MEMS pressure sensor and manufacturing method thereof

Abstract

The invention provides an MEMS pressure sensor and a manufacturing method thereof, the MEMS pressure sensor comprises a first device structure and a second device structure, the first device structure comprises a substrate, the front surface of which is provided with a first cavity; the device layer is formed above the front face of the substrate, a piezoresistor, an electrode and a wire connecting the electrode and the piezoresistor are formed in the device layer, and the piezoresistor is formed on the surface of the side, away from the substrate, of the device layer; the second device structure and the first device structure are bonded together, the second device structure comprises a cover plate, a second cavity is formed between the cover plate and the piezoresistor, a strain film is formed between the first cavity and the second cavity, and the piezoresistor is formed in the strain film. Compared with the prior art, the MEMS pressure sensor has the advantages that the piezoresistive region is hermetically protected by adopting a wafer bonding technology, and a sensitive structure with a pressed back surface is designed, so that the MEMS pressure sensor can stably work in severe environments such as high temperature, high humidity, high oil contamination and high pH value for a long time.

Description

[Technical Field]

[0001] This invention relates to the fields of sensor technology and micro-motor system technology, and in particular to a MEMS pressure sensor with pressure on the back and its fabrication method. [Background Technology]

[0002] MEMS (Micro-Electro-Mechanical System) pressure sensors are widely used in industries such as automotive, consumer electronics, industrial and energy sectors, healthcare, aerospace, and environmental monitoring due to their advantages such as miniaturization, low manufacturing cost, and mass production. The large-scale application of MEMS pressure sensors has accelerated the development of the Internet of Things (IoT), providing a solid sensing foundation for its automation and intelligentization.

[0003] Sensors frequently encounter impacts, drops, high temperatures, vibrations, oil contamination, and chemical corrosion in real-world working environments. However, current sensor packaging designs expose the piezoresistive region and the electrodes and gold wires on the front of the sensor to the environment. After being subjected to harsh environmental conditions, the gold wires may detach or break, and the pads may experience poor contact, leading to frequent sensor failures and malfunctions. Because traditional MEMS piezoresistive pressure sensors are subjected to pressure on the front (e.g., pressure on the device layer), and the piezoresistive resistors and wires are exposed to the working environment, they are ill-suited for harsh environments such as high temperature and humidity, high oil content, and high acid and alkali conditions.

[0004] Therefore, it is necessary to propose a new technical solution to address the above problems. [Summary of the Invention]

[0005] One of the objectives of this invention is to provide a MEMS pressure sensor and its fabrication method. The sensor uses wafer bonding technology to seal and protect the piezoresistive region, and isolates the piezoresistor, wires and other components from the harsh working environment. This allows the MEMS pressure sensor to operate stably for a long time in harsh environments such as high temperature, high humidity, high oil content and high acidity / alkalinity.

[0006] According to one aspect of the present invention, a MEMS pressure sensor is provided, comprising a first device structure and a second device structure. The first device structure includes: a substrate having a first cavity formed on its front side; a device layer formed above the front side of the substrate, wherein a piezoresistor, an electrode, and a wire connecting the electrode and the piezoresistor are formed in the device layer, the piezoresistor being formed on a side surface of the device layer away from the substrate and opposite to the first cavity; the second device structure is bonded to the first device structure, the second device structure including a cover plate forming a second cavity between the cover plate and the piezoresistor, a strain film forming between the first cavity and the second cavity, the piezoresistor being formed in the strain film, wherein when external pressure is applied to the back side of the substrate, the strain film deforms, thereby causing a change in the resistance of the piezoresistor.

[0007] According to another aspect of the present invention, a method for fabricating a MEMS pressure sensor is provided, comprising: providing a first device structure, the first device structure comprising: a substrate having a first cavity formed on its front side; a device layer formed above the front side of the substrate, wherein a piezoresistor, an electrode, and a wire connecting the electrode and the piezoresistor are formed in the device layer, the piezoresistor being formed on a side surface of the device layer away from the substrate and opposite to the first cavity; providing a second device structure, the second device structure comprising a cover plate; bonding the first device structure and the second device structure together, wherein a second cavity is formed between the cover plate and the piezoresistor, a strain film is formed between the first cavity and the second cavity, the piezoresistor being formed in the strain film, wherein when external pressure is applied to the back side of the substrate, the strain film deforms, thereby causing a change in the resistance of the piezoresistor.

[0008] Compared with the prior art, the present invention uses wafer bonding technology to seal and protect the piezoresistive region, and isolates the piezoresistor, wires and the harsh working environment. When external pressure is applied to the back of the substrate of the MEMS pressure sensor, the MEMS pressure sensor can work stably for a long time in harsh environments such as high temperature, high humidity, high oil, and high acidity and alkalinity. [Attached Image Description]

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0010] Figure 1This is a perspective view of a MEMS pressure sensor in one embodiment of the present invention;

[0011] Figure 2 As shown in one embodiment of the present invention Figure 1 A schematic planar view of the substrate shown;

[0012] Figure 3 As shown in one embodiment of the present invention Figure 1 The diagram shows a longitudinal cross-section of the MEMS pressure sensor.

[0013] Figure 4 For example, in one embodiment of the present invention Figure 3 The diagram shows a planar view of the device layer.

[0014] Figure 5 This is a schematic flowchart of a method for fabricating a MEMS pressure sensor according to one embodiment of the present invention.

