A MEMS acceleration sensor and a manufacturing method thereof

Abstract

The application provides a MEMS acceleration sensor and a preparation method thereof. In the MEMS acceleration sensor, a mass block on a single crystal silicon substrate is connected with a base frame through a cantilever beam and is suspended in the base frame, a first comb set is connected with the side surface adjacent to the base frame of the mass block, and a second comb set is connected with the side surface adjacent to the mass block of the base frame. The cantilever beam comprises a piezoresistor, and a piezoresistor detection circuit is formed between the conductive lead wire on the base frame and the piezoresistor. The first comb set and the second comb set between the mass block and the base frame are used as a buffer to control the piezofilm damping between the mass block and the base frame, so that the dynamic characteristics and the high overload resistance of the MEMS acceleration sensor are improved. In addition, the temporary connection comb is arranged to connect the mass block and the base frame in the preparation process, the stress on the cantilever beam in the process is reduced, the preparation yield and the structural reliability are improved, and the process risk is reduced by the position of the temporary connection comb.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of silicon micro-mechanical sensor, and particularly relates to a MEMS acceleration sensor and a preparation method thereof. BACKGROUND

[0002] As one of the most important MEMS detection devices in the field of inertial sensors, MEMS acceleration sensors are widely used in the fields of aerospace, industrial production, automotive electronics, medical care and the like. With the increasing demand of the huge MEMS sensor market for the performance, cost and size of the acceleration sensor chip, and the continuous progress of the MEMS silicon-based micro-machining technology, the MEMS acceleration sensor with high performance, small size, low cost and high overload resistance has become the goal pursued by MEMS manufacturers and researchers.

[0003] The existing MEMS acceleration sensor is usually manufactured by double-sided silicon micro-machining. First, KOH is used to thin the silicon wafer from the back side of the single crystal silicon wafer by secondary wet etching to form a single crystal silicon layer with different thicknesses, which are used to process cantilever beams and mass block structures respectively; then, a pressure-sensitive resistor and a wire interconnection are manufactured on the front side of the silicon wafer; next, a sensor support structure is formed by silicon-glass (or silicon-silicon) bonding; finally, the cantilever beam and the mass block structure are etched and released from the front side of the silicon wafer. The MEMS acceleration sensor prepared by this method has the following disadvantages: (1) the cantilever beam is prepared by large-area wet etching and thinning of the silicon wafer from the back side of the silicon wafer using KOH etching solution, which is affected by the 54.75° angle between the (100) crystal plane and the (111) crystal plane in the (100) silicon wafer, so that the chip size is large and the etching time is too long, and the etching depth consistency is not easy to control, which affects the consistency of the product; (2) the sensor support structure is prepared by bonding process, and different bonding materials will introduce thermal mismatch stress due to the difference in thermal expansion coefficient, which affects the detection accuracy of the sensor; even if silicon-silicon bonding is used, the high-temperature bonding process will also introduce residual stress, which affects the detection accuracy and long-term stability of the sensor; (3) the manufacturing process is relatively complex, the manufacturing cost is high, and the process is not compatible with the standard semiconductor process of IC.

[0004] To solve the above problems, in 2012, Wang Jiachao et al. of the Shanghai Institute of Microsystem and Information Technology of the Chinese Academy of Sciences developed a single-silicon single-sided integrated acceleration and pressure detection TPMS composite sensor chip, in which the cantilever beam and mass block structure of the acceleration sensor are directly processed by single-sided silicon technology, and the sensitivity of the sensor is improved by electroplating high-density copper mass block on the single crystal silicon film [J. Wang, X. Xia, and X. Li, "Monolithic Integration of Pressure Plus Acceleration Composite TPMS Sensors With a Single-Sided Micromachining Technology," Journal of Microelectromechanical Systems, vol. 21, no. 2, pp. 284-293, 2012]. Although the MEMS acceleration sensor prepared by this method has the characteristics of small chip size and low manufacturing cost, it also has the following shortcomings: (1) The residual stress introduced by the thermal mismatch between the copper mass block and the single crystal silicon will cause the sensor temperature characteristics to be very poor, and even the copper mass block will fall off; (2) The film damping in the motion direction of the sensor sensitive unit is difficult to control, and it is difficult to improve the dynamic characteristics of the sensor and the anti-overload capability is limited.

[0005] In 2015, Wang Jiachao et al. proposed a single-silicon single-sided manufacturing technology of silicon-based three-dimensional micro mechanical structure, and based on this technology, a "single crystal silicon cantilever beam + single crystal silicon mass block structure" MEMS acceleration sensor was processed [J. Wang and X. Li, "Single-Side Fabrication of Multilevel 3-D Microstructures for Monolithic Dual Sensors," Journal of Microelectromechanical Systems, vol. 24, no. 3, pp. 531-533, 2015.], which solved the problem of using electroplated high-density copper mass block to improve the sensitivity of the acceleration sensor developed by the team in 2012. However, the manufacturing process in this scheme is relatively complex, and the problem of difficult control of film damping in the motion direction of the sensor sensitive unit and limited anti-overload capability has not been solved, thereby hindering the high-performance development of high-sensitivity MEMS acceleration sensors.

[0006] In view of the above-mentioned shortcomings of the prior art, it is necessary to design a new acceleration sensor and its manufacturing method to solve the above-mentioned problems.

