Direct bonding MEMS all-SiC comb tooth capacitive acceleration sensor and preparation method thereof

Abstract

The invention belongs to the technical field of acceleration sensors, and discloses a direct bonding MEMS all-SiC comb tooth capacitive acceleration sensor and a preparation method thereof. A groove is formed in the surface of a SiC substrate wafer by using an MEMS body SiC processing technology, the SiC substrate wafer and a thinned chip wafer are subjected to high-strength bonding through a SiC direct bonding technology so as to construct a cavity, processing of a chip wafer mass block, comb teeth, a supporting beam and other suspension structures is realized through an MEMS technology, top packaging is carried out on the sensor through a bonding technology, and the sensor is subjected to high-strength packaging. And a high-performance complete structure of the capacitive comb-tooth type sensor is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of acceleration sensors, and in particular to a direct-bonded MEMS all-SiC comb-teeth capacitive acceleration sensor and a preparation method thereof. Background Art

[0002] Micro-electro-mechanical system (MEMS) sensors are miniature devices that integrate mechanical and electronic components, converting physical signals into electrical signals. Due to their advantages such as miniaturization, low cost, low energy consumption, and integration, MEMS sensors offer more efficient and cost-effective solutions than other sensor types. Consequently, they have become the mainstream testing technology of choice in consumer electronics and industrial applications. However, despite their numerous advantages, MEMS sensors also have limitations. Currently, MEMS sensors are primarily manufactured using silicon, a material whose performance is significantly affected by high temperatures. First, at high temperatures, silicon's semiconductor properties deteriorate, leading to degradation of electrical performance and reduced sensing accuracy. Second, high temperatures can cause structural degradation of silicon, affecting its mechanical stability and long-term reliability. These issues limit the application of silicon-based sensors in certain high-temperature industrial applications, such as automotive and aircraft engine monitoring systems. To overcome these limitations, researchers are turning to SiC, a third-generation semiconductor material that is resistant to high temperatures and can withstand even harsher conditions, to manufacture MEMS sensors. SiC boasts excellent thermal and physicochemical stability, high mechanical hardness, and strong wear resistance, capable of maintaining stable basic performance in environments up to several thousand degrees Celsius. Furthermore, SiC processing methods similar to those used for silicon have been developed, promising mass-produced, low-cost wafer-level manufacturing, making it an ideal semiconductor material for high-temperature applications. By using SiC, MEMS sensors can be designed for a wider range of scenarios, including harsh environments where traditional silicon-based sensors are unable to withstand.

[0003] Based on existing research, most current MEMS all-SiC accelerometers are based on the piezoresistive principle. This involves fabricating SiC wafers using a MEMS bulk SiC process to form a proof-mass-support beam-fixed anchor structure. One end of the support beam is connected to the fixed anchor, i.e., the fixed end of the chip, and the other end is connected to the suspended proof-mass, the primary sensing element. When the proof-mass is subjected to acceleration, the inertial force causes it to move, which in turn causes the support beam to bend. This leads to a change in the resistivity of SiC piezoresistors located in sensitive areas, such as the beam root. This resistance change is detected using a Wheatstone bridge structure, generating an electrical signal. This signal is proportional to the applied inertial force, allowing accurate inference of the acceleration acting on the proof-mass. Although SiC piezoresistive accelerometers can operate in certain high-temperature environments, the limitations of the piezoresistive material and the electrical isolation method result in relatively low sensor output sensitivity, resulting in a weak output voltage signal that is difficult to capture. Furthermore, the piezoresistive material exhibits significant temperature drift at high temperatures, leading to significant temperature effects and poor overall performance.

[0004] Compared to piezoresistive sensors, sensors based on capacitive detection generally offer higher sensitivity and linearity, are immune to factors like electron leakage, and possess inherent advantages in temperature effects, resulting in lower temperature impact and improved reliability in high-temperature environments. These sensors are an ideal choice for high-temperature SiC accelerometers. Currently, capacitive comb-tooth accelerometers on the market primarily utilize silicon materials and most employ a mass-support beam-fixed anchor structure. Unlike piezoresistive sensors, these sensors incorporate comb-tooth structures on the mass and anchor. When subjected to inertial forces, the mass displaces the teeth, causing a change in the spacing between the teeth and, consequently, capacitance, which is then converted and read using a bridge. However, a SiC-based MEMS capacitive comb-tooth accelerometer solution is currently unavailable. This is primarily due to two factors: Firstly, SiC material is extremely hard, making it difficult to fabricate such fine structures using simple etching methods in traditional MEMS processes. Secondly, forming a single layer of highly conductive thick film on a SiC wafer is challenging, requiring direct wafer bonding. Generally speaking, the main difficulty limiting the application of all-SiC materials in capacitor comb-tooth structures is the processing technology.

