MEMS resonator and method of manufacturing the same

Abstract

The application relates to the technical field of resonators, and discloses a MEMS resonator and a preparation method thereof. The preparation method of the MEMS resonator comprises the following steps: forming a first wafer, wherein the first wafer at least comprises a first monocrystalline silicon layer; forming a second wafer, wherein the second wafer at least comprises a second monocrystalline silicon layer and a piezoelectric material layer located on the second monocrystalline silicon layer; bonding the first wafer and the second wafer to form a laminated structure comprising the first monocrystalline silicon layer, the piezoelectric material layer and the second monocrystalline silicon layer, and performing high-doping treatment on the first monocrystalline silicon layer and the second monocrystalline silicon layer before or after bonding; and performing deep reactive ion etching on the laminated structure to form a resonator body, a connecting beam and an anchor, wherein the resonator body is arranged in a suspended mode, and the resonator body is connected with the anchor through the connecting beam. The application improves the electromechanical coupling efficiency and the quality factor of the MEMS resonator, and guarantees the temperature stability of the MEMS resonator.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of resonators, and particularly relates to a MEMS resonator and a preparation method thereof. BACKGROUND

[0002] A micro-electro-mechanical system (MEMS) can integrate mechanical components, driving components, electrical control systems, digital processing systems, etc. into a whole micro unit. An example of such a device is a MEMS resonator. As a kind of MEMS resonator, the working principle of a piezoelectric resonator is to excite acoustic wave oscillation in a piezoelectric material by an electrode through an electrical signal, so as to realize resonance of a specific frequency and wavelength. The piezoelectric resonator is widely used, for example, for timing reference, signal filtering, mass sensing, biological sensing, motion sensing, etc. With the development of electronic technology, the size and frequency stability of the piezoelectric resonator are significantly improved.

[0003] The piezoelectric resonator body structure in the related art is a composite structure of a piezoelectric material and a metal arranged on a silicon-based material. The metal serves as an electrode. However, due to the fact that the thermal expansion coefficient of the metal material is too high, the thermal expansion coefficient matching degree with the piezoelectric material layer is poor, and the stiffness (elastic modulus) is too high, and the metal material is prone to hardening with use, the piezoelectric resonator has problems of low electromechanical coupling efficiency, low quality factor (Q value), etc. SUMMARY

[0004] In view of this, the present application provides a MEMS resonator and a preparation method thereof to solve the above-mentioned technical problems.

[0005] In a first aspect, the embodiments of the present application disclose a preparation method of a MEMS resonator, comprising:

[0006] forming a first wafer, the first wafer comprising at least a first single crystal silicon layer;

[0007] forming a second wafer, the second wafer comprising at least a second single crystal silicon layer and a piezoelectric material layer on the second single crystal silicon layer;

[0008] bonding the first wafer and the second wafer to form a laminated structure comprising at least the first single crystal silicon layer, the piezoelectric material layer and the second single crystal silicon layer, and performing high-doping treatment on the first single crystal silicon layer and the second single crystal silicon layer before or after the bonding;

[0009] performing deep reactive ion etching on the laminated structure to form a resonator body, a connecting beam and an anchor, the resonator body being suspended, and the resonator body being connected to the anchor through the connecting beam.

[0010] In one possible example, the first wafer includes at least a first single-crystal silicon layer, and a piezoelectric material layer formed on the first single-crystal silicon layer.

[0011] In one possible example, the forming the first wafer includes:

[0012] A first silicon-on-insulator wafer is provided, which includes at least a first silicon layer, and a recess is formed on the first silicon layer;

[0013] A second silicon-on-insulator wafer is provided, which includes the first single-crystal silicon layer, and a first dielectric layer on the first single-crystal silicon layer;

[0014] The side of the first silicon layer with the recess and the first dielectric layer are bonded to form the first wafer in a silicon-on-insulator type, and the recess forms a cavity in the first wafer.

[0015] In one possible example, the forming the second wafer includes:

[0016] A third silicon-on-insulator wafer is provided, which includes at least a second silicon layer, a second dielectric layer, and the second single-crystal silicon layer formed in sequence on the second silicon layer;

[0017] An aluminum nitride layer is deposited on the second single-crystal silicon layer to form the piezoelectric material layer.

[0018] In one possible example, after the bonding of the first wafer and the second wafer, further including:

[0019] The second silicon layer and the second dielectric layer are etched and removed.

[0020] In one possible example, the bonding of the first wafer and the second wafer includes:

[0021] The first single-crystal silicon layer of the first wafer is fusion-bonded with the piezoelectric material layer of the second wafer; or,

[0022] The piezoelectric material layer on the first single-crystal silicon layer is fusion-bonded with the piezoelectric material layer on the second single-crystal silicon layer.

[0023] In one possible example, the deep reactive ion etching of the stacked structure includes:

[0024] A first isolation groove is formed on the second single-crystal silicon layer of the second wafer, which divides part of the second single-crystal silicon layer as a driving electrode, and another part of the second single-crystal silicon layer as a sensing electrode.

