Forming method of boss structure, preparation method of MEMS device and MEMS device

Abstract

The invention discloses a forming method of a boss structure, a preparation method of an MEMS device and the MEMS device, and the forming method of the boss structure comprises the steps: providing a cap wafer and a device wafer, enabling the front surface of the cap wafer to be provided with a cavity, and enabling the front surface of the device wafer and the front surface of the cap wafer to be bonded together to seal the cavity; forming a photoresist layer on the back surface of the device wafer; patterning the photoresist layer to form an opening, wherein the opening exposes the surface of the device wafer above the cavity; etching the device wafer exposed from the opening to a set depth to form a groove, the set depth being smaller than the design height of the boss structure; the thickness of the remaining device wafer above the cavity is trimmed through a trimming process, so that the depth of the groove reaches the design height of the boss structure, and the boss structure is formed in the non-etched area, located on the periphery of the groove, of the back face of the device wafer; and removing the photoresist layer. According to the method, the height difference of the bosses can be accurately controlled and adjusted, so that the capacitance value stability and the metal bonding stability of the MEMS device are improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor device manufacturing, and in particular to a method for forming a boss structure, a method for preparing a MEMS device, and a MEMS device. Background Art

[0002] MEMS (micro-electro-mechanical system) accelerometers and gyroscopes are very susceptible to dust, water vapor, mechanical factors and other factors during the dicing and packaging process due to their movable microstructures, which may cause device damage or device performance degradation. Therefore, MEMS accelerometers and gyroscopes require airtight packaging to prevent damage to the movable microstructures, and at the same time, maintain a stable gas damping coefficient to improve device performance.

[0003] The aluminum-germanium eutectic bonding process is often used in the production of MEMS accelerometers and gyroscopes. Taking the MEMS gyroscope as an example, its production process is as follows: Figure 1-Figure 3 As shown, first, a cap wafer is provided, the cap wafer has an opening, an oxide layer is deposited on the surface of the cap wafer, a device wafer is bonded to the cap wafer, a cavity is formed between the device wafer and the cap wafer, and the structure after bonding is as shown in FIG. Figure 1 As shown; then the top surface of the device wafer is thinned, a boss structure is directly etched on the top surface of the device wafer, and then a germanium layer of a certain thickness is formed on the boss through deposition and patterning processes, and then the device wafer above the cavity is etched to form an interdigitated electrode structure. The structure formed is as shown Figure 2 After that, the structure is flipped over and the germanium layer on the boss is bonded to the aluminum layer on the top surface of the substrate wafer. The device structure is as shown in FIG. Figure 3 shown.

[0004] The capacitance stability of a capacitive MEMS accelerometer or gyroscope refers to the ability of the accelerometer to maintain a constant capacitance value during the measurement process. Capacitance stability is critical to the performance and accuracy of the accelerometer or gyroscope, because changes in capacitance value will directly affect the output signal of the accelerometer. How to improve its stability is related to product yield and production cost.

[0005] In existing technologies, the capacitance stability of capacitive MEMS accelerometers or gyroscopes is affected by many factors, including temperature, humidity, pressure, electromagnetic interference, etc. In order to improve the capacitance stability, advanced manufacturing processes can be used to improve the accuracy and consistency of capacitors and to perform strict calibration and testing during the production process to ensure that the capacitance value is within the specified range. The height difference of the boss will have a certain impact on the capacitance. The greater the height difference of the boss, the greater the distance between the electrodes ( Figure 3As the distance h) from the end of the middle finger electrode to the top metal on the substrate wafer increases, the capacitance value will decrease. This is because the capacitance value is proportional to the area between the electrodes and inversely proportional to the distance. However, it is currently difficult to accurately control the height difference of the bosses from the etching process alone, which is not conducive to the stability of metal bonding and cannot ensure the stability of the capacitance value of the MEMS device. Summary of the invention

[0006] The purpose of the present invention is to provide a method for forming a boss structure, a method for preparing a MEMS device and a MEMS device, so as to achieve precise control and adjustment of the boss height difference, thereby improving the capacitance stability and metal bonding stability of the MEMS device.