[0005] The current SiC accelerometer adopts the piezoresistive effect scheme that basically uses SiC piezoresistive material. Although SiC has excellent high-temperature characteristics, it can realize signal detection in high-temperature environments and has strong process compatibility. However, due to the shortcomings of the piezoresistive principle itself, the sensor output signal is weak, the sensitivity is low, the temperature effect is obvious, and the performance is difficult to meet the application of certain high-precision occasions such as aerospace. Therefore, a scheme of processing capacitive comb-tooth accelerometers using SiC materials has been proposed. However, for now, due to the high hardness of SiC, it is difficult to process fine and suspended structures such as comb teeth. Therefore, the following scheme is mainly adopted: first, a sacrificial layer is deposited on the surface of the substrate, which is often made of silicon or silicon oxide. The material is deposited and patterned, and then a layer of SiC is deposited on the surface of the sacrificial layer. It is processed by femtosecond laser etching to etch a top comb-like pattern, and finally the sacrificial layer is removed to release the suspended comb-tooth structure. However, the deposited SiC layer has differences in thickness and uniformity, which makes it difficult to achieve high-precision control of structural parameters, affecting the sensor performance. In addition, during the removal of the sacrificial layer, large stress will be generated, and the fine comb-tooth structure is very fragile and easily broken. The slice rate and process reliability are low, the processing difficulty is high, and the consistency of devices prepared in batches is difficult to control. The complexity and cost of the deposition technology are also higher than those of traditional silicon-based material processing, which is not conducive to production. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides a direct-bonded MEMS all-SiC comb-tooth capacitive accelerometer and its preparation method to solve the problems in the prior art. To achieve the above technical objectives, the technical solution adopted by the present invention is:

[0007] A direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor, comprising: a substrate layer 1, a chip layer 4, and a cover layer 5;

[0008] The chip layer 4 is arranged between the substrate layer 1 and the cover layer 5;

[0009] The chip layer 4 includes a first fixed anchor point 2, a second fixed anchor point 7, and a sensitive mass block 8. The substrate layer 1 is provided with a substrate layer groove 3 for accommodating the sensitive mass block 8. The sensitive mass block 8 can move laterally within the substrate layer groove 3. Two first fixed anchor points 2 are provided on both sides of the sensitive mass block 8, and two second fixed anchor points 7 are provided on the other two sides of the sensitive mass block 8. The two first fixed anchor points 2 are located in the lateral movement direction of the sensitive mass block 8.

[0010] A comb tooth structure is provided between both sides of the sensitive mass block 8 and the two first fixed anchor points 2. The comb tooth structure includes movable comb teeth 10 and fixed comb teeth 11. The movable comb teeth 10 are fixedly connected to the sensitive mass block 8, and the fixed comb teeth 11 are fixedly connected to the first fixed anchor points 2. The movable comb teeth 10 and the fixed comb teeth 11 are staggered to form capacitor plates.

[0011] By applying different potentials to the electrodes on the two first fixed anchor points 2, when the sensitive mass block 8 moves laterally, the capacitance of the capacitor plate changes, thereby changing the potential on the two second fixed anchor points 7, and detecting the acceleration signal through the changed potential.

[0012] Furthermore, the chip layer 4 further includes an elastic support beam 9 , which is disposed between the second fixed anchor point 7 and the sensitive mass block 8 .

[0013] Furthermore, a chip electrode 12 is provided on the first fixed anchor point 2, and the chip electrode 12 is conductively connected to the fixed comb teeth 11; the cover layer 5 is provided with a current-leading through hole 6 corresponding to the position of the chip electrode 12 to realize the function of leading out the circuit.