[0015] Figure 6 For example, in one embodiment of the present invention Figure 5 The flowchart of step 100 is shown below;

[0016] Figure 7 For example, in one embodiment of the present invention Figure 5 The flowchart of step 200 is shown below;

[0017] Figures 8-19 For example, in one embodiment of the present invention Figure 6 The longitudinal section views corresponding to each step shown;

[0018] Figures 20-23 For example, in one embodiment of the present invention Figure 7 The longitudinal section views corresponding to each step shown;

[0019] Figure 24 For example, in one embodiment of the present invention Figure 5 The longitudinal section view corresponding to step 300 is shown below;

[0020] Figure 25 For example, in one embodiment of the present invention Figure 5 The longitudinal section view corresponding to step 400 is shown below;

[0021] Figure 26 For example, in one embodiment of the present invention Figure 5 The longitudinal section view corresponding to step 500 is shown.

Detailed Implementation Methods

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments. Unless otherwise specified, the terms "connected," "linked," and "connected" used herein to indicate electrical connection refer to direct or indirect electrical connection.

[0024] Please refer to Figure 1 The image shown is a perspective view of a MEMS pressure sensor according to one embodiment of the present invention; please refer to... Figure 2 As shown, this is an embodiment of the present invention. Figure 1 The diagram shows a planar view of the substrate; please refer to it. Figure 3 As shown, this is an embodiment of the present invention. Figure 1 The diagram shows a longitudinal cross-section of the MEMS pressure sensor; please refer to it. Figure 4 As shown, this is one embodiment of the present invention. Figure 3 The diagram shows a planar schematic of the device layer. Figures 1-3 The MEMS pressure sensor shown includes a first device structure A and a second device structure B.

[0025] The first device structure A includes a substrate 1 and a device layer 3. A first cavity 11 is formed on the front side of the substrate 1, specifically extending from the front side of the substrate 1 into the substrate 1. The device layer 3 is formed above the front side of the substrate 1, and contains a varistor 13, an electrode 14, and a wire 15 connecting the electrode 14 and the varistor 13. The varistor 13 is formed on the surface of the device layer 3 away from the substrate 1 (or on the front side of the device layer 3), and is opposite to the first cavity 11.

[0026] The second device structure B is bonded to the first device structure A. The second device structure B includes a cover plate 9, with a second cavity 21 formed between the cover plate 9 and the varistor 13. A strain film 22 is formed between the first cavity 11 and the second cavity 21, and the varistor 13 is formed in the strain film 22. When external pressure is applied to the back side of the substrate 1, the strain film 22 deforms, which in turn causes a change in the resistance of the varistor 13.

[0027] In a specific embodiment of the present invention, the depth of the first cavity 11 is 40 μm to 600 μm, and the thickness of the device layer 3 is 5 to 150 μm.

[0028] exist Figure 1 and Figure 3In the embodiment shown, the first device structure A further includes a plurality of pads 17, which are located above the surface of the device layer 3 away from the substrate 1 (or the front side of the device layer 3), and each pad 17 is electrically connected to the corresponding electrode 14.

[0029] exist Figure 1 and Figure 3 In the specific embodiment shown, multiple pads Pad17 are located outside the vertical projection area of ​​the second device structure B and the first device structure A, which facilitates wire bonding.

[0030] exist Figure 3 In the embodiment shown, the surface of device layer 3 away from substrate 1 (or the front side of device layer 3) is transformed into a conductor by ion implantation to form a heavily doped layer (or doped layer) 12. The heavily doped layer 12 is patterned and etched to form a varistor 13, an electrode 14, and a wire 15 connecting the electrode 14 and the varistor 13.

[0031] exist Figure 3 In the illustrated embodiment, the first device structure A further includes a first insulating layer 6 and a second metal thin film (unidentified). The first insulating layer 6 is located above the surface of the device layer 3 away from the substrate 1 (or the front side of the device layer 3). The first insulating layer 6 is patterned and etched to form a via 20 penetrating the first insulating layer 6. The second metal thin film (unidentified) is deposited on the first insulating layer 6. The second metal thin film (unidentified) is patterned and etched to form a pad 17 and a first bonding ring 16. The pad 17 fills the via 20 and is electrically connected to the corresponding electrode 14.

[0032] exist Figure 3 In the illustrated embodiment, the second device structure B further includes a second insulating layer 8 and a third metal thin film (unidentified). The second insulating layer 8 is formed on the front side of the cover plate 9; the third metal thin film (unidentified) is deposited on the surface of the second insulating layer 8 away from the cover plate 9, and the third metal thin film (unidentified) is patterned and etched to form a second bonding ring 7. When the first device structure A and the second device structure B are bonded, the first bonding ring 16 and the second bonding ring 7 are bonded to each other (i.e., gold-to-gold bonding). The semi-closed second cavity 21 in the first device structure A is converted to a closed state by the cover plate 9, the second insulating layer 8, and the bonding rings 16 and 7, and the varistor 13 and the wire 15 on the strain film 22 are seamlessly protected by the cover plate 9, the second insulating layer 8, and the bonding rings 16 and 7.