[0007] It should be noted that the above introduction to the technical background is only for the convenience of clearly and completely describing the technical scheme of the present application and facilitating the understanding of those skilled in the art, and the above technical scheme cannot be considered as known to those skilled in the art only because it is described in the part of the background of the present application. SUMMARY

[0008] In view of the above disadvantages of the prior art, the purpose of the present application is to provide a MEMS acceleration sensor and a preparation method thereof, which are used to solve the problems of difficult control of film damping and limited high overload resistance of the MEMS acceleration sensor in the prior art.

[0009] To achieve the above purpose, the present application provides a MEMS acceleration sensor, which comprises a single crystal silicon substrate and a conductive lead.

[0010] The single crystal silicon substrate comprises the acceleration sensitive unit and the base frame on the first surface, the acceleration sensitive unit comprises a mass block, a cantilever beam, a first comb tooth group and a second comb tooth group; the mass block is connected with the base frame through the cantilever beam and is suspended in the base frame, movable bottom surface gaps exist between the mass block and the bottom surface of the base frame close to the base frame, and movable side surface gaps exist between the side surface of the mass block close to the base frame and the side surface of the cantilever beam close to the base frame and not connected with the base frame.

[0011] The two ends of the side surface of the mass block adjacent to the base frame along the direction in which the cantilever beam extends are connected with the first comb tooth group, the two ends of the side surface of the base frame adjacent to the mass block along the direction in which the cantilever beam extends are connected with the second comb tooth group, and the adjacent first comb tooth group and the second comb tooth group are arranged in an interlaced manner and have a preset distance buffer gap.

[0012] The cantilever beam comprises a piezoresistor, the conductive lead is fixed on the base frame, and a piezoresistor detection circuit is formed between the conductive lead and the piezoresistor.

[0013] Optionally, the cantilever beam comprises oppositely arranged first and second ends, the first end of the cantilever beam is connected with the mass block, the second end of the cantilever beam is connected with the base frame, and the piezoresistor is located at the first end of the cantilever beam.

[0014] Optionally, the single crystal silicon substrate is a single crystal silicon substrate with a (111) crystal surface.

[0015] Optionally, the single crystal silicon substrate is an N-type silicon substrate or a P-type silicon substrate.

[0016] Optionally, the resistivity of the single crystal silicon substrate is greater than or equal to 1 Ω·cm and less than or equal to 10 Ω·cm.

[0017] The application further provides a preparation method of a MEMS acceleration sensor, which is used for preparing any of the MEMS acceleration sensors, and comprises the following steps:

[0018] providing a single crystal silicon wafer;

[0019] disposing a piezoresistor in the single crystal silicon wafer close to a first surface;

[0020] disposing a stop layer on the first surface of the single crystal silicon wafer;

[0021] patterning the stop layer to obtain a pattern of a lead hole and a temporary connecting comb tooth at a preset position of the piezoresistor;

[0022] disposing a first barrier layer on the stop layer, the first barrier layer covering a surface of the stop layer and filling a gap of the patterned stop layer;

[0023] patterning the first barrier layer, the stop layer and the single crystal silicon wafer to obtain a first pattern groove corresponding to a pattern of a base frame, a cantilever beam, a mass block, a first comb tooth group and a second comb tooth group;

[0024] covering all surfaces exposed by the first pattern groove with a second barrier layer;

[0025] removing the second barrier layer at the bottom of the first pattern groove and continuing to etch the single crystal silicon wafer downward by a preset depth;

[0026] etching the single crystal silicon wafer of the preset depth exposed by the bottom of the first pattern groove in a direction parallel to the first surface with the second barrier layer as a mask to release a connection between the bottom surface of the mass block and the cantilever beam and the base frame;

[0027] removing the first barrier layer and the second barrier layer to expose the pattern of the lead hole and the temporary connecting comb tooth in the stop layer;

[0028] disposing a conductive lead on the surface of the structure obtained so far, the conductive lead filling the lead hole and electrically connecting with the piezoresistor to form a piezoresistor detection circuit;

[0029] removing the temporary connecting comb tooth so that the mass block is connected with the base frame only through the cantilever beam.

[0030] Optionally, before disposing the piezoresistor, a first passivation layer is disposed on the first surface of the single crystal silicon wafer, and the stop layer is disposed on the first passivation layer.

[0031] Optionally, the etching stop layer is low-stress silicon nitride; and / or, the first barrier layer and / or the second barrier layer is a TEOS passivation layer.

[0032] Optionally, before the temporary connecting comb teeth are removed, one of the mass blocks is connected to the base frame by two or more temporary connecting comb teeth.

[0033] Optionally, the temporary connecting comb teeth are symmetrically distributed on both sides of the cantilever beam away from the cantilever beam.

[0034] As described above, the MEMS acceleration sensor and the preparation method thereof have the following beneficial effects:

[0035] By arranging the first comb group and the second comb group to be interlaced between the mass block and the base frame as a buffer, the film damping formed between the mass block and the base frame in the direction of sensor movement when acceleration exists can be controlled, thereby improving the dynamic characteristics of the MEMS acceleration sensor.

[0036] By the buffering of the first comb group and the second comb group, the risk of deformation and fracture of the cantilever beam caused by excessive acceleration of the mass block is reduced, and the high overload resistance of the MEMS acceleration sensor is improved.

[0037] By arranging the temporary connecting comb teeth to connect the mass block and the base frame during the preparation of the MEMS acceleration sensor, the risk of fracture of the cantilever beam caused by excessive thermal mismatch stress of different materials during the process of releasing the mass block and the cantilever beam by wet etching, and the inconsistency of the thickness of the photoresist coated during the subsequent preparation of the conductive lead after the mass block and the cantilever beam are released, are reduced, and the preparation yield and structural reliability are improved.