[0025] In one possible example, the deep reactive ion etching of the stack structure comprises:

[0026] Identifying a region of the top of the stack structure corresponding to the resonator body as a target region, and a region other than the target region as a peripheral region;

[0027] Forming a second isolation groove on the second monocrystalline silicon layer in the target region through a first mask, the second isolation groove being connected to the piezoelectric material layer;

[0028] Forming a ground electrode hole in the peripheral region through a second mask, the ground electrode hole being connected to the first dielectric layer by the second monocrystalline silicon layer;

[0029] Depositing an electrode material on the top of the stack structure through a third mask, forming a ground electrode on the ground electrode hole, and forming a drive electrode and a sense electrode on both sides of the second isolation groove in the target region;

[0030] Forming a first release hole and a second release hole on the stack structure through a fourth mask, the first release hole being connected to the first monocrystalline silicon layer by the second monocrystalline silicon layer, and the second release hole being connected to the cavity by the second monocrystalline silicon layer, to release a region of the resonator body, forming the resonator body, a connecting beam, and an anchor.

[0031] In one possible example, after the forming of the first release hole and the second release hole on the stack structure through the fourth mask, the method further comprises:

[0032] Introducing an acid etching gas into the second release hole to remove the first dielectric layer in the cavity.

[0033] In a second aspect, the embodiments of the present application disclose a MEMS resonator prepared by the MEMS resonator preparation method in any of the above embodiments, comprising: a resonator body, a connecting beam, and an anchor, the resonator body being suspended, and the resonator body being connected to the anchor through the connecting beam; the resonator body being a stack structure formed by bonding a first wafer and a second wafer, the stack structure comprising at least a first monocrystalline silicon layer, a piezoelectric material layer, and a second monocrystalline silicon layer, the first monocrystalline silicon layer, the piezoelectric material layer, and the second monocrystalline silicon layer being sequentially stacked.

[0034] In summary, compared with the prior art, the application discloses a MEMS resonator preparation method, which comprises the following steps: forming a first wafer, the first wafer comprising at least a first single-crystal silicon layer; forming a second wafer, the second wafer comprising at least a second single-crystal silicon layer and a piezoelectric material layer on the second single-crystal silicon layer; bonding the first wafer and the second wafer; forming a laminated structure comprising at least the first single-crystal silicon layer, the piezoelectric material layer and the second single-crystal silicon layer; and before or after the bonding, performing high-doping treatment on the first single-crystal silicon layer and the second single-crystal silicon layer, and performing deep reactive ion etching on the laminated structure to form a resonator body, a connecting beam and an anchor, wherein the resonator body is suspended, and the resonator body is connected with the anchor through the connecting beam. Through the above arrangement, the first wafer and the second wafer are bonded, the traditional metal electrode is replaced by the high-doped single-crystal silicon layer, the matching degree of the thermal expansion coefficient with the piezoelectric material layer is optimized, and the electromechanical coupling efficiency and the quality factor of the MEMS resonator are improved. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can also be obtained by those skilled in the art without any creative effort based on these drawings.

[0036] Figure 1 is a flowchart of the MEMS resonator preparation method of the application;

[0037] Figure 2 is a structural schematic diagram of a first laminated structure of the application;

[0038] Figure 3 is a structural schematic diagram of a second laminated structure of the application;

[0039] Figure 4 is a structural schematic diagram of a first MEMS resonator of the application;

[0040] Figure 5 is a structural schematic diagram of a second MEMS resonator of the application;

[0041] Figure 6 is a preparation structural variation diagram of a first wafer of the application;

[0042] Figure 7 is a preparation structural variation diagram of a laminated structure of the application;

[0043] Figure 8 is an etching structural schematic diagram of a first laminated structure of the application;

[0044] Figure 9is a schematic diagram of an etching structure of a second stack structure of the present application;

[0045] Figure 10 is a schematic diagram of an etching structure of a third stack structure of the present application;

[0046] Figure 11 is a schematic diagram of an etching structure of a fourth stack structure of the present application;

[0047] Figure 12 is a schematic diagram of an etching structure of a fifth stack structure of the present application. DETAILED DESCRIPTION

[0048] Reference will now be made to the drawings in which the various examples of aspects of the application will be shown. The following description in conjunction with the drawings will be used to illustrate the examples of aspects of the present application. Unless otherwise noted, like elements in different drawings have the same or similar reference numbers. The following description of examples of aspects of the present application is not representative of all aspects consistent with the present application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of the present application as detailed in the claims.

[0049] It should be noted that, as used in this document, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element. In the description of the various embodiments of the application, like reference numerals are used to denote like elements throughout.

[0050] It should be understood that the specific embodiments described herein are merely exemplary and do not limit the application.

