A resonant pressure sensor and a manufacturing method thereof

Abstract

The present invention provides a resonant pressure sensor and a manufacturing method thereof, which at least include a single-crystalline silicon wafer, a cavity and a vent hole, a polysilicon sensitive film, a torsion beam, a swing plate, a silicon island and an H-shaped resonant beam. The polysilicon film is used as the pressure-sensitive film, and the thickness can be uniformly controlled to be below 3 μm, which can improve the sensitivity and performance consistency of the sensor; the silicon island concentrates the film stress, and the torsion beam and the swing plate amplify the stress and then transfer it to the H-shaped resonant beam, enhancing the perception of the H-shaped resonant beam to external stress and improving the sensitivity of the device; the silicon island is arranged corresponding to the vent hole and has a size larger than that of the vent hole, avoiding damage to the polysilicon sensitive film during the formation of the vent hole, ensuring the performance stability of the device and improving the product yield. The sensitive structure of the present invention is formed by one-piece single-sided monolithic silicon processing without bonding, ensuring the stable performance of the device in a wide-temperature environment, and having the advantages of small size, low cost, simple process and being capable of being mixed-line produced with integrated circuit processes.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon micromachined sensing technology, and particularly to a resonant pressure sensor and a manufacturing method thereof. Background Art

[0002] MEMS silicon-based pressure sensor chips are widely used in industrial process control, aerospace, automotive electronics, oil exploration, deep-sea detection and other fields. In recent years, with the continuous progress of MEMS micromachining technology, the miniaturization, low cost and high performance of silicon-based MEMS pressure sensor chips have become the development trend of future sensors. Compared with piezoresistive pressure sensor chips, resonant pressure sensor chips are increasingly favored due to their advantages such as poor temperature sensitivity, high precision, high resolution, quasi-digital output and good long-term stability.

[0003] At present, MEMS silicon-based resonant pressure sensor chips are mainly fabricated by using SOI wafers combined with a multi-layer bonding structure [Yu Zheng, Sen Zhang, Deyong Chen, et al. A Micromachined Resonant Low-Pressure Sensor With High Quality Factor, IEEE Sensors Journal, Vol. 21, No. 18, pp: 19840-19846]. First, the top silicon in the SOI wafer is used to fabricate the resonant beam structure, and the buried oxide layer is etched to release the movable resonant beam. Secondly, the silicon deep reactive ion etching (DRIE) technology is used to etch the single crystal silicon of the Handle layer from the back of the wafer to a large depth to thin the Handle layer to form a pressure diaphragm structure. Finally, a vacuum bonding package is performed on the position where the resonant beam is located by using a silicon-glass or other vacuum bonding process. The resonant pressure sensor chips fabricated by this process have the following deficiencies: (1) The chip size is large, the process is complex, and the manufacturing cost is high; (2) Limited by the thickness uniformity of the single crystal silicon wafer itself (the thickness uniformity of the single crystal silicon wafer ≥ 3 μm), the thickness of the processed pressure diaphragm must be greater than 6 μm. Therefore, if the sensitivity of the sensor chip is to be further improved, it can only be achieved by sacrificing the chip size by increasing the diaphragm area; in addition, limited by the diaphragm thickness uniformity, it will also affect the performance characteristics of the sensor chip; (3) Since the chip is fabricated by using a multi-bonding process, affected by the thermal expansion coefficients between different bonding materials, residual stress at the bonding interface will inevitably be introduced, affecting the performance stability of the chip in a wide temperature range environment. In order to reduce the cost, Xiamen University uses a silicon-silicon fusion bonding process to replace the expensive SOI wafer to fabricate the pressure-sensitive structure layer and the single crystal silicon resonant layer. Although the chip cost is reduced to a certain extent, the process complexity is increased, and the structure of the sensor chip with multiple bondings still cannot be avoided [Xiaohui Du, LiyingWang, Anlin Li, et al., High Accuracy Resonant Pressure Sensor With Balanced-Mass DETF Resonator and Twinborn Diaphragms, Journal of MicroelectromechanicalSystems, Vol. 26, No. 1, pp: 235-245].

[0004] Therefore, it is necessary to design a new MEMS silicon-based resonant pressure sensor chip to solve the above deficiencies of the traditional silicon-based resonant pressure sensor chips, and to achieve the small size, high performance and low cost of the MEMS silicon-based resonant pressure sensor chips. Summary of the Invention

[0005] In view of the disadvantages of the above-mentioned prior art, the purpose of the present invention is to provide a resonant pressure sensor and a manufacturing method thereof, which are used to solve the problems of large chip size, complex manufacturing process, limitations of the thickness and uniformity of single-crystalline silicon thin films, and performance stability caused by residual stress after multiple bondings in the prior art.

