A MEMS wet etching processing method and MEMS sensor

Abstract

The present invention discloses a MEMS wet etching processing method and a MEMS sensor. The processing method includes depositing a protective material layer above a dielectric layer on the surface of a wafer; etching the protective material layer and the dielectric layer at a starting etching position to expose the silicon substrate below the dielectric layer; wet etching the exposed silicon substrate with KOH or TMAH to form a hollow cavity of a preset depth below the dielectric layer, and then cleaning the wafer; and using a dry etching process to etch the entire surface of the wafer to remove the protective material layer, wherein the depth of the entire surface etching is equal to the thickness of the protective material layer. The above-mentioned wet etching processing method deposits a protective material layer, etches at a starting position to expose the silicon substrate, and then etches the silicon substrate to form an internal cavity. This avoids damage to the thin film structure above the hollow cavity caused by the processing after the hollow cavity is formed. By reducing the operation of the wafer with the thin film formed, the product yield is improved and the device function is fully guaranteed.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to a MEMS wet etching processing method and a MEMS sensor. Background Art

[0002] Some MEMS (Micro-Electro-Mechanical System) sensors (such as thermopile sensors) require a cavity structure within the sensor, with a suspended membrane above the cavity structure, to achieve specific functions. Common cavity preparation processes can be categorized as backside etching or frontside etching. Backside etching typically uses an isotropic dry RIE (Reaction Ion Etching) process (such as the Bosch process) to form a nearly vertical hollow cavity, or an anisotropic wet etching process using potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) to form a hollow cavity with a specific angle. For frontside etching, xenon difluoride (XeF2) etching is typically used to form an isotropic hollow cavity.

[0003] When anisotropic wet etching processes (such as KOH or TMAH) are performed on the front side of a wafer with exposed metal (such as in the flat electrode area), chemical reactions occur with common electrode materials (usually Al, Cu, etc.), causing metal corrosion or delamination, affecting circuit function and device packaging quality. If there is no metal exposed on the wafer surface, after completing the hollow cavity etching and obtaining the thin film structure, it is usually necessary to perform spin coating or spray coating of photoresist, exposure, development, and cleaning, all of which may damage the thin film structure above the hollow cavity. Therefore, the existing preparation methods for MEMS sensors have the problem of not being able to efficiently etch the internal cavity. Summary of the Invention

[0004] The embodiments of the present invention provide a MEMS wet etching method and a MEMS sensor, aiming to solve the problem in the prior art methods for preparing MEMS sensors that an internal cavity cannot be obtained by etching efficiently.

[0005] In a first aspect, an embodiment of the present application provides a MEMS wet etching method, wherein the etching method is used to etch a wafer, wherein the wafer includes a dielectric layer and a silicon substrate stacked in sequence; the dielectric layer has at least one electrode embedded therein, and the method includes:

[0006] depositing a protective material layer over the dielectric layer on the surface of the wafer;

[0007] Etching the protective material layer and the dielectric layer at a starting etching position to expose the silicon substrate below the dielectric layer; the starting etching position is a starting position where etching solution is required;

[0008] Performing KOH or TMAH wet etching on the exposed silicon substrate at the starting etching position to form a hollow cavity with a preset depth below the dielectric layer, and then cleaning the wafer;

[0009] The wafer surface is fully etched using a dry etching process to remove the protective material layer, and the depth of the full-surface etching is equal to the thickness of the protective material layer.

[0010] The MEMS wet etching processing method, wherein the depositing of the protective material layer on the surface of the wafer includes applying a plasma enhanced chemical vapor deposition process or a low pressure chemical vapor deposition process to deposit the protective material layer.

[0011] In the MEMS wet etching processing method, the thickness of the protective material layer is 100-1000 nm.

[0012] In the MEMS wet etching processing method, the protective material layer is a SiO layer or a SiN layer.

[0013] In the MEMS wet etching processing method, the protective material layer is an AlN layer or an Al2O3 layer.

[0014] The MEMS wet etching processing method, wherein, after depositing a protective material layer above the dielectric layer on the surface of the wafer, further comprises:

[0015] Etching is performed on the electrode, with the etching depth being equal to the depth of the dielectric layer originally covering the electrode.

[0016] The MEMS wet etching processing method, wherein the etching is performed above the electrode, and the size of the obtained etching opening is not larger than the outer contour size of the electrode.

[0017] In the MEMS wet etching processing method, the cross-section of the hollow cavity etched below the dielectric layer is in the shape of an inverted trapezoid.

[0018] The MEMS wet etching processing method, wherein the protective material layer and the dielectric layer are etched at the starting etching position, and the width of the obtained etching groove is 1-50um.

