Method for protecting anodic bonding surface in deep silicon etching

Abstract

The invention provides a method for protecting an anodic bonding surface in deep silicon etching, which comprises the following steps of: providing a wafer, and sequentially forming a protective layer and a barrier layer on the surface of the wafer; patterning the barrier layer and the protective layer by utilizing photoetching and etching processes; preparing a required structure through a deep silicon etching process by taking the patterned barrier layer as an etching mask; and removing the barrier layer by using a dry etching process, and removing the protective layer by using a dry photoresist removing process. A protective layer easy to remove is additionally arranged between a bonding surface and an etching barrier layer in deep silicon etching, and when the barrier layer is removed through subsequent dry etching, the problem that the roughness of the bonding surface becomes high due to ion bombardment can be prevented through the protective layer on the bonding surface.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a method for protecting an anode bonding surface during deep silicon etching. Background Art

[0002] Wafer bonding is widely used in MEMS (Micro-Electro-Mechanical System) processes, and the roughness of the bonding surface of the wafer has a direct impact on the bonding strength. Some semiconductor devices, especially some MEMS devices, such as piezoelectric sensors, inertial sensors and gas sensors, need to be processed into a large cavity structure based on SOI (Silicon-On-Insulator) wafers and finally realize their corresponding functions through wafer bonding. The manufacture of large cavity structures requires deep silicon etching of the silicon layer to form a large cavity on it. The manufacturing method of large cavities has certain difficulties in the process. In addition to using photoresist to define the morphology to be etched, it is also necessary to first deposit a thin film barrier layer with a higher selectivity ratio relative to silicon material under the photoresist to support the etching depth required for deep silicon etching. Silicon dioxide material is usually selected.

[0003] When performing the final wafer bonding process, the roughness requirement for the bonding surface is very high, usually less than 3 nanometers to ensure a good final bonding effect. When anodic bonding is required, the thin film barrier layer needs to be removed first. At this time, the BOX layer (buried oxide layer) of the SOI wafer is exposed due to the formation of the cavity structure and cannot be removed by wet etching. It can only be removed by dry etching. During the removal process, the wafer surface (i.e., the final bonding surface) will also be bombarded by the etching gas and become rough. The roughness of the final bonding surface is usually at the level of hundreds of nanometers, and the final bonding effect cannot be guaranteed.

[0004] Therefore, it is necessary to provide a method for protecting the anodic bonding surface during deep silicon etching, so as to protect the wafer bonding surface, improve its roughness and enhance the subsequent bonding strength.

[0005] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0006] The object of the present invention is to provide a method for protecting the anode bonding surface during deep silicon etching, so as to obtain a semiconductor device with low bonding surface roughness and good bonding effect.

[0007] In order to solve the above problems, a method for protecting an anodic bonding surface during deep silicon etching is provided below, comprising:

[0008] S1. providing a wafer, and sequentially forming a protective layer and a barrier layer on the surface of the wafer;

[0009] S2, patterning the barrier layer and the protective layer by photolithography and etching processes;

[0010] S3, using the patterned barrier layer as an etching mask, preparing the desired structure through a deep silicon etching process;

[0011] S4. Remove the barrier layer by using a dry etching process, and remove the protective layer by using a dry stripping process.

[0012] By adding an easily removable protective layer between the bonding surface and the etching barrier layer in deep silicon etching, when the barrier layer is subsequently removed by dry etching, the presence of the protective layer on the bonding surface can prevent the bonding surface from becoming rougher due to ion bombardment.

[0013] In step S1, the formation of the protective layer includes spin coating polyimide on the surface of the wafer and performing a curing treatment, and the curing temperature is between 350° C. and 400° C. Polyimide material has good high temperature resistance, mechanical properties and chemical stability, and is easy to remove by dry etching.

[0014] In step S1, the barrier layer is formed by a low temperature deposition process, wherein the deposition temperature of the low temperature deposition process is lower than the temperature of the curing process. The use of low temperature deposition can reduce the outgassing phenomenon of the polyimide layer and better ensure the stability of the process.

[0015] In step S1, the barrier layer is a silicon dioxide layer, which is a common barrier layer in deep silicon etching process, has a very high etching selectivity with silicon, and the process is more mature.

[0016] In step S2, it includes:

[0017] S201, spin coating a photoresist on the surface of the barrier layer and performing exposure and development treatment to obtain a photoresist pattern;

[0018] S202, using the photoresist pattern as an etching mask, patterning the barrier layer and the protective layer through a dry etching process;

[0019] S203, removing the remaining photoresist on the surface of the blocking layer by using a wet stripping process.

[0020] The pattern is transferred to the protective layer and the barrier layer, and the patterned barrier layer can be used as an etching mask to obtain the final structure through deep silicon etching.