[0051] In the following description, the suffixes "module", "part" or "unit" used for components are merely intended for facilitating description of the present application, and are not intended to limit the present application. Therefore, "module", "part" or "unit" can be mixedly used.

[0052] In the description of this application, it should be noted that the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0053] The technical solutions shown in this application will be described in detail below through specific embodiments. It should be noted that the order of description of the following embodiments is not intended to limit the priority of the embodiments.

[0054] Please refer to Figure 1 and combined Figures 2 to 4 The MEMS resonator fabrication method of this application includes:

[0055] S101, forming a first wafer 1, the first wafer 1 including at least a first single-crystal silicon layer 11.

[0056] S102, forming a second wafer 2, the second wafer 2 including at least a second single-crystal silicon layer 21 and a piezoelectric material layer 3 located on the second single-crystal silicon layer 21.

[0057] S103, the first wafer 1 and the second wafer 2 are bonded to form a stacked structure 4 including at least a first single-crystal silicon layer 11, a piezoelectric material layer 3 and a second single-crystal silicon layer 21, and the first single-crystal silicon layer 11 and the second single-crystal silicon layer 21 are subjected to high doping treatment before or after bonding.

[0058] S104, deep reactive ion etching is performed on the stacked structure 4 to form the resonator body 10, the connecting beam 20 and the anchor 30. The resonator body 10 is suspended, and the resonator body 10 is connected to the anchor 30 via the connecting beam 20.

[0059] Thus, the first monocrystalline silicon layer 11, the piezoelectric material layer 3 and the second monocrystalline silicon layer 21 are tightly combined by bonding, and the high-doped first monocrystalline silicon layer 11 and the second monocrystalline silicon layer 21 on both sides of the piezoelectric material layer 3 are more suitable for the piezoelectric material layer 3 after bonding, that is, the thermal expansion coefficients of the two monocrystalline silicon layers on both sides after bonding are closer to the piezoelectric material layer 3, which can significantly reduce the accumulation of thermal stress and avoid the warping, cracking, failure and other situations of the resonator in high-temperature process or long-term work, and the first monocrystalline silicon layer 11 and the second monocrystalline silicon layer 21 in the stacked structure 4 after bonding can be selected as electrodes as needed, the interface is reliable, the stability is high, there is no risk of metal electrode migration and peeling, and the symmetric structure of the first monocrystalline silicon layer 11-piezoelectric material layer 3-second monocrystalline silicon layer 21 is realized by bonding, so that the resonator is mechanically symmetric, the stress distribution is uniform, the parasitic loss and stress concentration can be reduced, and the electromechanical coupling efficiency and the quality factor Q value can be improved.

[0060] Therefore, the bonding process is adopted to realize the tight combination of the above-mentioned different material layers, which is more stable than simply depositing or sputtering the electrode layer, the overall structure formed by bonding has good uniformity, which helps to reduce residual stress and improve resonator consistency and production yield.

[0061] Compared with the metal as the electrode in the related art, the first monocrystalline silicon layer 11 and the second monocrystalline silicon layer 21 can effectively adjust the equivalent capacitance, conductivity and the matching degree of the thermal expansion coefficient with the piezoelectric material layer 3 as the electrode by adjusting the doping type, doping concentration and thickness setting without affecting the mechanical properties, and since the hardness of the monocrystalline silicon layer is stable, the attenuation is small even at high temperature, so that the overall temperature coefficient of the resonator is small, thereby the resonator can have high electromechanical coupling efficiency, quality factor and temperature stability.

[0062] With reference to the foregoing description, the resonator body 10, the connecting beam 20 and the anchor 30 are formed by the following steps. Figure 4 The stacked structure 4 including at least the first monocrystalline silicon layer 11, the piezoelectric material layer 3 and the second monocrystalline silicon layer 21 is patterned and processed, and deep reactive ion etching is adopted to realize high-aspect-ratio structure separation, so as to accurately construct the three-dimensional structure characteristics of the MEMS resonator, that is, the resonator body 10, the connecting beam 20 and the anchor 30.

[0063] It should be noted that the resonator body 10 is composed of at least the stacked structure of the first monocrystalline silicon layer 11, the piezoelectric material layer 3 and the second monocrystalline silicon layer 21, and is released to a suspended state, which is used for mechanical resonance under the action of a driving voltage, and the cross-sectional shape of the resonator body 10 can be rectangular, circular or other regular shapes.

[0064] In order to realize the suspension of the resonator body 10, the release of the sacrificial layer or the slotting from the back can be combined in the etching process.

[0065] The anchor 30 is used for fixing and can be directly connected to the base or substrate layer. The connecting beam 20 can be an elastic beam, but is not limited to this. A common piezoelectric resonator adopts a cantilever beam structure, a double-end fixed beam, a bridge beam structure, etc. The connecting beam 20 not only serves as a physical support, but also provides an electrical connection path, so that the single crystal silicon layer extends to the anchor 30.

