WO2022226914A1

WO2022226914A1 - Piezoelectric mems silicon resonator having beam structure, forming method therefor, and electronic device

Info

Publication number: WO2022226914A1
Application number: PCT/CN2021/091101
Authority: WO
Inventors: 张孟伦; 杨清瑞; 宫少波
Original assignee: 天津大学
Priority date: 2021-04-29
Filing date: 2021-04-29
Publication date: 2022-11-03

Abstract

The present invention provides a piezoelectric MEMS silicon resonator having a beam structure, a forming method therefor, and an electronic device. The forming method comprises: providing, as a substrate, an SOI silicon wafer having a lower cavity, a device silicon layer being provided above the lower cavity; sequentially forming a lower electrode, a piezoelectric layer, and an upper electrode; etching the device silicon layer to form a beam structure; forming a sacrificial layer on a current semiconductor structure; growing an encapsulation material on the sacrificial layer to form a thin film encapsulation layer, and then etching to form a through hole at a location, above a beam structure region, in the thin film encapsulation layer; removing the sacrificial layer above a vibration region of the beam structure to form an upper cavity, and retaining the sacrificial layer above a fixed end of the beam structure; growing the encapsulation material again to seal the through hole; forming an electrical-connection through hole that passes through the thin film encapsulation layer and the retained sacrificial layer; and forming an electrode connection in the electrical-connection through hole. The piezoelectric MEMS silicon resonator manufactured by the forming method can maintain a high device vacuum degree for a long time, and implement a high quality factor and long-term stability of the resonator.

Description

Piezoelectric MEMS silicon resonator with beam structure, method for forming the same, and electronic device

technical field

The invention relates to the technical field of resonators, in particular to a piezoelectric MEMS silicon resonator and a method for forming the same, and an electronic device.

Background technique

The resonator utilizes the phenomenon that the resonant frequency can be changed by the measured physical quantity, and has the advantages of high repeatability, high resolution and high sensitivity. Micro-Electro-Mechanical System (MEMS) resonators with high quality factor have been widely used in sensors, oscillators and actuators to obtain high mechanical sensitivity.

The vacuum packaging of devices in the MEMS process is a difficult point in the entire process. The formation of a stable vacuum environment through packaging is crucial to the reliability and high quality factor of MEMS devices. The quality of the package determines the quality and service life of the entire device. Good packaging can prevent the vacuum from being damaged by potential contaminants (such as dust particles, water vapor, and gas molecules) in the subsequent process and during the use of the device. Therefore, the packaging technology that can maintain the vacuum degree of MEMS devices for a long time is the main obstacle to the commercialization of MEMS devices.

Currently, the most commonly used MEMS device packaging method is the method of bonding caps on the MEMS device. The process of bonding caps on MEMS devices can be achieved by various methods, mainly including anodic bonding of glass and silicon, thermocompression bonding of glass and silicon, and bonding of silicon and silicon through an intermediate gold layer. As the bonding material for the interlayer, phosphosilicate glass (PSG) or glass frit, has been used to bond glass to silicon, due to the application of the bonding material it is possible to incorporate more topological structures during the bonding process cover. In order to further improve the quality of the bonding, local heating can be performed in the bonding area. The advantages include: better control of the bonding temperature and higher temperature in the bonding area than the device can be obtained, reducing the impact on the temperature-sensitive materials in the whole device. Thermal budget concerns. A bonding process using polysilicon and gold as a localized heating technique for microheaters has been used in MEMS production. In addition, getters are sometimes used to control the pressure in the cavity, reducing the effects of outgassing from bonding layers and device materials.

Although technicians continue to improve the quality of bonding packaging, the density of the bonding interface layer cannot reach the same order of magnitude as that of the silicon substrate, so it is still impossible to completely avoid the leakage of the bonding layer in the long-term use of the device. In addition, the bonding material also has a certain phenomenon of releasing gas, and even if there is a getter, the gas release problem cannot be completely solved. Therefore, the device using the existing packaging process cannot effectively maintain the vacuum degree inside after packaging, and this problem is still the bottleneck of devices that need to work under vacuum, such as MEMS resonators. Since the vacuum degree in the resonant cavity of the prior art decreases with time and increases the damping of the resonator, it is difficult to maintain the long-term stability of the quality factor of the resonator. Therefore, it is urgent to develop a reliable packaging technology to effectively maintain a high vacuum degree in the resonant cavity for a long time, so as to improve the quality factor and service life of the resonant sensor.