[0014] Furthermore, a shallow cover layer groove 13 and a deep cover layer groove 14 are provided at the bottom of the cover layer 5. The shallow cover layer groove 13 is used to accommodate the second fixed anchor point 7 and the first fixed anchor point 2, and the deep cover layer groove 14 is used to accommodate the sensitive mass block 8 and the comb structure.

[0015] A method for preparing a direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor, applied to the direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor, comprises the following steps:

[0016] Step 1, preparation of substrate layer 1:

[0017] Step 1.1: Prepare the required HPSI type 4H-SiC wafer for cleaning;

[0018] Step 1.2: Prepare a Ni metal mask and perform photolithography: A Ni metal mask is used as the mask material. A seed layer is deposited on the wafer surface using magnetron sputtering, followed by electroplating. A five-point film thickness test is used to ensure that the uniformity of the Ni mask is within 3%. Photoresist is spin-coated, and the Ni metal is wet-etched to pattern it.

[0019] Step 2, preparation of cover layer 5:

[0020] Step 2.1: Prepare the required HPSI type 4H-SiC wafer for cleaning;

[0021] Step 2.2: Etching the shallow groove 13 of the cover layer: using Ni metal as a mask, spin-coating photoresist, and wet etching the Ni metal to pattern it;

[0022] Step 2.3: Etching the deep groove 14 of the cover layer: Use a Ni metal mask to perform ICP dry etching, and control the etching depth to be consistent with the thickness of the chip layer 4;

[0023] Step 2.4: Etching of the lead-through hole 6: Etching is performed using a femtosecond laser drilling method:

[0024] Step 3: Preparation and bonding of chip layer 4:

[0025] Step 3.1: Prepare the required highly doped 4H-SiC wafer and Si wafer for cleaning:

[0026] Step 3.2: Si wafer bonding: Use a bonding machine to activate the clean 4H-SiC wafer and Si wafer surfaces and bond them;

[0027] Step 3.3: Thin the bonded 4H-SiC wafer using a wafer thinning machine:

[0028] Step 3.4: Substrate 1 SiC bonding: Bond the thinned wafer to the previously prepared wafer, with the highly doped 4H-SiC wafer facing the grooved surface of the substrate 1 wafer. Direct bonding is performed after activation treatment.

[0029] Step 3.5: Si wafer removal: Prepare a high concentration of KOH solution and wet-etch the Si wafer from the surface of the 4H-SiC wafer. Clean the wafer after removal.

[0030] Step 3.6: Ohmic contact: Use the LiftOff process to prepare the electrode metal system, spin-coat the photoresist, and pattern it through exposure and development. Use magnetron sputtering to sputter the three layers of Ti / Ni / Au metal separately to ensure sufficient contact between the metal and the semiconductor. Then perform rapid high-temperature annealing to complete the ohmic contact preparation:

[0031] Step 3.7: Chip sensitive structure etching: Use Ni metal as a mask and use the ICP dry etching process to dry-etch the exposed area to etch out the sensitive mass block 8 and comb-tooth structure on the chip layer 4;

[0032] Step 3.8: Cover plate packaging and power lead: The prepared cover plate layer 5 wafer and the chip layer 4 wafer are directly bonded by SiC, with the grooved surface of the cover plate layer 5 facing the surface of the chip layer 4. After bonding, the power lead holes 6 are filled with conductive Ag paste and sintered at high temperature to realize circuit lead-out.

[0033] The present invention has the following beneficial effects: the present invention can realize the development of MEMS capacitive comb-tooth acceleration sensors based on bulk SiC technology, realize the effective extraction of acceleration signals in high-temperature environments, and achieve test conditions above 600°C through the application of SiC high-temperature resistant materials, making the performance of the sensor more stable in high-temperature environments. In addition, the present sensor adopts SiC direct bonding technology and bulk SiC technology to break through the difficult processing problem of the capacitive comb-tooth structure, and realizes the preparation of acceleration sensors based on the capacitive comb-tooth detection principle. Compared with other types of acceleration sensors, the sensitivity, linearity and other performance of the present sensor are further improved. Furthermore, by adopting a multi-layer bonding process of homogeneous SiC materials, the packaging and circuit lead-out of the sensor are realized, the process preparation steps are reduced, and the sensor packaging volume is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A three-dimensional schematic diagram of the sensor of the present invention;

