Preparation method of composite substrate and composite substrate
By employing a multi-step thinning process and controlling the reserved thickness during coarse and fine grinding, combined with wet etching, the problem of damage extension of the device substrate during mechanical grinding was solved, and high-yield composite substrate fabrication was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-04-07
AI Technical Summary
Existing technologies struggle to thin device substrates with cavity structures to below 10 μm and have low yields, primarily due to the difficulty in controlling mechanical stress and damage generated during mechanical polishing processes, leading to substrate breakage.
A multi-step thinning process is adopted, including rough grinding, fine grinding, wet etching and chemical mechanical polishing. The reserved thicknesses for rough grinding and fine grinding are controlled to be 120μm and 60μm, respectively. Combined with the wet etching process, the thinning process of the device substrate is precisely controlled to avoid damage extending inward.
It significantly improves the fabrication yield of composite substrates, ensuring that the device substrate does not break when thinned to below 10μm, and maintaining thickness uniformity and surface quality.
Smart Images
Figure CN121816038A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and in particular to a method for preparing a composite substrate and the composite substrate itself. Background Technology
[0002] Composite substrates with cavity structures are widely used in semiconductor devices such as microelectromechanical systems (MEMS) and advanced sensors. These composite substrates typically include a support substrate, a device substrate, and an insulating layer disposed between the support substrate and the device substrate. The surface of the support substrate facing the device substrate has a cavity structure.
[0003] As semiconductor devices continue to miniaturize, the substrate thinning process faces increasingly severe challenges. In particular, for the aforementioned composite substrates with cavity structures, the presence of the cavity structure leaves the substrate in a suspended state, directly affecting the support provided by the supporting substrate and thus significantly limiting further substrate thinning. Summary of the Invention
[0004] In view of this, the present application provides a method for preparing a composite substrate and a composite substrate in order to solve at least one problem existing in the background art.
[0005] In a first aspect, embodiments of this application provide a method for preparing a composite substrate, the method comprising: A wafer bonding structure to be processed is provided, the wafer bonding structure including a support substrate, a device substrate, and an insulating layer located between the support substrate and the device substrate, wherein the support substrate has a cavity structure on a first surface side, and the first surface is disposed facing the second surface of the device substrate; Thinning the device substrate to a predetermined thickness from a third surface, wherein the third surface is the surface opposite to the second surface, and the predetermined thickness is less than or equal to 10 μm; thinning the device substrate to the predetermined thickness includes: The device substrate is thinned using a mechanical polishing process, which includes: using a coarse polishing process to thin the device substrate to a first preset thickness, the first preset thickness being greater than or equal to 120 μm; and using a fine polishing process to thin the device substrate to a second preset thickness, the second preset thickness being greater than or equal to 60 μm. The device substrate is thinned to a third preset thickness using a wet etching process, and then the thickness of the device substrate is thinned to the preset thickness using a chemical mechanical polishing process.
[0006] In conjunction with the first aspect of this application, in an optional embodiment, the first preset thickness is 120μm~170μm.
[0007] In conjunction with the first aspect of this application, in an optional embodiment, the second preset thickness is 60μm to 100μm.
[0008] In conjunction with the first aspect of this application, in an optional embodiment, during the process of thinning the device substrate to the first preset thickness using the coarse grinding process, the thickness of the device substrate is monitored using a contact thickness measurement method; during the process of thinning the device substrate to the second preset thickness using the fine grinding process, the thickness of the device substrate is monitored using a non-contact thickness measurement method.
[0009] In conjunction with the first aspect of this application, in an optional embodiment, the coarse grinding process includes: The thickness of the device substrate is reduced to more than 150 μm using a first coarse grinding process, and the grinding removal rate of the first coarse grinding process is 5.5 μm / min to 6.5 μm / min; The thickness of the device substrate is reduced by 15μm to 25μm using a second coarse grinding process, and the grinding removal rate of the second coarse grinding process is 4.7μm / min to 5.3μm / min; The thickness of the device substrate is reduced by 8μm to 12μm using a third coarse grinding process, and the grinding removal rate of the third coarse grinding process is 3.8μm / min to 4.2μm / min.
[0010] In conjunction with the first aspect of this application, in an optional embodiment, the fine grinding process includes: The thickness of the device substrate is reduced by 12μm to 18μm using a first fine grinding process, and the grinding removal rate of the first fine grinding process is 2.5μm / min to 3.5μm / min; The thickness of the device substrate is reduced by 8μm to 12μm using a second fine grinding process, and the grinding removal rate of the second fine grinding process is 0.7μm / min to 1.3μm / min; The thickness of the device substrate is reduced by 4μm to 6μm using a third fine grinding process, and the grinding removal rate of the third fine grinding process is 0.4μm / min to 0.6μm / min.
[0011] In conjunction with the first aspect of this application, in an optional embodiment, the difference between the third preset thickness and the preset thickness is 2μm to 10μm.
[0012] In conjunction with the first aspect of this application, in an optional embodiment, the corrosion removal rate of the wet etching process is 0.4 μm / min to 1.0 μm / min.