SUMMARY OF THE INVENTION

In view of this, the present invention proposes a piezoelectric MEMS silicon resonator with a beam structure with low cost, high quality factor, and high stability, a method for forming the same, and an electronic device including the piezoelectric MEMS silicon resonator with a beam structure. equipment.

A first aspect of the present invention is a method for forming a piezoelectric MEMS silicon resonator with a beam structure, comprising: providing an SOI silicon wafer with a lower cavity as a substrate, wherein the lower cavity in the SOI silicon wafer with a lower cavity is There is a device silicon layer above the cavity; a lower electrode, a piezoelectric layer and an upper electrode are sequentially formed on the substrate; the device silicon layer is etched to form the beam structure, wherein the device silicon layer serves as the forming a driven layer of the beam structure; forming a sacrificial layer on the current semiconductor structure, the sacrificial layer completely covering the current semiconductor structure; growing an encapsulation material on the sacrificial layer to form a thin film encapsulation layer, and then forming a thin film encapsulation layer on the thin film Etching via holes above the beam structure area in the encapsulation layer; removing the sacrificial layer above the vibration area of the beam structure to form an upper cavity, and retaining the sacrificial layer above the fixed end of the beam structure ; Grow the encapsulation material again to close the through holes; form electrical connection through holes through the thin film encapsulation layer and the remaining sacrificial layer; and form electrode connections in the electrical connection through holes.

Optionally, the beam structure is a cantilever beam or a fixed beam, or a multi-beam structure including the cantilever beam or the fixed beam.

Optionally, the driven layer is doped single crystal silicon, and the doping concentration is greater than or equal to 10 ¹⁹ cm ^-3 .

Optionally, there is an insulating layer under the device silicon layer, and the method further includes: etching the device silicon layer to form the beam structure while etching the insulating layer, wherein the device silicon layer and The insulating layers all serve as driven layers of the beam structure.

Optionally, the sacrificial layer is silicon oxide, photoresist or polymer.

Optionally, the packaging material is monocrystalline silicon or polycrystalline silicon.

Optionally, the method of growing the packaging material is epitaxial growth.

Optionally, the thin film encapsulation layer has a thickness of 10 to 100 microns, or 20 to 50 microns.

Optionally, the thickness of the sacrificial layer is greater than 10 microns.

Optionally, when the encapsulation material is polysilicon, the step of opening a hole above the beam structure region in the thin film encapsulation layer is replaced by the following step: etching the polysilicon thin film through an electrochemical reaction encapsulation layer to transform it into a porous thin-film encapsulation layer of porous polysilicon.

Optionally, it also includes: before the step of providing the SOI silicon wafer with the lower cavity as the substrate, forming a getter layer inside the lower cavity; or/and, before the step of forming the sacrificial layer Then, before the step of growing the encapsulation material to form the thin film encapsulation layer, a getter layer is formed on the sacrificial layer.

Optionally, the piezoelectric layer material is aluminum nitride or doped aluminum nitride.

The second aspect of the present invention provides a piezoelectric MEMS silicon resonator with a beam structure, which is manufactured by the forming method disclosed in the present invention.

A third aspect of the present invention provides a piezoelectric MEMS silicon resonator with a beam structure, comprising: a substrate, the top of the substrate has a lower cavity; a beam structure located on the substrate, the beam structure It includes a driven layer, a lower electrode, a piezoelectric layer and an upper electrode sequentially stacked from bottom to top; a support structure, the support structure is located above the fixed end of the beam structure; a thin film encapsulation layer, the thin film encapsulation layer covers the a beam structure and the support structure, an upper cavity is formed between the thin film encapsulation layer and the beam structure; and an electrode connection, the electrode connection penetrates the support structure and the thin film encapsulation layer.

Optionally, the material of the thin film encapsulation layer is monocrystalline silicon or polycrystalline silicon.

Optionally, the height of the upper cavity is greater than 10 microns.

Optionally, a getter layer is also included, and the getter layer is located inside the upper cavity and/or the lower cavity.

A fourth aspect of the present invention provides an electronic device including the piezoelectric MEMS silicon resonator with a beam structure disclosed in the present invention.

