A high-sensitivity MEMS differential pressure sensor and its preparation method

Abstract

The present invention discloses a high-sensitivity micro-mechanical system (MEMS) differential pressure sensor and a preparation method thereof, wherein the differential pressure sensor comprises a silicon nitride (SiN) with an etched window. x ) thin films, silicon (Si) substrates, SiN x Suspended structure self-supporting film, PdSe2 polycrystalline ultra-thin film, metal electrode and surface passivation layer. Ultra-thin PdSe2 has significant piezoresistive effect and ultra-thin suspended SiN x The device has a high pressure differential stress sensing characteristic, and the high Young's modulus SiN x The device ensures the reliability of differential pressure sensing. The Wheatstone bridge formed by the optimized metal electrode structure suppresses temperature drift, ensuring the accuracy of differential pressure measurement. Advantages of this invention include compatibility with silicon-based semiconductor processes, high yield, strong repeatability, good stability, and high device sensitivity.

Description

Technical Field

[0001] The present invention relates to the fields of microelectronic devices and pressure sensing, and in particular to a high-sensitivity MEMS pressure differential sensor device and a preparation method thereof. Background Art

[0002] Micromechanical systems (MEMS) are a technology fabricated using semiconductor materials, integrating mechanical components, sensors, actuators, and electronics on a common silicon substrate, with feature sizes ranging from a few millimeters to micrometers. Piezoresistive pressure sensors are one of the most widely reported and fastest-growing MEMS devices. A variety of two-dimensional materials have been used in MEMS piezoresistive or flexible piezoresistive devices, but they suffer from low sensitivity, poor stability, and difficulty in fabrication. Temperature effects are a major factor. Because the fabrication process for a MEMS device is generally lengthy, the higher the temperature during a particular step, the more limited the compatible fabrication steps, including electrode deposition and material packaging. Palladium diselenide (PdSe2), a novel two-dimensional transition metal chalcogenide, exhibits low crystallographic symmetry, making its band gap more susceptible to changes under stress, resulting in more pronounced conductivity changes and strain-sensitive properties. Furthermore, PdSe2 can be fabricated at relatively low temperatures through the selenization reaction of palladium films, offering significant semiconductor process compatibility and high application value in the field of MEMS differential pressure sensors. Summary of the Invention

[0003] The purpose of the present invention is to provide a high-sensitivity MEMS pressure difference sensor device and a preparation method thereof, by forming a double-sided silicon nitride (SiN x ) on a silicon substrate by photolithography and wet etching to obtain SiN x Free-standing thin films, SiN x Polycrystalline PdSe2 thin films and metal electrodes are deposited on a self-supporting film. Connecting the metal electrodes to an external testing system allows for measurement of parameters such as the piezoresistive effect and pressure sensitivity of the PdSe2 film after bending under stress. This results in high yield, strong repeatability, high sensitivity, and high stability.

[0004] To achieve the above object, the present invention provides a high-sensitivity MEMS pressure difference sensor device, comprising a metal electrode, a PdSe2 polycrystalline film, a suspended SiN x Free-standing membranes, silicon substrates, and SiN with etched windows x Thin film, in which the suspended structure of SiN x PdSe2 polycrystalline film and metal electrode are deposited on the self-supporting film. The PdSe2 polycrystalline film is encapsulated with packaging material. The silicon substrate is located on the SiN xFree-standing membrane and SiN with etched windows x between films.

[0005] In a preferred embodiment of the present invention, the size of the silicon nitride film etching window is 0.3 mm×0.3 mm to 2 mm×2 mm.

[0006] In another preferred embodiment of the present invention, the thickness of the silicon substrate is 180-220 μm.

[0007] In a preferred embodiment of the present invention, the metal electrode material is a gold film, a chromium / gold composite film, an indium / gold composite film, a platinum film or a palladium film, and its thickness is 40 to 100 nanometers. The size of the metal electrode is 0.4 mm × 0.4 mm to 1.5 mm × 1.5 mm.

[0008] In another preferred embodiment of the present invention, the PdSe2 polycrystalline thin film has a "U"-like shape, an inner diameter of 50 to 400 microns, and a thickness of 5 to 15 nanometers.

