the edge position, so that the hydrogen content between the graphite ring 11 near the center position and the wafer substrate 4 is less than the hydrogen content between the graphite ring 11 near the edge position and the wafer substrate 4.

[0108] As mentioned above, the thermal conductivity of hydrogen is much lower than that of graphite. During the heating process, since the hydrogen content between the graphite ring 11 and the wafer substrate 4 near the center is relatively low, the heating rate of the graphite ring 11 at this position to the wafer substrate 4 is relatively fast; while the hydrogen content between the graphite ring 11 and the wafer substrate 4 near the edge is relatively high, the heating rate of the graphite ring 11 at this position to the wafer substrate 4 is relatively slow. Thus, the temperature balance of the wafer substrate 4 at the center and the edge is achieved.

[0109] At the same time, the heat transfer efficiency of the graphite tray 1 as a whole gradually decreases from the center of the circle 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 finally 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 formed due to 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 of the circle toward the edge, and the diameter of the graphite tray 1 is 6 inches to 8 inches, the root mean square average value of the contour ordinate of the upper surface roughness of the outermost graphite ring 11 is 1μm-500μm; the root mean square average value of the contour ordinate of the upper surface roughness of the innermost graphite ring 11 is 100nm-500nm; the root mean square average value of the contour ordinate of the upper surface roughness of the graphite ring 11 between the innermost graphite ring 11 and the outermost graphite ring 11 is 0.1μm-100μm.

[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 contour of the upper surface roughness is in 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 contour of the upper surface roughness is in the order of μm; for the graphite ring 11 with a diameter between the maximum and minimum values, the upper surface roughness is adjusted by means of fine grinding and rough polishing by adjusting the coarseness of the abrasive, and the typical value of the upper surface roughness is 0.1μm-100μm. Finally, the upper surface roughness of the entire graphite tray 1 formed by the concentric nesting of each graphite ring 11 is gradually increased from the center position to the edge position, so that the heat transfer efficiency of the graphite ring 11 to the wafer substrate 4 gradually decreases from the center position to the edge position, achieving a uniform temperature field effect of the wafer substrate 4.

[0113] The following is an example 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 in 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 sleeved on the outer circumference 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 The cross-sectional view of the limiting graphite ring is shown. The limiting graphite ring 12 has a groove structure, and the limiting graphite ring 12 is fixed to the outer periphery of the graphite ring 11 through the groove structure. When the wafer substrate 4 is placed on the graphite tray 1, the inner side wall of the extending portion of the limiting graphite tray that is higher than the graphite ring 11 is attached to the side wall of the wafer substrate 4, thereby fixing 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 The structure shown, that is, 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, and 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. When performing the epitaxial process, the inner side wall of the limiting graphite ring 12 that is higher than the graphite ring 11 is in close contact with the side wall 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 at different ambient temperatures. The following takes the example that the temperature at the center of the wafer substrate 4 is higher than the temperature at the edge as an example to illustrate: In some embodiments, the difference between the inner and outer diameters of each graphite ring 11 remains consistent. At this time, the overall surface roughness change rate of the graphite tray 1 is uniform, and the thermal conductivity change rate at each position on the wafer substrate 4 is uniform;

[0119] In some embodiments, 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. At this time, the change rate of the upper surface roughness at the center of the graphite tray 1 as a whole is greater than the change rate of the upper surface roughness at the edge, so that the heat transfer efficiency at the center is rapidly reduced, effectively improving the problem that the temperature at the center is higher than that at the edge.

[0120] In some embodiments, 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. 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, and the temperature field uniformity at the edge position is effectively balanced.

[0121] In the actual production process, the difference between the inner and outer diameters of the graphite ring 11 can also 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, 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, which effectively improves 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, and the temperature field uniformity at the edge position is effectively balanced.

[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 disk 13 .

[0124] See also Figure 3 and Figure 4 A graphite disc 13 is arranged at the center of the graphite tray 1, and 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 the heating process, and prevents the uneven heat transfer problem on the back thereof.

[0125] In the third embodiment of the present application, Figure 8 and Fig. 9 As shown, Figure 8 A schematic diagram of the structure of a graphite tray provided in the third embodiment of the present application; Fig. 9 for Figure 8 The cross-sectional view of the graphite tray is shown in FIG. 1. In this embodiment, the center of the graphite tray 1 is a hollow area 112.