[0013] In conjunction with the first aspect of this application, in an alternative embodiment, the total thickness change of the device substrate reduced to the preset thickness is less than or equal to 0.6 μm.
[0014] Secondly, embodiments of this application provide a composite substrate, which is prepared using the composite substrate preparation method described in any one of the first aspects.
[0015] Compared with the prior art, the embodiments of this application have the following beneficial effects: In the composite substrate preparation method provided in this application embodiment, firstly, the device substrate is thinned using a mechanical polishing process. In this mechanical polishing process, the device substrate is first thinned quickly and efficiently through coarse polishing, and then further thinned through fine polishing to remove the damage layer introduced on the surface of the device substrate by coarse polishing. At the same time, the thickness uniformity and warpage of the wafer bonding structure are corrected. By controlling the minimum reserved thickness of the device substrate during coarse polishing and fine polishing to 120 μm and 60 μm respectively, it is possible not only to avoid damage to the device substrate during the mechanical polishing process, but also to prevent the mechanical stress, microcracks and other damage generated on the surface of the device substrate by the mechanical polishing process from extending excessively into the device substrate and to prevent the concentration of device substrate area above the cavity structure. Next, the device substrate is further thinned using a wet etching process. This step can further remove the damage layer introduced on the surface of the device substrate by the mechanical polishing process. Finally, the device substrate is further thinned using a chemical mechanical polishing process. This step can precisely control the amount of thinning of the device substrate, reducing the thickness of the device to less than 10 μm, ensuring the thickness uniformity and surface quality of the device substrate. In the embodiments of this application, by precisely controlling the timing of switching from coarse grinding to fine grinding and the timing of stopping fine grinding in the mechanical polishing process, the integrity of the device substrate can be ensured, and the excessive extension and concentration of surface mechanical damage to the device substrate can be avoided. Combined with wet etching and chemical mechanical polishing processes, the device substrate can be thinned to below 10 μm, ensuring that the device substrate is not damaged, while ensuring the thickness uniformity and surface quality of the device substrate, thereby significantly improving the preparation yield of composite substrates.
[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description
[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a partial surface morphology image of the device substrate of sample 1 in test group 1 under fluorescent light; Figure 2 This is a partial surface morphology image of the device substrate of sample 5 in test group 1 under fluorescent light; Figure 3 The image shows the surface defect detection results of the device substrate of sample 1 in test group 2; Figure 4 This is a partial surface morphology diagram of the device substrate of sample 1 in test group 2; Figure 5 A schematic flowchart illustrating the method for preparing the composite substrate provided in this application embodiment; Figures 6 to 11 This is a schematic diagram of the composite substrate provided in the embodiments of this application during the preparation process. Detailed Implementation
[0018] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the specific embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the disclosure of the present application to those skilled in the art.
[0019] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of this application. However, it will be apparent to those skilled in the art that this application can be practiced without one or more of these details. In other instances, to avoid confusion with this application, some technical features well-known in the art have not been described; that is, not all features of actual embodiments are described herein, nor are well-known functions and structures described in detail.
[0020] In the accompanying drawings, for clarity, the dimensions of layers, areas, and elements, as well as their relative dimensions, may be exaggerated. The same reference numerals denote the same elements throughout.
[0021] When an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. Although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this application, the first element, component, area, layer, or portion discussed below may be referred to as a second element, component, area, layer, or portion. And the discussion of a second element, component, area, layer, or portion does not imply that the first element, component, area, layer, or portion necessarily exists in this application.
[0022] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship of one element or feature shown in the figure to other elements or features. In addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below” or “under” the other element or feature will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.
[0023] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. The terms “comprising” and / or “including,” when used in this specification, identify the presence of said features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.
[0024] To fully understand this application, detailed steps and structures will be presented in the following description to illustrate the technical solution of this application. Preferred embodiments of this application are described in detail below; however, in addition to these detailed descriptions, this application may have other implementation methods.
[0025] Composite substrates with cavity structures generally include a support substrate, a device substrate, and an insulating layer disposed between the support substrate and the device substrate. The support substrate has a cavity structure on its surface facing the device substrate. In the fabrication process of this type of composite substrate, it is usually necessary to thin the device substrate from the side away from the bonding surface to meet the thickness requirements of the semiconductor device. Currently, mechanical polishing is often the first thinning process for device substrates because it can quickly and efficiently thin the substrate, and it is a mature process with good controllability and low cost. However, mechanical polishing introduces significant mechanical stress, which can easily cause mechanical damage to the device substrate or even lead to its breakage. Related technologies employ a combination of coarse polishing (using a coarse grinding wheel with a low mesh size) and fine polishing (using a fine grinding wheel with a high mesh size) to ensure thinning efficiency and reduce mechanical damage to the device substrate. After mechanical polishing, processes such as wet etching are used to further thin the device substrate while removing the mechanical polishing damage layer on the surface of the device substrate.
