MEMS pressure sensor with stress isolation structure and preparation method thereof

Abstract

The invention discloses an MEMS pressure sensor with a stress isolation structure and a preparation method of the MEMS pressure sensor. The MEMS pressure sensor comprises a packaging shell, a metal lead, a chip with an isolation structure, chip bonding glue and a metal frame. In the chip with the isolation structure, a pressure sensitive area is integrally connected with the chip through a bias cantilever beam or a folding beam, the pressure sensitive area is in a suspended state and can completely isolate residual stress caused by a packaging shell and chip adhesive, and meanwhile, the bias cantilever beam or the folding beam is relatively large in thickness, so that the influence of impact vibration on a sensitive film of a pressure sensor can be avoided; the stability and reliability of the pressure sensor are improved, the processing technology is simple, and batch production can be realized.

Description

Technical Field

[0001] The invention relates to MEMS sensor technology, and in particular to a MEMS pressure sensor with a stress isolation structure and a preparation method thereof. Background Art

[0002] MEMS pressure sensor is a pressure sensor manufactured based on micro-electromechanical system (MEMS) technology, which has the characteristics of small size, high precision, low power consumption and high reliability. MEMS pressure sensor is widely used in the fields of automobile, medical, aerospace, etc., which can realize real-time monitoring of pressure and improve production efficiency and product quality.

[0003] Packaging is one of the most important links in the research and development process of MEMS pressure sensors. Packaging is not only the key to the miniaturization of sensors, but also plays a role in mechanical support, electrical connection, environmental protection, etc. in the sensor, making MEMS pressure sensors stable and reliable in various measurement environments.

[0004] Packaging usually involves the connection of multiple materials such as silicon-based chips, metals, glue and plastic resins. Due to the mismatch of thermal expansion coefficients between packaging materials, residual stress will inevitably be introduced, which will cause the output signal of the MEMS pressure sensor to drift. At the same time, the packaging stress gradually changes over time, seriously affecting the reliability and long-term stability of the MEMS pressure sensor.

[0005] Reducing packaging stress is a key factor in achieving high performance and high stability of MEMS sensors. Optimizing the packaging structure is the most commonly used method to reduce packaging stress. Patent "Stress isolation device packaging and manufacturing method" (application number 202210365822.4) Figure 1 As shown, a cantilever beam structure is used to effectively isolate the sensitive chip and the packaging shell to reduce the packaging stress. The patent "An acceleration sensor structure and preparation method for reducing potting stress" (application number 201710688342.0) proposes a staggered annular groove structure to elastically connect the sensitive chip and the packaging shell to reduce the packaging stress. Although the above method can reduce the packaging stress, it cannot achieve complete isolation of the packaging stress. At the same time, it increases the size of the sensor chip or the difficulty of the process, which is not conducive to the mass production of MEMS sensors. Summary of the invention

[0006] In view of the defects and shortcomings of the prior art, the purpose of the present invention is to provide a MEMS pressure sensor with a stress isolation structure and a preparation method thereof. The structure can not only achieve complete isolation of packaging stress, but also has little effect on the overall size of the pressure sensor chip. At the same time, the processing technology is simple, the product has good reliability and consistency, and batch manufacturing can be achieved.

[0007] The specific scheme adopted by the present invention is:

[0008] An isolation groove is designed around the sensitive membrane of the pressure sensor chip to completely isolate the sensitive membrane from the area on the chip with packaging materials. The sensitive membrane area structure is in a suspended state, and the sensitive membrane is connected to the entire chip through a biased cantilever beam or folded beam structure. The two have the same thickness, but are slightly smaller than the overall thickness of the chip. The metal connection is led out through the biased cantilever beam or folded beam structure, and the varistor on the sensitive membrane constitutes a Wheatstone full-bridge circuit.

[0009] In the above scheme, the sensitive area structure is connected to the chip as a whole through an offset cantilever beam or a folded beam to achieve complete isolation.

[0010] In the above solution, the thickness of the sensitive area structure is the same as that of the offset cantilever beam or folded beam, but is slightly smaller than the overall size of the chip, so that the bottom surface of the sensitive area is higher than the entire chip, ensuring that the sensitive area structure is in a suspended state.

[0011] In the above scheme, the varistor forms a Wheatstone full-bridge circuit, the metal wires are led out through a cantilever beam or a folded beam structure, and the metal pads are distributed on the two corners of the chip to ensure that the plastic encapsulation resin can be completely covered during packaging.

