MEMS acceleration sensor and preparation method thereof

Abstract

The invention provides an MEMS acceleration sensor and a preparation method thereof, in the MEMS acceleration sensor, a mass block on a monocrystalline silicon substrate is connected with a base frame through a cantilever beam and is suspended in the base frame, the side surface, adjacent to the base frame, of the mass block is connected with a first comb tooth group, and the side surface, adjacent to the mass block, of the base frame is connected with a second comb tooth group; the cantilever beam comprises a piezoresistor, and a piezoresistor detection circuit is formed between the conductive lead on the substrate frame and the piezoresistor. The first comb tooth set and the second comb tooth set between the mass block and the base frame are used as buffering, pressed film damping between the mass block and the base frame is controlled, and the dynamic characteristic and the high overload resistance of the MEMS acceleration sensor are improved; in addition, temporary connecting comb teeth are arranged in the preparation process to connect the mass block and the substrate frame, the stress borne by the cantilever beam in the technological process is reduced, and the preparation yield and the structural reliability are improved. And finally, the adverse risk of the process is reduced by temporarily connecting the positions of the comb teeth.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon micromechanical sensors, and in particular relates to a MEMS acceleration sensor and a preparation method thereof. Background Art

[0002] MEMS accelerometers are one of the most important MEMS detection devices in the field of inertial sensors and are widely used in aerospace, industrial production, automotive electronics, health care and other fields. With the increasing demand for performance, cost, size and other aspects of accelerometer chips in the huge MEMS sensor market, combined with the continuous advancement of MEMS silicon-based micromachining technology, high-performance, small-size, low-cost and high-overload-resistant MEMS accelerometers have become the goal that MEMS manufacturers and researchers are constantly pursuing.

[0003] Existing MEMS accelerometers are usually manufactured using double-sided silicon micromachining. First, KOH is used to wet-etch and thin the back of a single-crystal silicon wafer to form single-crystal silicon layers of different thicknesses, which are subsequently used to process cantilever beams and mass block structures. Then, varistors and lead interconnects are made on the front of the silicon wafer. Next, a sensor support structure is formed through silicon-glass (or silicon-silicon) bonding. Finally, the cantilever beam and mass block structure are released by etching from the front of the silicon wafer. The MEMS acceleration sensors prepared by this type of method have the following shortcomings: (1) KOH etching solution is used to wet-etch and thin the silicon wafer from the back of the silicon wafer to prepare the cantilever beam. Due to the 54.75° angle between the (100) crystal plane and the (111) crystal plane in the (100) silicon wafer, the chip size is very large after processing and the etching time is too long. The consistency of the etching depth is difficult to control, which affects the consistency of the product; (2) The sensor support structure is prepared by a bonding process. Due to the different thermal expansion coefficients between different bonding materials, thermal mismatch stress will be introduced, affecting the detection accuracy of the sensor; even if the same material is used for silicon-silicon bonding, the high-temperature bonding process will introduce residual stress, affecting the detection accuracy and long-term stability of the sensor; (3) The manufacturing process is relatively complex, the manufacturing cost is high, and it is not compatible with IC standard semiconductor processes.

[0004] To solve the above problems, in 2012, Wang Jiachou and others from the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, developed a TPMS composite sensor chip with single-sided integrated acceleration and pressure detection on a single silicon wafer. The cantilever beam and mass block structure of the acceleration sensor are directly processed by the single-sided silicon process, and the sensitivity of the sensor is improved by electroplating a 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 sensors prepared by this method have the characteristics of small chip size and low manufacturing cost, they also have the following shortcomings: (1) The residual stress introduced by the thermal mismatch between the copper mass block and the single crystal silicon will lead to poor temperature characteristics of the sensor, and even the copper mass block will fall off; (2) The compression film damping in the movement direction of the sensor sensitive unit is difficult to control, which makes it difficult to improve the dynamic characteristics of the sensor and has limited overload resistance.

[0005] In 2015, Wang Jiachou et al. proposed a single-wafer single-sided manufacturing technology for silicon-based three-dimensional micromechanical structures, and based on this technology, they processed a MEMS acceleration sensor with a "single-crystal silicon cantilever beam + single-crystal silicon mass block structure" [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 blocks to improve sensitivity in the acceleration sensor developed by their team in 2012. However, the manufacturing process in this scheme is relatively complicated, and it still does not solve the problem of difficult control of the squeeze film damping in the direction of motion of the sensor sensitive unit and limited overload resistance, thus hindering the high-performance development of high-sensitivity MEMS acceleration sensors.