[0035] Figure 2 is a three-dimensional schematic diagram of the cover layer;

[0036] Figure 3 This is a schematic diagram of the sensor after packaging;

[0037] Figure 4 Schematic diagram of a top view of a chip layer;

[0038] Figure 5 is a flow chart of the preparation process of the present invention;

[0039] Figure 6 Schematic diagram of the etching area of the substrate layer and the cover layer shallow groove, the shaded part in the figure is the etching area;

[0040] Figure 7 Schematic diagram of the etching area of the deep groove of the cover layer, where the shaded area is the etching area;

[0041] Figure 8 Schematic diagram of the etching area of the lead-in via hole, where the shaded area is the etching area;

[0042] Figure 9 Schematic diagram of the etching area of the sensitive structure of the chip layer, where the shaded area is the etching area;

[0043] In the figure: 1-substrate layer, 2-first fixed anchor point, 3-substrate layer groove, 4-chip layer, 5-cover layer, 6-electrical through hole, 7-second fixed anchor point, 8-sensitive mass block, 9-support beam, 10-movable comb teeth, 11-fixed comb teeth, 12-chip electrode, 13-cover layer shallow groove, 14-cover layer deep groove. DETAILED DESCRIPTION

[0044] The following is a combination of the embodiments of the present invention Figures 1-9 , the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0045] like Figure 1-Figure 4 , a direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor, comprising: a substrate layer 1, a chip layer 4 and a cover layer 5;

[0046] The chip layer 4 is arranged between the substrate layer 1 and the cover layer 5;

[0047] The chip layer 4 includes a first fixed anchor point 2, a second fixed anchor point 7, and a sensitive mass block 8. The substrate layer 1 is provided with a substrate layer groove 3 for accommodating the sensitive mass block 8. The sensitive mass block 8 can move laterally within the substrate layer groove 3. Two first fixed anchor points 2 are provided on both sides of the sensitive mass block 8, and two second fixed anchor points 7 are provided on the other two sides of the sensitive mass block 8. The two first fixed anchor points 2 are located in the lateral movement direction of the sensitive mass block 8.

[0048] A comb tooth structure is provided between both sides of the sensitive mass block 8 and the two first fixed anchor points 2. The comb tooth structure includes movable comb teeth 10 and fixed comb teeth 11. The movable comb teeth 10 are fixedly connected to the sensitive mass block 8, and the fixed comb teeth 11 are fixedly connected to the first fixed anchor points 2. The movable comb teeth 10 and the fixed comb teeth 11 are staggered to form capacitor plates.

[0049] By applying different potentials to the electrodes on the two first fixed anchor points 2, when the sensitive mass block 8 moves laterally, the capacitance of the capacitor plate changes, thereby changing the potential on the two second fixed anchor points 7, and detecting the acceleration signal through the changed potential.

[0050] Furthermore, the chip layer 4 further includes an elastic support beam 9 , which is disposed between the second fixed anchor point 7 and the sensitive mass block 8 .

[0051] Furthermore, a chip electrode 12 is provided on the first fixed anchor point 2, and the chip electrode 12 is conductively connected to the fixed comb teeth 11; the cover layer 5 is provided with a current-leading through hole 6 corresponding to the position of the chip electrode 12 to realize the function of leading out the circuit.

[0052] Furthermore, a shallow cover layer groove 13 and a deep cover layer groove 14 are provided at the bottom of the cover layer 5. The shallow cover layer groove 13 is used to accommodate the second fixed anchor point 7 and the first fixed anchor point 2, and the deep cover layer groove 14 is used to accommodate the sensitive mass block 8 and the comb structure.