[0009] The present invention provides a high-sensitivity MEMS pressure differential sensor device and a preparation method thereof, comprising the following steps:

[0010] Step 1: Photolithography is used to obtain a designed etching pattern on the silicon nitride film. The silicon nitride film in the patterned portion is etched cleanly using reactive ion etching to obtain a silicon nitride film with an etching window, and the silicon substrate under the silicon nitride film in the patterned area is exposed;

[0011] Step 2: Place a double-sided silicon nitride-coated silicon substrate with a silicon nitride film having an etching window into a strong alkaline solution, and wet-etch the silicon substrate at a constant temperature until a suspended silicon nitride self-supporting film is etched;

[0012] Step 3: Photolithography is used to obtain a designed device pattern on one side of the suspended silicon nitride free-standing film; a palladium film is deposited on the side of the developed device pattern, and the deposited palladium film is selenized to obtain a palladium diselenide polycrystalline film;

[0013] Step 4: Photolithography is used to obtain a designed electrode pattern on one side of the silicon nitride self-supporting film of the suspended structure, and a metal electrode is deposited on one side of the electrode pattern.

[0014] Step 5: Encapsulate the palladium diselenide polycrystalline thin film using a packaging material.

[0015] In a preferred embodiment of the present invention, the method for preparing the silicon nitride film with the etching window in step 1 is as follows:

[0016] Step 1-1: The silicon substrate coated with silicon nitride film on both sides was ultrasonically cleaned with acetone, anhydrous ethanol and deionized water for 5 minutes respectively, and then dried with nitrogen gas;

[0017] Step 1-2: Obtain an etched window pattern using photolithography;

[0018] Step 1-3: Place the substrate in the RIE vacuum chamber, use the photoresist as a mask, and use carbon tetrafluoride (CF4), oxygen (O2), and argon (Ar) to perform reactive ion etching on the silicon nitride in the developed pattern area. The flow rate of CF4, O2, and Ar is controlled by a mass flow meter (MFC) to a volume ratio of 1:1:2, and the etching power density is 0.06W / cm 2 ~0.12W / cm 2 , etching time is 200 to 400 s, and a silicon nitride film with an etching window is obtained.

[0019] In another preferred embodiment of the present invention, the method for preparing the silicon nitride self-supporting film with a suspended structure in step 2 is as follows:

[0020] Step 2-1: Place the substrate with the silicon nitride film with the etched window into the degumming solution and soak it for 5 minutes to remove the residual photoresist. Then, take out the substrate, rinse it with deionized water, and blow it dry with nitrogen gas.

[0021] Step 2-2: Place the dried substrate in a strong alkaline solution and etch it at a constant temperature of 80°C for 2.5 hours using a constant temperature oil bath stirring platform to obtain a silicon nitride self-supporting film with a suspended structure.

[0022] In a preferred embodiment of the present invention, the strong alkaline solution is potassium hydroxide (KOH) with a mass fraction of 40 wt%.

[0023] In a preferred embodiment of the present invention, the preparation method of the palladium film in step 3 is as follows:

[0024] Step 3-1: The silicon substrate with the suspended silicon nitride free-standing film was ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 5 minutes, and then dried with nitrogen gas;

[0025] Step 3-2: Obtaining a device pattern of the palladium film by photolithography;

[0026] Step 3-3: Place the substrate after device pattern exposure into the chamber of the magnetron sputtering coating system and pump the vacuum degree to 2×10 4 Pa, and then high-purity argon gas is introduced to adjust the pressure to 3.5 Pa;

[0027] Step 3-4: Use an RF source to ignite the argon gas and bombard the target. After a 5-minute pre-sputtering process, deposit an 8-15 nm thick palladium film using RF power sputtering. After deposition, remove the substrate and place it in a stripping solution. Once the photoresist is completely removed, rinse the substrate with deionized water and blow dry with nitrogen.

