MEMS Packaging Structure and Fabrication Method

Abstract

The application provides a MEMS packaging structure and a preparation method thereof. By forming a slanted via hole with an inner sidewall slanted to the same side of the normal line of the substrate on a cover plate, and combining a conventional thin film deposition process to deposit a shielding layer, the slanted aperture edge provides a more effective 'bridge' effect for the deposited thin film, so that the thin film can quickly grow laterally on the top of the aperture and shield the aperture. Meanwhile, the slanted hole wall forms a physical shield for the deposition particles incident in a random direction, further reducing the amount of material entering the cavity and deposited on the sensitive MEMS structure. This method achieves the beneficial effects of significantly reducing the deposition in the cavity, maintaining the high performance of the MEMS device, avoiding internal contamination and sticking, improving the applicability of the packaging, and good process compatibility.

Description

Technical Field

[0001] This invention relates to the field of MEMS packaging structure fabrication, and in particular to a MEMS packaging structure and its fabrication method. Background Technology

[0002] Microelectromechanical systems (MEMS) devices, especially microstructures that are extremely sensitive to the environment, such as cantilever beam sensors (approximately 100-200 µm long and 10 µm wide), typically require encapsulation in a sealed cavity environment. This encapsulation is designed to provide comprehensive protection, including protection against dust, moisture, and gas contamination, as well as providing necessary mechanical protection to ensure the long-term stability and reliability of the device.

[0003] In wafer-level packaging (WLP) of MEMS devices, a common cavity formation strategy involves building a sacrificial layer and a capping layer over the MEMS structure. After cavity formation, etchant is typically introduced through vias (also known as vent holes) on the capping layer to remove the internal sacrificial layer, thereby releasing the MEMS structure and forming the final cavity. Once the sacrificial layer is successfully removed, these vias must be reliably shielded to maintain the hermeticity of the cavity, which is crucial for the performance of the MEMS device. Currently, the common method for shielding vias is to use thin-film deposition techniques, i.e., depositing a dense thin film (such as plasma-enhanced chemical vapor deposition (PECVD) silicon nitride, silicon oxide, etc.) over the vias. However, the via shapes commonly used in existing technologies are vertical or near-vertical straight-wall structures. When using conventional thin-film deposition methods (especially chemical vapor deposition techniques with a certain degree of conformity) to shield these straight-walled vias, a significant technical challenge arises: the deposited material not only covers the outside and upper edge of the vias, but also inevitably penetrates deep into the vias and is uniformly deposited on the inner wall of the formed MEMS cavity and the surface of sensitive MEMS structures (such as the surface of a cantilever beam). Even a thin film accidentally deposited inside a cavity can have a series of negative impacts on the performance of MEMS devices: performance drift—increasing the effective mass of a MEMS resonator or cantilever beam, thereby altering its natural frequency, resonant characteristics, and response speed, leading to performance deviations from design values; damping effect—the additional film may alter the airflow dynamics inside the cavity or form an inhomogeneous layer on the surface of sensitive structures, increasing airflow damping or surface friction, thus significantly reducing the device's quality factor (Q value) and sensitivity; internal contamination—the deposit may not be dense enough, generating particles, or in extreme cases, causing adhesion of sensitive structures such as cantilever beams, severely impairing device function and reliability; stress introduction—deposited films often contain internal stress, which may be transmitted to sensitive MEMS structures, causing them to bend and deform, thereby affecting the device's accuracy and long-term stability. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a MEMS packaging structure and its fabrication method, which solves the problems of contamination and performance degradation caused by the entry of deposited material into the cavity where the MEMS structure is formed during the deposition process of the shielding layer due to the use of vertical or nearly vertical straight-walled through-hole structures in the prior art.

[0005] To achieve the above and other related objectives, the present invention provides a method for fabricating a MEMS packaging structure, the method comprising:

[0006] A MEMS device structure is provided, wherein the MEMS device structure comprises, from bottom to top, a substrate, a MEMS structure, and an initial cavity covering the MEMS structure, and the initial cavity is filled with a sacrificial layer.

[0007] A cover plate is formed on the initial cavity, and a plurality of inclined through holes are formed through the cover plate to expose the sacrificial layer; wherein the inner sidewalls of the inclined through holes are inclined toward the same side of the substrate normal;

[0008] The sacrificial layer is removed using a release etching process to form a cavity and levitate the MEMS structure.

[0009] A shielding layer is deposited on the cover plate to shield the inclined through-hole.

[0010] Optionally, the tilt angle of the inclined via relative to the substrate normal is 5° to 60°.

[0011] Optionally, the inclined through hole has two inner straight walls, and the two inner straight walls are parallel to each other.