[0006] To achieve the above purpose and other related purposes, the present invention provides a resonant pressure sensor, which at least includes:

[0007] A single-crystalline silicon wafer, which is a (111) single-crystalline silicon wafer and includes a first surface and a second surface arranged oppositely;

[0008] A cavity, which is embedded inside the single-crystalline silicon wafer, and the cavity is provided with air vents that are connected and pass through the second surface;

[0009] A pressure-sensing module, which includes a polysilicon sensitive thin film located above the cavity, and a stress conduction mechanism and an H-shaped resonant beam located above the polysilicon sensitive thin film. The stress conduction mechanism is symmetrically located at both ends of the H-shaped resonant beam and includes a silicon island corresponding to the air vent, torsion beams and swing plates that are parallel and spaced apart from the silicon island. Among them, both ends of the H-shaped resonant beam are fixedly supported at the central positions of the torsion beams and are suspended above the polysilicon sensitive thin film, and the swing plates are located on both sides of the H-shaped resonant beam and are connected to the torsion beams;

[0010] Bonding pads, which are located on the single-crystalline silicon wafer and are interconnected with the H-shaped resonant beam through metal leads to complete the excitation and pickup signal detection of the H-shaped resonant beam.

[0011] Preferably, the H-shaped resonant beam, the torsion beams, the swing plates and the silicon island are integrally formed from the single-crystalline silicon wafer. The H-shaped resonant beam is made of single-crystalline silicon, and the torsion beams, the swing plates and the silicon island include single-crystalline silicon and silicon oxide layers located on the upper and lower surfaces of the single-crystalline silicon.

[0012] Preferably, the number of the air vents is 2, and the size of the air vents is smaller than the size of the silicon island.

[0013] Preferably, the number of the bonding pads is 4. The bonding pads are located at both ends of the torsion beams and are connected to the H-shaped resonant beam along the torsion beams through metal leads.

[0014] Preferably, the polysilicon sensitive thin film is a hexagonal thin film, the cavity is a hexagonal cavity corresponding to the shape of the polysilicon sensitive thin film, and the polysilicon sensitive thin film directly forms the upper surface of the cavity.

[0015] Preferably, the six edges of the polysilicon sensitive film are arranged along the <110> crystal orientation, and the H-shaped resonant beam is arranged along the <211> crystal orientation.

[0016] Preferably, along the polysilicon sensitive film and On the single-crystal silicon wafer along the crystal orientation edge, a plurality of etching through-holes are arranged at intervals. After forming the cavity, the silicon oxide layer and the polysilicon sensitive film through the etching through-holes, they are filled with polysilicon. The aperture adjustment of the etching through-holes can control the thickness of the polysilicon sensitive film, and the depth of the etching through-holes determines the thickness of the stress conduction mechanism and the H-shaped resonant beam.

[0017] The present invention also provides a manufacturing method of a resonant pressure sensor. The manufacturing method at least includes the following steps:

[0018] S1: Provide a single-crystal silicon wafer. The single-crystal silicon wafer includes a first surface and a second surface which are oppositely arranged. Form a first oxide layer on the first surface and the second surface of the single-crystal silicon wafer.

[0019] S2: Form a plurality of etching through-holes arranged at intervals on the first surface and the first oxide layer of the single-crystal silicon wafer. Deposit a layer of silicon nitride layer on the first oxide layer of the first surface. At the same time, the side walls and the bottom of the etching through-holes are also covered by the silicon nitride layer.

[0020] S3: Etch and remove the silicon nitride layer on the first oxide layer and the bottom of the etching through-holes. Continue to etch downward along the etching through-holes for a set depth to determine the depth of the cavity.

[0021] S4: Perform anisotropic wet etching inside the single-crystal silicon wafer through the etching through-holes to form a cavity structure. Form a second oxide layer on the inner surface of the cavity.

[0022] S5: Deposit a polysilicon layer on the first oxide layer of the first surface to fill the etching through-holes. While filling, a layer of polysilicon sensitive film will be deposited on the inner surface of the cavity. Etch and remove the polysilicon layer on the first surface.

[0023] S6: Etch out a vent hole on the second surface. The vent hole is communicated with the cavity.

