Monolithic integrated MEMS pressure and acceleration compound sensor and method of manufacturing the same
By integrating MEMS pressure and acceleration sensors on a single chip, and utilizing silicon-based vertical interconnects and a unique multi-wing sensitive membrane structure, the problems of nonlinearity and low integration in existing sensors have been solved, realizing a composite sensor with high sensitivity and high linearity, suitable for automotive, aerospace and other fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI UNIV
- Filing Date
- 2023-05-29
- Publication Date
- 2026-06-26
Smart Images
Figure CN116462153B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a MEMS sensor and its fabrication method, particularly a monolithically integrated MEMS pressure and acceleration composite sensor and its fabrication method, belonging to the field of microelectromechanical systems (MEMS) sensor technology. Background Technology
[0002] As is well known, MEMS pressure sensors and MEMS accelerometers are widely used in various fields. Due to the thin film quality of MEMS pressure sensors, the sensor output under vibration will be superimposed with the effects of acceleration, resulting in a nonlinear output. With the maturity of micro-nano fabrication technology, monolithically integrated multi-sensor technology is gradually becoming a new development trend due to its advantages such as low price, high integration, and good chip consistency.
[0003] Currently, known composite sensors, such as CN 104062464 A and CN 103792036 A, are mostly integrated using a parallel interconnect method. Although the parallel interconnect structure is simple to fabricate and integrate, it has not significantly improved the integration density of composite sensors. Another known composite sensor using a vertical interconnect method, see CN 104944359 A, connects the upper pressure sensor silicon wafer by bonding, and fabricates a metal electrode layer on the upper layer and a lower electrode to form a capacitive pressure sensor. This capacitive pressure sensor narrows the application range of composite sensors, and because the fabrication process requires multiple bonding connections between the two sensors, the operation is complex, affecting the integration effect and accuracy. Furthermore, it has the drawback of being unable to fabricate the surface pattern under the pressure sensor membrane, thus failing to meet all the designer's needs. Summary of the Invention
[0004] To overcome the above-mentioned shortcomings of the prior art, the present invention provides a monolithic integrated MEMS pressure and acceleration composite sensor and its fabrication method, which not only solves the problems of low sensitivity and low integration of existing micromechanical composite pressure sensors, but also has a more reasonable fabrication process and stronger versatility.
[0005] One technical solution adopted by the present invention to solve its technical problem is:
[0006] A monolithically integrated MEMS pressure and acceleration composite sensor includes a MEMS pressure sensor and a MEMS acceleration sensor integrated via a silicon-based vertical interconnect; the MEMS pressure sensor and the MEMS acceleration sensor are respectively arranged on two opposing working surfaces of the silicon substrate;
[0007] The MEMS pressure sensor is a piezoresistive sensor, comprising a multi-wing-shaped sensitive membrane formed on the upper surface of the silicon substrate. The surface of the multi-wing-shaped sensitive membrane has peninsula structures, island structures, and a central boss structure. Multiple peninsula structures and island structures are staggered around the outer periphery of the central boss structure and arranged symmetrically with the central boss structure as the center. A first piezoresistive device is disposed on the upper surface of each peninsula structure.
[0008] The MEMS accelerometer includes a multi-cantilever beam structure disposed on the lower surface of the silicon substrate. The multi-cantilever beam structure includes multiple cantilever beams formed by etching and a central mass block. There is a cavity between the cantilever beams and the central mass block. A second piezoresistive device is disposed on the upper surface of each cantilever beam.
[0009] Optionally, a cavity structure or a cavity + membrane structure is provided between the MEMS pressure sensor and the MEMS acceleration sensor.
[0010] Optionally, the multi-wing sensitive membrane is configured as a four-wing sensitive membrane structure, which mainly consists of four symmetrical peninsula structures, four symmetrical island structures and a central boss structure of uniform thickness.
[0011] Optionally, the composite sensor has an overall centrally symmetrical structure, with the MEMS pressure sensor and the MEMS accelerometer arranged vertically aligned and located in the center of the silicon substrate; the MEMS accelerometer uses a vertical through-hole to lead out wires.