[0026] As semiconductor devices continue to miniaturize, the thickness of the device substrate needs to be increasingly thinner. Currently, thinning processes struggle to reduce the substrate thickness to below 10 μm, resulting in very low yields for composite substrates with thicknesses below 10 μm in actual manufacturing. The inventors considered that, due to the presence of the cavity structure, mechanical stress and microcracks generated on the substrate surface during rough and fine grinding can easily extend into the substrate and concentrate in the area above the cavity structure. While the substrate may not be temporarily damaged during rough and fine grinding, these potential damages extending deep into the substrate could be a major factor limiting substrate thinning to below 10 μm. Furthermore, the smaller the allowable thickness after rough and fine grinding, the more severe the potential damage inside the substrate. Therefore, the inventors conducted experimental research focusing on the relationship between the allowable thickness of the substrate after rough and fine grinding and substrate breakage in mechanical polishing processes, ultimately obtaining two sets of experimental results as shown in Table 1. In Experiment 1, the substrate thinning process included: first, a coarse grinding process to thin the substrate to 110 μm, followed by a fine grinding process to thin it to 60 μm; then, a wet etching process to thin it to 13 μm; and finally, a chemical mechanical polishing (CMP) process to further thin the substrate to 10 μm. Experiment 2 followed essentially the same substrate thinning process as Experiment 1, except that the coarse grinding process thinned the substrate to 120 μm, and the fine grinding process thinned it to 50 μm. Ten parallel samples were tested in both Experiment 1 and Experiment 2. During the final CMP process, most samples in both Experiment 1 and Experiment 2 showed substrate damage. Specific statistical results are shown in Table 1.
[0027] Table 1
[0028] As shown in Table 1, if the reserved thickness of the device substrate after rough grinding or fine grinding is too small, it is easy for the device substrate to be damaged in the subsequent chemical mechanical polishing process, making it difficult to safely reduce the thickness of the device substrate to below 10 μm. In experimental groups 1 and 2, the number of samples with undamaged device substrates accounted for only about 50% of the total number of samples, indicating a very low yield of composite substrate preparation. Figure 1 and Figure 2 These are surface morphology images of the device substrates of samples 1 and 5 in experimental group 1 under fluorescent light. Figure 1 and Figure 2 It can be seen that obvious damage was observed on the surface of the device substrates of both samples 1 and 5 in test group 1 (e.g., Figure 1 and Figure 2 (As indicated by the middle arrow). Figure 3This is a diagram showing the surface defect detection results of the device substrate of sample 1 in test group 2. Figure 4 This is a partial surface morphology diagram of the device substrate of sample 1 in test group 2. Figure 3 Red defects in the image (e.g.) Figure 3 The area within the dashed box represents a larger defect, corresponding to a break in the device substrate surface. Defects in other colors represent normal small particle contamination on the device substrate surface. Figure 4 These are images taken under an optical microscope. Figure 4 Damaged areas (such as) Figure 4 (As shown within the dashed box) Figure 3 The red defect points in the image are... Figure 4 It can be seen that the device substrate surface of sample 1 in test group 2 showed obvious damage, and the damage was close to the cavity structure. The problem caused by the insufficient thickness of the device substrate after rough or fine grinding is that the damage caused by the mechanical stress of grinding is more likely to extend into the interior of the remaining device substrate and tend to concentrate in the device substrate area above the cavity structure. The wet etching process only removes the surface damaged layer, and these potential damages that extend into the device substrate remain in the device substrate, making the device substrate prone to damage during subsequent chemical mechanical polishing.
[0029] Based on this, embodiments of this application provide a method for preparing a composite substrate. Please refer to... Figure 5 The method for preparing the composite substrate provided in this application includes: Step S101: Provide a wafer bonding structure to be processed. The wafer bonding structure includes a support substrate, a device substrate, and an insulating layer located between the support substrate and the device substrate. The first surface of the support substrate has a cavity structure, and the first surface is disposed facing the second surface of the device substrate. Step S102, thinning the device substrate to a preset thickness from the third surface of the device substrate, wherein the third surface is the surface opposite to the second surface, and the preset thickness is less than or equal to 10 μm; thinning the device substrate to the preset thickness includes: The device substrate is thinned using a mechanical polishing process, which includes: using a coarse polishing process to thin the device substrate to a first preset thickness, the first preset thickness being greater than or equal to 120 μm; and using a fine polishing process to thin the device substrate to a second preset thickness, the second preset thickness being greater than or equal to 60 μm. The device substrate is thinned to a third preset thickness using a wet etching process; The thickness of the device substrate is reduced to a preset thickness using a chemical mechanical polishing process.
[0030] In this embodiment, a mechanical polishing process is used to thin the device substrate. This process involves first rapidly and efficiently thinning the substrate through coarse polishing, followed by further thinning through fine polishing. This removes the damage layer introduced by the coarse polishing and corrects the thickness uniformity and warpage of the wafer bonding structure. By controlling the minimum allowable thickness of the device substrate during coarse and fine polishing to 120 μm and 60 μm respectively, damage to the device substrate during mechanical polishing is prevented. Furthermore, the mechanical stress and microcracks generated on the surface of the device substrate during mechanical polishing are prevented from extending excessively into the substrate and from concentrating in the area above the cavity structure. Next, a wet etching process is used to further thin the device substrate, further removing the damage layer introduced by the mechanical polishing process. Finally, a chemical mechanical polishing process is used to further thin the device substrate, precisely controlling the thinning amount to reduce the device thickness to below 10 μm while ensuring thickness uniformity and surface quality. In the embodiments of this application, by precisely controlling the timing of switching from coarse grinding to fine grinding and the timing of stopping fine grinding in the mechanical polishing process, the integrity of the device substrate can be ensured, and the excessive extension and concentration of surface mechanical damage to the device substrate can be avoided. Combined with wet etching and chemical mechanical polishing processes, the device substrate can be thinned to below 10 μm, ensuring that the device substrate is not damaged, while ensuring the thickness uniformity and surface quality of the device substrate, thereby significantly improving the preparation yield of composite substrates.