[0028] In another preferred embodiment of the present invention, the preparation method of the palladium diselenide polycrystalline thin film in step 4 is as follows:

[0029] Step 4-1: Place the magnetron palladium-plated substrate in the quartz tube of a PECVD tube furnace and adjust it to the central high-temperature area. Place a sufficient amount of high-purity selenium (Se) powder (99.99%) in a quartz boat and place the quartz boat upstream.

[0030] Step 4-2: Use a mechanical pump to evacuate the quartz tube to reduce the pressure to less than 5 Pa. Then, introduce high-purity argon gas to expel the remaining gas in the tube and adjust the pressure to 10 Pa.

[0031] Step 4-3: Set the heating parameters of the tube furnace to heat from room temperature to 250°C in 15 minutes and keep at this temperature for 30 minutes;

[0032] Step 4-4: After the tube furnace is cooled naturally to room temperature, nitrogen is introduced into the quartz tube to restore the pressure inside the tube to standard atmospheric pressure, and then the substrate is removed to obtain a palladium diselenide polycrystalline thin film.

[0033] In a preferred embodiment of the present invention, the preparation method of the metal electrode in step 5 is as follows:

[0034] Step 5-1: Place the substrate with the electrode pattern developed into the vacuum chamber of the thermal evaporation coating machine and evacuate the chamber until the pressure reaches 1×10 5 Below Pa;

[0035] Step 5-2: sequentially deposit 5nm~8nm Cr and 40nm~80nm Au;

[0036] Step 5-3: Place the substrate with the metal electrode vapor deposited in the degumming solution. After the photoresist is removed, rinse it with anhydrous ethanol and deionized water in sequence, and finally blow it dry with nitrogen.

[0037] The differential pressure sensor provided by the present invention utilizes the excellent flexibility, deformation sensitivity and electrical properties of the palladium diselenide polycrystalline film, and the piezoresistive effect produced by deformation and bending under the action of stress. By connecting the metal electrodes deposited on the palladium diselenide to an external testing system, parameters such as the piezoresistive effect and pressure sensitivity of the palladium diselenide film after bending and deformation under stress can be tested, thereby achieving the effect of monitoring air pressure. The sensor has good development potential in the fields of vocalization, micro-microphones and breathing.

[0038] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a schematic diagram of the cross-sectional structure of a device according to a preferred embodiment of the present invention.

[0040] Figure 2 It is a schematic diagram of the device planar structure of a preferred embodiment of the present invention.

[0041] Figure 3 The figure is a curve relationship diagram of the pressure and output voltage of a device of a preferred embodiment of the present invention after being connected into a Wheatstone bridge structure. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to the embodiments.

[0043] Example 1

[0044] like Figure 1 As shown, a high-sensitivity MEMS pressure difference sensor device comprises a metal electrode (2), a palladium diselenide polycrystalline film (3), a suspended silicon nitride self-supporting film (4), a silicon substrate (5), and a silicon nitride film (6) with an etching window, arranged from top to bottom. The palladium diselenide polycrystalline film (3) and the metal electrode (2) are deposited on the suspended silicon nitride self-supporting film (4), the palladium diselenide polycrystalline film (3) is encapsulated with an encapsulation material (1), and the silicon substrate (5) is located between the suspended silicon nitride self-supporting film (4) and the silicon nitride film (6) with the etching window. The preparation method thereof comprises using a silicon substrate coated with silicon nitride on both sides as a substrate, obtaining a suspended silicon nitride self-supporting film by reactive ion etching and wet etching, depositing a palladium film on the self-supporting film, and selenizing the palladium film by chemical vapor deposition to obtain a palladium diselenide polycrystalline film, finally depositing a metal electrode, and encapsulating the palladium diselenide polycrystalline film (3) with an encapsulation material (1). The specific steps are as follows:

[0045] 1. Photolithography is performed on a single-sided silicon nitride film on a silicon substrate (5) to obtain an etching pattern. The substrate is placed in a RIE vacuum chamber; using the photoresist as a mask, carbon tetrafluoride (CF4), oxygen (O2), and argon (Ar) are used to perform reactive ion etching on the silicon nitride in the patterned area after development. The flow rates of CF4, O2, and Ar are controlled by a mass flow meter (MFC) to a volume ratio of 1:1:2, and the etching power density is 0.06 W / cm 2 ~0.12W / cm 2 , etching time 200 ~ 400s, to obtain a silicon nitride film with an etching window;