[0012] Optionally, the silicon substrate includes an N-type single-crystal silicon wafer and an upper surface thermal oxygen silicon dioxide layer and a lower surface thermal oxygen silicon dioxide layer respectively disposed on its front and back surfaces, with the MEMS pressure sensor and the MEMS acceleration sensor respectively disposed on the upper surface thermal oxygen silicon dioxide layer and the lower surface thermal oxygen silicon dioxide layer.
[0013] This technical solution's monolithically integrated MEMS pressure and acceleration composite sensor not only integrates a MEMS pressure sensor and a MEMS acceleration sensor in the vertical direction, significantly improving the integration of the composite sensor; in particular, the unique multi-wing sensitive membrane structure and central boss structure enable the MEMS pressure sensor to have both high sensitivity and high linearity. At the same time, the MEMS pressure sensor of this invention adopts the piezoresistive sensing principle, which has stronger versatility compared to the capacitive pressure sensing principle of existing composite sensors.
[0014] Another technical solution adopted by the present invention to solve its technical problem is:
[0015] A method for fabricating a monolithic integrated MEMS pressure and acceleration composite sensor includes the following steps:
[0016] Step 1: Prepare silicon-based materials;
[0017] Step 2: Fabricate the internal structure of the MEMS pressure sensor on the front side of the silicon substrate;
[0018] In step 21: photolithography of the piezoresistive pattern of the first piezoresistive device, wet etching of the upper surface thermal oxygen silicon dioxide layer to expose the N-type single crystal silicon wafer, and sequential combination of boron ion implantation and thermal diffusion processes to form the piezoresistive lightly doped region of the first piezoresistive device; rapid annealing, and then deposition of the first silicon nitride layer using low-pressure chemical vapor deposition.
[0019] Step 22: The photolithography mask is then etched to open the first metal contact hole, concentrated boron is injected to form the piezoresistive heavily doped region of the first piezoresistive device, and then the first silicon dioxide layer is deposited using low-pressure chemical vapor deposition.
[0020] Step 23: Using a photomask and deep reactive ion etching (DRIE), multiple rows of first micro-holes are formed on the surface of the first insulating layer. A first tetraethyl orthosilicate layer is deposited on the upper surface and the surface of the first micro-holes. A pressure cavity height is etched on the exposed silicon surface at the bottom of the first micro-holes using DIE. Based on the anisotropic etching characteristics of N-type single-crystal silicon wafers, the wafer is immersed in 25% tetramethylammonium hydroxide etchant at 80°C for lateral etching. A cavity structure is formed by sacrificing the bare silicon along the orientation. First polysilicon is deposited into the first micro-holes to seal the pressure cavity. The deposited first tetraethyl orthosilicate layer and the first polysilicon are removed, and the silicon wafer is flattened.
[0021] Step 3: Fabricate a MEMS accelerometer on the back side of a silicon substrate;
[0022] In step 31, the N-type single crystal silicon wafer is inverted, and steps 21 and 22 are repeated on the lower surface hot-oxidized silicon dioxide layer to form a second silicon dioxide layer, a second lightly doped region of the second piezoresistive device and a second heavily doped region of the piezoresistive device, and a second silicon nitride layer is deposited using low-pressure chemical vapor deposition.
[0023] Step 32: Use photolithography and ion etching to form a cantilever beam and a central mass block. Form multiple rows of second micro-holes on the cantilever beam and the central mass block. Then, use the same method as in step 23 to release the cantilever beam and the central mass block.
[0024] Step 33: Fabricate through-silicon vias (TSVs) using deep reactive ion etching (DRIE), fabricate a second insulating layer using plasma-enhanced chemical vapor deposition (PECVD), and fabricate a barrier layer and a seed layer using physical vapor deposition (PEVD). Fill the vias with copper to form a through-hole containing a copper core. The copper core has TSV metal bumps on its upper and lower surfaces. Open the second metal contact area of the second piezoresistive device. At this time, sputter a metal layer on the lower surface of the silicon wafer and then pattern it to form a second metal lead. Connect the second metal lead and the lead wire to the TSV metal bumps on the upper and lower surfaces, respectively. Deposit a third silicon dioxide on the lower surface of the silicon wafer to make the silicon wafer flat.
[0025] Step 4: Fabricate the upper surface of the pressure sensor on the front side of the silicon substrate;
[0026] Specifically, the process involves etching the upper layer of the silicon wafer to form an upper isolated island structure, a peninsula structure, and a central boss structure; photolithography is then performed again to open the first metal contact hole area; a metal layer is sputtered onto the top of the silicon wafer; and then patterning and sintering are performed to form the first metal lead.