[0007] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a method for forming a boss structure, comprising:

[0008] Providing a cap wafer and a device wafer, wherein the front side of the cap wafer has a cavity, and bonding the front side of the device wafer and the front side of the cap wafer together to seal the cavity;

[0009] forming a photoresist layer on the back side of the device wafer;

[0010] Patterning the photoresist layer to form an opening, wherein the opening exposes the surface of the device wafer above the cavity;

[0011] Etching the device wafer exposed by the opening to a set depth to form a groove, wherein the set depth is less than a designed height of the boss structure;

[0012] The thickness of the device wafer remaining above the cavity is trimmed by a trimming process so that the depth of the groove reaches the designed height of the boss structure, and the boss structure is formed in the unetched area of ​​the back side of the device wafer located outside the groove;

[0013] The photoresist layer is removed.

[0014] Optionally, after bonding the front side of the device wafer and the front side of the cap wafer together to seal the cavity, the method further comprises:

[0015] The thickness of the device wafer above the cavity is measured.

[0016] Optionally, after etching the device wafer exposed by the opening to a set depth to form a groove, the method further comprises:

[0017] The thickness of the device wafer remaining above the cavity is measured.

[0018] Optionally, after trimming the thickness of the device wafer remaining above the cavity by a trimming process, the method further includes:

[0019] The thickness of the remaining device wafer above the cavity is measured to determine whether it reaches an expected value.

[0020] Optionally, before trimming the thickness of the device wafer remaining above the cavity by a trimming process, the method further includes:

[0021] The difference between the designed height of the boss structure and the set depth is calculated to obtain the thickness of the device wafer that needs to be removed in the trimming process.

[0022] Optionally, the trimming process adopts an Ion Beam trimming process.

[0023] In a second aspect, the present invention provides a method for preparing a MEMS device, comprising:

[0024] Forming a boss structure on the back side of the device wafer using the boss structure forming method described in the first aspect;

[0025] forming a first metal bonding layer on the surface of the boss structure;

[0026] forming an interdigitated electrode structure in the device wafer above the cavity;

[0027] Providing a base wafer, wherein an insulating layer is formed on the front side of the base wafer, a wiring layer is formed in the insulating layer, a second metal bonding layer corresponding to the boss structure is formed on the insulating layer, and the second metal bonding layer is connected to the wiring layer;

[0028] The back side of the device wafer is bonded to the front side of the base wafer through the first metal bonding layer and the second metal bonding layer.

[0029] In a third aspect, the present invention provides a MEMS device, wherein the MEMS device is obtained by using the method for preparing the MEMS device described in the second aspect.

[0030] The beneficial effects of the present invention are:

[0031] The method for forming a boss structure of the present invention comprises the following steps: firstly forming a photoresist layer on the back side of a device wafer, then patterning the photoresist layer to form an opening exposing the device wafer above the cavity, then etching the device wafer exposed by the opening to a set depth, and then trimming the thickness of the device wafer remaining above the cavity by a trimming process, so that the etching depth of the device wafer reaches the designed height of the boss structure, thereby forming a boss structure on the back side of the device wafer. Compared with the prior art, the present invention can realize precise control and adjustment of the boss height difference by adding a trimming process to compensate for the fluctuation of the etching process, thereby improving the uniformity of the boss height difference on the entire wafer, which is beneficial to improving the stability of subsequent metal bonding.

[0032] Furthermore, in the MEMS device preparation method of the present invention, since the boss structure forming method of the present invention is used to prepare the boss structure on the back side of the device wafer, the height difference of the steps on the wafer surface can be precisely controlled to ensure the accuracy of the distance between the bonding electrodes of the device wafer and the substrate wafer, thereby effectively ensuring the stability of the device capacitance value and improving the yield and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art 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.

[0034] Figure 1-Figure 3 The figure is a schematic diagram of the device structure corresponding to each step in the existing MEMS gyroscope manufacturing process.

