Silicon-based MEMS three-axis acceleration sensor and manufacturing method thereof

Abstract

The invention relates to the technical field of semiconductor chip manufacturing, in particular to a silicon-based MEMS three-axis acceleration sensor and a manufacturing method thereof, and the sensor comprises a first sensing unit, a second sensing unit, a third sensing unit, a device layer, an anchor point, a lower cover plate and an upper cover plate. The first sensing unit, the second sensing unit and the third sensing unit are all arranged on the device layer, the second axis sensing unit and the third axis sensing unit are embedded into the first sensing unit, and the three sensing units share the same anchor point; the first sensing unit is used for detecting Z-axis acceleration, the second sensing unit is used for detecting X-axis acceleration, and the third sensing unit is used for detecting Y-axis acceleration; packaging the device layer by using an upper cover plate and a lower cover plate; according to the invention, the three sensing units share one anchor point, so that the stress of the device is effectively reduced, and the complexity of electrical wiring is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor chip manufacturing, and in particular to a silicon-based MEMS three-axis acceleration sensor and a manufacturing method thereof. Background Art

[0002] MEMS accelerometer is a miniature acceleration sensor manufactured using micro-nano technology. It can measure the acceleration of an object in a sensitive direction and convert it into an electrical signal output. MEMS accelerometers can be divided into capacitive, piezoresistive and resonant types. MEMS capacitive accelerometers can be divided into comb-tooth capacitors and plate capacitors according to the detection method. Generally, plate capacitors are mostly used to measure the torsion pendulum structure of the Z axis. The detection principle of MEMS capacitive accelerometers is mainly based on the capacitive effect. Its core part includes a movable sensing mass block and two symmetrical fixed electrodes, which maintain a small distance between them. When the sensing mass block is displaced by a force, this displacement will change the distance between the mass block and the fixed electrode, thereby causing a change in the capacitance value, which can accurately deduce the acceleration of the object.

[0003] Existing three-axis accelerometers are generally composed of three axial accelerometers. Each axial accelerometer has an independent structure, and anchor points are distributed on the mass block. The anchor points will bring greater stress to the device. In addition, during the process, the arrangement and routing of the three axial devices for electrical connection is also relatively complicated. Generally speaking, the three accelerometers are arranged in parallel, which makes the chip area larger. Z-axis accelerometers are mostly implemented through torsion pendulums. Torsion pendulum accelerometers generally respond to acceleration by directly measuring changes in capacitance, and have low sensitivity. Summary of the invention

[0004] In order to solve the problems existing in the above prior art, the present invention proposes a silicon-based MEMS three-axis acceleration sensor, which includes: a first sensitive unit, a second sensitive unit, a third sensitive unit, a device layer, an anchor point, a lower cover plate and an upper cover plate; the first sensitive unit, the second sensitive unit and the third sensitive unit are all arranged in the device layer, the second axis sensitive unit and the third axis sensitive unit are embedded in the first sensitive unit, and the three sensitive units share the same anchor point; the first sensitive unit is used to detect Z-axis acceleration, the second sensitive unit is used to detect X-axis acceleration, and the third sensitive unit is used to detect Y-axis acceleration; the device layer is packaged by using an upper cover plate and a lower cover plate.

[0005] A method for manufacturing a silicon-based MEMS triaxial acceleration sensor, the method comprising:

[0006] Step 1, obtaining a glass disc, and etching the glass disc to form an anchor point structure and a cavity;

[0007] Step 2, performing anodic bonding on the silicon wafer and the glass wafer;

[0008] Step 3: Perform DRIE on the silicon wafer to etch out the sensitive structure of the device layer;

[0009] Step 4: depositing metal at the device layer anchor point;

[0010] Step 5, take another glass disc and perform cavity etching;

[0011] Step 6: Depositing metal on the surface of the glass wafer;

[0012] Step 7, etching a through hole on the glass wafer;

[0013] Step 8: Anodically bond the glass disc and the sensitive structure to obtain an acceleration sensor.

