Method for processing a MEMS fused quartz resonator sensor

Abstract

The application discloses a processing method of a MEMS fused quartz resonant sensor, and comprises the following steps: fused quartz wafer cleaning, circularly polarized femtosecond Bessel laser-induced processing, wet etching, high-temperature flame spraying, high-temperature precision annealing, magnetron sputtering deposition of a chromium layer and a gold layer, negative photoresist spraying, negative photoresist mask electrode layer, photoresist development, gold layer and chromium layer etching patterning, cleaning and removing surface residual photoresist, activating the wafer surface by using a low-concentration alkaline solution, pretreating a quartz base, using high-temperature glue to bond the base and a lower magnetic cap, activating the base surface, aligning and adhering the base and a sensor wafer and performing vacuum static pressing, vacuum high-temperature hydrogen atmosphere annealing, and assembling a magnetic core and an upper magnetic cap. The processing method can effectively reduce the surface roughness of the resonator after processing, reduce thermal elastic damping and stress unevenness, and finally improve the quality factor of the sensor.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical sensor technology, and relates to a method for fabricating a MEMS fused silica resonant sensor, specifically a method for fabricating an electromagnetically driven, high-quality MEMS fused silica resonant sensor. Background Technology

[0002] Sensors based on microelectromechanical systems (MEMS) technology are characterized by their small size, low power consumption, long lifespan, mass production capability, and low cost. Among them, resonant sensors, as a type of sensor, are widely used for measuring various physical parameters, including temperature, pressure, stress, angular velocity, and acceleration, and have extremely broad market prospects.

[0003] The quality factor is the most important parameter of a resonator, reflecting its damping ratio and energy dissipation during vibration. It is the ratio of the total energy of the resonator to the dissipated energy in each vibration cycle, and can intuitively represent the mechanical amplification factor and the sensitivity of the sensor. The higher the quality factor, the lower the mechanical and thermal noise of the resonator, the higher the sensitivity of the sensor to the measured parameter, and the faster the response speed.

[0004] Currently, most planar resonators are fabricated using silicon-based materials. However, silicon-based materials suffer from thermoelastic damping, reaching a performance bottleneck that hinders significant improvements in sensor performance. Fused silica, with its low coefficient of thermal expansion, is an ideal material for fabricating high-Q gyroscopes. For example, hemispherical resonator gyroscopes and tuning forks in three-dimensional shell resonators are made using fused silica, achieving quality factors in the tens of millions. Compared to the need for separate fabrication of high-quality three-dimensional shell resonators, two-dimensional planar fabrication based on MEMS technology offers a cost advantage, enabling mass production and providing significant advantages in terms of size and cost.

[0005] Since fused silica is non-conductive, electrodes need to be metallized on its surface to achieve driving and signal detection via electrostatic, electromagnetic, or piezoelectric methods. Electrostatic driving force is significantly affected by the electrode spacing, requiring strict control over processing and assembly errors. A large electrode spacing results in insufficient electrostatic force, while a small spacing makes the sensor susceptible to electrostatic nonlinearity, affecting sensor performance. Piezoelectric driving requires depositing piezoelectric material on the sensor surface and patterning it through etching. This method is costly, has high thermoelastic damping, and struggles to achieve a high quality factor. Electromagnetic driving, on the other hand, is simple to manufacture and has high precision tolerance, making it the most ideal signal driving and detection method. Currently, there are patent reports on the fabrication methods of fused silica resonators, and related research reports have achieved relatively high quality factors (typically between 100,000 and 400,000). However, it still has certain drawbacks. For example, the method involves first creating a metal film layer in the sensor structure and then protecting it with inert adhesive before releasing the structure. This method cannot perform high-temperature annealing heat treatment at around 1100℃, as the metal film layer will be damaged and detached at high temperatures. To further improve the quality factor of fused silica resonators, breakthroughs are needed in both sensor structure and metal film layer to further reduce thermoelastic damping loss and surface loss. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for fabricating MEMS fused silica resonant sensors that can significantly improve the quality factor of sensors.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0008] A method for fabricating a MEMS fused silica resonant sensor includes the following steps:

[0009] (1) Clean the fused silica wafer to remove surface contaminants;

[0010] (2) A circularly polarized femtosecond Bessel laser is used to induce drilling along the desired processing trajectory on the surface of a fused silica wafer to process the structure to be released.