[0035] Figure 4-Figure 9 The present invention is a schematic diagram of a device structure corresponding to each step of a method for forming a boss structure according to an embodiment of the present invention.

[0036] Figure 10-13 The present invention is a schematic diagram of a device structure corresponding to each step of a method for preparing a MEMS device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] The following is a further detailed description of a filter chip packaging structure and a wafer-level packaging method of the present invention in combination with the accompanying drawings and specific embodiments. According to the following description and drawings, the advantages and features of the present invention will be clearer. However, it should be noted that the concept of the technical solution of the present invention can be implemented in a variety of different forms and is not limited to the specific embodiments described herein. The drawings are all in a very simplified form and are not in precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0038] The terms "first", "second", etc. in the specification and claims are used to distinguish between similar elements and are not necessarily used to describe a specific order or time sequence. It is to be understood that, where appropriate, these terms used in this way are interchangeable, for example, so that the embodiments of the invention described herein can be operated in an order other than that described or shown herein. Similarly, if the method described herein includes a series of steps, the order of these steps presented herein is not necessarily the only order in which these steps can be performed, and some of the steps described may be omitted and / or some other steps not described herein may be added to the method. If the components in a certain figure are the same as the components in other figures, although these components can be easily identified in all figures, in order to make the description of the figures clearer, this specification will not mark all the same component numbers in each figure.

[0039] Example 1

[0040] like Figure 4-Figure 9 As shown, this embodiment provides a method for forming a boss structure, comprising:

[0041] S1: Figure 4 As shown, a cap wafer 101 and a device wafer 102 are provided, the front surface of the cap wafer 101 has a cavity, and the front surface of the device wafer 102 is bonded to the front surface of the cap wafer 101 to seal the cavity;

[0042] In this embodiment, the front side of the cap wafer 101 has a cavity and is covered with a dielectric layer 103 for bonding. The material of the dielectric layer 103 can be any suitable dielectric material, including but not limited to at least one of silicon oxide, silicon nitride, silicon oxynitride, silicon carbonitride and the like. In this embodiment, it is silicon oxide. The front side of the device wafer 102 is bonded to the front side of the cap wafer 101 to close the cavity. In this embodiment, the materials of the cap wafer 101 and the device wafer 102 are both silicon.

[0043] In this embodiment, after bonding the front surface of the device wafer 102 and the front surface of the cap wafer 101 together to seal the cavity, the method further includes:

[0044] The thickness of the device wafer 102 above the cavity is measured (previous value measurement).

[0045] S2: Figure 5 As shown, a photoresist layer 104 is formed on the back side of the device wafer 102;

[0046] In this step, photoresist is spin-coated on the back side of the device wafer 102 to form a photoresist layer 104 .

[0047] S3: Figure 6 As shown, the photoresist layer 104 is patterned to form an opening, and the opening exposes the surface of the device wafer 102 above the cavity;

[0048] In this step, the photoresist is patterned by exposure and development, and the openings on the patterned photoresist expose the surface of the device wafer 102 above the cavity.

[0049] S4: Figure 7 As shown, the device wafer 102 exposed by the opening is etched to a set depth to form a groove, and the set depth is less than the designed height of the boss structure 105;

[0050] This step can adopt a dry etching process, and use a photoresist mask to etch the device wafer 102 (silicon layer) above the cavity to a set depth. The depth of etching the silicon layer in this step is less than the designed height of the boss structure 105. For example, the preset etching value is a (μm), and the designed height of the boss structure 105 is z (μm), then a<z.

[0051] In this embodiment, after etching the device wafer 102 exposed by the opening to a set depth to form a groove, the method further includes:

[0052] The thickness of the remaining device wafer 102 above the cavity is measured. That is, a median measurement is performed to determine whether the etching depth of this step reaches the expected value a by the difference between the thickness of the silicon layer above the cavity before etching and the remaining thickness of the silicon layer after etching.

[0053] Before executing step S5, the method further includes:

[0054] The difference between the designed height of the boss structure 105 and the set depth is calculated to obtain the thickness of the device wafer 102 that needs to be removed by the trimming process, that is, the thickness of the device wafer 102 that needs to be removed by the trimming process is k=za.