[0031] Below, in conjunction with Figures 6 to 11 The preparation method of the composite substrate provided in the embodiments of this application and its corresponding beneficial effects will be further described in detail.
[0032] First, please refer to Figures 6 to 8 Step S101 is executed to provide a wafer bonding structure to be processed. The wafer bonding structure includes a support substrate 100, a device substrate 200, and an insulating layer 300 located between the support substrate 100 and the device substrate 200. The support substrate 100 has a cavity structure 102 on the first surface 101 side, and the first surface 101 is disposed facing the second surface 201 of the device substrate 200.
[0033] In this embodiment, the material of the support substrate 100 can be, for example, silicon, germanium, or silicon-germanium. The material of the device substrate 200 can be, for example, silicon, germanium, or silicon-germanium. The material of the insulating layer 300 can be, for example, an oxide (specifically, silicon oxide) or a nitride (specifically, silicon nitride). In a specific example, both the support substrate 100 and the device substrate 200 are made of silicon, and the insulating layer 300 is made of silicon oxide. Therefore, the device substrate 200 can also be referred to as the top silicon layer, the insulating layer 300 can also be referred to as the buried oxide layer, and the support substrate 100 can also be referred to as the bottom silicon layer.
[0034] In the actual preparation process, firstly, please refer to... Figure 6 and Figure 7 An insulating layer 300 can be grown on the first surface 101 of the supporting substrate 100. Specifically, for example, at least one of a deposition process and / or a thermal oxidation process can be used to grow the insulating layer 300. Next, please refer to Figure 8 The support substrate 100 and the device substrate 200 are bonded with the first surface 101 facing the second surface 201. Next, the bonded sheets can be heat-treated (also known as annealing) at a high temperature to enhance the bonding force. Specifically, the heat treatment temperature can be between 500℃ and 1200℃, for example, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, 1200℃, or any value between any two of the above ranges. This effectively enhances the bonding force, thereby better meeting the strength requirements of subsequent processes such as thinning and polishing of the device substrate 200.
[0035] In this embodiment, the insulating layer 300 serves two purposes: firstly, it isolates the support substrate 100 and the device substrate 200; secondly, if the materials of the support substrate 100 and the device substrate 200 are different and their coefficients of thermal expansion differ significantly, the insulating layer 300 can effectively buffer the impact of the large difference in the coefficients of thermal expansion between the two materials on the bonding effect.
[0036] It should be noted that, as Figure 7As shown, the cavity structure 102 can be a patterned cavity structure. When the insulating layer 300 is grown on the first surface 101 of the supporting substrate 100, the insulating layer 300 covers the first surface 101 and the inner wall of the cavity structure 102 but does not completely fill the cavity structure 102. This is because the insulating layer 300 is typically very thin, generally less than or equal to 1 μm. For example, the thickness of the insulating layer 300 grown using a thermal oxidation process is typically tens of nanometers. In some other embodiments of this application, the insulating layer 300 can also be grown on the second surface 201 of the device substrate 200. As mentioned above, since the insulating layer 300 is very thin, when the insulating layer 300 is grown on the second surface 201 of the device substrate 200, its supporting effect on the device substrate 200 can be basically ignored during the subsequent thinning process.
[0037] Next, please refer to Figures 9 to 11 Step S102 involves thinning the device substrate 200 to a preset thickness from its third surface 301, where the third surface 301 is the surface opposite to the second surface 201, and the preset thickness is less than or equal to 10 μm. Thinning the device substrate 200 to the preset thickness includes: Step S1021: Please refer to Figure 9 The device substrate 200 is thinned using a mechanical polishing process, which may include: using a coarse polishing process to thin the device substrate 200 to a first preset thickness, the first preset thickness being greater than or equal to 120 μm; and using a fine polishing process to thin the device substrate 200 to a second preset thickness, the second preset thickness being greater than or equal to 60 μm.
[0038] In this embodiment, coarse grinding refers to mechanical grinding using a coarse grinding wheel with a lower mesh size, typically 300# to 1000#. Coarse grinding has the advantages of high efficiency, low cost, mature technology, and good controllability. Fine grinding, on the other hand, uses a fine grinding wheel with a higher mesh size, typically 4000# to 8000#. Fine grinding involves less mechanical stress than coarse grinding, which improves the smoothness and uniformity of the surface after grinding.
