A method for manufacturing a MEMS device and a MEMS device

Abstract

The application provides a manufacturing method of a MEMS device and the MEMS device, and the manufacturing method comprises the following steps: providing a first wafer and a second wafer, the second wafer is bonded on one side of the first wafer, and the first wafer and the second wafer form a first cavity; sequentially arranging a first mask layer and a second mask layer on the side of the second wafer away from the first wafer, the material of the second mask layer is different from that of the first mask layer; etching the second wafer according to the second mask layer to form a plurality of comb tooth structures arranged at intervals at positions corresponding to the first cavity, and removing the second mask layer; etching the second wafer according to the first mask layer to form a boss, the boss is located outside the first cavity in orthographic projection, and the first mask layer is removed. According to the application, the second wafer is etched to form the comb tooth structure first, then the second wafer is etched to form the boss, and the first mask layer is arranged before etching the comb tooth structure, so that the problem that the thickness of the photoresist on the vertical support anchor point is insufficient and the vertical support anchor point appears a groove is solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a method for fabricating a MEMS device and a MEMS device. Background Technology

[0002] MEMS sensors are a new type of sensor manufactured using microelectronics and micromachining technologies. They are characterized by small size, light weight, low cost, low power consumption, high reliability, high added value, suitability for mass production, ease of integration, and the potential for intelligent implementation. In a typical MEMS structure, a vertical support anchor point design is required to achieve mechanical isolation between the comb teeth and the bottom electrode. The step height of the vertical support anchor point determines the sensitivity and shock resistance of the out-of-plane inertial unit along the Z-axis.

[0003] However, in traditional MEMS devices, grooves appear on the sides of the vertical support anchors when etching the comb structure, which reduces the mechanical strength of the support anchors. Summary of the Invention

[0004] The problem solved by this invention is that grooves appear at the vertical support anchor points during the fabrication of existing MEMS devices.

[0005] To address the above problems, this invention provides a method for fabricating a MEMS device, the method comprising: A first wafer and a second wafer are provided, wherein the second wafer is bonded to one side of the first wafer and together with the first wafer forms a first cavity; A first mask layer and a second mask layer are sequentially disposed on the side of the second wafer away from the first wafer, and the material of the second mask layer is different from the material of the first mask layer; The second wafer is etched according to the second mask layer to form a plurality of spaced comb-tooth structures at positions corresponding to the first cavity, and the second mask layer is removed. The second wafer is etched according to the first mask layer to form a boss, the orthogonal projection of the boss being located outside the first cavity, and the first mask layer is removed.

[0006] Optionally, before etching the second wafer according to the first mask layer to form the bump, the fabrication method further includes: A first thermal oxide layer is provided on the outer surface of the second wafer, the outer surface of the comb structure, and the outer surface of the first cavity.

[0007] Optionally, etching the second wafer according to the first mask layer to form the boss includes: The second wafer is etched on the side away from the first wafer and the comb structure is etched on the side away from the first wafer to form the protrusion at the position corresponding to the first mask layer.

[0008] Optionally, when removing the first mask layer, the manufacturing method further includes: removing the first thermal oxidation layer.

[0009] Optionally, after providing the first wafer, the fabrication method further includes: forming a second thermal oxide layer on the outer surface of the first wafer.

[0010] Optionally, the material of the first mask layer includes silicon oxide, silicon nitride, or TEOS, and the material of the second mask layer includes photoresist.

[0011] Optionally, the material of the first thermal oxide layer includes thermally oxidized silicon.

[0012] Optionally, a third wafer is provided, on which a metal bonding layer is disposed; The metal bonding layer of the third wafer is bonded to the protrusion on the second wafer to form a second cavity; The projections of the second cavity and the first cavity onto the surface of the second wafer partially or completely overlap.

[0013] Optionally, the material of the metal bonding layer is one or more of chromium, gold, titanium, platinum, and titanium-tungsten.

[0014] This application also provides a MEMS device, which is manufactured using any of the methods described above.

[0015] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages: 1. The MEMS device fabrication method provided in this application involves first etching a second wafer to form a comb structure based on a second mask layer, and then etching the second wafer to form bosses (i.e., vertical support anchors) based on a first mask layer. Since the first mask layer is set before etching the comb structure, and the first mask layer is set on the second wafer with a flat surface, the problem of insufficient photoresist thickness at the vertical support anchors due to height differences, which could lead to trench defects on the sides of the vertical support anchors during comb structure formation, is avoided. Furthermore, since the material of the second mask layer is different from that of the first mask layer, the first mask layer is not damaged during the removal of the second mask layer, ensuring the accuracy and structural integrity of the subsequent boss etching.