[0055] S5: Figure 8 As shown, the thickness of the device wafer 102 remaining above the cavity is trimmed by a trimming process so that the depth of the groove reaches the designed height of the boss structure 105, and the boss structure 105 is formed in the unetched area on the back side of the device wafer 102 located outside the groove;

[0056] In this step, the trimming process preferably uses the Ion Beam trimming process to trim the thickness of the device wafer 102 (silicon layer) remaining above the cavity. The thickness of the silicon layer above the cavity is accurately adjusted through the trimming process, and the silicon layer with a thickness of k (μm) is removed, so that the depth of the etched groove reaches the designed height of the step, thereby ensuring that the height of the formed boss structure 105 is consistent with the designed height, thereby improving the uniformity of the height difference of the boss structure 105.

[0057] In this embodiment, after trimming the thickness of the device wafer 102 remaining above the cavity by a trimming process, the method further includes:

[0058] The thickness of the remaining device wafer 102 above the cavity is measured to determine whether it reaches the expected value. That is, post-measurement is performed to determine whether the height of the boss structure 105 reaches the designed height by measuring the thickness of the silicon layer above the cavity after trimming.

[0059] S6: Fig. 9 As shown, the photoresist layer 104 is removed.

[0060] In this step, the residual photoresist layer 104 on the surface of the boss structure 105 is removed through a stripping process, thereby forming a highly precisely controlled boss structure 105 on the front side of the device wafer 102 .

[0061] This method compensates for the fluctuation of the etching process by adding a Trimming process and accurately adjusts the depth of the etched groove, so as to achieve accurate control and adjustment of the height difference of the boss structure 105, thereby improving the uniformity of the boss height difference on the entire wafer, which is beneficial to improving the stability of subsequent metal bonding.

[0062] Example 2

[0063] This embodiment provides a method for preparing a MEMS device, comprising:

[0064] S201: Form a boss structure 105 on the back side of the device wafer 102 using the method for forming the boss structure 105 described in the first aspect, such as Fig. 9 As shown;

[0065] S202: Fig.10 As shown, a first metal bonding layer 106 is formed on the surface of the boss structure 105;

[0066] In this embodiment, the material of the first metal bonding layer 106 is germanium.

[0067] The method of forming the first metal bonding layer 106 includes:

[0068] A germanium layer covering the boss structure 105 and the surface of the device wafer 102 is formed on the back side of the device wafer 102, and then the germanium layer is patterned to remove the germanium layer outside the top surface of the boss structure 105, leaving only the germanium layer on the top surface of the boss structure 105, to form a first metal bonding layer 106. The germanium layer can be formed by physical vapor deposition such as magnetron sputtering and evaporation or chemical vapor deposition.

[0069] S203: Fig.11 As shown, an interdigitated electrode structure 107 is formed in the device wafer 102 above the cavity;

[0070] In this step, the device wafer 102 above the cavity can be etched by an etching process to form an interdigitated electrode structure 107, in which the gaps between the interdigitated fingers of the interdigitated electrode structure 107 are connected to the cavity; the etching process preferably adopts a dry etching process.

[0071] S204: Fig.12 As shown, a base wafer 200 is provided, an insulating layer 201 is formed on the front side of the base wafer 200, a wiring layer is formed in the insulating layer 201, a second metal bonding layer 202 corresponding to the boss structure 105 is formed on the insulating layer 201, and the second metal bonding layer 202 is connected to the wiring layer;

[0072] In this embodiment, the material of the second metal bonding layer 202 is aluminum, and the position of the second metal bonding layer 202 on the front side of the base wafer 200 corresponds one-to-one to the first metal bonding layer 106 on the protruding structure. The material of the insulating layer 201 can be any suitable dielectric material, including but not limited to at least one of silicon oxide, silicon nitride, silicon oxynitride, silicon carbonitride, etc., and in this embodiment, it is silicon oxide.