[0039] Typically, the thickness of the device substrate 200 is several hundred or even thousands of micrometers. In this embodiment, rough grinding can quickly and efficiently thin the device substrate 200, removing most of its thickness. However, the mechanical stress during rough grinding is relatively high, which can generate mechanical stress and even microcracks (introducing a damage layer) on the surface and subsurface of the device substrate 200. In particular, the area of the device substrate 200 corresponding to the cavity location is more prone to cracking or even collapse due to local stress concentration. Therefore, by controlling the minimum reserved thickness of the device substrate 200 during rough grinding to 120 μm, it is possible to ensure that the device substrate 200 is not damaged during the rough grinding stage, while effectively avoiding damage to the surface layer of the device substrate 200 caused by the rough grinding process. The mechanical stress and microcracks generated during the rough grinding process cause damage that extends and concentrates excessively into the device substrate 200. Further thinning of the device substrate 200 by fine grinding removes the surface damage layer generated during the rough grinding process and corrects the thickness uniformity and warpage of the wafer bonding structure. However, the mechanical stress during fine grinding still causes some damage to the surface of the device substrate 200. Therefore, by controlling the minimum allowable thickness of the device substrate 200 during fine grinding to 60 μm, it is possible to ensure that the device substrate 200 is not damaged during the fine grinding stage, and to effectively prevent the mechanical stress and microcracks generated on the surface of the device substrate 200 from extending and concentrating excessively into the device substrate 200. In other words, in this embodiment, by precisely controlling the timing of the switch from rough grinding to fine grinding and the timing of stopping fine grinding in the mechanical grinding process, the integrity of the device substrate 200 can be ensured, and the excessive extension and concentration of surface mechanical damage into the device substrate 200 can be prevented. This avoids the problem of the device substrate 200 being easily damaged due to these potential internal damages during subsequent thinning processes.
[0040] In some embodiments, the first preset thickness can be 120μm to 170μm, for example, it can be 120μm, 130μm, 140μm, 150μm, 160μm, 170μm or any value between any two of the above ranges. This is beneficial for increasing the thinning rate of the device substrate 200 while ensuring that the device substrate 200 is not damaged, shortening the process cycle, and improving production efficiency.
[0041] In some embodiments, the second preset thickness can be 60μm to 100μm, for example, it can be 60μm, 70μm, 80μm, 90μm, 100μm or any value between any two of the above ranges. This is beneficial for increasing the thinning rate of the device substrate 200 while ensuring that the device substrate 200 is not damaged, shortening the process cycle, and improving production efficiency.
[0042] In some embodiments, during the process of thinning the device substrate 200 to a first preset thickness using a coarse grinding process, a contact thickness measurement method can be used to monitor the thickness of the device substrate 200; during the process of thinning the device substrate 200 to a second preset thickness using a fine grinding process, a non-contact thickness measurement method can be used to monitor the thickness of the device substrate 200.
[0043] In this embodiment, the thickness of the device substrate 200 is monitored using a contact-type thickness measurement method during the rough grinding stage. This method is simple, convenient, and low-cost. However, by the fine grinding stage, the device substrate 200 is already quite thin, and the contact-type thickness measurement method would exert pressure on the device substrate 200, increasing the risk of damage, particularly in the area corresponding to the cavity structure 102. Therefore, when switching from the rough grinding process to the fine grinding process, simultaneously switching the method of monitoring the thickness of the device substrate 200 from contact to non-contact helps reduce damage to the device substrate 200 during thickness monitoring, better ensuring the integrity of the device substrate 200, and thus better ensuring the yield of the composite substrate.
[0044] In some embodiments, the coarse grinding process may include: first, using a first coarse grinding process to reduce the thickness of the device substrate 200 to more than 150 μm, wherein the grinding removal rate of the first coarse grinding process is 5.5 μm / min to 6.5 μm / min, for example, it can be 5.5 μm / min, 6.0 μm / min, 6.5 μm / min, or any value between any two of the above numerical ranges; second, using a second coarse grinding process to reduce the thickness of the device substrate 200 by 15 μm to 25 μm, for example, it can be 15 μm, 20 μm, 25 μm, or any value between any two of the above numerical ranges, wherein the grinding removal rate of the second coarse grinding process is 4.7 μm / min to 5.3 μm / min, for example, The speed can be 4.7 μm / min, 4.9 μm / min, 5.1 μm / min, 5.3 μm / min, or any value between any two of the above ranges; furthermore, the thickness of the device substrate 200 is reduced by 8 μm to 12 μm using a third coarse grinding process, for example, it can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, or any value between any two of the above ranges, and the grinding removal rate of the third coarse grinding process is 3.8 μm / min to 4.2 μm / min, for example, it can be 3.8 μm / min, 3.9 μm / min, 4.0 μm / min, 4.1 μm / min, 4.2 μm / min, or any value between any two of the above ranges.
[0045] In this embodiment, the coarse grinding process is divided into three stages, with the grinding removal rate and removal amount decreasing sequentially. This better ensures that the device substrate 200 is not damaged during the coarse grinding stage, and also better prevents the mechanical stress, microcracks and other damage generated on the surface of the device substrate 200 during the coarse grinding process from excessively extending and concentrating into the interior of the device substrate 200. Moreover, it is convenient to stop the coarse grinding process in time when the thickness is close to the first preset thickness, which is conducive to further improving the preparation yield of the composite substrate.