[0016] 2. The MEMS device fabrication method provided in this application embodiment, before etching the second wafer according to the first mask layer to form the protrusion, also provides a first thermal oxide layer on the outer surface of the second wafer, the outer surface of the first mask layer, the outer surface of the comb structure, and the outer surface of the first cavity. By providing the first thermal oxide layer, the sidewalls of the comb structure can be protected at all times during the etching process, avoiding lateral ion bombardment. Furthermore, the first thermal oxide layer provided on the front surface of the second wafer and the comb structure can be simultaneously etched away during ion bombardment, without adversely affecting the normal formation of the protrusion.

[0017] 3. The method for fabricating a MEMS device provided in this application further includes removing the first thermal oxide layer when removing the first mask layer. Since the materials of the first mask layer and the first thermal oxide layer are similar or have similar corrosion resistance properties, the first mask layer and the first thermal oxide layer can be removed simultaneously by immersion in the same corrosion solution, simplifying the process steps and improving the fabrication efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the fabrication process of MEMS devices in the prior art; Figure 2 This is a schematic diagram illustrating the state of trench defects generated during the fabrication of MEMS devices in the existing technology. Figure 3 A schematic diagram of trench defects in existing MEMS devices; Figure 4 A schematic flowchart illustrating the fabrication method of the MEMS device provided in the embodiments of this application; Figure 5 for Figure 4 The process flow diagram corresponding to the manufacturing method shown; Figure 6 for Figure 4 The diagram illustrates the manufacturing method in which a first thermal oxidation layer is set to protect the sidewalls of the comb tooth structure.

[0019] Explanation of reference numerals in the attached figures: 1. MEMS device; 11. First wafer; 12. First mask layer; 101. First cavity; 13. Second mask layer; 14. Second wafer; 15. Comb structure; 16. First thermal oxide layer; 17. Boss; 18. Second thermal oxide layer; 201. Germanium; 202. Groove. Detailed Implementation

[0020] To make the above-mentioned objectives, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0021] In typical sandwich-structure MEMS devices, a vertical support anchor point (STD) structure, i.e., a boss 17, is usually introduced to achieve mechanical isolation between the movable comb teeth and the bottom electrode. The STD is usually designed to be higher than the two side planes, thus forming a certain step height. The step height serves as a vertical structure to provide electrical connection and also prevents mechanical collisions under high G impacts. The performance of mechanical collision protection is proportional to the STD height, which directly determines the detection sensitivity and shock resistance reliability of the out-of-plane inertial sensing unit in the Z-axis direction. It is a key structural parameter affecting device performance.

[0022] like Figure 1 As shown, Figure 1 This is a schematic diagram of the fabrication process of MEMS devices in the prior art. In the prior art process, the formation of the STD structure and the subsequent etching of the device pattern usually adopt a step-by-step etching scheme: first, the STD main structure is defined by the first etching process to form a height difference; on this basis, the second etching is performed to complete the patterning of the germanium 201 deposition layer (Ge-dep) in the STD mesa region; finally, the comb structure 15 of the device core is defined by the third etching.

[0023] However, when the step height formed by the STD is high, the photoresist mask exhibits significant poor conformal properties at the STD sidewalls and step corners. Specifically, this manifests as follows: Figure 2 and Figure 3 As shown, Figure 2 This is a schematic diagram illustrating the state of trench defects generated during the fabrication of MEMS devices in the existing technology. Figure 3 This diagram illustrates a trench defect in a current MEMS device. The photoresist thickness at the STD edge region is significantly thinner. During subsequent etching of the comb structure (FS), the local mask protection is insufficient, leading to premature photoresist consumption and over-etching of the substrate, resulting in a trench 202 defect in the STD region. Simply increasing the photoresist thickness to improve sidewall coverage would reduce lithographic resolution, thereby degrading the linewidth control accuracy of the FS structure and affecting device dimensional consistency and electrical performance.

[0024] Therefore, this application provides a method for fabricating a MEMS device and a MEMS device for solving the above-mentioned technical problems. Please refer to the following for details. Figure 4 and Figure 5 , Figure 4 This is a schematic flowchart illustrating the fabrication method of the MEMS device provided in the embodiments of this application. Figure 5 for Figure 4 The process flow diagram corresponding to the fabrication method shown in this application embodiment provides a method for fabricating a MEMS device 1, which includes the following steps: S110. A first wafer and a second wafer are provided, wherein the second wafer is bonded to one side of the first wafer and forms a first cavity with the first wafer.

