SOI wafer and method for manufacturing same

Abstract

The present invention provides an SOI wafer and a manufacturing method thereof, by performing a thermal oxidation process, forming a buried oxide layer on the front surface of a support substrate and / or the front surface of a device substrate, and forming an oxide layer of a first thickness on the back surface of the support substrate, after a bonding process, performing a reinforcement heat treatment process to solidify the SOI wafer, and then performing a mechanical grinding process. The thickness difference between the buried oxide layer between the supporting substrate and the device substrate and the oxide layer on the back face of the supporting substrate and / or the grinding stress in the mechanical grinding process is adjusted so that the bending degree of the SOI wafer can meet a preset value. According to the invention, the thickness difference between the back oxide layer of the supporting substrate in the SOI wafer and the buried oxide layer between the supporting substrate and the device substrate is adjusted, and the grinding stress in the mechanical grinding process is matched, so that the bending degree of the SOI wafer meets the preset value, the overall bending degree of the SOI wafer is reduced, and the yield of the SOI wafer is improved. And the SOI wafer in the subsequent double-sided chemical mechanical polishing process is more uniform and controllable.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to an SOI wafer and a method for manufacturing the same. Background Art

[0002] Silicon on insulator (SOI) technology has become one of the mainstream products in most electronic materials fields. The core feature of this special silicon-based semiconductor manufacturing technology is to form a thin top layer of silicon on the insulator. This structure makes SOI devices perform well in many aspects, such as low power consumption, radiation resistance, and high speed. As the integration of automotive-grade SOI material on-board chips becomes higher and higher, the high uniformity of the top silicon thickness becomes particularly important.

[0003] BESOI (Bond and Etch-back SOI) technology mainly manufactures SOI wafers by bonding and thinning. First, two silicon wafers are bonded together, and then the top silicon is obtained by back thinning to form an SOI wafer. The control of the thickness and uniformity of the top silicon film is the core key technology of BESOI. The uneven thickness of the top silicon of the SOI wafer will lead to unstable device performance, inconsistent current density of local electron channels, uneven thermal effects and even line width changes.

[0004] Mechanical grinding is one of the main processes in SOI wafer manufacturing. Its main function is to thin the back of the SOI wafer device substrate to a certain thickness. Because the main grinding wheel material for mechanical grinding is diamond, the wafer will deform and the curvature will change under pure mechanical action. At the same time, a damaged layer will be produced on the back of a thick wafer after mechanical grinding.

[0005] If the curvature of the SOI wafer after the mechanical grinding process is too large, the contact area and contact pressure between the SOI wafer and the polishing pad will change during the double-sided chemical mechanical polishing process, resulting in uneven polishing. This uneven polishing effect will further aggravate the curvature of the SOI wafer, which in turn makes the uniformity of the SOI wafer in the double-sided chemical mechanical polishing uncontrollable. Summary of the invention

[0006] The object of the present invention is to provide an SOI wafer and a method for manufacturing the same, so as to solve the problem that the SOI wafer has a large curvature after a mechanical grinding process, resulting in uncontrollable uniformity in a double-sided chemical mechanical polishing process.

[0007] In order to solve the above technical problems, the present invention provides a method for manufacturing an SOI wafer, comprising:

[0008] Providing a support substrate and a device substrate, wherein the support substrate includes a front side and a back side that are opposite to each other, and the device substrate includes a front side and a back side that are opposite to each other;

[0009] Performing a thermal oxidation process to form a buried oxide layer on the front side of the support substrate and / or the front side of the device substrate, and forming an oxide layer of a first thickness on the back side of the support substrate;

[0010] Performing a bonding process to bond the front side of the support substrate and the front side of the device substrate, wherein the buried oxide layer is located between the support substrate and the device substrate, so as to form an SOI wafer;

[0011] Performing a strengthening heat treatment process to solidify the SOI wafer;

[0012] Performing a mechanical grinding process to reduce the thickness of the back side of the device substrate of the SOI wafer;

[0013] The thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back of the support substrate and / or the grinding stress in the mechanical grinding process are adjusted so that the curvature of the SOI wafer meets a preset value.

[0014] Optionally, a preset value of the curvature of the SOI wafer after the mechanical grinding process is less than 50 μm.

[0015] Optionally, an oxidation process is used to adjust the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back side of the support substrate, and the oxidation process is located before the bonding process or after the bonding process.

[0016] Optionally, when the oxidation process is before the bonding process, the oxidation process is the thermal oxidation process; when the oxidation process is after the bonding process, the oxidation process is performed separately or integrated into the reinforcement heat treatment process.

[0017] Optionally, the process gas of the reinforcement heat treatment process includes at least one of oxygen, a mixed gas of oxygen and hydrogen, and an inert gas.