[0038] By arranging the temporary connecting comb teeth near the symmetric position of the cantilever beam, the risk of adverse effects of the cantilever beam during the preparation process is further reduced. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 A perspective view schematic diagram of the MEMS acceleration sensor in the present application is shown.

[0040] Figure 2 A partial cross-sectional perspective view schematic diagram of the MEMS acceleration sensor in the present application is shown.

[0041] Figure 3 A structure side cross-sectional view schematic diagram of a single crystal silicon wafer including a first passivation layer in step 1 of the preparation method of the MEMS acceleration sensor in the present application is shown.

[0042] Figure 4 A structure side sectional view diagram showing the structure in step 2 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0043] Figure 5 A structure side sectional view diagram showing the structure in step 3 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0044] Figure 6 A structure side sectional view diagram showing the structure in step 4 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0045] Figure 7 A structure side sectional view diagram showing the structure in step 5 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0046] Figure 8 A structure side sectional view diagram showing the structure in step 6 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0047] Figure 9 A structure side sectional view diagram showing the structure in step 7 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0048] Figure 10 A structure side sectional view diagram showing the structure in step 8 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0049] Figure 11 A structure side sectional view diagram showing the structure in step 9 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0050] Figure 12 A structure side sectional view diagram showing the structure in step 10 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0051] Figure 13 A structure side sectional view diagram showing the structure in step 11 of the method for manufacturing the MEMS acceleration sensor of the present application.

[0052] Explanation of element reference numerals

[0053] 10, MEMS acceleration sensor; 11, base frame; 12, mass; 13, cantilever beam; 14, first comb-tooth group; 15, second comb-tooth group; 16, piezoresistor; 17, conductive lead; 18, pad;

[0054] 21. Movable bottom surface clearance; 22. Movable side surface clearance; 23. Buffer clearance;

[0055] 31. Monocrystalline silicon wafer; 32. First passivation layer; 33. Marking stop layer; 34. Lead hole; 35. First barrier layer; 36. First patterned groove; 37. Second barrier layer; 38. Preset depth. Detailed Implementation

[0056] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand 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, and 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.

[0057] In the detailed description of embodiments of the present invention, for ease of explanation, the schematic diagrams illustrating the device structure may be partially enlarged without adhering to the general scale, and the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. Furthermore, in actual manufacturing, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0058] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the accompanying drawings for devices in use or operation.

[0059] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0060] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0061] In the prior art, the MEMS acceleration sensor 10 is difficult to control the squeeze film damping between the mass block 12 and the base frame 11 in the motion direction, and the improvement of the overload capacity is also limited; especially in the process of realizing a MEMS acceleration sensor 10 with higher sensitivity, a larger mass block 12 and a thinner cantilever beam 13 are needed, which leads to greater squeeze film damping between the mass block 12 and the base frame 11 during the movement of the mass block 12, and greater stress on the cantilever beam 13, so that the cantilever beam 13 is more likely to deform or break, affecting the measurement accuracy and reliability of the MEMS acceleration sensor 10, and therefore the overload capacity is further limited, which is not conducive to the current application requirements of miniaturization, high sensitivity and high performance of the MEMS acceleration sensor 10.

[0062] The application provides a MEMS acceleration sensor 10, as shown in the drawings, Figures 1-2 The application provides a MEMS acceleration sensor 10, as shown in the drawings, Figure 1 The application provides a MEMS acceleration sensor 10, as shown in the drawings, Figure 2 The application provides a MEMS acceleration sensor 10, as shown in the drawings, Figure 2 The application provides a MEMS acceleration sensor 10, as shown in the drawings, Figure 1 The application provides a MEMS acceleration sensor 10, as shown in the drawings,

[0063] The single crystal silicon substrate includes the acceleration sensitive unit and the base frame 11 on the first surface, the acceleration sensitive unit includes the mass block 12, the cantilever beam 13, the first comb tooth group 14 and the second comb tooth group 15; the mass block 12 is connected with the base frame 11 through the cantilever beam 13 and is suspended in the base frame 11, and movable bottom surface gaps 21 exist between the mass block 12 and the bottom surface of the base frame 11 close to the base frame 11, and movable side surface gaps 22 exist between the mass block 12 and the base frame 11 close to the side surface of the base frame 11 and the side surface of the cantilever beam 13 close to the base frame 11 and not connected with the base frame 11;

[0064] The side surface of the mass block 12 adjacent to the base frame 11 is connected with the first comb tooth group 14 at both ends along the extension direction of the cantilever beam 13, the side surface of the base frame 11 adjacent to the mass block 12 is connected with the second comb tooth group 15 at both ends along the extension direction of the cantilever beam 13, and the adjacent first comb tooth group 14 and the second comb tooth group 15 are arranged in a staggered manner and have a preset distance buffer gap 23;

[0065] The cantilever beam 13 includes a piezoresistor 17, the conductive lead 17 is fixed on the base frame 11, and a piezoresistor detection circuit is formed between the conductive lead 17 and the piezoresistor 17.