[0066] The resonator body 10 and the connecting beam 20 can be integrated and fixedly connected at one end to the anchor 30.

[0067] In combination with the foregoing embodiments, the first single crystal silicon layer 11 can serve as a bottom electrode of the MEMS resonator, and the second single crystal silicon layer 21 can serve as a top electrode of the MEMS resonator. The two together form an electro-mechanical energy conversion structure through the intermediate piezoelectric material layer 3. Thus, the first single crystal silicon layer 11 and the second single crystal silicon layer 21 are electrically coupled to the external package contacts through the connecting beam 20 and the anchor 30, so as to correspond to the sensing electrode and the driving electrode of the MEMS resonator, respectively. Thus, the MEMS resonator can receive a piezoelectric actuation driving signal and can externally sense a piezoelectric output signal indicating mechanical movement of the resonant structure.

[0068] Further, a conduction path is formed between the first single crystal silicon layer 11 and the second single crystal silicon layer 21 and the external package contacts through the anchor 30 and the connecting beam 20. For example, the single crystal silicon layer can be extended outside the resonator body 10 to form on the connecting beam 20 and the anchor 30, so as to form a conduction path on the connecting beam 20 and the anchor 30. Then, a driving voltage is applied to generate an electric potential on the piezoelectric material layer 3, so as to actuate the resonator body 10 to mechanically resonate.

[0069] In one example, referring to Figure 3 When the stack structure 4 is subjected to deep reactive ion etching, the first isolation groove 5a can be formed on the second single crystal silicon layer 21 of the second wafer 2. The first isolation groove 5a divides part of the second single crystal silicon layer 21 into a driving electrode and divides another part of the second single crystal silicon layer 21 into a sensing electrode.

[0070] Preferably, the first wafer 1 can serve as a support base of the MEMS resonator of the embodiments of the present application, and the thickness of the first single crystal silicon layer 11 includes 18 um. The thickness can not only provide sufficient support, but also ensure that a microstructure with a high aspect ratio can be formed in a deep reactive ion etching (DRIE) process, so as to effectively maintain the suspended state of the resonator body 10.

[0071] Preferably, the thickness of the piezoelectric material layer 3 includes 0.25 um. The thickness can ensure that the piezoelectric effect is significant, while avoiding the problem of excessive residual stress and energy leakage caused by excessive thickness, so as to improve the electromechanical coupling efficiency.

[0072] Preferably, the thickness of the second monocrystalline silicon layer 21 includes 2um, which can reduce the stiffness of the laminated structure 4 while ensuring its operation as a low-resistance electrode, avoiding adverse effects on the vibration mode of the resonator body 10.

[0073] In the implementation process, the bonding of the first wafer 1 and the second wafer 2 can specifically include fusion bonding of the first monocrystalline silicon layer 11 of the first wafer 1 and the piezoelectric material layer 3 of the second wafer 2. Through fusion bonding, atomic-level diffusion bonding can be achieved at the interface between the first monocrystalline silicon layer 11 and the piezoelectric material layer 3, forming a high-strength bonding interface that can withstand thermal stress during subsequent high-temperature processes and long-term operation of the resonator. In addition, fusion bonding is an intermediate layer-free bonding, completely avoiding failure problems caused by aging and peeling of the intermediate layer. Direct bonding of the monocrystalline silicon layer and the piezoelectric material layer 3 can avoid the problem of thermal expansion mismatch at the interface, improve the overall thermal stability of the resonator, and improve the electromechanical coupling efficiency and quality factor Q value.

[0074] In one example, the first monocrystalline silicon layer 11 can also have a piezoelectric material layer 3, i.e., the first wafer 1 at least includes the first monocrystalline silicon layer 11 and the piezoelectric material layer 3 on the first monocrystalline silicon layer 11, thereby constructing a double-sided piezoelectric layer structure of the resonator. Bonding of the first wafer 1 and the second wafer 2 can specifically include fusion bonding of the piezoelectric material layer 3 on the first monocrystalline silicon layer 11 and the piezoelectric material layer 3 on the second monocrystalline silicon layer 21, i.e., piezoelectric-piezoelectric interface bonding. Thereby, a symmetrical piezoelectric driving structure can be formed, which is helpful to the symmetry and stability of the resonant mode, and can also increase the electric-acoustic energy conversion efficiency. Compared with a single-layer piezoelectric structure, the electromechanical coupling coefficient is higher, and the design of the symmetrical piezoelectric material layer 3 on the upper and lower sides makes the stress distribution uniform, reduces the warping of the resonator body and energy leakage, and further improves the quality factor (Q value).

[0075] In one example, the first monocrystalline silicon layer 11 and the second monocrystalline silicon layer 21 are subjected to high-doping treatment. Taking the high-doping of the first monocrystalline silicon layer 11 as an example, a layer of phosphosilicate glass (PSG) can be deposited on the surface of the first monocrystalline silicon layer 11 through chemical vapor deposition (such as PECVD), and then high-temperature annealing at 1000℃ is performed to complete P-doping of the first monocrystalline silicon layer 11. After that, the PSG can be removed by etching or wet etching.