[0033] exist Figure 3In the illustrated embodiment, the first device structure A further includes a buried oxide layer 2, a dielectric layer 4, and a contact layer 5. The buried oxide layer 2 is located between the device layer 3 and the front side of the substrate 1. The dielectric layer 4 is deposited on a patterned and etched heavily doped layer 12. The dielectric layer 4 is patterned and etched to form multiple contact electrode holes 18 penetrating the dielectric layer 4, exposing electrodes 14. The contact layer 5 is obtained by depositing a first metal thin film on the surface of the dielectric layer 4 with the multiple contact electrode holes 18. The contact layer 5 is patterned and etched to form multiple independent contact electrodes 19, which fill the contact electrode holes 18 and are electrically connected to the corresponding electrodes 14. A first insulating layer 6 is formed on the surface of the contact layer 5 away from the dielectric layer 4. Pads 17 fill vias 20 and are electrically connected to the corresponding contact electrodes 19, thereby connecting the pads 17 to the corresponding electrodes 14 via the contact electrodes 5.

[0034] In a specific embodiment of the present invention, a buried oxide layer 2 is bonded on the top (or front) of the substrate 1, and a device layer 3 is bonded on the top (or side surface away from the substrate 1) of the buried oxide layer 2.

[0035] exist Figure 2 and Figure 3 In the embodiment shown, a vent hole 10 is formed on the back side of the substrate 1. The vent hole 10 is opposite to and communicates with the first cavity 11 to form a back cavity (not labeled) that extends from the back side of the substrate 1 to the front side of the substrate 1.

[0036] In a specific embodiment of the present invention, the back side of the substrate 1 is etched with a vent hole 10, and the vent hole 10 is etched with a first cavity 11 corresponding to the front side of the substrate 1.

[0037] exist Figure 3 and Figure 4 In the illustrated embodiment, the first cavity 11 is a symmetrical cavity with an axis of symmetry C; there are four piezoresistors 13, denoted as first piezoresistor 13a, second piezoresistor 13b, third piezoresistor 13c, and fourth piezoresistor 13d. There are four electrodes 14, denoted as first electrode 14a, second electrode 14b, third electrode 14c, and fourth electrode 14d. The four piezoresistors 13a, 13b, 13c, and 13d are longitudinally distributed along the axis of symmetry C of the first cavity 11; the first piezoresistor 13a and the second piezoresistor 13b are symmetrical about the axis of symmetry C of the first cavity 11 and are located in the middle of the strain film 22; the third piezoresistor 13c and the fourth piezoresistor 13d are located at the edge of the strain film 22.

[0038] exist Figure 4In the illustrated embodiment, the third varistor 13c includes a first half 13c1, a first connecting part 13c2, and a second half 13c3 connected in sequence. The first half 13c1 and the second half 13c3 are symmetrical about the axis of symmetry C of the first cavity 11. The first connecting part 13c2 is located on the axis of symmetry C of the first cavity 11. One end of the first half 13c1 is connected to the first connecting part 13c2, and one end of the second half 13c3 is connected to the first connecting part 13c2. The fourth varistor 13d includes a third half 13d1, a second connecting part 13d2, and a fourth half 13d3 connected in sequence. The third half 13d1 and the fourth half 13d3 are symmetrical about the axis of symmetry C of the first cavity 11. The second connecting part 13d2 is located on the axis of symmetry C of the first cavity 11. One end of the third half 13d1 is connected to the second connecting part 13d2, and one end of the fourth half 13d3 is connected to the second connecting part 13d2.

[0039] exist Figure 4 In the illustrated embodiment, the first electrode 14a is connected to the other end of the first half 13c1 of the third varistor 13c via a wire 15, and the first electrode 14a is connected to one end of the first varistor 13a via a wire 15; the second electrode 14b is connected to the other end of the second half 13c3 of the third varistor 13c via a wire 15, and the second electrode 14b is connected to one end of the second varistor 13b via a wire 15; the first electrode 14a and the second electrode 14b are symmetrical about the axis of symmetry C of the first cavity 11; the third electrode 14c is connected to the other end of the fourth half 13d3 of the fourth varistor 13d via a wire 15. The third electrode 14c is connected to the other end of the second varistor 13b via wire 15; the fourth electrode 14d is connected to the other end of the third half 13d1 of the fourth varistor 13d via wire 15, and the fourth electrode 14d is connected to the other end of the first varistor 13a via wire 15; the third electrode 14c and the fourth electrode 14d are symmetrical about the axis of symmetry C of the first cavity 11; the first varistor 13a, the second varistor 13b, the third varistor 13c, the fourth varistor 13d, wire 15, the first electrode 14a, the second electrode 14b, the third electrode 14c, and the fourth electrode 14d constitute a Wheatstone bridge.

[0040] exist Figure 4 In the illustrated embodiment, the first varistor 13a and the second varistor 13b are separated by a trench (not labeled); the first half 13c1 and the second half 13c3 of the third varistor 13c are separated by a trench (not labeled); and the third half 14d1 and the fourth half 14d3 of the fourth varistor 14d are separated by a trench (not labeled).

[0041] In summary, the varistor 13 is distributed longitudinally parallel to the axis of symmetry C of the first cavity 11. The varistor 13 extends to the surrounding electrode area through the heavily doped layer 12. The surrounding electrode area is separated by trenches so that the four varistors 13a, 13b, 13c, and 13d of the device layer 3 can be easily connected to form a Wheatstone bridge.

[0042] exist Figures 1-3 In the specific embodiment shown, the first cavity 11 is an irregularly shaped symmetrical cavity, and the second cavity 21 is a vacuum cavity.

[0043] Figures 1-3 The working principle of the MEMS pressure sensor shown is as follows.

