CN110937570A

CN110937570A - MEMS device wafer level packaging method and packaging structure

Info

Publication number: CN110937570A
Application number: CN201911334504.6A
Authority: CN
Inventors: 陈福成
Original assignee: SMIC Manufacturing Shaoxing Co Ltd
Current assignee: SMIC Manufacturing Shaoxing Co Ltd
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2020-03-31

Abstract

The invention provides a wafer-level packaging method and a packaging structure of an MEMS device, which are characterized in that before bonding an MEMS device wafer and a cap wafer, a decomposable material is formed on the inner surface of a specific cavity on the cap wafer, after bonding the MEMS device wafer and the cap wafer, the decomposable material in a sealed cavity is decomposed by using a corresponding process to generate gas so as to achieve the purpose of adjusting the air pressure vacuum degree in the sealed cavity, and the MEMS device with multiple functions can be integrated on a single chip.

Description

MEMS device wafer level packaging method and packaging structure

Technical Field

The invention relates to the technical field of MEMS (micro-electromechanical systems) device packaging, in particular to a wafer-level packaging method and a packaging structure of an MEMS device.

Background

With the application of MEMS devices in 3C electronic products (such as mobile phones, etc.) becoming more and more widespread, and with the increasing functional requirements of people on electronic products, the demand for single-chip integration of multiple MEMS devices is becoming greater and greater, for example, common MEMS devices on mobile phones at present include gyroscope sensors, acceleration sensors, pressure sensors, magnetometers, microphones, and the like, and capacitive inertial MEMS sensors (including 3-axis gyroscopes and 3-axis accelerometers) with 6 degrees of freedom have been integrated on a single chip of some products at present, and inertial MEMS sensors with 9 degrees of freedom integrated on a single chip will also appear in the future.

However, each MEMS device has its own cavity requirement, and the vacuum requirement of the cavity of each MEMS device is different, for example, the vacuum requirement of the cavity of the gyro sensor is the highest, and the vacuum requirement of the cavity of the acceleration sensor is the second, and the pressure sensor generally requires the air pressure in the cavity to be around the normal pressure because the diaphragm of the pressure sensor needs to have the air pressure support.

The inventor finds that the existing packaging method of the MEMS device is difficult to meet the requirements of different vacuum degrees required by a plurality of different MEMS devices when the MEMS devices are integrated on a single chip.

Disclosure of Invention

The invention aims to provide a wafer-level packaging method and a packaging structure of an MEMS device, so as to meet the requirements of different vacuum degrees required by various MEMS devices during single-chip integration.

To solve the above-mentioned object, the present invention provides a wafer level packaging method for MEMS device, comprising:

providing an MEMS device wafer and a cap wafer, wherein mechanical microstructures of at least two MEMS devices with different functions are formed on the MEMS wafer;

forming cavities corresponding to the mechanical microstructures of the MEMS devices one to one on the cap wafer;

forming a patterned gas release layer on the cap wafer by using a decomposable material capable of decomposing gas under a preset condition, wherein the patterned gas release layer covers the inner surface of the cavity to be pressurized and exposes the bonding surface of the cap wafer and the inner surfaces of the other cavities;

bonding the MEMS device wafer and the cap wafer, wherein each cavity of the cap wafer encloses the mechanical microstructure of the corresponding MEMS device;

and applying the preset condition to the bonded wafer structure so that the gas release layer in the corresponding cavity decomposes gas to increase the gas pressure in the cavity.

Optionally, the step of forming the patterned gas release layer comprises: firstly, covering a decomposable material with a certain thickness on the surface of the cap wafer, and then removing the redundant decomposable material through a selective removal process to form the patterned gas release layer; alternatively, the step of forming the patterned gas release layer comprises: and under the shielding of a graphic mask plate, coating or depositing the cap wafer by adopting the decomposable material to form the graphic gas release layer.

Optionally, the selective removal process is a laser irradiation decomposition process or a selective etching process.

Optionally, the method of applying the preset condition comprises heating and/or light irradiation.

Optionally, the decomposable material is completely decomposed to a gas under preset conditions, or the decomposable material is decomposed to a gas and a solid under preset conditions.