[0076] The high-doping treatment on the first single crystal silicon layer 11 and the second single crystal silicon layer 21 can be performed before the bonding of the first wafer 1 and the second wafer 2, that is, the first wafer 1 is formed, the first wafer 1 at least includes the first single crystal silicon layer 11, and the high-doping treatment is performed on the first single crystal silicon layer 11; the second wafer 2 is formed, the second wafer 2 at least includes the second single crystal silicon layer 21, and the piezoelectric material layer 3 is located on the second single crystal silicon layer 21, and the high-doping treatment is performed on the second single crystal silicon layer 21; the first wafer 1 and the second wafer 2 are bonded to form the laminated structure 4 at least including the first single crystal silicon layer 11, the piezoelectric material layer 3 and the second single crystal silicon layer 21; the deep reactive ion etching is performed on the laminated structure 4 to form the resonator body 10, the connecting beam 20 and the anchor 30, the resonator body 10 is suspended, and the resonator body 10 is connected with the anchor 30 through the connecting beam 20.

[0077] Alternatively, the high-doping treatment on the first single crystal silicon layer 11 and the second single crystal silicon layer 21 can be performed after the bonding of the first wafer 1 and the second wafer 2, that is, the first wafer 1 is formed, the first wafer 1 at least includes the first single crystal silicon layer 11; the second wafer 2 is formed, the second wafer 2 at least includes the second single crystal silicon layer 21, and the piezoelectric material layer 3 is located on the second single crystal silicon layer 21; the first wafer 1 and the second wafer 2 are bonded to form the laminated structure 4 at least including the first single crystal silicon layer 11, the piezoelectric material layer 3 and the second single crystal silicon layer 21; the high-doping treatment is performed on the first single crystal silicon layer 11 and the second single crystal silicon layer 21; the deep reactive ion etching is performed on the laminated structure 4 to form the resonator body 10, the connecting beam 20 and the anchor 30, the resonator body 10 is suspended, and the resonator body 10 is connected with the anchor 30 through the connecting beam 20.

[0078] It should be noted that, based on the design of the forming process of the laminated structure 4, the first single crystal silicon layer 11 has the reverse polarity parabolic TCF, and the inherent parabolic TCF of the piezoelectric material layer 3 is offset by the reverse polarity parabolic TCF of the first single crystal silicon layer 11, the first-order and second-order TCFs of the piezoelectric material layer 3 in the expected range (-40℃-85℃) are the net TCF, and the net TCF is less than 50ppm, thereby ensuring that the MEMS resonator has high temperature stability, and the crystal defects of the first single crystal silicon layer 11 and the second single crystal silicon layer 21 are few, the mechanical loss is low, and after being bonded with the piezoelectric material layer 3, the vibration energy loss can be significantly reduced, so that the MEMS resonator has high quality factor.

[0079] It can be understood that the TCF refers to a temperature coefficient of frequency, also known as a temperature compensation coefficient, which is a characteristic parameter used to describe the change of the resonator frequency with temperature. Generally, the TCF coefficient is expressed in ppm / ℃, which means that the resonator frequency changes by a certain proportion when the temperature increases or decreases by 1℃.

[0080] In one example, the first single crystal silicon layer 11, the piezoelectric material layer 3 and the second single crystal silicon layer 21 form a symmetrically stacked structure. If the resonator structure has asymmetry, reference is made to Figure 5 If the resonator body 10 and the connecting beam 20 are asymmetric with respect to the X direction in the figure, then a large energy loss is likely to occur at the resonator anchor 30 connection, which will result in a poor resonator quality factor. Therefore, the structures of the resonator can be adjusted by means of laser ablation to eliminate the asymmetry, thereby ensuring the quality factor of the resonator.

[0081] In one possible implementation of the present application, reference is made to Figure 6 The forming of the first wafer 1 comprises:

[0082] A first silicon-on-insulator wafer is provided, which at least comprises a first silicon layer 101, and a recess 102 is formed on the first silicon layer 101;

[0083] A second silicon-on-insulator wafer is provided, which comprises a first single crystal silicon layer 11 and a first dielectric layer 103 on the first single crystal silicon layer 11;

[0084] The side of the first silicon layer 101 with the recess 102 and the first dielectric layer 103 are bonded to form a first silicon-on-insulator (C-SOI) wafer 1, and the recess 102 forms a cavity 104 in the first wafer 1.

[0085] The cavity 104 provides a prefabricated space for the suspended arrangement of the resonator body 10 to facilitate the release of the resonator body 10, and the first silicon layer 101 serves as a support base structure. It can be understood that, due to the thin thickness of the single crystal silicon in the resonator body 10, the first silicon layer 101 provides support for subsequent bonding, etching and other processes to improve process reliability, and of course also serves as a support layer for the resonator.