According to the technical solution of the present invention, based on a piezoelectric MEMS silicon resonator (PSR) resonator, a silicon thin film packaging technology is adopted. Compared with the traditional packaging technology, because it does not need a bonding layer, the air tightness is better, and a higher vacuum degree (<1Pa) can be achieved; at the same time, it avoids the release of gas from the bonding material and the leakage of the bonding interface. Vacuum drift. In addition, high temperature heating is required in the production steps of epitaxial packaging, and the PSRs packaged with silicon thin film packaging technology in the example of the present invention are all made of high temperature resistant materials, such as aluminum nitride piezoelectric layers, so the process is compatible in production. Therefore, Silicon thin film packaging technology has great advantages for high temperature device packaging such as PSR.

Description of drawings

For purposes of illustration and not limitation, the present invention will now be described in accordance with preferred embodiments thereof, particularly with reference to the accompanying drawings, wherein:

1 to 9 are schematic process diagrams of a method for forming a piezoelectric MEMS silicon resonator with a beam structure according to an embodiment of the present invention;

10 is a schematic cross-sectional view of a piezoelectric MEMS silicon resonator having a beam structure according to the first embodiment of the present invention;

11 is a schematic cross-sectional view of a piezoelectric MEMS silicon resonator having a beam structure according to a second embodiment of the present invention;

12 is a schematic cross-sectional view of a piezoelectric MEMS silicon resonator having a beam structure according to a third embodiment of the present invention.

Detailed ways

The current bonding packaging technology used in MEMS device fabrication engineering is difficult to maintain the vacuum degree of the cavity in the device for a long time due to the poor airtightness of the bonding interface and the release of gas from the bonding material, thus affecting the quality factor and reliability of the device. In view of the problems existing in the prior art, the piezoelectric MEMS silicon resonator with beam structure and the method for forming the same according to the embodiment of the present invention, the core is to use the method of single crystal silicon epitaxy and selective etching to fabricate the beam structure of the resonator, and A piezoelectric thin film is deposited over single crystal silicon to form the resonator. The technical solution of the present invention realizes encapsulation by epitaxial thin-layer silicon and removing sacrificial materials, avoiding the existence of bonding interface and bonding material, and at the same time, the air tightness of the epitaxial interface is much higher than that of the bonding interface, so it can be realized in a longer time. A high vacuum is maintained inside the cavity. The technical solution of the present invention is simple and easy to implement, and the fabricated device has the advantages of low cost, high quality factor, high stability and the like.

In order to make the skilled person understand better, the structure and material of each part in the drawings in the description are explained first:

100: Package structure, including:

101: Metal connection area, the specific material can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or a composite of the above metals or their alloys.

102: Electrical isolation layer, the specific material can be selected from silicon oxide, aluminum nitride or aluminum oxide, etc.

103b: Metallized connection, the specific materials are the same as 101.

104: Thin film encapsulation layer, the material can be selected from monocrystalline silicon or polycrystalline silicon.

200: Beam structure. It should be noted that the beam structure may specifically be a cantilever beam or a fixed beam, or a multi-beam structure including a cantilever beam or a fixed beam, for example: a tuning fork structure composed of two cantilever beams, or a multi-cantilever beam A comb-like structure composed of beams. For the purpose of simple description, the cantilever beam is used in the drawings of the present invention, but this is only an example and not a limitation. Beam structure 200 includes:

201: Upper electrode, the same material as 101.

202: Piezoelectric layer, which can be selected from materials such as aluminum nitride, zinc oxide, and PZT, and includes a rare earth element doped material with a certain atomic ratio of the above materials. The piezoelectric layer materials are preferably aluminum nitride and doped aluminum nitride, because aluminum nitride has excellent thermal compatibility, even at a high temperature above 1100 degrees Celsius (such as epitaxial growth of single crystal silicon or polycrystalline silicon requires a high temperature of about 1000 degrees) It is still possible to keep the piezoelectric properties of the device from deteriorating.

203: the lower electrode, the material is the same as that of 101.

204: The driven layer, the material can be selected from single crystal silicon, aluminum nitride, gallium arsenide or sapphire, etc. The driven layer can be processed from the device silicon layer in the SOI type substrate.

300: cavity, including: upper cavity 301 and lower cavity 302.

400: Substrate, including:

401: insulating layer, generally silicon dioxide.

402: backing substrate, the material is the same as that of 104.

500: a sacrificial layer, the material may be silicon oxide, photoresist, polymer material, and the like.

