Sealing structure for MEMS device and preparation method thereof

Abstract

The embodiment of the invention relates to a sealing structure for an MEMS device and a preparation method thereof, and the sealing structure comprises a device wafer which comprises at least one MEMS device and a structure gap for accommodating the MEMS device; the cover plate wafer is in bonding connection with the device wafer; the cover plate wafer comprises a concave cavity structure, an air guide groove structure and a plugging structure; the concave cavity structure and the structural gap form an internal cavity; the air guide groove structure is connected with the inner cavity, the blocking structure and the air guide groove structure intersect and intersect at a blocking part, and the blocking part seals the inner cavity. According to the technical scheme provided by the invention, the blocking structure made of the high-temperature backflow material is arranged on one side or two sides of the air guide groove structure, and the air guide groove structure is blocked by utilizing the fluidity of the high-temperature backflow material under specific conditions, so that the sealing of the inner cavity of the MEMS device is realized.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, specifically to a sealing structure for MEMS devices and its fabrication method. Background Technology

[0002] Microelectromechanical systems (MEMS) are miniature devices or systems that integrate microsensors, microactuators, micromechanical structures, micropower sources, signal processing and control circuits, high-performance electronic integrated devices, interfaces, and communication.

[0003] Existing technologies include the use of epitaxial sealing (epi-seal) to fabricate sealed cavities for MEMS devices. This mainly involves using selective epitaxial silicon (SEIS) to seal vent holes pre-fabricated on the front cover of the cavity, thereby achieving a sealed cavity for the MEMS device. However, this process is complex and challenging.

[0004] Eutectic bonding technology can also be used to fabricate sealed cavities, such as using common eutectic bonding methods like Au-Si and Au-Sn. However, this technology has extremely high requirements for surface flatness and roughness, a narrow process window, and stringent parameter control. Bonding quality is highly dependent on the precise matching of temperature, pressure, and time. The narrow process window complicates process development and optimization, and places high demands on equipment stability. Wafer-level eutectic bonding also has high material costs; commonly used bonding materials such as Au are very expensive. There is also a mismatch in the coefficient of thermal expansion between the semiconductor wafer and the metal eutectic alloy bonding layer, which can generate thermal stress during heating and cooling, leading to failure. During bonding and subsequent heat treatment, brittle intermetallic compounds may form between different metals, reducing the mechanical reliability of the bonding interface. Finally, the potential contamination problem must be considered when using eutectic bonding. In device design, the bonding region and isolation structure need to be designed separately to prevent contamination of the core device by the flow of the bonding metal eutectic. The additional bonding region also leads to a larger final device size, increasing device cost. Summary of the Invention

[0005] Based on the above-mentioned situation of the prior art, the purpose of this invention is to provide a sealing structure for MEMS devices and its preparation method, which utilizes the flowability of high-temperature reflow material under specific conditions to seal the venting channel, thereby achieving the sealing of the microcavity of the MEMS device.

[0006] To achieve the above objectives, according to one aspect of the present invention, a sealing structure for MEMS devices is provided, comprising: A device wafer, comprising at least one MEMS device and structural gaps for accommodating the MEMS device; A cover plate wafer is bonded to the device wafer; the cover plate wafer includes a cavity structure, a gas guide groove structure, and a sealing structure; the gap between the cavity structure and the structure forms an internal cavity. The air guide groove structure is connected to the internal cavity, and the sealing structure intersects with the air guide groove structure at the sealing part, and the sealing part seals the internal cavity.

[0007] Furthermore, the sealing structure is formed using a high-temperature reflux material.

[0008] Furthermore, the cover plate wafer includes multiple sealing structures; the multiple sealing structures are spaced apart along the length direction of the gas guide groove structure.

[0009] Furthermore, the air guide groove structure and the concave cavity structure are located on the same horizontal plane.

[0010] Furthermore, the sealing structure is symmetrically distributed on both sides of the air guide groove structure.

[0011] Furthermore, the cover plate wafer includes multiple cavity structures, and the gas guide groove structure connects two or more cavity structures.

[0012] Furthermore, the high-temperature reflow material includes one of phosphosilicate glass, borosilicate glass, and boron-doped phosphosilicate glass.