[0024] S7: Etch and remove the first oxide layer covered by the H-shaped resonant beam area on the first surface. Sputter a metal thin film and pattern it to form metal leads and pads.

[0025] S8: A stress conduction mechanism composed of a graphitized H-shaped resonant beam, a silicon island, a torsion beam, and a swing plate. Etch away parts of the first oxide layer, single-crystalline silicon, and the second oxide layer except for the H-shaped resonant beam and the stress conduction mechanism to expose the polysilicon sensitive film.

[0026] S9: Etch away the second oxide layer under the H-shaped resonant beam so that the H-shaped resonant beam floats above the polysilicon sensitive film.

[0027] Preferably, the number of the vent holes is 2. The vent holes are located below the silicon island and have a size smaller than that of the silicon island.

[0028] Preferably, there are 4 pads. The pads are located at both ends of the torsion beam and are connected to the H-shaped resonant beam along the torsion beam through metal leads.

[0029] Preferably, the corrosion through holes are arranged at intervals along the and crystal orientation of the single-crystalline silicon wafer.

[0030] Preferably, the cavity is a hexagonal cavity, the polysilicon sensitive film is a hexagonal film, and all six sides are arranged along the <110> crystal orientation. The H-shaped resonant beam is arranged along the <211> crystal orientation.

[0031] As described above, a resonant pressure sensor and its manufacturing method according to the present invention have the following beneficial effects: The resonant pressure sensor at least includes a single-crystalline silicon wafer, a cavity embedded inside the single-crystalline silicon wafer, vent holes communicating with the cavity and penetrating the single-crystalline silicon wafer, a polysilicon sensitive film located above the cavity, and a stress conduction mechanism including a torsion beam, a swing plate, and a silicon island and an H-shaped resonant beam located above the polysilicon sensitive film. Among them, the stress conduction mechanism is symmetrically located at both ends of the H-shaped resonant beam. The present invention uses a polysilicon film as the pressure-sensitive film, and the film thickness is uniform and controllable, and can be controlled below 3 μm, thereby improving the sensitivity and performance consistency of the resonant pressure sensor; under the action of the pressure to be measured, the upper and lower surfaces of the polysilicon sensitive film generate deformation due to the pressure difference. The silicon island concentrates the film stress and amplifies the film stress through the torsion beam and the swing plate and then transmits it to the H-shaped resonant beam, enhancing the perception degree of the H-shaped resonant beam to external stress and further improving the sensitivity of the resonant pressure sensor; the silicon island is correspondingly located above the vent hole and has a size larger than that of the vent hole, so as to avoid damaging the polysilicon sensitive film during the formation of the vent hole, ensure the performance stability of the resonant pressure sensor, and improve the product yield.

[0032] In terms of manufacturing, the resonant pressure sensor is formed by monolithic single-sided silicon integrated processing, without the need for a bonding process, and there is no residual stress at the bonding interface, ensuring the stable performance of the sensor in a wide temperature environment; the thickness of the polysilicon sensitive film is controllable, and with the amplification of the torsion beam and the swing plate, high sensitivity can be achieved without sacrificing size, having the advantages of small size, low cost, simple process, and being able to be produced in a mixed line with integrated circuit processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It shows a schematic structural diagram of a resonant pressure sensor in an embodiment of the present invention.

[0034] Figure 2 It shows a schematic partial cross-sectional structural diagram of a resonant pressure sensor in an embodiment of the present invention.

[0035] Figures 3a - 3i It shows a schematic structural diagram corresponding to the manufacturing process of a resonant pressure sensor of the present invention.

[0036] DESCRIPTION OF REFERENCE NUMERALS

[0037] 100 Monocrystalline silicon wafer

[0038] 110 First surface

[0039] 120 Second surface

[0040] 200 Polysilicon sensitive film

[0041] 310 H-shaped resonant beam

[0042] 320 Silicon island

[0043] 330 Torsion beam

[0044] 340 Swing plate

[0045] 410 Pad

[0046] 420 Metal lead

[0047] 500 Etching through-hole

[0048] 600 Cavity

[0049] 610 Vent hole

[0050] 700 First oxide layer

[0051] 800 Second oxide layer

[0052] 900 Silicon nitride layer

[0053] Steps S1 to S9 DETAILED DESCRIPTION OF THE INVENTION

[0054] The embodiments of the present invention will be described below through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0055] When detailing the embodiments of the present invention, for the convenience of description, the cross-sectional views showing the device structure will be enlarged locally in a non-general proportion, and the schematic diagrams are only examples and should not limit the scope of protection of the present invention herein. In addition, in actual production, three-dimensional spatial dimensions including length, width, and depth should be included.

