A method for fabricating wafer-level packaged MEMS inertial devices

Abstract

This invention relates to a method for fabricating wafer-level packaged MEMS inertial devices, comprising: S1, fabricating a substrate wafer with several grooves on its upper surface, and bonding a device layer wafer to the upper surface of the substrate wafer; S2, thinning and patterning the device layer wafer to obtain a movable sensing structure, the movable sensing structure including an accelerometer structure and a gyroscope structure; S3, filling the movable sensing structure with a sacrificial material, and growing a dielectric thin film layer on the sacrificial material; S4, releasing the sacrificial material to form an accelerometer structure cavity and a gyroscope structure cavity between the dielectric thin film layer and the substrate wafer; S5, fabricating the accelerometer structure cavity as a nitrogen chamber and the gyroscope structure cavity as a vacuum chamber. This invention saves the processing of a cap wafer, reduces process steps, lowers costs, and enables the integration of devices with different atmospheres onto the same chip, improving chip integration and reducing the final device size.

Description

Technical Field

[0001] This invention relates to the field of inertial sensing technology, specifically to a method for fabricating a wafer-level packaged MEMS inertial device. Background Technology

[0002] MEMS inertial sensors are miniaturized inertial measurement devices manufactured using microelectronics and microfabrication technologies. They consist of accelerometers and gyroscopes, as well as combinations thereof. Accelerometers measure the acceleration of an object, while gyroscopes measure its angular velocity. The combined measurement of acceleration and angular velocity can be used to describe the motion state of an object.

[0003] MEMS inertial sensors are generally composed of a MEMS sensing chip and an ASIC chip packaged together. The MEMS sensing chip typically consists of three functional layers: an electrically conductive substrate layer, a movable sensing structure layer, and a hermetically sealed cavity cap layer. The three-layer structure is formed by bonding three wafers together using a wafer bonding process.

[0004] Existing wafer-level packaged MEMS inertial sensing chips typically use multi-layer wafer bonding to seal a movable sensing structure that detects inertial physical quantities into a miniature cavity. The sealed cavity is made of a capped wafer with solder, which is fabricated through a bonding process. This process is complex and costly. At the same time, because the gas atmosphere inside the accelerometer and gyroscope cavities is different, the two chips are usually fabricated separately and integrated together through a package. This results in a large device size, which is not conducive to miniaturization. Summary of the Invention

[0005] The purpose of this invention is to provide a method for fabricating wafer-level packaged MEMS inertial devices, which can at least solve some of the defects in the prior art.

[0006] To achieve the above objectives, embodiments of the present invention provide the following technical solution: a method for fabricating a wafer-level packaged MEMS inertial device, comprising the following steps:

[0007] S1, fabricate a substrate wafer with several grooves on its upper surface, and bond a device layer wafer to the upper surface of the substrate wafer;

[0008] S2, the device layer wafer is thinned and patterned to obtain a movable sensitive structure, which includes an accelerometer structure and a gyroscope structure;

[0009] S3, fill the movable sensitive structure with sacrificial material, and grow a dielectric thin film layer on the sacrificial material;

[0010] S4, release the sacrificial material to form an accelerometer structure cavity and a gyroscope structure cavity between the dielectric thin film layer and the substrate wafer;

[0011] S5, the accelerometer structural cavity is made into a nitrogen chamber and the gyroscope structural cavity is made into a vacuum chamber.

[0012] Furthermore, step S3 specifically includes:

[0013] Fill the movable sensitive structure with sacrificial material until the sacrificial material covers the movable sensitive structure.

[0014] The sacrificial material is patterned.

[0015] The dielectric thin film layer is then grown on the sacrificial material.

[0016] Furthermore, in step S4, the method of releasing the sacrificial material includes: opening a first release hole on the dielectric film layer above the accelerometer structure, and releasing the sacrificial material corresponding to the accelerometer structure through the first release hole to form an accelerometer structure cavity.

[0017] Furthermore, in step S5, the accelerometer structure cavity is made into a nitrogen chamber by sealing the first release hole in a nitrogen atmosphere, thereby filling the accelerometer structure cavity with nitrogen.

[0018] Furthermore, before growing the dielectric thin film layer on the sacrificial material, a getter is first fabricated on the corresponding sacrificial material surface of the gyroscope structure.

