MEMS capacitive pressure and acceleration composite sensor and preparation method thereof

Abstract

The invention relates to an MEMS capacitive pressure and acceleration composite sensor and a preparation method thereof. An acceleration detection part of the composite sensor and an upper electrode of a pressure sensor are formed on the same upper layer silicon; the lower cavity structure of the acceleration sensor, the lower electrode of the pressure sensor and the pressure detection cavity are all positioned on the silicon substrate at the lower layer; the acceleration sensor structure and the pressure sensor structure are arranged at an interval along the horizontal direction; a top cover is arranged at a position, corresponding to the acceleration detection component, above the upper-layer silicon; and an upper cavity structure is formed between the bottom surface of the top cover and the top surface of the acceleration detection component. The composite sensor has the characteristics of high precision, high sensitivity and strong structural stability, and the manufacturing process compatibility of the pressure sensor part and the acceleration sensor part is high, and the process flow is simple.

Description

Technical Field

[0001] The invention relates to the technical field of MEMS sensors, in particular to a MEMS capacitive pressure and acceleration composite sensor and a preparation method thereof. Background Art

[0002] With the miniaturization of MEMS sensor technology, more and more sensor chips integrate multiple functional units on one chip, and even include peripheral CMOS circuits, forming a systematic composite integrated sensor structure. This highly integrated sensor has the characteristics of strong functions, high precision and small size, which reduces the chip cost of the sensor and improves the market competitiveness of the sensor. At present, there are mainly two types of multifunctional composite sensors that integrate pressure detection and acceleration detection. The first is the integration of piezoresistive pressure sensor and piezoresistive acceleration sensor, and the second is the integration of capacitive pressure sensor and capacitive acceleration sensor.

[0003] The integration of the first piezoresistive pressure sensor and the piezoresistive acceleration sensor has the following disadvantages:

[0004] Piezoresistive pressure sensors usually place four varistors on a silicon diaphragm and convert resistance changes into output voltage through a Wheatstone bridge circuit. The temperature drift problem affects the accuracy. Piezoresistive accelerometers usually use a cantilever beam piezoresistive structure, which has the disadvantages of low sensitivity, poor temperature characteristics, and difficult multi-axis design. Therefore, it is not suitable for certain application scenarios that require high precision, high sensitivity, high stability, and multi-axis detection.

[0005] The second integration of capacitive pressure sensor and capacitive acceleration sensor has the following disadvantages:

[0006] There is a type of accelerometer with a capacitive seesaw structure. The disadvantage is that its fixed electrode and variable electrode are usually composed of different wafer layers. In order to achieve high sensitivity, the distance between the two wafer layers is very small, which makes it easy to produce adhesion, reliability problems, and complex implementation process. At the same time, in order to increase the sensitivity of the seesaw structure and make it produce more obvious vibration or displacement when it is input by external acceleration, additional counterweights are usually set on the movable mass block. The existence of counterweights will lead to area waste, which is not conducive to the miniaturization design of sensor chips.

[0007] Another type is to stack the capacitive pressure sensor vertically on top of the capacitive acceleration sensor. Although this effectively utilizes the vertical space and reduces the chip usage area, this design will increase the number of process layers and process steps for chip processing, and will also increase the difficulty of device stress control, resulting in poor structural stability, ultimately affecting the chip manufacturing yield. Summary of the invention

[0008] In view of the shortcomings of the prior art, the present invention provides a MEMS capacitive pressure and acceleration composite sensor and a preparation method thereof, which solves the technical problems of poor longitudinal structural stability caused by excessive number of semiconductor process layers, complex processes, and difficulty in controlling film stress required for existing sensors.

[0009] The technical solution adopted by the present invention is as follows:

[0010] The present invention provides a method for preparing a MEMS capacitive pressure and acceleration composite sensor, comprising the following steps:

[0011] S1, forming a lower electrode of the pressure sensor in a partial area of ​​the upper surface of the silicon substrate by ion implantation;

[0012] S2, providing an oxide layer on the upper surface of the silicon substrate to form a lower structure;

[0013] S3, setting a lower cavity of the acceleration sensor on the lower structure by dry etching, wherein an anchor point for fixing is provided in the lower cavity; the lower cavity of the acceleration sensor and the lower electrode of the pressure sensor are arranged at intervals in the horizontal direction;