[0044] When external pressure is applied to the back side of substrate 1, the strain film 22 deforms. The resistance of the four varistors 13 on the film changes due to this deformation. Furthermore, the varistors 13c and 13d located at the film edge and the varistors 13a and 13b located at the film center have opposite resistance polarities because the direction of the force is opposite. According to the characteristics of a Wheatstone bridge, there is a potential difference between the first output terminal Vout and the second output terminal Vout' of the Wheatstone bridge composed of varistors 13, and this output potential difference is directly proportional to the pressure applied to the back side of substrate 1.

[0045] It should be noted that, in Figure 1 and Figure 3 In the illustrated embodiment, cover plate 9 is cover plate silicon. In other embodiments, cover plate 9 may also be anodic bonded borosilicate glass, and a TGV through-glass via (i.e., glass through-hole) is added on the pad 17 to connect to the pad 17.

[0046] According to another aspect of the present invention, a method for fabricating a MEMS pressure sensor is provided. Please refer to... Figure 5 As shown, it is a flowchart illustrating the fabrication method of a MEMS pressure sensor in one embodiment of the present invention. Figure 5 The fabrication method of the MEMS pressure sensor shown includes the following steps.

[0047] Step 100, as follows Figure 19 As shown, a first device structure is provided.

[0048] Step 200, as follows Figure 23 As shown, a second device structure is provided. Figure 23 The second device structure shown includes a cover plate 9.

[0049] Step 300, as follows Figure 24 As shown, Figure 19 The first device structure shown and Figure 23The second device structure shown is bonded together. A second cavity 21 is formed between the cover plate 9 and the varistor 13, and a strain film 22 is formed between the first cavity 11 and the second cavity 21. The varistor 13 is formed in the strain film 22.

[0050] Figure 19 The first device structure shown includes a substrate 1 and a device layer 3. A first cavity 11 is formed on the front side of the substrate 1, specifically extending from the front side of the substrate 1 into the substrate 1. The device layer 3 is formed above the front side of the substrate 1, and contains a varistor 13, an electrode 14, and a wire 15 connecting the electrode 14 and the varistor 13. The varistor 13 is formed on the surface of the device layer 3 away from the substrate 1 (or on the front side of the device layer 3), and is opposite to the first cavity 11.

[0051] in, Figure 19 The schematic diagram of device layer 3 shown can be found in [reference]. Figure 4 As shown, in Figure 4 and Figure 19 In the illustrated embodiment, the first cavity 11 is a symmetrical cavity with an axis of symmetry C; there are four piezoresistors 13, denoted as first piezoresistor 13a, second piezoresistor 13b, third piezoresistor 13c, and fourth piezoresistor 13d. There are four electrodes 14, denoted as first electrode 14a, second electrode 14b, third electrode 14c, and fourth electrode 14d. The four piezoresistors 13a, 13b, 13c, and 13d are longitudinally distributed along the axis of symmetry C of the first cavity 11; the first piezoresistor 13a and the second piezoresistor 13b are symmetrical about the axis of symmetry C of the first cavity 11 and are located in the middle of the strain film 22; the third piezoresistor 13c and the fourth piezoresistor 13d are located at the edge of the strain film 22.

[0052] exist Figure 4 In the illustrated embodiment, the third varistor 13c includes a first half 13c1, a first connecting part 13c2, and a second half 13c3 connected in sequence. The first half 13c1 and the second half 13c3 are symmetrical about the axis of symmetry C of the first cavity 11. The first connecting part 13c2 is located on the axis of symmetry C of the first cavity 11. One end of the first half 13c1 is connected to the first connecting part 13c2, and one end of the second half 13c3 is connected to the first connecting part 13c2. The fourth varistor 13d includes a third half 13d1, a second connecting part 13d2, and a fourth half 13d3 connected in sequence. The third half 13d1 and the fourth half 13d3 are symmetrical about the axis of symmetry C of the first cavity 11. The second connecting part 13d2 is located on the axis of symmetry C of the first cavity 11. One end of the third half 13d1 is connected to the second connecting part 13d2, and one end of the fourth half 13d3 is connected to the second connecting part 13d2.

[0053] exist Figure 4 In the illustrated embodiment, the first electrode 14a is connected to the other end of the first half 13c1 of the third varistor 13c via a wire 15, and the first electrode 14a is connected to one end of the first varistor 13a via a wire 15; the second electrode 14b is connected to the other end of the second half 13c3 of the third varistor 13c via a wire 15, and the second electrode 14b is connected to one end of the second varistor 13b via a wire 15; the first electrode 14a and the second electrode 14b are symmetrical about the axis of symmetry C of the first cavity 11; the third electrode 14c is connected to the other end of the fourth half 13d3 of the fourth varistor 13d via a wire 15. The third electrode 14c is connected to the other end of the second varistor 13b via wire 15; the fourth electrode 14d is connected to the other end of the third half 13d1 of the fourth varistor 13d via wire 15, and the fourth electrode 14d is connected to the other end of the first varistor 13a via wire 15; the third electrode 14c and the fourth electrode 14d are symmetrical about the axis of symmetry C of the first cavity 11; the first varistor 13a, the second varistor 13b, the third varistor 13c, the fourth varistor 13d, wire 15, the first electrode 14a, the second electrode 14b, the third electrode 14c, and the fourth electrode 14d constitute a Wheatstone bridge.

[0054] exist Figure 4 In the illustrated embodiment, the first varistor 13a and the second varistor 13b are separated by a trench (not labeled); the first half 13c1 and the second half 13c3 of the third varistor 13c are separated by a trench (not labeled); and the third half 14d1 and the fourth half 14d3 of the fourth varistor 14d are separated by a trench (not labeled).