[0046] In some embodiments, the fine grinding process may include: using a first fine grinding process to reduce the thickness of the device substrate 200 by 12μm to 18μm, for example, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm or any value between any two of the above numerical ranges, wherein the grinding removal rate of the first fine grinding process is 2.5μm / min to 3.5μm / min, for example, 2.5μm / min, 3.0μm / min, 3.5μm / min or any value between any two of the above numerical ranges; and using a second fine grinding process to reduce the thickness of the device substrate 200 by 8μm to 12μm, for example, 8μm, 9μm, 10μm, 11μm, 12μm or any value between any two of the above numerical ranges, wherein the second fine grinding process... The grinding removal rate of the process is 0.7 μm / min to 1.3 μm / min, for example, it can be 0.7 μm / min, 0.8 μm / min, 0.9 μm / min, 1.0 μm / min, 1.1 μm / min, 1.2 μm / min, 1.3 μm / min or any value between any two of the above ranges; the thickness of the device substrate 200 is reduced by 4 μm to 6 μm using a third fine grinding process, for example, it can be 4 μm, 5 μm, 6 μm or any value between any two of the above ranges, and the grinding removal rate of the third fine grinding process is 0.4 μm / min to 0.6 μm / min, for example, it can be 0.4 μm / min, 0.5 μm / min, 0.6 μm / min or any value between any two of the above ranges.
[0047] In this embodiment, the fine grinding process is divided into three stages, with the grinding removal rate and removal amount decreasing sequentially. This better ensures that the device substrate 200 is not damaged during the fine grinding stage, and also better prevents the mechanical stress, microcracks and other damage generated on the surface of the device substrate 200 during the fine grinding process from excessively extending and concentrating into the interior of the device substrate 200. Moreover, it is convenient to stop the fine grinding process in time when the thickness is close to the second preset thickness, which is conducive to further improving the preparation yield of the composite substrate.
[0048] It is understandable that in mechanical polishing processes, it is difficult to control the surface after polishing to achieve a relatively smooth surface. In actual fabrication processes, the third surface 301 of the device substrate 200 after fine polishing can be controlled to be either convex or concave. By uniformly controlling whether the third surface 301 of the device substrate 200 is convex or concave during the fine polishing process, it is beneficial to simplify the control of subsequent wet etching and chemical mechanical polishing processes. This avoids the need for frequent adjustments to subsequent processes based on the uncertain morphology of the third surface 301 after fine polishing, thereby simplifying the process and improving its stability and controllability. Consequently, it is easier to better control the thickness uniformity of the finally thinned device substrate 200.
[0049] In some specific embodiments, after the fine grinding process, the third surface 301 of the device substrate 200 can be a convex surface. This is beneficial for controlling the thickness uniformity of the device substrate 200 in conjunction with subsequent wet etching processes. This will be further explained below.
[0050] Furthermore, when the third surface 301 of the device substrate 200 is convex or concave, the total thickness variation of the wafer bonding structure can be controlled to be less than or equal to 0.5 μm. Here, the convex or concave surface can also be referred to as a micro-convex surface or a micro-concave surface.
[0051] The above total thickness variation is known in the industry as TTV.
[0052] Step S1022: Please refer to Figure 10 The device substrate 200 is thinned to a third preset thickness using a wet etching process.
[0053] Wet etching is a stress-free process that does not cause mechanical damage to the device substrate 200. It can also further remove the damaged layer on the surface of the device substrate 200 introduced by the mechanical polishing process, and reduce the amount of removal in the subsequent chemical mechanical polishing process, thereby improving the thinning efficiency. This ensures that the thickness of the device substrate 200 can be reduced to less than 10 μm without defects such as cracking.
[0054] In actual fabrication processes, wafer bonding structures can be immersed in an etching solution. By controlling the composition, concentration, temperature, and time of the etching solution, the etching rate can be precisely controlled, thereby effectively controlling the thinning amount of the device substrate 200. Furthermore, multiple wafer bonding structures can be processed simultaneously, which helps improve production efficiency.
[0055] When the third surface 301 of the device substrate 200 is convex after the grinding process, wet etching can be performed while the wafer bonding structure is rotating (for example, the wafer bonding structure can be placed on a rotatable support within the etching tank). This allows the etching removal rate of the wet etching process to gradually decrease from the center to the edge of the device substrate 200 along the radial direction, thereby reshaping the morphology of the third surface 301 of the device substrate 200 during the wet etching process and improving the thickness uniformity of the device substrate 200. In other words, controlling the third surface 301 of the device substrate 200 to be convex after the grinding process allows for better control of the thickness uniformity of the device substrate 200 in conjunction with the wet etching process, thus facilitating the control of the final thickness uniformity of the thinned device substrate 200. Specifically, after the wet etching process, the total thickness variation of the wafer bonding structure can be less than or equal to 0.4 μm.