[0027] Step 5: Perform bonding connections and encapsulation on the back side of the silicon substrate.
[0028] Optionally, step 1 specifically includes: first cleaning and pre-baking the N-type monocrystalline silicon wafer, then performing double-sided thermal oxidation, and then forming an upper surface thermal oxidation silicon dioxide layer and a lower surface thermal oxidation silicon dioxide layer on the upper and lower surfaces of the N-type monocrystalline silicon wafer, respectively, as the front and back sides of the silicon substrate.
[0029] Optionally, step 5 specifically includes: removing the second insulating layer at the edge to expose the silicon wafer, then forming a glass cavity by anodic bonding with glass, and finally encapsulating and assembling it.
[0030] Another technical solution adopted by the present invention to solve its technical problem is:
[0031] A method for fabricating a monolithically integrated MEMS pressure and acceleration composite sensor includes the following steps:
[0032] Steps 1 through 5 are the same as described above;
[0033] Steps 21 and 22 in step 2 are the same as those described above, but step 23 is not included.
[0034] Step 31 in step 3 is as follows: Invert the N-type single crystal silicon wafer and use photomask lithography and deep reactive ion etching to form the basic shape of the cantilever beam and the central mass block; repeat the above steps 21 and 22 on the lower surface thermal oxygen silicon dioxide layer to form the second silicon dioxide layer, the second piezoresistive lightly doped region and the second piezoresistive heavily doped region of the MEMS accelerometer.
[0035] Step 32 is as follows: Multiple rows of second micro-holes are formed on the cantilever beam and the central mass block, and a second tetraethyl orthosilicate layer is deposited on the lower surface, the upper surface, and the surface of the second micro-holes. The exposed silicon surface at the bottom of the second micro-holes is etched using deep reactive ion etching. The second micro-holes on the mass block are etched downwards by a predetermined distance, and the cantilever beam is etched downwards by a predetermined distance. According to the anisotropic etching characteristics of N-type single crystal silicon wafers, the wafer is immersed in 25% tetramethylammonium hydroxide etchant at 80°C for lateral etching. The cantilever beam and the central mass block are released by sacrificing the bare silicon along the orientation. A second polycrystalline silicon is deposited into the second micro-holes to seal the pressure chamber. The deposited second tetraethyl orthosilicate layer and the second polycrystalline silicon are removed, and the silicon wafer is flattened.
[0036] Step 33 is the same as described above.
[0037] Optionally, step 31 may further include: etching a pattern on the back side of the silicon wafer after the cantilever beam and central mass block are formed.
[0038] Compared with existing technologies, the above two fabrication methods are applicable to sensor integration of various structures and have a certain degree of versatility. They realize the monolithic integration of multiple sensors in a vertical structure, and complete the composite fabrication of the sensor using only a single silicon wafer, without the need for multiple bonding connections between two sensors. The composite sensor obtained by this fabrication method is small in size, highly sensitive, and has good stability, and can be widely used in multiple fields such as automobiles, aerospace, and manufacturing. Attached Figure Description
[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0040] Figure 1 This is a front perspective view of a composite sensor according to Embodiment 1 of the present invention.
[0041] Figure 2 yes Figure 1 Sectional view at point AA.
[0042] Figure 3 This is a perspective view of the back of a composite sensor according to an embodiment 1 of the present invention.
[0043] Figures 4 to 12 This is a schematic diagram of the structure involved in each step of the preparation method of the composite sensor in Embodiment 1 of the present invention.
[0044] Figure 13 This is a cross-sectional view of the composite sensor at point AA in another embodiment of the present invention.