[0126] See also Figure 8 and Fig. 9 At this time, the center of the graphite tray 1 is a hollow area 112. On the one hand, the hollow area 112 provides a space for the innermost graphite ring to release the deformation caused by heat, preventing the graphite tray 1 from being damaged or deformed due to 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 implementations 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 Fig. 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 breakage problem 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 is in the range of 10 μm (micrometer) 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-100 μm, which can avoid deformation and breakage of the graphite rings 11 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 uniformly set; 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 of 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. Fig.10 As shown, Fig.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 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 position; or the roughness of the upper surface of the graphite substrate gradually increases from the center of the circle toward the edge position;

[0137] S103, roughly grinding or polishing the lower surface of the graphite substrate to keep the thickness of the graphite substrate uniform, so as to form 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 in contact 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 process, the hydrogen content in the typical ambient gas is 99%. At this time, the hydrogen content between the position with greater surface roughness on the graphite tray 1 and the wafer substrate 4 is relatively high, while the hydrogen content between the position with less surface roughness on the graphite tray 1 and the wafer substrate 4 is relatively low. 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 position with greater surface roughness on the graphite tray is lower than the heat transfer efficiency between the two at the position with less surface roughness on the graphite tray, thereby achieving temperature balance between the center position and the edge position of the wafer substrate 4.

[0141] Specifically, since the theoretical thermal conductivity of hydrogen is 0.1805 W / mK (watt / (meter·Kelvin)), which is much lower than the thermal conductivity of graphite 129 W / m·K, the heat transfer efficiency at the position with more hydrogen content between the graphite tray 1 and the wafer substrate 4 is lower than the heat transfer efficiency at the position with less hydrogen content between the graphite tray 1 and the wafer substrate 4, that is, when the graphite tray 1 whose upper surface roughness gradually decreases from the center of the circle to the edge position is used, the heat transfer efficiency at the position near the center of the circle between the graphite tray 1 and the wafer substrate 4 is lower than the heat transfer efficiency at the position near the edge between the two; when the graphite tray 1 whose surface roughness gradually increases from the center of the circle to the edge position is used, the heat transfer efficiency at the position near the center of the circle between the graphite tray 1 and the wafer substrate 4 is higher than the heat transfer efficiency at the position near the edge between the two. The uniform thickness of the graphite tray 1 avoids the introduction of excessive hydrogen due to the height difference between the graphite tray 1 and the wafer substrate 4, and ensures the overall heat transfer efficiency of the graphite tray 1. Therefore, during the heat transfer process, the temperature balance between the center position and the edge position of the graphite tray 1 is achieved.

[0142] This embodiment achieves 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 along the diameter direction during the epitaxial process, ultimately achieving improvement of the deposition temperature field distribution within the surface of the wafer substrate 4.

[0143] In addition, the lower surface of the graphite substrate is roughened so that the thickness of each position of the graphite substrate is uniformly set. Therefore, during the heat transfer process, the temperature balance between the center position and the edge position of the graphite tray 1 is achieved.

[0144] In the prior art, the doping concentration distribution of the formed epitaxial wafer is uneven due to the uneven temperature field of the wafer substrate 4. 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 formed epitaxial wafer, improving the warpage of the epitaxial wafer formed due to thermal stress, and reducing the bending degree (BOW) value of the epitaxial wafer formed. BOW is usually used to describe the bending degree of the wafer caused by stress or other factors during the processing process; it can also reduce the paired basal plane dislocation (BPD) caused by thermal stress.

[0145] In some implementations of the present application, such as Fig.11 As shown, Fig.11 This is a flow chart for preparing the graphite tray of the second embodiment of the present application. When preparing the graphite tray 1 in the second embodiment, in S102, the upper surface roughness treatment is performed 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 position; or, before the upper surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge position, it also includes:

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

[0147] In this way, when a graphite tray 1 whose surface roughness gradually decreases from the center of the circle toward the edge position is used, step S102 performs 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 position, which may include: performing roughness 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 position; and, among two adjacent graphite rings 11, 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 the other graphite ring 11 away from the center of the circle.