[0013] According to another aspect of the present invention, a method for fabricating a sealing structure for a MEMS device is provided, comprising the steps of: S11. Form a device wafer including at least one MEMS device, and form a structural gap on the device wafer for accommodating the MEMS device. S12. Form a cover plate wafer, and form a cavity structure and a gas guide groove structure connected to the cavity structure on the cover plate wafer; form discrete sealing structures on one or both sides of the gas guide groove structure respectively. S13. Bond the device wafer and the cover plate wafer to form a bonded wafer, such that the cavity structure and the gap between the structures form an internal cavity. S14. A vertical exhaust structure is formed on the device wafer, the vertical exhaust structure penetrating the device wafer and connecting to the gas guide groove structure; the atmosphere, gas pressure and / or vacuum degree of the internal cavity are adjusted by the vertical exhaust structure; S15. The discrete sealing structure is subjected to high-temperature reflux treatment, so that the discrete sealing structure flows and is connected through the gas guide groove structure to form a sealing part in the gas guide groove structure.

[0014] Furthermore, the discrete sealing structures are symmetrically distributed on both sides of the length direction of the air guide channel structure.

[0015] Furthermore, it also includes the following steps: S16. The vertical exhaust structure is filled by additive manufacturing process.

[0016] In summary, this invention provides a sealing structure for MEMS devices and its fabrication method. The sealing structure includes: a device wafer, comprising at least one MEMS device and a structural gap for accommodating the MEMS device; a cover wafer bonded to the device wafer; the cover wafer comprising a cavity structure, a gas guide groove structure, and a sealing structure; the cavity structure and the structural gap form an internal cavity; the gas guide groove structure connects to the internal cavity; the sealing structure intersects with the gas guide groove structure at a sealing portion, and the sealing portion seals the internal cavity. The technical solution provided by this invention achieves initial sealing of the internal cavity of the MEMS device by setting a sealing structure composed of high-temperature reflow material on one or both sides of the gas guide groove structure, utilizing the flowability of the high-temperature reflow material under specific conditions to seal the gas guide groove structure. Further strengthening the sealing effect is achieved by filling the vertical exhaust structure using additive manufacturing processes. This simplifies the fabrication process of the sealed microcavity, reduces process development difficulty, eliminates process by-product residues within the microcavity, and eliminates the need to consider bonding areas and potential contamination issues. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for fabricating a sealing structure for MEMS devices provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the cross-sectional structure of the device wafer provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the cross-sectional structure of the cover plate wafer provided in an embodiment of the present invention; Figure 4 This is a top view schematic diagram of the cover plate wafer fabrication process provided in an embodiment of the present invention; Figure 5 yes Figure 4 The cross-sectional view along the AA direction on the cover plate wafer shown; Figure 6 This is a schematic diagram of the bonded wafer structure formed after bonding the device wafer and the cover wafer according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the thinned bonding wafer structure provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of fabricating a vertical venting structure on a bonding wafer according to an embodiment of the present invention; Figure 9 This is a top view of the cover plate wafer after high-temperature reflow treatment provided in an embodiment of the present invention. Figure 10 This is a schematic diagram of the cross-sectional structure of the sealing structure after high-temperature reflux treatment provided in an embodiment of the present invention; Figure 11 This is a schematic diagram of the cross-sectional structure of the sealing structure after filling the vertical exhaust structure provided in the embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0019] It should be noted that, unless otherwise defined, the technical or scientific terms used in one or more embodiments of the present invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in one or more embodiments of the present invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the element or object listed following the word and its equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0020] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings. An embodiment of the present invention provides a method for fabricating a sealing structure for MEMS devices. Figure 1 The flowchart illustrates a method for fabricating a sealing structure for MEMS devices according to an embodiment of the present invention, as shown below. Figure 1 As shown, the preparation method includes the following steps: S11. Form a device wafer 10 including at least one MEMS device, and form a structural gap 105 on the device wafer 10 for accommodating the MEMS device. Figure 2 The diagram shows a cross-sectional view of a device wafer according to an embodiment of the present invention. The steps for forming the device wafer 10 can be referred to... Figure 2The device is fabricated using MEMS or semiconductor processes on silicon wafers, sequentially forming a device support layer 101, a dielectric isolation layer 102, a MEMS device layer 103, a MEMS device anchoring structure 104, a MEMS device structural gap 105, a MEMS device movable structure 106, and a vertical interconnect structure 107. The vertical interconnect structure 107 penetrates the dielectric isolation layer 102 and the MEMS device layer 103, serving as the electrical connection for the MEMS device. The device support layer 101 is made of a conductive material, such as silicon, doped polysilicon, or metal; the dielectric isolation layer 102 is made of an insulating material, such as silicon dioxide or silicon nitride; and the vertical interconnect structure 107 is made of a conductive material, such as silicon, doped polysilicon, or metal.