[0056] For the convenience of description, spatial relationship terms such as "beneath", "below", "lower", "under", "above", "on" may be used herein to describe the relationship between one element or feature shown in the drawings and other elements or features. It will be understood that these spatial relationship terms are intended to cover other directions of the device in use or operation in addition to the directions depicted in the drawings. In addition, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there can be one or more intervening layers. As used herein, "between... and..." means including the endpoint values.

[0057] In the context of the present application, the structure in which the first feature is "above" the second feature described may include embodiments where the first and second features are formed in direct contact, and may also include embodiments where additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0058] It should be noted that the illustrations provided in this embodiment only schematically illustrate the basic concept of the present invention. Therefore, only the components related to the present invention are shown in the illustrations, rather than being drawn according to the number, shape, and size of the components in actual implementation. The types, quantities, and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0059] Regarding the concepts of "upper" and "lower" in the text, to make the expression clearer, it is stipulated that the direction perpendicular to the first surface of the single-crystalline silicon wafer is "upper", and the direction perpendicular to the second surface of the single-crystalline silicon wafer is "lower".

[0060] As Figures 1 - 2 shown, the present invention provides a resonant pressure sensor, and the resonant pressure sensor at least includes a single-crystalline silicon wafer 100, a cavity 600 and a vent hole 610, a pressure-sensitive module including a polysilicon sensitive film 200, a stress conduction mechanism and an H-shaped resonant beam 310, and a pad 410.

[0061] Specifically, the single-crystal silicon wafer 100 is an ordinary N-type or P-type (111) single-sided or double-sided polished single-crystal silicon wafer, including a first surface 110 and a second surface 120 which are oppositely arranged, and the cost is low. The cavity 600 is formed inside the single-crystal silicon wafer 100, and is a cavity structure conforming to the shape of the polysilicon sensitive film 200, located below the polysilicon sensitive film 200, and is used to suspend the polysilicon sensitive film 200 to sense the pressure to be measured in the cavity 600; each surface of the cavity 600 is covered with a polysilicon film with a uniform thickness, and the upper polysilicon film is the polysilicon sensitive film 200; the depth of the cavity 600 is controllable. When the pressure difference between the front and back surfaces of the polysilicon sensitive film 200 exceeds the full scale, a reasonable cavity depth design can provide reliable overload protection for the polysilicon sensitive film 200, and the specific depth can be set according to the actual application environment, and no excessive limitation is made here.

[0062] The vent hole 610 penetrates through the second surface 120 of the single-crystal silicon wafer 100 and communicates with the cavity 600. Through the vent hole 610, the cavity 600 can be connected to different external pressures to be measured. In this embodiment, the vent hole 610 is a square structure and the number is one. However, according to actual requirements, the number of the vent holes 610 can be two, and its shape can also be other shapes such as circular, and no strict limitation is made here.

[0063] The stress conduction mechanism and the H-shaped resonant beam 310 are located above the polysilicon sensitive film 200, and the stress conduction mechanism is located at both ends of the H-shaped resonant beam 310. The stress conduction mechanism includes a silicon island 320, a torsion beam 330 and a swing plate 340. The silicon island 320 is correspondingly located above the vent hole 610. The torsion beam 330 and the swing plate 340 are arranged in parallel and spaced apart from the silicon island 320. Among them, both ends of the H-shaped resonant beam 310 are fixedly supported at the central position of the torsion beam 330 and suspended above the polysilicon sensitive film 200. The swing plate 340 is located on both sides of the H-shaped resonant beam 310 and is connected to the torsion beam 330. Under the action of the pressure to be measured, the upper and lower surfaces of the polysilicon sensitive film 200 are deformed due to the pressure difference. The silicon island 320 concentrates the external pressure sensed by the polysilicon sensitive film 200, and after being amplified by the torsion beam 330 and the swing plate 340, it is transmitted to the H-shaped resonant beam 310, changing the resonant frequency of the H-shaped resonant beam 310, enhancing the perception degree of the H-shaped resonant beam 310 to external stress, and improving the sensitivity of the resonant pressure sensor.

[0064] The size of the silicon island 320 is larger than that of the vent hole 610, so as to ensure that the vent hole 610 is always within the range of the silicon island 320. During the process of etching to form the vent hole 610, even if over-etching occurs, since the silicon island 320 has a thick position and is not a sensitive thin film, it will not affect the device performance, thus improving the yield of the resonant pressure sensor.