Optionally, the gas generated by the decomposition of the decomposable material under the preset conditions comprises at least one of nitrogen, hydrogen, carbon monoxide and carbon dioxide.

Optionally, the preset condition is heating to a preset temperature, the decomposable material comprises barium azodicarboxylate, the preset temperature is 240-250 ℃, and the decomposable material can decompose nitrogen, carbon monoxide, carbon dioxide and barium carbonate under the preset condition.

Optionally, after bonding the MEMS device wafer and the cap wafer and before applying the preset condition to the bonded wafer structure, etching a surface of the MEMS device wafer, which faces away from the cap wafer, to form a back cavity.

Based on the same conception, the invention also provides an MEMS device wafer level packaging structure which is manufactured by adopting the MEMS device wafer level packaging method and has at least two MEMS devices with different functions.

Optionally, the MEMS device wafer level package structure includes at least two of a gyroscope sensor, an acceleration sensor, a pressure sensor, a magnetometer, and a microphone.

Compared with the prior art, the technical scheme provided by the invention has the following beneficial effects:

1. before bonding the MEMS device wafer and the cap wafer, a decomposable material is formed on the inner surface of a specific cavity on the cap wafer, and after the MEMS device wafer and the cap wafer are bonded, the decomposable material in the sealed cavity is decomposed by utilizing a corresponding process to generate gas so as to achieve the purpose of adjusting the air pressure and vacuum degree in the sealed cavity, so that the MEMS devices with multiple functions can be integrated on a single chip.

2. Further, the decomposable material can be barium azodicarboxylate, and after the MEMS device wafer and the cap wafer are bonded, the barium azodicarboxylate in the sealed cavity can be decomposed to generate nitrogen, carbon monoxide, carbon dioxide and barium carbonate when the MEMS device wafer and the cap wafer are heated to a preset temperature of 240-250 ℃. The generated nitrogen, carbon monoxide, carbon dioxide and barium carbonate can not chemically react with other structures on the MEMS device wafer and the cap wafer, and the adopted thermal decomposition temperature is low, so that the performance of the device finally obtained after packaging can not be influenced by the scheme.

Drawings

FIG. 1 is a schematic flow chart of a wafer level packaging method for MEMS devices according to an embodiment of the present invention;

fig. 2A to 2D are schematic cross-sectional views of the device structure in the wafer-level packaging method of the MEMS device shown in fig. 1.

Detailed Description

The technical solution proposed by the present invention will be further described in detail with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.

Referring to fig. 1, an embodiment of the invention provides a wafer level packaging method for a MEMS device, including the following steps:

s1, providing an MEMS device wafer and a cap wafer, wherein mechanical microstructures of at least two MEMS devices with different functions are formed on the MEMS wafer;

s2, forming cavities corresponding to the mechanical microstructures of the MEMS devices one to one on the cap wafer;

s3, forming a patterned gas release layer on the cap wafer by adopting a decomposable material capable of decomposing gas under preset conditions, wherein the patterned gas release layer covers the inner surface of the cavity needing pressurization and exposes the bonding surface of the cap wafer and the inner surfaces of the other cavities;

s4, bonding the MEMS device wafer and the cap wafer, wherein each cavity of the cap wafer encloses the mechanical microstructure of the corresponding MEMS device;

and S5, applying the preset conditions to the bonded wafer structure to enable the gas release layer in the corresponding cavity to decompose gas to increase the gas pressure in the cavity.