[0018] Optionally, when the oxidation process is integrated into the reinforcement heat treatment process, the process gas of the reinforcement heat treatment process includes at least one of oxygen and a mixed gas of oxygen and hydrogen. In the reinforcement heat treatment process, the oxide layer on the back side of the supporting substrate is increased to a second thickness, and the thickness of the oxide layer on the back side of the supporting substrate is greater than the thickness of the buried oxide layer between the supporting substrate and the device substrate. The difference in thickness between the oxide layer on the back side of the supporting substrate and the buried oxide layer between the supporting substrate and the device substrate is adjusted so that the curvature of the SOI wafer meets a preset value.

[0019] Optionally, the reinforcement heat treatment process includes a first reinforcement temperature and a second reinforcement temperature, wherein the first reinforcement temperature is used to increase the oxide layer on the back side of the supporting substrate to a second thickness, and the first reinforcement temperature is, for example, 800°C to 1000°C, and the second reinforcement temperature is used to increase the bonding force of the SOI wafer, and the second reinforcement temperature is 1100°C to 1250°C.

[0020] Optionally, when the process gas of the reinforcement heat treatment process includes an inert gas, the oxide layer on the back side of the supporting substrate remains unchanged during the reinforcement heat treatment process, and the grinding stress in the mechanical grinding process is adjusted so that the curvature of the SOI wafer meets a preset value.

[0021] Optionally, the strengthening temperature of the strengthening heat treatment process is 1100°C to 1250°C.

[0022] Optionally, the mechanical grinding process includes a fine grinding process, and the grinding stress in the fine grinding process is achieved by adjusting the mesh number of a fine grinding wheel, and the mesh number of the fine grinding wheel is greater than or equal to 1000 meshes.

[0023] Optionally, the thickness of the back side of the device substrate removed by the fine grinding process is greater than 10 μm.

[0024] Based on the same inventive concept, the present invention also provides an SOI wafer, which is manufactured using any of the above-mentioned SOI wafer manufacturing methods, and includes an oxide layer, a supporting substrate, a buried oxide layer and a device substrate stacked in sequence from bottom to top; the curvature of the SOI wafer is less than 50μm.

[0025] In the manufacturing method of the SOI wafer provided by the present invention, a buried oxide layer is formed on the front side of the support substrate and / or the front side of the device substrate by performing a thermal oxidation process, and an oxide layer of a first thickness is formed on the back side of the support substrate. After the bonding process, a reinforcement heat treatment process is performed to solidify the SOI wafer, and then a mechanical grinding process is performed to thin the thickness of the SOI wafer, wherein the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back side of the support substrate and / or the grinding stress in the mechanical grinding process are adjusted so that the curvature of the SOI wafer meets a preset value. The present invention adjusts the thickness difference between the oxide layer on the back side of the support substrate and the buried oxide layer between the support substrate and the device substrate in the SOI wafer, matches the grinding stress in the mechanical grinding process, so that the curvature of the SOI wafer meets the preset value, reduces the overall curvature of the SOI wafer, and makes the SOI wafer in the subsequent double-sided chemical mechanical polishing process more uniform and controllable. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Those skilled in the art will appreciate that the accompanying drawings are provided for a better understanding of the present invention and do not constitute any limitation on the scope of the present invention.

[0027] Figure 1 It is a schematic diagram of SOI wafer bending caused by damage caused by the mechanical grinding process in which the thickness of the back oxide layer of the supporting substrate in the SOI wafer of the prior art is less than or equal to the buried oxide layer.

[0028] Figure 2 It is a flow chart of a method for manufacturing an SOI wafer according to an embodiment of the present invention.

[0029] Figures 3 to 8 It is a schematic structural diagram corresponding to the steps of the method for manufacturing an SOI wafer according to an embodiment of the present invention.

[0030] Fig. 9 1 is a graph showing the relationship between the thickness difference between the back oxide layer and the buried oxide layer of the support substrate and the curvature of the SOI wafer according to an embodiment of the present invention.

[0031] Fig.10 This is a graph showing the relationship between the grinding wheel grit of 20 μm and the curvature of the SOI wafer according to an embodiment of the present invention.

[0032] In the attached figure:

[0033] 10-support substrate; 10a-front side of support substrate; 10b-back side of support substrate; 11-first buried oxide layer; 12-oxide layer; 20-device substrate; 20a-front side of device substrate; 20b-back side of device substrate; 21-second buried oxide layer; 22-damage layer; 30-buried oxide layer. DETAILED DESCRIPTION

[0034] In order to make the purpose, advantages and features of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the drawings is often a part of the actual structure. In particular, the emphasis of each drawing is different, and sometimes different scales are used.