[0045] Explanation of the reference numerals in the figure:
[0046] 1-Silicon-based; 1-1-N-type monocrystalline silicon wafer; 1-2-Upper surface thermal oxidative silicon dioxide layer; 1-3-Lower surface thermal oxidative silicon dioxide layer; 1-4-Cavity structure;
[0047] 2-MEMS pressure sensor; 2-1-Multi-wing-shaped sensitive membrane; 2-2-Peninsula structure; 2-3-Island structure; 2-4-First piezoresistive device; 2-5-Central boss structure; 2-6-First silicon nitride layer; 2-7-First lightly doped piezoresistive region; 2-8-First heavily doped piezoresistive region; 2-9-First metal contact hole; 2-10-First silicon dioxide layer; 2-11-First micropore; 2-12-First tetraethyl orthosilicate layer; 2-13-First polycrystalline silicon; 2-14-First metal lead;
[0048] 3-MEMS accelerometer; 3-1-Cantilever beam; 3-2-Central mass block; 3-3-Cavity; 3-4-Second piezoresistive device; 3-5-Second piezoresistive lightly doped region; 3-6-Second piezoresistive heavily doped region; 3-7-Second silicon nitride layer; 3-8-Second silicon dioxide layer; 3-9-Second metal lead; 3-10-Third silicon dioxide layer; 3-11-Through hole containing copper core; 3-12-Lead wire;
[0049] 4-1-Glass; 4-2-Glass cavity. Detailed Implementation
[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. Example
[0051] Figures 1 to 12 The figure shows a structural schematic diagram of a preferred embodiment 1 of the present invention. A monolithically integrated MEMS pressure and acceleration composite sensor includes a MEMS pressure sensor and a MEMS acceleration sensor integrated through silicon-based vertical interconnects; the MEMS pressure sensor and the MEMS acceleration sensor are respectively arranged on two opposing working surfaces of the silicon substrate.
[0052] The MEMS pressure sensor is a piezoresistive sensor, comprising a multi-wing-shaped sensitive membrane formed on the upper surface of the silicon substrate. The surface of the multi-wing-shaped sensitive membrane has peninsula structures, island structures, and a central boss structure. Multiple peninsula structures and island structures are staggered around the outer periphery of the central boss structure and arranged symmetrically with the central boss structure as the center. A first piezoresistive device is disposed on the upper surface of each peninsula structure.
[0053] The MEMS accelerometer includes a multi-cantilever beam structure disposed on the lower surface of the silicon substrate. The multi-cantilever beam structure includes multiple cantilever beams formed by etching and a central mass block. There is a cavity between the cantilever beams and the central mass block. A second piezoresistive device is disposed on the upper surface of each cantilever beam.
[0054] In this embodiment 1, a cavity + membrane structure is provided between the MEMS pressure sensor and the MEMS acceleration sensor.
[0055] In this embodiment 1, the multi-wing sensitive membrane is configured as a four-wing sensitive membrane structure, which mainly consists of four symmetrical peninsula structures, four symmetrical island structures, and a central boss structure of uniform thickness. More specifically, the membrane length of the four-wing sensitive membrane structure is 3 mm, the membrane thickness is 25 μm, the thickness of the four symmetrical peninsula structures, the four island structures, and the central boss structure is uniformly 15 μm, and the width of the wing structures is 0.3 mm. This structure enables the MEMS pressure sensor to have high sensitivity and high reliability.
[0056] In this embodiment 1, the composite sensor has an overall centrally symmetrical structure. The MEMS pressure sensor and the MEMS accelerometer are arranged vertically and are located in the center of the silicon substrate. The MEMS accelerometer uses a vertical through-hole to lead out wires for easy packaging.
[0057] In this embodiment 1, the silicon substrate includes an N-type single crystal silicon wafer and an upper surface thermal oxygen silicon dioxide layer and a lower surface thermal oxygen silicon dioxide layer respectively disposed on its front and back surfaces. The MEMS pressure sensor and the MEMS acceleration sensor are respectively disposed on the upper surface thermal oxygen silicon dioxide layer and the lower surface thermal oxygen silicon dioxide layer.
[0058] Composite sensors are often used in automotive TPMS monitoring systems to sense the vehicle's motion status. Vertically integrated composite sensors will be used more effectively and with higher precision in automotive tire pressure monitoring systems as well as in aerospace and medical fields.
[0059] Meanwhile, this embodiment 1 also provides a method for fabricating a monolithic integrated MEMS pressure and acceleration composite sensor, including the following steps:
[0060] Step 1: Prepare silicon-based materials;
[0061] Specifically, the process involves first cleaning and pre-baking the N-type monocrystalline silicon wafer, then performing double-sided thermal oxidation, and finally forming an upper surface thermal oxidation silicon dioxide layer and a lower surface thermal oxidation silicon dioxide layer on the upper and lower surfaces of the N-type monocrystalline silicon wafer, respectively, to serve as the front and back sides of the silicon substrate.