[0055] In summary, the varistor 13 is distributed longitudinally parallel to the axis of symmetry C of the first cavity 11. The varistor 13 extends to the surrounding electrode area through the heavily doped layer 12. The surrounding electrode area is separated by trenches so that the four varistors 13a, 13b, 13c, and 13d of the device layer 3 can be easily connected to form a Wheatstone bridge.

[0056] Please refer to Figure 6 As shown, this is one embodiment of the present invention. Figure 5 The diagram shown illustrates the process of providing the first device structure (i.e., step 100). Please refer to... Figures 8-19 As shown, this is one embodiment of the present invention. Figure 6 The longitudinal section views corresponding to each step are shown. Figure 6 The first device structure shown includes the following steps.

[0057] Step 101, as follows Figure 8As shown, a substrate 1 with a front side and a back side is provided. For example, an N(100) double-polished substrate 1 is prepared.

[0058] Step 102, as follows Figure 9 As shown, the first cavity 11 is etched on the front side of the substrate 1, and the back alignment mark 23 is etched on the back side of the substrate 1.

[0059] Step 103, as follows Figure 10 and Figure 11 As shown, the buried oxide layer 2 and the device layer 3 are sequentially stacked and bonded from the front side of the substrate 1. For example, the buried oxide layer 2 and the device layer 3 are combined together on the front side of the substrate 1 by SOI (Silicon-on-Insulator Bonding).

[0060] Step 104, as follows Figure 12 As shown, a heavily doped layer (or doped layer) 12 is formed on the surface of device layer 3 away from substrate 1 (or the front side of device layer 3) by ion implantation to become conductive. A varistor 13, an electrode 14, and a wire 15 connecting the electrode 14 and the varistor 13 are formed by patterning and etching the heavily doped layer 12. For example, silicon oxide is grown on the front side of device layer 3 by thermal oxidation, and ion implantation is performed on the surface of device layer 3 using silicon oxide as a mask to form a heavily doped layer 12. The silicon oxide on the surface is then removed by wet etching. Dry etching is then performed on the front side of device layer 3 to form four varistors 13, four electrodes 14, and wires 15, thereby constructing a Wheatstone bridge.

[0061] Step 105, as follows Figure 13 As shown, a thin film is deposited on the front side (i.e. the side surface away from the substrate 1) of the patterned and etched heavily doped layer 12 to form a dielectric layer 4.

[0062] Step 106, as follows Figure 14 As shown, the patterned and etched dielectric layer 4 forms a plurality of contact electrode holes 18, which expose the electrodes 14. For example, the patterned surface of the dielectric layer 4 (i.e., the surface away from the substrate 1) is used to dry etch four contact electrode holes 18.

[0063] Step 107, as follows Figure 15 As shown, a first metal thin film is deposited on the front side (i.e., the side away from the substrate 1) of the dielectric layer 4, which has multiple contact electrode holes 18, to obtain a contact layer 5. The contact layer 5 is patterned and etched to form multiple independent contact electrodes 19. The contact electrodes 19 fill the contact electrode holes 18 and are electrically connected to the corresponding electrodes 14. For example, a metal thin film is sputtered on the surface of the dielectric layer 4 to obtain the contact layer 5. The metal thin film 5 is patterned to form four independent contact electrodes 19 through patterning and wet etching processes. The metal will fill the contact electrode holes 18 to connect the electrodes 14 and the contact electrodes 19.

[0064] Step 108, as follows Figure 16 As shown, a first insulating layer 6 is deposited on the surface of the contact layer 5 where the contact electrode 19 is formed (i.e., the surface away from the substrate 1). For example, a silicon oxide thin film is deposited on the surface of the contact layer 5 by plasma chemical vapor deposition, and the first insulating layer 6 is formed by chemical mechanical polishing.

[0065] Step 109, as follows Figure 17 As shown, the first insulating layer 6 is patterned and etched to form a via 20. For example, the first insulating layer 6 is patterned on the front side (i.e., the side surface away from the substrate 1), and the via 20 is etched out by dry etching.

[0066] Step 110, as follows Figure 18 As shown, a second metal thin film (unidentified) is deposited on the first insulating layer 6 where the via 20 is formed. The second metal thin film (unidentified) is patterned and etched to form pads 17 and a first bonding ring 16. The pads 17 fill the via 20 and are electrically connected to the corresponding contact electrodes 19. For example, a metal thin film is deposited on the surface of the first insulating layer 6, and patterned and wet etched to etch out the pads 17 and the first bonding ring 16. The metal will fill the via 20 to connect the contact electrodes 19 and the pads 17.

[0067] Step 111, as follows Figure 19 As shown, the first insulating layer 6 is patterned and etched to form a second cavity 21 above and around the varistor 13, and a strain film 22 is formed between the first cavity 11 and the second cavity 21. Specifically, the surface of the first insulating layer 6 is patterned, and grooves 24 on both sides of the bonding ring 16 are etched into the first insulating layer 6 by wet etching, and the silicon oxide above and around the varistor 13 is removed to form the second cavity 21. Thus, a strain film 22 is formed between the first cavity 11 and the second cavity 21.