[0046] 2. The substrate of the silicon nitride film (6) with the etched window is immersed in a degumming solution to remove the residual photoresist, and then the substrate is taken out and rinsed with deionized water and blown dry with nitrogen; the dried substrate is placed in a 40wt% potassium hydroxide (KOH) solution and etched at a constant temperature of 80°C for 2.5 hours using a constant temperature oil bath stirring platform to obtain a silicon nitride self-supporting film (4) with a suspended structure.

[0047] 3. Photolithography is used to obtain a PdSe2 device pattern on one side of the silicon nitride self-supporting film (4) with a suspended structure. The substrate with the exposed device pattern is placed in the cavity of the magnetron sputtering coating system and the vacuum degree is drawn to 2×10 -4 Pa, then 80 sccm of high-purity argon is introduced to adjust the pressure to 3.5 Pa. An RF source is used to ignite the argon gas and bombard the target. After 5 minutes of pre-sputtering, an 8nm palladium (Pd) film is sputter-deposited. After deposition is complete, the RF magnetron sputtering coating equipment is turned off, the substrate is removed, and the substrate is immersed in a degumming solution. After the photoresist is completely removed, the substrate is rinsed with deionized water and blown dry with nitrogen.

[0048] 4. Place the substrate with the Pd film deposited thereon and a sufficient amount of high-purity selenium (Se) powder (99.99%) in a quartz tube of a plasma enhanced chemical vapor deposition (PECVD) tube furnace, evacuate the quartz tube to make the air pressure in the tube lower than 5 Pa, then introduce high-purity argon gas to exhaust the remaining gas in the tube and adjust the air pressure to 10 Pa; set the heating parameters of the tube furnace, heat the temperature from room temperature to 250°C in 15 minutes and keep it warm for 30 minutes; wait for the tube furnace to cool down naturally and return to room temperature, introduce nitrogen into the quartz tube to restore the tube to standard atmospheric pressure, then take out the substrate to obtain a palladium diselenide polycrystalline thin film (3).

[0049] 5. Photolithography the substrate to obtain the electrode pattern, place it in the vacuum chamber of the thermal evaporation coating machine, place the chromium evaporation boat and the gold evaporation boat in the vacuum chamber, and evacuate the chamber until the pressure reaches 2×10 -5 Pa or less. First, a 5nm thick Cr film was evaporated at a rate of 0.03nm / s, and then a 50nm thick Au film was evaporated at a rate of 0.05nm / s. After the deposition was completed, the substrate was removed and the substrate with the metal electrode was immersed in acetone. After removing the photoresist, it was rinsed with anhydrous ethanol and deionized water in sequence, and finally dried with nitrogen.

[0050] 6. Spin-coat polymethyl methacrylate electron beam photoresist on one side of the palladium diselenide polycrystalline film (3), perform electron beam exposure on the metal electrode (2) area, develop, expose the electrode area, and complete the packaging.

[0051] Implementation Case 2

[0052] like Figure 1 As shown, a high-sensitivity MEMS pressure difference sensor device comprises a metal electrode (2), a palladium diselenide polycrystalline film (3), a suspended silicon nitride self-supporting film (4), a silicon substrate (5), and a silicon nitride film (6) with an etching window, arranged from top to bottom. The palladium diselenide polycrystalline film (3) and the metal electrode (2) are deposited on the suspended silicon nitride self-supporting film (4), the palladium diselenide polycrystalline film (3) is packaged with a packaging material (1), and the silicon substrate (5) is located between the suspended silicon nitride self-supporting film (4) and the silicon nitride film (6) with the etching window. The palladium diselenide polycrystalline film (3) can be prepared by a chemical vapor deposition (CVD) method, and its preparation method is as follows:

[0053] 1. Place the substrate with the Pd film deposited on it and a sufficient amount of high-purity selenium (Se) powder (99.99%) in the quartz tube of a chemical vapor deposition (CVD) tube furnace. Evacuate the quartz tube to reduce the pressure to less than 5 Pa. Then, introduce high-purity argon gas to exhaust the remaining gas in the tube and adjust the pressure to 10 Pa.