[0019] In a second aspect, an embodiment of the present application further provides a MEMS sensor, which is manufactured by the MEMS wet etching method described in the first aspect above, wherein the MEMS sensor includes a wafer, the wafer including a dielectric layer and a silicon substrate stacked in sequence, and the thickness of the silicon substrate is greater than the thickness of the dielectric layer;

[0020] At least one electrode is embedded in the dielectric layer; the surfaces of the electrodes are exposed; and a hollow cavity is provided below the dielectric layer.

[0021] An embodiment of the present invention provides a MEMS wet etching processing method and a MEMS sensor. The processing method includes depositing a protective material layer above a dielectric layer on the surface of a wafer; etching the protective material layer and the dielectric layer at a starting etching position to expose the silicon substrate below the dielectric layer; performing KOH or TMAH wet etching on the exposed silicon substrate at the starting etching position to form a hollow cavity of a preset depth below the dielectric layer, and then cleaning the wafer; and using a dry etching process to etch the entire surface of the wafer to remove the protective material layer, wherein the depth of the entire surface etching is equal to the thickness of the protective material layer. The above-mentioned wet etching processing method deposits a protective material layer, etches at a starting position to expose the silicon substrate, and then etches the silicon substrate to form an internal hollow cavity structure, thereby avoiding damage to the thin film structure above the hollow cavity caused by processes such as photoresist coating and baking after the hollow cavity is formed. By reducing the operation of the wafer with the thin film formed, the product yield is improved and the device function is fully guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A flowchart of a MEMS wet etching method according to an embodiment of the present invention;

[0024] Figure 2 Another flow chart of the MEMS wet etching processing method provided by an embodiment of the present invention;

[0025] Figure 3 A schematic diagram of the processing process of the MEMS wet etching processing method provided in an embodiment of the present invention;

[0026] Figure 4 A schematic diagram of another processing process of the MEMS wet etching processing method provided by an embodiment of the present invention;

[0027] Figure 5 A cross-sectional structural diagram of a MEMS sensor provided in an embodiment of the present invention;

[0028] Figure numerals: 1, wafer; 11, dielectric layer; 12, silicon substrate; 13, electrode; 2, protective material layer; 3, hollow cavity; 14, etching groove. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0031] It should also be understood that the terminology used in this specification is for the purpose of describing specific embodiments only and is not intended to limit the present invention. As used in this specification and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It should further be understood that the term "and / or" as used in this specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, including and including these combinations.

[0032] The specific embodiment of the present application discloses a MEMS wet etching method, wherein the etching method is used to etch a wafer, wherein the wafer includes a dielectric layer and a silicon substrate stacked in sequence; at least one electrode is embedded in the dielectric layer, and the initial structure of the wafer is as follows Figure 3 As shown in (a) or Figure 4 See (a) in the figure. Figure 1 As shown in the figure, the wet etching processing method in the first embodiment of the present application includes steps S1 to S4.

[0033] S1. Depositing a protective material layer above the dielectric layer on the surface of the wafer.

[0034] First, a protective material layer 2 is deposited on the dielectric layer 11 on the surface of the wafer 1. The protective material layer 2 can be used to protect the dielectric layer 11 and the exposed electrode 13. Figure 4In (a), the electrode 13 in the initial wafer 1 is embedded in the dielectric layer 11, and the surface of the electrode 13 is exposed; the deposited protective material layer 2 covers the exposed electrode 13 and the surface of the dielectric layer 11, as shown in FIG. Figure 4 As shown in (b).

[0035] In a more specific embodiment, depositing the protective material layer 2 on the surface of the wafer 1 includes applying a plasma enhanced chemical vapor deposition (PECVD) process or a low pressure chemical vapor deposition (LPCVD) process to obtain the protective material layer 2. Specifically, the protective material layer 2 has a thickness of 100-1000 nm. The protective material layer 2 must be a non-etchable material or a material with an extremely slow etching rate; the protective material layer 2 is a SiO layer or a SiN layer; or, the protective material layer 2 is an AlN layer or an Al2O3 layer.

[0036] S2. Etching the protective material layer and the dielectric layer at a starting etching position to expose the silicon substrate below the dielectric layer.

[0037] At the starting etching position, the protective material layer 2 and the dielectric layer 11 are etched to expose the silicon substrate 12 beneath the dielectric layer 11. At this point, the silicon substrate 12 does not need to be completely exposed; only a small etching groove 14 is required. The bottom surface of the etching groove 14 formed at this time serves as the upper end surface of the silicon substrate. Specifically, the starting etching position is the starting point where etching with the etching solution is required.

[0038] like Figure 3 Middle (d) and Figure 4 As shown in (c), the side of the electrode 13 close to the center of the wafer 1 can be used as the starting etching position. The starting etching position can be one or more, such as setting two starting etching positions on the side of the electrodes 13 on both sides close to the center of the wafer 1.