The present invention will be further described below in conjunction with the accompanying drawings. As shown in FIGS. 1 to 9 , the method for forming a piezoelectric MEMS silicon resonator with a beam structure according to an embodiment of the present invention mainly includes the following nine steps.

Step 1: Provide the substrate.

Specifically, as shown in FIG. 1 , an SOI silicon wafer with a lower cavity can be directly provided as a substrate, and the substrate includes a back substrate 402 made of silicon material, an insulating layer 401 made of silicon dioxide material, the lower cavity 302 and A device silicon layer 204 of silicon material. In the implementation, the SOI silicon wafer with cavity can also be used, but the substrate can be gradually fabricated by the following methods: providing a silicon substrate; forming an insulating layer on the top surface of the silicon substrate; etching grooves on the top of the current semiconductor structure; A sacrificial layer is filled in the groove; a device silicon layer of silicon material is formed over the current semiconductor structure; the sacrificial layer is removed to form a lower cavity; and the current semiconductor structure is used as a substrate.

Step 2: Deposit the lower electrode, the active layer and the upper electrode in sequence.

Specifically, as shown in FIG. 2 , molybdenum is first deposited on the substrate, and then the molybdenum electrode is patterned by etching the molybdenum electrode by using the patterned photoresist as a mask to obtain the lower electrode 203 . A second layer of aluminum nitride piezoelectric layer is deposited, and silicon oxide is deposited on the aluminum nitride, and then the silicon oxide is wet-etched with the photoresist as a mask, and then the aluminum nitride is etched with the silicon oxide as a hard mask. It is patterned by dry etching to obtain the piezoelectric layer 202 . Referring to the fabrication process of the lower electrode, the upper electrode 201 is fabricated.

Step 3: Etch the device silicon layer to form the beam structure.

Specifically, as shown in FIG. 3, a layer of silicon oxide is deposited on the structure obtained in the previous step, then the photoresist is used as a mask, and HF is used as an etchant to etch the silicon oxide; and then the patterned silicon oxide is used to etch the silicon oxide. As a hard mask, the silicon is dry etched until the device silicon layer 204 and insulating layer 401 of the SOI are etched through to release the beam structure. At this time, the device silicon layer 204 is transformed into the driven layer 204 . Then, optionally, the insulating layer 401 under the driven layer 204 is removed with BOE. If the insulating layer 401 is left, the insulating layer can be used for temperature compensation.

Step 4: forming a sacrificial layer.

Specifically, as shown in FIG. 4 , a sacrificial layer 500 of silicon oxide material is grown on the structure obtained in the previous step, and the sacrificial layer 500 completely covers the structure of FIG. 3 . The top of the sacrificial layer 500 may be higher than the upper surface of the upper electrode 201 by more than 10 microns (adjustable as required, and the amplitude is required to be greater than that of the beam structure), and then the silicon oxide is patterned. In particular, the material of the sacrificial layer 500 may also be a photoresist, a polymer material, or the like.

Step 5: Growing an encapsulation material on the sacrificial layer to form a thin film encapsulation layer, and then etching through holes in the thin film encapsulation layer above the beam structure regions.

Specifically, as shown in FIG. 5 , the polysilicon material is first grown on the structure obtained in the previous step to form the thin film encapsulation layer 104 , and then the thin film encapsulation layer 104 is located above the beam structure area, that is, above the upper cavity area. , etching multiple vias. The thickness of the thin film encapsulation layer 104 is about 10 to 100 microns, preferably 20 to 50 microns. If the thin film encapsulation layer 104 is too thin, the encapsulation vacuum degree cannot be guaranteed for a long time. Optionally, the manner of growing the encapsulation material may specifically be epitaxial growth. Optionally, when the encapsulation material is polysilicon, in addition to etching, the thin film encapsulation layer 104 of polysilicon can also be etched through electrochemical reaction in the step of forming the through hole, so as to transform it into a porous thin film of polysilicon with a porous structure. Encapsulation layer 104 .

Step 6: Remove the local sacrificial layer.