[0073] S205: Fig.13 As shown, the back side of the device wafer 102 is bonded to the front side of the base wafer 200 through the first metal bonding layer 106 and the second metal bonding layer 202 .

[0074] In this embodiment, the first metal layer and the second metal layer may be aligned and bonded together using an aluminum-germanium eutectic bonding process. The MEMS device finally formed in this embodiment may be a capacitive MEMS accelerometer or a gyroscope.

[0075] In the MEMS device preparation method of this embodiment, since the boss structure 105 is prepared on the back side of the device wafer 102 by adopting the formation method of the boss structure 105 of Example 1, the height difference of the steps on the surface of the device wafer 102 can be accurately controlled, thereby ensuring the accuracy of the distance between the bonding electrodes of the device wafer 102 and the base wafer 200 (the distance from the end of the fork finger to the top metal of the base wafer 200), thereby effectively ensuring the stability of the device capacitance value and improving the yield and product quality.

[0076] Example 3

[0077] This embodiment provides a MEMS device, and the MEMS device is obtained by using the preparation method of the MEMS device described in Embodiment 2.

[0078] The MEMS device of this embodiment may be a capacitive MEMS accelerometer or gyroscope. Since it is prepared by the method of Embodiment 2, the stability of the capacitance value of the MEMS device is ensured, and the performance of the device and the yield of the product are improved.

[0079] It should be noted that the various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the structural embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0080] The above description is only a description of the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention. Any changes or modifications made by a person skilled in the art in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A method for forming a boss structure, characterized in that: include: Providing a cap wafer and a device wafer, wherein the front side of the cap wafer has a cavity, and bonding the front side of the device wafer and the front side of the cap wafer together to seal the cavity; forming a photoresist layer on the back side of the device wafer; Patterning the photoresist layer to form an opening, wherein the opening exposes the surface of the device wafer above the cavity; Etching the device wafer exposed by the opening to a set depth to form a groove, wherein the set depth is less than a designed height of the boss structure; The thickness of the device wafer remaining above the cavity is trimmed by a trimming process so that the depth of the groove reaches the designed height of the boss structure, and the boss structure is formed in the unetched area of ​​the back side of the device wafer located outside the groove; The photoresist layer is removed.

2. The method for forming a boss structure according to claim 1, characterized in that: After bonding the front side of the device wafer and the front side of the cap wafer together to seal the cavity, the method further includes: The thickness of the device wafer above the cavity is measured.

3. The method for forming a boss structure according to claim 1, characterized in that: After etching the device wafer exposed by the opening to a set depth to form a groove, the method further comprises: The thickness of the device wafer remaining above the cavity is measured.

4. The method for forming a boss structure according to claim 1, characterized in that: After trimming the thickness of the device wafer remaining above the cavity by a trimming process, the method further includes: The thickness of the remaining device wafer above the cavity is measured to determine whether it reaches an expected value.

5. The method for forming a boss structure according to claim 1, characterized in that: Before trimming the thickness of the device wafer remaining above the cavity by a trimming process, the method further includes: The difference between the designed height of the boss structure and the set depth is calculated to obtain the thickness of the device wafer that needs to be removed in the trimming process.

6. The method for forming a boss structure according to claim 1, characterized in that: The trimming process adopts the Ion Beam trimming process.

7. A method for preparing a MEMS device, characterized in that: include: Forming a boss structure on the back side of the device wafer using the boss structure forming method of claims 1 to 6; forming a first metal bonding layer on the surface of the boss structure; forming an interdigitated electrode structure in the device wafer above the cavity; Providing a base wafer, wherein an insulating layer is formed on the front side of the base wafer, a wiring layer is formed in the insulating layer, a second metal bonding layer corresponding to the boss structure is formed on the insulating layer, and the second metal bonding layer is connected to the wiring layer; The back side of the device wafer is bonded to the front side of the base wafer through the first metal bonding layer and the second metal bonding layer.

8. A MEMS device, characterized in that: The MEMS device is obtained by the preparation method of the MEMS device according to claims 1-7.

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