[0068] Please refer to Figure 7 As shown, this is one embodiment of the present invention. Figure 5 The diagram shown illustrates the process of providing the second device structure (i.e., step 200). Please refer to... Figures 20-23 As shown, this is one embodiment of the present invention. Figure 7 The longitudinal section views corresponding to each step are shown. Figure 7 The second device structure shown includes the following steps.

[0069] Step 201, as follows Figure 20 As shown, a cover plate 9 with a front and a back is provided. For example, another N(100) double-shot cover plate 9 is prepared.

[0070] Step 202, as follows Figure 21 As shown, a second insulating layer 8 is deposited on the front side of the cover plate 9. For example, a silicon oxide thin film is deposited on the front side of the cover plate 9 to obtain the second insulating layer 8.

[0071] Step 203, as follows Figure 22 As shown, a third metal thin film (unidentified) is deposited on the second insulating layer 8, and the third metal thin film is patterned and etched to form the second bonding ring 7. For example, a metal thin film is deposited on the surface of the second insulating layer 8, and the second bonding ring 7 is obtained by patterning and wet etching.

[0072] Step 204, as follows Figure 23 As shown, the second insulating layer 8 is patterned and etched into the cover plate 9 to form a trench 25 located outside the second bonding ring 7, as shown in the diagram. Figure 19 The first device structure A shown and as follows Figure 23 After the second device structure B shown is bonded, the trench 25 is opposite to the pad 17. Alternatively, the trench 25 extends from the surface of the second insulating layer 8 away from the cover plate 9, penetrating the second insulating layer 8 into the cover plate 9. For example, the surface of the second insulating layer 8 is patterned, and silicon oxide is etched into the cover plate 9 using dry etching, followed by deep silicon etching to form the trench 25, whose depth exceeds half the thickness of the cover plate 9.

[0073] Step 300, as follows Figure 24 As shown, it will be as follows Figure 19 The first device structure shown and as follows Figure 23 The second device structure shown is bonded together via bonding ring 16 and bonding ring 7. Thus, as... Figure 19 In the first device structure shown, the semi-closed second cavity 21 is converted into a closed state through the cover plate 9, the second insulating layer 8, and the bonding rings 16 and 7. The varistor 13 and the wire 15 on the strain thin film 22 are seamlessly protected by the cover plate 9, the second insulating layer 8, and the bonding rings 16 and 7. For example, by bonding the first bonding ring 16 on the front side of the first insulating layer 6 and the second bonding ring 7 on the front side of the second insulating layer 8 in a vacuum environment through gold-gold bonding, the second cavity 21 is converted from a semi-closed state into a vacuum cavity 21.

[0074] Figure 5 The fabrication method of the MEMS pressure sensor shown also includes the following steps.

[0075] Step 400, such as Figure 25 As shown, in Figure 19 The first device structure shown and as follows Figure 23After the second device structure shown is bonded, patterning and etching are performed on the back side of substrate 1 to form a vent 10. The vent 10 is opposite to and communicates with the first cavity 11 to form a back cavity (not shown) extending from the back side of substrate 1 to the front side of substrate 1. For example, patterning is performed on the back side of substrate 1, and the vent 10 is formed by deep silicon etching.

[0076] Step 500, such as Figure 26 As shown, the back side of the bonded cover plate 9 is ground to remove the bottom of the groove 25, exposing the pad 17. Specifically, the thickness of the cover plate 9 is reduced by half through a grinding process, thereby exposing the pad 17.

[0077] In conclusion, as follows: Figure 19 The first device structure shown also includes multiple pads 17, which are located above the surface of device layer 3 away from substrate 1 (or the front side of device layer 3). Each pad 17 is electrically connected to a corresponding electrode 14. Figure 26 As shown, multiple pads Pad17 are located outside the vertical projection area of ​​the second device structure of the first device structure, which facilitates wire bonding.

[0078] It should be noted that, in Figures 8-26 In the illustrated embodiment, cover plate 9 is cover plate silicon. In other embodiments, cover plate 9 may also be anodic bonded borosilicate glass, and a TGV through-glass via (i.e., glass through-hole) is added on the pad 17 to connect to the pad 17.

[0079] In summary, the MEMS pressure sensor and its fabrication method provided by this invention have one or more of the following beneficial effects:

[0080] 1. This invention has high sensitivity and good linearity;

[0081] 2. This invention uses wafer bonding technology to seal and protect the piezoresistive region, and isolates the piezoresistor, wires, and pads from the harsh working environment. The back side of the substrate of the MEMS pressure sensor can withstand external pressure, so the MEMS pressure sensor can work stably for a long time in harsh environments such as high temperature, high humidity, high oil, and high acidity / alkalinity.

[0082] 3. The present invention has a simple structure, low process cost, and can be mass-produced.

[0083] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0084] It should be noted that any modifications made by those skilled in the art to the specific embodiments of the present invention do not depart from the scope of the claims. Accordingly, the scope of the claims is not limited to the foregoing specific embodiments.

Claims

1. A MEMS pressure sensor, characterized in that, It includes a first device structure and a second device structure. The first device structure includes: A substrate having a first cavity formed on its front side; A device layer is formed on the front side above the substrate. A varistor, an electrode, and a wire connecting the electrode and the varistor are formed in the device layer. The varistor is formed on the side surface of the device layer away from the substrate and is opposite to the first cavity. The second device structure is bonded to the first device structure. The second device structure includes a cover plate, and a second cavity is formed between the cover plate and the varistor. A strain film is formed between the first cavity and the second cavity, and the varistor is formed in the strain film. When external pressure is applied to the back side of the substrate, the strain film deforms, which in turn causes the resistance of the varistor to change.