[0014] S4, bonding an upper layer of silicon to the lower structure, wherein the upper layer of silicon covers the entire surface of the lower structure;

[0015] S5, reducing the thickness of the upper silicon layer;

[0016] S6, setting a detection component on the thinned upper silicon layer by setting a groove structure and using an etching process, wherein the detection component includes an acceleration detection component corresponding to the lower cavity of the acceleration sensor and an upper electrode of the pressure sensor corresponding to the lower electrode of the pressure sensor;

[0017] S7, providing a protective layer on the surface of the acceleration detection component, and removing the oxide layer on the surface of the lower electrode of the pressure sensor through the slot of the upper electrode of the pressure sensor, so that a gap is formed between the bottom surface of the upper electrode of the pressure sensor and the top surface of the lower electrode of the pressure sensor;

[0018] S8, removing the remaining protective layer;

[0019] S9, providing an isolation dielectric layer on the detection component, filling the corresponding slots and performing surface flattening, so that the gap is sealed to form a pressure detection cavity;

[0020] S10, etching contact holes and filling them with metal, and depositing and patterning metallization layers on the isolation dielectric layer to lead out electrical signals of the sensor;

[0021] S11, etching the isolation dielectric layer, releasing the acceleration detection component, and releasing the isolation dielectric layer on the top of the upper electrode of the pressure sensor to form a pressure sensitive film;

[0022] S12, disposing a top cover above the acceleration detection component, and forming a closed upper cavity of the acceleration sensor between the lower surface of the top cover and the upper surface of the acceleration detection part.

[0023] Further technical solutions are:

[0024] In step S11, a groove is provided above the pressure detection cavity, which penetrates the entire isolation dielectric layer and the bottom surface of the groove is located in the upper silicon layer, thereby forming the pressure sensitive membrane, which can be deformed toward the pressure detection cavity when subjected to force.

[0025] The oxide layer is formed by depositing silicon oxide.

[0026] The oxide layer on the surface of the lower electrode of the pressure sensor is removed by etching with hydrofluoric acid gas.

[0027] The protective layer is formed by spraying or spin coating photoresist.

[0028] The lower electrode of the pressure sensor adopts ion implantation to form a resistor, and the implanted ions are boron or other elements used to make electrodes.

[0029] The isolation dielectric layer is silicon oxide and / or silicon nitride and is formed by chemical vapor deposition.

[0030] The bottom of the top cover is bonded to the metal on the surface of the isolation dielectric layer by glass slurry.

[0031] The acceleration detection component comprises a comb-tooth structure detection body, an elastic beam and an anchor point.

[0032] The present invention also provides a MEMS capacitive pressure and acceleration composite sensor manufactured according to the manufacturing method, wherein the acceleration detection component and the upper electrode of the pressure sensor of the composite sensor are formed on the same upper silicon layer;

[0033] The lower cavity of the acceleration sensor, the lower electrode of the pressure sensor and the pressure detection cavity are all located on the lower silicon substrate;

[0034] The lower cavity of the acceleration sensor and the pressure detection cavity are arranged at intervals in the horizontal direction;

[0035] A top cover is provided above the upper silicon layer at a position corresponding to the acceleration detection component, and a sealed upper cavity of the acceleration sensor is formed between the bottom surface of the top cover and the top surface of the acceleration detection component.

[0036] The beneficial effects of the present invention are as follows:

[0037] The present invention combines a comb-tooth structure differential capacitive acceleration sensor and a capacitive pressure sensor, solving the technical problems of low sensitivity, poor temperature characteristics, and difficulty in realizing multi-axis design in the existing piezoresistive acceleration sensor combined with piezoresistive pressure sensor solutions. It has the following advantages:

[0038] The composite sensor prepared by the present invention combines a capacitive acceleration sensor and a capacitive pressure sensor together, and the upper electrode of the pressure sensor and the acceleration detection component are formed on the same silicon layer and are arranged at intervals in the horizontal direction. The overall structure adopts a three-layer structure of a top cover, an upper silicon layer, and a silicon substrate, with a small number of layers and a stable structure.

[0039] The pressure sensitive film of the pressure sensor of the present invention is formed by arranging a groove on the upper silicon layer. The groove is designed in an annular shape, so that the pressure sensitive film is more likely to deform when subjected to force, thereby improving the sensitivity of the pressure sensor.

[0040] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The figure is a schematic diagram of the process of the preparation method according to the embodiment of the present invention.