[0062] Specifically, the N-type single crystal silicon wafer is an n-type (111) silicon wafer, and the thickness of the upper and lower surface hot-oxygen silicon dioxide layers is set to 1.5 μm.
[0063] Step 2: Fabricate the internal structure of the MEMS pressure sensor on the front side of the silicon substrate;
[0064] In step 21: the piezoresistive pattern of the first piezoresistive device is photolithographically formed, the upper surface thermal oxide silicon dioxide layer is wet-etched to expose the N-type single crystal silicon wafer, and the combination of boron ion implantation and thermal diffusion processes is performed sequentially to form the piezoresistive lightly doped region of the first piezoresistive device; rapid annealing is performed, and then the first silicon nitride layer is deposited using low-pressure chemical vapor deposition (LPCVD).
[0065] Step 22: The photomask is then etched to open the first metal contact hole, concentrated boron is injected to form the heavily doped piezoresistive region of the first piezoresistive device, and then the first silicon dioxide layer is deposited using LPCVD, which can be 0.5 μm thick.
[0066] Step 23: Using a photomask and deep reactive ion etching (DRIE), multiple rows of first micropores are formed on the surface of the first insulating layer, and a first tetraethyl orthosilicate (TEOS) layer is deposited on the upper surface and the surface of the first micropores. A pressure cavity height is etched on the exposed silicon surface at the bottom of the first micropores using the DRIE method. According to the anisotropic etching characteristics of N-type single-crystal silicon wafers (111), the wafer is immersed in 25% tetramethylammonium hydroxide etchant at 80°C for lateral etching, by sacrificing the edge <110> Oriented bare silicon to form a cavity structure; depositing first polycrystalline silicon into the first micropore to seal the pressure cavity, removing the deposited first tetraethyl orthosilicate layer and the first polycrystalline silicon, and flattening the silicon wafer.
[0067] More specifically, the height of the cavity structure can be set to 150 μm, and the first piezoresistive device is symmetrically distributed in... <211> and <110> Crystal orientation.
[0068] Step 3: Fabricate a MEMS accelerometer on the back side of a silicon substrate;
[0069] In step 31, the N-type single crystal silicon wafer is inverted, and steps 21 and 22 are repeated on the lower surface hot-oxidized silicon dioxide layer to form a second silicon dioxide layer, a second lightly doped region of the second piezoresistive device and a second heavily doped region of the piezoresistive device. A second silicon nitride layer is deposited using low-pressure chemical vapor deposition (LPCVD) and the thickness can be 0.5 μm.
[0070] Step 32: Use photolithography and ion etching to form a cantilever beam and a central mass block. Form multiple rows of second micro-holes on the cantilever beam and the central mass block. Then, use the same method as in step 23 to release the cantilever beam and the central mass block.
[0071] Step 33: Fabricate through-silicon vias (TSVs) using DRIE technology, with a diameter of up to 10 μm. Fabricate a second insulating layer using plasma-enhanced chemical vapor deposition (PECVD), and a barrier layer and seed layer using physical vapor deposition (PVD). Fill the vias with copper to form a through-hole containing a copper core. The copper core has through-silicon via metal bumps on its upper and lower surfaces. Open the second metal contact area of the second piezoresistive device. At this point, sputter a metal layer on the lower surface of the silicon wafer, then pattern it to form a second metal lead. Connect the second metal lead and the lead wire to the through-silicon via metal bumps on the upper and lower surfaces, respectively. Deposit a third silicon dioxide on the lower surface of the silicon wafer to make the wafer flat.
[0072] Step 4: Fabricate the upper surface of the pressure sensor on the front side of the silicon substrate;
[0073] Specifically, the process involves etching the upper layer of the silicon wafer to form an upper isolated island structure, a peninsula structure, and a central boss structure; photolithography is then performed again to open the first metal contact hole area; a metal layer is sputtered onto the top of the silicon wafer; and then patterning and sintering are performed to form the first metal lead.