[0012] Another object of the present invention is to provide a method for preparing the MEMS pressure sensor with the package stress isolation structure, comprising the following steps:

[0013] 1. Photolithography and etching are performed on the front side of silicon wafer 1 to form a cavity;

[0014] 2. Silicon dioxide is deposited on the front side of silicon wafer 1 and bonded to the front side of silicon wafer 2 to form bonding wafer 1;

[0015] 3. The front side of the bonding sheet 1 is thinned to form a sensitive membrane;

[0016] 4. Thermally oxidize silicon dioxide on the front side of the bonding wafer 1, perform photolithography and implant the P- and P+ regions;

[0017] 5. The bonding wafer 1 is pushed forward, silicon dioxide is deposited on the front side, and photolithography etching is performed to form contact holes;

[0018] 6. Metal is sputtered on the front of the bonding sheet 1, and an electrical signal interface is formed by photolithography and etching;

[0019] 7. Silicon nitride is deposited on the front side of the bonding sheet 1, and photolithography and etching are performed to expose the metal pad;

[0020] 8. Photolithography and etching are performed on the back side of the bonding sheet 1 to form a pit;

[0021] 9. The front side of the bonding wafer 1 is photolithographically processed and deeply etched to form an isolation groove structure to release the sensitive area structure.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] The offset cantilever beam or folded beam structure proposed in the present invention isolates the sensitive membrane area structure from the packaging shell, and the residual stress generated by the packaging shell is completely isolated outside the sensitive membrane. At the same time, the sensitive area structure is suspended and does not contact the patch glue, thereby avoiding the influence of residual stress caused by the patch glue. The offset cantilever beam or folded beam has a large thickness, so the influence of impact vibration on the sensitive membrane of the MEMS pressure sensor can be avoided. Compared with the traditional cantilever beam structure, the offset cantilever beam or folded beam can completely isolate the packaging stress and requires less space, so the size of the sensor chip will not be increased additionally. This greatly reduces the processing cost while improving the stability and reliability of the MEMS pressure sensor, and can be widely used in various pressure sensor chip packages. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a front schematic diagram of the existing MEMS sensor cantilever beam stress isolation structure;

[0025] Figure 2 This is a schematic diagram of the overall structure of a MEMS pressure sensor with a stress isolation structure according to Embodiment 1;

[0026] Figure 3 This is a cross-sectional schematic diagram of a MEMS pressure sensor with a stress isolation structure according to Embodiment 1;

[0027] Figure 4 It is a front schematic diagram of the offset cantilever beam stress isolation structure of Example 1;

[0028] Figure 5 It is a front schematic diagram of the folded beam stress isolation structure of Example 1;

[0029] Figure 6 It is a cross-sectional schematic diagram of a pressure sensor without an isolation structure;

[0030] Figure 7 (a) to (i) are schematic diagrams of the process of preparing a MEMS pressure sensor with a stress isolation structure according to Embodiment 2; DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0032] Embodiment 1:

[0033] A MEMS pressure sensor with a stress isolation structure, such as Figures 2 to 5As shown, it includes a packaging shell 1, a metal lead 2, an isolation structure chip 3, an adhesive 4 and a metal frame 5. The isolation structure chip 3 includes a sensitive film 6, a core 7 in contact with the packaging shell, and an offset cantilever beam 8 or a folded beam 9. During the chip packaging process, the isolation structure chip 3 is fixed to the metal frame 5 by the adhesive 4. The adhesive 4 needs to be cured at a certain temperature, and the curing temperature range is generally 150-250°C. The back of the isolation structure chip 3 is partially etched so that the sensitive film structure area is in a suspended state. During the chip bonding process, this part does not contact the adhesive. After the chip bonding is completed, the epoxy resin is integrally encapsulated to integrate the chip and the frame. The epoxy resin shell needs to be cured at a certain temperature, and the curing temperature is generally 150-250°C. During the packaging process, the packaging shell 1 is in direct contact with the chip 3, but due to the existence of the isolation structure, the sensitive film 6 is not in direct contact with the packaging shell 1.

[0034] The sensor chip material is single crystal silicon, with a thermal expansion coefficient of about 2.6e-6m / k, the thermal expansion coefficient of the adhesive material is 8.6e-5m / k, and the thermal expansion coefficient of the packaging shell material is 3.6e-5m / k.

[0035] Embodiment 2:

[0036] The cross section of a pressure sensor without isolation structure is as follows Figure 6 As shown, the stress state of the pressure sensor without isolation structure after packaging can be calculated by finite element simulation. The residual stress of the sensitive film after packaging is high, which can cause the output voltage to change, with a maximum change of 30mv.

[0037] Compared with the chip without isolation structure, the stress of the chip after packaging of the existing MEMS sensor cantilever beam stress isolation structure is reduced, the maximum stress is reduced from 638MPa to 352MPa, and the output voltage is reduced from 30mv to 12mv, with a maximum reduction of 60%.

[0038] Compared with the chip without isolation structure, the stress of the chip after packaging with biased cantilever beam stress isolation structure is significantly reduced. The maximum stress is reduced from 638MPa to 0MPa, and the output voltage is reduced from 30mv to 0mv, with a maximum reduction of 100%, achieving complete isolation of packaging stress.