[0042] Figure 2 It is a schematic diagram of the process from forming the lower electrode of the pressure sensor to forming the detection function part of the preparation method according to an embodiment of the present invention.

[0043] Figure 3 It is a schematic diagram of the process from forming a detection function unit to depositing and patterning a metallization layer according to an embodiment of the preparation method of the present invention.

[0044] Figure 4 It is a schematic diagram of the process of the preparation method according to an embodiment of the present invention from deposition and patterning of the metallization layer to final completion.

[0045] Figure 5 FIG. 4 is a top view of a pressure sensitive membrane according to an embodiment of the present invention.

[0046] In the figure: 100, silicon substrate; 110, lower cavity of acceleration sensor; 200, upper silicon layer; 300, top cover; 301, upper cavity of acceleration sensor; 400, lower electrode of pressure sensor; 500, protective layer; 600, pressure detection cavity; 700, pressure sensitive membrane; 800, groove. DETAILED DESCRIPTION

[0047] The specific implementation of the present invention is described below with reference to the accompanying drawings.

[0048] See also Figure 1, a method for preparing a MEMS capacitive pressure and acceleration composite sensor of this embodiment comprises the following steps:

[0049] like Figure 2 As shown:

[0050] S1. Forming a lower electrode 400 of the pressure sensor in a partial area of ​​the upper surface of the silicon substrate 100 by ion implantation.

[0051] The silicon substrate 100 may be made of P or N type silicon, and the lower electrode 400 of the pressure sensor may be formed by ion implantation, and correspondingly, P+ or N+ type ions may be used, such as boron or other element ions used to make electrodes.

[0052] S2. An oxide layer is provided on the upper surface of the silicon substrate 100 to form a lower structure.

[0053] The oxide layer may be formed by depositing silicon oxide.

[0054] S3. The acceleration sensor lower cavity 110 is arranged on the lower structure by dry etching. The top inside the acceleration sensor lower cavity 110 is used to form an anchor point ①. The acceleration sensor lower cavity 110 and the pressure sensor lower electrode 400 are arranged horizontally spaced apart.

[0055] The lower cavity 110 of the acceleration sensor is finally formed in the silicon substrate 100 .

[0056] S4. Bonding an upper silicon layer 200 on the lower structure, wherein the upper silicon layer 200 covers the entire surface of the lower structure.

[0057] Among them, the bonding process is anodic bonding, and since it is bonded to the upper silicon layer through the oxide layer, it is silicon-oxygen bonding here.

[0058] S5. Thinning the thickness of the upper silicon layer 200 using a silicon wafer thinning process.

[0059] Since the upper silicon layer 200 is to be used to form a detection layer later, it needs to be thinned to a suitable thickness to meet usability and improve sensitivity. The final thickness can be adjusted according to the range and sensitivity requirements of the sensor.

[0060] The thickness of the upper silicon layer 200 after thinning is set according to actual needs, and in this embodiment, 10 to 100 microns can be selected.

[0061] S6. Forming a detection component on the thinned upper silicon layer 200 by setting a groove structure and using an etching process, the detection component includes an acceleration detection component corresponding to the lower cavity 110 of the acceleration sensor, and an upper electrode of the pressure sensor corresponding to the lower electrode 400 of the pressure sensor.

[0062] The trench structure may be etched using an anisotropic dry etching process.

[0063] Wherein, the acceleration detection component includes a comb-tooth structure detection body, an elastic beam and an anchor point (i.e., corresponding to the position of the above-mentioned anchor point ①). The detection body includes a movable mass block and a fixed electrode. The anchor point portion is located at the first end of the movable mass block. The anchor point portion is connected to the first end of the movable mass block through the elastic beam. A comb-tooth differential capacitor group is formed between the movable mass block and the fixed electrode along one or more directions to achieve the measurement of acceleration in one or more directions. The acceleration detection component is in the form of a "cantilever beam". The entire movable mass block is located on one side of the anchor point portion. Any out-of-plane acceleration will cause the movable mass block to move out-of-plane as a whole. There is no need to set up an additional counterweight block. The area utilization rate of the movable mass block is high, which is conducive to reducing the chip size.

[0064] like Figure 3 As shown:

[0065] S7. A protective layer 500 is provided on the surface of the acceleration detection component, and the oxide layer on the surface of the lower electrode 400 of the pressure sensor is removed through the slot hole (hollow area) of the upper electrode of the pressure sensor, so that a gap is formed between the bottom surface of the upper electrode of the pressure sensor and the top surface of the lower electrode 400 of the pressure sensor.