Referring to fig. 2A to 2C, in step S1, a MEMS device wafer 300 and a cap wafer 200 are provided. The MEMS device wafer 300 has at least two mechanical microstructures (not shown) of MEMS devices with different functions formed therein, and the corresponding MEMS devices may be an acceleration sensor, a gyroscope sensor, a pressure sensor, a microphone, a speaker, a magnetic sensor, and the like. And when the mechanical microstructure of at least one of the MEMS devices is a movable mechanical structure, a cavity for providing a moving space for the mechanical microstructure of the MEMS device is further formed on the MEMS device wafer 300 in a region corresponding to the MEMS device. As an example, a mechanical microstructure 300a of one MEMS device and a mechanical microstructure 300b of another MEMS device are formed in the MEMS device wafer 300, the two mechanical microstructures have different vacuum degrees of cavities, a lower cavity (not marked in the figure) is formed between the mechanical microstructure 300a and the substrate of the MEMS device wafer 300, a through hole (not marked in the figure) communicating the lower cavity is formed in the mechanical microstructure 300a, no through hole is formed in the mechanical microstructure 300b, and a back cavity is formed on the back surface of the substrate of the MEMS device wafer 300 in the region where the mechanical microstructure 300a is located. The MEMS device wafer 300 in this step may further have a sealing ring (not shown) surrounding the mechanical microstructure of each MEMS device, a plurality of bonding pads (not shown) located outside the sealing ring, and a bonding structure for bonding, etc. The cap wafer 200 may be a cover plate material such as silicon, glass, or ceramic material as is well known to those skilled in the art. As an example, the cap wafer 200 is a silicon wafer.

With continued reference to fig. 2A, in step S2, the cap wafer 200 may be etched by an anisotropic etching process to form upper cavities on the cap wafer 200 corresponding to the respective mechanical microstructures one by one. In this embodiment, an upper cavity 201a corresponding to the mechanical microstructure 300a and subsequently enclosing the mechanical microstructure 300a to provide a cavity thereto is formed on the cap wafer 200, and an upper cavity 201b corresponding to the mechanical microstructure 300b and subsequently enclosing the mechanical microstructure 300b to provide a cavity thereto is also formed on the cap wafer 200.

With continued reference to fig. 2A and 2B, in step S3, a decomposable material capable of decomposing a gas under a predetermined condition may be selected, and a film 202 of the decomposable material is covered on the cap wafer 200 by a certain thickness through a suitable film forming process such as spin coating or vapor deposition, wherein the predetermined condition capable of decomposing a gas by the decomposable material may include at least one of heating, light irradiation including laser irradiation, and the like, and the decomposable material is completely decomposed into a gas under the predetermined condition, or the decomposable material is decomposed into a gas and a solid under the predetermined condition. The gas generated by the decomposition of the decomposable material under the predetermined condition is a gas that does not react with the cap wafer 200 and the MEMS device wafer 300, and includes at least one small molecule gas of nitrogen, hydrogen, carbon monoxide and carbon dioxide, for example. The decomposable material may be an organic substance such as polypropylene carbonate, polycyclohexene carbonate, polynorbornene, etc., or an inorganic substance. For example, the decomposable material is barium azodicarboxylate which can decompose nitrogen, carbon monoxide, carbon dioxide and barium carbonate when heated to a preset temperature of 240-250 ℃, and the gas evolution is 170-175 ml/g, so that the vacuum degree in the formed cavity can be adjusted by decomposing the barium azodicarboxylate to generate corresponding gas through subsequent heating; for example, the decomposable material is a silane compound, and can be decomposed under laser irradiation conditions or heating conditions to generate hydrogen gas and/or nitrogen gas, or can generate a solid such as amorphous silicon or silicon dioxide, and thus the degree of vacuum in the cavity formed can be adjusted by decomposing the compound to generate a corresponding gas by laser irradiation or heating in the subsequent step. The material of decomposable material film 202 is not limited to a single substance, and may be a mixture of two or more decomposable compounds. After the decomposable material film 202 is formed, an appropriate selective removal process is selected based on the material properties of the decomposable material to remove excess decomposable material film 202 to form a patterned gas release layer 202' on the cap wafer 200. Wherein, the selective removal process is a laser irradiation decomposition process or a selective etching process (such as a plasma etching process). The patterned gas release layer 202 'covers the inner surfaces of the cavities to be pressurized and exposes the bonding surface of the cap wafer 200 and the inner surfaces of the remaining cavities, and in this embodiment, the gas release layer 202' exposes the bonding surface of the cap wafer 200 and the inner surfaces of the upper cavities 201a and covers the inner surfaces (including the sidewalls and the top wall) of the upper cavities 201 b.

