MEMS wet etching processing method and MEMS sensor

Abstract

The invention discloses an MEMS wet etching processing method and an MEMS sensor. The processing method comprises the following steps: 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 the initial etching position to expose the silicon substrate below the dielectric layer; carrying out KOH or TMAH wet etching on the exposed silicon substrate so as to etch below the dielectric layer to form a hollow cavity with a preset depth, and then cleaning the wafer; and performing whole-surface etching on the surface of the wafer by using a dry etching process to remove the protective material layer, wherein the whole-surface etching depth is equal to the thickness of the protective material layer. According to the wet etching processing method, the protection material layer is deposited, the silicon substrate is etched at the initial position to expose the silicon substrate, and then the silicon substrate is etched to form the internal cavity, so that damage to a thin film structure above the hollow cavity caused by a processing technology after the hollow cavity is formed is avoided, and the processing efficiency is improved by reducing operation on a wafer on which a thin film is formed. The product yield is improved; and the function completeness of the device is ensured.

Description

Technical Field

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

[0002] In some MEMS (Micro-Electro-Mechanical System) sensors (such as thermopile sensors), a cavity structure needs to be arranged inside the sensor, and there is a suspended film above the cavity structure to achieve specific functions. Common cavity preparation processes can be divided into back etching or front etching. Back etching usually uses an isotropic dry RIE (Reaction Ion Etching) process (such as Bosch process) to form a nearly vertical hollow cavity, or uses an anisotropic wet etching process with potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH) to form a hollow cavity with a specific angle. For front etching, xenon difluoride (XeF2) etching is usually used to form an isotropic etched hollow cavity.

[0003] When performing an anisotropic wet etching process (such as KOH or TMAH) on the front side of a wafer with metal exposure on the wafer surface (such as a flat electrode area, etc.), a chemical reaction will occur with common electrode materials (usually Al, Cu, etc.), resulting in metal corrosion or peeling, affecting the circuit function and device packaging quality; if there is no metal exposure on the wafer surface, after completing the etching of the hollow cavity and obtaining a thin film structure, it is usually necessary to perform steps such as spin coating or spraying, exposure, development, and cleaning of photoresist, and these steps may damage the thin film structure above the hollow cavity. Therefore, the existing technical methods for preparing MEMS sensors have the problem of being unable to efficiently etch and process to obtain an internal cavity. Summary of the Invention

[0004] An embodiment of the present invention provides a MEMS wet etching processing method and a MEMS sensor, aiming to solve the problem that the existing technical methods for preparing MEMS sensors cannot efficiently etch and process to obtain an internal cavity.

[0005] In a first aspect, an embodiment of the present application provides a MEMS wet etching processing method, wherein the etching processing method is used to etch a wafer, and 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 above the dielectric layer on the wafer surface; Etch the protective material layer and the dielectric layer at the starting etching position to expose the silicon substrate below the dielectric layer; the starting etching position is the starting position where an etching solution is required for etching. Perform wet etching of the exposed silicon substrate with KOH or TMAH at the starting etching position to etch a hollow cavity with a preset depth below the dielectric layer, and then clean the wafer. Use a dry etching process to perform full-surface etching on the wafer surface to remove the protective material layer, and the depth of the full-surface etching is equal to the thickness of the protective material layer.

[0006] The MEMS wet etching processing method, wherein depositing the protective material layer on the wafer surface includes depositing the protective material layer by applying plasma-enhanced chemical vapor deposition process or low-pressure chemical vapor deposition process.

[0007] The MEMS wet etching processing method, wherein the thickness of the protective material layer is 100 - 1000 nm.

[0008] The MEMS wet etching processing method, wherein the protective material layer is a SiO layer or a SiN layer.

[0009] The MEMS wet etching processing method, wherein the protective material layer is an AlN layer or an Al2O3 layer.

[0010] The MEMS wet etching processing method, wherein after depositing the protective material layer above the dielectric layer on the wafer surface, it further includes: Perform etching above the electrode, and the etching depth is equal to the depth of the dielectric layer originally covering above the electrode.

[0011] The MEMS wet etching processing method, wherein for the etching performed above the electrode, the size of the obtained etching opening is not greater than the outer contour size of the electrode.