[0086] Preferably, the recess 102 is formed on the first silicon layer 101, which can specifically comprise: depositing an intermediate dielectric layer 101a on the first silicon layer 101, forming a photoresist mask 101b on the intermediate dielectric layer 101a, and the photoresist mask 101b has a photoetching pattern that exposes the recess 102, then etching the first silicon-on-insulator wafer to form the recess 102 on the first silicon layer 101, and then removing the photoresist mask 101b and the intermediate dielectric layer 101a.

[0087] Optionally, the intermediate dielectric layer 101a comprises a silicon dioxide layer.

[0088] Preferably, in the process of forming the first wafer 1, the first single crystal silicon layer 11 can be subjected to high-doping treatment. Specifically, a layer of phosphorus-silicon glass 11a is deposited on the surface of the first single crystal silicon layer 11 by chemical vapor deposition (such as PECVD), and then high-temperature annealing at 1000℃ is performed to complete P-doping of the first single crystal silicon layer 11. After that, the phosphorus-silicon glass layer 11a can be removed by etching or wet etching. It can be understood that, in the process of forming the second wafer 2, the second single crystal silicon layer 21 can also be subjected to high-doping treatment, and the high-doping treatment process is the same as above.

[0089] In a possible implementation of the present application, with reference to Figure 7 The forming of the second wafer 2 comprises:

[0090] A third silicon-on-insulator wafer is provided, which at least comprises a second silicon layer 201, a second dielectric layer 202 and a second single crystal silicon layer 21 are formed on the second silicon layer 201 in sequence, and an aluminum nitride layer is deposited on the second single crystal silicon layer 21 to form the piezoelectric material layer 3.

[0091] That is, the forming material of the piezoelectric material layer 3 comprises aluminum nitride (AlN), which has excellent piezoelectric properties, good thermal conductivity, chemical stability and good compatibility with the silicon substrate, and the c-axis preferred orientation structure thereof can provide a higher piezoelectric response on a specific crystal face.

[0092] Of course, the forming material of the piezoelectric material layer 3 of the embodiment of the present application is not limited to this, and can also include but is not limited to zinc oxide, lead zirconate titanate, lithium niobate, gallium nitride, indium nitride, scandium aluminum nitride or quartz, etc.

[0093] Preferably, based on the forming processes of the first wafer 1 and the second wafer 2, after the first wafer 1 and the second wafer 2 are bonded, the second silicon layer 201 and the second dielectric layer 202 are etched and removed.

[0094] Then, in the process of bonding the first wafer 1 and the second wafer 2, the first single crystal silicon layer 11 of the first wafer 1 and the piezoelectric material layer 3 of the second wafer 2 can be considered to be fusion bonded, thereby forming a stacked structure 4, so as to facilitate subsequent patterning processing of the stacked structure 4, and deep reactive ion etching is adopted to realize structure separation with high aspect ratio, so as to accurately construct the three-dimensional structure features of the MEMS resonator, i.e., the resonator body 10, the connecting beam 20 and the anchor 30.

[0095] In a possible implementation of the present application, the deep reactive ion etching of the stacked structure 4 comprises:

[0096] a、With reference to Figure 8 , the region of the top of the laminated structure 4 corresponding to the resonator body 10 is a target region M, and the region other than the target region M is a peripheral region N.

[0097] That is, through the region division, the laminated structure 4 is etched by deep reactive ion etching, which facilitates the patterning of the etching process to realize the division of the functional structure and the peripheral support structure in the subsequent process.

[0098] b、With reference to Figure 8 , a second isolation groove 5b connected to the piezoelectric material layer 3 is formed on the second single crystal silicon layer 21 in the target region M by the first mask 401.

[0099] In this step, the first mask 401 has a photoetching pattern exposing the second isolation groove 5b, and the second isolation groove 5b connected to the piezoelectric material layer 3 can be formed by etching the photoetching pattern.

[0100] Then, the second isolation groove 5b can be regarded as dividing the second single crystal silicon layer 21 into two parts, that is, the second isolation groove 5b plays the role of an electrical isolation groove to prevent electrode crosstalk and isolate the sensing electrode and the driving electrode formed on the second single crystal silicon layer 21 subsequently.

[0101] After the second isolation groove 5b is formed, the first mask 401 is removed.

[0102] c、With reference to Figure 9 , a ground electrode hole 6a connected to the first dielectric layer 103 is formed in the peripheral region N by the second mask 402.

[0103] In this step, the second mask 402 has a photoetching pattern exposing the ground electrode hole 6a, and the ground electrode hole 6a connected to the first dielectric layer 103 can be formed by etching the photoetching pattern.

[0104] Among them, the ground electrode hole 6a can be symmetrically distributed in the peripheral region N relative to the target region M.

[0105] After the ground electrode hole 6a is formed, the second mask 402 is removed.