[0074] Step 5: Perform bonding connections and encapsulation on the back side of the silicon substrate;
[0075] Specifically, the process involves removing the second insulating layer at the edge to expose the silicon wafer, then forming a glass cavity through anodic bonding with glass, followed by final encapsulation. The bonding glass can be 7740 glass. Example
[0076] exist Figure 13 In another embodiment 2 shown, a monolithic integrated MEMS pressure and acceleration composite sensor is provided. The structure is basically the same as that of embodiment 1. The only difference is that in this embodiment 2, a cavity structure is provided between the MEMS pressure sensor and the MEMS acceleration sensor, and the membrane structure in embodiment 1 is not present.
[0077] In this embodiment 2, a method for fabricating a monolithically integrated MEMS pressure and acceleration composite sensor is provided, including the following steps:
[0078] Step 1: Prepare silicon-based materials;
[0079] Specifically, the process involves first cleaning and pre-baking the N-type monocrystalline silicon wafer, then performing double-sided thermal oxidation, and finally forming an upper surface thermal oxidation silicon dioxide layer and a lower surface thermal oxidation silicon dioxide layer on the upper and lower surfaces of the N-type monocrystalline silicon wafer, respectively, to serve as the front and back sides of the silicon substrate.
[0080] Step 2: Fabricate the internal structure of the MEMS pressure sensor on the front side of the silicon substrate;
[0081] In step 21: the piezoresistive pattern of the first piezoresistive device is photolithographically formed, the upper surface thermal oxide silicon dioxide layer is wet-etched to expose the N-type single crystal silicon wafer, and the combination of boron ion implantation and thermal diffusion processes is performed sequentially to form the piezoresistive lightly doped region of the first piezoresistive device; rapid annealing is performed, and then the first silicon nitride layer is deposited using low-pressure chemical vapor deposition (LPCVD).
[0082] Step 22: The photomask is then etched to open the first metal contact hole, and concentrated boron is injected to form the heavily doped piezoresistive region of the first piezoresistive device. Then, the first silicon dioxide layer is deposited using LPCVD, which can be 0.5 μm thick.
[0083] Step 3: Fabricate a MEMS accelerometer on the back side of a silicon substrate;
[0084] In step 31, the N-type single crystal silicon wafer is inverted and the basic shape of the cantilever beam and the central mass block is formed by photolithography and deep reactive ion etching (DRIE). Steps 21 and 22 are repeated on the lower surface thermal oxide silicon dioxide layer to form the second silicon dioxide layer, the second piezoresistive light doped region and the second piezoresistive heavy doped region of the MEMS accelerometer.
[0085] Step 32: Form multiple rows of second micropores on the cantilever beam and the central mass block, and deposit a second tetraethyl orthosilicate layer on the lower surface, the upper surface, and the surface of the second micropores. Etch the exposed silicon surface at the bottom of the second micropores using the DRIE method. Continue etching the second micropores on the mass block downwards by a predetermined distance, and continue etching the cantilever beam downwards by a predetermined distance. According to the anisotropic etching characteristics of N-type single crystal silicon wafers, immerse the wafer in 25% tetramethylammonium hydroxide etchant at 80°C for lateral etching. By sacrificing the bare silicon along the orientation, the cantilever beam and the central mass block are released. Deposit a second polysilicon into the second micropores to seal the pressure chamber, remove the deposited second tetraethyl orthosilicate layer and the second polysilicon, and flatten the silicon wafer.
[0086] Step 33: Fabricate through-silicon vias (TSVs) using DRIE technology, with a diameter of up to 10 μm. Fabricate a second insulating layer using plasma-enhanced chemical vapor deposition (PECVD), and a barrier layer and seed layer using physical vapor deposition (PVD). Fill the vias with copper to form a through-hole containing a copper core. The copper core has through-silicon via metal bumps on its upper and lower surfaces. Open the second metal contact area of the second piezoresistive device. At this point, sputter a metal layer on the lower surface of the silicon wafer, then pattern it to form a second metal lead. Connect the second metal lead and lead wire to the through-silicon via metal bumps on the upper and lower surfaces, respectively. Deposit a third silicon dioxide on the lower surface of the silicon wafer to make the wafer flat.