[0056] In some embodiments, the etching removal rate of the wet etching process can be from 0.4 μm / min to 1.0 μm / min, for example, it can be 0.4 μm / min, 0.5 μm / min, 0.6 μm / min, 0.7 μm / min, 0.8 μm / min, 0.9 μm / min, 1.0 μm / min, or any value between any two of the above ranges. This allows for control over both the thinning rate and the amount of thinning of the device substrate 200.
[0057] For example, the etching solution may include a tetramethylammonium hydroxide solution, and more specifically, the etching solution may be a tetramethylammonium hydroxide (TMAH) solution. The mass fraction of the tetramethylammonium hydroxide solution may be 0.7% to 5%, for example, 0.7%, 1%, 2%, 3%, 4%, 5%, or any value between any two of the above ranges. The temperature of the wet etching process may be 25°C to 100°C, for example, 25°C, 35°C, 45°C, 55°C, 65°C, 75°C, 85°C, 95°C, 100°C, or any value between any two of the above ranges.
[0058] The uniformity of wet etching is limited, making it difficult to achieve the required uniformity and smoothness on the wafer surface. Therefore, chemical mechanical polishing (CMP) is subsequently used to thin the substrate 200 to a predetermined thickness. If the allowance for CMP is too small, it hinders the improvement of the final substrate 200's thickness uniformity and surface quality; conversely, if the allowance is too large, the relatively slow removal rate of CMP compromises the thinning efficiency. Therefore, in some specific embodiments, the difference between the third predetermined thickness and the predetermined thickness can be 2μm to 10μm, for example, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any value within any two of these ranges.
[0059] Step S1023: Please refer to Figure 11 The thickness of the device substrate 200 is reduced to a preset thickness using a chemical mechanical polishing process.
[0060] Chemical mechanical polishing (CMP) can more precisely control the polishing removal rate and amount, and has strong controllability. It is easy to reduce the thickness of the device substrate 200 to below 10 μm, ensuring that the device substrate 200 is not damaged. At the same time, it can better ensure the thickness uniformity, surface flatness and smoothness of the device substrate 200, thereby improving the preparation yield of composite substrates.
[0061] When the third surface 301 of the device substrate 200 is convex after wet etching, the polishing removal rate of the central and edge regions of the device substrate 200 can be adjusted according to the geometric "micro-convex" morphology of the wafer bonding structure, thereby ensuring the thickness uniformity of the device substrate 200.
[0062] In some embodiments, the total thickness change of the device substrate 200 thinned to a preset thickness is less than or equal to 0.6 μm.
[0063] The total thickness variation (TTV) of the device substrate 200 is less than or equal to 0.6 μm, which ensures that the difference between the actual thickness and the preset thickness at each point of the device substrate 200 after thinning to the preset thickness is within ±0.3 μm. The composite substrate preparation method provided in this application embodiment not only ensures the integrity of the device substrate 200, but also effectively ensures the thickness uniformity of the device substrate 200.
[0064] The effects of the composite substrate preparation method in this application will be further illustrated below with reference to Examples 1 to 3.
[0065] Example 1 In this embodiment, the method for preparing the composite substrate includes the following steps: Step 1: Provide a wafer bonding structure to be processed. The wafer bonding structure includes a support substrate, a device substrate, and an insulating layer located between the support substrate and the device substrate. The first surface of the support substrate has a cavity structure, and the first surface is disposed facing the second surface of the device substrate. Step 2: Thin the device substrate from its third surface, specifically including the following steps. (1) The device substrate is thinned to a first preset thickness using a coarse grinding process: First, the device substrate is thinned to 150 μm using a first coarse grinding process with a grinding removal rate of 6 μm / min; Next, the device substrate is thinned to 130 μm using a second coarse grinding process with a grinding removal rate of 5 μm / min; Next, the device substrate is thinned to 120 μm using a third coarse grinding process with a grinding removal rate of 4 μm / min; (2) The device substrate is thinned to a second preset thickness using a fine grinding process: First, the device substrate is thinned to 105 μm using a first fine grinding process with a grinding removal rate of 3 μm / min; next, the device substrate is thinned to 95 μm using a second fine grinding process with a grinding removal rate of 1 μm / min; next, the device substrate is thinned to 90 μm using a third fine grinding process with a grinding removal rate of 0.5 μm / min. (3) The device substrate is thinned to the third preset thickness by wet etching process: The wafer bonding structure after step (2) is placed in a TMAH solution with a mass fraction of 2.5% and wet etched at 60°C until the thickness of the device substrate is reduced to 13μm. (4) The thickness of the device substrate is reduced to 10 μm (preset thickness) by chemical mechanical polishing process.
[0066] Example 2 In this embodiment, the preparation method of the composite substrate is basically the same as that in Example 1, except that: In step 2: In step (3), wet etching is performed until the thickness of the device substrate is reduced to 10 μm, that is, the third preset thickness is adjusted to 10 μm; In step (4), chemical mechanical polishing is used to reduce the thickness of the device substrate to 7 μm, that is, the preset thickness is adjusted to 7 μm.