2. The MEMS pressure sensor according to claim 1, characterized in that, The first device structure also includes multiple pads. The plurality of pads are located above the surface of the device layer on the side away from the substrate, and each pad is electrically connected to the corresponding electrode.

3. The MEMS pressure sensor according to claim 2, characterized in that, The plurality of pads are located outside the vertical projection area of ​​the second device structure onto the first device structure.

4. The MEMS pressure sensor according to claim 2, characterized in that, The surface of the device layer away from the substrate is ion-implanted to form a heavily doped layer. The heavily doped layer is patterned and etched to form the varistor, electrodes, and wires.

5. The MEMS pressure sensor according to claim 4, characterized in that, The first device structure further includes a first insulating layer and a second metal thin film. The first insulating layer is located above the surface of the device layer away from the substrate. The first insulating layer is patterned and etched to form vias. The second metal thin film is deposited on the first insulating layer. The second metal thin film is patterned and etched to form pads and a first bonding ring. The pads fill the vias and are electrically connected to the corresponding electrodes. The second device structure further includes a second insulating layer and a third metal thin film. The second insulating layer is formed on the front side of the cover plate. The third metal thin film is deposited on the surface of the second insulating layer away from the cover plate, and the third metal thin film is patterned and etched to form a second bonding ring. When the first device structure and the second device structure are bonded together, the first bonding ring and the second bonding ring are bonded to each other.

6. The MEMS pressure sensor according to claim 5, characterized in that, The first device structure also includes a buried oxide layer, a dielectric layer, and a contact layer. The buried oxide layer is located between the device layer and the substrate; The dielectric layer is deposited on the patterned and etched heavily doped layer, and the dielectric layer is patterned and etched to form a plurality of contact electrode holes, which expose the electrodes. The contact layer is obtained by depositing a first metal thin film on the surface of the dielectric layer having a plurality of contact electrode holes. The contact layer is patterned and etched to form a plurality of contact electrodes. The contact electrodes fill the contact electrode holes and are electrically connected to the corresponding electrodes. The first insulating layer is formed on the side of the contact layer away from the dielectric layer, and the pads fill the vias and are electrically connected to the corresponding contact electrodes.

7. The MEMS pressure sensor according to claim 1, characterized in that, A vent hole is formed on the back side of the substrate. The vent hole is opposite to and communicates with the first cavity to form a back cavity extending from the back side of the substrate to the front side of the substrate.

8. The MEMS pressure sensor according to any one of claims 1-7, characterized in that, The first cavity is a symmetrical cavity, which has an axis of symmetry; The varistor consists of four resistors, which are respectively designated as the first varistor, the second varistor, the third varistor, and the fourth varistor. There are four electrodes, which are respectively referred to as the first electrode, the second electrode, the third electrode, and the fourth electrode; The four piezoresistors are longitudinally distributed along the axis of symmetry of the first cavity, wherein the first piezoresistor and the second piezoresistor are symmetrical about the axis of symmetry of the first cavity and are located in the middle of the strain film; the third piezoresistor and the fourth piezoresistor are located at the edge of the strain film.

9. The MEMS pressure sensor according to claim 8, characterized in that, The third varistor includes a first half, a first connecting part, and a second half connected in sequence. The first half and the second half are symmetrical about the axis of symmetry of the first cavity. The first connecting part is located on the axis of symmetry of the first cavity. One end of the first half is connected to the first connecting part, and one end of the second half is connected to the first connecting part. The fourth varistor includes a third half, a second connecting part, and a fourth half connected in sequence. The third half and the fourth half are symmetrical about the axis of symmetry of the first cavity. The second connecting part is located on the axis of symmetry of the first cavity. One end of the third half is connected to the second connecting part, and one end of the fourth half is connected to the second connecting part.

10. The MEMS pressure sensor according to claim 9, characterized in that, The first electrode is connected to the other end of the first half of the third varistor via the wire, and the first electrode is connected to one end of the first varistor via the wire; The second electrode is connected to the other end of the second half of the third varistor via the wire, and the second electrode is connected to one end of the second varistor via the wire; The first electrode and the second electrode are symmetrical about the axis of symmetry of the first cavity; The third electrode is connected to the other end of the fourth half of the fourth varistor via the wire, and the third electrode is connected to the other end of the second varistor via the wire. The fourth electrode is connected to the other end of the third half of the fourth varistor via the wire, and the fourth electrode is connected to the other end of the first varistor via the wire. The third and fourth electrodes are symmetrical about the axis of symmetry of the first cavity; The first varistor, the second varistor, the third varistor, the fourth varistor, the wire, the first electrode, the second electrode, the third electrode, and the fourth electrode constitute a Wheatstone bridge.

11. The MEMS pressure sensor according to claim 10, characterized in that, The first varistor and the second varistor are isolated by a trench. The first and second halves of the third varistor are separated by a trench. The third and fourth halves of the fourth varistor are separated by a trench.

12. The MEMS pressure sensor according to claim 8, characterized in that, The second cavity is a vacuum cavity; The first cavity is an irregularly shaped symmetrical cavity.