[0087] Step 4: Fabricate the upper surface of the pressure sensor on the front side of the silicon substrate;
[0088] Specifically, the process involves etching the upper layer of the silicon wafer to form an upper isolated island structure, a peninsula structure, and a central boss structure; photolithography is then performed again to open the first metal contact hole area; a metal layer is sputtered onto the top of the silicon wafer; and then patterning and sintering are performed to form the first metal lead.
[0089] Step 5: Perform bonding connections and encapsulation on the back side of the silicon substrate;
[0090] Specifically, the process involves removing the second insulating layer at the edge to expose the silicon wafer, then forming a glass cavity through anodic bonding with glass, followed by final encapsulation. The bonding glass can be 7740 glass.
[0091] In summary, this embodiment 2 includes the same steps as embodiment 1, namely steps 1 to 5, 21, 22, and 33. It also includes steps different from embodiment 1: step 2 does not include step 23; and steps 31 and 32 in step 3 are different.
[0092] Furthermore, the advantage of Embodiment 2 over Embodiment 1 lies in the additional step that step 31 may further include: etching a pattern on the back side of the silicon wafer after the cantilever beam and central mass block are formed. Thus, Embodiment 2 achieves the unique function of selectively etching patterns on the back side of the sensitive film.
[0093] The above descriptions are merely two preferred embodiments of the present invention, and not all or only the embodiments. Two sensors can be fabricated separately and vertically connected using TSV technology and bonding, or the sensors can be integrated using parallel interconnection.
[0094] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications and equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.
Claims
1. A monolithically integrated MEMS pressure and acceleration composite sensor, comprising a MEMS pressure sensor and a MEMS acceleration sensor integrated via silicon-based vertical interconnects; characterized in that: The MEMS pressure sensor and the MEMS accelerometer are respectively arranged on two working surfaces opposite to each other on the silicon substrate. The MEMS pressure sensor is a piezoresistive sensor, comprising a multi-wing-shaped sensitive membrane formed on the upper surface of the silicon substrate. The surface of the multi-wing-shaped sensitive membrane has peninsula structures, island structures, and a central boss structure. Multiple peninsula structures and island structures are staggered around the outer periphery of the central boss structure and arranged symmetrically with the central boss structure as the center. A first piezoresistive device is disposed on the upper surface of each peninsula structure. The MEMS accelerometer includes a multi-cantilever beam structure disposed on the lower surface of the silicon substrate. The multi-cantilever beam structure includes multiple cantilever beams formed by etching and a central mass block. There is a cavity between the cantilever beams and the central mass block. A second piezoresistive device is disposed on the upper surface of each cantilever beam.
2. The monolithically integrated MEMS pressure and acceleration composite sensor according to claim 1, characterized in that: A cavity structure or a cavity + membrane structure is provided between the MEMS pressure sensor and the MEMS acceleration sensor.
3. The monolithically integrated MEMS pressure and acceleration composite sensor according to claim 2, characterized in that: The multi-wing sensitive membrane is designed as a four-wing sensitive membrane structure, which mainly consists of four symmetrical peninsula structures, four symmetrical island structures and a central boss structure of uniform thickness.
4. The monolithically integrated MEMS pressure and acceleration composite sensor according to claim 3, characterized in that: The composite sensor has an overall centrally symmetrical structure. The MEMS pressure sensor and the MEMS accelerometer are arranged vertically and are located in the center of the silicon substrate. The MEMS accelerometer uses a vertical through-hole to lead out wires.
5. A monolithically integrated MEMS pressure and acceleration composite sensor according to claim 1, 2, 3, or 4, characterized in that: The silicon substrate includes an N-type single-crystal silicon wafer and an upper surface thermal oxygen silicon dioxide layer and a lower surface thermal oxygen silicon dioxide layer respectively disposed on its front and back surfaces. The MEMS pressure sensor and the MEMS acceleration sensor are respectively disposed on the upper surface thermal oxygen silicon dioxide layer and the lower surface thermal oxygen silicon dioxide layer.