Specifically, as shown in FIG. 6 , the sacrificial layer above the vibration area of the beam structure is removed to form an upper cavity, and the sacrificial layer above the fixed end of the beam structure is retained. The sacrificial layer 500 of the silicon oxide material below can be etched away through the through holes on the polysilicon thin film encapsulation layer 104 with HF vapor or solution to obtain the upper cavity 301. At the same time, a part of silicon oxide needs to be left on the right side of the beam structure to ensure subsequent electrical connections. The two electrodes will not be short-circuited. Therefore, the vias should not be too far to the right in step 5. In particular, the method of removing the sacrificial layer here is easy according to the type of material used to deposit the sacrificial layer 500 in step 5; if it is photoresist, it should be removed by developing solution or NMP, and if it is polymer, heating and decomposing methods can be selected. Remove, if it is other materials, choose the corresponding method.

Step 7: The encapsulation material is grown again to close the vias.

First, as shown in Figure 7, the cavity is cleaned with high temperature hydrogen and chlorine gas, and then the epitaxial polysilicon is continued in a vacuum environment, so that the through hole is completely covered.

Step 8: Form electrical connection vias.

Specifically, as shown in FIG. 8 , a layer of aluminum nitride is first deposited, and an electrical isolation layer 102 of aluminum nitride material is patterned above the connection between the upper and lower electrodes, respectively, and then polysilicon is dry-etched using the aluminum nitride as a mask, Then, the silicon oxide is dry-etched to the molybdenum electrodes; the connection holes are oxidized to prevent subsequent electrical connections from short-circuiting through the polysilicon. Electrical connection vias penetrate through the thin film encapsulation layer and the preserved sacrificial layer.

Step 9: Forming Electrode Connections.

Specifically, as shown in FIG. 9 , metal copper is first deposited to fill the electrical connection vias, and then copper etching solution is used to remove the copper on the thin film encapsulation layer, leaving only the copper inside the electrical connection vias; finally, gold is deposited and carried out Patterning results in a metal connection region 101 and a metallized connection 103b.

The method for forming a piezoelectric MEMS silicon resonator with a beam structure according to the embodiment of the present invention may further include the following step: before the step of providing the SOI silicon wafer with the lower cavity as the substrate, forming a getter inside the lower cavity or/and, forming a getter layer over the sacrificial layer after the step of forming the sacrificial layer and before the step of growing the encapsulation material to form the thin film encapsulation layer. In this way, the upper cavity and/or the lower cavity of the finally obtained piezoelectric MEMS silicon resonator with beam structure can have a getter layer, which can better maintain the vacuum degree in the cavity.

In the method for forming a piezoelectric MEMS silicon resonator with a beam structure according to an embodiment of the present invention, the driven layer may be doped single crystal silicon, and the doping concentration is greater than or equal to 10 ¹⁹ cm ⁻³ . The doping method can be as follows: (1) Doping in the single crystal growth process, such as Czochralski (CZ), doping the doping element into the polysilicon raw material, and then using the doped single crystal silicon to make the SOI type substrate; (2) The dopant is diffused into the top silicon material of the SOI by means of high temperature diffusion, or the SOI is made by diffusion-doped silicon wafer; (3) the top silicon material of the SOI is doped by the method of ion implantation. By controlling the doping concentration, the equivalent temperature coefficient of the beam structure can be adjusted, thereby eliminating or reducing the temperature drift effect of the device, which is beneficial for the device to avoid errors caused by temperature changes, and can improve the reliability of the device.

In the method for forming the piezoelectric MEMS silicon resonator with the beam structure according to the embodiment of the present invention, the step of "removing the insulating layer under the driven layer" may also be omitted. In other words, the insulating layer under the driven layer remains. The insulating layer 401 remaining in this embodiment can also be used as a temperature compensation layer of the beam structure 200 to improve the temperature drift problem of the device. It should be noted that, if materials such as SiO ₂ are used as the temperature compensation material, the temperature compensation layer can also be arranged on the surface of the upper electrode, between the upper electrode and the piezoelectric active layer, between the piezoelectric active layer and the lower electrode, and between the lower electrode. and the driven layer or in two or more of the above interfaces.

The piezoelectric MEMS silicon resonator with a beam structure according to the embodiment of the present invention can be produced by the method for forming a piezoelectric MEMS silicon resonator with a beam structure of the present invention.