[0065] The pad 410 is located on the single-crystalline silicon wafer 100 and is interconnected with the H-shaped resonant beam 310 through a metal lead 420, thereby completing the excitation and pickup signal detection of the H-shaped resonant beam 310. As Figure 1 shown, there are 4 pads 410. The pads 410 are located at both ends of the torsion beam 330 and are connected to the H-shaped resonant beam 310 along the torsion beam 330 through metal leads 420. However, the metal leads at both ends of the same torsion beam 330 are not directly connected and are distributed along the H-shaped resonant beam 310 at the center position of the torsion beam 330 to achieve connection. Therefore, the pads 410 on the same side of the H-shaped resonant beam 310 are a pair, which are excitation electrodes or pickup electrodes. The beam on the same side as the excitation electrode is the excitation beam, and the beam on the same side as the pickup electrode is the pickup beam. If a vertical electric field is added to the upper surface of the H-shaped resonant beam 310 and a periodic alternating voltage is applied to pads A and B, then the beams on the same side as A and B are excitation beams. The excitation beams are vibrated by the Lorentz force and at the same time drive the pickup beams on the C and D sides to vibrate; since the pickup beams vibrate to cut the magnetic induction lines, an induced electromotive force change is generated between pads C and D, and the natural frequency of the H-shaped resonant beam 310 and the external pressure value are measured according to the magnitude of the induced electromotive force. This embodiment is a non-limiting example, and other connection methods can also be adopted according to actual requirements.

[0066] More specifically, in this embodiment, along the single-crystalline silicon wafer 100 and A plurality of etching through-holes 500 are arranged at intervals in the crystal orientation. After forming the cavity 600, the silicon oxide layer in the cavity 600, and the polysilicon sensitive film 200 through the etching through-holes 500, the cavity is filled with polysilicon. The formed cavity 600 is a hexagonal cavity, and the polysilicon sensitive film 200 is a hexagonal polysilicon film, and its six sides are all arranged along the <110> crystal orientation. Pattern the single-crystal silicon above the polysilicon sensitive film 200 and the silicon oxide layers on its upper and lower surfaces, and etch to form the H-shaped resonant beam 310, the torsion beam 330, the swing plate 340, and the silicon island 320. The H-shaped resonant beam 310 is arranged along the <211> crystal orientation, and the torsion beam 330, the swing plate 340, and the silicon island 320 are symmetrically located at both ends of the H-shaped resonant beam 310. Among them, the H-shaped resonant beam 310 is single-crystal silicon, and there is no residual stress affecting its external force perception. The torsion beam 330, the swing plate 340, and the silicon island 320 include single-crystal silicon and silicon oxide layers on the upper and lower surfaces of the single-crystal silicon. The residual stresses of the silicon oxide layers on the upper and lower surfaces cancel each other out, so as not to have an adverse effect on the pressure sensing module and improve the detection performance of the resonant pressure sensor.

[0067] As Figures 3a - 3i described above, the present invention also provides a manufacturing method of a resonant pressure sensor, and the manufacturing method includes the following steps:

[0068] Step S1: Provide a single-crystal silicon wafer 100, the single-crystal silicon wafer 100 includes a first surface 110 and a second surface 120 which are oppositely arranged, and form a first oxide layer 700 on the first surface 110 and the second surface 120 of the single-crystal silicon wafer 100.

[0069] Specifically, as Figure 3a shown, the single-crystal silicon wafer 100 is an ordinary N-type or P-type (111) single-sided or double-sided polished single-crystal silicon wafer, including a first surface 110 and a second surface 120 which are oppositely arranged. A first oxide layer 700 is formed on the first surface 110 and the second surface 120 of the single-crystal silicon wafer by thermal oxidation. In this embodiment, the first oxide layer is a 1-μm silicon oxide layer.

[0070] Step S2: Form a plurality of etching through-holes 500 arranged at intervals on the first surface 110 and the first oxide layer 700 of the single-crystal silicon wafer 100, deposit a layer of silicon nitride layer 900 on the first oxide layer 700 of the first surface 110, and at the same time, the silicon nitride layer 900 also covers the side walls and the bottom of the etching through-holes 500.