[0006] In view of the above-mentioned deficiencies in the prior art, it is necessary to design a new acceleration sensor and a manufacturing method thereof 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 providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because these solutions are described in the background technology part of the present application. Summary of the invention

[0008] In view of the above shortcomings of the prior art, an object of the present invention is to provide a MEMS acceleration sensor and a preparation method thereof, so as to solve the problems in the prior art that the squeeze film damping of the MEMS acceleration sensor is difficult to control and the high overload resistance is limited.

[0009] To achieve the above object, the present invention provides a MEMS acceleration sensor, the MEMS acceleration sensor comprising: a single crystal silicon substrate and a conductive lead;

[0010] The single crystal silicon substrate comprises the acceleration sensitive unit and a base frame located on the first surface, wherein 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 to the base frame through the cantilever beam and suspended in the base frame, a movable bottom surface gap exists between the bottom surface of the mass block and the cantilever beam close to the base frame and the base frame, and a movable side surface gap exists 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 to the base frame and the base frame;

[0011] Both ends of the side surface of the mass block adjacent to the base frame in the direction in which the cantilever beam extends are connected to the first comb tooth groups, and both ends of the side surface of the base frame adjacent to the mass block in the direction in which the cantilever beam extends are connected to the second comb tooth groups, and adjacent first comb tooth groups and second comb tooth groups are arranged alternately with each other and there is a buffer gap of a preset distance between them;

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

[0013] Optionally, the cantilever beam comprises a first end and a second end that are arranged opposite to each other, the first end of the cantilever beam is connected to the mass block, the second end of the cantilever beam is connected to the base frame, and the varistor 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 plane.

[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 1Ω·cm and less than or equal to 10Ω·cm.

[0017] The present invention also provides a method for preparing a MEMS acceleration sensor, the method for preparing any one of the above-mentioned MEMS acceleration sensors, the method comprising:

[0018] Provide monocrystalline silicon wafers;

[0019] Disposing a varistor at a position close to the first surface in the single crystal silicon wafer;

[0020] Disposing an etching stop layer on the first surface of the single crystal silicon wafer;

[0021] Patterning the stop layer to obtain a pattern that reveals the lead holes of the varistor and the temporary connection comb teeth at a preset position;

[0022] Disposing a first barrier layer on the stop layer, wherein the first barrier layer covers the surface of the stop layer and fills the gaps 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 the patterns of the base frame, the cantilever beam, the mass block, the first comb tooth group and the second comb tooth group;

[0024] Covering all surfaces exposed by the first pattern grooves 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 to a preset depth;

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

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

[0028] A conductive lead is arranged on the surface of the structure thus obtained, wherein the conductive lead fills the lead hole and is electrically connected to the varistor to form a varistor detection circuit;

[0029] The temporary connection comb teeth are removed, so that the mass block is connected to the base frame only through the cantilever beam.

[0030] Optionally, before providing the varistor, a first passivation layer is provided on the first surface of the single crystal silicon wafer, and the stop layer is provided on the first passivation layer.

[0031] Optionally, 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.

[0032] Optionally, before removing the temporary connection comb teeth, one of the mass blocks is connected to the base frame via two or more of the temporary connection comb teeth.

[0033] Optionally, the temporary connection comb teeth are symmetrically distributed at positions on both sides of the cantilever beam away from the cantilever beam with the cantilever beam as the symmetry axis.

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

[0035] The present invention provides a first comb tooth group and a second comb tooth group arranged in an interlaced manner between the mass block and the base frame as a buffer, so as to control the squeeze film damping formed between the mass block and the base frame in the direction of sensor movement when acceleration exists, thereby improving the dynamic characteristics of the MEMS acceleration sensor;

[0036] The present invention reduces the risk of deformation and fracture of the cantilever beam caused by excessive acceleration of the mass block through the buffering of the first comb tooth group and the second comb tooth group, thereby improving the high overload resistance of the MEMS acceleration sensor.