A piezoelectric MEMS silicon resonator with a beam structure according to an embodiment of the present invention includes: a substrate, the top of the substrate has a lower cavity; a beam structure located on the substrate, the beam structure includes followers stacked sequentially from bottom to top layer, lower electrode, piezoelectric layer and upper electrode; support structure, the support structure is located above the fixed end of the beam structure; thin film encapsulation layer, the thin film encapsulation layer covers the beam structure and the support structure, and an upper cavity is formed between the thin film encapsulation layer and the beam structure ; and electrode connections that run through the support structure and the thin film encapsulation layer. Wherein, the material of the thin film encapsulation layer may be monocrystalline silicon or polycrystalline silicon. The thickness of the thin film encapsulation layer may be 10 to 100 microns, or 20 to 50 microns. The height of the upper cavity may be greater than 10 microns. In addition, a getter may be included in the resonator, the getter being located inside the upper cavity and/or the lower cavity. The material of the getter may be titanium (Ti) and titanium alloys, zirconium (Zr) and zirconium alloys.

According to the piezoelectric MEMS silicon resonator having a beam structure according to an embodiment of the present invention, the beam structure is a cantilever beam or a fixed beam, or a multi-beam structure including a cantilever beam or a fixed beam.

The piezoelectric MEMS silicon resonator with beam structure according to the first embodiment of the present invention is shown in FIG. 10 . In the resonator, the cavity 300 is surrounded by the package structure 100 and the substrate 400 , and includes an upper cavity 301 and a lower cavity 302 . The function of the cavity 300 is to provide a certain space for the vibration of the beam structure, and a relatively high degree of vacuum needs to be maintained in the cavity 300 to reduce the damping of the vibration of the beam. The upper cavity 301 is formed by removing the sacrificial material after growing the epitaxial thin film encapsulation layer, and the lower cavity 302 is formed by etching the top of the base silicon material, or directly using an SOI silicon wafer with a cavity. Electrical connection through holes exist on the package structure 100 , that is, metal is deposited in the hole structure to realize the communication between the upper and lower electrodes of the beam structure 200 and the external circuit. Before depositing the metal, the surfaces of the vias and the thin film encapsulation layer are oxidized to form an isolation layer 102 for preventing short circuits between the two electrodes. The beam structure 200 is located in the cavity between the package structure 100 and the substrate 400 , and from top to bottom are: an upper electrode 201 , a piezoelectric layer 202 , a lower electrode 203 and a driven layer 204 . The left end of the beam structure 200 is the free end, and the right end is the fixed end. The support structure 500 is located above the fixed end of the beam structure 200 .

The piezoelectric MEMS silicon resonator with beam structure according to the second embodiment of the present invention is shown in FIG. 11 . As shown in FIG. 11 , the difference between this embodiment and the embodiment shown in FIG. 10 is that the driven layer 204 is doped single crystal silicon, and the doping concentration is greater than or equal to 10 ¹⁹ cm ⁻³ . By controlling the doping concentration, the equivalent temperature coefficient of the beam structure can be adjusted, thereby overcoming or reducing the temperature drift effect of the device, which is beneficial for the device to avoid errors caused by temperature changes and improve the reliability of the device.

The piezoelectric MEMS silicon resonator with beam structure according to the third embodiment of the present invention is shown in FIG. 12 . As shown in FIG. 12 , the difference between this embodiment and the embodiment shown in FIG. 10 remains the insulating layer 401 under the driven layer 402 . The insulating layer 401 can also be used as a temperature compensation layer of the beam structure 200 to improve the temperature drift problem of the device.

The electronic device according to the embodiment of the present invention includes the piezoelectric MEMS silicon resonator having the beam structure according to the embodiment of the present invention.

According to the technical solution of the present invention, based on the piezoelectric MEMS silicon resonator (PSR) resonator, the silicon thin film packaging technology is adopted. Compared with the traditional packaging technology, because it does not need a bonding layer, the air tightness is better, and a higher vacuum degree (<1Pa) can be achieved; at the same time, it avoids the release of gas from the bonding material and the leakage of the bonding interface. Vacuum drift. In addition, high temperature heating is required in the production steps of epitaxial packaging, and the PSRs packaged with silicon thin film packaging technology in the example of the present invention are all made of high temperature resistant materials, such as aluminum nitride piezoelectric layers, so the process is compatible in production. Therefore, Silicon thin film packaging technology has great advantages for high temperature device packaging such as PSR.