[0011] (3) The fused quartz obtained in step (2) is subjected to wet etching to release the borehole closure area and retain the required sensor structure;

[0012] (4) Polish the surface and sidewalls of the sensor structure by high-temperature flame burning;

[0013] (5) Perform high-temperature precision annealing;

[0014] (6) A chromium layer and a gold layer are deposited sequentially on the surface of the structure by magnetron sputtering;

[0015] (7) Spray negative photoresist onto the metal-plated surface;

[0016] (8) Negative photoresist overlay electrode layer;

[0017] (9) Photoresist development;

[0018] (10) Patterning of gold and chromium layer etching;

[0019] (11) Clean and remove residual photoresist from the surface;

[0020] (12) The sensor wafer surface was activated using an alkaline solution;

[0021] (13) The quartz base was pre-treated by corrosion with hydrofluoric acid solution or potassium hydroxide solution and then cleaned.

[0022] (14) Use high-temperature adhesive to bond the quartz base to the lower magnetic cap;

[0023] (15) The surface of the quartz base is activated by immersion in an alkaline solution;

[0024] (16) Align and bond the quartz base with the sensor wafer, and then apply vacuum static pressure;

[0025] (17) Annealing in a vacuum high-temperature hydrogen atmosphere;

[0026] (18) Assemble the magnetic core and the upper magnetic cap.

[0027] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (4), the flame type used for high-temperature flame burning is a mixture of propane and oxygen, the flow rate of propane is 1.2L / min to 3L / min, the flow rate of oxygen is 1L / min to 8L / min, and the temperature of the high-temperature flame is 1300℃ to 1700℃.

[0028] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (5), the high-temperature precision annealing process is as follows: the temperature is raised to 1000℃~1150℃ at a rate of 500℃ / min~800℃ / min, held at the temperature for 6h~12h, then lowered to 800℃ at a rate of 1℃ / min~3℃ / min and held at the temperature for 1h~6h, and finally cooled with the furnace.

[0029] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (2), the process conditions for circularly polarized femtosecond Bessel laser-induced processing are: laser wavelength of 800nm, pulse width of 200fs~6000fs, single pulse energy of 40μj~250μj, and pulse drilling spacing of 1μm~7μm.

[0030] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (3), the wet etching uses a 5% to 30% mass fraction hydrofluoric acid solution or an 8 mol / L to 10 mol / L potassium hydroxide solution, heated in a water bath at 20°C to 80°C and subjected to ultrasonic oscillation, with an ultrasonic power of 0 to 800W for ultrasonic wet etching.

[0031] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (6), the thickness of the chromium layer is 5nm to 30nm and the thickness of the gold layer is 50nm to 500nm; in step (7), the coating thickness of the negative photoresist is 3μm to 15μm.

[0032] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (11), piranha solution or acetone is used to clean and remove residual photoresist on the surface.

[0033] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (12), the alkaline solution is an ammonia solution, a TMAH (tetramethylaminohydroxide) solution, a KOH solution, or a NaOH solution, the alkaline solution is a low-concentration alkaline solution, and the mass fraction of the alkaline solution is 1% to 12%.

[0034] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (15), the alkaline solution is an ammonia solution, a TMAH (tetramethylaminohydroxide) solution, a KOH solution, or a NaOH solution, the alkaline solution is a low-concentration alkaline solution, and the mass fraction of the alkaline solution is 1% to 12%.

[0035] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (13), the temperature of the etching pretreatment is 70℃~90℃ and the time of the etching pretreatment is 30min~50min.

[0036] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (14), the high-temperature adhesive must meet the following requirements: temperature resistance ≥240℃.

[0037] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (16), the vacuum degree of the vacuum static pressure is 0.1 Pa to 20000 Pa, and the vacuum static pressure time is 8 h to 24 h.