[0021] S12. Form a cover plate wafer 20, and form a cavity structure 204 and a gas guide groove structure 206 connected to the cavity structure 204 on the cover plate wafer 20; form discrete sealing structures 207 on one or both sides of the gas guide groove structure 206 respectively. Figure 3 The diagram shows a cross-sectional view of the cover plate wafer according to an embodiment of the present invention. The steps for forming the cover plate wafer 20 can be referred to... Figure 3 The cover plate support layer 201, dielectric isolation layer 202, cover plate layer 203, cavity structure 204, support pillar structure 205, gas guide groove structure 206, and discrete sealing structure 207 are sequentially formed using MEMS or semiconductor processes on silicon wafers. The cover plate support layer 201 is made of a conductive material, such as silicon, doped polycrystalline silicon, or metal; the dielectric isolation layer 202 is made of an insulating material, such as silicon dioxide or silicon nitride; the cover plate layer 203 is also made of a conductive material; and the support pillar structure 205 provides insulation and support. Figure 4 The diagram shows a top view of the cover plate wafer fabrication process according to an embodiment of the present invention. Figure 5 It shows Figure 4 The cross-sectional view along the AA direction on the cover plate wafer shown is as follows. Figure 4 and Figure 5 As shown, discrete blocking structures 207 are formed on one or both sides of the air guide groove structure 206. The blocking structures 207 do not pass through the air guide groove structure 206 at this time, and the air guide groove structure 206 is connected to the cavity structure 204. A single blocking structure 207 or multiple blocking structures 207 can be provided for a single air guide groove structure 206, with the multiple blocking structures 207 spaced apart along the length of the air guide groove structure 206. The blocking structure 207 can be provided on one side of the air guide groove structure 206, such as... Figure 4 As shown in the sealing structure 207 on the left, symmetrically distributed separation structures can also be set on both sides of the length of the air guide groove structure 206, such as... Figure 4The sealing structure 207 on the right is shown.

[0022] S13. Bond the device wafer 10 and the cover wafer 20 to form a bonded wafer 30, so that the cavity structure 204 and the structural gap 105 constitute an internal cavity. Figure 6 The diagram shows a schematic of the bonded wafer structure formed after the device wafer and the cover wafer are bonded. According to some optional embodiments, the bonded wafer 30 can also be thinned, so that the device support layer 101 structure is thinned into a thinned device support layer 301. Figure 7 The diagram shows a schematic of the thinned bonded wafer structure.

[0023] S14. For the bonding wafer 30, or the thinned bonding wafer 30, form a vertical exhaust structure 310 on the device wafer 10. Figure 8 The diagram shows a schematic of fabricating a vertical venting structure on a bonded wafer, such as... Figure 8 As shown, the vertical exhaust structure 310 penetrates the device wafer 10 and connects to the gas guide groove structure 206; the atmosphere, gas pressure and / or vacuum degree of the internal cavity can be adjusted through the vertical exhaust structure 310.

[0024] S15. The discrete sealing structure 207 is subjected to high-temperature reflux treatment, so that the discrete sealing structure 207 flows and is connected through the gas guide groove structure 206, forming a sealing part 208 in the gas guide groove structure 206. Figure 9 The diagram shows a top view of the cover plate wafer after the sealing structure has undergone high-temperature reflow treatment. Figure 10 The diagram shows a cross-sectional view of the sealing structure after high-temperature reflow treatment of the sealing structure. High-temperature reflow treatment can be performed in a vacuum environment or under specific atmospheres and pressures to fabricate different MEMS sealing structures. With multiple sealing structures 207, multiple sealing portions 208 are correspondingly formed in the gas guide groove structure 206, thereby improving the reliability of the seal. Even if a single sealing portion 208 fails to completely seal due to process fluctuations, other sealing portions 208 can still provide an effective seal, thus improving the process tolerance and product yield. In the above embodiment, the sealing structures 207 are symmetrically distributed along both sides of the gas guide groove structure 206. During the high-temperature reflow process, the high-temperature reflow material from both sides can simultaneously and uniformly flow to and converge at the center of the gas guide groove structure 206. This balanced flow avoids the offset or distortion of the sealing portion 208 due to excessive stress on one side, ensuring that the formed sealing portion 208 is centered and reducing internal stress.

[0025] S16. The vertical exhaust structure 310 is filled by additive manufacturing process. Figure 11The diagram shows a cross-sectional view of the sealing structure after filling the vertical exhaust structure according to an embodiment of the present invention. The vertical exhaust structure 310 can be filled by additive manufacturing processes such as CVD or epitaxy, thereby further consolidating the sealing effect achieved in step S15 and forming a stable and reliable MEMS sealing structure.