[0035] As used in the present invention, the singular forms "one", "an" and "the" include plural objects, the term "or" is usually used to include the meaning of "and / or", the term "several" is usually used to include the meaning of "at least one", and the term "at least two" is usually used to include the meaning of "two or more". In addition, the terms "first", "second" and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first", "second" and "third" can explicitly or implicitly include one or at least two of the features. In addition, as used in the present invention, an element is arranged on another element, which usually only indicates that there is a connection, coupling, matching or transmission relationship between the two elements, and the connection, coupling, matching or transmission between the two elements can be direct or indirect through an intermediate element, and cannot be understood as indicating or implying the spatial position relationship between the two elements, that is, an element can be in any orientation such as inside, outside, above, below or on one side of another element, unless the content clearly indicates otherwise. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] The inventors have found that the double-sided chemical mechanical polishing process is a combination of polishing liquid and mechanical action, which mainly removes the damaged layer formed by the mechanical grinding process and improves the uniformity and roughness of the SOI wafer. In the double-sided chemical mechanical polishing process, the SOI wafer needs to be fixed on the polishing machine, and the surface is flattened by the combined action of the polishing pad and the polishing liquid. If the curvature of the SOI wafer is too large, the contact area and contact pressure between the SOI wafer and the polishing pad will change during the double-sided chemical mechanical polishing process, resulting in uneven polishing effect. Specifically, when polishing an SOI wafer with a large curvature, its raised part may be subjected to greater pressure, thereby being over-polished; while the concave part may be subjected to less pressure and under-polished. This uneven polishing effect will further aggravate the curvature of the SOI wafer, forming a vicious circle. How to control the curvature of the SOI wafer before polishing is a difficult point.

[0037] Figure 1 The figure is a schematic diagram of SOI wafer bending caused by the damage of the back oxide layer of the supporting substrate in the prior art being less than or equal to the buried oxide layer and superimposed by the mechanical grinding process. Figure 1As shown, when the thickness of the back oxide layer 12 of the supporting substrate 10 in the SOI wafer is less than or equal to the buried oxide layer 30 between the supporting substrate 10 and the device substrate 20, the SOI wafer will bend. And the damage layer 22 caused by the mechanical stress in the mechanical grinding process will also cause the SOI wafer to bend. The curvature of the wafer refers to the radius of curvature of the wafer surface, which is usually used to describe the curvature of the wafer in a plane. The magnitude of the curvature can directly affect the distribution of the force on the wafer, thereby affecting the stability of the wafer during the processing and the quality of the finished product. Generally speaking, the smaller the curvature of the wafer, the smoother the wafer surface, which is conducive to the subsequent process.

[0038] Therefore, the core idea of ​​the present invention is to form a buried oxide layer on the front side of the support substrate and / or the front side of the device substrate by performing a thermal oxidation process, and to form an oxide layer of a first thickness on the back side of the support substrate, and after the bonding process, to perform a reinforcement heat treatment process to solidify the SOI wafer, and then to perform a mechanical grinding process to thin the thickness of the SOI wafer, wherein the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back side of the support substrate and / or the grinding stress in the mechanical grinding process are adjusted so that the curvature of the SOI wafer meets a preset value. The present invention adjusts the thickness difference between the oxide layer on the back side of the support substrate and the buried oxide layer between the support substrate and the device substrate in the SOI wafer, and matches the grinding stress in the mechanical grinding process so that the curvature of the SOI wafer meets a preset value, thereby reducing the overall curvature of the SOI wafer and making the SOI wafer in the subsequent double-sided chemical mechanical polishing process more uniform and controllable.

[0039] Specifically, Figure 2 FIG. 1 is a flow chart of a method for manufacturing an SOI wafer according to an embodiment of the present invention. Figure 2 As shown, this embodiment provides a method for manufacturing an SOI wafer, comprising:

[0040] Step S10, providing a support substrate and a device substrate, wherein the support substrate includes a front side and a back side that are oppositely disposed, and the device substrate includes a front side and a back side that are oppositely disposed;

[0041] Step S20, performing a thermal oxidation process to form a buried oxide layer on the front side of the support substrate and / or the front side of the device substrate, and forming an oxide layer of a first thickness on the back side of the support substrate;

[0042] Step S30, performing a bonding process to bond the front side of the support substrate and the front side of the device substrate, wherein the buried oxide layer is located between the support substrate and the device substrate, so as to form an SOI wafer;

[0043] Step S40, performing a reinforcement heat treatment process to solidify the SOI wafer;

[0044] Step S50, performing a mechanical grinding process to thin the back side thickness of the device substrate of the SOI wafer; wherein, the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back side of the support substrate and / or the grinding stress in the mechanical grinding process are adjusted so that the curvature of the SOI wafer meets a preset value.

[0045] Specifically, an oxidation process is used to adjust the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back of the support substrate, and the oxidation process is located before the bonding process or after the bonding process. When the oxidation process is located before the bonding process, the oxidation process is the thermal oxidation process; when the oxidation process is located after the bonding process, the oxidation process is performed separately or integrated in the reinforcement heat treatment process.

[0046] Figures 3 to 8 1 is a schematic diagram of the structure corresponding to the steps of the method for manufacturing an SOI wafer according to an embodiment of the present invention. Figures 3 to 8 The specific embodiments of the present invention are described in detail.