[0066] The present application can control the squeeze film damping formed between the mass 12 and the base frame 11 in the direction of sensor motion when acceleration exists within a certain range by setting the first comb tooth group 14 and the second comb tooth group 15 interlaced between the mass 12 and the base frame 11 as a buffer, thereby improving the dynamic characteristics of the MEMS acceleration sensor 10; at the same time, the first comb tooth group 14 and the second comb tooth group 15 can reduce the risk of deformation and fracture of the cantilever beam 13 caused by excessive acceleration of the mass 12, thereby improving the high overload resistance of the MEMS acceleration sensor 10 and facilitating the performance improvement of the MEMS acceleration sensor 10 in terms of miniaturization and high sensitivity.

[0067] In one embodiment, as shown in Figures 1-2 The cantilever beam 13 includes oppositely arranged first and second ends, the first end of the cantilever beam 13 is connected with the mass 12, the second end of the cantilever beam 13 is connected with the base frame 11, and the piezoresistor 17 is located at the first end of the cantilever beam 13.

[0068] The present application can maximize the deformation of the cantilever beam 13 to reflect on the resistance change of the piezoresistor 17, thereby maximizing the sensitivity of the MEMS acceleration sensor 10.

[0069] Preferably, the single crystal silicon substrate is a (111) crystal plane single crystal silicon substrate.

[0070] The present application can perform a process compatible with a semiconductor process on a single surface of the first surface, thereby realizing the preparation of the MEMS acceleration sensor 10 with simple manufacturing process, low cost and suitability for mass production, and facilitating the miniaturization of the MEMS acceleration sensor 10.

[0071] Preferably, as shown in Figure 1 The cantilever beam 13 and the mass 12 are arranged along the <211> crystal direction.

[0072] The present application can maximize the etching speed of the single crystal silicon substrate when manufacturing the cantilever beam 13 and the mass 12, thereby further improving the preparation efficiency of the MEMS acceleration sensor 10.

[0073] Preferably, the single crystal silicon substrate is an N-type silicon substrate.

[0074] The application uses an N-shaped silicon substrate as a single-crystal silicon substrate for manufacturing a MEMS acceleration sensor 10, and utilizes the smaller piezoresistive coefficient of the N-shaped silicon substrate to achieve higher sensitivity of the MEMS acceleration sensor 10.

[0075] In one embodiment, the single-crystal silicon substrate is a P-type silicon substrate.

[0076] Preferably, the resistivity of the single-crystal silicon substrate is greater than or equal to 1 Ω·cm and less than or equal to 10 Ω·cm.

[0077] The application sets the resistivity range of the single-crystal silicon substrate to ensure that the resistivity of the single-crystal silicon substrate can facilitate the preparation of the piezoresistor 17, while avoiding excessive heat dissipation, thermal noise, signal noise, working voltage, and other performance indicators of the MEMS acceleration sensor 10.

[0078] In one embodiment, the acceleration-sensitive unit includes one mass block 12 and one cantilever beam 13, and the cantilever beam 13 includes one piezoresistor 17, and the piezoresistor 17 forms a piezoresistor detection circuit through the conductive lead 17.

[0079] In one embodiment, the acceleration-sensitive unit includes one mass block 12 and one cantilever beam 13, and the cantilever beam 13 includes two piezoresistors 17, and the two piezoresistors 17 form a Wheatstone half-bridge detection circuit through the conductive lead 17.

[0080] In one embodiment, as shown in Figures 1-2 the acceleration-sensitive unit includes two mass blocks 12 and two cantilever beams 13, each of the cantilever beams 13 includes two piezoresistors 17, and the four piezoresistors 17 form a Wheatstone full-bridge detection circuit through the conductive lead 17.

[0081] Specifically, the acceleration-sensitive unit can also set other numbers of mass blocks 12, cantilever beams 13, and piezoresistors 17 according to application requirements to balance the performance requirements of the volume and sensitivity of the MEMS acceleration sensor 10.

[0082] In one embodiment, as shown in Figures 1-2 the MEMS acceleration sensor 10 further includes a pad 18, and the pad 18 is electrically connected with a preset position of the conductive lead 17 to lead out the input end and the output end of the piezoresistor detection circuit to a welding point.

[0083] Specifically, the larger area of the pad 18 is conducive to improving the reliability of the electrical connection between the conductive lead 17 and the outside world, thereby improving the reliability of the MEMS acceleration sensor 10.

[0084] In one embodiment, the first surface of the MEMS acceleration sensor 10 is not provided with the conductive lead 17, the pad 18, the movable side gap 22, and the surface of the buffer gap 23, and the surface of each of the first passivation layer 32 described in the following preparation method, and the surface of the first passivation layer 32 is provided with the stop layer 33, and the first passivation layer 32 and the stop layer 33 are reserved in the preparation process to protect the surface of the MEMS acceleration sensor 10 to reduce the risk of yield or reliability decline caused by external influences.