[0026] Embodiments of the present invention also provide a sealing structure for MEMS devices, which can be fabricated using the method provided in the above embodiments of the present invention. The sealing structure for MEMS devices can house the core MEMS devices and provide a specific environmental atmosphere. This specific environmental atmosphere includes, but is not limited to, vacuum, inert gases within a specified pressure range, reducing gases, etc. The core MEMS devices include, but are not limited to, resonators, accelerometers, gyroscopes, pressure sensors, and other sensitive structures. By placing the core MEMS devices within the MEMS sealed cavity structure, the stability of the device can be greatly improved. The sealing structure provided in the embodiments of the present invention employs a lower-cost and simpler process, achieving a sealing structure with good sealing effect. There are no process byproducts remaining in the internal microcavity, and there is no need to consider bonding areas and potential contamination issues. Figure 11 As shown, the sealing structure includes a device wafer 10 and a cover wafer 20 bonded together. The device wafer 10 includes at least one MEMS device and a structural gap 105 for accommodating the MEMS device. The device wafer 10 is formed, for example, from a silicon wafer using MEMS or semiconductor processes, and is combined with… Figure 2 The device wafer 10 includes, in a bottom-up fabrication order, a device support layer 101, a dielectric isolation layer 102, a MEMS device layer 103, a fixed anchoring structure for the MEMS device 104, a structural gap for accommodating the MEMS device 105, a movable structure for the MEMS device 106, and a vertical interconnect structure 107.

[0027] The cover wafer 20 is bonded to the device wafer 10. The cover wafer 20 is formed from a silicon wafer, for example, using MEMS or semiconductor processes. The cover wafer 20 includes a cavity structure 204, a gas channel structure 206, and a sealing structure 207. Figure 3 The cover plate wafer 20 includes, in the order of bottom to top, a cover plate support layer 201, a dielectric isolation layer 202, a cover plate layer 203, a cavity structure 204, a support pillar structure 205, a gas guide groove structure 206, and a sealing structure 207.

[0028] like Figure 10 As shown, in the bonded wafer 30 formed by bonding the cover plate wafer 20 and the device wafer 10, the cavity structure 204 and the structural gap 105 constitute an internal cavity, and the gas guide groove structure 206 and the cavity structure 204 are located on the same horizontal plane. Figure 9As shown, the gas guide groove structure 206 is connected to the internal cavity through the concave cavity structure 204. The sealing structure 207 intersects with the gas guide groove structure 206 at the sealing part 208, thereby sealing the internal cavity. The sealing structure 207 is formed using a high-temperature reflow material, which includes one of phosphosilicate glass, borosilicate glass, and boron-doped phosphosilicate glass.

[0029] The sealing structure 207 is a long strip structure that intersects with the air guide groove structure 206. The part where the sealing structure 207 intersects with the air guide groove structure 206 is the sealing part 208. The sealing part 208 seals the corresponding part of the air guide groove structure 206 to achieve the sealing of the internal cavity connected to the air guide groove structure 206. Figure 9 The shapes shown are schematic and are not intended to limit the shape of the sealing structure 207 of the present invention.

[0030] According to some optional embodiments, a single blocking structure 207 can be provided for a single air guide groove structure 206, or multiple blocking structures 207 can be provided, with the multiple blocking structures 207 spaced apart along the length direction of the air guide groove structure 206. The blocking structure 207 can be provided on one side of the air guide groove structure 206, such as... Figure 9 As shown in the sealing structure 207 on the left, symmetrically distributed separation structures can also be provided on both sides of the air guide groove structure 206, such as... Figure 9 The sealing structure 207 on the right is shown.

[0031] According to certain optional embodiments, the cover wafer 20 may include a plurality of cavity structures 204, such as Figure 10 As shown, the corresponding device wafer 10 may include multiple MEMS devices and multiple structural gaps 105 for accommodating the MEMS devices. In the bonding wafer 30, multiple cavity structures 204 are connected to the multiple structural gaps 105 in a one-to-one correspondence to form internal cavities. On the cover wafer 20 with multiple cavity structures 204, one or more air guide groove structures 206 may be provided, and the air guide groove structures 206 connect two or more cavity structures 204.