[0037] The present invention provides a temporary connection comb-tooth connection forming mass block and a base frame in the process of preparing the MEMS acceleration sensor, thereby reducing the risk of cantilever beam fracture due to 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 lead preparation process after the mass block and the cantilever beam are released, thereby improving the preparation yield and structural reliability.

[0038] The present invention cooperates with the temporary connection comb teeth to be arranged at symmetrical positions close to the cantilever beam, thereby further reducing the risk of defects occurring in the cantilever beam during the preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Shown is a schematic perspective view of a MEMS acceleration sensor in the present invention.

[0040] Figure 2 Shown is a schematic diagram of a partial cross-sectional stereoscopic view of the MEMS acceleration sensor of the present invention.

[0041] Figure 3 The figure shows a schematic side cross-sectional view of a structure presented by a single crystal silicon wafer including a first passivation layer in step 1 of an example of a method for preparing a MEMS acceleration sensor of the present invention.

[0042] Figure 4 It is a schematic diagram of a side cross-sectional view of the structure presented by setting a varistor in step 2 of the method for preparing a MEMS acceleration sensor of the present invention.

[0043] Figure 5 It is a schematic diagram of a side cross-sectional view of the structure presented by providing a stop layer in step 3 of the method for preparing a MEMS acceleration sensor of the present invention.

[0044] Figure 6 It is a schematic diagram of a side cross-sectional view of the structure presented by the patterned stop layer in step 4 of the method for preparing the MEMS acceleration sensor of the present invention.

[0045] Figure 7 It is a schematic diagram of a side cross-sectional view of the structure presented by providing a first barrier layer in step 5 of the method for preparing a MEMS acceleration sensor of the present invention.

[0046] Figure 8 It is a schematic diagram of a side cross-sectional view of the structure presented by forming a first pattern groove in step 6 of the method for preparing a MEMS acceleration sensor of the present invention.

[0047] Fig. 9 It is a schematic side cross-sectional view of the structure presented by covering the second barrier layer in step 7 of the method for preparing the MEMS acceleration sensor of the present invention.

[0048] Fig.10 It is a schematic diagram of a side cross-sectional view of the structure presented by etching a single crystal silicon wafer to a preset depth in step 8 of the method for preparing a MEMS acceleration sensor of the present invention.

[0049] Fig.11 It is a schematic diagram of a side cross-sectional view of the structure presented by releasing the mass block and the cantilever beam in step 9 of the method for preparing the MEMS acceleration sensor of the present invention.

[0050] Fig.12 It is a schematic side cross-sectional view of the structure presented by removing the first barrier layer and the second barrier layer in step 10 of the method for preparing the MEMS acceleration sensor of the present invention.

[0051] Fig.13 It is a schematic diagram of a side cross-sectional view of the structure presented by providing conductive leads in step 11 of the method for preparing a MEMS acceleration sensor of the present invention.

[0052] Component number description

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

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

[0055] 31. Single crystal silicon wafer; 32. First passivation layer; 33. Stop layer; 34. Lead hole; 35. First barrier layer; 36. First graphic groove; 37. Second barrier layer; 38. Preset depth. DETAILED DESCRIPTION

[0056] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0057] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the schematic diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0058] For convenience of description, spatially relative terms such as "under", "below", "below", "below", "above", "on", etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatially relative terms are intended to encompass other orientations of the device in use or operation in addition to the orientation depicted in the drawings.

[0059] In the context of the present application, a structure in which a first feature is described as being "above" a second feature may include embodiments in which the first and second features are in direct contact, and may also include 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 used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0061] In the prior art, it is difficult for the MEMS acceleration sensor 10 to control the squeeze film damping between the mass block 12 and the base frame 11 in the direction of movement, and the improvement of the overload resistance is also relatively limited; especially in order to achieve a MEMS acceleration sensor 10 with higher sensitivity, it is necessary to use a larger mass block 12 and a thinner cantilever beam 13, which results in greater squeeze film damping between the mass block 12 and the base frame 11 during movement, and greater force on the cantilever beam 13, which is more prone to deformation or breakage, affecting the accuracy and reliability of the measurement results of the MEMS acceleration sensor 10. Therefore, the overload resistance is further limited, which is not conducive to the current MEMS acceleration sensor 10 application requirements for miniaturization, high sensitivity and high performance.