[0038] In the above-mentioned processing method of MEMS fused silica resonant sensor, preferably, in step (17), the conditions for vacuum high-temperature hydrogen atmosphere annealing are as follows: the annealing atmosphere is a mixture of H2 and Ar or a mixture of H2 and N2, the H2 flow rate is 5 sccm to 10 sccm, the Ar or N2 flow rate is 90 sccm to 95 sccm, the annealing temperature is 250℃ to 400℃, the annealing pressure is 1000 Pa to 15000 Pa, and the annealing time is 2 h to 6 h.

[0039] Compared with the prior art, the advantages of the present invention are as follows:

[0040] This invention provides a method for fabricating a MEMS fused silica resonant sensor. This method is a fabrication method for electromagnetically driven, high-quality MEMS fused silica resonators. It is compatible with post-processing of the fused silica structure and metal electrode post-processing, further improving the sensor's quality factor. Compared to existing reported fabrication methods (e.g., first fabricating a metal film layer on the sensor structure and then protecting it with inert adhesive before releasing the structure, which cannot perform high-temperature annealing heat treatment at around 1100°C because the metal film layer will be damaged and detached at high temperatures), the method of this invention can achieve high-temperature annealing of the structure, high-temperature flame polishing, and annealing of the metal film layer, effectively improving the quality factor of the fused silica sensor. Its core features include using flame polishing technology to reduce surface roughness, using high-temperature precision annealing and direct bonding to reduce stress inhomogeneity, using coating spraying photolithography to overlay high-precision metal electrodes on the fused silica structure surface, and using vacuum hydrogen atmosphere annealing to densify the metal film layer, reducing thermoelastic damping and resistivity. The method of this invention can effectively reduce the surface roughness of the resonator after processing (from 0.6 μm to about 3 nm), reduce thermoelastic damping and stress non-uniformity, and ultimately improve the quality factor of the sensor (above 1.2 million). Attached Figure Description

[0041] Figure 1 This is a process flow diagram of the fabrication method of the MEMS fused silica resonant sensor in Embodiment 1 of the present invention. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0043] Example 1

[0044] A method for fabricating a MEMS fused silica resonant sensor according to the present invention, such as... Figure 1 As shown, it includes the following steps:

[0045] (1) The fused silica wafer 101 with a thickness of 500μm was cleaned using the standard cleaning process;

[0046] (2) A circularly polarized femtosecond Bessel laser is used to drill holes along the desired processing trajectory on the surface of fused silica 101 to create the structure to be released 102. The pulse width of the circularly polarized femtosecond laser used in this invention is adjustable from 200 fs to 6000 fs, and the single pulse energy is adjustable from 40 to 250 μJ. After drilling, cracks will be generated due to volume expansion. The cracks will connect two adjacent through holes, which will facilitate the solution to penetrate into the interior of the structure and release the desired structure. When the femtosecond laser acts on the interior of the material, it will cause the fused silica to vaporize instantaneously and remelt and deposit at the edge of the micropores, creating a hot-melt zone. Considering the uniformity of drilling and cracking, and to reduce the area of ​​the hot-melt zone, circularly polarized light is used in this embodiment, with a laser wavelength of 800 nm, a femtosecond laser pulse width of 800 fs, a single pulse energy of 180 μJ, and a pulse drilling spacing of 2 μm.

[0047] (3) Wet etching is used to etch the fused silica wafer processed in step (2), releasing the drilled hole closure region 103 and leaving the required sensor structure. Hydrofluoric acid or potassium hydroxide solution can be used to etch the drilled sample. Due to the corrosion of the solution, the micropores and cracks will widen. Depending on the thickness of the processed sample, the widening will result in different sizes, and the closed area formed by the pores and cracks will detach from the wafer. In this embodiment, a 25% mass fraction hydrofluoric acid solution is added for water bath heating and ultrasonic oscillation to release the resonator structure. To improve the corrosion rate and uniformity, the corrosion temperature is 80℃ and the ultrasonic power is 800W. According to the experimental results, for a 500μm thick fused silica wafer material, when the micropore and crack expansion width is 13μm, the drilled hole closure region will detach from the wafer after 4 minutes of etching, leaving the resonator structure.