[0021] In step S202, the dry etching is performed by a dielectric film etcher. Using a dielectric film etcher to etch the dielectric film is an industry standard, and the process is more mature and has good compatibility.

[0022] After step S4, a second wafer is provided, and the wafer is anodically bonded to the second wafer.

[0023] Before the anodic bonding, the wafer is cleaned to remove impurities that may be introduced during the dry stripping process, thereby improving the performance of the device.

[0024] Compared with the prior art, the beneficial effects of the present invention mainly include the following: the present invention solves the problem that the bonding surface roughness is too large in the traditional anodic bonding process after deep silicon etching, thereby affecting the bonding effect. Compared with the traditional process, the feature of the present invention is that an additional protective layer is used to protect the bonding surface when the barrier layer is dry-etched, thereby solving the problem of the bonding surface roughness being too large in the traditional process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 This is a schematic diagram of the structure after deep silicon etching in the prior art provided by the present invention.

[0027] Figure 2 A flow chart of a method for protecting an anodic bonding surface during deep silicon etching provided by the present invention. DETAILED DESCRIPTION

[0028] The above and other technical contents, features and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front or back, etc., are only referenced to the directions of the attached drawings. Therefore, the directional terms used are used to illustrate and not to limit the present invention.

[0029] The following will describe the various embodiments of the present application in detail with reference to the accompanying drawings. However, it will be appreciated by those skilled in the art that in the various embodiments of the present application, many technical details are provided in order to enable the reader to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solution claimed in the present application can be implemented.

[0030] Some semiconductor devices, especially some MEMS devices, such as piezoelectric sensors, inertial sensors and gas sensors, need to process large cavity structures based on SOI (Silicon-On-Insulator) wafers and finally realize their corresponding functions through wafer bonding. Figure 1 This is a schematic diagram of the structure after deep silicon etching of a large cavity structure in the prior art. Figure 1 As shown, the SOI wafer includes a bottom silicon layer 1, a buried oxide layer 2 and a top silicon layer 3. The large cavity structure is manufactured by deep silicon etching. In order to support the etching depth required for deep silicon etching, a thin film barrier layer with a higher selectivity to silicon material is usually formed on the surface of the top silicon layer 3 before etching, that is, a barrier layer 4. When anodic bonding is to be performed later, this barrier layer 4 needs to be removed. At this time, the buried oxide layer 2 of the SOI wafer is already exposed, and the barrier layer 4 cannot be removed by wet etching, but can only be removed by dry etching. In the process of dry etching to remove the barrier layer 4, the surface of the top silicon layer 3 (i.e., the final bonding surface) will also become rough due to the bombardment of the etching gas, usually at the level of hundreds of nanometers, and the final bonding effect cannot be guaranteed.

[0031] The steps in the following embodiments do not correspond one to one with the summary of the invention.

[0032] Embodiment 1:

[0033] like Figure 2 Shown is a flow chart of a method for protecting an anodic bonding surface during deep silicon etching provided by the present invention.

[0034] refer to Figure 2 The present invention provides a method for protecting an anodic bonding surface during deep silicon etching, the method comprising the following steps:

[0035] Step 1: Provide a wafer.

[0036] refer to Figure 2 In a, the wafer provided in this embodiment is an SOI wafer, which includes a bottom silicon layer 1, a buried oxide layer 2 and a top silicon layer 3 from bottom to top.

[0037] SOI wafers are widely used in MEMS device preparation, so SOI wafers are used as examples. The present application does not limit the specific material and form of the wafer, for example, it can be a single crystal silicon wafer or other semiconductor wafers.

[0038] Step 2: forming a protective layer 5 on the surface of the wafer.

[0039] Reference Figure 2In b, in this embodiment, the protection layer 5 is formed by spin coating a polyimide material on the surface of the wafer and performing a curing process.

[0040] In this embodiment, the material of the protective layer 5 is polyimide because the material can usually withstand high temperatures and is easily removed by dry etching. In other embodiments, other materials with similar properties may also be used. In this embodiment, the curing temperature of the polyimide is 350° C., and in other embodiments, the curing temperature may be between 350° C. and 400° C.

[0041] Step 3: forming a barrier layer 4 on the surface of the protective layer 5 .

[0042] Reference Figure 2 In b, in this embodiment, the barrier layer 4 is formed on the surface of the protective layer 5 by a low temperature deposition process, and the deposition temperature is lower than the curing temperature of the polyimide material used. If the deposition temperature is too high, the polyimide may outgas, which will affect the process and equipment.

[0043] In this embodiment, the barrier layer 4 is made of silicon dioxide. The silicon dioxide film is used because the etching selectivity of silicon dioxide to silicon is very high in the deep silicon etching process, which is common in the industry. The function of the barrier layer 4 is to serve as an etching mask for structural definition in the subsequent deep silicon etching.