[0071] Specifically, as Figure 3bAs shown, a plurality of spaced-apart etch vias 500 are formed on the first oxide layer 700 of the first surface by using reactive ion etching (RIE) technology. The etch vias 500 are arranged at intervals along the and crystal orientation of the single-crystalline silicon wafer 100. The aperture size of the etch vias 500 determines the deposition time of the subsequent polysilicon sensitive film 200, and can control the thickness of the polysilicon sensitive film 200. The single-crystalline silicon wafer 100 is further etched in the etch vias 500 by using deep reactive ion etching (Deep-RIE) technology to deepen the depth of the etch vias 500. The depth of the etch vias 500 is the thickness of the subsequent H-shaped resonant beam 310, and also determines the thicknesses of the subsequent torsion beam 330, swing plate 340 and silicon island 320. Then, a layer of silicon nitride layer 900 is deposited on the first oxide layer 700 of the first surface 110 by using low-pressure chemical vapor deposition (LPCVD) process. At the same time, the silicon nitride layer 900 also covers the side walls and the bottom of the etch vias 500. In this embodiment, the depth of the etch vias 500 is 7 μm, and the silicon nitride layer 900 is a low-stress silicon nitride layer of 0.2 μm.

[0072] Step S3: Etch and remove the silicon nitride layer on the first oxide layer 700 and at the bottom of the etch vias 500, and continue to etch downward along the etch vias 500 by a set depth to determine the depth of the cavity 600.

[0073] Specifically, as Figure 3c shown, reactive ion etching (RIE) technology is used to etch and remove the silicon nitride layer on the first oxide layer and at the bottom of the etch vias, and then deep reactive ion etching (Deep-RIE) technology is used to continue to etch the single-crystalline silicon wafer 100 downward along the bottom of the etch vias 500 to determine the depth of the subsequent cavity 600. In this embodiment, the depth of the cavity 600 is 20 μm.

[0074] Step S4: Anisotropic wet etching is performed inside the single-crystalline silicon wafer 100 through the etch vias 500 to form a cavity structure, and a second oxide layer 800 is formed on the inner surface of the cavity 600.

[0075] Specifically, as Figure 3dAs shown, anisotropic wet etching is performed inside the single-crystalline silicon wafer 100 through the etching through-hole 500 using a KOH or TMAH etching solution until a cavity structure with (111) crystal planes on all eight faces is formed. A certain thickness of oxide layer is formed on the inner surface of the cavity 600 through a thermal oxidation process, and this oxide layer is the second oxide layer 800. Since the sidewalls of the etching through-hole 500 are covered with a silicon nitride layer and will not be oxidized, after subsequent filling with low-stress polysilicon, the overall residual stress of the etching through-hole 500 is very small and will not have an adverse impact on the performance of the resonant pressure sensor. In this embodiment, the second oxide layer 800 is a silicon oxide layer with a thickness of 2 μm.

[0076] Step S5: Deposit a polysilicon layer on the first oxide layer 700 on the first surface 110 to fill the etching through-hole 500. During the filling process, a polysilicon sensitive film will be deposited on the inner surface of the cavity 600, and then etch away the polysilicon layer on the first surface 110.

[0077] Specifically, as Figure 3e shown, use low-pressure chemical vapor deposition (LPCVD) process to deposit polysilicon to fill the etching through-hole 500. During the filling process, a certain thickness of polysilicon layer will also be deposited on each inner surface of the cavity 600, and then etch away the excess polysilicon on the first surface. Theoretically, the aperture of the etching through-hole 500 is the sum of the thickness 200 of the polysilicon sensitive film and the thickness of the second oxide layer 800. Adjusting the aperture size of the etching through-hole 500 can control the thickness of the polysilicon sensitive film 200. In this embodiment, a 4-μm polysilicon layer is deposited above the first surface 110, and a polysilicon layer of about 2 μm can be formed inside the cavity 600.

[0078] Step S6: Etch out an air vent 610 on the second surface 120, and the air vent 610 is in communication with the cavity 600.

[0079] Specifically, as Figure 3f shown, use deep reactive ion etching (Deep-RIE) of silicon to etch away the single-crystalline silicon layer and the polysilicon thin film layer, and use reactive ion etching (RIE) technology to etch away the first oxide layer 700 and the second oxide layer 800, so as to etch out an air vent 610 on the second surface 120 to make it communicate with the cavity 600 for connecting the external pressure to be measured. To avoid over-etching from affecting the performance of the resonant pressure sensor, the air vent 610 is correspondingly located below the silicon island 320 and its size is smaller than that of the silicon island 320.