[0019] Furthermore, in step S4, the method of releasing the sacrificial material further includes: opening a second release hole on the dielectric film layer above the gyroscope structure, and releasing the sacrificial material corresponding to the gyroscope structure through the second release hole to form a gyroscope structure cavity.

[0020] Furthermore, in step S5, the method of making the gyroscope structure cavity into a vacuum chamber is as follows: the second release hole is sealed under a vacuum atmosphere, and the getter is activated.

[0021] Furthermore, in step S1, the method for fabricating a substrate wafer with several grooves on its upper surface is specifically as follows:

[0022] Several grooves are etched on the upper surface of the substrate wafer, and the grooves are spaced apart.

[0023] An oxide layer is grown on the upper surface of the substrate wafer;

[0024] Polycrystalline silicon is grown on the oxide layer outside the groove to form conductive lines.

[0025] Furthermore, the sacrificial material is polyimide or amorphous carbon.

[0026] Furthermore, the material of the dielectric thin film layer is amorphous silicon, silicon oxide, or silicon nitride, and the thickness is 2~30μm.

[0027] Compared with the prior art, the beneficial effects of the present invention are: a wafer-level packaged MEMS inertial device fabrication method saves the processing of a cap wafer, reduces process steps, lowers costs, and enables devices with different atmospheres to be integrated on the same chip, improving chip integration and reducing the final device size. Attached Figure Description

[0028] Figure 1 A schematic diagram illustrating the fabrication of a groove on a substrate in a wafer-level packaged MEMS inertial device fabrication method provided in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the oxide layer growth process in a wafer-level packaged MEMS inertial device fabrication method provided in an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram illustrating the growth of polycrystalline silicon on the oxide layer outside the groove, as provided in an embodiment of the present invention, for a method of fabricating a wafer-level packaged MEMS inertial device.

[0031] Figure 4 This is a schematic diagram illustrating the bonding of a device layer wafer to a substrate layer wafer in a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention.

[0032] Figure 5 This is a schematic diagram illustrating the thinning of the device layer wafer in a method for fabricating a wafer-level packaged MEM image inertial device according to an embodiment of the present invention.

[0033] Figure 6 This is a schematic diagram illustrating the patterning process performed on the device layer wafer as part of a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention.

[0034] Figure 7 This is a schematic diagram illustrating the method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention, showing the filling of sacrificial material.

[0035] Figure 8 A schematic diagram illustrating the fabrication method of a wafer-level packaged MEMS inertial device according to an embodiment of the present invention, showing the formation of a getter on the upper surface of the sacrificial material;

[0036] Figure 9This is a schematic diagram illustrating the patterning process on the sacrificial material in a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention.

[0037] Figure 10 This is a schematic diagram of the growth of a dielectric thin film layer in a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention.

[0038] Figure 11 A schematic diagram illustrating a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention, wherein a first release hole is opened above the accelerometer structure, and sacrificial material in the accelerometer structure is released through the first release hole;

[0039] Figure 12 This is a schematic diagram illustrating the sealing of the first release hole under a nitrogen atmosphere in a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention.

[0040] Figure 13 A schematic diagram illustrating a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention, wherein a second release hole is opened above the gyroscope structure, and the sacrificial material in the gyroscope structure is released through the second release hole;

[0041] Figure 14 This is a schematic diagram illustrating the sealing of the second release hole under a vacuum atmosphere in a method for fabricating a wafer-level packaged MEMS inertial device according to an embodiment of the present invention.