[0148] Or, 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 close to the center of the circle is greater than the upper surface roughness of the other graphite ring 11 away from the center of the circle.

[0149] When a graphite tray 1 whose surface roughness gradually increases from the center of the circle toward the edge position is used, step S102 performs upper surface roughness treatment on the graphite substrate so that the upper surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge position, and may also include: performing roughness 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 position; and, among two adjacent graphite rings 11, the maximum value of the upper surface roughness of the graphite ring 11 close to the center of the circle is less than the minimum value of the upper surface roughness of the other graphite ring 11 away 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 close to the center is smaller than the upper surface roughness of the other graphite ring 11 far 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 implementations of the present application, the lower surface of the graphite substrate is roughly ground or polished to keep the thickness of the graphite substrate uniform, 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 kept 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 kept uniform.

[0153] The lower surface of the graphite ring 11 is subjected to roughness treatment. When the lower surface roughness of each graphite ring 11 needs to be kept consistent, the graphite rings are assembled before the lower surface roughness treatment. The assembly method is to concentrically nest the graphite rings 11 with specific upper surface roughness one by one according to the diameter. Then the assembled graphite tray 1 is subjected to lower surface roughness treatment, that is, rough grinding or polishing, so that the thickness H at each position of the graphite substrate is uniformly set, and the lower surface of each graphite ring 11 is ensured to have the same roughness. The technical effect achieved is the same as that in the aforementioned embodiment, and will not be repeated here.

[0154] like Fig.11 As shown, in this embodiment, after the lower surface of the graphite substrate is roughly ground or polished in step S103, the method further includes:

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

[0156] S106, 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 extending portion is used to fix the wafer.

[0157] In this embodiment, the graphite ring 11 after the roughness treatment is ultrasonically cleaned and pickled with hydrochloric acid to remove the metal residue 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 fits against the side wall of the wafer substrate 4 to fix the wafer substrate 4.

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

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

[0161] like Fig.12 As shown, the epitaxial device also has: an upper half-moon graphite piece 22, a lower half-moon graphite piece 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, and a graphite tray placement platform 26 is provided in the tray groove 251. 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 drive the graphite tray 1 placed thereon to rotate along the center of the graphite tray 1. In addition, the area between the upper graphite cover plate 24 and the lower graphite cover plate 25 forms a reaction space 100. The epitaxial device also has: an injection door 27, a tail exhaust door 28, and an airflow channel 29. An upstream graphite piece 30 is provided on the outer side of the graphite tray 1 close to the injection door 27, and a downstream graphite piece 31 is provided on the outer side of the graphite tray 1 close to the tail exhaust door 28. The height of the upstream graphite piece 30 is higher than the height of the downstream graphite piece 31.

[0162] In the epitaxial growth device of this embodiment, before chemical vapor deposition, the quartz cylinder 2 is filled with ambient gas hydrogen. When the quartz cylinder 2 is filled with ambient gas, the reaction gas is input into the quartz cylinder 2. When a wafer is formed with silicon-containing material, the reaction gas can be a silicon-containing reaction gas; when a wafer with gallium nitride or gallium arsenide as the material needs to be formed, the reaction gas can also be a silicon-free reaction gas, and the internal space of the quartz cylinder 2 is heated by the heating device 21 located above and below the quartz cylinder 2. The heat is transferred from the heating device 21 to the upper half-moon graphite piece 22 and the lower half-moon graphite piece 23. The upper half-moon graphite piece 22 and the lower half-moon graphite piece 23 transfer the heat to the reaction space 100 formed between the upper graphite cover plate 24 and the lower graphite cover plate 25. The ambient gas is heated, and the reaction gas is continuously heated during the flow process. The wafer substrate 4 placed on the upper surface of the graphite tray is heated by the reaction gas, the ambient gas and the graphite tray 1 together. 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 (degrees Celsius) - 1700°C.

[0163] For details, see Fig.12 The reaction gas enters the quartz cylinder 2 through the injection door 27, and the reaction gas 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. There is an expansion gap 111 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 heat expansion and inability to release deformation.

[0164] The reaction gas flows in the accommodation space through the upstream graphite member 30 toward the wafer substrate 4 located on the upper surface of the graphite tray 1. Fig.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 to make the reaction gas more uniform.