[0039] Embodiment three:

[0040] A method for preparing a MEMS pressure sensor with a stress isolation structure, comprising: 1. Photolithography and etching are performed on the front side of the silicon wafer 1 to form a cavity, such as Figure 7 (a) 2. Silicon dioxide is deposited on the front of silicon wafer 1 and bonded to the front of silicon wafer 2 to form bonding wafer 1. Figure 7 (b) 3. The front side of the bonding sheet 1 is thinned to form a sensitive film, such as Figure 7 (c) 4. Thermally oxidize silicon dioxide on the front side of the bonding wafer 1, perform photolithography and implant the P- and P+ regions, such as Figure 7 (d) 5. The bonding sheet 1 is pushed forward, silicon dioxide is deposited on the front side, and contact holes are formed by photolithography etching, such as Figure 7 (e) 6. Metal is sputtered on the front of the bonding sheet 1, and then photoetched to form an electrical signal interface, such as Figure 7 (f) 7. Silicon nitride is deposited on the front of the bonding sheet 1, and photolithography and etching are performed to expose the metal pad, such as Figure 7 (g) as shown; 8. The back side of the bonding sheet 1 is photolithographically and etched to form a pit, such as Figure 7 (h) 9. The front side of the bonding sheet 1 is photolithographically and deeply etched to form an isolation groove structure to release the sensitive area structure, such as Figure 7 (i) as shown.

[0041] The MEMS pressure sensor with an offset cantilever beam or folded beam stress isolation structure proposed in the present invention structurally realizes complete isolation of the sensitive membrane of the pressure sensor from the packaging shell and the adhesive glue. The residual stress caused by the different thermal expansion coefficients of various materials during the packaging process will not be transmitted to the sensitive membrane. Therefore, the output signal will not be offset after the chip is packaged, thereby ensuring the accuracy and reliability of the chip measurement. At the same time, the thickness of the isolation structure is relatively thick, which can avoid the influence of impact vibration on the sensitive membrane of the MEMS pressure sensor.

[0042] The isolation structure proposed in the present invention has little effect on the overall size of the sensor chip and will not cause a substantial increase in production costs. At the same time, the processing technology is relatively simple, the product has good reliability and consistency, and batch production can be achieved.

Claims

1. A MEMS pressure sensor with a stress isolation structure, characterized in that: include: Package shell, metal leads, chip with isolation structure, die bonding glue and metal frame; The pressure sensitive film area in the chip with the isolation structure is connected to the whole chip through the stress isolation structure, and the pressure sensitive film area is in a suspended state; The stress isolation structure is a biased cantilever beam and a folded beam structure; the metal lead is located on the chip with the isolation structure to achieve electrical connection, the metal frame is connected to the chip with the isolation structure through adhesive, and the packaging shell is in direct contact with the chip with the isolation structure and the metal frame to achieve integrated packaging of the pressure sensor.

2. The MEMS pressure sensor with stress isolation structure according to claim 1, characterized in that: The thickness of the pressure sensitive film area is the same as that of the stress isolation structure and is smaller than the overall thickness of the chip.

3. The MEMS pressure sensor with stress isolation structure according to claim 1, characterized in that: The pressure sensitive membrane area is in a suspended state.

4. The MEMS pressure sensor with a stress isolation structure according to claim 1, characterized in that: The chip with the isolation structure is connected to the metal frame via an adhesive.

5. The MEMS pressure sensor with stress isolation structure according to claim 1, characterized in that: The packaging shell adopts plastic packaging resin to realize integrated packaging of the pressure sensor.

6. A method for preparing a MEMS pressure sensor with a stress isolation structure, characterized in that: The following steps are involved: 1) Photolithography and etching are performed on the front side of the silicon wafer 1 to form a cavity; 2) Silicon dioxide is deposited on the front side of silicon wafer 1 and bonded to the front side of silicon wafer 2 to form a bonded wafer; 3) The front side of the bonding sheet is thinned to form a sensitive membrane; 4) Thermally oxidize silicon dioxide on the front side of the bonding wafer, perform photolithography and implant the P- and P+ regions; 5) The bonding wafer is advanced, silicon dioxide is deposited on the front side, and contact holes are formed by photolithography and etching; 6) Metal is sputtered on the front of the bonding wafer, and the electrical signal interface is formed by photolithography and etching; 7) Silicon nitride is deposited on the front side of the bonding wafer, and photolithography and etching are performed to expose the metal pad; 8) Photolithography and etching on the back of the bonding wafer to form a pit; 9) The front side of the bonding wafer is photolithographically processed and deeply etched to form an isolation groove structure to release the sensitive area structure.

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