[0042] In the attached figures: 1-substrate wafer; 10-substrate layer; 12-oxide layer; 13-polysilicon; 2-device wafer; 3-sacrificial material; 4-getter; 5-dielectric thin film layer; 50-first release hole; 51-second release hole; 52-first sealing material; 53-second sealing material; 6-accelerometer structure; 60-first chamber; 61-first movable sensing structure; 7-gyroscope structure; 70-second chamber; 71-second movable sensing structure; 8-nitrogen chamber; 9-vacuum chamber. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Please see Figures 1 to 14This invention provides a method for fabricating a wafer-level packaged MEMS inertial device, comprising the following steps: S1, fabricating a substrate wafer 1 with a plurality of grooves 11 on its upper surface, and bonding a device layer wafer 2 to the upper surface of the substrate wafer, such as... Figures 1 to 4 As shown; S2, the device layer wafer 2 is thinned and patterned to obtain a movable sensitive structure, which includes an accelerometer structure 6 and a gyroscope structure 7, as shown. Figure 5 and Figure 6 As shown; S3, fill the movable sensitive structure with sacrificial material 3, and grow a dielectric thin film layer 5 on the sacrificial material, the dielectric thin film layer 5 covering the sacrificial material 3, as shown. Figures 7 to 10 As shown; S4, the sacrificial material 3 is released to form an accelerometer structure cavity and a gyroscope structure cavity between the dielectric thin film layer 5 and the substrate wafer 1, as shown. Figure 11 As shown; S5, the accelerometer structure cavity is fabricated into a nitrogen chamber 8 and the gyroscope structure 7 cavity is fabricated into a vacuum chamber 9, as shown. Figures 12 to 14 In this embodiment, the method saves the processing of one cap wafer, reduces process steps, lowers costs, and enables the integration of devices with different atmospheres onto the same chip, improving chip integration and reducing the final device size. Specifically, the dielectric thin film layer 5 can subsequently replace the cap wafer, avoiding the need for reprocessing the cap wafer. Figure 11 and Figure 13 In this structure, due to the coverage of the dielectric thin film layer 5, a square chamber can be formed at the location where the sacrificial material 3 disappears after the sacrificial material is released, in conjunction with the dielectric thin film layer 5. This chamber, combined with the movable sensing structure, forms the accelerometer structure 6 and the gyroscope structure 7, specifically as follows: Figure 14 As shown, the image is divided by a dashed line. To the left of the dashed line is the accelerometer structure 6, which includes a first chamber 60 and a first movable sensing structure 61. The first chamber 60 and the first movable sensing structure 61 are connected and filled with nitrogen gas. To the right of the dashed line is the gyroscope structure 7, which includes a second chamber 70 and a second movable sensing structure 71. The second chamber 70 and the second movable sensing structure 71 are connected and are in a vacuum environment.

[0045] Please see Figure 6 , Figure 7 and Figure 9 The S3 step specifically involves: filling the movable sensitive structure with sacrificial material 3 until the sacrificial material 3 covers the movable sensitive structure; patterning the sacrificial material 3; and then growing the dielectric thin film layer 5 on the sacrificial material 3. In this embodiment, as shown in... Figure 5 After the device layer wafer 2 shown is thinned and polished, it is as follows: Figure 6The patterning process shown in the figure involves photolithography, etching, and cleaning on the device layer wafer 2. This patterning process allows for the fabrication of movable sensitive structures on the device layer wafer 2. Then, as shown in the figure... Figure 7 As shown, sacrificial material 3 is filled into the movable sensitive structure. After filling, the sacrificial material 3 is continued to be filled until the sacrificial material 3 forms a layer covering the upper surface of the movable sensitive structure. Then... Figure 9 The patterning process shown is crucial for separating the accelerometer structure 6 and the gyroscope structure 7. It essentially defines the locations of the accelerometer structure 6 and the gyroscope structure 7. After subsequent processes such as fabricating the dielectric thin film layer 5, releasing the sacrificial material 3, and fabricating the nitrogen chamber and vacuum chamber, the final accelerometer structure 6 and gyroscope structure 7 can be obtained.

[0046] Please see Figure 11 and Figure 12 In step S4, the method of releasing the sacrificial material 3 includes: opening a first release hole 50 on the dielectric film layer 5 above the accelerometer structure 6, and releasing the sacrificial material 3 corresponding to the accelerometer structure 6 through the first release hole 50 to form an accelerometer structure cavity. Preferably, in step S5, the method of making the accelerometer structure cavity into a nitrogen chamber 8 is: sealing the first release hole 50 with a first sealing material 52 under a nitrogen atmosphere, so that the cavity of the accelerometer structure 6 is filled with nitrogen 8. In this embodiment, the accelerometer structure 6 is ultimately filled with nitrogen, so the sacrificial material 3 is first released through the first release hole 50, and then the first release hole 50 is sealed under a nitrogen atmosphere, so that the cavity of the accelerometer structure 6 is filled with nitrogen.

[0047] Please see Figure 8 and Figure 9 In step S2, before growing the dielectric thin film layer 5 on the sacrificial material 3, a getter 4 is first fabricated on the surface of the corresponding sacrificial material 3 of the gyroscope structure. In this embodiment, the getter 4 is fabricated to maintain the vacuum environment of the gyroscope structure 7 by activating the getter 4 subsequently.