[0014] Beneficial effects of the present invention:

[0015] (1) The present invention uses three sensing units to share one anchor point, effectively reducing the stress of the device;

[0016] (2) The present invention conducts electricity directly through the device layer and sets pad points in the anchor point area for external electrical connection, effectively reducing the complexity of electrical routing;

[0017] (3) The three sensitive units of the present invention all use a differential method to measure acceleration, which can effectively reduce measurement errors and maintain good linearity and sensitivity.

[0018] (4) In the present invention, the second sensitive unit and the third sensitive unit are embedded in the first sensitive unit, which effectively reduces the space and the chip area.

[0019] (5) The present invention realizes the process by anodic bonding, and the process difficulty is relatively low. Since the thermal expansion coefficients of the silicon wafer and Pyrex7740 are substantially the same when the temperature is below 300°C, this method can effectively reduce the stress problem caused by the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 A schematic diagram of a silicon-based MEMS tri-axial acceleration sensor provided by an embodiment of the present invention;

[0022] Figure 2A schematic structural diagram of a silicon-based MEMS tri-axial acceleration sensor provided in an embodiment of the present invention;

[0023] Figure 3 An exploded diagram of a silicon-based MEMS tri-axial acceleration sensor provided by an embodiment of the present invention;

[0024] Figure 4 The three sensitive units of a silicon-based MEMS three-axis acceleration sensor provided by an embodiment of the present invention share an anchor point;

[0025] Figure 5 A schematic diagram of a first sensitive unit of a silicon-based MEMS three-axis acceleration sensor provided by an embodiment of the present invention;

[0026] Figure 6 A schematic diagram of a second sensitive unit of a silicon-based MEMS three-axis acceleration sensor provided by an embodiment of the present invention;

[0027] Figure 7 A schematic diagram of a third sensitive unit of a silicon-based MEMS tri-axial acceleration sensor provided by an embodiment of the present invention;

[0028] Figure 8 A process flow chart of a silicon-based MEMS triaxial acceleration sensor provided by an embodiment of the present invention;

[0029] In the figure, 1, first sensitive unit; 2, second sensitive unit; 3, third sensitive unit; 4, device layer; 5, anchor point; 6, lower cover plate; 7, upper cover plate; 101, first sensitive unit spring beam; 102, first sensitive unit mass frame; 103, three-axis sensitive unit anchor point; 104, first sensitive unit detection electrode. 201, second sensitive unit mass frame; 202, second sensitive unit spring beam; 203, second sensitive unit detection electrode moving comb teeth; 204, second sensitive unit fixed comb teeth anchor point; 205, second sensitive unit detection electrode fixed comb teeth. 301, third sensitive unit mass frame; 302, third sensitive unit spring beam; 303, third sensitive unit detection electrode moving comb teeth; 304, third sensitive unit detection electrode fixed comb teeth; 305, third sensitive unit detection electrode fixed comb teeth anchor point. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0032] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features; in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0033] A silicon-based MEMS three-axis acceleration sensor, such as Figures 1 to 7 As shown, the device includes: a first sensitive unit, a second sensitive unit, a third sensitive unit, a device layer, an anchor point, a lower cover plate and an upper cover plate; the first sensitive unit, the second sensitive unit and the third sensitive unit are all arranged in the device layer, the second axis sensitive unit and the third axis sensitive unit are embedded in the first sensitive unit, and the three sensitive units share the same anchor point; the first sensitive unit is used to detect Z-axis acceleration, the second sensitive unit is used to detect X-axis acceleration, and the third sensitive unit is used to detect Y-axis acceleration; the device layer is packaged using an upper cover plate and a lower cover plate.

[0034] As one of the implementation modes, the acceleration sensor is composed of three axial accelerometers, and the three axial accelerometers move through their own spring beams and mass frames respectively, and are connected through the same anchor point.