[0025] In some embodiments, an oxide film is deposited on the surface of the first wafer 11, and a photoresist is coated and patterned on the surface of the oxide film. The patterned photoresist is then used as a mask layer to etch the first wafer 11 to form a groove on the first wafer 11. The mask layer is then removed. When the second wafer 14 is bonded to the first wafer 11, the second wafer 14 completely seals the groove to form a first cavity 101.

[0026] The material of the first wafer 11 includes semiconductor materials such as silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbide (SiC), silicon carbide (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP), or other compound semiconductors.

[0027] In some embodiments, after providing the first wafer 11, the fabrication method further includes: forming a second thermal oxide layer 18 on the outer surface of the first wafer 11. For example, a thermal oxide layer is further grown on the side surface of the first wafer 11 where a groove has been formed by a thermal oxidation process.

[0028] S120. A first mask layer and a second mask layer are sequentially disposed on the side of the second wafer away from the first wafer, and the material of the second mask layer is different from that of the first mask layer.

[0029] For example, a first mask layer 12 is first formed on the side of the second wafer 14 away from the first wafer 11, and the first mask layer 12 is patterned to expose a portion of the second wafer 14. Then, a second mask layer 13 is formed on the side of the second wafer 14 where the first mask layer 12 is formed, i.e., on the exposed second wafer 14 and the first mask layer 12, and the second mask layer 13 is patterned to expose a portion of the second wafer 14. The pattern of the first mask layer 12 is consistent with the pattern of the subsequently formed protrusion, and the pattern of the second mask layer 13 is consistent with the pattern of the subsequently formed comb structure 15.

[0030] In addition, the orthographic projection of the first mask layer 12 on the first wafer 11 falls within the orthographic projection of the second mask layer 13 on the first wafer 11. Thus, during the process of etching the second wafer 14 based on the second mask layer 13 to form the comb structure 15, the presence of the first mask layer 12 can prevent damage to the protrusion 17 to be formed when the second mask layer 13 has uneven thickness due to height difference.

[0031] It should be noted that the materials of the first mask layer 12 and the second mask layer 13 are different, so that the structure of the first mask layer 12 is not damaged when the second mask layer 13 is removed, thus ensuring the accuracy of subsequent etching.

[0032] In some embodiments, the material of the first mask layer 12 may be TEOS, silicon dioxide, silicon nitride or other insulating materials with excellent etching selectivity, and its thickness may be precisely controlled according to the requirements of subsequent etching processes; the material of the second mask layer 13 includes photoresist.

[0033] S130. The second wafer is etched according to the second mask layer to form a plurality of spaced comb-tooth structures at positions corresponding to the first cavity, and the second mask layer is removed.

[0034] For example, a patterned second mask layer 13 exposes the surface of the second wafer 14 corresponding to the region of the first cavity 101. The second wafer 14 is etched using the second mask layer 13 as a mask to form a trench through the second wafer 14. The trench is used to form a comb structure 15 in the second wafer 14. The comb structure 15 includes comb-shaped protrusions spaced apart by the trench.

[0035] In some embodiments, the second mask layer 13 is removed by means of plasma ashing or wet stripping.

[0036] S140. The second wafer is etched according to the first mask layer to form a boss, the orthogonal projection of the boss is located outside the first cavity, and the first mask layer is removed.

[0037] In some embodiments, etching the second wafer 14 according to the first mask layer 12 to form the boss 17 includes etching the side of the second wafer 14 away from the first wafer 11 and the side of the comb structure 15 away from the first wafer 11 to form the boss 17 at a location corresponding to the first mask layer 12. For example, along a direction perpendicular to the second wafer 14, the exposed areas on the second wafer 14 not covered by the first mask layer 12 are etched to a first depth to form the boss 17 on the second wafer 14, and the first mask layer 12 is removed.

[0038] The orthographic projection of the boss 17 is located outside the first cavity 101, meaning that the projections of the boss 17 and the first cavity 101 on the surface of the first wafer 11 are offset from each other. The boss 17 can provide space for the subsequent formation of the second cavity, and the boss 17 can also serve as a support for components that need to be suspended within the functional layer that are subsequently formed.