[0012] Optionally, the inclined through hole has two inner straight walls, and the two inner straight walls are not parallel to each other.

[0013] Optionally, both inner walls of the inclined through hole are stepped, and the stepped inner walls are composed of several alternately connected horizontal and inclined surfaces.

[0014] Optionally, the cover plate is made of silicon, and the inclined through hole is formed by etching the cover plate with potassium hydroxide etchant; or the cover plate is made of silicon dioxide, and the inclined through hole is formed by etching the cover plate with hydrofluoric acid solution or hydrofluoric acid buffer solution.

[0015] Optionally, the inclined via is formed using an ion beam etching process, wherein the ion beam etching process parameters include the incident angle of the ion beam.

[0016] Optionally, the method for forming the shielding layer includes one or more combinations of sputtering, electron beam evaporation, low-pressure chemical vapor deposition, plasma-enhanced chemical vapor deposition, and inductively coupled plasma chemical vapor deposition.

[0017] Optionally, after depositing the shielding layer on the cover plate, the method further includes a step of forming an electrode lead-out structure that penetrates the shielding layer and the cover plate and is electrically connected to the MEMS structure using photolithography and etching processes.

[0018] The present invention also provides a MEMS packaging structure, which is prepared by the MEMS packaging structure preparation method described in any one of the above claims.

[0019] As described above, the MEMS packaging structure and its fabrication method of the present invention have the following beneficial effects: by forming an inclined through-hole with its inner sidewall inclined to the same side as the substrate normal on the cover plate, and combining it with conventional thin film deposition processes to deposit a shielding layer, the inclined aperture edge provides a more effective "bridging" effect for the deposited thin film, allowing the thin film to grow laterally rapidly at the top of the aperture and shield the aperture, rather than directly filling the entire inclined through-hole downwards. Simultaneously, the inclined aperture wall physically shields randomly incident deposition particles, further reducing the amount of material entering the cavity and depositing on the sensitive MEMS structure. This method significantly reduces intracavity deposits, mitigating the negative impact on key parameters such as the intrinsic frequency, Q value, sensitivity, and mechanical response characteristics of the MEMS device, thereby effectively maintaining the original design performance and long-term stability of the device. Furthermore, this method also reduces the risk of internal contamination and adhesion, maintaining a high degree of cleanliness inside the cavity and avoiding adhesion, short circuits, or other reliability problems caused by additional particles or non-uniform thin films. This method utilizes existing mature deposition processes to complete the deposition, eliminating the need for complex or immature specialized equipment and processes. This improves process stability and controllability, reduces production costs, and expands the applicability of packaging technology. This enables MEMS device types highly sensitive to internal contamination (such as high-Q resonators, high-precision inertial sensors, and optical MEMS) to more effectively adopt this wafer-level thin-film packaging technology. Attached Figure Description

[0020] Figure 1 The diagram shows a flow chart of the method for fabricating the MEMS packaging structure of the present invention.

[0021] Figure 2 The diagram shows a schematic representation of the two inner straight walls of the inclined through hole of the present invention being parallel to each other.

[0022] Figure 3 and Figure 4 The diagram shows a tilted through-hole of the present invention with two inner straight walls that are not parallel to each other.

[0023] Figure 5 The diagram shows that both inner walls of the inclined through hole of the present invention are stepped.

[0024] Figure 6 The diagram shows a schematic of the deposition of a shielding layer on the cover plate according to the present invention.

[0025] Component designation explanation

[0026] 10 Substrate, 11 MEMS structure, 12 Initial cavity, 13 Sacrificial layer, 14 Cover plate, 15 Inclined via, 16 Cavity, 17 Shielding layer, 18 Protective layer, Steps S1~S4. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] Please see Figures 1 to 6 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0029] This embodiment provides a method for fabricating a MEMS packaging structure, such as... Figure 1 As shown, the preparation method includes:

[0030] S1, providing a MEMS device structure, the MEMS device structure including, from bottom to top, a substrate, a MEMS structure and an initial cavity covering the MEMS structure, the initial cavity being filled with a sacrificial layer;

[0031] S2, a cover plate is formed on the initial cavity, and a plurality of inclined through holes are formed through the cover plate to expose the sacrificial layer; wherein the inner sidewalls of the inclined through holes are inclined toward the same side of the substrate normal;

[0032] S3, the sacrificial layer is removed using a release etching process to form a cavity and to levitate the MEMS structure;

[0033] S4, deposit a shielding layer on the cover plate to shield the inclined through hole.