It should be noted that the method for forming the patterned gas release layer 202' by using decomposable materials is not limited to the above-mentioned manner, and in other embodiments of the present invention, the following method may be used: the cap wafer 200 is coated or deposited with decomposable material under the shadow of a patterned mask to form the patterned gas release layer 202'. The gases generated by the decomposition of the preferred decomposable material are all non-toxic gases to facilitate environmental protection during the production process and to ensure the safe use of the final product in the hands of the user. In addition, when the decomposable material is a material that needs to be decomposed by laser irradiation of a specific wavelength to generate a gas, the cap wafer 200 is preferably a light-transmitting material. Of course, the choice of decomposable material is not limited to the above examples, and any other suitable decomposable material known to those skilled in the art may be chosen, such as some magnetosensitive material, material capable of decomposing a gas in a magnetic field, such as some material capable of decomposing a gas upon application of electricity, and so forth.

Referring to fig. 2B and 2C, in step S4, a cap wafer 200 may be bonded to a MEMS device wafer 300 by selecting a suitable bonding method, wherein a gas release layer 202' is to be placed facing a corresponding mechanical microstructure in the MEMS device wafer 300. In this embodiment, the gas release layer 202' is placed facing the mechanical microstructure 300b in the MEMS device wafer 300. An upper cavity 201a on the cap wafer 200 and a corresponding lower cavity in the MEMS device wafer 300 are communicated through a through hole in the mechanical microstructure 300a to form a closed cavity 301a, and the closed cavity 301a seals the mechanical microstructure 300a therein; the upper cavity 201b on the cap wafer 200 and the corresponding lower cavity in the MEMS device wafer 300 are aligned and combined together to form a closed cavity 301b, and the closed cavity 301b seals the mechanical microstructure 300b therein. The bonding method may be selected from anodic bonding, fusion bonding, eutectic bonding or solder bonding. In one example, when the MEMS device wafer 300 has an aluminum (Al) bonding structure formed thereon and the cap wafer 200 has a germanium (Ge) structure formed thereon, then the bonding method is Al-Ge eutectic bonding.

Referring to fig. 2D, in step S5, according to the characteristics of the decomposable material used in step S3, corresponding conditions are applied to the bonded structure so as to decompose the gas releasing layer 202' in the bonded structure. The decomposition degree of the gas release layer 202 'is determined by the requirement of the vacuum degree in the closed cavity 301b, and may be full decomposition or partial decomposition, and fig. 2D shows the case where the gas release layer 202' is partially decomposed. As an example, the decomposable material of the gas releasing layer 202 'is a heat decomposable material, and after the cap wafer 200 and the MEMS device wafer 300 are bonded, the bonded structure is baked to heat the cap wafer 200 to a decomposition temperature of the decomposable material of the gas releasing layer 202' to enable the gas releasing layer 202 'to decompose gas to adjust the gas pressure within the cavity 301b, and the degree of adjustment of the gas pressure within the cavity 301b may depend on the length of time for which the decomposition temperature is maintained, the longer the time for which the decomposition temperature is maintained, the more gas decomposed by the gas releasing layer 202', and the greater the gas pressure within the cavity 301 b. At this time, the thickness of the gas release layer 202' formed in step S3 needs to be determined according to the adjustment requirement of the gas pressure inside the cavity 301 b. Alternatively, the decomposable material in the gas releasing layer 202 'may be completely decomposed into gas in this step to avoid generation of residues on the inner walls of the cavities 301b and the mechanical microstructures 300b to affect the device performance, and in this case, the decomposition rate of the decomposable material in the gas releasing layer 202' may be controlled by finely controlling the preset conditions to avoid problems that the decomposition of the gas releasing layer 202 'is not uniform and that the granular or blocky gas releasing layer 202' is peeled off from the inner walls of the cavities 301b to the mechanical microstructures 300b during the decomposition to affect the device performance. In other embodiments of the present invention, the gas releasing layer 202 'may also be decomposed into gas and solid, and the generated solid may be used as a part of the inner wall of the cavity 301b later, in which case the decomposition rate of the decomposable material in the gas releasing layer 202' can be controlled by finely controlling the preset conditions, so as to avoid the problems that the gas releasing layer 202 'is decomposed unevenly, the granular or block-shaped gas releasing layer 202' is peeled off from the inner wall of the cavity 301b to the mechanical microstructure 300b during the decomposition, and the solid generated by the decomposition microstructure is attached to the mechanical microstructure 300 b.