[0054] 2. Set the heating parameters of the tube furnace, heat it from room temperature to 300°C in 15 minutes and keep it warm for 30 minutes; wait for the tube furnace to cool down naturally and return to room temperature, introduce nitrogen into the quartz tube to restore the tube to standard atmospheric pressure, then take out the substrate to obtain a palladium diselenide polycrystalline thin film (3).

[0055] Implementation Case 3

[0056] like Figure 1 As shown, a high-sensitivity MEMS pressure difference sensor device comprises a metal electrode (2), a palladium diselenide polycrystalline film (3), a suspended silicon nitride self-supporting film (4), a silicon substrate (5), and a silicon nitride film (6) with an etching window, arranged from top to bottom. The palladium diselenide polycrystalline film (3) and the metal electrode (2) are deposited on the suspended silicon nitride self-supporting film (4), the palladium diselenide polycrystalline film (3) is packaged with a packaging material (1), and the silicon substrate (5) is located between the suspended silicon nitride self-supporting film (4) and the silicon nitride film (6) with the etching window. The packaging material can be a polyimide (PI) positive photoresist, and the specific packaging method is as follows:

[0057] 1: Spin-coating PI positive photoresist on one side of the palladium diselenide polycrystalline film (3) and baking at 100° C. to 120° C. for 2 min to 5 min;

[0058] 2: exposing and developing the metal electrode (2) region to expose the electrode region;

[0059] 3: Place the substrate in a tube furnace, increase the temperature to 100℃~150℃ and keep it warm for 1 hour, then increase the temperature to 180℃~200℃ and keep it warm for 1 hour; then increase the temperature to 250℃~270℃ and keep it warm for 1 hour, then increase it to 300℃ and keep it warm for 1.5 hours, finally cool it down to 60℃ in 90 minutes, and then naturally cool it down to room temperature to complete the curing of the PI photoresist, take out the substrate, and complete the packaging.

[0060] Implementation Case 4

[0061] like Figure 2 As shown, a high-sensitivity MEMS pressure difference sensor device has a suspended silicon nitride self-supporting film (10) on the front, and is deposited with four groups of PdSe2 polycrystalline films (6-9), 12 metal electrodes (11-18) and 4 electrode leads (19-22), wherein a portion of the PdSe2 polycrystalline films (6) and (8) are deposited on the suspended silicon nitride self-supporting film (10), and the PdSe2 polycrystalline films (7) and (9) are completely deposited on the silicon nitride film. The metal electrodes (11-18) and the electrode leads (19-22) are formed by depositing 5-8 nm Cr and 50-60 nm Au. The palladium diselenide polycrystalline films (6-9) are shaped like a "U", with an inner diameter of 50-400 μm and a thickness of 5-15 nm. The metal electrodes (12, 13) are connected via electrode leads (19), the metal electrodes (14, 15) are connected via electrode leads (20), the metal electrodes (16, 17) are connected via electrode leads (21), and the metal electrodes (11, 18) are connected via electrode leads (22). The device is placed in a test system, and the silicon nitride self-supporting film (10) of the suspended structure is deformed by controlling the air pressure to achieve the effect of bending the device. An input voltage is applied to both ends of the metal electrodes (11, 14) (or (15, 18)), and the output voltage at both ends of the metal electrodes (13, 16) (or (12, 17)) is tested, that is, when the device is connected into a Wheatstone bridge structure, the electrical properties of the PdSe2 polycrystalline thin film (7, 9) deposited on the silicon nitride self-supporting film (10) of the suspended structure are measured. A pressure difference is continuously applied to the device up to a maximum of 60kPa, and then the pressure difference is gradually unloaded to 0kPa. The relationship between the output voltage and the pressure difference is as follows: Figure 3 As shown. The sensitivity K of the pressure sensor is defined as the ratio of the response change to the excitation change, which can be understood as the ratio of the voltage change to the pressure change: K = ΔV / ΔP. After testing, when the pressure is between 0kPa and 60kPa, the response sensitivity can be as high as 1.04mV kPa -1 .