[0085] The application also provides a preparation method of a MEMS acceleration sensor 10, which is used to prepare any one of the MEMS acceleration sensors 10 described above, and the preparation method comprises the following steps:

[0086] Step 1: providing a single crystal silicon wafer 31;

[0087] Step 2: providing a piezoresistor 17 near the first surface in the single crystal silicon wafer 31;

[0088] Step 3: providing a stop layer 33 on the first surface of the single crystal silicon wafer 31;

[0089] Step 4: patterning the stop layer 33 to obtain a pattern of a lead hole 34 exposing the piezoresistor 17 and a temporary connection comb tooth at a predetermined position;

[0090] Step 5: providing a first barrier layer 35 on the stop layer 33, the first barrier layer 35 covering the surface of the stop layer 33 and filling the voids of the patterned stop layer 33;

[0091] Step 6: patterning the first barrier layer 35, the stop layer 33, and the single crystal silicon wafer 31 to obtain a first pattern groove 36 corresponding to the patterns of the base frame 11, the cantilever beam 13, the mass block 12, the first comb tooth group 14, and the second comb tooth group 15;

[0092] Step 7: covering all the surfaces exposed by the first pattern groove 36 with a second barrier layer 37;

[0093] Step 8: removing the second barrier layer 37 at the bottom of the first pattern groove 36 and continuing to etch the single crystal silicon wafer 31 to a predetermined depth 38;

[0094] Step 9: etching the single crystal silicon wafer 31 exposed by the first pattern groove 36 to the predetermined depth 38 in a direction parallel to the first surface with the second barrier layer 37 as a mask to release the connection between the bottom surface of the mass block 12 and the cantilever beam 13 and the base frame 11;

[0095] Step 10: removing the first barrier layer 35 and the second barrier layer 37 to expose the pattern of the lead hole 34 and the temporary connecting comb tooth in the stop layer 33;

[0096] Step 11: providing the conductive lead 17 on the surface of the structure obtained so far, the conductive lead 17 filling the lead hole 34 and electrically connecting with the pressure sensitive resistor 17 to form a pressure sensitive resistor detection circuit;

[0097] Step 12: removing the temporary connecting comb tooth so that the mass 12 is connected with the base frame 11 only through the cantilever beam 13.

[0098] The preparation method of the MEMS acceleration sensor 10 of the present application will be described in detail below with reference to the accompanying drawings, and it should be noted that the above sequence does not strictly represent the preparation method sequence of the MEMS acceleration sensor 10 protected by the present application, and those skilled in the art can change it according to the actual preparation steps.

[0099] First, step 1 is performed, as shown in Figure 3 , a single crystal silicon wafer 31 is provided.

[0100] In one embodiment, after step 1, as shown in Figure 3 , a first passivation layer 32 is provided on the first surface of the single crystal silicon wafer 31 before the pressure sensitive resistor 17 is provided; in step 3, the stop layer 33 is provided on the first passivation layer 32.

[0101] In one embodiment, the first passivation layer 32 is silicon dioxide.

[0102] In one embodiment, when the first passivation layer 32 is silicon dioxide, the thickness of the silicon dioxide is 2000 angstroms.

[0103] In one embodiment, the silicon dioxide as the first passivation layer 32 is obtained by thermal oxidation on the first surface of the single crystal silicon wafer 31.

[0104] The present application obtains silicon dioxide as the first passivation layer 32 by thermal oxidation, so that the obtained first passivation layer 32 has a dense structure and better passivation protection effect.

[0105] Specifically, the first passivation layer 32 can also use other suitable passivation layer materials.

[0106] Then, step 2 is performed, as shown in Figure 4 , the pressure sensitive resistor 17 is provided in the single crystal silicon wafer 31 near the first surface.

[0107] In one embodiment, the pressure sensitive resistor 17 is provided in the single crystal silicon wafer 31 near the first surface by ion implantation.

[0108] In one embodiment, a varistor 17 is disposed within the monocrystalline silicon wafer 31 near the first surface using a diffusion method.

[0109] In one embodiment, the varistor 17 is disposed within the monocrystalline silicon wafer 31 using a boron diffusion method.

[0110] In one embodiment, before setting the varistor 17, a first passivation layer 32 is formed on the first surface of the monocrystalline silicon wafer 31. Before setting the varistor 17, photoresist is applied to the first passivation layer 32, and then photolithography and etching are performed to expose the position of the varistor 17 on the first surface of the monocrystalline silicon wafer 31, so as to set the varistor 17. After setting the varistor 17, the photoresist is removed, and then an annealing process is performed.

[0111] Next, proceed to step 3, as follows: Figure 5 As shown, a stop-mark layer 33 is provided on the first surface of the single-crystal silicon wafer 31.

[0112] In one embodiment, the stop layer 33 is low-stress silicon nitride.

[0113] This invention uses low-stress silicon nitride as the stop layer 33 to reduce structural deformation, cracks and other defects caused by large stress between different layers due to temperature changes during the fabrication process, which is beneficial to improving the reliability of the MEMS accelerometer sensor 10 fabrication process. At the same time, the use of silicon nitride can avoid unevenness on the surface of the single crystal silicon wafer 31 under the stop layer 33 during the subsequent etching process, thus avoiding affecting the sensing accuracy of the MEMS accelerometer sensor 10.

[0114] In one embodiment, the stop layer 33 is low-stress silicon nitride, deposited using LPCVD (Low Pressure Chemical Vapor Deposition).

[0115] Then, proceed to step 4, as follows: Figure 6 As shown, the stop mark layer 33 is graphically represented to obtain a graphic showing the lead hole 34 of the varistor 17 and the temporary connection comb teeth at a preset position (not shown in the figure, but it is also in the graphical stop mark layer 33 and the first passivation layer 32, but not on the same cross-section as the lead hole 34).

[0116] Specifically, in this embodiment, the temporary connecting comb teeth and the lead wire hole 34 are not on the same cross-section. In actual practice, the temporary connecting comb teeth can also be on the same cross-section as the lead wire hole 34, and can be set according to actual needs.

[0117] In one embodiment, photoresist is first applied to the stop layer 33, then photolithography is performed to obtain patterned photoresist, and then the stop layer 33 is wet-etched by RIE (Reactive Ion Etching) or BOE (Buffered Oxide Etch).