[0044] In other embodiments, other materials can be used to form the barrier layer 4, as long as the deposition temperature of the thin film process is low and the etching selectivity of the silicon material is relatively high. From the application point of view, any thin film process with a deposition temperature below 350° C. can be used, such as low-temperature silicon nitride thin film.

[0045] Step 4: Prepare the required structure on the wafer using photolithography and etching processes.

[0046] Reference Figure 2 Specifically, a photoresist layer is first formed on the surface of the barrier layer 4, and then the pattern is transferred to the photoresist layer through exposure, development and other steps to obtain a photoresist pattern to achieve pattern definition; then, according to the photoresist pattern, the barrier layer 4 and the protective layer 5 are etched, and the pattern is transferred to the barrier layer 4 and the protective layer 5 to pattern them; then, the remaining photoresist material on the surface of the barrier layer 4 is removed through a wet stripping process; finally, a deep silicon etching process is performed using the barrier layer 4 as an etching mask until the final desired structure is prepared, such as Figure 2 As shown in c.

[0047] In this embodiment, the barrier layer 4 and the protective layer 5 are etched by a dielectric film etcher, because the dielectric film etcher used for etching the dielectric film is an industry standard. In other embodiments, other dry etching methods may also be used directly.

[0048] Step 5: Remove the remaining barrier layer 4 using a dry etching process.

[0049] Because anodic bonding will be performed later, the barrier layer 4 on the surface must be removed completely. Because the buried oxide layer 2 of the SOI wafer is exposed at this time, the barrier layer 4 cannot be removed by wet etching, but can only be removed by dry etching.

[0050] During the dry etching of the barrier layer 4, since there is a layer of polyimide material under the barrier layer 4, the final bonding surface of the wafer (i.e., the surface of the top silicon layer 3) will not be damaged during the bombardment of the etching gas, and the bonding surface can be well protected, thereby obtaining a bonding surface that meets the final bonding roughness requirements.

[0051] Step 6: Remove the remaining protective layer 5 using a dry stripping process.

[0052] The dry stripping process for polyimide materials usually adopts a plasma dry etching process with oxygen as the main etching gas. This step is a prior art and will not be described in detail here. At this point, the structure preparation work on the wafer has been completed, and anodic bonding can be performed later.

[0053] Step 7: Provide a second wafer and perform anodic bonding.

[0054] The product obtained after step 6 is cleaned to remove impurities that may be introduced during the dry stripping process, and then an anodic bonding process is performed with the provided second wafer.

[0055] In order to facilitate the description, some common English nouns or letters used in the present invention are only used for exemplary reference rather than restrictive interpretation or specific usage, and the protection scope of the present invention should not be limited by their possible Chinese translations or specific letters.

[0056] It should also be noted that, in this document, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

Claims

1. A method for protecting an anodic bonding surface during deep silicon etching, characterized in that: include: S1. providing a wafer, and sequentially forming a protective layer and a barrier layer on the surface of the wafer; S2, patterning the barrier layer and the protective layer by using photolithography and etching processes; S3, using the patterned barrier layer as an etching mask, preparing the desired structure through a deep silicon etching process; S4. Remove the barrier layer by using a dry etching process, and remove the protective layer by using a dry stripping process.

2. A method for protecting an anodic bonding surface in deep silicon etching according to claim 1, characterized in that: In step S1, the formation of the protection layer includes spin coating polyimide on the surface of the wafer and performing a curing treatment, and the temperature of the curing treatment is between 350°C and 400°C.

3. A method for protecting an anodic bonding surface in deep silicon etching according to claim 2, characterized in that: In step S1 , the barrier layer is formed by a low temperature deposition process, wherein the deposition temperature of the low temperature deposition process is lower than the temperature of the curing process.

4. A method for protecting an anodic bonding surface in deep silicon etching according to claim 1, characterized in that: In step S1, the barrier layer is a silicon dioxide layer.

5. The method for protecting an anodic bonding surface during deep silicon etching according to claim 1, characterized in that: In step S2, it includes: S201, spin coating a photoresist on the surface of the barrier layer and performing exposure and development treatment to obtain a photoresist pattern; S202, using the photoresist pattern as an etching mask, patterning the barrier layer and the protective layer through a dry etching process; S203, removing the remaining photoresist on the surface of the blocking layer by using a wet stripping process.

6. A method for protecting an anodic bonding surface in deep silicon etching according to claim 5, characterized in that: In step S202, the dry etching is performed by a dielectric film etcher.

7. A method for protecting an anodic bonding surface during deep silicon etching according to claim 1, characterized in that: After step S4, a second wafer is provided, and the wafer is anodically bonded to the second wafer.

8. A method for protecting an anodic bonding surface during deep silicon etching according to claim 7, characterized in that: Before the anodic bonding, the wafer is cleaned.

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