[0047] like Figure 3 As shown, a support substrate 10 is provided, the support substrate 10 includes a front side 10a and a back side 10b of the support substrate which are arranged opposite to each other, and the support substrate 10 is used to support the device substrate 20 when the device substrate 20 is thinned. The diameter of the support substrate 10 is, for example, 200 mm or 300 mm.

[0048] like Figure 4 As shown, a device substrate 20 is provided, and the device substrate 20 includes a front side 20a of the device substrate and a back side 20b of the device substrate which are arranged opposite to each other. The diameter of the device substrate 20 is, for example, 200 mm or 300 mm. The device substrate 20 provides an operating platform for subsequent processes, and can be any substrate for carrying semiconductor integrated circuit components known to those skilled in the art, and can be a bare chip or a wafer processed by an epitaxial growth process. In detail, the substrate of the device substrate 20 is, for example, a silicon-on-insulator (SOI) substrate, a bulk silicon substrate, a germanium substrate, a germanium silicon substrate, an indium phosphide (InP) substrate, a gallium arsenide (GaAs) substrate, or a germanium-on-insulator substrate. In this embodiment, the device substrate 20 is a silicon substrate.

[0049] like Figure 3 and Figure 4As shown, a thermal oxidation process is performed to form a buried oxide layer on the support substrate 10 and / or the device substrate 20; specifically, the buried oxide layer can be formed by performing a thermal oxidation process only on one of the support substrate 10 or the device substrate 20, or by performing a thermal oxidation process on both of the support substrate 10 and the device substrate 20. A person skilled in the art can make a selection based on the thickness of the buried oxide layer. In this embodiment, a buried oxide layer is formed on both the front surface 10a of the support substrate and the front surface 20a of the device substrate, that is, a first buried oxide layer 11 is formed on the front surface 10a of the support substrate, and a second buried oxide layer 21 is formed on the front surface 20a of the device substrate. While the first buried oxide layer 11 is formed on the front surface 10a of the support substrate, an oxide layer 12 is formed on the back surface 10b of the support substrate. At this time, the thickness of the oxide layer 12 on the back surface 10b of the support substrate is the first thickness, and the thickness of the first buried oxide layer 11 on the front surface 10a of the support substrate and the oxide layer 12 on the back surface 10b of the support substrate are the same. When the oxidation process for adjusting the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back of the support substrate is located before the bonding process, the oxidation process is the thermal oxidation process. The thermal oxidation process forms different thickness differences by forming buried oxide layers of different thicknesses on the device substrate and the support substrate. For example, when the first buried oxide layer 11 and the oxide layer 12 are 0.8μm, and the second buried oxide layer 21 is 0.2μm, the buried oxide layer is 1um, and the difference between the oxide layer 12 and the buried oxide layer is -0.2μm. For example, when the first buried oxide layer 11 and the oxide layer 12 are 0.9μm, and the second buried oxide layer 21 is 0.1μm, the buried oxide layer is 1um, and the difference between the oxide layer 12 and the buried oxide layer is -0.1μm. For example, when the first buried oxide layer 11 and the oxide layer 12 are 1μm, and the second buried oxide layer 21 is 0μm, the buried oxide layer is 1um, and the difference between the oxide layer 12 and the buried oxide layer is 0μm.

[0050] like Figure 5 As shown, a bonding process is performed to bond the front side 10a of the support substrate and the front side 20a of the device substrate, and the buried oxide layer is located between the support substrate 10 and the device substrate 20, so as to form an SOI wafer. That is, the first buried oxide layer 11 and the second buried oxide layer 21 are located between the support substrate 10 and the device substrate 20. In other words, the first buried oxide layer 11 and the second buried oxide layer 21 are in contact and bonded.

[0051] After the bonding process of forming the SOI wafer, a strengthening heat treatment process is performed to solidify the SOI wafer. The process gas of the strengthening heat treatment process includes at least one of oxygen, a mixed gas of oxygen and hydrogen, and an inert gas.

[0052] When the oxidation process is after the bonding process, the oxidation process is performed separately or integrated in the reinforcement heat treatment process. The oxidation process can be performed separately before or after the reinforcement heat treatment process. When the oxidation process is performed separately, the thickness of the oxide layer on the back of the support substrate of the SOI wafer can be obtained according to the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back of the support substrate.