[0034] The method for fabricating the MEMS packaging structure in this embodiment involves forming a tilted via with its inner sidewall sloping towards the same side as the substrate normal on a cover plate, and then depositing a shielding layer using conventional thin-film deposition processes. The tilted via edge provides a more effective "bridging" effect for the deposited thin film, allowing the film to grow rapidly laterally at the top of the via and shield it, rather than directly filling the entire tilted via downwards. Simultaneously, the tilted via wall physically shields randomly incident deposition particles, further reducing the amount of material entering the cavity and depositing on the sensitive MEMS structure. This method significantly reduces intracavity deposits, mitigating the negative impact on key parameters such as the MEMS device's intrinsic frequency, Q value, sensitivity, and mechanical response characteristics, thereby effectively maintaining the device's original design performance and long-term stability. Furthermore, this method reduces the risk of internal contamination and adhesion, maintaining a high level of cleanliness inside the cavity and avoiding adhesion, short circuits, or other reliability issues caused by additional particles or non-uniform films. This method can utilize existing mature deposition processes to complete the deposition without introducing complex or immature special equipment and processes, improving process stability and controllability, reducing production costs, and expanding the applicability of packaging technology. This enables MEMS device types that are highly sensitive to internal contamination (such as high-Q resonators, high-precision inertial sensors, optical MEMS, etc.) to more effectively adopt this wafer-level thin-film packaging technology.

[0035] The following is combined with Figures 2 to 6 The fabrication method of the MEMS packaging structure of the embodiment will be described in detail.

[0036] like Figures 2 to 5 As shown, step S1 is performed first to provide a MEMS device structure. The MEMS device structure includes, from bottom to top, a substrate 10, a MEMS structure 11, and an initial cavity 12 covering the MEMS structure 11. The initial cavity 12 is filled with a sacrificial layer 13.

[0037] Specifically, as an example, the substrate 10 includes a silicon substrate, and the size of the substrate 10 is preferably wafer-level. The material type and size of the substrate 10 can be selected according to actual needs, and no excessive restrictions are imposed here.

[0038] As an example, other functional films or other functional structures may also be formed on the substrate 10. The specific configuration can be determined according to the actual needs of the MEMS packaging structure, and no excessive restrictions are imposed here.

[0039] As an example, the MEMS structure 11 includes a cantilever beam structure, a MEMS resonator structure or other sensitive structures. The MEMS structure 11 can be fabricated using conventional techniques in the art, which will not be elaborated on here.

[0040] As an example, a protective layer 18 is also formed on the outer side of the sacrificial layer 13, and the sacrificial layer 13 inside the protective layer 18 forms the initial cavity 12. After the sacrificial layer 13 is subsequently removed, the initial cavity 12 forms a cavity 16 (see reference). Figure 6 The method of forming the initial cavity 12 will not be elaborated here.

[0041] like Figures 2 to 5 As shown, step S2 is continued, a cover plate 14 is formed on the initial cavity 12, and a plurality of inclined through holes 15 are formed through the cover plate 14 to expose the sacrificial layer 13; wherein, the inner sidewall of the inclined through holes 15 is inclined toward the same side of the normal of the substrate 10.

[0042] Specifically, unlike the vertical or nearly vertical straight wall structure commonly used in the prior art, the inner wall of the inclined through-hole 15 is not perpendicular to the surface of the substrate 10. It is then shielded by conventional thin film deposition process. The inclined aperture edge provides a more effective "bridging" effect for the deposited thin film. The thin film will grow laterally quickly at the top of the aperture and shield the aperture, instead of directly filling the entire inclined through-hole 15 downwards.

[0043] As an example, the tilt angle between the inclined through hole 15 and the normal of the substrate 10 is 5° to 60°. The specific angle can be adjusted according to the material of the cover plate 14 and the process of forming the inclined through hole 15. No excessive restrictions are imposed here.

[0044] As a specific example, such as Figure 2 As shown, the inclined through hole 15 has two inner straight walls, and the two inner straight walls are parallel to each other.

[0045] As another specific example, such as Figure 3 and Figure 4 As shown, the inclined through hole 15 has two inner straight walls, and the two inner straight walls are not parallel to each other.

[0046] As a further better example, such as Figure 3 As shown, the two inner straight walls form the inclined through hole 15 with an upper aperture smaller than the lower aperture. When the shielding layer 17 is subsequently deposited on the cover plate 14, the upper aperture will form a natural "bottleneck" effect, which will restrict the deposited material from entering the aperture, thereby reducing the amount of material entering the cavity. The film will grow laterally rapidly at the upper aperture and cover the aperture.