[0032] According to some optional embodiments, the cover wafer 20 further includes a vertical exhaust structure 310, which penetrates the device wafer 10 and connects to the venting groove structure 206. This vertical exhaust structure 310 is used to adjust the atmosphere, pressure, and / or vacuum level of the internal cavity via the venting groove structure 206 during the fabrication of the MEMS device. The venting groove structure 206 is connected to the internal cavity, thus allowing the vertical exhaust structure 310 to adjust the atmosphere, pressure, and / or vacuum level of the internal cavity via the venting groove structure 206 during the fabrication of the MEMS device. After the MEMS device fabrication is completed, the vertical exhaust structure 310 is filled using an additive manufacturing process, such as... Figure 11As shown, this forms a stable and reliable MEMS sealing structure.

[0033] In summary, the embodiments of the present invention relate to a sealing structure for MEMS devices and its fabrication method. The sealing structure includes: a device wafer, comprising at least one MEMS device and a structural gap for accommodating the MEMS device; a cover wafer, bonded to the device wafer; the cover wafer includes a cavity structure, a gas guide groove structure, and a sealing structure; the cavity structure and the structural gap form an internal cavity; the gas guide groove structure connects to the internal cavity; the sealing structure intersects with the gas guide groove structure at a sealing portion, and the sealing portion seals the internal cavity. The above-mentioned technical solution provided by the present invention achieves preliminary sealing of the internal cavity of the MEMS device by setting a sealing structure composed of high-temperature reflow material on one or both sides of the gas guide groove structure, utilizing the flowability of the high-temperature reflow material under specific conditions to seal the gas guide groove structure; and further enhances the sealing effect by filling the vertical exhaust structure using additive manufacturing processes. This simplifies the fabrication process of the sealed microcavity, reduces the difficulty of process development, eliminates process by-product residues within the microcavity, and eliminates the need to consider bonding areas and potential contamination issues.

[0034] It should be understood that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of this invention, technical features of the above embodiments or different embodiments can also be combined, steps can be implemented in any order, and many other variations exist regarding different aspects of one or more embodiments of the invention as described above; for the sake of brevity, they are not provided in the details. The specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A sealing structure for MEMS devices, characterized in that, include: A device wafer, comprising at least one MEMS device and structural gaps for accommodating the MEMS device; The cover wafer is bonded to the device wafer. The cover plate wafer includes a cavity structure, a gas guide groove structure, and a sealing structure; the gap between the cavity structure and the structure forms an internal cavity. The air guide groove structure is connected to the internal cavity, and the sealing structure intersects with the air guide groove structure at the sealing part, and the sealing part seals the internal cavity.

2. The sealing structure according to claim 1, characterized in that, The sealing structure is formed using a high-temperature reflux material.

3. The sealing structure according to claim 2, characterized in that, The cover plate wafer includes multiple sealing structures; the multiple sealing structures are spaced apart along the length direction of the gas guide groove structure.

4. The sealing structure according to claim 3, characterized in that, The air guide groove structure and the concave cavity structure are located on the same horizontal plane.

5. The sealing structure according to claim 4, characterized in that, The sealing structures are symmetrically distributed on both sides of the air guide groove structure.

6. The sealing structure according to claim 5, characterized in that, The cover plate wafer includes multiple cavity structures, and the gas guide groove structure connects two or more cavity structures.

7. The sealing structure according to any one of claims 2, characterized in that, The high-temperature reflow material includes one of phosphosilicate glass, borosilicate glass, and boron-doped phosphosilicate glass.

8. A method for fabricating a sealing structure for MEMS devices, characterized in that, Including the following steps: S11. Form a device wafer including at least one MEMS device, and form a structural gap on the device wafer for accommodating the MEMS device. S12. Form a cover plate wafer, and form a cavity structure and a gas guide groove structure connected to the cavity structure on the cover plate wafer; form discrete sealing structures on one or both sides of the gas guide groove structure respectively. S13. Bond the device wafer and the cover plate wafer to form a bonded wafer, such that the cavity structure and the gap between the structures form an internal cavity. S14. A vertical exhaust structure is formed on the device wafer, the vertical exhaust structure penetrating the device wafer and connecting to the gas guide groove structure; the atmosphere, gas pressure and / or vacuum degree of the internal cavity are adjusted by the vertical exhaust structure; S15. The discrete sealing structure is subjected to high-temperature reflux treatment, so that the discrete sealing structure flows and is connected through the gas guide groove structure to form a sealing part in the gas guide groove structure.

9. The method according to claim 8, characterized in that, The discrete sealing structures are symmetrically distributed on both sides of the length of the air guide channel structure.

10. The method according to claim 8 or 9, characterized in that, It also includes the following steps: S16. The vertical exhaust structure is filled by additive manufacturing process.

Images