[0035] As one of the implementation modes, the first-axis sensitive unit comprises a first-axis mass frame, a first-axis torsion beam, a first-axis detection electrode and an anchor point. When subjected to acceleration in the Z direction, the first-axis torsion beam drives the mass frame to torsionally swing. At this time, the gap between the first-axis mass frame and the detection capacitor above changes, causing the capacitance value to change with acceleration, thereby detecting the acceleration of the Z axis.

[0036] As one of the implementations, the second-axis sensitive unit includes a second-axis mass frame, a common anchor point with the first-axis sensitive unit and the third-axis sensitive unit, a second-axis spring beam, and a second-axis comb-tooth detection capacitor. When subjected to X-axis acceleration, the second-axis spring beam drives the second-axis mass frame to move toward the X-axis, and at this time, the spacing between the second-axis comb-tooth capacitors changes, thereby detecting the acceleration of the X-axis.

[0037] As one of the implementation modes, the third-axis sensitive unit includes a third-axis mass frame, a common anchor point with the first-axis sensitive unit and the second-axis sensitive unit, a third-axis spring beam, and a third-axis comb-tooth detection capacitor. When subjected to Y-axis acceleration, the third-axis spring beam drives the third-axis mass frame to move toward the Y-axis, and at this time, the spacing between the third-axis comb-tooth capacitors changes, thereby detecting the acceleration of the Y-axis.

[0038] As one of the implementation modes, the first-axis sensitive unit capacitor comb teeth are divided into a first electrode plate and a second electrode plate, which are fixed on the lower cover plate. The first electrode plate and the second electrode plate can be differentiated when subjected to acceleration, thereby effectively increasing the sensitivity of the device.

[0039] As one of the implementation methods, the second-axis sensitive unit capacitor comb teeth are divided into two parts, the upper and lower parts, and the structural arrangement is centrally symmetrical. The detection comb teeth are fixed on the lower cover plate by anchor points. The upper and lower parts of the capacitor comb teeth can be differentially subjected to acceleration, effectively increasing the sensitivity of the device.

[0040] As one of the implementation methods, the third-axis sensitive unit capacitor comb teeth are divided into four parts, and the detection comb teeth are fixed on the lower cover plate by anchor points. The upper and lower parts of the capacitor comb teeth on the right and the upper and lower parts of the capacitor outputs on the left can be differentiated respectively when subjected to acceleration, thereby effectively increasing the sensitivity of the device.

[0041] As one of the implementation modes, the second sensitive unit and the third sensitive unit both include movable comb teeth and fixed comb teeth that match each other in a comb-like manner, wherein the movable comb teeth of the second sensitive unit and the movable comb teeth of the third sensitive unit are respectively fixed on the lower cover plate.

[0042] As one of the implementation modes, the first sensitive unit includes a Z-axis detection structure, and the Z-axis detection structure is a parallel plate capacitor structure, including a first plate and a second plate respectively fixed on the upper cover.

[0043] As one of the implementation modes, the sensor is realized by an anodic bonding process, which reduces the stress of the device, and the electrical signal is directly led out from the anchor point of the device layer, which simplifies the wiring.

[0044] A silicon-based MEMS three-axis acceleration sensor, the overall structure is as follows Figure 1 , 2 As shown in Figure 3, it is composed of a lower device layer 4, an anchor point 5, a lower cover plate 6 and an upper cover plate 7. The device is generally made of semiconductor silicon material, and the device layer can be selected from SOI. The device is composed of a first sensitive unit 1, a second sensitive unit 2 and a third sensitive unit 3, wherein the first sensitive unit structure has a hollow in the middle, and the second sensitive unit 2 and the third sensitive unit 3 are embedded in the hollow part inside the first sensitive unit. The dynamic mass frames of the three sensitive units are connected and fixed to the lower cover plate through an anchor point, and the electrical signals of the three sensitive units are connected and output through the same anchor point.

[0045] Figure 4 It is an anchor point structure shared by three sensitive units of a silicon-based MEMS tri-axis acceleration sensor.