[0048] Please see Figure 13 and Figure 14In step S4, the method of releasing the sacrificial material 3 further includes: opening a second release hole 51 on the dielectric film layer 5 above the gyroscope structure 7, and releasing the sacrificial material 3 corresponding to the gyroscope structure 7 through the second release hole 51 to form a gyroscope structure cavity. Preferably, in step S5, the method of making the gyroscope structure cavity into a vacuum chamber 9 is: sealing the second release hole 51 under a vacuum atmosphere, and activating the getter 4 to maintain the vacuum level in the cavity of the gyroscope structure 7. In this embodiment, the gyroscope structure 7 ultimately needs a vacuum environment 9 in the cavity, so the sacrificial material 3 in the cavity of the gyroscope structure 7 can be released first using the second release hole 51, and then the air in the empty cavity can be extracted. Then, the second release hole 51 can be sealed with the second sealing material 53. In order to maintain the vacuum level, the getter 4 can be activated. In this embodiment, the fabrication of the gyroscope structure 7 and the aforementioned accelerometer structure 6 can be performed sequentially. The first release hole 50 or the second release hole 51 can be opened first. This prevents both structures from being filled with nitrogen or becoming a vacuum in a nitrogen or vacuum environment, improving fabrication efficiency. For example, if the first release hole 50 and the second release hole 51 are opened simultaneously, both the cavity of the accelerometer structure 6 and the cavity of the gyroscope structure 7 will be filled with nitrogen in a nitrogen-filled environment. Therefore, after closing the release hole of the accelerometer structure 6, the nitrogen in the gyroscope structure 7 must be removed first.

[0049] Please see Figure 1 , Figure 2 and Figure 3 In step S1, the method for fabricating a substrate wafer 1 with a plurality of grooves 11 on its upper surface specifically involves: etching a plurality of grooves 11 on the upper surface of the substrate wafer 1, with each groove 11 spaced apart; growing an oxide layer 12 on the upper surface of the substrate wafer 1; and growing polysilicon on the oxide layer 12 outside the grooves 11 to form conductive lines. In this embodiment, the substrate wafer is processed before being bonded to the device wafer 2 to facilitate the fabrication of a movable sensitive structure in conjunction with the device wafer 2.

[0050] The following are specific embodiments of the present invention:

[0051] Combination Figures 1 to 14 The fabrication method of this wafer-level packaged MEMS inertial device will be explained step by step:

[0052] Please see Figure 1 A plurality of grooves 11 are formed by recessing downward on the upper surface of the substrate. The grooves 11 are spaced apart. Specifically, the substrate is formed by photolithography, etching, cleaning and other processes. The depth of the grooves 11 is 0.5~20μm.

[0053] Please see Figure 2 An oxide layer 12 is grown on the upper surface of the substrate after the groove 11 is fabricated. Specifically, the thickness of the oxide layer 12 is 0.5~4μm.

[0054] Please see Figure 3 Polysilicon 13 is grown on the oxide layer 12 outside the groove 11 and conductive lines are formed to form a substrate wafer 1. Specifically, polysilicon 13 is grown on the surface and patterned to form conductive lines. The resistance of polysilicon 13 is <0.1Ω·cm.

[0055] Please see Figure 4 The device layer wafer 2 is bonded to the substrate layer wafer 1. Specifically, the substrate layer wafer 1 and the device layer wafer 2 do not require pattern alignment and are directly fused together, with the resistance of the device layer wafer 2 being <0.1Ω·cm.

[0056] Please see Figure 5 The device layer wafer 2 is then thinned. Specifically, the device layer wafer 2 is thinned and polished to a thickness of 10~100um.

[0057] Please see Figure 6 The movable sensitive structure is obtained by patterning the device layer wafer 2. Specifically, the patterning process includes photolithography, etching, and cleaning to fabricate the movable sensitive structure on the device layer wafer 2. This structure is the prototype of the accelerometer structure 6 and the gyroscope structure 7.

[0058] Please see Figure 7 The movable sensitive structure is filled with sacrificial material until it covers the movable sensitive structure. Specifically, the sacrificial material is polyimide (PI) or amorphous carbon (aC) to perform surface planarization.

[0059] Please see Figure 8 A getter 4 is formed on the upper surface of the sacrificial material 3. Specifically, the getter 4 (titanium-based or zirconia-based material) is deposited on the surface and patterned.

[0060] Please see Figure 9 The sacrificial material 3 is patterned to form the accelerometer structure 6 and the gyroscope structure 7. Specifically, the patterning process includes photolithography, etching, and cleaning.