[0047] In other examples, such as Figure 4As shown, the inclined through-hole 15 with an upper aperture larger than the lower aperture can also be formed. When the shielding layer 17 is subsequently deposited on the cover plate 14, the larger upper aperture provides a wider "bridging" platform for the deposited material, making it easier for the material to accumulate at the orifice and quickly cover the orifice.

[0048] As another concrete example, such as Figure 5 As shown, both inner walls of the inclined through-hole 15 are stepped, and the stepped inner walls are composed of several alternately connected horizontal and inclined surfaces. When the shielding layer 17 is subsequently deposited on the cover plate 14, the stepped inner walls provide multiple "steps" or "platforms" for the deposited material. During the thin film deposition process, the deposited material accumulates on each horizontal surface. Through layered accumulation, the deposited material more easily forms a dense shielding layer 17 at the orifice, thereby improving sealing efficiency and airtightness. Simultaneously, the stepped inner walls form multiple physical shielding layers, which block the deposited material when it enters the inclined through-hole 15, thus reducing the amount of material entering the cavity.

[0049] As an example, the inclined through-hole 15 can be formed using a wet etching process, but it is not limited to this. Other processes can also be used to form the inclined through-hole 15, and no excessive restrictions are imposed here.

[0050] As a further example, the cover plate 14 is made of silicon, and the inclined through-hole 15 is formed by etching the cover plate 14 with potassium hydroxide (KOH) etchant. KOH etching has anisotropic characteristics and can precisely etch according to the crystal orientation of silicon. By adjusting the etching time and conditions, the depth, width, and tilt angle of the inclined through-hole 15 can be precisely controlled. As another further example, the cover plate 14 is made of silicon dioxide, and the inclined through-hole 15 is formed by etching the cover plate 14 with hydrofluoric acid solution or hydrofluoric acid buffer solution. No excessive limitations are made here regarding the material of the cover plate 14 and the method of forming the inclined through-hole 15.

[0051] As an example, the inclined via 15 is formed using an ion beam etching process. The ion beam etching process parameters include the incident angle of the ion beam. By changing the incident angle of the ion beam, the inclined via 15 with a specific tilt angle can be formed. By step etching, the inclined via 15 with a stepped inner sidewall can be formed.

[0052] like Figure 6 As shown, step S3 is performed, in which the sacrificial layer 13 is removed using a release etching process to form a cavity and to levitate the MEMS structure.

[0053] As an example, the sacrificial layer 13 can be removed using either a dry or wet etching process to form the cavity 16. The etchant rapidly connects to the sacrificial layer 13 through the inclined via 15 to remove the sacrificial layer 13. Specifically, when the sacrificial layer 13 is made of silicon dioxide, a gaseous hydrogen fluoride release etching process can be used to remove the sacrificial layer 13, or a buffered oxide etchant (BOE etchant) plus supercritical drying process can be used for wet etching of the sacrificial layer 13. In this way, during the release of the sacrificial layer 13, the etchant can quickly and freely enter the cavity 16 from the inclined via 15.

[0054] like Figure 6 As shown, step S4 is continued, where a shielding layer 17 is deposited on the cover plate 14 to shield the inclined through hole 15.

[0055] Specifically, the main function of the shielding layer 17 in shielding the inclined through-holes 15 is to prevent contamination inside the cavity 16. In one embodiment, the shielding layer 17 can completely seal all the openings of the inclined through-holes 15. In another embodiment, the shielding layer 17 may not completely seal all the openings of the inclined through-holes 15. In yet another embodiment, the shielding layer 17 may completely seal a large portion of the openings of the inclined through-holes 15, leaving the remaining smaller portion unshielded. As long as it can isolate impurities, filling liquid, or other contaminants from entering the cavity 16 and causing contamination, it is sufficient. The degree to which the shielding layer 17 shields the inclined through-holes 15 is not excessively limited here.

[0056] As an example, the method for forming the shielding layer 17 includes one or more combinations of sputtering, electron beam evaporation, low-pressure chemical vapor deposition (LPCVD), plasma-enhanced chemical vapor deposition (PECVD), and inductively coupled plasma chemical vapor deposition. Specifically, it includes, but is not limited to, sputtering SiO2, sputtering SiN, sputtering metal, electron beam evaporation of metal, electron beam evaporation of SiO2, electron beam evaporation of SiN, PECVD SiNx, LPCVD SiNx, etc. That is, the deposition can be completed using existing mature deposition processes without the need to introduce complex or immature special equipment and processes, which improves the stability and controllability of the process, reduces production costs, and expands the applicability of packaging technology.

[0057] As an example, after depositing the shielding layer 17 on the cover plate 14, the method further includes forming an electrode lead-out structure (not shown) that penetrates the shielding layer 17 and the cover plate 14 and is electrically connected to the MEMS structure 11 using photolithography and etching processes.