[0062] The present invention provides a MEMS acceleration sensor 10, such as Figure 1-Figure 2 As shown, Figure 1 is an overall stereogram of the MEMS acceleration sensor 10, Figure 2 is a partial cross-sectional stereoscopic view of the MEMS acceleration sensor 10, Figure 2 The section line is Figure 1 AA' in the figure, the MEMS acceleration sensor 10 comprises: a single crystal silicon substrate and a conductive lead 17;

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

[0064] Both ends of the side surface of the mass block 12 adjacent to the base frame 11 along the direction in which the cantilever beam 13 extends are connected to the first comb tooth group 14, and both ends of the side surface of the base frame 11 adjacent to the mass block 12 along the direction in which the cantilever beam 13 extends are connected to the second comb tooth group 15, and the adjacent first comb tooth groups 14 and second comb tooth groups 15 are arranged alternately with each other and there is a buffer gap 23 of a preset distance;

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

[0066] The present invention provides a first comb tooth group 14 and a second comb tooth group 15 which are arranged in an interlaced manner between the mass block 12 and the base frame 11 as a buffer, so that the squeeze film damping formed between the mass block 12 and the base frame 11 in the direction of sensor movement when acceleration exists can be controlled within a certain range, thereby improving the dynamic characteristics of the MEMS acceleration sensor 10; at the same time, through the buffering of the first comb tooth group 14 and the second comb tooth group 15, the risk of deformation and fracture of the cantilever beam 13 caused by excessive acceleration of the mass block 12 is reduced, the high overload resistance of the MEMS acceleration sensor 10 is improved, and it is beneficial to the miniaturization and high sensitivity performance improvement of the MEMS acceleration sensor 10.

[0067] In one embodiment, Figure 1-Figure 2 As shown, the cantilever beam 13 includes a first end and a second end that are relatively arranged. The first end of the cantilever beam 13 is connected to the mass block 12 , the second end of the cantilever beam 13 is connected to the base frame 11 , and the varistor 17 is located at the first end of the cantilever beam 13 .

[0068] The present invention arranges the piezoresistor 17 at one end of the cantilever beam 13 connected to the base frame 11 so that the deformation of the cantilever beam 13 can be reflected in the resistance change of the piezoresistor 17 to the maximum extent, thereby maximizing the sensitivity of the MEMS acceleration sensor 10.

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

[0070] The present invention uses a single crystal silicon substrate with a (111) crystal plane to perform a process compatible with semiconductor technology on a single surface of the first surface, thereby achieving the preparation of a MEMS acceleration sensor 10 with a simple manufacturing process, low cost, and suitable for large-scale quantitative production, and is also conducive to the miniaturization of the MEMS acceleration sensor 10.

[0071] Preferably, if Figure 1 As shown, the cantilever beam 13 and the mass block 12 are <211> Crystal connection arrangement.

[0072] The present invention is achieved by the cantilever beam 13 and the mass block 12 along the <211> The crystal orientation connection arrangement is matched with the single crystal silicon substrate of the (111) crystal plane, so that the etching speed of the single crystal silicon substrate can be maximized when manufacturing the cantilever beam 13 and the mass block 12, thereby further improving the manufacturing efficiency of the MEMS acceleration sensor 10.

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

[0074] The present invention uses an N-shaped silicon substrate as a single crystal silicon substrate for manufacturing the MEMS acceleration sensor 10 and utilizes the smaller piezoresistance coefficient of the N-shaped silicon substrate to achieve a 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 1Ω·cm and less than or equal to 10Ω·cm.

[0077] The present invention sets the resistivity range of the single crystal silicon substrate to ensure that the resistivity of the single crystal silicon substrate can realize the convenient preparation of the varistor 17, while avoiding excessive effects of heat dissipation, thermal noise, signal noise, operating voltage, etc. on other performance indicators of the MEMS acceleration sensor 10.

[0078] In one embodiment, the acceleration sensitive unit includes a mass block 12 and a cantilever beam 13 , the cantilever beam 13 includes a 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 the mass block 12 and the cantilever beam 13 , the cantilever beam 13 includes two piezoresistors 17 , and the two piezoresistors 17 form a Wheatstone half-bridge detection circuit through the conductive leads 17 .