[0053] The substrate layer 1 of the present invention serves as the fixed frame of the chip body, supporting the mass block-support beam-fixed anchor point structure of the acceleration sensor chip. A substrate layer groove 3 is machined on its upper surface through etching technology, thereby ensuring the movable structure of the sensor chip. Within the chip layer 4, the movable mass block 8 is arranged in the central area of the chip and connected to the second fixed anchor point 7 via two U-shaped support beams 9. To ensure that the support beams 9 have a certain degree of mobility, the shallow groove 13 in the cover layer needs to be slightly larger than the area of the support beams 9. At the same time, due to the influence of gravity, the mass block will sink to a certain extent, so the deep groove 14 in the cover layer needs to be maintained at a certain depth. Equally spaced fixed comb teeth 11 are arranged on both sides of the sensitive mass block 8, and equally spaced movable comb teeth are also arranged on the fixed anchor point 2. The two parts of the comb teeth are staggered to form a series of capacitor plates. The total capacitance of the sensor is the sum of these capacitor plates, and its capacitance varies with the change in the spacing between the plates. The surface of the fixed anchor point is arranged with a Ti / Ni / Au metal system. The metal contacts the SiC wafer, forming an ohmic contact between the two, which acts as an electrode to lead out the electrical signal. The different fixed anchor points are intermittent and independent, and are only fixed by a non-conductive bottom layer to ensure electrical isolation between the electrodes. At this time, it is only necessary to apply different potentials to the chip electrodes 12 on the first fixed anchor points 2 on both sides to form a certain potential difference. When the sensitive mass block 8 moves laterally, the capacitance of the chip capacitor plates changes, and the potential on the second fixed anchor point 7 will also change, thereby detecting the acceleration signal.

[0054] The sensor of the present invention uses the capacitive acceleration sensing principle. The sensor's bottom layer is a non-conductive SiC substrate layer 1. A substrate layer groove 3 is formed on its upper surface using SiC etching technology. The acceleration sensor's chip layer 4 is bonded using bonding technology. Etching further patterns the device layer, releasing the sensitive mass 8, support beam 9, movable comb teeth 10, and fixed comb teeth 11. The first fixed anchor point 2 and the second fixed anchor point 7 are also patterned. A U-shaped support beam 9 connects one end to the second fixed anchor point 7 and the other end to the sensitive mass 8. A constant voltage source is connected to the first fixed anchor points 2 on both sides, forming a series of capacitor plates between the comb teeth. Under the action of inertial force, the sensitive mass 8 translates, driving the movable comb teeth 10 to move, causing the distance between it and the fixed comb teeth 11 to change, thereby causing a change in capacitance. By detecting the change in the voltage value of the second fixed anchor point 7, the acceleration signal can be detected. This voltage value is proportional to the acceleration signal. The top layer is a non-conductive SiC cover layer 5. The bottom layer is patterned with shallow cover grooves 13 and deep cover grooves 14 based on the chip layer 4 to ensure mutual matching with the chip layer 4. The deep cover grooves 14 ensure the movement of the sensitive mass 8. The surface of the cover layer 5 is provided with electrical lead-through holes 6. Through vertical electrical interconnection technology, they contact the chip electrodes 12 on the sensor surface, enabling sensor chip packaging and electrical signal extraction, ultimately realizing a complete acceleration sensor.

[0055] The present invention is mainly based on the etching and bonding process in the bulk processing process, and simultaneously completes the metal layer processing and high-temperature annealing process. The preparation method includes: preparing wafers, including two 4H-SiC wafers (HPSI), an N-type 4H-SiC wafer (highly doped) and a Si wafer; cleaning, using NMP soaking, acetone soaking, ethanol rinsing, deionized water rinsing and other processes to complete the cleaning of the wafers to ensure the cleanliness of the material; etching and grooving the bottom layer, taking a 4H-SiC wafer (HPSI) and sputtering a Ni seed layer on its surface, and electroplating a Ni mask, while spin-coating photoresist, exposing and developing, and then patterning the metal Ni mask, etching grooves, that is, the substrate layer 1, for standby use; etching and grooving the cover plate, similarly Take another 4H-SiC wafer (HPSI) and repeat the Ni mask etching process several times to complete the etching of the lead-in hole 6, the cover layer shallow groove 13 and the cover layer deep groove 14, which is the cover layer 5 for standby use; for bottom layer bonding, take an N-type 4H-SiC wafer (highly doped) and a Si wafer, activate their surfaces, and perform direct bonding. Use a wafer thinning machine to thin and polish the bonded N-type 4H-SiC wafer (highly doped), and then bond this side to the SiC wafer of the substrate layer 1. Pay attention to aligning the cavity area, and then use potassium hydroxide solution to wet remove The surface of the Si wafer is prepared through the above steps to complete the preparation of the substrate layer 1 and the chip layer 4; Ohmic contact, this step requires the realization of ohmic contact between the metal and the surface semiconductor. The solution of the present invention adopts Ti / Ni / Au metal system to realize ohmic contact, and the preparation and patterning of the metal system are realized through the LiftOff process, and the ohmic contact is formed through a high-temperature rapid annealing process; the chip layer 4 is etched, and the upper surface of the chip layer 4 is again masked with Ni, sputtered and electroplated with Ni mask, spin-coated with photoresist, developed and exposed, and etched to release the sensitive mass block 8, support beam 9, and movable comb teeth 10 suspension structure. , complete the graphic design of the first fixed anchor point 2 and the second fixed anchor point 7; top bonding, take the SiC wafer of the cover layer 5, activate it and the surface of the chip layer 4, and directly bond the SiC to realize the packaging of the sensor; vertical electrical interconnection, open a lead-in through hole 6 on the surface of the cover layer 5, corresponding to the chip electrode 12 of the chip layer 4, use vertical electrical interconnection technology, use high-temperature silver paste sintering, fill the through hole, realize the electrical connection between the sensor chip and the outside world, and realize the packaging structure of the chip; scribing, the last step is to use a diamond cutting knife or laser scribing method to scribing to complete the chip separation. The above process steps can complete the overall preparation of the MEMS capacitive comb accelerometer.