6. A method for fabricating a monolithically integrated MEMS pressure and acceleration composite sensor, characterized in that, Includes the following steps: Step 1: Silicon substrate preparation: First, clean and pre-baked N-type monocrystalline silicon wafers, then perform double-sided thermal oxidation. Next, form upper surface thermal oxidation silicon dioxide layer and lower surface thermal oxidation silicon dioxide layer on the upper and lower surfaces of the N-type monocrystalline silicon wafers, respectively, to serve as the front and back sides of the silicon substrate. Step 2: Fabricate the internal structure of the MEMS pressure sensor on the front side of the silicon substrate; In step 21: photolithography of the piezoresistive pattern of the first piezoresistive device, wet etching of the upper surface thermal oxygen silicon dioxide layer to expose the N-type single crystal silicon wafer, and sequential combination of boron ion implantation and thermal diffusion processes to form the first piezoresistive lightly doped region of the first piezoresistive device; rapid annealing, and then deposition of the first silicon nitride layer using low-pressure chemical vapor deposition. Step 22: The photolithography mask is then etched to open the first metal contact hole, concentrated boron is injected to form the piezoresistive heavily doped region of the first piezoresistive device, and then the first silicon dioxide layer is deposited using low-pressure chemical vapor deposition. Step 3: Fabricate a MEMS accelerometer on the back side of a silicon substrate; In step 31, the N-type single-crystal silicon wafer is inverted, and the basic shape of the cantilever beam and central mass block is formed using photolithography and deep reactive ion etching. Based on steps 311 and 312, a second silicon dioxide layer, a second lightly doped region of the second piezoresistive device, and a second heavily doped region of the piezoresistive device are formed on the lower surface using a thermally oxidized silicon dioxide layer. A second silicon nitride layer is then deposited using low-pressure chemical vapor deposition. Step 311: Photolithography of the piezoresistive pattern of the second piezoresistive device, wet etching of the lower surface thermal oxygen silicon dioxide layer to expose the N-type single crystal silicon wafer, and sequential combination of boron ion implantation and thermal diffusion processes to form the second piezoresistive lightly doped region of the second piezoresistive device; rapid annealing, and then deposition of the second silicon nitride layer using low-pressure chemical vapor deposition. Step 312: The photomask is then etched to open the second metal contact hole, concentrated boron is injected to form the heavily doped piezoresistive region of the second piezoresistive device, and then a second silicon dioxide layer is deposited using low-pressure chemical vapor deposition. Step 32: Form multiple rows of second micropores on the cantilever beam and the central mass block, and deposit a second tetraethyl orthosilicate layer on the lower surface and the surface of the second micropores. Etch the exposed silicon surface at the bottom of the second micropores using deep reactive ion etching. Continue etching the second micropores on the mass block downwards by a predetermined distance, and continue etching the cantilever beam downwards by a predetermined distance. Based on the anisotropic etching characteristics of N-type single-crystal silicon wafers, immerse the wafer in 25% tetramethylammonium hydroxide etchant at 80°C for lateral etching. By sacrificing the bare silicon along the orientation, the cantilever beam and the central mass block are released. Deposit a second polysilicon into the second micropores to seal the pressure chamber, remove the deposited second tetraethyl orthosilicate layer and the second polysilicon, and flatten the silicon wafer. Step 33: Fabricate through-silicon vias (TSVs) using deep reactive ion etching (DRIE) technology. Fabricate a second insulating layer using plasma-enhanced chemical vapor deposition (PECVD). Fabricate a barrier layer and a seed layer using physical vapor deposition (PECVD). Fill the TSVs with metallic copper to form a through-hole containing a copper core. The copper core has TSV metal bumps on its upper and lower surfaces. Open the second metal contact area of the second piezoresistive device. Sputter a metal layer on the lower surface of the silicon wafer and then pattern it to form a second metal lead. Connect the second metal lead and the lead wire to the TSV metal bumps on the upper and lower surfaces, respectively. Deposit a third silicon dioxide on the lower surface of the silicon wafer to make the silicon wafer flat. Step 4: Fabricate the upper surface of the pressure sensor on the front side of the silicon substrate; Specifically, the process involves etching the upper layer of the silicon wafer to form an upper isolated island structure, a peninsula structure, and a central boss structure; photolithography is then performed again to open the first metal contact hole area; a metal layer is sputtered on the top of the silicon wafer; and then patterning and sintering are performed to form the first metal lead. Step 5: Bond and encapsulate the silicon substrate on the back side.
7. The method for fabricating a monolithically integrated MEMS pressure and acceleration composite sensor according to claim 6, characterized in that, Step 31 also includes etching a pattern on the back of the silicon wafer after the cantilever beam and central mass block are formed.