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

[0081] Specifically, other numbers of mass blocks 12 , cantilever beams 13 and piezoresistors 17 may be provided in the acceleration sensitive unit according to application requirements, so as to balance the performance requirements of the volume and sensitivity of the MEMS acceleration sensor 10 .

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

[0083] Specifically, the larger pad 18 is helpful to improve 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 where the conductive leads 17, the pads 18, the movable side gaps 22, and the buffer gaps 23 are not provided is provided with the first passivation layer 32 as described in the following preparation method, and the surface of the first passivation layer 32 is provided with a stop layer 33. The first passivation layer 32 and the stop layer 33 are retained in the preparation process to protect the surface of the MEMS acceleration sensor 10 to reduce the risk of decreased yield or reliability due to external influences.

[0085] The present invention further provides a method for preparing a MEMS acceleration sensor 10, wherein the method is used to prepare any one of the above-mentioned MEMS acceleration sensors 10, and the method comprises:

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

[0087] Step 2: Disposing a varistor 17 at a position close to the first surface in the single crystal silicon wafer 31;

[0088] Step 3: Disposing an etching 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 that reveals the lead hole 34 of the varistor 17 and the temporary connection comb teeth at a preset position;

[0090] Step 5: Disposing a first barrier layer 35 on the stop layer 33 , wherein the first barrier layer 35 covers the surface of the stop layer 33 and fills the gaps 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 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 downward to a preset depth 38;

[0094] Step 9: Using the second barrier layer 37 as a mask, etching the single crystal silicon wafer 31 to a preset depth 38 exposed at the bottom of the first pattern groove 36 in a direction parallel to the first surface, thereby releasing the connection between the bottom surfaces 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 lead hole 34 and the temporary connection comb pattern in the stop layer 33;

[0096] Step 11: a conductive lead 17 is arranged on the surface of the structure thus obtained, the conductive lead 17 fills the lead hole 34 and is electrically connected to the varistor 17 to form a varistor detection circuit;

[0097] Step 12: remove the temporary connection comb teeth, so that the mass block 12 is connected to the base frame 11 only through the cantilever beam 13.

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

[0099] First, proceed to step 1, such as Figure 3 As shown, a single crystal silicon wafer 31 is provided.

[0100] In one embodiment, after step 1, Figure 3 As shown, before the varistor 17 is provided, a first passivation layer 32 is provided on the first surface of the single crystal silicon wafer 31 ; 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, silicon dioxide is obtained as the first passivation layer 32 on the first surface of the single crystal silicon wafer 31 by thermal oxidation.

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

[0105] Specifically, the first passivation layer 32 may also be made of other suitable passivation layer materials.

[0106] Then, proceed to step 2, such as Figure 4 As shown, a varistor 17 is disposed in the single crystal silicon wafer 31 at a position close to the first surface.

[0107] In one embodiment, the varistor 17 is disposed in the single crystal silicon wafer 31 near the first surface by using an ion implantation method.

[0108] In one embodiment, the varistor 17 is disposed in the single crystal silicon wafer 31 near the first surface by a diffusion method.

[0109] In one embodiment, the varistor 17 is disposed in the single crystal silicon wafer 31 by a boron diffusion method.

[0110] In one embodiment, before setting the varistor 17, a first passivation layer 32 is set on the first surface of the single crystal silicon wafer 31. Before setting the varistor 17, photoresist is coated on the first passivation layer 32 and then photolithography and etching are performed to expose the first surface of the single crystal silicon wafer 31 corresponding to the preset position of the varistor 17 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, such as Figure 5 As shown, an etching stop layer 33 is disposed 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] The present invention uses low-stress silicon nitride as the stop layer 33, thereby reducing the structural deformation, cracks and other adverse problems caused by large stress between different layers due to temperature changes during the preparation process, which is beneficial to improving the reliability of the MEMS acceleration sensor 10 preparation process; at the same time, the use of silicon nitride can avoid making the surface of the single crystal silicon wafer 31 under the stop layer 33 uneven during the subsequent etching process, thereby avoiding affecting the sensing accuracy of the MEMS acceleration sensor 10.