[0039] The protective material layer 2 and the dielectric layer 11 are etched, and the width of the resulting etched groove 14 is preferably 1-50 μm. The etched groove 14 is used to inject the etching solution into the silicon substrate 12 for etching in the subsequent wet etching process. Therefore, the width of the etched groove 14 must match the overall size of the sensor device. If the overall size of the sensor device is large and a larger hollow cavity 3 needs to be etched, a larger etched groove 14 can be etched to increase the etching speed of the hollow cavity 3. If the overall size of the sensor device is small, a smaller etched groove 14 can be etched to obtain a smaller width.

[0040] S3, performing KOH or TMAH wet etching on the exposed silicon substrate at the starting etching position to form a hollow cavity with a preset depth under the dielectric layer, and then cleaning the wafer.

[0041] Furthermore, the exposed silicon substrate 12 is further etched in the etching groove 14 formed at the starting etching position, specifically by using a KOH or TMAH wet etching process, thereby etching a hollow cavity 3 below the dielectric layer 11. The etching process here corresponds to Figure 3 Middle (e) and Figure 4 The processing steps shown in (d) are as follows. KOH wet etching is to mix potassium hydroxide (KOH), isopropyl alcohol, and water to obtain an etching solution. The etching solution can selectively etch single crystal silicon in different directions. For example, 23.4wt% KOH, 13.3wt% isopropyl alcohol, and 63.3wt% H2O are mixed together to obtain an etching solution. Wafer 1 is immersed in the etching solution, and the etching solution etches wafer 1 through the above-mentioned etching tank 14. The etching solution is heated to ensure that the etching proceeds at a stable rate. TMAH wet etching is to prepare a corresponding etching solution by using tetramethylhydroxylamine (TMAH). Wafer 1 is immersed in the etching solution, and the etching solution etches wafer 1 through the above-mentioned etching tank 14. The etching solution is heated to ensure that the etching proceeds at a specific stable rate. After etching is completed, the etching solution remaining in the silicon substrate 12 is discharged to obtain a wafer 1 having a hollow cavity 3. The etching depth of the hollow cavity 3 can be controlled. For example, increasing the etching time can increase the depth of the etched hollow cavity 3. After etching is completed, the wafer 1 is rinsed with distilled water.

[0042] The cross section of the hollow cavity 3 obtained by etching below the dielectric layer 11 using the above etching method is in the shape of an inverted trapezoid. The specific structure of the obtained hollow cavity 3 is as follows: Figure 5 shown.

[0043] S4. Using a dry etching process to perform full-surface etching on the surface of the wafer to remove the protective material layer, the full-surface etching depth is equal to the thickness of the protective material layer.

[0044] Further, the dry etching process is used to etch the entire surface of the wafer 1. At this time, the material of a certain depth on the surface of the wafer 1 can be etched away. The protective material layer 2 can be removed by etching the entire surface, thereby obtaining a complete sensor component. Here, the entire surface etching process corresponds to Figure 3 Middle (f) and Figure 4The processing step shown in (e) above is shown. Because protective material layer 2 needs to be removed, the depth of the full-surface etching performed here is equal to the thickness of protective material layer 2. Regardless of whether the surface of electrode 13 is covered by dielectric layer 11 or protective material layer 2, full-surface etching can remove either dielectric layer 11 or protective material layer 2, exposing electrode 13 and ultimately obtaining the sensor assembly.

[0045] See also Figure 2 As shown in the figure, the wet etching processing method in the second embodiment of the present application includes steps S1~S4 and S11.

[0046] exist Figure 1 After step S1 shown in , the method further includes step S11 of etching above the electrode, wherein the etching depth is equal to the depth of the dielectric layer originally covering the electrode.

[0047] like Figure 3 In (a), the electrode 13 in the initial wafer 1 is embedded in the dielectric layer 11, and the surface of the electrode 13 is not exposed. The surface of the electrode 13 is also covered with the dielectric layer 11; the deposited protective material layer 2 covers the surface of the dielectric layer 11, as shown in FIG. Figure 3 As shown in (b). After the deposition of the protective material layer 2 is completed, the material covering the electrode 13 is etched. At this time, the etching depth is controlled. Specifically, the etching depth needs to be controlled to be equal to the depth of the dielectric layer 11 originally covering the electrode 13. That is, the structure obtained after the etching is completed is as shown Figure 3 As shown in (c), at this time, the thickness of the dielectric layer 11 covering the electrode 13 is equal to the thickness of the deposited protection material layer 2.