[0056] like Figure 5-Figure 9 Specifically, the present invention also relates to a method for preparing a direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor, which is applied to the direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor, and includes the following steps:

[0057] Step 1, preparation of substrate layer 1:

[0058] Step 1.1: Prepare and clean the wafer. Prepare the required HPSI type 4H-SiC wafer and clean the wafer before starting the subsequent process.

[0059] Step 1.2: Prepare a metal Ni mask and perform photolithography. The mask material uses a Ni metal mask, and a seed layer is sputtered on the wafer surface by magnetron sputtering, and then prepared by electroplating. A 5-point film thickness test method is required to ensure that the uniformity of the Ni mask is within 3%. Spin-coat the photoresist, wet-etch the Ni metal, and pattern it. The etching pattern of this step is as follows Figure 6 As shown, the exposed area is subjected to ICP dry etching, and attention is paid to controlling the etching depth to 10 μm. The dark filled area is the area that needs to be etched.

[0060] The above process completes the groove preparation of the substrate layer 1.

[0061] Step 2, preparation of cover layer 5:

[0062] Step 2.1: Wafer preparation and cleaning: Prepare the required HPSI type 4H-SiC wafer and clean the wafer before starting the subsequent process.

[0063] Step 2.2: Etching of the shallow groove 13 of the cover layer. Use Ni metal as a mask, spin-coat photoresist, wet-etch Ni metal, and pattern it. The etching pattern of this step is as follows: Figure 6 As shown, ICP dry etching is performed on the exposed area, and the dark-filled area is the area that needs to be etched.

[0064] Step 2.3: Etching of the cover layer deep groove 14: ICP dry etching is also performed using a Ni metal mask. The etching pattern of this step is as follows Figure 7 As shown, the dark-filled area is the area that needs to be etched, and the etching depth is controlled to be consistent with the thickness of the chip layer 4 of 50 μm.

[0065] Step 2.4: Etching of the lead-through hole 6. Since this etching is a deep etching and the precision requirement is low, femtosecond laser drilling is selected for etching. The etching pattern of this step is as follows Figure 8 As shown, the dark filled area is the area that needs to be etched.

[0066] The above process completes the preparation of the cover layer 5 .

[0067] Step 3: Preparation and bonding of chip layer 4:

[0068] Step 3.1: Wafer preparation and cleaning: Prepare the required highly doped 4H-SiC wafer and Si wafer, and clean the wafer before starting the subsequent process.

[0069] Step 3.2: Si wafer bonding: Use a bonding machine to activate the clean 4H-SiC wafer and Si wafer surfaces and bond them.

[0070] Step 3.3: Wafer thinning. Use a wafer thinning machine to thin the bonded 4H-SiC wafer until the 4H-SiC wafer layer is thinned to 50μm. During the process, pay attention to controlling the thinning rate and intensity to prevent large thickness errors caused by excessive thinning rates, which may affect sensor performance.