[0066] The protective layer 500 may be formed by spraying or spin coating photoresist, or other protective materials commonly used in semiconductor manufacturing processes may be used.

[0067] The protective layer 500 can prevent the structure of the acceleration sensor detection component from being damaged during the process of removing the oxide layer on the surface of the lower electrode 400 of the pressure sensor, thereby effectively protecting the acceleration sensor detection component and facilitating the removal of the oxide layer above the upper electrode of the pressure sensor.

[0068] Specifically, the oxide layer on the surface of the lower electrode 400 of the pressure sensor may be removed by etching with hydrofluoric acid gas.

[0069] S8, removing the remaining protection layer 500.

[0070] S9, setting an isolation dielectric layer on the detection functional part, filling the corresponding slots and performing surface flattening, so that the gap is sealed to form a pressure detection cavity 600.

[0071] Wherein, the isolation dielectric layer is silicon oxide and / or silicon nitride and is provided by chemical vapor deposition.

[0072] The isolation dielectric layer mainly serves as electrical isolation and fills the groove in the upper electrode of the pressure sensor to form a cavity 600. The surface of the isolation dielectric layer is easy to flatten, which is convenient for subsequent process operations and can effectively control stress.

[0073] S10, etching contact holes and filling them with metal, and depositing and patterning metallization layers on the isolation dielectric layer, so as to lead out the electrical signals of the sensors.

[0074] Specifically, etching is performed downward from the surface of the isolation dielectric layer to the lower electrode 400 of the pressure sensor and the upper electrode of the pressure sensor, and a contact hole is formed and filled with metal, and then the metal is patterned as shown in red in the figure, thereby leading out the upper and lower electrode signals of the pressure sensor part. Similarly, the contact hole of the acceleration sensor part is etched and filled with metal, and then metal is deposited on the surface for patterning. Since the detection part of the acceleration sensor is located in the upper silicon layer 200, the etched contact hole only needs to be etched to the upper silicon layer 200.

[0075] like Figure 4 As shown:

[0076] S11 , etching the isolation dielectric layer, releasing the acceleration detection component, and releasing the isolation dielectric layer on top of the upper electrode of the pressure sensor to form a pressure sensitive film 700 .

[0077] The acceleration detection component after release is the structure formed by etching in S6. The pressure sensitive film 700 and the lower electrode 400 of the pressure sensor are located above and below the pressure detection cavity 600, respectively.

[0078] S12, a top cover 300 is arranged above the acceleration detection component, and a closed upper cavity 301 is formed between the lower surface of the top cover 300 and the upper surface of the acceleration detection component.

[0079] The material of the top cover 300 is also silicon. The bottom of the top cover 300 is bonded to the metal on the surface of the isolation dielectric layer by glass paste.

[0080] As a specific implementation, in step S11, a groove 800 is set above the pressure detection cavity 600, which runs through the entire isolation dielectric layer and the bottom surface of the groove is located in the upper silicon layer 200, thereby forming the pressure sensitive membrane 700, which can be deformed toward the pressure detection cavity 600 when subjected to force.

[0081] like Figure 5 As shown, the groove 800 has an annular structure, so that the pressure sensitive film 700 is easy to deform when subjected to force in all directions, thereby improving the sensitivity of the pressure sensor.

[0082] This embodiment also provides a MEMS capacitive pressure and acceleration composite sensor manufactured according to the manufacturing method, see Figure 3 , the acceleration detection component and the upper electrode of the pressure sensor are formed on the same upper silicon layer 200;

[0083] The acceleration sensor lower cavity 110, the pressure sensor lower electrode 400 and the pressure detection cavity 600 are all located in the lower silicon substrate 100;

[0084] The lower cavity 110 of the acceleration sensor and the pressure detection cavity 600 are arranged horizontally spaced apart, and the specific spacing distance is set according to the actual requirements of the product;

[0085] A top cover 300 is provided above the upper silicon layer 200 at a position corresponding to the acceleration detection component, and a sealed upper cavity 301 is formed between the bottom surface of the top cover 300 and the top surface of the acceleration detection component.

[0086] In the entire device, the top cover 300 and the silicon substrate 100 play a supporting and fixing role, and the fixed electrode and the anchor point 1 are connected to the silicon substrate 100 .