[0012] The MEMS wet etching processing method, wherein the cross-section of the hollow cavity etched below the dielectric layer is in an inverted trapezoid shape.

[0013] The MEMS wet etching processing method, wherein for the etching of the protective material layer and the dielectric layer at the starting etching position, the width of the obtained etching groove is 1 - 50 um.

[0014] Second aspect, an embodiment of the present application further provides a MEMS sensor, which is manufactured by the MEMS wet etching processing method as described in the first aspect above. Among them, the MEMS sensor includes a wafer, the wafer includes a dielectric layer and a silicon substrate stacked in sequence, and the thickness of the silicon substrate is greater than that of the dielectric layer; At least one electrode is embedded in the dielectric layer; the surfaces of the electrodes are all exposed; a hollow cavity is provided below the dielectric layer.

[0015] 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 the dielectric layer on the surface of the wafer; etching the protective material layer and the dielectric layer at the 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 etch a hollow cavity with a preset depth below the dielectric layer and then cleaning the wafer; using a dry etching process to perform a full-surface etching on the surface of the wafer to remove the protective material layer, and the depth of the full-surface etching is equal to the thickness of the protective material layer. The above wet etching processing method deposits a protective material layer, etches at the starting position to expose the silicon substrate and then etches the silicon substrate to form an internal hollow cavity structure, avoiding damage to the thin film structure above the hollow cavity caused by processes such as coating and baking photoresist after forming the hollow cavity, and improving the product yield and ensuring the complete function of the device by reducing the operation on the wafer with the formed thin film. Description of the Drawings

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 It is a flowchart of the MEMS wet etching processing method provided by the embodiment of the present invention; Figure 2 It is another flowchart of the MEMS wet etching processing method provided by the embodiment of the present invention; Figure 3 It is a schematic diagram of the processing process of the MEMS wet etching processing method provided by the embodiment of the present invention; Figure 4 It is another schematic diagram of the processing process of the MEMS wet etching processing method provided by the embodiment of the present invention; Figure 5 It is a cross-sectional structure diagram of the MEMS sensor provided by the embodiment of the present invention; Reference numerals: 1, wafer; 11, dielectric layer; 12, silicon substrate; 13, electrode; 2, protective material layer; 3, hollow cavity; 14, etching groove. Detailed implementation manners

[0018] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0019] It should be understood that when used in this specification and the appended claims, the terms "comprises" and "comprising" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0020] It should also be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms. It should be further understood that the term " / and / " used in the specification of the present invention and the appended claims refers to any combination and all possible combinations of one or more of the related listed items, and includes these combinations.

[0021] The specific embodiments of the present application disclose a wet etching processing method for MEMS. Among them, the etching processing method is used to etch a wafer, and 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 Figure 3 shown in (a) of Figure 4 or Figure 1 shown in (a) of

[0022] S1. Deposit a protective material layer above the dielectric layer on the surface of the wafer.

[0023] First, deposit a protective material layer 2 above 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. As Figure 4 shown in (a) ofFigure 4 as shown in (b) of

[0024] 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 process (PECVD) or a low pressure chemical vapor deposition process (LPCVD) to deposit the protective material layer 2. Specifically, the thickness of the protective material layer 2 is 100 - 1000 nm. The protective material layer 2 must be a non-etchable material or a material with an extremely slow etching rate; wherein, the protective material layer 2 is a SiO layer or a SiN layer; alternatively, the protective material layer 2 is an AlN layer or an Al2O3 layer.

[0025] S2. Etch the protective material layer and the dielectric layer at the starting etching position to expose the silicon substrate under the dielectric layer.

[0026] Etch the protective material layer 2 and the dielectric layer 11 at the starting etching position, so as to expose the silicon substrate 12 under the dielectric layer 11; at this time, it is not necessary to completely expose the silicon substrate 12, only a smaller etching groove 14 needs to be formed, and the bottom surface of the formed etching groove 14 at this time is the upper end surface of the silicon substrate. Specifically, the starting etching position is the starting position where an etching solution needs to be used for etching.

[0027] As Figure 3 shown in (d) of Figure 4 and (c) of , one side of the electrode 13 close to the center of the wafer 1 can be used as the starting etching position, and the starting etching position can be one or more, such as setting two starting etching positions on both sides of the electrode 13 close to the center of the wafer 1 respectively.