[0048] (4) High-temperature flame polishing is used to polish the surface and sensor sidewalls. High-temperature flame treatment produces several excellent effects: firstly, it improves surface quality; secondly, it strengthens the structure, giving the fused silica higher mechanical strength; and thirdly, it remelts residual defects after corrosion, solving the resonance error and instability caused by micro-cracks and edge chipping. The temperature of the high-temperature flame needs to be close to the melting point of the fused silica to remelt the surface of the fused silica resonator. In this embodiment, the temperature of the high-temperature flame is 1600°C, which changes the sidewall 111 of the resonator from a corroded water ripple shape to a planar state, reducing the surface roughness from several micrometers to the sub-nanometer level. Flame types that can be used for flame polishing include oxyhydrogen flames, propane flames, or methane flames. In this embodiment, a mixture of propane and oxygen is used to achieve flame polishing. To solve the structural deformation caused by flame impact, this embodiment uses a low-flow-rate flame, with a propane flow rate of 1.2 L / min and an oxygen flow rate of 8 L / min.

[0049] (5) High-temperature precision annealing is used to reduce stress after flame polishing. Fused silica is an amorphous material with an amorphous structure. The annealing temperature must be lower than or equal to the phase transition temperature of 1150°C. Otherwise, the material will transform into a crystalline structure. When the temperature drops to 300°C, the crystalline structure will generate a cristobalite phase, leading to volume expansion and ultimately causing the fused silica to shatter or produce a large number of cracks on the surface of the structure. Fused silica glass has a very small coefficient of thermal expansion and has high resistance to rapid cooling and heating. However, excessively high cooling rates will generate residual stress inside the structure. To ensure temperature uniformity during annealing, strict requirements are placed on the cooling rate. In this embodiment, the annealing process for a 500μm thick four-inch wafer is as follows: the temperature is increased from room temperature to 1150°C at a rate of 500°C / min, held at that temperature for 8 hours, then decreased to 800°C at a rate of 2°C / min and held for 1 hour. Finally, it is cooled to room temperature (usually 25°C) in the furnace.

[0050] (6) A chromium and gold layer is deposited on the surface of the structure using magnetron sputtering. There are four ways to deposit the film on the surface: The first is to protect and deposit the film on the surface of the structure using a mechanical mask, which can directly create patterned electrodes on the surface of a microstructure. However, this method is only suitable for processing metal layers with large linewidths. If the linewidth is less than tens of micrometers, it is impossible to pattern high-quality metal electrodes on the surface of the structure. The second method is to deposit the film directly after the first or second step, and then use a photoresist spin coating and a mask to overlay the metal layer. In the third step of etching, other inert adhesives are used to protect the metal electrodes. However, this method cannot continue to the steps (4) and (5). The third method is to spray photoresist on the structure after the third step, then develop the required electrode layer by photolithography and magnetron sputter the metal layer on the surface. The first method involves removing residual photoresist by peeling off the metal layer from the photoresist surface, leaving the electrode layer. However, this method has two problems: first, residual metal film remains at the electrode edges; after photoresist etching and development, the interface exhibits trapezoidal sidewalls, and the metal film deposited on these sidewalls cannot be peeled off by acetone and piranha solution; second, the peeled metal film adheres to the patterned electrode surface, causing a short circuit. The fourth method, adopted in this invention, involves first depositing a film on the structural layer, then using photoresist spraying and photolithography to pattern the photoresist into the desired electrode structure. Next, the metal electrode layer is patterned under the protection of the photoresist. The advantage of this method is that the resonator can be flame-polished and annealed at high temperature before deposition, avoiding the electrode edge residue and short circuit problems encountered in the third method. The metal electrodes are used for electromagnetic drive and detection; high resistance can easily cause electrode heating, affecting the resonator frequency. To reduce the resistance of the metal electrodes, in this embodiment, the sputtered chromium layer thickness is 10 nm, and the gold layer thickness is 500 nm.