[0165] When the reaction gas passes through the surface of the wafer substrate 4, the reaction gas reacts with hydrogen under the action of high temperature, and the reactants are deposited on the upper surface of the wafer substrate 4, forming a wafer epitaxial sheet on the upper surface of the wafer substrate 4. In 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, and 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, and 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, the graphite tray 1 heats the wafer substrate 4. Since 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 gradually increases from the center of the circle toward the edge, the heat transfer efficiency at the position with more hydrogen content on the graphite tray 1 is lower than the heat transfer efficiency at the position with less hydrogen content on the graphite tray 1, that is, the heat transfer efficiency at the position near the center of the circle between the graphite tray 1 and the wafer substrate 4 is lower than the heat transfer efficiency at the position near the edge between the two, or the heat transfer efficiency at the position near the center of the circle between the graphite tray 1 and the wafer substrate 4 is higher than the heat transfer efficiency at the position near the edge between the two. The uniform thickness H of the graphite tray 1 avoids the introduction of excessive hydrogen due to the height difference between the graphite tray 1 and the wafer substrate 4, and ensures the overall heat transfer efficiency of the 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 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 tube 2 through the injection door 27 by a clamp.

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

[0170] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial 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 protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A graphite tray, characterized in that: The graphite tray (1) is circular and has a uniform thickness; The roughness of the upper surface of the graphite tray (1) gradually decreases from the center of the circle toward the edge; Alternatively, the surface roughness of the graphite tray (1) gradually increases from the center of the circle toward the edge.

2. The graphite tray according to claim 1, characterized in that: 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); 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 as it moves away from the center of the circle 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 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 roughness of the same graphite ring (11) is the same; and 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.

4. The graphite tray according to claim 3, characterized in that: The root mean square average value of the profile ordinate of the upper surface roughness of the innermost 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 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) between the innermost graphite ring (11) and the outermost graphite ring (11) is 0.1 μm-100 μm.

5. 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; and of 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.

6. The graphite tray according to claim 5, characterized in that: 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) between the innermost graphite ring (11) and the outermost graphite ring (11) is 0.1 μm-100 μm.

7. 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 towards the center of the circle, and the inner side wall of the extending portion is used to fix the wafer substrate (4).

8. 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.

9. 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 the hollow area (112).

10. 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) 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.

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

12. The graphite tray according to any one of claims 1 to 11, 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 of a corresponding position on the upper surface.

13. A method for preparing a graphite tray, characterized in that: Providing a circular graphite substrate; 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 the surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge; The lower surface of the graphite substrate is roughly ground or polished to keep the thickness of the graphite substrate uniform, so as to form a graphite tray.

14. The preparation method according to claim 13, characterized in that: Before the upper surface roughness treatment is performed 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 position; or the upper surface roughness of the graphite substrate gradually increases from the center of the circle toward the edge position, 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).

15. The preparation method according to claim 13, characterized in that: The step of performing a 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, comprises: The upper surface of each of the graphite rings (11) is subjected to roughening treatment so that the upper surface roughness of each graphite ring (11) gradually decreases 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; or, The upper surface of each of the graphite rings (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 of the circle is greater than the upper surface roughness of the other graphite ring (11) farther from the center of the circle.

16. The preparation method according to claim 13, characterized in that: The step of performing a 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, comprises: The upper surface of each of the graphite rings (11) is subjected to roughening 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 of the graphite rings (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 of the circle is smaller than the upper surface roughness of the other graphite ring (11) farther from the center of the circle.

17. The preparation method according to claim 13, characterized in that: The step of roughly grinding or polishing the lower surface of the graphite substrate to keep the thickness of the graphite substrate uniform 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.

18. The preparation method according to claim 17, 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 extended portion is used to fix the wafer.

19. An epitaxial growth device, characterized in that: include: Quartz tube (2); Heating devices (21) are provided above and below the quartz cylinder (2); The quartz cylinder (2) is provided with a reaction space (100) inside which reaction gas and ambient gas can be introduced; A rotatable graphite tray placement platform (26) is provided in the reaction space (100); The graphite tray placement platform (26) is placed with the graphite tray (1) according to any one of claims 1 to 12.

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