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

[0115] Then, proceed to step 4, such as Figure 6 As shown, the stop layer 33 is patterned to obtain a pattern of the lead hole 34 of the varistor 17 and the temporary connection comb teeth at a preset position (not shown in the figure, it is also in the patterned stop layer 33 and the first passivation layer 32 like the lead hole 34, but not on the same section as the lead hole 34).

[0116] Specifically, the temporary connection comb teeth and the lead wire holes 34 in the figure of this embodiment are not on the same cross section. In actual situations, the temporary connection comb teeth and the lead wire holes 34 can also be on the same cross section and can be set according to actual needs.

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

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

[0119] The present invention provides a temporary connection comb-tooth connection between the mass block 12 and the base frame 11 in the process of preparing the MEMS acceleration sensor 10, thereby reducing the risk of the cantilever 13 being broken due to excessive thermal mismatch stress of different materials during the process of releasing the mass block 12 and the cantilever beam 13 by wet etching, and the risk of the cantilever beam 13 being deformed and broken due to the inconsistency of the thickness of the photoresist coated during the subsequent preparation of the conductive lead 17 after the mass block 12 and the cantilever beam 13 are released. In particular, the present invention protects the thinner cantilever beam 13 in the highly sensitive MEMS acceleration sensor 10 during the preparation process, thereby improving the preparation yield and structural reliability.

[0120] Specifically, when the stop layer 33 is patterned using a photoresist, after the first passivation layer 32 is patterned, the remaining photoresist is removed.

[0121] Next, proceed to step 5, such as Figure 7 As shown, a first barrier layer 35 is disposed on the stop layer 33 , and the first barrier layer 35 covers the surface of the stop layer 33 and fills the gaps of the patterned stop 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 blocking protection layer when etching the lead hole 34 is performed subsequently.

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

[0125] In one embodiment, the thickness of the first barrier layer 35 is set to 10000 angstroms.

[0126] Then, proceed to step 6, such as Figure 8As shown, the first barrier layer 35, the stop layer 33 and the single crystal silicon wafer 31 are patterned 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.

[0127] Specifically, Figure 8 As shown, the first graphic groove 36 connects the mass block 12 to the base frame 11 through the cantilever beam 13 and the temporary connection comb teeth, and there is a movable side gap 22 between the side of the mass block 12 close to the base frame 11 and the base frame 11, and there is a movable side gap 22 between the side of the cantilever beam 13 close to the base frame 11 and not connected 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 block 12 adjacent to the base frame 11 along the direction in which the cantilever beam 13 extends, and the second comb tooth group 15 is connected to both ends of the side of the base frame 11 adjacent to the mass block 12 along the direction in which the cantilever beam 13 extends, and the first comb tooth group 14 and the second comb tooth group 15 are arranged alternately with each other and there is a buffer gap 23 of a preset distance.

[0128] In one embodiment, after applying photoresist on the first barrier layer 35, photolithography is performed to obtain a patterned photoresist corresponding to the first pattern groove 36; RIE is performed using the patterned photoresist as a mask to pattern the first barrier layer 35, the stop layer 33 and the first passivation layer 32 to expose the first surface of the single crystal silicon wafer 31; DRIE (Deep Reactive Ion Etching) is then used to etch the first surface of the single crystal silicon wafer 31 to obtain 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; the depth of DRIE etching is the thickness of the cantilever beam 13, the mass block 12, the first comb tooth group 14 and the second comb tooth group 15.

[0129] Next, proceed to step 7, such as Fig. 9 As shown, all surfaces exposed from the first graphic grooves 36 are covered with a second barrier layer 37 .

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

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

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

[0133] The present invention uses the TEOS passivation layer as the first barrier layer 35 and the second barrier layer 37, so that the subsequent removal of the remaining first barrier layer 35 and the second barrier layer 37 is more convenient and faster, thereby further improving the process efficiency.

[0134] Then, proceed to step 8, such as Fig.10 As shown, the second barrier layer 37 at the bottom of the first pattern groove 36 is removed and the single crystal silicon wafer 31 is continuously etched downward to a preset depth 38 .