[0051] (7) A negative photoresist is sprayed onto the metal-plated side using a spraying method. This method uses a spraying device to dilute the photoresist and then granulates it using ultrasonic atomization or air pressure atomization, and then coats it onto the surface of the wafer. As can be seen from the aforementioned steps, this invention limits the use of photoresist spraying to achieve the patterning of the metal electrode. In step (3), the wafer has already been etched through by wet etching, and there are a large number of through holes and microstructures on the wafer. The commonly used spin coating method cannot complete the coating protection. Secondly, this invention limits the use of negative photoresist, which can effectively remove the metal on the sidewalls in the subsequent metal etching steps. In step (5), the metal film layer is not only attached to the wafer surface 201, but also to the wafer sidewall 202. The metal film layer on the sidewall will significantly reduce the quality factor of the sensor. By using a spraying method, negative photoresist 211 will be attached to the wafer surface, and negative photoresist 212 will also be attached to the sidewall. It is worth noting that, due to edge effects, the photoresist sprayed on the structure is not uniformly distributed. The photoresist is thinner on the sidewalls of the resonator structure, and has a certain arc-shaped morphology at the edges. To achieve full coverage of the structure, this embodiment uses HTG910 photoresist with a spraying thickness of 12μm.

[0052] (8) Electrode Layer Overlay. In this step, after ultraviolet light passes through the through-holes in the mask, the negative photoresist 221, which has the same shape as the electrode layer, undergoes a property change when irradiated by ultraviolet light. It will not be corroded in the developer, while the surface areas 222 and sidewalls 223 that are not irradiated by ultraviolet light remain unchanged and are corroded in the developer to expose the metal plating. The photolithography in this step can be performed using mask overlay or laser direct writing lithography to process a metal electrode protective layer with a linewidth of several micrometers. The former has high processing efficiency, while the latter has the highest processing precision. In this embodiment, mask overlay is used to modify the photoresist, and the ultraviolet light dose is 320mJ to process a metal electrode protective layer with a linewidth of 10 micrometers.

[0053] (9) Photoresist Development. In this step, the photoresist on the surface of metal electrode 231 is retained, while the photoresist 222 and 223 on surfaces 241 and 242, which are not exposed to ultraviolet light, are etched by the solution. In this embodiment, the developing solution used is TMAH solution, and the developing time is 1.5 min.

[0054] (10) Metal etching patterning. First, the wafer is immersed in a gold etching solution to remove the gold layer on the surface where there is no photoresist protection. Then, the wafer is immersed in a chromium etching solution to remove the chromium metal in the unprotected areas. At this point, both metal layers 241 and 242 are completely etched away, leaving photoresist 221 and the metal electrode 231 it protects. In this embodiment, the immersion time in the gold etching solution is 4 min (25°C), and the immersion time in the chromium etching solution is 30 s. No metal residue was found in the metal layer 241 area by surface energy dispersive spectroscopy analysis.

[0055] (11) Cleaning with piranha solution or acetone to remove residual photoresist from the surface. This step removes residual photoresist 221 from the surface of the metal electrode. In this embodiment, piranha solution was used to remove the residual photoresist from the surface.

[0056] (12) The wafer surface was activated using a low-concentration alkaline solution. This step was to generate a large number of suspended hydroxyl groups on the bonding surface 311 of the fused silica wafer. The low-concentration alkaline activation solution could be an ammonia solution, TMAH (tetramethylaminohydroxide) solution, KOH solution, or NaOH solution, with a mass fraction between 1% and 12%. In this embodiment, a 5% ammonia solution was used as the bonding activation solution, and the immersion activation time was 1.5 min. Experimental results showed good bonding with the substrate, with a bonding strength higher than 34 MPa.

[0057] (13) The fused silica base to be used is etched with hydrofluoric acid or potassium hydroxide and then cleaned according to standard procedures. In this embodiment, the quartz base 411 is machined by mechanical grinding and is square in shape with a groove 412 in the middle for assembling the magnetic core. The edge bonding surface 413 is bonded to the sensor bonding surface 311. Mechanical grinding will generate a large number of micron-level defects at the grinding interface. According to the glass strength theory, when defects are present, the fracture energy of quartz glass decreases sharply, and the quartz glass is prone to fracture along the defect crack under the induction of external force. Therefore, in this embodiment, the quartz base is pretreated with a 20% mass fraction hydrofluoric acid solution for 30 minutes at a temperature of 70°C. This process effectively reduces the micro-crack defects in the fused silica base.