[0053] like Figure 6 As shown, in some embodiments, when the oxidation process is integrated into the reinforcement heat treatment process, the process gas of the reinforcement heat treatment process includes at least one of oxygen and a mixed gas of oxygen and hydrogen. Then, in the reinforcement heat treatment process, the oxide layer 12 on the back side 10b of the supporting substrate is increased to a second thickness, and the thickness of the oxide layer 12 on the back side 10b of the supporting substrate is greater than the thickness of the buried oxide layer between the supporting substrate 10 and the device substrate 20. The difference in thickness between the oxide layer 12 on the back side 10b of the supporting substrate and the buried oxide layer between the supporting substrate 10 and the device substrate 20 is adjusted so that the curvature of the SOI wafer meets a preset value. That is, when the thickness of the oxide layer 12 on the back side 10b of the supporting substrate is less than or equal to the thickness of the buried oxide layer between the supporting substrate 10 and the device substrate 20, the curvature of the SOI wafer is increased. Conversely, when the thickness of the oxide layer 12 on the back side 10b of the supporting substrate is greater than the thickness of the buried oxide layer between the supporting substrate 10 and the device substrate 20, the curvature of the SOI wafer is reduced. Therefore, this embodiment increases the difference in thickness between the oxide layer 12 on the back side 10b of the supporting substrate and the buried oxide layer between the supporting substrate 10 and the device substrate 20 so that the curvature of the SOI wafer meets a preset value. The preset value of the curvature of the SOI wafer is less than 50μm. More preferably, the preset value of the curvature of the SOI wafer is less than 40μm. The reinforcement heat treatment process includes a first reinforcement process and a second reinforcement process, that is, a first reinforcement temperature and a second reinforcement temperature. The first reinforcement process is used to increase the oxide layer 12 on the back side 10b of the support substrate to a second thickness, and the first reinforcement temperature is, for example, 800° C. to 1000° C. The second reinforcement process is used to improve the bonding force of the SOI wafer, and the second reinforcement temperature is 1100° C. to 1250° C. It is worth emphasizing that those skilled in the art can also increase the oxide layer 12 on the back side 10b of the support substrate to a second thickness by increasing the process time of the first reinforcement process.

[0054] like Figure 5As shown, in another embodiment, when the process gas of the reinforcement heat treatment process includes an inert gas, such as Ar, N2 or He, the oxide layer 12 on the back side 10b of the support substrate remains unchanged during the reinforcement heat treatment process, and the grinding stress in the mechanical grinding process is adjusted so that the curvature of the SOI wafer meets the preset value. Since the oxide layer 12 on the back side 10b of the support substrate in this embodiment remains unchanged, there is no need for a low-temperature process for growing an oxide layer. In this embodiment, there is only a temperature for increasing the bonding force of the SOI wafer, and the reinforcement temperature of the reinforcement heat treatment process is, for example, 1100°C to 1250°C.

[0055] like Figure 7 and Figure 8 As shown, a mechanical grinding process is performed to reduce the thickness of the back side 20b of the device substrate of the SOI wafer; wherein the thickness difference between the buried oxide layer between the support substrate 10 and the device substrate 20 and the oxide layer 12 on the back side 10b of the support substrate and / or the grinding stress in the mechanical grinding process are adjusted so that the curvature of the SOI wafer meets a preset value. The preset value of the curvature of the SOI wafer is less than 50μm, and more preferably, the preset value of the curvature of the SOI wafer is less than 40μm.

[0056] Specifically, Figure 7 As shown, the thickness of the oxide layer 12 on the back side 10b of the support substrate does not increase in the reinforcement heat treatment process. Therefore, it is necessary to adjust the grinding stress in the mechanical grinding process so that the curvature of the SOI wafer meets the preset value. The mechanical grinding process includes a rough grinding process and a fine grinding process, wherein the mesh number of the fine grinding wheel in the fine grinding process has a significant effect on the curvature of the SOI wafer. The grinding stress in the fine grinding process is achieved by adjusting the mesh number of the fine grinding wheel. Therefore, the mesh number of the fine grinding wheel in the fine grinding process is matched so that the curvature of the SOI wafer meets the preset value. The mesh number of the fine grinding wheel is greater than or equal to 1000 meshes. Preferably, the mesh number of the fine grinding wheel is, for example, 2000 mesh to 5000 meshes. The thickness of the back side of the device substrate removed by the fine grinding process is greater than 10μm. Preferably, the thickness of the back side of the device substrate removed by the fine grinding process is greater than 20μm. The mechanical grinding process thins the back side of the device substrate of the SOI wafer to a thickness of X.

[0057] like Figure 8As shown, the thickness of the oxide layer 12 on the back side 10b of the support substrate increases a second thickness in the reinforcement heat treatment process, and the curvature of the SOI wafer meets a preset value by increasing the thickness difference between the oxide layer 12 on the back side 10b of the support substrate and the buried oxide layer between the support substrate 10 and the device substrate 20. A mechanical grinding process is performed to thin the thickness of the back side 20b of the device substrate of the SOI wafer. In this embodiment, it is not necessary to adjust the grinding stress by adjusting the mesh count of the fine grinding wheel to adjust the curvature of the SOI wafer. Those skilled in the art may also simultaneously use two technical solutions: the thickness difference between the oxide layer 12 on the back side 10b of the support substrate and the buried oxide layer between the support substrate 10 and the device substrate 20 and adjusting the grinding stress of the mechanical grinding process to adjust the curvature of the SOI wafer.