[0046] Figure 5 It is a schematic diagram of the structure of the first sensitive unit of a silicon-based MEMS three-axis acceleration sensor. The sensitive unit includes a spring beam 101, wherein 101 is a double-end fixed-support beam, 103 is an anchor point connected to the mass frame, and the mass frame 102 is twisted when subjected to Z-axis impact. The detection electrode 104 is attached to the upper cover plate. When the mass frame 102 is twisted, the gap between the electrode 104 attached to the upper cover plate changes, and the change condition is that one section of the gap becomes larger and the other section of the gap becomes smaller. At this time, the capacitance values ​​at both ends also change accordingly. By differentiating the capacitance values ​​at both ends, the relationship between the acceleration and the capacitance can be obtained, thereby detecting the acceleration in the sensitive direction.

[0047] Figure 6 The present invention is a schematic diagram of the structure of the second sensitive unit of a silicon-based MEMS triaxial acceleration sensor. The sensitive unit includes a spring beam 202, wherein 202 is a U-shaped beam. When subjected to a load in the X direction, the spring beam 202 drives the mass frame 201 to displace. At this time, the detection comb electrode 203 attached to the mass frame moves, and the spacing between the comb electrode 205 fixed on the anchor point 204 changes. The comb capacitance value of the device changes, and the upper and lower comb electrodes of the second sensitive unit can be differentiated. At this time, the acceleration in the sensitive direction is detected by obtaining the relationship between the acceleration and the capacitance.

[0048] Figure 7 The present invention is a schematic diagram of the structure of the third sensitive unit of a silicon-based MEMS three-axis acceleration sensor. The sensitive unit includes a spring beam 302, wherein 302 is a U-shaped beam. When subjected to a load in the Y direction, the spring beam 302 drives the mass frame 301 to displace. At this time, the detection comb electrode 303 attached to the mass frame moves, and the spacing between the comb electrode 304 fixed on the anchor point 305 changes, and the comb capacitance value of the device changes. The upper and lower comb electrodes at the left and right ends of the mass frame of the third sensitive unit can be differentiated. At this time, the acceleration in the sensitive direction is detected by obtaining the relationship between the acceleration and the capacitance change.

[0049] A method for manufacturing a silicon-based MEMS triaxial acceleration sensor, the method comprising:

[0050] Step 1, obtaining a glass disc, and etching the glass disc to form an anchor point structure and a cavity;

[0051] Step 2, performing anodic bonding on the silicon wafer and the glass wafer;

[0052] Step 3: Perform DRIE on the silicon wafer to etch out the sensitive structure of the device layer;

[0053] Step 4: depositing metal at the device layer anchor point;

[0054] Step 5, take another glass disc and perform cavity etching;

[0055] Step 6: Depositing metal on the surface of the glass wafer;

[0056] Step 7, etching a through hole on the glass wafer;

[0057] Step 8: Anodically bond the glass disc and the sensitive structure to obtain an acceleration sensor.

[0058] In this embodiment, the thickness of the silicon wafer is 10-30 μm.

[0059] Figure 8 This is a process flow chart of a silicon-based MEMS triaxial acceleration sensor. 401 is Pyrex7740, 402 is etching a cavity structure from Pyrex7740, 403 is anodically bonding the etched Pyrex7740 to a silicon wafer, 404 is DRIE on the bonded wafer to etch out the sensitive structure of the device layer, and 405 is metal deposition at the anchor point of the sensitive structure. 406 is another piece of Pyrex7740, 407 is etching the cavity of Pyrex7740, 408 is metal deposition on the surface of Pyrex7740, 409 is further etching the exposed metal pad point, and 410 is anodically bonding the etched Pyrex7740 to the sensitive structure to obtain a MEMS acceleration sensor.

[0060] The detection structure of each direction of the silicon-based MEMS three-axis acceleration sensor of this embodiment is compact and independent, easy to detect, not easily disturbed, and has higher detection accuracy.