[0039] Understandably, during the etching of the second wafer 14 and the formation of the protrusion 17 in the comb structure 15, ion bombardment from both the forward and lateral directions can easily damage the sides of the comb structure 15, thereby affecting the overall structural stability and functionality of the device. Therefore, please refer to [further details needed]. Figure 6 , Figure 6 for Figure 4 The diagram illustrates the fabrication method where a first thermal oxide layer is provided to protect the sidewalls of the comb structure. To ensure the sidewalls of the comb structure 15 are not damaged, before etching the second wafer 14 according to the first mask layer 12 to form the boss 17, the fabrication method further includes: providing a first thermal oxide layer 16 on the outer surface of the second wafer 14, the outer surface of the comb structure 15, and the outer surface of the first cavity 101. By providing the first thermal oxide layer 16, the sidewalls of the comb structure 15 can be protected at all times during the etching process, avoiding lateral ion bombardment. Furthermore, the first thermal oxide layer 16 provided on the front surfaces of the second wafer 14 and the comb structure 15 can be simultaneously etched away during ion bombardment, without adversely affecting the normal formation of the boss 17.

[0040] In some embodiments, the material of the first thermal oxide layer 16 includes at least one of silicon oxide and thermally oxidized silicon.

[0041] In some embodiments, the fabrication method further includes removing the first thermal oxide layer 16 when removing the first mask layer 12. Since the materials of the first mask layer 12 and the first thermal oxide layer 16 are similar or have similar corrosion resistance properties, the first mask layer 12 and the first thermal oxide layer 16 can be removed simultaneously by immersion in the same corrosive solution, which simplifies the process steps and improves the fabrication efficiency.

[0042] In some embodiments, the fabrication method further includes: providing a third wafer on which a metal bonding layer is disposed; bonding the metal bonding layer of the third wafer to a protrusion 17 on a second wafer 14 to form a second cavity; wherein the projections of the second cavity and the first cavity 101 on the surface of the second wafer 14 partially or completely overlap.

[0043] In this process, gold-silicon bonding is achieved by sputtering metal material onto the third wafer to form a metal bonding layer on the third wafer.

[0044] In some embodiments, the material of the metal bonding layer is one or more of chromium, gold, titanium, platinum, and titanium-tungsten. For example, the metal bonding layer is a two-layer structure of chromium and gold; or a three-layer structure of titanium, platinum, and gold; or a two-layer structure of titanium-tungsten and gold.

[0045] This application also provides a MEMS device 1, which is manufactured using the method described in any of the above claims, and will not be repeated here. Although the present invention has been disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for fabricating a MEMS device, characterized in that, The manufacturing method includes: A first wafer and a second wafer are provided, wherein the second wafer is bonded to one side of the first wafer and together with the first wafer forms a first cavity; A first mask layer and a second mask layer are sequentially disposed on the side of the second wafer away from the first wafer, and the material of the second mask layer is different from the material of the first mask layer; The second wafer is etched according to the second mask layer to form a plurality of spaced comb-tooth structures at positions corresponding to the first cavity, and the second mask layer is removed. The second wafer is etched according to the first mask layer to form a boss, the orthogonal projection of the boss being located outside the first cavity, and the first mask layer is removed.

2. The manufacturing method according to claim 1, characterized in that, Prior to etching the second wafer according to the first mask layer to form the bump, the fabrication method further includes: A first thermal oxide layer is provided on the outer surface of the second wafer, the outer surface of the comb structure, and the outer surface of the first cavity.

3. The manufacturing method according to claim 2, characterized in that, The step of etching the second wafer according to the first mask layer to form the bump includes: The second wafer is etched on the side away from the first wafer and the comb structure is etched on the side away from the first wafer to form the protrusion at the position corresponding to the first mask layer.

4. The manufacturing method according to claim 2, characterized in that, When removing the first mask layer, the manufacturing method further includes: removing the first thermal oxidation layer.

5. The manufacturing method according to any one of claims 1 to 4, characterized in that, After providing the first wafer, the fabrication method further includes: forming a second thermal oxide layer on the outer surface of the first wafer.

6. The manufacturing method according to any one of claims 1 to 4, characterized in that, The material of the first mask layer includes silicon oxide, silicon nitride, or TEOS, and the material of the second mask layer includes photoresist.

7. The manufacturing method according to any one of claims 2 to 4, characterized in that, The material of the first thermal oxide layer includes thermally oxidized silicon.

8. The manufacturing method according to any one of claims 1 to 4, characterized in that, A third wafer is provided, on which a metal bonding layer is disposed; The metal bonding layer of the third wafer is bonded to the protrusion on the second wafer to form a second cavity; The projections of the second cavity and the first cavity onto the surface of the second wafer partially or completely overlap.

9. The manufacturing method according to claim 8, characterized in that, The material of the metal bonding layer is one or more of chromium, gold, titanium, platinum, and titanium-tungsten.

10. A MEMS device, characterized in that, The MEMS device is manufactured using the method described in any one of claims 1-9.

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