[0061] Please see Figure 10 A dielectric thin film layer 5 is grown, which covers the sacrificial material 3 and the getter 4. Specifically, the dielectric thin film layer 5 (amorphous silicon, silicon oxide, or silicon nitride) is grown at low temperature and its surface is planarized, with a thickness of 2-30 μm.

[0062] Please see Figure 11A first release hole 50 is formed on the dielectric film layer 5 above the accelerometer structure 6, and the sacrificial material 3 in the accelerometer structure 6 is released through the first release hole 50.

[0063] Please see Figure 12 The first release hole 50 is sealed under a nitrogen atmosphere, filling the accelerometer structure 6 with nitrogen. Specifically, a filling material (dense metal material such as aluminum or titanium) is grown under normal or negative pressure nitrogen atmosphere to seal the release hole.

[0064] Please see Figure 13 A second release hole 51 is formed on the dielectric film layer 5 above the gyroscope structure 7, and the sacrificial material 3 in the gyroscope structure 7 is released through the second release hole 51.

[0065] Please see Figure 14 The second release hole 51 is sealed under a vacuum atmosphere, and the getter 4 is activated to maintain the vacuum level in the gyroscope structure 7. Specifically, under a vacuum atmosphere, a filling material (dense metal material such as aluminum or titanium) is grown to seal the release hole, and the getter 4 is activated by heating to maintain a high vacuum inside the cavity.

[0066] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a wafer-level packaged MEMS inertial device, characterized in that, Includes the following steps: S1, fabricate a substrate wafer with several grooves on its upper surface, and bond a device layer wafer to the upper surface of the substrate wafer; S2, the device layer wafer is thinned and patterned to obtain a movable sensitive structure, which includes an accelerometer structure and a gyroscope structure; S3, fill the movable sensitive structure with sacrificial material, and grow a dielectric thin film layer on the sacrificial material; S4, a first release hole is opened on the dielectric thin film layer above the accelerometer structure, the sacrificial material is released through the first release hole, and the first release hole is sealed. A second release hole is opened on the dielectric thin film layer above the gyroscope structure, the sacrificial material is released through the second release hole, and the second release hole is sealed. After the sacrificial material is released, an accelerometer structure cavity and a gyroscope structure cavity are formed between the dielectric thin film layer and the substrate wafer. S5, the accelerometer structural cavity is made into a nitrogen chamber and the gyroscope structural cavity is made into a vacuum chamber.

2. The method for fabricating a wafer-level packaged MEMS inertial device as described in claim 1, characterized in that, The S3 step is specifically as follows: Fill the movable sensitive structure with sacrificial material until the sacrificial material covers the movable sensitive structure. The sacrificial material is patterned. The dielectric thin film layer is then grown on the sacrificial material.

3. The method for fabricating a wafer-level packaged MEMS inertial device as described in claim 1, characterized in that, In step S5, the accelerometer structure cavity is made into a nitrogen chamber by sealing the first release hole in a nitrogen atmosphere, thereby filling the accelerometer structure cavity with nitrogen.

4. The method for fabricating a wafer-level packaged MEMS inertial device as described in claim 1, characterized in that, Before growing a dielectric thin film layer on the sacrificial material, a getter is first fabricated on the corresponding sacrificial material surface of the gyroscope structure.

5. The method for fabricating a wafer-level packaged MEMS inertial device as described in claim 4, characterized in that, In step S5, the method of making the gyroscope structure cavity into a vacuum chamber is as follows: the second release hole is sealed in a vacuum atmosphere, and the getter is activated.

6. The method for fabricating a wafer-level packaged MEMS inertial device as described in claim 1, characterized in that: In step S1, the method for fabricating a substrate wafer with several grooves on its upper surface is as follows: Several grooves are etched on the upper surface of the substrate wafer, and the grooves are spaced apart. An oxide layer is grown on the upper surface of the substrate wafer; Polycrystalline silicon is grown on the oxide layer outside the groove to form conductive lines.

7. The method for fabricating a wafer-level packaged MEMS inertial device as described in claim 1, characterized in that: The sacrificial material is polyimide or amorphous carbon.

8. The method for fabricating a wafer-level packaged MEMS inertial device as described in claim 1, characterized in that: The dielectric thin film layer is made of amorphous silicon, silicon oxide, or silicon nitride, and has a thickness of 2 to 30 μm.

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