[0118] In one embodiment, such as Figure 6 As shown, when a first passivation layer 32 is provided under the stop mark layer 33, the stop mark layer 33 and the first passivation layer 32 under the stop mark layer 33 are etched by RIE or BOE to expose the pattern of the varistor 17 and the temporary connection comb teeth.

[0119] This invention reduces the risk of cantilever beam 13 fracture due to excessive thermal mismatch stress between different materials during the wet etching process of releasing mass block 12 and cantilever beam 13, by setting a temporary connecting comb tooth connection between the mass block 12 and the substrate frame 11 during the fabrication of MEMS accelerometer 10. It also reduces the risk of cantilever beam 13 deformation and fracture due to inconsistent photoresist thickness during the fabrication of subsequent conductive leads 17 after the release of mass block 12 and cantilever beam 13. In particular, it plays a protective role in the fabrication process of the thinner cantilever beam 13 in the high-sensitivity MEMS accelerometer 10, thereby improving the fabrication yield and structural reliability.

[0120] Specifically, when patterning the stop layer 33 with photoresist, after patterning the first passivation layer 32, the remaining photoresist is removed.

[0121] Next, proceed to step 5, as follows: Figure 7 As shown, a first barrier layer 35 is provided on the stop mark layer 33, the first barrier layer 35 covers the surface of the stop mark layer 33 and fills the gaps of the patterned stop mark layer 33.

[0122] In one embodiment, the first barrier layer 35 is a TEOS (Tetraethoxysilane) passivation layer.

[0123] Specifically, the TEOS passivation layer serves as a protective barrier during the subsequent etching of the lead hole 34.

[0124] In one embodiment, the first barrier layer 35 is deposited using LPCVD.

[0125] In one embodiment, the thickness of the first barrier layer 35 is set to 10,000 angstroms.

[0126] Then, proceed to step 6, as follows: Figure 8As shown, the first blocking layer 35, the etching-stop layer 33 and the single crystal silicon wafer 31 are patterned to obtain the first patterned grooves 36 corresponding to the patterns of the base frame 11, the cantilever beam 13, the mass 12, the first comb-tooth group 14 and the second comb-tooth group 15.

[0127] Specifically, as shown in FIG. 4, the first patterned grooves 36 are formed on the first blocking layer 35, the etching-stop layer 33 and the single crystal silicon wafer 31. Figure 8 As shown, the first patterned grooves 36 connect the mass 12 to the base frame 11 through the cantilever beam 13, and the temporary connecting comb teeth, and movable side gaps 22 exist between the side of the mass 12 close to the base frame 11 and the base frame 11, and between the side of the cantilever beam 13 close to the base frame 11 and the base frame 11; the first comb-tooth group 14 is connected to both ends of the side of the mass 12 adjacent to the base frame 11 along the extending direction of the cantilever beam 13, and the second comb-tooth group 15 is connected to both ends of the side of the base frame 11 adjacent to the mass 12 along the extending direction of the cantilever beam 13, and the first comb-tooth group 14 and the second comb-tooth group 15 are staggered and have a preset distance buffer gap 23.

[0128] In one embodiment, after the first blocking layer 35 is coated with photoresist, the first patterned grooves 36 are obtained by photoetching; the first blocking layer 35, the etching-stop layer 33 and the first passivation layer 32 are patterned by RIE using the patterned photoresist as a mask, and the first surface of the single crystal silicon wafer 31 is exposed; then, the first surface of the single crystal silicon wafer 31 is etched by DRIE (Deep Reactive Ion Etching) to obtain the patterns of the base frame 11, the cantilever beam 13, the mass 12, the first comb-tooth group 14 and the second comb-tooth group 15; the depth of DRIE etching is the thickness of the cantilever beam 13, the mass 12, the first comb-tooth group 14 and the second comb-tooth group 15.

[0129] Next, step 7 is performed, as shown in FIG. 6, the second blocking layer 37 is coated on all the surfaces exposed by the first patterned grooves 36. Figure 9

[0130] In one embodiment, the second blocking layer 37 is a TEOS passivation layer.

[0131] Specifically, the second blocking layer 37 serves as a mask for subsequent downward etching of the single crystal silicon wafer 31.

[0132] In one embodiment, the thickness of the second blocking layer 37 is set to 4000 angstroms.

[0133] ​The present application uses TEOS passivation layer as the first barrier layer 35 and the second barrier layer 37, which makes the operation more convenient and faster when removing the remaining first barrier layer 35 and the second barrier layer 37, thereby further improving the process efficiency.

[0134] Then, step 8 is performed, as shown in FIG. 8, the second barrier layer 37 at the bottom of the first patterned groove 36 is removed and the first surface of the single crystal silicon wafer 31 exposed at the bottom of the first patterned groove 36 is etched down to a preset depth 38. Figure 10

[0135] In one embodiment, the RIE dry etching is used to remove the second barrier layer 37 at the bottom of the first patterned groove 36, and the first surface of the single crystal silicon wafer 31 at the bottom of the first patterned groove 36 is exposed.

[0136] In one embodiment, the DRIE etching is used to etch the exposed first surface of the single crystal silicon wafer 31 to a preset depth 38.