[0080] Step S7: Etch away the first oxide layer 700 covering the H-shaped resonant beam 310 region on the first surface 110, sputter a metal thin film and pattern it to form metal leads 420 and pads 410, as Figure 3g shown.

[0081] Step S8: Pattern the stress conduction mechanism composed of the H-shaped resonant beam 310, silicon island 320, torsion beam 330 and swing plate 340, and etch away the first oxide layer 700, single-crystalline silicon, and the second oxide layer 800 outside the H-shaped resonant beam 310 and the stress conduction mechanism to expose the polysilicon sensitive film 200.

[0082] Specifically, as Figure 3h shown, use deep reactive ion etching of silicon to etch away the single-crystalline silicon above the polysilicon sensitive film 200 except for the H-shaped resonant beam, silicon island, torsion beam and swing plate, and use reactive ion etching technology to remove part of the first oxide layer 700 and the second oxide layer 800 to expose the polysilicon sensitive film 200 below. In this embodiment, the polysilicon force-sensitive film 200 is a hexagonal structure.

[0083] Step S9: Etch away the second oxide layer 800 below the H-shaped resonant beam 310 to make the H-shaped resonant beam 310 suspended above the polysilicon sensitive film 200. As Figure 3i shown, in this embodiment, use gaseous HF etching to etch away the second oxide layer 800 below the H-shaped resonant beam 310 to release the H-shaped resonant beam 310.

[0084] In summary, a resonant pressure sensor and its manufacturing method according to the present invention have the following beneficial effects: The resonant pressure sensor at least includes a single-crystal silicon wafer, a cavity embedded inside the single-crystal silicon wafer, a vent hole communicating with the cavity and penetrating the single-crystal silicon wafer, a polysilicon sensitive film located above the cavity, and a stress conduction mechanism including a torsion beam, a swing plate, and a silicon island located above the polysilicon sensitive film, and an H-shaped resonant beam, wherein the stress conduction mechanism is symmetrically located at both ends of the H-shaped resonant beam. The present invention uses a polysilicon film as the pressure-sensitive film, and the film thickness is uniform and controllable, and can be controlled below 3 μm, thereby improving the sensitivity and performance consistency of the resonant pressure sensor; under the action of the pressure to be measured, the upper and lower surfaces of the polysilicon sensitive film generate deformation due to the pressure difference, and the silicon island concentrates the film stress and amplifies the film stress through the torsion beam and the swing plate and then transmits it to the H-shaped resonant beam, enhancing the perception of the H-shaped resonant beam to external stress and further improving the sensitivity of the resonant pressure sensor; the silicon island is correspondingly located above the vent hole and has a size larger than that of the vent hole, so as to avoid damaging the polysilicon sensitive film during the formation of the vent hole, ensure the performance stability of the resonant pressure sensor, and improve the product yield.

[0085] In terms of manufacturing, the resonant pressure sensor is formed by single-chip single-sided monolithic silicon integration processing, without a bonding process, and there is no residual stress at the bonding interface, ensuring the stable performance of the sensor in a wide temperature environment; the thickness of the polysilicon sensitive film is controllable, and with the amplification of the torsion beam and the swing plate, it can have high sensitivity without sacrificing size, and has the advantages of small size, low cost, simple process, and can be mixed-line produced with integrated circuit processes.

[0086] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A resonant pressure sensor, characterized in that, The resonant pressure sensor at least includes: A single-crystal silicon wafer, which is a (111) single-crystal silicon wafer and includes a first surface and a second surface arranged opposite to each other; A cavity, which is embedded inside the single-crystal silicon wafer, and the cavity is provided with vent holes that are connected and pass through the second surface; A pressure sensing module, which includes a polysilicon sensitive film located above the cavity, and a stress conduction mechanism and an H-shaped resonant beam located above the polysilicon sensitive film. The stress conduction mechanism is symmetrically located at both ends of the H-shaped resonant beam and includes a silicon island corresponding to the vent hole, torsion beams arranged in parallel and spaced apart from the silicon island, and a swing plate. Among them, both ends of the H-shaped resonant beam are fixedly supported at the central positions of the torsion beams and are suspended above the polysilicon sensitive film, and the swing plate is located on both sides of the H-shaped resonant beam and is connected to the torsion beam; Bonding pads, which are located on the single-crystal silicon wafer and are interconnected with the H-shaped resonant beam through metal leads to complete the excitation of the H-shaped resonant beam and the detection of the pick-up signal.