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

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

[0137] Specifically, the preset depth 38 is the thickness of the sacrificial layer subsequently used to release the connection between the mass block 12 and the cantilever beam 13 and the base frame 11; after etching away the second barrier layer 37 at the bottom of the first graphic groove 36, the second barrier layer 37 can be used as a mask to only etch the first surface of the single crystal silicon wafer 31 exposed at the bottom of the first graphic groove 36, and only the position of the single crystal silicon wafer 31 etched to the preset depth 38 will be etched by the etching solution in step 9 along a direction parallel to the first surface, while the side wall above the preset depth 38 blocked by the second barrier layer 37 will not be 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 predetermined depth 38 is 10 microns.

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

[0140] Specifically, the connection between the bottom surfaces 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 surfaces 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 teeth.

[0141] In one embodiment, a TMAH (Tetramethylammonium hydroxide) solution is used to wet-etch the sacrificial layer of the single crystal silicon wafer 31 to a preset depth 38, along a direction parallel to the first surface, so as to release the connection between the bottom surfaces of the mass block 12 and the cantilever beam 13 and the base frame 11.

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

[0143] Then, proceed to step 10, such as Fig.12 As shown, the first barrier layer 35 and the second barrier layer 37 are removed, revealing the lead hole 34 and the temporary connection comb pattern in the stop layer 33 .

[0144] Next, proceed to step 11, such as Fig.13 As shown, a conductive lead 17 is arranged on the surface of the structure thus obtained, and the conductive lead 17 fills the lead hole 34 and is electrically connected to the varistor 17 to form a varistor detection circuit.

[0145] In one embodiment, the conductive lead 17 is provided by sputtering a metal aluminum film and then performing a patterning process.

[0146] In one embodiment, the thickness of the metal aluminum film is 10,000 angstroms.

[0147] In one embodiment, when the MEMS acceleration sensor 10 further includes a pad 18 , the pad 18 may be formed simultaneously during metal sputtering and patterning.

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

[0149] The present invention can protect the surface of the metal aluminum film from being oxidized or damaged by arranging an aluminum alloy on the metal aluminum film, thereby improving the reliability of the conductive lead 17 and the pad 18.

[0150] Finally, step 12 is performed to remove the temporary connection comb teeth, so that the mass block 12 is connected to the base frame 11 only through the cantilever beam 13 .

[0151] Specifically, after performing 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 includes the base frame 11 and the acceleration sensitive unit, and 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.

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

[0153] In one embodiment, the temporary connection comb teeth are removed by dry etching.

[0154] The present invention uses a dry etching method to remove temporary connection comb teeth, which can reduce the impact of removing the temporary connection comb teeth on the acceleration sensitive unit of the single crystal silicon substrate, thereby further improving the process yield of the MEMS acceleration sensor 10.

[0155] In one embodiment, before the temporary connection comb teeth are removed, one of the mass blocks 12 is connected to the base frame 11 via two or more of the temporary connection comb teeth.

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

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

[0158] The present invention arranges the temporary connection comb teeth symmetrically away from the cantilever beam 13 so that the temporary connection comb teeth can share as much stress from the mass block 12 as possible with the cantilever beam 13, further reducing the risk of deformation, rupture and other defects of the cantilever beam 13 during the preparation process, thereby improving the process yield of the MEMS acceleration sensor 10.

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

[0160] In summary, the MEMS acceleration sensor and the preparation method thereof of the present invention can control the squeeze film damping formed between the mass block and the base frame in the direction of sensor movement when there is acceleration by setting a first comb tooth group and a second comb tooth group arranged in an interlaced manner between the mass block and the base frame as a buffer, thereby improving the dynamic characteristics of the MEMS acceleration sensor; at the same time, through the buffering of the first comb tooth group and the second comb tooth group, the risk of deformation and fracture of the cantilever beam caused by excessive acceleration of the mass block movement is reduced, and the high overload resistance of the MEMS acceleration sensor is improved; in addition, by setting temporary connection comb teeth to connect the mass block and the base frame in the process of preparing the MEMS acceleration sensor, the risk of cantilever beam fracture due to excessive thermal mismatch stress of different materials during wet etching to release the mass block and the cantilever beam is reduced, as well as the inconsistency of the thickness of the photoresist coated in the subsequent conductive lead preparation process after the mass block and the cantilever beam are released, thereby improving the preparation yield and structural reliability; finally, the temporary connection comb teeth are arranged at a symmetrical position close to the cantilever beam, which further reduces the risk of defective cantilever beam during the preparation process.