[0048] In a more specific embodiment, the etching is performed on the electrode 13, and the size of the etching opening obtained is not larger than the outer contour size of the electrode 13. In order to avoid the surface of the electrode 13 being completely exposed and to meet the structural design of the actual device, the size of the etching opening obtained during the etching of the dielectric layer 11 covering the electrode 13 must be no larger than the outer contour size of the electrode 13, such as Figure 3 As shown in (c), the width of the etched opening is significantly smaller than the width of the electrode 13. Here, the etched opening only needs to partially expose the electrode 13 and achieve a stable electrical connection with an external device, without completely exposing the electrode 13.

[0049] The embodiment of the present invention further provides a MEMS sensor, which is manufactured by the MEMS wet etching method described in the above embodiment. Figure 5As shown, the MEMS sensor includes a wafer 1, which includes a dielectric layer 11 and a silicon substrate 12 stacked in sequence, and the thickness of the silicon substrate 12 is greater than the thickness of the dielectric layer 11; at least one electrode 13 is embedded in the dielectric layer 11; the surfaces of the electrodes 13 are exposed; and a hollow cavity 3 is provided under the dielectric layer 11.

[0050] Specifically, through the above etching method, a hollow cavity 3 can be etched below the dielectric layer 11. The cross section of the hollow cavity 3 is inverted trapezoidal. At least one etching groove 14 is opened in the dielectric layer 11 on both sides of the hollow cavity 3.

[0051] An embodiment of the present invention provides a MEMS wet etching processing method and a MEMS sensor. The processing method includes depositing a protective material layer above a dielectric layer on the surface of a wafer; etching the protective material layer and the dielectric layer at a starting etching position to expose the silicon substrate below the dielectric layer; performing KOH or TMAH wet etching on the exposed silicon substrate at the starting etching position to form a hollow cavity of a preset depth below the dielectric layer, and then cleaning the wafer; and using a dry etching process to etch the entire surface of the wafer to remove the protective material layer, wherein the depth of the entire surface etching is equal to the thickness of the protective material layer. The above-mentioned wet etching processing method deposits a protective material layer, etches at a starting position to expose the silicon substrate, and then etches the silicon substrate to form an internal hollow cavity structure, thereby avoiding damage to the thin film structure above the hollow cavity caused by processes such as photoresist coating and baking after the hollow cavity is formed. By reducing the operation of the wafer with the thin film formed, the product yield is improved and the device function is fully guaranteed.

[0052] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and such modifications or substitutions are intended to be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A MEMS wet etching method, characterized in that: The etching method is used to etch a wafer, wherein the wafer includes a dielectric layer and a silicon substrate stacked in sequence; at least one electrode is embedded in the dielectric layer, and the method includes: depositing a protective material layer over the dielectric layer on the surface of the wafer; Etching the protective material layer and the dielectric layer at a starting etching position to expose the silicon substrate below the dielectric layer; the starting etching position is a starting position where etching solution is required; Performing KOH or TMAH wet etching on the exposed silicon substrate at the starting etching position to form a hollow cavity with a preset depth below the dielectric layer, and then cleaning the wafer; Performing full-surface etching on the wafer surface using a dry etching process to remove the protective material layer, wherein the full-surface etching depth is equal to the thickness of the protective material layer; After depositing a protective material layer on the dielectric layer on the surface of the wafer, the method further includes: Etching is performed above the electrode, and the etching depth is equal to the depth of the dielectric layer originally covering the electrode; the etching opening size obtained by etching above the electrode is not larger than the outer contour size of the electrode; the cross-section of the hollow cavity etched below the dielectric layer is an inverted trapezoid.

2. The MEMS wet etching method according to claim 1, wherein: Depositing the protective material layer on the dielectric layer on the surface of the wafer includes applying a plasma enhanced chemical vapor deposition process or a low pressure chemical vapor deposition process to deposit the protective material layer.

3. The MEMS wet etching method according to claim 2, wherein: The thickness of the protective material layer is 100-1000 nm.

4. The MEMS wet etching method according to claim 3, wherein: The protective material layer is a SiO layer or a SiN layer.

5. The MEMS wet etching method according to claim 3, wherein: The protective material layer is an AlN layer or an Al2O3 layer.

6. The MEMS wet etching method according to claim 1, wherein: The protective material layer and the dielectric layer are etched at the starting etching position, and the width of the obtained etching groove is 1-50um.

7. A MEMS sensor, manufactured by the MEMS wet etching method according to any one of claims 1 to 6, characterized in that: The MEMS sensor includes a wafer, wherein the wafer includes a dielectric layer and a silicon substrate stacked in sequence, and the thickness of the silicon substrate is greater than the thickness of the dielectric layer; At least one electrode is embedded in the dielectric layer; the surfaces of the electrodes are exposed; and a hollow cavity is provided below the dielectric layer.

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