[0067] Example 3 In this embodiment, the preparation method of the composite substrate is basically the same as that in Example 1, except that: In step 2: In step (2), the device substrate is thinned to 60 μm using the third fine grinding process, that is, the second preset thickness is adjusted to 60 μm; In step (3), wet etching is performed to reduce the thickness of the device substrate to 6 μm, that is, the third preset thickness is adjusted to 6 μm; In step (4), the thickness of the device substrate is thinned to 3 μm using the chemical mechanical polishing process, that is, the preset thickness is adjusted to 3 μm.
[0068] For each of Examples 1 to 3, 25 parallel samples were set up to detect the surface damage of the device substrate in the final composite substrate obtained in each example. The specific results are shown in Table 2.
[0069] Table 2
[0070] As shown in Table 2, the composite substrate fabrication method of this application can reduce the thickness of the device substrate to below 10 μm (even to 3 μm) while ensuring that the device substrate is not damaged. Furthermore, testing revealed that the surface particles of the device substrate are within the normal range, and the thickness uniformity of the device substrate can achieve a TTV of less than or equal to 0.6 μm. This indicates that, in this application, by precisely controlling the timing of the transition from coarse to fine grinding and the timing of stopping fine grinding in the mechanical polishing process, the integrity of the device substrate can be ensured, and excessive extension and concentration of surface mechanical damage to the interior can be avoided. Combined with wet etching and chemical mechanical polishing processes, the device substrate can be effectively thinned to below 10 μm, ensuring that the device substrate is not damaged, while maintaining thickness uniformity and surface quality, thereby significantly improving the yield of composite substrate fabrication.
[0071] This application also provides a composite substrate, which is prepared by the composite substrate preparation method described in any of the above embodiments.
[0072] It should be understood that the above embodiments are exemplary and not intended to encompass all possible implementations. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of this application that may not be explicitly described. Therefore, the above embodiments only illustrate several implementations of this application and do not limit the scope of protection of this patent application.
Claims
1. A method for preparing a composite substrate, characterized in that, The method includes: A wafer bonding structure to be processed is provided, the wafer bonding structure including a support substrate, a device substrate, and an insulating layer located between the support substrate and the device substrate, wherein the support substrate has a cavity structure on a first surface side, and the first surface is disposed facing the second surface of the device substrate; Thinning the device substrate to a predetermined thickness from a third surface, wherein the third surface is the surface opposite to the second surface, and the predetermined thickness is less than or equal to 10 μm; thinning the device substrate to the predetermined thickness includes: The device substrate is thinned using a mechanical polishing process, which includes: using a coarse polishing process to thin the device substrate to a first preset thickness, the first preset thickness being greater than or equal to 120 μm; and using a fine polishing process to thin the device substrate to a second preset thickness, the second preset thickness being greater than or equal to 60 μm. The device substrate is thinned to a third preset thickness using a wet etching process; The thickness of the device substrate is reduced to the preset thickness using a chemical mechanical polishing process.
2. The method for preparing the composite substrate according to claim 1, characterized in that, The first preset thickness is 120μm~170μm.
3. The method for preparing the composite substrate according to claim 1, characterized in that, The second preset thickness is 60μm~100μm.
4. The method for preparing the composite substrate according to claim 1, characterized in that, During the process of thinning the device substrate to the first preset thickness using the coarse grinding process, the thickness of the device substrate is monitored using a contact thickness measurement method; during the process of thinning the device substrate to the second preset thickness using the fine grinding process, the thickness of the device substrate is monitored using a non-contact thickness measurement method.
5. The method for preparing the composite substrate according to claim 1, characterized in that, The coarse grinding process includes: The thickness of the device substrate is reduced to more than 150 μm using a first coarse grinding process, and the grinding removal rate of the first coarse grinding process is 5.5 μm / min to 6.5 μm / min; The thickness of the device substrate is reduced by 15μm to 25μm using a second coarse grinding process, and the grinding removal rate of the second coarse grinding process is 4.7μm / min to 5.3μm / min; The thickness of the device substrate is reduced by 8μm to 12μm using a third coarse grinding process, and the grinding removal rate of the third coarse grinding process is 3.8μm / min to 4.2μm / min.
6. The method for preparing the composite substrate according to claim 1, characterized in that, The fine grinding process includes: The thickness of the device substrate is reduced by 12μm to 18μm using a first fine grinding process, and the grinding removal rate of the first fine grinding process is 2.5μm / min to 3.5μm / min; The thickness of the device substrate is reduced by 8μm to 12μm using a second fine grinding process, and the grinding removal rate of the second fine grinding process is 0.7μm / min to 1.3μm / min; The thickness of the device substrate is reduced by 4μm to 6μm using a third fine grinding process, and the grinding removal rate of the third fine grinding process is 0.4μm / min to 0.6μm / min.
7. The method for preparing the composite substrate according to claim 1, characterized in that, The difference between the third preset thickness and the preset thickness is 2μm~10μm.
8. The method for preparing the composite substrate according to claim 1, characterized in that, The corrosion removal rate of the wet etching process is 0.4 μm / min to 1.0 μm / min.
9. The method for preparing the composite substrate according to any one of claims 1 to 8, characterized in that, The total thickness change of the device substrate when thinned to the preset thickness is less than or equal to 0.6 μm.
10. A composite substrate, characterized in that, The composite substrate was prepared using the method described in any one of claims 1 to 9.