It should be noted that the step S5 may be performed in the last step of the MEMS device packaging, that is, there may be other steps between the steps S5 and S4, for example, after the step S4 and before the step S5, the side of the MEMS device wafer 300 facing away from the cap wafer 200 is etched to form a back cavity.

In summary, in the wafer-level packaging method for the MEMS device in this embodiment, before the MEMS device wafer and the cap wafer are bonded, a decomposable material is formed on the inner surface of a specific cavity on the cap wafer, and after the MEMS device wafer and the cap wafer are bonded, the decomposable material in the sealed cavity is decomposed by using a corresponding process to generate a gas, so as to achieve the purpose of adjusting the degree of vacuum of air pressure in the sealed cavity, so that the MEMS device with multiple functions can be integrated on a single chip.

Based on the same inventive concept, please refer to fig. 2D, an embodiment of the present invention further provides a MEMS device wafer level packaging structure, which is manufactured by the MEMS device wafer level packaging method of the present invention, and the MEMS device wafer level packaging structure has at least two MEMS devices with different functions, specifically, the MEMS device wafer level packaging structure includes a cap wafer 200, a MEMS device wafer 300,

cavities

301a and 301b located between the cap wafer 200 and the MEMS device wafer 300, a mechanical microstructure 300a enclosed by the cavity 301a, and a mechanical microstructure 300b enclosed by the cavity 301 b. Optionally, the MEMS device comprises at least two of a gyroscope sensor, an acceleration sensor, a pressure sensor, a magnetometer, and a microphone.

The wafer-level packaging structure of the MEMS device is prepared by adopting the wafer-level packaging method of the MEMS device, so that different requirements of air pressure and vacuum degrees in different sealed cavities can be met, and the MEMS devices with multiple functions can be integrated on a single chip. The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.

Claims

1. A wafer-level packaging method for MEMS devices is characterized by comprising the following steps:

2. The MEMS device wafer level packaging method of claim 1, wherein the step of forming the patterned gas release layer comprises: firstly, covering a decomposable material with a certain thickness on the surface of the cap wafer, and then removing the redundant decomposable material through a selective removal process to form the patterned gas release layer; alternatively, the step of forming the patterned gas release layer comprises: and under the shielding of a graphic mask plate, coating or depositing the cap wafer by adopting the decomposable material to form the graphic gas release layer.

3. The wafer-level packaging method for the MEMS device as claimed in claim 2, wherein the selective removal process is a laser irradiation decomposition process or a selective etching process.

4. The wafer level packaging method for the MEMS device as claimed in any one of claims 1 to 3, wherein the method for applying the preset condition comprises heating and/or light irradiation.

5. The wafer-level packaging method for MEMS devices of claim 4, wherein the decomposable material is completely decomposed into a gas under a predetermined condition or the decomposable material is decomposed into a gas and a solid under a predetermined condition.

6. The wafer-level packaging method for MEMS devices of claim 5, wherein the gas generated by decomposition of the decomposable material under the predetermined conditions comprises at least one of nitrogen, hydrogen, carbon monoxide and carbon dioxide.

7. The wafer-level packaging method for MEMS devices of claim 5 or 6, wherein the predetermined condition is heating to a predetermined temperature, the decomposable material comprises barium azodicarboxylate, the predetermined temperature is 240-250 ℃, and the decomposable material can decompose nitrogen, carbon monoxide, carbon dioxide and barium carbonate under the predetermined condition.

8. The MEMS device wafer level packaging method of claim 1, wherein after bonding the MEMS device wafer and the cap wafer and before applying the predetermined condition to the bonded wafer structure, a side of the MEMS device wafer facing away from the cap wafer is etched to form a back cavity.

9. An MEMS device wafer level packaging structure, which is characterized by being manufactured by the MEMS device wafer level packaging method of any one of claims 1-8, and the MEMS device wafer level packaging structure is provided with at least two MEMS devices with different functions.

10. The MEMS device wafer level package structure of claim 9, wherein the MEMS device wafer level package structure includes at least two of a gyroscope sensor, an acceleration sensor, a pressure sensor, a magnetometer, and a microphone.