[0106] d、With reference to Figure 10 , an electrode material is deposited on the top of the laminated structure 4 by the third mask 403, a ground electrode 6 is formed on the ground electrode hole 6a, and a driving electrode 71 and a sensing electrode 72 are formed on both sides of the second isolation groove 5b in the target region M.

[0107] In this step, the third mask 403 has a deposition pattern exposing the ground electrode hole 6a, and the third mask 403 has a deposition pattern exposing the driving electrode 71 and the sensing electrode 72, and the ground electrode 6, the driving electrode 71 and the sensing electrode 72 are formed by depositing electrode material on the deposition pattern.

[0108] After the ground electrode 6, the driving electrode 71 and the sensing electrode 72 are formed, the third mask 403 is removed.

[0109] The driving electrode 71 and the sensing electrode 72 are located in the target area M and can be symmetrically distributed relative to the second isolation groove 5b.

[0110] The design of the ground electrode 6 in the peripheral area N can effectively reduce the parasitic capacitance effect, suppress electromagnetic interference and signal crosstalk, and further improve the resonator quality factor and enhance the reliability.

[0111] Preferably, the electrode material includes polysilicon and metal Ge, that is, the ground electrode 6 includes a polysilicon layer 601 and a metal layer 602, and the metal layer 602 is located on top of the polysilicon layer 601.

[0112] In addition, the deposition structure of the driving electrode 71 and the sensing electrode 72 is the same as that of the ground electrode 6, and also includes a polysilicon layer and a metal layer.

[0113] e、Reference Figure 11 The fourth mask 404 is used to form a first release hole 81 and a second release hole 91 on the laminated structure 4, the first release hole 81 is connected to the first silicon layer 101 by the second single crystal silicon layer 21, and the second release hole 91 is connected to the cavity 104 by the second single crystal silicon layer 21, so as to release the area of the resonator body 10, form the resonator body 10, the connecting beam 20 and the anchor 30.

[0114] In this step, the fourth mask 404 has a lithography pattern exposing the first release hole 81 and the second release hole 91, and then the first release hole 81 connected to the first silicon layer 101 and the second release hole 91 connected to the cavity 104 can be formed by etching the lithography pattern.

[0115] The second release hole 91 is located in the target area M and can be symmetrically distributed relative to the second isolation groove 5b, and the first release hole 81 can be located in the peripheral area N close to the target area M, or at the connection between the target area M and the peripheral area N, so as to release the resonator body 10 corresponding to the target area M.

[0116] In addition, after the first release hole 81 and the second release hole 91 are formed, the fourth mask 404 is removed.

[0117] Preferably, after forming the first release hole 81 and the second release hole 91 on the laminated structure 4 by the fourth mask 404, the method further comprises: introducing an acid etching gas into the second release hole 91 to remove the first dielectric layer 103 in the cavity 104, thereby ensuring the structure effect of the resonator body 10 being suspended.

[0118] The first dielectric layer 103 and the second dielectric layer 202 can be a silicon dioxide layer.

[0119] Optionally, the acid etching gas is a hydrofluoric acid gas.

[0120] It can be understood that the first release hole 81 does not represent that the structures on both sides of the corresponding first release hole 81 on the first silicon layer 101 are completely separated, and the first release hole 81 has a connecting structure that is not connected to the driving electrode 71 and the sensing electrode 72, and the second release hole 91 is the same, for example, the second release hole 91 has a connecting beam 20 connected to the resonator body 10.

[0121] The application further discloses a MEMS resonator prepared by the MEMS resonator composite preparation method.

[0122] The MEMS resonator comprises a resonator body 10, a connecting beam 20, and an anchor 30.

[0123] In the implementation process, the resonator body 10 is suspended, and the resonator body 10 is connected to the anchor 30 through the connecting beam 20, wherein the resonator body 10 is a laminated structure 4 formed by bonding the first wafer 1 and the second wafer 2, the laminated structure 4 comprises at least a first single-crystal silicon layer 11, a piezoelectric material layer 3, and a second single-crystal silicon layer 21, and the first single-crystal silicon layer 11, the piezoelectric material layer 3, and the second single-crystal silicon layer 21 are sequentially laminated.

[0124] In a possible implementation of the application, the second single-crystal silicon layer 21 is provided with a first isolation groove 5a connected to the piezoelectric material layer 3, the first isolation groove 5a divides part of the second single-crystal silicon layer 21 into a driving electrode, and divides another part of the second single-crystal silicon layer 21 into a sensing electrode.

[0125] For other working principles and processes of the MEMS resonator, refer to the foregoing description of the MEMS resonator composite preparation method of the embodiment, which will not be described here.

[0126] The MEMS resonator and the composite preparation method thereof are described in detail above, and the principles and implementation manners of the application are described by using specific examples. It should be noted that the description of each embodiment in the application has its own emphasis, and the parts not described or recorded in a certain embodiment can be referred to the related description of other embodiments.