[0087] Those skilled in the art can understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a MEMS capacitive pressure and acceleration composite sensor, characterized in that: The following steps are involved: S1, forming a lower electrode (400) of a pressure sensor in a partial area of ​​the upper surface of a silicon substrate (100) by ion implantation; S2, providing an oxide layer on the upper surface of the silicon substrate (100) to form a lower structure; S3, setting a lower cavity (110) of the acceleration sensor on the lower structure by dry etching, wherein an anchor point for fixing is provided inside the lower cavity; the lower cavity (110) of the acceleration sensor and the lower electrode (400) of the pressure sensor are arranged at intervals in the horizontal direction; S4, bonding an upper layer of silicon (200) on the lower structure, wherein the upper layer of silicon (200) covers the entire surface of the lower structure; S5, reducing the thickness of the upper silicon layer (200); S6, arranging a groove structure and arranging a detection component on the thinned upper silicon layer (200) by using an etching process, the detection component comprising an acceleration detection component corresponding to the lower cavity (110) of the acceleration sensor and an upper electrode of the pressure sensor corresponding to the lower electrode (400) of the pressure sensor; S7, providing a protective layer (500) on the surface of the acceleration detection component, and removing the oxide layer on the surface of the lower electrode (400) of the pressure sensor through the slot of the upper electrode of the pressure sensor, so that a gap is formed between the bottom surface of the upper electrode of the pressure sensor and the top surface of the lower electrode (400) of the pressure sensor; S8, removing the remaining protective layer (500); S9, providing an isolation dielectric layer on the detection component, filling the corresponding slots and performing surface flattening, so that the gap is sealed to form a pressure detection cavity (600); S10, etching contact holes and filling them with metal, and depositing and patterning metallization layers on the isolation dielectric layer to lead out electrical signals of the sensor; S11, etching the isolation dielectric layer, releasing the acceleration detection component, and releasing the isolation dielectric layer on top of the upper electrode of the pressure sensor to form a pressure sensitive film (700); S12, a top cover (300) is arranged above the acceleration detection component, and a sealed upper cavity (301) of the acceleration sensor is formed between the lower surface of the top cover (300) and the upper surface of the acceleration detection part.

2. The preparation method according to claim 1, characterized in that: In step S11, a groove (800) is provided above the pressure detection cavity (600), which penetrates the entire isolation dielectric layer and the bottom surface of the groove is located in the upper silicon layer (200), thereby forming the pressure sensitive film (700), which can be deformed toward the pressure detection cavity (600) when subjected to force.

3. The preparation method according to claim 1, characterized in that: The oxide layer is formed by depositing silicon oxide.

4. The preparation method according to claim 1, characterized in that: The oxide layer on the surface of the lower electrode (400) of the pressure sensor is removed by etching with hydrofluoric acid gas.

5. The preparation method according to claim 1, characterized in that: The protective layer (500) is formed by spraying or spin coating photoresist.

6. The preparation method according to claim 1, characterized in that: The lower electrode (400) of the pressure sensor is formed into a resistor by ion implantation, and the implanted ions are boron or other elements used to make electrodes.

7. The preparation method according to claim 1, characterized in that: The isolation dielectric layer is silicon oxide and / or silicon nitride and is formed by chemical vapor deposition.

8. The preparation method according to claim 1, characterized in that: The bottom of the top cover (300) is bonded to the metal on the surface of the isolation dielectric layer by glass paste.

9. The preparation method according to claim 1, characterized in that: The acceleration detection component comprises a comb-tooth structure detection body, an elastic beam and an anchor point.

10. A MEMS capacitive pressure and acceleration composite sensor made according to the preparation method according to any one of claims 1 to 9, characterized in that: The acceleration detection component of the composite sensor and the upper electrode of the pressure sensor are formed on the same upper silicon layer (200); The lower cavity (110) of the acceleration sensor, the lower electrode (400) of the pressure sensor and the pressure detection cavity (600) are all located on the lower silicon substrate (100); The lower cavity (110) of the acceleration sensor and the pressure detection cavity (600) are arranged at intervals in the horizontal direction; A top cover (300) is provided above the upper silicon layer (200) at a position corresponding to the acceleration detection component, and a sealed upper cavity (301) of the acceleration sensor is formed between the bottom surface of the top cover and the top surface of the acceleration detection component.

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