[0061] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A silicon-based MEMS triaxial acceleration sensor, characterized in that: include: A first sensitive unit, a second sensitive unit, a third sensitive unit, a device layer, an anchor point, a lower cover plate and an upper cover plate; the first sensitive unit, the second sensitive unit and the third sensitive unit are all arranged in the device layer, the second axis sensitive unit and the third axis sensitive unit are embedded in the first sensitive unit, and the three sensitive units share the same anchor point; the first sensitive unit is used to detect Z-axis acceleration, the second sensitive unit is used to detect X-axis acceleration, and the third sensitive unit is used to detect Y-axis acceleration; the device layer is packaged by an upper cover plate and a lower cover plate.

2. A silicon-based MEMS triaxial acceleration sensor according to claim 1, characterized in that: The first sensitive unit adopts a torsion pendulum accelerometer, including: a first-axis mass frame, a first-axis torsion pendulum beam and a first-axis detection electrode; when the first sensitive unit is subjected to acceleration in the Z direction, the first-axis torsion pendulum beam drives the mass frame to torsionally pendulum, at which time the gap between the first-axis mass frame and the upper detection capacitor changes, and the capacitance value changes with the acceleration, thereby detecting the acceleration of the Z axis.

3. The silicon-based MEMS triaxial acceleration sensor according to claim 1, characterized in that: The second sensitive unit includes a second-axis mass frame, a second-axis spring beam and a second-axis comb-tooth detection capacitor; when the sensor is subjected to X-axis acceleration, the second-axis spring beam drives the second-axis mass frame to move toward the X-axis, at which time the spacing between the second-axis comb-tooth capacitors changes, and the X-axis acceleration is detected.

4. The silicon-based MEMS triaxial acceleration sensor according to claim 3, characterized in that: The second axis comb teeth detection capacitor is respectively composed of the second sensitive unit detection electrode movable comb teeth and the second sensitive unit detection electrode fixed comb teeth. The second sensitive unit detection electrode movable comb teeth and the second sensitive unit detection electrode fixed comb teeth correspond to each other to form a second axis comb teeth detection capacitor.

5. The silicon-based MEMS triaxial acceleration sensor according to claim 4, characterized in that: The movable comb teeth of the second sensitive unit detection electrode and the fixed comb teeth of the second sensitive unit detection electrode are both divided into upper and lower parts, and the structural arrangement is centrally symmetrical. The upper and lower capacitive comb teeth are differentially subjected to acceleration.

6. The silicon-based MEMS triaxial acceleration sensor according to claim 1, characterized in that: The third sensitive unit adopts a comb-tooth capacitive accelerometer, including a third-axis mass frame, a third-axis spring beam and a third-axis comb-tooth detection capacitor; when the sensor is subjected to Y-axis acceleration, the third-axis spring beam drives the third-axis mass frame to move toward the Y-axis, and at this time, the spacing between the third-axis comb-tooth capacitors changes, detecting the acceleration of the Y-axis.

7. The silicon-based MEMS triaxial acceleration sensor according to claim 6, characterized in that: The third-axis comb-tooth detection capacitor adopts a comb-tooth structure and is divided into four parts; the upper and lower parts of the right-side capacitor comb teeth and the upper and lower parts of the left-side capacitor outputs are differentially applied when subjected to acceleration.

8. A method for manufacturing a silicon-based MEMS triaxial acceleration sensor, the method being used to manufacture the silicon-based MEMS triaxial acceleration sensor according to claim 1, characterized in that: include: Step 1, obtaining a glass disc, and etching the glass disc to form an anchor point structure and a cavity; Step 2, performing anodic bonding on the silicon wafer and the glass wafer; Step 3: Perform DRIE on the silicon wafer to etch out the sensitive structure of the device layer; Step 4: depositing metal at the device layer anchor point; Step 5, take another glass disc and perform cavity etching; Step 6: Depositing metal on the surface of the glass wafer; Step 7, etching a through hole on the glass wafer; Step 8: Anodically bond the glass disc and the sensitive structure to obtain an acceleration sensor.

9. A method for manufacturing a silicon-based MEMS triaxial acceleration sensor, characterized in that: The thickness of the silicon wafer is 10 to 30 μm.

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