[0127] The above merely describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, and each technical feature of the technical solutions of the present application can be combined arbitrarily, in order to make the description simple, each technical feature in the above embodiments is not described in all possible combinations, and any equivalent structure or equivalent flow conversion made by using the content of the present application specification and drawings, or directly or indirectly applied in other related technical fields, as long as the combination of these technical features does not exist contradiction, are also included in the patent protection scope of the present application.

Claims

1. A method for fabricating a MEMS resonator, characterized in that, include: Forming a first wafer, the first wafer comprising at least a first single-crystal silicon layer, wherein forming the first wafer comprises: providing a first silicon-on-insulator (SiI) wafer, the first SiI wafer comprising at least a first silicon layer, forming a groove on the first silicon layer; providing a second SiI wafer, the second SiI wafer comprising the first single-crystal silicon layer and a first dielectric layer on the first single-crystal silicon layer; bonding one side of the first silicon layer having the groove to the first dielectric layer to form the first SiI-type first wafer, and the groove forming a cavity within the first wafer; A second wafer is formed, the second wafer comprising at least a second single-crystal silicon layer and a piezoelectric material layer located on the second single-crystal silicon layer; The first wafer and the second wafer are bonded to form a stacked structure including at least the first single-crystal silicon layer, the piezoelectric material layer and the second single-crystal silicon layer, and the first single-crystal silicon layer and the second single-crystal silicon layer are subjected to high doping treatment before or after the bonding is performed. The stacked structure is subjected to deep reactive ion etching to form a resonator body, a connecting beam, and an anchor. The resonator body is suspended in the air, and the resonator body is connected to the anchor via the connecting beam.

2. The MEMS resonator fabrication method as described in claim 1, characterized in that, The first wafer includes at least a first single-crystal silicon layer and a piezoelectric material layer formed on the first single-crystal silicon layer.

3. The MEMS resonator fabrication method as described in claim 1, characterized in that, The formation of the second wafer includes: A third silicon-on-insulator wafer is provided, the third silicon-on-insulator wafer comprising at least a second silicon layer, wherein a second dielectric layer and a second monocrystalline silicon layer are sequentially formed on the second silicon layer; An aluminum nitride layer is deposited on the second single-crystal silicon layer to form the piezoelectric material layer.

4. The MEMS resonator fabrication method as described in claim 3, characterized in that, After bonding the first wafer and the second wafer, the process further includes: The second silicon layer and the second dielectric layer are etched away.

5. The MEMS resonator fabrication method as described in claim 2, characterized in that, The bonding of the first wafer and the second wafer includes: The first single-crystal silicon layer of the first wafer is fused and bonded to the piezoelectric material layer of the second wafer; or, The piezoelectric material layer on the first single-crystal silicon layer is fused and bonded to the piezoelectric material layer on the second single-crystal silicon layer.

6. The method for fabricating a MEMS resonator as described in claim 1, characterized in that, The deep reactive ion etching of the stacked structure includes: A first isolation trench is formed on the second single-crystal silicon layer of the second wafer. The second single-crystal silicon layer in the first isolation trench is used as a driving electrode in one part and as a sensing electrode in the other part.

7. The MEMS resonator fabrication method as described in claim 4, characterized in that, The deep reactive ion etching of the stacked structure includes: The area at the top of the stacked structure corresponding to the resonator body is designated as the target area, and the area excluding the target area is designated as the peripheral area. A second isolation trench is formed on the second monocrystalline silicon layer in the target region through a first mask, and the second isolation trench is connected to the piezoelectric material layer. A grounding electrode hole is formed in the peripheral region by means of a second mask, and the grounding electrode hole is connected to the first dielectric layer by the second monocrystalline silicon layer; Electrode material is deposited on top of the stacked structure through a third mask, a ground electrode is formed on the ground electrode hole, and a drive electrode and a sensing electrode are formed on both sides of the second isolation groove in the target area. A first release hole and a second release hole are formed on the stacked structure by a fourth mask. The first release hole is connected to the first silicon layer by the second single crystal silicon layer, and the second release hole is connected to the cavity by the second single crystal silicon layer to release the area of ​​the resonator body, thereby forming the resonator body, connecting beam and anchor.

8. The method for fabricating a MEMS resonator as described in claim 7, characterized in that, After forming the first release hole and the second release hole on the stacked structure through the fourth mask, the method further includes: Acidic gas is introduced into the second release hole to remove the first dielectric layer inside the cavity.

9. A MEMS resonator, fabricated by the MEMS resonator fabrication method according to any one of claims 1 to 8, characterized in that, include: The resonator body, the connecting beam, and the anchor are provided. The resonator body is suspended in the air and the resonator body is connected to the anchor via the connecting beam. The resonator body is a stacked structure formed by bonding a first wafer and a second wafer. The stacked structure includes at least a first single-crystal silicon layer, a piezoelectric material layer and a second single-crystal silicon layer, which are stacked sequentially.

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