[0062] The preferred embodiments of the present invention have been described in detail above. It should be understood that numerous modifications and variations based on the concepts of the present invention are possible without inventive effort by those skilled in the art. Therefore, any technical solution that can be derived by one skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A high-sensitivity MEMS differential pressure sensor device, characterized in that: The invention comprises a packaging material (1), a metal electrode (2), a palladium diselenide polycrystalline film (3), a silicon nitride self-supporting film (4) with a suspended structure, a silicon substrate (5), and a silicon nitride film (6) with an etching window, which are arranged from top to bottom. The palladium diselenide polycrystalline film (3) and the metal electrode (2) are deposited on the silicon nitride self-supporting film (4) with a suspended structure. The palladium diselenide polycrystalline film (3) is packaged with the packaging material (1). The silicon substrate (5) is located between the silicon nitride self-supporting film (4) with a suspended structure and the silicon nitride film (6) with an etching window.

2. The high-sensitivity MEMS differential pressure sensor device according to claim 1, wherein the metal electrode (2) is made of a gold film, a chromium / gold composite film, an indium / gold composite film, a platinum film or a palladium film, and has a thickness of 40 to 100 nanometers. The size of the metal electrode (2) is 0.4 mm × 0.4 mm to 1.5 mm × 1.5 mm.

3. The high-sensitivity MEMS differential pressure sensor device according to claim 1, wherein the palladium diselenide polycrystalline film (3) is shaped like a "U" with an inner diameter of 50 to 400 microns and a thickness of 5 to 15 nanometers.

4. The high-sensitivity MEMS differential pressure sensor device according to claim 1, wherein: The thickness of the silicon nitride film (6) with the etching window and the silicon nitride self-supporting film (4) with the suspended structure is 50 to 200 nanometers, and the thickness of the silicon substrate (5) is 100 to 300 micrometers.

5. The high-sensitivity MEMS differential pressure sensor device according to claim 1, wherein: The size of the etching window is 0.3 mm×0.3 mm to 2 mm×2 mm.

6. The high-sensitivity MEMS differential pressure sensor device according to claim 1, wherein: The packaging material (1) is a polymethyl methacrylate film, a polyimide film or a parylene film, and its thickness is 0.5 micrometer to 2 micrometers.

7. A method for preparing a high-sensitivity MEMS differential pressure sensor according to any one of claims 1 to 5, characterized in that: The steps include: Step 1: etching a window on one of the silicon nitride films on the double-sided silicon nitride film substrate using a standard reactive plasma in a MEMS process to obtain a silicon nitride film with an etched window (6); Step 2: using a standard wet silicon etching method in MEMS processing technology, the silicon under the window is reactively etched to obtain a silicon nitride self-supporting film (4) with a suspended structure on the other side; Step 3: depositing a palladium film on one side of the silicon nitride self-supporting film (4) with a suspended structure, and subjecting the deposited palladium film to a selenization reaction to obtain a palladium diselenide polycrystalline film (3); Step 4: On one side of the suspended silicon nitride self-supporting film (4), a patterned metal electrode (2) is deposited using a standard semiconductor process and connected to the palladium diselenide polycrystalline film (3); Step 5: Encapsulate the palladium diselenide polycrystalline film (3) using standard semiconductor technology and packaging materials (1).

8. The method for preparing a high-sensitivity MEMS differential pressure sensor according to claim 7, wherein: The preparation method of the palladium diselenide polycrystalline thin film (3) in step 3 is as follows: Step 4-1: depositing a palladium film on one side of the silicon nitride self-supporting film (4) with a suspended structure; Step 4-2: Place the substrate with the palladium film deposited thereon and a sufficient amount of high-purity selenium powder into a tubular heating furnace, and heat and selenize the palladium film by chemical vapor deposition to obtain a palladium diselenide polycrystalline thin film (3); the heating temperature is 150-400°C.

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