[0058] (14) The base and the lower magnetic cap are bonded using high-temperature adhesive. High-temperature adhesive 421 is evenly spin-coated into the groove 412 of the base, and then the matching lower magnetic cap 511 is inserted into the groove and hot-pressed and kept at a constant temperature to solidify the high-temperature adhesive. It is particularly noteworthy that this step has high requirements for the performance of the adhesive, which must withstand a high temperature of 240°C and preferably has a low Young's modulus. In the subsequent high-temperature annealing step, on the one hand, the high-temperature adhesive needs to withstand the annealing temperature, and on the other hand, the magnetic core 511 has a high coefficient of thermal expansion, while the quartz base has a low coefficient of thermal expansion. The high-temperature adhesive is used to bond the two together, and a low Young's modulus is required to avoid excessive thermal stress at high temperatures that could cause the base to crack. The base pretreatment in step (13) is to avoid base cracking caused by excessive stress under high temperature conditions. In this embodiment, triple bond 3732 high-temperature adhesive is used to bond the base and the magnet, and it is cured at 100°C for half an hour. No base cracking occurred in the subsequent high-temperature annealing process.

[0059] (15) Immerse the substrate in a low-concentration alkaline solution to activate the bonding surface. This step is the same as step (12), using the same process to generate a large number of suspended hydroxyl functional groups on the bonding surface 601 of the quartz substrate.

[0060] (16) Align and bond the substrate with the sensor wafer, and then perform vacuum static pressing. This step causes the hydroxyl functional groups on the bonding interface 701 to undergo dehydration polymerization, generating silicon-oxygen bonds to form a permanent bond, achieving a high-strength bond between the wafer and the substrate. After the hydroxyl groups dehydrate, a water molecule will be generated at the bonding interface. At the same time, a large number of water molecules remain at the bonding interface in the bonding activation solution, which need to be removed. In this embodiment, a bonding device was used to achieve high-precision alignment between the wafer and the substrate, and the structure was cold-pressed. The cold-pressing vacuum degree was 20000 Pa, and the cold-pressing time was 24 hours. This step can effectively remove the residual water molecules at the interface, achieving pre-bonding between the wafer and the sample.

[0061] (17) The strength is improved and the film layer is densified by vacuum high-temperature hydrogen atmosphere annealing; after pre-bonding, high-temperature treatment is required to make the bonding interface stronger. Numerous studies have reported that annealing of metal electrodes can effectively improve the quality factor of the resonator. However, the resistance of the metal film layer increases threefold when annealed in a high vacuum environment. Electron spectrometry analysis shows that the increased resistance is due to the migration of chromium metal to the electrode surface during annealing, reacting with residual oxygen molecules to form chromium oxide, leading to an increase in the resistivity of the metal electrode and a decrease in the adhesion between the metal electrode and the wafer. To solve these problems, this embodiment uses high-temperature reducing hydrogen atmosphere annealing. The sensor is annealed in a gas atmosphere of 10 sccm H2 and 90 sccm Ar, with an annealing vacuum of 10000 Pa, an annealing temperature of 350℃, and an annealing time of 4 hours. Through this process, the bonding strength reaches 34 MPa, and the metal electrode resistance decreases by 32%-38% compared to before annealing.

[0062] (18) Assemble the magnetic core 801 and the upper magnetic cap 512; the last step is to install the magnetic core and the upper magnetic cap to complete the sensor manufacturing process, and the sensor quality factor reaches 1.21 million.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A method for fabricating a MEMS fused silica resonant sensor, characterized in that, Includes the following steps: (1) Clean the fused silica wafer to remove surface contaminants; (2) A circularly polarized femtosecond Bessel laser is used to induce drilling along the desired processing trajectory on the surface of a fused silica wafer to process the structure to be released. (3) The fused quartz obtained in step (2) is subjected to wet etching to release the borehole closure area and retain the required sensor structure; (4) Polish the surface and sidewalls of the sensor structure by high-temperature flame burning; (5) Perform high-temperature precision annealing; (6) A chromium layer and a gold layer are deposited sequentially on the surface of the structure by magnetron sputtering; (7) Spray negative photoresist onto the metal-plated surface; (8) Negative photoresist overlay electrode layer; (9) Photoresist development; (10) Patterning of gold and chromium layer etching; (11) Clean and remove residual photoresist from the surface; (12) The sensor wafer surface was activated using an alkaline solution; (13) The quartz base was pre-treated by corrosion with hydrofluoric acid solution or potassium hydroxide solution and then cleaned. (14) Use high-temperature adhesive to bond the quartz base to the lower magnetic cap; (15) The surface of the quartz base is activated by immersion in an alkaline solution; (16) Align and bond the quartz base with the sensor wafer, and then apply vacuum static pressure; (17) Annealing in a vacuum high-temperature hydrogen atmosphere; (18) Assemble the magnetic core and the upper magnetic cap.