[0058] After the mechanical grinding process, the SOI wafer is subjected to a double-sided chemical mechanical polishing process, and the double-sided chemical mechanical polishing process removal amount is set to Y, and XY is required to be greater than or equal to 10μm. The target thickness T of the device substrate of the SOI wafer after the double-sided chemical mechanical polishing process is XY. The thickness of the device substrate of the SOI wafer is calculated by the double-sided polishing machine laser test. If the thickness of the device substrate of the SOI wafer reaches XY, the machine polishing automatically stops. The uniformity of the SOI wafer after the double-sided chemical mechanical polishing process is less than 0.3μm.

[0059] like Figure 7 and Figure 8 As shown, this embodiment also provides an SOI wafer, which is manufactured by the SOI wafer manufacturing method described in any of the above items, and includes an oxide layer 12, a supporting substrate 10, a buried oxide layer and a device substrate 20 stacked in sequence from bottom to top; the curvature of the SOI wafer is less than 50μm, and more preferably, the preset value of the curvature of the SOI wafer is less than 40μm.

[0060] The inventors conducted experimental research and verification. In the first experimental group, an SOI wafer was provided, including a support substrate 10 (handle wafer) and a device substrate 20 (donor wafer), wherein the thickness of the first buried oxide layer 11 on the front side of the support substrate is 800nm, and the thickness of the second buried oxide layer 21 on the front side of the device substrate is 200nm, that is, the sum of the thicknesses of the first buried oxide layer 11 and the second buried oxide layer 21 is 1μm (the thickness of the second buried oxide layer 21 is 0.2μm, and the thickness of the first buried oxide layer 11 is 0.8μm), and the thickness of the oxide layer 12 on the back side 10b of the support substrate is 0.8μm. The SOI wafer is subjected to a reinforcement heat treatment process, which includes a first reinforcement process and a second reinforcement process. The process temperature of the first reinforcement process is 950°C, the atmosphere is a mixed gas of oxygen and hydrogen, and the process time of the first reinforcement process is 4 hours and 28 minutes. The process temperature of the second reinforcement process is 1200°C, the atmosphere is a mixed gas of oxygen and hydrogen, and the process time of the second reinforcement process is 2 hours. After the reinforcement heat treatment process, the thickness of the oxide layer 12 on the back side 10b of the supporting substrate is 1.4μm. That is, the thickness difference between the oxide layer 12 on the back side 10b of the supporting substrate and the sum of the thickness of the first buried oxide layer and the second buried oxide layer (that is, the thickness difference between the oxide layer 12 and the buried oxide layer) is 0.4μm. The SOI wafer is placed in an edge grinder with the front side facing up, the edge of the SOI wafer is processed, and the stress damage caused by grinding is eliminated by corrosion; mechanical grinding is performed using a grinding wheel, and coarse grinding and fine grinding can be used. The mesh number of the fine grinding wheel is 2000 mesh, and the removal amount of the back side of the device wafer in the fine grinding SOI wafer is 20μm, and the back side of the device wafer in the SOI wafer is thinned to a thickness of 15μm; double-sided chemical mechanical polishing is performed on the SOI wafer, and the carrier thickness is 790μm. The double-sided polishing removal amount is set to 3μm, and the thickness of the device wafer of the SOI wafer is calculated by the laser test of the double-sided polishing machine. After reaching the target thickness, the machine polishing automatically stops. The same process flow is set up for the second experimental group, the third experimental group, the first comparison group, the fourth experimental group, the fifth experimental group, the sixth experimental group, the second comparison group and the third comparison group. It is worth emphasizing that the reinforcement heat treatment process and mechanical grinding process in different experimental groups and different comparison groups are different, and different reinforcement heat treatment processes are used to obtain the required thickness difference between the oxide layer and the buried oxide layer. The thickness difference between the oxide layer and the buried oxide layer in the second experimental group is 0.4μm, and the mesh number of the fine grinding wheel is 5000 mesh. The thickness difference between the oxide layer and the buried oxide layer in the third experimental group is 0.4μm, and the mesh number of the fine grinding wheel is 8000 mesh. The thickness difference between the oxide layer and the buried oxide layer in the first comparative group is 0μm, and the mesh number of the fine grinding wheel is 2000 mesh. The thickness difference between the oxide layer and the buried oxide layer in the fourth experimental group is 0μm, and the mesh number of the fine grinding wheel is 5000 mesh. The thickness difference between the oxide layer and the buried oxide layer in the fifth experimental group is 0μm, and the mesh number of the fine grinding wheel is 8000 mesh.The thickness difference between the oxide layer and the buried oxide layer in the sixth experimental group is -0.4 μm, and the fine grinding wheel mesh is 8000 mesh. The thickness difference between the oxide layer and the buried oxide layer in the second comparative group is -0.4 μm, and the fine grinding wheel mesh is 5000 mesh. The thickness difference between the oxide layer and the buried oxide layer in the third comparative group is -0.4 μm, and the fine grinding wheel mesh is 2000 mesh.