[0137] Specifically, the preset depth 38 is the thickness of the sacrificial layer used to release the connection between the mass block 12, the cantilever beam 13 and the base frame 11; after the second barrier layer 37 at the bottom of the first patterned groove 36 is etched, the second barrier layer 37 can be used as a mask to etch only the first surface of the single crystal silicon wafer 31 exposed at the bottom of the first patterned groove 36, and only the position of the single crystal silicon wafer 31 etched to the preset depth 38 will be etched by the solution used in step 9 in the direction parallel to the first surface, while the sidewall above the preset depth 38 is shielded by the second barrier layer 37 and is not etched, thereby releasing the connection between the bottom surface of the mass block 12 and the cantilever beam 13 and the base frame 11.

[0138] In one embodiment, the preset depth 38 is 10 microns.

[0139] Next, step 9 is performed, as shown in FIG. 9, the second barrier layer 37 is used as a mask to etch the single crystal silicon wafer 31 exposed at the bottom of the first patterned groove 36 to a preset depth 38 in the direction parallel to the first surface, thereby releasing the connection between the bottom surface of the mass block 12 and the cantilever beam 13 and the base frame 11. Figure 11

[0140] Specifically, the connection between the bottom surface of the mass block 12 and the cantilever beam 13 and the base frame 11 is released, so that a movable bottom surface gap 21 is formed between the bottom surface of the mass block 12 and the cantilever beam 13 and the base frame 11, and the mass block 12 is suspended in the base frame 11 through the cantilever beam 13 and the temporary connection comb.

[0141] ​​In one embodiment, a TMAH (Tetramethylammonium hydroxide) solution is used to perform a wet etching on the exposed sacrificial layer of the single crystal silicon wafer 31 to a preset depth 38 in a direction parallel to the first surface, so as to release the connection between the mass 12 and the base frame 11.

[0142] Specifically, after the connection between the mass 12 and the base frame 11 is released, the connection between the mass 12, the cantilever beam 13 and the base frame 11 in a direction perpendicular to the first surface is released, so as to obtain the movable bottom surface gap 21.

[0143] Then, step 10 is performed, as shown in Figure 12 The first barrier layer 35 and the second barrier layer 37 are removed, and the pattern of the lead hole 34 and the temporary connection comb tooth in the stop etching layer 33 are exposed.

[0144] Next, step 11 is performed, as shown in Figure 13 The conductive lead 17 is arranged on the surface of the structure obtained so far, the conductive lead 17 fills the lead hole 34 and is electrically connected with the piezoresistor 17 to form a piezoresistor detection circuit.

[0145] In one embodiment, the method of arranging the conductive lead 17 is to sputter a metal aluminum thin film and then perform a patterning process.

[0146] In one embodiment, the thickness of the metal aluminum thin film is 10000 angstroms.

[0147] In one embodiment, when the MEMS acceleration sensor 10 further includes a pad 18, the pad 18 can be formed at the same time when the metal is sputtered and patterned.

[0148] In one embodiment, an aluminum alloy is arranged on the patterned metal aluminum thin film.

[0149] By arranging the aluminum alloy on the metal aluminum thin film, the surface of the metal aluminum thin film can be protected from being oxidized or damaged, and the reliability of the conductive lead 17 and the pad 18 is improved.

[0150] Finally, step 12 is performed, the temporary connection comb tooth is removed, and the mass 12 is connected with the base frame 11 only through the cantilever beam 13.

[0151] Specifically, after step 12, the MEMS acceleration sensor 10 including a single crystal silicon substrate and a conductive lead 17 is obtained, the single crystal silicon substrate including the base frame 11 and an acceleration sensitive unit, the acceleration sensitive unit including the mass block 12, the cantilever beam 13, the first comb tooth group 14 and the second comb tooth group 15.

[0152] Specifically, the "single crystal silicon wafer 31" mentioned in the present application is used to prepare a single crystal silicon substrate including an acceleration sensitive unit and a base frame 11 before the MEMS acceleration sensor 10 is formed.

[0153] In one embodiment, the method of dry etching is used to remove the temporary connecting comb teeth.

[0154] The present application can reduce the impact on the acceleration sensitive unit of the single crystal silicon substrate when removing the temporary connecting comb teeth by using the method of dry etching to remove the temporary connecting comb teeth, thereby further improving the process yield of the MEMS acceleration sensor 10.

[0155] In one embodiment, before the temporary connecting comb teeth are removed, one mass block 12 is connected to the base frame 11 through two or more temporary connecting comb teeth.

[0156] Specifically, different numbers of temporary connecting comb teeth can be set as needed to meet the specific application requirements of the stress between the mass block 12 and the cantilever beam 13.

[0157] In one embodiment, the temporary connecting comb teeth are symmetrically distributed on both sides of the cantilever beam 13 away from the cantilever beam 13 with the cantilever beam 13 as the axis of symmetry.

[0158] The present application sets the symmetric position of the temporary connecting comb teeth away from the cantilever beam 13, so that the temporary connecting comb teeth can share as much stress as possible from the cantilever beam 13 from the mass block 12, further reducing the risk of deformation, cracking and other adverse effects of the cantilever beam 13 during preparation, and improving the process yield of the MEMS acceleration sensor 10.

[0159] Specifically, the appropriate position of the temporary connecting comb teeth can also be selected according to the actual application requirements to optimize the sharing effect of the temporary connecting comb teeth on the stress of the cantilever beam 13.