13. A method for fabricating a MEMS pressure sensor, characterized in that, It includes: A first device structure is provided, the first device structure comprising: a substrate having a first cavity formed on its front side; a device layer formed above the front side of the substrate, wherein a varistor, an electrode, and a wire connecting the electrode and the varistor are formed in the device layer, the varistor being formed on the surface of the device layer away from the substrate, and the varistor being opposite to the first cavity; A second device structure is provided, the second device structure including a cover plate; The first device structure and the second device structure are bonded together, a second cavity is formed between the cover plate and the varistor, a strain film is formed between the first cavity and the second cavity, and the varistor is formed in the strain film. When external pressure is applied to the back side of the substrate, the strain film deforms, which in turn causes the resistance of the varistor to change.

14. The method for fabricating a MEMS pressure sensor according to claim 13, characterized in that, The first cavity is a symmetrical cavity, which has an axis of symmetry; There are four varistors, which are respectively labeled as the first varistor, the second varistor, the third varistor, and the fourth varistor; there are four electrodes, which are respectively labeled as the first electrode, the second electrode, the third electrode, and the fourth electrode. The four piezoresistors are longitudinally distributed along the axis of symmetry of the first cavity, wherein the first piezoresistor and the second piezoresistor are symmetrical about the axis of symmetry of the first cavity and are located in the middle of the strain film; the third piezoresistor and the fourth piezoresistor are located at the edge of the strain film. The third varistor includes a first half, a first connecting part, and a second half connected in sequence. The first half and the second half are symmetrical about the axis of symmetry of the first cavity. The first connecting part is located on the axis of symmetry of the first cavity. One end of the first half is connected to the first connecting part, and one end of the second half is connected to the first connecting part. The fourth varistor includes a third half, a second connecting part, and a fourth half connected in sequence. The third half and the fourth half are symmetrical about the axis of symmetry of the first cavity. The second connecting part is located on the axis of symmetry of the first cavity. One end of the third half is connected to the second connecting part, and one end of the fourth half is connected to the second connecting part. The first electrode is connected to the other end of the first half of the third varistor via the wire, and the first electrode is connected to one end of the first varistor via the wire; the second electrode is connected to the other end of the second half of the third varistor via the wire, and the second electrode is connected to one end of the second varistor via the wire; the first electrode and the second electrode are symmetrical about the axis of symmetry of the first cavity; The third electrode is connected to the other end of the fourth half of the fourth varistor via the wire, and the third electrode is connected to the other end of the second varistor via the wire; the fourth electrode is connected to the other end of the third half of the fourth varistor via the wire, and the fourth electrode is connected to the other end of the first varistor via the wire; the third electrode and the fourth electrode are symmetrical about the axis of symmetry of the first cavity; The first varistor, the second varistor, the third varistor, the fourth varistor, the wire, the first electrode, the second electrode, the third electrode, and the fourth electrode constitute a Wheatstone bridge. The first and second varistors are isolated by a trench; the first and second halves of the third varistor are isolated by a trench; and the third and fourth halves of the fourth varistor are isolated by a trench.

15. The method for fabricating a MEMS pressure sensor as described in claim 13, characterized in that, The second cavity is a vacuum cavity. The first device structure further includes a plurality of pads located above the surface of the device layer away from the substrate, each pad being electrically connected to a corresponding electrode. The plurality of pads are located outside the vertical projection area of ​​the second device structure onto the first device structure.

16. The method for fabricating a MEMS pressure sensor according to claim 13 or 14, characterized in that, The first device structure includes: Provides a substrate with a front and a back side; A first cavity is etched on the front side of the substrate; A buried oxide layer and a device layer are sequentially stacked and bonded from the front side of the substrate; A heavily doped layer is formed on the surface of the device layer away from the substrate by ion implantation, and the varistor, electrode and wire are formed by patterning and etching the heavily doped layer; Thin film deposition is performed on the surface of the heavily doped layer away from the substrate after patterning and etching to form a dielectric layer; The dielectric layer is patterned and etched to form a plurality of contact electrode holes, the contact electrode holes exposing the electrodes; A first metal thin film is formed on the surface of the dielectric layer having a plurality of contact electrode holes to obtain a contact layer; The contact layer is patterned and etched to form a plurality of independent contact electrodes, which fill the contact electrode holes and are electrically connected to the corresponding electrodes. A first insulating layer is deposited on the surface of the contact layer on which the contact electrode is formed; The first insulating layer is patterned and etched to form through-holes; A second metal film is deposited on the surface of the first insulating layer in which the via is formed. The second metal film is patterned and etched to form pads and a first bonding ring. The pads fill the via and are electrically connected to the corresponding contact electrode. The first insulating layer is patterned and etched to form the second cavity above and around the varistor, and the second cavity is sealed after the first device structure and the second device structure are bonded together. The provision of the second device includes: Provides a cover with a front and a back; A second insulating layer is deposited on the front side of the cover plate; A third metal film is deposited on the second insulating layer, and the third metal film is patterned and etched to form a second bonding ring.

17. The method for fabricating a MEMS pressure sensor according to claim 16, characterized in that, It also includes patterning and etching on the back side of the substrate after the first and second device structures are bonded to form vent holes. The air vent is opposite to and communicates with the first cavity to form a back cavity extending from the back side of the substrate to the front side of the substrate.

18. The method for fabricating a MEMS pressure sensor according to claim 17, characterized in that, The provision of the second device further includes patterning and etching the second insulating layer into the cover plate to form a trench located outside the bonding ring. After the first device structure and the second device structure are bonded, the trench is opposite to the pad. The method for fabricating the MEMS pressure sensor also includes grinding the back side of the bonded cover plate to remove the bottom of the groove, thereby exposing the pads.

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