2. The resonant pressure sensor according to claim 1, wherein: The H-shaped resonant beam, the torsion beam, the swing plate, and the silicon island are integrally formed from the single-crystal silicon wafer. The H-shaped resonant beam is made of single-crystal silicon, and the torsion beam, the swing plate, and the silicon island include single-crystal silicon and silicon oxide layers on the upper and lower surfaces of the single-crystal silicon; 3. The resonant pressure sensor according to claim 1, wherein: The number of the vent holes is 2, and the size of the vent holes is smaller than the size of the silicon island; 4. The resonant pressure sensor according to claim 1, wherein: There are 4 bonding pads, which are located at both ends of the torsion beam and are connected to the H-shaped resonant beam along the torsion beam through metal leads; 5. The resonant pressure sensor according to claim 1, wherein: The polysilicon sensitive film is a hexagonal film, the cavity is a hexagonal cavity corresponding to the shape of the polysilicon sensitive film, and the polysilicon sensitive film directly forms the upper surface of the cavity; 6. The resonant pressure sensor according to claim 5, characterized in that: The six edges of the polysilicon sensitive film are arranged in the <110> crystal orientation, and the H-shaped resonant beam is arranged in the <211> crystal orientation; 7. The resonant pressure sensor according to claim 6, wherein: Along the polysilicon sensitive film and A plurality of etching through-holes are arranged at intervals on the single-crystalline silicon wafer at the crystal orientation edge. After the cavity, the silicon oxide layer and the polysilicon sensitive film are formed through the etching through-holes, they are filled with polysilicon. The adjustment of the aperture of the etching through-holes can control the thickness of the polysilicon sensitive film, and the depth of the etching through-holes determines the thickness of the stress conduction mechanism and the H-shaped resonant beam.

8. A manufacturing method of a resonant pressure sensor, characterized in that, The manufacturing method includes the following steps: S1: Provide a single-crystal silicon wafer, which includes a first surface and a second surface arranged opposite to each other, and form a first oxide layer on the first surface and the second surface of the single-crystal silicon wafer; S2: Form a plurality of corrosion through-holes arranged at intervals on the first surface of the single-crystal silicon wafer and the first oxide layer, deposit a layer of silicon nitride layer on the first oxide layer on the first surface, and at the same time, the silicon nitride layer also covers the side walls and the bottom of the corrosion through-holes; S3: Etch and remove the silicon nitride layer on the first oxide layer and at the bottom of the corrosion through-holes, and continue to etch downward along the corrosion through-holes by a set depth to determine the depth of the cavity; S4: Perform anisotropic wet etching inside the single-crystal silicon wafer through the corrosion through-holes to form a cavity structure, and form a second oxide layer on the inner surface of the cavity; S5: Deposit a polysilicon layer on the first oxide layer on the first surface to fill the corrosion through-holes. During the filling process, a polysilicon sensitive film will be deposited on the inner surface of the cavity, and etch and remove the polysilicon layer on the first surface; S6: Etch ventilation holes on the second surface, and the ventilation holes are communicated with the cavity; S7: Etch and remove the first oxide layer covered by the H-shaped resonant beam region on the first surface, sputter a metal thin film and pattern it to form metal leads and pads; S8: Pattern the stress conduction mechanism composed of the H-shaped resonant beam, silicon island, torsion beam and swing plate, and etch away the first oxide layer, single-crystalline silicon and the second oxide layer except for the H-shaped resonant beam and the stress conduction mechanism to expose the polysilicon sensitive film; S9: Etch and remove the second oxide layer under the H-shaped resonant beam to make the H-shaped resonant beam suspended above the polysilicon sensitive film.

9. The manufacturing method of the resonant pressure sensor according to claim 8, characterized in that: The number of the ventilation holes is 2, the ventilation holes are located under the silicon island and the size is smaller than that of the silicon island.

10. The manufacturing method of the resonant pressure sensor according to claim 8, characterized in that: There are 4 pads, the pads are located at both ends of the torsion beam and are connected to the H-shaped resonant beam along the torsion beam through metal leads.

11. The manufacturing method of the resonant pressure sensor according to claim 8, characterized in that: The corrosion via holes are arranged at intervals along the and crystal orientations of the single crystal silicon wafer.

12. The manufacturing method of the resonant pressure sensor according to claim 11, characterized in that: The cavity is a hexagonal cavity, the polysilicon sensitive film is a hexagonal film, and six sides are arranged along the <110> crystal direction, and the H-shaped resonant beam is arranged along the <211> crystal direction.

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