[0061] Table 1 The influence of the thickness difference between the oxide layer and the buried oxide layer and the grinding wheel number on the uniformity of SOI wafer

[0062] Group Ox3-Ox1 Grinding wheel mesh Wafer bow TTV Experimental Group 1 0.4μm 2000 46.8 0.3μm Experimental Group 2 0.4μm 5000 12.8 0.2μm Experimental Group 3 0.4μm 8000 -21.2 0.2μm Comparison group 1 0μm 2000 82 0.7μm Experimental Group 4 0μm 5000 48 0.3μm Experimental Group 5 0μm 8000 14 0.2μm Experimental Group 6 -0.4μm 8000 44.4 0.3μm Comparison group 2 -0.4μm 5000 78.4 0.6μm Comparison group 3 -0.4μm 2000 112.4 1.1μm

[0063] Fig. 9 1 is a graph showing the relationship between the thickness difference between the back oxide layer and the buried oxide layer of the support substrate and the curvature of the SOI wafer according to an embodiment of the present invention. Fig.10 This is a graph showing the relationship between the grinding wheel grit of 20 μm and the curvature of the SOI wafer according to an embodiment of the present invention. Fig. 9 In the figure, the horizontal axis is the thickness difference between the oxide layer and the buried oxide layer, in micrometers (μm), and the vertical axis is the curvature (Bow), in micrometers (μm). Fig.10 In the figure, the horizontal axis is the number of fine grinding wheels, in mesh. The vertical axis is the curvature, in micrometers (μm). Fig. 9 and Fig.10As shown, as the thickness difference between the back oxide layer 12 and the buried oxide layer of the supporting substrate increases, the curvature of the SOI wafer decreases. As the number of fine grinding wheels increases, the curvature of the SOI wafer decreases. Table 1 shows the effect of the thickness difference between the oxide layer and the buried oxide layer and the number of fine grinding wheels on the uniformity of the SOI wafer. In Table 1, Ox3 is the thickness of the back oxide layer 12 of the supporting substrate, and Ox1 is the thickness of the buried oxide layer between the device substrate and the supporting substrate. As shown in Table 1, the thickness difference between the oxide layer and the buried oxide layer of the SOI wafers in the first experimental group, the second experimental group, and the third experimental group is 0.4μm. As the number of fine grinding wheels increases, the curvature of the SOI wafer decreases successively and is less than 50μm, and then the TTV (Total Thickness Variation) after the double-sided chemical mechanical polishing process is less than or equal to 0.3μm. That is, when the thickness difference between the oxide layer and the buried oxide layer of the SOI wafer is large, even if the number of fine grinding wheels is small, the curvature of the SOI wafer can meet the preset value, that is, the curvature of the SOI wafer can meet the preset value only by adjusting the thickness difference between the oxide layer and the buried oxide layer of the SOI wafer. In the comparison group 1, the fourth experimental group and the fifth experimental group, the thickness difference between the oxide layer and the buried oxide layer of the SOI wafer is 0. As the number of fine grinding wheels increases, the curvature of the SOI wafer decreases successively. The curvature of the SOI wafer in the comparison group 1 is greater than 50μm, and the curvature of the SOI wafer in the fourth experimental group and the fifth experimental group is less than 50μm. It can be seen that when the thickness difference between the oxide layer and the buried oxide layer of the SOI wafer is 0, the curvature of the SOI wafer can be met by increasing the number of fine grinding wheels, that is, the curvature of the SOI wafer can be met by adjusting the number of fine grinding wheels. The thickness difference between the oxide layer and the buried oxide layer in the sixth experimental group is -0.4μm, but the fine grinding wheel number is high, the curvature of the SOI wafer is less than 50μm, and the TTV after the double-sided chemical mechanical polishing process is less than or equal to 0.3μm. It can be seen that when the thickness difference between the oxide layer and the buried oxide layer of the SOI wafer is a negative number, that is, when the thickness of the oxide layer is less than the thickness of the buried oxide layer, the curvature of the SOI wafer can also be made to meet the preset value by increasing the fine grinding wheel number, that is, the curvature of the SOI wafer can be made to meet the preset value only by adjusting the fine grinding wheel number. The thickness difference between the oxide layer and the buried oxide layer in the second and third comparison groups is still -0.4μm, but the fine grinding wheel number is reduced, the curvature of the SOI wafer becomes larger and is greater than 50μm, and the TTV after the double-sided chemical mechanical polishing process is greater than 0.3μm.