[0028] Among them, when etching the protective material layer 2 and the dielectric layer 11, the width of the obtained etching groove 14 is preferably 1 - 50 um. The etching groove 14 is used to inject the etching solution into the silicon substrate 12 for etching in the subsequent wet etching. Therefore, the width of the etching groove 14 needs to 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-width etching groove 14 can be correspondingly etched to improve the etching speed of the hollow cavity 3; if the overall size of the sensor device is small, a smaller-width etching groove 14 can be correspondingly etched.

[0029] S3. Perform wet etching of the exposed silicon substrate with KOH or TMAH at the starting etching position to etch a hollow cavity with a preset depth under the dielectric layer and then clean the wafer.

[0030] Further, the exposed silicon substrate 12 is further etched within the etched groove 14 formed at the starting etching position. Specifically, the KOH or TMAH wet etching process can be used to etch a hollow cavity 3 under the dielectric layer 11. The etching process here corresponds to Figure 3 that shown in (e) in Figure 4 and the processing steps shown in (d) in. The KOH wet etching process is to mix potassium hydroxide (KOH), isopropyl alcohol, and water to obtain an etching solution. The etching solution can selectively etch single-crystalline silicon in different directions. For example, an etching solution is obtained by mixing 23.4 wt% KOH, 13.3 wt% isopropyl alcohol, and 63.3 wt% H2O. The wafer 1 is immersed in the etching solution. The etching solution etches the wafer 1 through the above-mentioned etched groove 14, and the etching solution is heated to ensure that the etching proceeds at a stable rate. The TMAH wet etching process is to prepare a corresponding etching solution with tetramethylammonium hydroxide (TMAH). The wafer 1 is immersed in the etching solution. The etching solution etches the wafer 1 through the above-mentioned etched groove 14, and the etching solution is heated to ensure that the etching proceeds at a specific stable rate. After the etching is completed, the residual etching solution in the silicon substrate 12 is discharged, and the wafer 1 with the hollow cavity 3 can be obtained. The etching depth of the hollow cavity 3 can be controlled. For example, increasing the etching time can increase the depth of the hollow cavity 3 obtained by etching. After the etching is completed, the wafer 1 is cleaned with distilled water.

[0031] The cross-section of the hollow cavity 3 etched under the dielectric layer 11 by the above etching method is trapezoidal in reverse, and the specific structure of the obtained hollow cavity 3 is as shown in Figure 5 shown.

[0032] S4. Use a dry etching process to perform a full-surface etching on the surface of the wafer to remove the protective material layer, and the depth of the full-surface etching is equal to the thickness of the protective material layer.

[0033] Further use a dry etching process to perform a full-surface etching on the surface of the wafer 1. At this time, a certain depth of material on the surface of the wafer 1 can be etched away. By the full-surface etching, the protective material layer 2 can be removed, and thus a complete sensor assembly can be obtained. The full-surface etching process here corresponds to Figure 3 that shown in (f) in Figure 4 and the processing steps shown in (e) in. Since the protective material layer 2 needs to be removed, the depth of the full-surface etching here is equal to the thickness of the protective material layer 2. Whether the surface of the electrode 13 is covered with the dielectric layer 11 or the protective material layer 2, the dielectric layer 11 or the protective material layer 2 covering the surface of the electrode 13 can be removed by the full-surface etching, so that the electrode 13 is exposed and finally the sensor assembly is obtained.

[0034] Please refer to Figure 2, as shown in the figure, the wet etching processing method in the second embodiment of the present application includes steps S1 to S4 and S11.

[0035] After step S1 shown in Figure 1 , it further includes step S11 of etching above the electrode, and the etching depth is equal to the depth of the dielectric layer originally covered above the electrode.

[0036] As shown in Figure 3 (a), in the initial wafer 1, the electrode 13 is embedded in the dielectric layer 11, and the surface layer of the electrode 13 is not exposed, and the surface layer of the electrode 13 is also covered with the dielectric layer 11; then the deposited protective material layer 2 covers the surface layer of the dielectric layer 11, specifically as shown in Figure 3 (b). After the deposition of the protective material layer 2 is completed, the material covered above 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 covered above the electrode 13; that is, the obtained structure after etching is as shown in Figure 3 (c). At this time, the thickness of the dielectric layer 11 covered above the electrode 13 is equal to the thickness of the deposited protective material layer 2.