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

[0162] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A MEMS acceleration sensor, characterized in that: The MEMS acceleration sensor comprises: a single crystal silicon substrate and a conductive lead; The single crystal silicon substrate comprises the acceleration sensitive unit and a base frame located on the first surface, wherein 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 to the base frame through the cantilever beam and suspended in the base frame, a movable bottom surface gap exists between the bottom surface of the mass block and the cantilever beam close to the base frame and the base frame, and a movable side surface gap exists 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 to the base frame and the base frame; Both ends of the side surface of the mass block adjacent to the base frame in the direction in which the cantilever beam extends are connected to the first comb tooth groups, and both ends of the side surface of the base frame adjacent to the mass block in the direction in which the cantilever beam extends are connected to the second comb tooth groups, and adjacent first comb tooth groups and second comb tooth groups are arranged alternately with each other and there is a buffer gap of a preset distance between them; The cantilever beam includes a varistor, the conductive lead is fixed on the base frame, and a varistor detection circuit is formed between the conductive lead and the varistor.

2. The MEMS acceleration sensor according to claim 1, characterized in that: The cantilever beam comprises a first end and a second end which are arranged opposite to each other, the first end of the cantilever beam is connected to the mass block, the second end of the cantilever beam is connected to the base frame, and the varistor is located at the first end of the cantilever beam.

3. The MEMS acceleration sensor according to claim 1, characterized in that: The single crystal silicon substrate is a single crystal silicon substrate with a (111) crystal plane.

4. The MEMS acceleration sensor 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 MEMS acceleration sensor according to claim 1, characterized in that: The resistivity of the single crystal silicon substrate is greater than or equal to 1Ω·cm and less than or equal to 10Ω·cm.

6. A method for preparing a MEMS acceleration sensor, characterized in that: The preparation method is used to prepare the MEMS acceleration sensor according to any one of claims 1 to 5, and the preparation method comprises: Provide monocrystalline silicon wafers; Disposing a varistor at a position close to the first surface in the single crystal silicon wafer; Disposing an etching stop layer on the first surface of the single crystal silicon wafer; Patterning the stop layer to obtain a pattern that reveals the lead holes of the varistor and the temporary connection comb teeth at a preset position; Disposing a first barrier layer on the stop layer, wherein the first barrier layer covers the surface of the stop layer and fills the gaps of the patterned stop layer; Patterning the first barrier layer, the stop layer and the single crystal silicon wafer to obtain a first pattern groove corresponding to the patterns of the base frame, the cantilever beam, the mass block, the first comb tooth group and the second comb tooth group; Covering all surfaces exposed by the first pattern grooves with a second barrier layer; Removing the second barrier layer at the bottom of the first pattern groove and continuing to etch the single crystal silicon wafer downward to a preset depth; Using the second barrier layer as a mask, etching the single crystal silicon wafer to a preset depth exposed at the bottom of the first pattern groove in a direction parallel to the first surface, thereby releasing the connection between the mass block and the bottom surface of the cantilever beam and the base frame; removing the first barrier layer and the second barrier layer to expose the lead hole and the temporary connection comb pattern in the stop layer; A conductive lead is arranged on the surface of the structure thus obtained, wherein the conductive lead fills the lead hole and is electrically connected to the varistor to form a varistor detection circuit; The temporary connection comb teeth are removed so that the mass block is connected to the base frame only through the cantilever beam.

7. The method for preparing a MEMS acceleration sensor according to claim 6, characterized in that: Before the varistor is provided, a first passivation layer is provided on the first surface of the single crystal silicon wafer, and the stop layer is provided on the first passivation layer.

8. The method for preparing a MEMS acceleration sensor according to claim 6, 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.

9. The method for preparing a MEMS acceleration sensor according to claim 6, characterized in that: Before removing the temporary connection comb teeth, one of the mass blocks is connected to the base frame via two or more of the temporary connection comb teeth.

10. The method for preparing a MEMS acceleration sensor according to claim 6 or 9, characterized in that: The temporary connection comb teeth are symmetrically distributed on both sides of the cantilever beam at positions away from the cantilever beam with the cantilever beam as a symmetry axis.

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