[0064] From the above, it can be seen that in the manufacturing method of the SOI wafer provided by the embodiment of the present invention, a buried oxide layer is formed on the front side of the supporting substrate and / or the front side of the device substrate by performing a thermal oxidation process, and an oxide layer of a first thickness is formed on the back side of the supporting substrate. After the bonding process, a reinforcement heat treatment process is performed to solidify the SOI wafer, and then a mechanical grinding process is performed to thin the thickness of the SOI wafer, wherein the thickness difference between the buried oxide layer between the supporting substrate and the device substrate and the oxide layer on the back side of the supporting substrate and / or the grinding stress in the mechanical grinding process are adjusted so that the curvature of the SOI wafer meets the preset value. The present invention adjusts the thickness difference between the oxide layer on the back side of the supporting substrate and the buried oxide layer between the supporting substrate and the device substrate in the SOI wafer, matches the grinding stress in the mechanical grinding process, so that the curvature of the SOI wafer meets the preset value, reduces the overall curvature of the SOI wafer, and makes the SOI wafer in the subsequent double-sided chemical mechanical polishing process more uniform and controllable.

[0065] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.

Claims

1. A method for manufacturing an SOI wafer, characterized in that: include: Providing a support substrate and a device substrate, wherein the support substrate includes a front side and a back side that are opposite to each other, and the device substrate includes a front side and a back side that are opposite to each other; Performing a thermal oxidation process to form a buried oxide layer on the front side of the support substrate and / or the front side of the device substrate, and forming an oxide layer of a first thickness on the back side of the support substrate; Performing a bonding process to bond the front side of the support substrate and the front side of the device substrate, wherein the buried oxide layer is located between the support substrate and the device substrate, so as to form an SOI wafer; Performing a strengthening heat treatment process to solidify the SOI wafer; Performing a mechanical grinding process to reduce the thickness of the back side of the device substrate of the SOI wafer; The thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back of the support substrate and / or the grinding stress in the mechanical grinding process are adjusted so that the curvature of the SOI wafer meets a preset value.

2. The method for manufacturing an SOI wafer according to claim 1, characterized in that: A preset value of the curvature of the SOI wafer after the mechanical grinding process is less than 50 μm.

3. The method for manufacturing an SOI wafer according to claim 1, characterized in that: An oxidation process is used to adjust the thickness difference between the buried oxide layer between the support substrate and the device substrate and the oxide layer on the back side of the support substrate. The oxidation process is located before or after the bonding process.

4. The method for manufacturing an SOI wafer according to claim 3, characterized in that: When the oxidation process is located before the bonding process, the oxidation process is the thermal oxidation process; when the oxidation process is located after the bonding process, the oxidation process is performed separately or integrated into the reinforcement heat treatment process.

5. The method for manufacturing an SOI wafer according to claim 4, characterized in that: The process gas of the reinforcement heat treatment process includes at least one of oxygen, a mixed gas of oxygen and hydrogen, and an inert gas.

6. The method for manufacturing an SOI wafer according to claim 5, characterized in that: When the oxidation process is integrated into the reinforcement heat treatment process, the process gas of the reinforcement heat treatment process includes at least one of oxygen and a mixed gas of oxygen and hydrogen. In the reinforcement heat treatment process, the oxide layer on the back side of the support substrate is increased to a second thickness, and the thickness of the oxide layer on the back side of the support substrate is greater than the thickness of the buried oxide layer between the support substrate and the device substrate. The difference in thickness between the oxide layer on the back side of the support substrate and the buried oxide layer between the support substrate and the device substrate is adjusted so that the curvature of the SOI wafer meets a preset value.

7. The method for manufacturing an SOI wafer according to claim 6, characterized in that: The reinforcement heat treatment process includes a first reinforcement temperature and a second reinforcement temperature. The first reinforcement temperature is used to increase the oxide layer on the back side of the supporting substrate to a second thickness. The first reinforcement temperature is, for example, 800°C to 1000°C. The second reinforcement temperature is used to increase the bonding force of the SOI wafer. The second reinforcement temperature is 1100°C to 1250°C.

8. The method for manufacturing an SOI wafer according to claim 5, characterized in that: When the process gas of the reinforcement heat treatment process includes an inert gas, the oxide layer on the back side of the support substrate remains unchanged during the reinforcement heat treatment process, and the grinding stress in the mechanical grinding process is adjusted so that the curvature of the SOI wafer meets a preset value.

9. The method for manufacturing an SOI wafer according to claim 8, characterized in that: The strengthening temperature of the strengthening heat treatment process is 1100°C to 1250°C.

10. The method for manufacturing an SOI wafer according to claim 8, characterized in that: The mechanical grinding process includes a fine grinding process, and the grinding stress in the fine grinding process is achieved by adjusting the mesh number of the fine grinding wheel, and the mesh number of the fine grinding wheel is greater than or equal to 1000 meshes.

11. The method for manufacturing an SOI wafer according to claim 10, characterized in that: The thickness of the back side of the device substrate removed by the fine grinding process is greater than 10 μm.

12. An SOI wafer, characterized in that: The SOI wafer is manufactured by the manufacturing method of any one of claims 1 to 11, comprising an oxide layer, a support substrate, a buried oxide layer and a device substrate stacked in sequence from bottom to top; the curvature of the SOI wafer is less than 50 μm.

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