[0037] In a more specific embodiment, when etching above the electrode 13, the obtained etching opening size is not larger than the outer contour size of the electrode 13. To avoid the complete exposure of the surface layer of the electrode 13 and meet the structural design of the actual device, during the etching of the dielectric layer 11 covered above the electrode 13, the obtained etching opening size needs to be not larger than the outer contour size of the electrode 13. As shown in Figure 3 (c), the width of the etching opening is significantly smaller than the width of the electrode 13. Here, the obtained etching opening only needs to partially expose the electrode 13 and be able to achieve stable electrical connection with external devices, without completely exposing the electrode 13.

[0038] The embodiment of the present invention also provides a MEMS sensor, which is manufactured by the MEMS wet etching processing method as described in the above embodiment. As shown in Figure 5 , the MEMS sensor includes a wafer 1, the wafer 1 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 all exposed; a hollow cavity 3 is provided below the dielectric layer 11.

[0039] Specifically, through the above etching processing method, a hollow cavity 3 can be etched below the dielectric layer 11, and the cross-section of the hollow cavity 3 is trapezoidal in reverse. At least one etching groove 14 is opened at the dielectric layer 11 on both sides of the hollow cavity 3.

[0040] 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 wet etching of the exposed silicon substrate with KOH or TMAH at the starting etching position to etch a hollow cavity with a preset depth below the dielectric layer and then cleaning the wafer; using a dry etching process to perform a full-surface etching on the surface of the wafer to remove the protective material layer, and the depth of the full-surface etching is equal to the thickness of the protective material layer. The above wet etching processing method deposits a protective material layer, etches at the starting position to expose the silicon substrate and then etches the silicon substrate to form an internal hollow cavity structure, avoiding damage to the thin film structure above the hollow cavity caused by processes such as coating and baking photoresist after forming the hollow cavity. By reducing operations on the wafer with the formed thin film, the product yield is improved and the device functions are ensured to be complete.

[0041] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A MEMS wet etching processing method, characterized in that, The described etching process is used to etch a wafer, which 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 above the dielectric layer on the surface of the wafer; Etching the protective material layer and the dielectric layer at the starting etching position to expose the silicon substrate below the dielectric layer; the starting etching position is the starting position where an etching solution is required for etching; Performing wet etching of the exposed silicon substrate with KOH or TMAH at the starting etching position to etch a hollow cavity with a preset depth below the dielectric layer, and then cleaning the wafer; Using a dry etching process to perform full-surface etching on the surface of the wafer to remove the protective material layer, and the depth of the full-surface etching is equal to the thickness of the protective material layer.

2. The MEMS wet etching processing method according to claim 1, wherein The depositing of the protective material layer on the surface of the wafer includes depositing the protective material layer by applying plasma-enhanced chemical vapor deposition process or low-pressure chemical vapor deposition process.

3. The MEMS wet etching processing method according to claim 2, characterized in that, The thickness of the protective material layer is 100 - 1000 nm.

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

5. The MEMS wet etching processing method according to claim 3, characterized in that, The protective material layer is an AlN layer or an Al2O3 layer.

6. The MEMS wet etching processing method according to any one of claims 1-5, characterized in that, After depositing the protective material layer above the dielectric layer on the surface of the wafer, it further includes: Etching above the electrode, and the etching depth is equal to the depth of the dielectric layer originally covering above the electrode.

7. The MEMS wet etching processing method according to claim 6, characterized in that, When etching above the electrode, the size of the obtained etching opening is not larger than the outer contour size of the electrode.

8. The MEMS wet etching processing method according to claim 7, characterized in that, The cross-section of the hollow cavity etched below the dielectric layer is in an inverted trapezoid shape.

9. The MEMS wet etching processing method according to claim 8, wherein When etching the protective material layer and the dielectric layer at the starting etching position, the width of the obtained etching groove is 1 - 50 um.

10. A MEMS sensor, which is manufactured by the MEMS wet etching processing method according to any one of claims 1-9, wherein, The MEMS sensor includes a wafer, which 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 all exposed; a hollow cavity is provided below the dielectric layer.

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