[0071] Step 3.4: Substrate Layer 1 SiC Bonding: Bond the thinned wafer to the previously prepared substrate layer 1 wafer, with the highly doped 4H-SiC wafer surface facing the grooved surface of the substrate wafer. After activation treatment, perform direct bonding.

[0072] Step 3.5: Si wafer removal. Prepare a high-concentration KOH solution and wet-etch the Si wafer from the surface of the 4H-SiC wafer. After removal, clean the wafer to prepare for subsequent chip layer 4 electrode preparation and sensitive structure etching.

[0073] Step 3.6: Ohmic contact. Use the LiftOff process to prepare the electrode metal system, spin-coat the photoresist, expose and develop it to pattern it, and use magnetron sputtering to sputter the three layers of Ti / Ni / Au metal separately to ensure full contact between the metal and the semiconductor. The metal pattern of this step is as follows Figure 7 As shown, rapid high-temperature annealing is then performed to complete the ohmic contact preparation.

[0074] Step 3.7: Etching of chip sensitive structures. Ni metal is used as a mask and ICP dry etching process is used to dry etch the exposed area. The etching pattern is as follows: Figure 9 As shown, the dark-filled area is the area that needs to be etched. This step is mainly to etch out the sensitive mass block 8, comb-tooth structure, etc. on the chip layer 4. Since the comb-tooth structure and the support beam 9 are fragile, attention should be paid to controlling the gas ratio and etching time during the etching process to ensure that the substrate layer 1 is etched and the active structures such as the sensitive mass block 8 and comb-tooth structure are released, while preventing excessive etching from causing structural fracture.

[0075] Step 3.8: Cover plate packaging and electrical connection. The prepared cover plate layer 5 wafer is directly bonded to the chip layer 4 wafer using SiC. The grooved surface of the cover plate 5 is aligned with the surface of the chip layer 4. Careful alignment is required during the bonding process. After achieving a high-strength bond, the through-holes are filled with conductive Ag paste and sintered at high temperature to connect the chip electrodes to the sensor surface.

[0076] The above completes the acceleration sensor and packaging power supply.

[0077] The present invention utilizes MEMS bulk SiC processing technology to create grooves on the surface of the SiC substrate wafer. Through SiC direct bonding technology, it is bonded with the thinned chip wafer with high strength to construct a cavity. Then, through MEMS technology, the chip wafer mass block, comb teeth, support beam and other suspended structures are processed. Finally, the sensor is top-packaged through bonding technology to form a complete structure of a high-performance capacitive comb-tooth sensor.

[0078] The MEMS capacitive comb-tooth acceleration sensor described in the present invention is made of all SiC material, and relies on keys and technologies to realize the processing of sensitive suspended structures such as comb teeth, avoiding the process reliability and processing difficulty problems caused by the sacrificial layer process. At the same time, the acceleration sensor prepared by the present invention can achieve an operating temperature above 600°C, has the advantages of high sensitivity and low temperature effect of capacitive sensors, and can realize reliable extraction of acceleration information at ultra-high temperatures.

[0079] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various deformations, modifications, and substitutions made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor, characterized in that: include: A substrate layer (1), a chip layer (4) and a cover layer (5); The chip layer (4) is arranged between the substrate layer (1) and the cover layer (5); The chip layer (4) comprises a first fixed anchor point (2), a second fixed anchor point (7) and a sensitive mass block (8); a substrate layer groove (3) for accommodating the sensitive mass block (8) is provided on the substrate layer (1); the sensitive mass block (8) is laterally movable in the substrate layer groove (3); two first fixed anchor points (2) are respectively provided on both sides of the sensitive mass block (8); two second fixed anchor points (7) are respectively provided on the other two sides of the sensitive mass block (8); the two first fixed anchor points (2) are located in the lateral movement direction of the sensitive mass block (8); Comb teeth structures are provided between both sides of the sensitive mass block (8) and the two first fixed anchor points (2), the comb teeth structure comprising movable comb teeth (10) and fixed comb teeth (11), the movable comb teeth (10) being fixedly connected to the sensitive mass block (8), the fixed comb teeth (11) being fixedly connected to the first fixed anchor points (2), and the movable comb teeth (10) and the fixed comb teeth (11) being staggered to form capacitor plates; By applying different electric potentials to the electrodes on the two first fixed anchor points (2), when the sensitive mass block (8) moves laterally, the capacitance of the capacitor plate changes, thereby causing the electric potentials on the two second fixed anchor points (7) to change, and detecting acceleration signals through the changed electric potentials.