2. The fabrication method of the MEMS fused silica resonant sensor according to claim 1, characterized in that, In step (4), the flame type used for high-temperature flame combustion is a mixture of propane and oxygen, the flow rate of propane is 1.2L / min to 3L / min, the flow rate of oxygen is 1L / min to 8L / min, and the temperature of the high-temperature flame is 1300℃ to 1700℃.

3. The fabrication method of the MEMS fused silica resonant sensor according to claim 1, characterized in that, In step (5), the high-temperature precision annealing process is as follows: the temperature is raised to 1000℃ to 1150℃ at a rate of 500℃ / min to 800℃ / min, held at the temperature for 6h to 12h, then lowered to 800℃ at a rate of 1℃ / min to 3℃ / min and held for 1h to 6h, and finally cooled with the furnace.

4. The fabrication method of the MEMS fused silica resonant sensor according to claim 1, characterized in that, In step (2), the process conditions for circularly polarized femtosecond Bessel laser-induced laser are: laser wavelength of 800nm, pulse width of 200fs~6000fs, single pulse energy of 40μj~250μj, and pulse hole spacing of 1μm~7μm.

5. The fabrication method of the MEMS fused silica resonant sensor according to any one of claims 1 to 3, characterized in that, In step (3), the wet corrosion is carried out using a 5% to 30% hydrofluoric acid solution or an 8 mol / L to 10 mol / L potassium hydroxide solution, heated in a water bath at 20°C to 80°C and subjected to ultrasonic oscillation with an ultrasonic power of 0 to 800W.

6. The fabrication method of the MEMS fused silica resonant sensor according to any one of claims 1 to 3, characterized in that, In step (6), the thickness of the chromium layer is 5nm to 30nm, and the thickness of the gold layer is 50nm to 500nm; in step (7), the coating thickness of the negative photoresist is 3μm to 15μm.

7. The fabrication method of the MEMS fused silica resonant sensor according to any one of claims 1 to 3, characterized in that, In step (11), piranha solution or acetone is used to clean and remove residual photoresist from the surface.

8. The fabrication method of the MEMS fused silica resonant sensor according to any one of claims 1 to 3, characterized in that, In step (12), the alkaline solution is an ammonia solution, a TMAH solution, a KOH solution, or a NaOH solution, and the alkaline solution is a low-concentration alkaline solution with a mass fraction of 1% to 12%. In step (15), the alkaline solution is an ammonia solution, a TMAH solution, a KOH solution, or a NaOH solution, and the alkaline solution is a low-concentration alkaline solution with a mass fraction of 1% to 12%.

9. The fabrication method of the MEMS fused silica resonant sensor according to any one of claims 1 to 3, characterized in that, In step (13), the temperature of the corrosion pretreatment is 70℃~90℃, and the time of the corrosion pretreatment is 30min~50min; In step (14), the high-temperature adhesive must meet the following requirements: temperature resistance ≥240℃.

10. The fabrication method of the MEMS fused silica resonant sensor according to any one of claims 1 to 3, characterized in that, In step (16), the vacuum degree of the vacuum static pressure is 0.1 Pa to 20000 Pa, and the vacuum static pressure time is 8 h to 24 h; In step (17), the conditions for vacuum high-temperature hydrogen atmosphere annealing are as follows: the annealing atmosphere is a mixture of H2 and Ar or a mixture of H2 and N2, the H2 flow rate is 5 sccm to 10 sccm, the Ar or N2 flow rate is 90 sccm to 95 sccm, the annealing temperature is 250℃ to 400℃, the annealing pressure is 1000 Pa to 15000 Pa, and the annealing time is 2 h to 6 h.

Images