[0058] Specifically, other functional conductive structures (not shown) are also formed around the protective layer 18, such as a metal layer. The functional conductive structures are in contact with the electrodes of the MEMS structure 11. The electrode lead-out structure passes through the shielding layer 17 and the cover plate 14, and is electrically connected to the electrodes of the MEMS structure 11 through the functional conductive structures to meet the packaging requirements. The specific structure can be set according to the product requirements, and will not be elaborated in detail here.

[0059] This embodiment also provides a MEMS packaging structure, which can be prepared using the above-described MEMS packaging structure preparation method, but is not limited to this. Other suitable preparation methods are also possible, and their beneficial effects can be found in the specific description of the preparation method, which will not be repeated here.

[0060] In summary, the MEMS packaging structure and its fabrication method of this invention utilize a tilted via formed on a cover plate with its inner sidewalls inclined towards the same side as the substrate normal, combined with a conventional thin-film deposition process to deposit a shielding layer. The tilted aperture edge provides a more effective "bridging" effect for the deposited thin film, allowing the film to grow rapidly laterally at the top of the aperture and shield it, rather than directly filling the entire tilted via. Simultaneously, the tilted aperture walls physically shield randomly incident deposition particles, further reducing the amount of material entering the cavity and depositing on the sensitive MEMS structure. This method significantly reduces intracavity deposits, mitigating the negative impact on key parameters of the MEMS device such as its intrinsic frequency, Q value, sensitivity, and mechanical response characteristics, thereby effectively maintaining the original design performance and long-term stability of the device. Furthermore, this method reduces the risk of internal contamination and adhesion, maintaining a high degree of cleanliness inside the cavity and avoiding adhesion, short circuits, or other reliability issues caused by additional particles or non-uniform films. This method utilizes existing mature deposition processes to complete the deposition, eliminating the need for complex or immature specialized equipment and processes. This improves process stability and controllability, reduces production costs, and expands the applicability of packaging technology. This enables MEMS device types highly sensitive to internal contamination (such as high-Q resonators, high-precision inertial sensors, and optical MEMS) to more effectively adopt this wafer-level thin-film packaging technology. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and possesses high industrial applicability.

[0061] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for fabricating a MEMS packaging structure, characterized in that, The preparation method comprises: providing a MEMS device structure comprising, from bottom to top, a substrate, a MEMS structure, and an initial cavity covering the MEMS structure, the initial cavity being filled with a sacrificial layer; forming a cover plate on the initial cavity, and forming a plurality of inclined through holes penetrating through the cover plate to expose the sacrificial layer, wherein the inner side walls of the inclined through holes are inclined toward the same side of the normal line of the substrate; removing the sacrificial layer by a release etching process to form a cavity and suspend the MEMS structure; depositing a shielding layer on the cover plate to shield the inclined through holes.

2. The method of claim 1, wherein: The inclined angle of the inclined through holes with respect to the normal line of the substrate is 5°-60°.

3. The method of claim 1, wherein: The inclined through holes have two inner side straight walls, and the two inner side straight walls are parallel to each other.

4. The method of claim 1, wherein: The inclined through holes have two inner side straight walls, and the two inner side straight walls are not parallel to each other.

5. The method of claim 1, wherein: The two inner side walls of the inclined through holes are both in a stepped shape, and the inner side walls in the stepped shape are composed of a plurality of alternately connected horizontal surfaces and inclined surfaces.

6. The method of claim 1, wherein: The material of the cover plate is silicon, and the inclined through holes are formed by etching the cover plate using a potassium hydroxide etchant; or the material of the cover plate is silicon dioxide, and the inclined through holes are formed by etching the cover plate using a hydrofluoric acid solution or a hydrofluoric acid buffer solution.

7. The method of claim 1, wherein: The inclined through holes are formed by an ion beam etching process, and the ion beam etching process parameters include the incident angle of the ion beam.

8. The method of claim 1, wherein: The method for forming the shielding layer comprises one or more combinations of sputtering, electron beam evaporation, low-pressure chemical vapor deposition, plasma-enhanced chemical vapor deposition, and inductively coupled plasma chemical vapor deposition.

9. The method of claim 1, wherein: After depositing the shielding layer on the cover plate, the method further comprises the step of forming an electrode lead-out structure penetrating through the shielding layer and the cover plate and electrically connected to the MEMS structure by using a photolithography and etching process.

10. A MEMS package structure, characterized by: The MEMS packaging structure is prepared by using the preparation method according to any one of claims 1 to 9.

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