[0160] In summary, the MEMS acceleration sensor and the preparation method thereof can control the squeeze film damping formed between the mass block and the base frame in the direction of sensor movement when acceleration exists by setting the first comb group and the second comb group arranged in a staggered manner as a buffer, thereby improving the dynamic characteristics of the MEMS acceleration sensor; meanwhile, the buffer of the first comb group and the second comb group reduces the risk of deformation and fracture of the cantilever beam caused by excessive acceleration of the mass block, thereby improving the high overload resistance of the MEMS acceleration sensor; in addition, by setting the temporary connecting comb to connect the mass block and the base frame in the process of preparing the MEMS acceleration sensor, the risk of fracture of the cantilever beam caused by excessive thermal mismatch stress of different materials in the process of releasing the mass block and the cantilever beam by wet etching, and the inconsistency of the thickness of the photoresist coated in the subsequent conductive wire preparation process after the mass block and the cantilever beam are released, is reduced, thereby improving the preparation yield and structural reliability; finally, the temporary connecting comb is set close to the symmetric position of the cantilever beam, thereby further reducing the risk of failure of the cantilever beam in the preparation process.

[0161] Therefore, the present application effectively overcomes the various shortcomings in the prior art and has high industrial utilization value.

[0162] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A method for fabricating a MEMS accelerometer, characterized in that, The fabrication method is used for a MEMS accelerometer, which includes a single-crystal silicon substrate and conductive leads. The single-crystal silicon substrate includes an acceleration-sensitive unit and a substrate frame located on a first surface. The acceleration-sensitive unit includes a mass block, a cantilever beam, a first comb tooth group, and a second comb tooth group. The mass block is connected to the substrate frame via the cantilever beam and suspended within the substrate frame. There are movable bottom surface gaps between the mass block and the bottom surface of the cantilever beam near the substrate frame and the substrate frame. There are movable side surface gaps between the side of the mass block near the substrate frame and the side of the cantilever beam near the substrate frame but not connected to the substrate frame and the substrate frame. The first comb tooth group is connected to both ends of the side of the mass block adjacent to the base frame along the direction of the cantilever beam, and the second comb tooth group is connected to both ends of the side of the base frame adjacent to the mass block along the direction of the cantilever beam. The adjacent first comb tooth groups and second comb tooth groups are staggered and have a buffer gap of a preset distance. The cantilever beam includes a varistor, and the conductive lead is fixed to the base frame. The conductive lead and the varistor together form a varistor detection circuit. The preparation method includes: Provide monocrystalline silicon wafers; A varistor is disposed within the single-crystal silicon wafer near the first surface; An anti-marking layer is formed on the first surface of the single-crystal silicon wafer; The stop-mark layer is graphically represented to obtain a pattern that exposes the lead holes of the varistor and the temporary connection teeth at preset positions; A first barrier layer is provided on the stop-mark layer, the first barrier layer covers the surface of the stop-mark layer and fills the gaps of the patterned stop-mark layer; The first barrier layer, the stop layer and the single crystal silicon wafer are graphically represented to obtain the first patterned groove corresponding to the patterns of the substrate frame, cantilever beam, mass block, first comb tooth group and second comb tooth group. A second barrier layer covers all surfaces exposed by the first patterned groove; Remove the second barrier layer at the bottom of the first patterned groove and continue etching the single-crystal silicon wafer to a predetermined depth; Using the second barrier layer as a mask, the monocrystalline silicon wafer exposed at a predetermined depth at the bottom of the first patterned groove is etched along a direction parallel to the first surface, thereby releasing the connection between the bottom surface of the mass block and the cantilever beam and the base frame. Remove the first and second blocking layers to expose the pattern of the lead hole and the temporary connection comb teeth in the stop layer; Conductive leads are provided on the surface of the structure obtained therefrom. The conductive leads fill the lead holes and are electrically connected to the varistor to form a varistor detection circuit. Remove the temporary connecting comb teeth so that the mass block is connected to the base frame only through the cantilever beam.

2. The method for fabricating a MEMS accelerometer according to claim 1, characterized in that, The cantilever beam includes a first end and a second end disposed opposite to each other. The first end of the cantilever beam is connected to the mass block, and the second end of the cantilever beam is connected to the base frame. The varistor is located at the first end of the cantilever beam.

3. The method for fabricating a MEMS accelerometer according to claim 1, characterized in that, The monocrystalline silicon substrate is a monocrystalline silicon substrate with a (111) crystal plane.

4. The method for fabricating a MEMS accelerometer according to claim 1 or 3, characterized in that, The single-crystal silicon substrate is an N-type silicon substrate or a P-type silicon substrate.

5. The method for fabricating a MEMS accelerometer according to claim 1, characterized in that, The resistivity of the single-crystal silicon substrate is greater than or equal to 1 Ω·cm and less than or equal to 10 Ω·cm.

6. The method for fabricating a MEMS accelerometer according to claim 1, characterized in that, Before setting the varistor, a first passivation layer is set on the first surface of the single crystal silicon wafer, and the stop layer is set on the first passivation layer.

7. The method for fabricating a MEMS accelerometer according to claim 1, characterized in that, The stop layer is low-stress silicon nitride; and / or, the first barrier layer and / or the second barrier layer is a TEOS passivation layer.

8. The method for fabricating a MEMS accelerometer according to claim 1, characterized in that, Before the temporary connecting comb teeth are removed, one of the mass blocks is connected to the base frame via two or more of the temporary connecting comb teeth.

9. The method for fabricating a MEMS accelerometer according to claim 1 or 8, characterized in that, The temporary connecting comb teeth are symmetrically distributed on both sides of the cantilever beam away from the cantilever beam, with the cantilever beam as the axis of symmetry.

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