The above-mentioned specific embodiments do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

A method for forming a piezoelectric MEMS silicon resonator with a beam structure, comprising:

A SOI silicon wafer with a lower cavity is provided as a substrate, and a device silicon layer is provided above the lower cavity in the SOI silicon wafer with a lower cavity;

forming a lower electrode, a piezoelectric layer and an upper electrode in sequence on the substrate;

etching the device silicon layer to form the beam structure, wherein the device silicon layer serves as a driven layer of the beam structure;

forming a sacrificial layer on the current semiconductor structure, the sacrificial layer completely covering the current semiconductor structure;

growing an encapsulation material over the sacrificial layer to form a thin film encapsulation layer, and then etching vias in the thin film encapsulation layer above the beam structure regions;

removing the sacrificial layer over the vibration region of the beam structure to form an upper cavity, and leaving the sacrificial layer over the fixed end of the beam structure;

growing the encapsulation material again to close the via;

forming electrical connection vias penetrating the thin film encapsulation layer and the preserved sacrificial layer;

Electrode connections are formed in the electrical connection vias.
The forming method according to claim 1, wherein the beam structure is a cantilever beam or a fixed beam, or a multi-beam structure including the cantilever beam or the fixed beam.
The forming method according to claim 1, wherein the driven layer is doped single crystal silicon, and the doping concentration is greater than or equal to 10 19 cm -3 .
The forming method according to claim 1, wherein an insulating layer is further provided under the device silicon layer, and the method further comprises: etching the device silicon layer to form the beam structure and simultaneously etching the an insulating layer, wherein both the device silicon layer and the insulating layer serve as driven layers of the beam structure.
The forming method according to any one of claims 1 to 4, wherein the sacrificial layer is silicon oxide, photoresist or polymer.
The forming method according to any one of claims 1 to 4, wherein the packaging material is monocrystalline silicon or polycrystalline silicon.
The forming method according to any one of claims 1 to 4, wherein the method of growing the packaging material is epitaxial growth.
The method according to any one of claims 1 to 4, wherein the thin film encapsulation layer has a thickness of 10 to 100 microns, or 20 to 50 microns.
The forming method according to any one of claims 1 to 4, wherein the thickness of the sacrificial layer is greater than 10 microns.
The forming method according to any one of claims 1 to 4, wherein when the encapsulation material is polysilicon, the step of opening a hole above the beam structure region in the thin film encapsulation layer is replaced for the following steps:

The thin film encapsulation layer of polysilicon is etched through electrochemical reaction, so as to be transformed into a porous thin film encapsulation layer of polysilicon with a porous structure.
The forming method according to any one of claims 1 to 4, characterized in that, further comprising:

before the step of providing the SOI silicon wafer with the lower cavity as the substrate, forming a getter layer inside the lower cavity; or/and,

A getter layer is formed over the sacrificial layer after the step of forming the sacrificial layer and before the step of growing the encapsulation material to form the thin film encapsulation layer.
The forming method according to any one of claims 1 to 4, wherein the piezoelectric layer material is aluminum nitride or doped aluminum nitride.
A piezoelectric MEMS silicon resonator with a beam structure, characterized in that it is obtained by the forming method according to any one of claims 1 to 12.
A piezoelectric MEMS silicon resonator with a beam structure, characterized in that it includes:

a substrate, the top of the substrate has a lower cavity;

a beam structure located on the substrate, the beam structure including a driven layer, a lower electrode, a piezoelectric layer and an upper electrode sequentially stacked from bottom to top;

a support structure located above the fixed end of the beam structure;

a thin film encapsulation layer, the thin film encapsulation layer covers the beam structure and the support structure, and an upper cavity is formed between the thin film encapsulation layer and the beam structure; and

Electrode connections are made through the support structure and the thin film encapsulation layer.
The resonator according to claim 14, wherein the beam structure is a cantilever beam or a fixed beam, or a multi-beam structure including the cantilever beam or the fixed beam.
The resonator according to claim 14, wherein the material of the thin film encapsulation layer is monocrystalline silicon or polycrystalline silicon.
The resonator according to any one of claims 14 to 16, wherein the thin film encapsulation layer has a thickness of 10 to 100 microns, or 20 to 50 microns.
The resonator according to any one of claims 14 to 16, wherein the height of the upper cavity is greater than 10 microns.
The resonator according to any one of claims 14 to 16, further comprising a getter layer, the getter layer being located inside the upper cavity and/or the lower cavity.
An electronic device, characterized by comprising the piezoelectric MEMS silicon resonator with a beam structure according to any one of claims 13 to 19 .