2. A direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor according to claim 1, characterized in that: The chip layer (4) further comprises an elastic support beam (9), wherein the support beam (9) is arranged between the second fixed anchor point (7) and the sensitive mass block (8).

3. The direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor according to claim 1, characterized in that: A chip electrode (12) is provided on the first fixed anchor point (2), and the chip electrode (12) is conductively connected to the fixed comb teeth (11); and a current-leading through hole (6) corresponding to the position of the chip electrode (12) is provided on the cover layer (5) to realize the function of leading out the circuit.

4. The direct-bonded MEMS all-SiC comb-tooth capacitive acceleration sensor according to claim 1, characterized in that: A cover plate layer shallow groove (13) and a cover plate layer deep groove (14) are provided at the bottom of the cover plate layer (5); the cover plate layer shallow groove (13) is used to accommodate the second fixed anchor point (7) and the first fixed anchor point (2); and the cover plate layer deep groove (14) is used to accommodate the sensitive mass block (8) and the comb tooth structure.

5. A method for preparing a direct-bonded MEMS all-SiC comb-teeth capacitive acceleration sensor, applied to a direct-bonded MEMS all-SiC comb-teeth capacitive acceleration sensor according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1, preparation of substrate layer (1): Step 1.1: Prepare the required HPSI type 4H-SiC wafer for cleaning; Step 1.2: Prepare a Ni metal mask and perform photolithography: A Ni metal mask is used as the mask material. A seed layer is deposited on the wafer surface using magnetron sputtering, followed by electroplating. A five-point film thickness test is used to ensure that the uniformity of the Ni mask is within 3%. Photoresist is spin-coated, and the Ni metal is wet-etched to pattern it. Step 2, preparation of cover layer (5): Step 2.1: Prepare the required HPSI type 4H-SiC wafer for cleaning; Step 2.2: Etching the shallow groove (13) of the cover layer: using Ni metal as a mask, spin-coating photoresist, and wet etching the Ni metal to pattern it; Step 2.3: Etching the deep groove (14) of the cover layer: using a Ni metal mask to perform ICP dry etching, and controlling the etching depth to be consistent with the thickness of the chip layer (4); Step 2.4: Etching of the lead-through hole (6): Etching is performed using a femtosecond laser drilling method: Step 3, chip layer (4) preparation and bonding: Step 3.1: Prepare the required highly doped 4H-SiC wafer and Si wafer for cleaning: Step 3.2: Si wafer bonding: Use a bonding machine to activate the clean 4H-SiC wafer and Si wafer surfaces and bond them; Step 3.3: Thin the bonded 4H-SiC wafer using a wafer thinning machine: Step 3.4: Substrate layer (1) SiC bonding: Bond the thinned wafer to the previously prepared wafer, with the highly doped 4H-SiC wafer surface facing the grooved surface of the substrate layer (1) wafer, and perform direct bonding after activation treatment; Step 3.5: Si wafer removal: Prepare a high concentration of KOH solution and wet-etch the Si wafer from the surface of the 4H-SiC wafer. Clean the wafer after removal. Step 3.6: Ohmic contact: Use the LiftOff process to prepare the electrode metal system, spin-coat the photoresist, and pattern it through exposure and development. Use magnetron sputtering to sputter the three layers of Ti / Ni / Au metal separately to ensure sufficient contact between the metal and the semiconductor. Then perform rapid high-temperature annealing to complete the ohmic contact preparation: Step 3.7: Chip sensitive structure etching: Ni metal is used as a mask, and an ICP dry etching process is used to dry-etch the exposed area to etch out the sensitive mass block (8) and comb-tooth structure on the chip layer (4); Step 3.8: Cover plate packaging and power lead: The prepared cover plate layer (5) wafer and the chip layer (4) wafer are directly bonded with SiC, with the grooved surface of the cover plate layer (5) facing the surface of the chip layer (4). After bonding, the power lead hole (6) is filled with conductive Ag paste and sintered at high temperature to realize circuit lead-out.

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