A SU8 glue-based MEMS device and packaging method

Abstract

This invention belongs to the field of optical device technology and discloses a MEMS device and packaging method based on SU8 adhesive. The method includes a structural substrate and a packaging wafer anoly bonded by an SU8 adhesive bonding ring. The packaging wafer has grooves to form a moving microcavity. A getter is deposited within the moving microcavity of the packaging wafer. The moving microcavity also accommodates a movable MEMS structure disposed on the surface of the structural substrate. Chip pads and metal leads are laid on the outer side of the moving microcavity. The packaging wafer also has an anti-reflow groove located at one end of the packaging wafer near the SU8 adhesive bonding ring. This invention uses SU8 adhesive to fabricate a polymer bonding ring on a complex packaging wafer with a microcavity. By optimizing the SU8 adhesive pretreatment process and designing an anti-reflow structure, contamination of the device due to SU8 adhesive flow is avoided. Polymer wafer-level bonding is used to achieve MEMS device packaging, and chip separation is achieved through two dicing operations. This method has advantages such as low temperature, low stress, flexible process, and low cost.

Description

Technical Field

[0001] This invention belongs to the field of optical device technology, and more specifically, relates to a MEMS device based on SU8 adhesive and its packaging method. Background Technology

[0002] Microelectromechanical systems (MEMS) typically utilize silicon or non-silicon materials as their mechanical structures, and are sensor systems with mechanical properties fabricated using micromachining processes. These systems include micromechanical components such as sensors and actuators, as well as high-performance integrated electronic circuitry, making them integrated devices that collect, analyze, and process information and execute action commands. MEMS devices have evolved based on microelectronics technology. In addition to the basic functions of electronic devices, MEMS devices typically include movable structures, optical elements, microcavities, and various functional thin films. Therefore, MEMS device packaging presents unique requirements. For example, most MEMS packages require the fabrication of microcavities to provide space for movable structures; gyroscopes, infrared sensors, and pressure sensors require vacuum packaging to meet basic operating conditions; and optical components, filters, and accelerometers require hermetically sealed packaging to prevent external moisture and other contaminants from affecting device performance and reliability. Due to the unique characteristics of MEMS packaging technology, packaging costs account for more than 70% of the total cost of a MEMS device, becoming a bottleneck for the development and industrialization of MEMS technology.

[0003] MEMS device packaging methods mainly include wafer-level packaging, device-level packaging, and system-level packaging. Compared with other packaging methods, wafer-level packaging completes the packaging of all devices on the wafer through a single bonding process, which facilitates mass production, is highly efficient, and greatly reduces the packaging cost of MEMS devices. It has become an important development direction for MEMS device packaging.

[0004] MEMS device wafer-level packaging primarily employs wafer bonding technologies, such as direct bonding, anodic bonding, eutectic bonding, and polymer adhesive bonding. Direct bonding and anodic bonding require high temperatures and strong electric fields to achieve high-performance bonding, which can easily lead to problems such as dopant diffusion and metal lead melting and deformation. Eutectic bonding is complex and costly. In contrast, adhesive bonding using polymers as an intermediate layer offers advantages such as low bonding temperature, flexible processes, and low requirements on the wafer surface, making it very suitable for MEMS devices with low packaging vacuum requirements. SU8 adhesive is a photosensitive material commonly used for adhesive bonding. It can be used to create bonding rings on the packaging wafer through photolithography to achieve hermetically sealed packaging of the device. At the same time, SU8 adhesive has good insulation and flowability, facilitating the lead connection of MEMS devices. However, it is generally necessary to fabricate microcavities of tens or even hundreds of micrometers on the MEMS packaging wafer to provide movement space for MEMS devices. For some complex MEMS devices, it is also necessary to fabricate leads and microvias. These complex structures make it very difficult and result in poor uniformity when spin-coating SU8 adhesive on the packaging wafer. Summary of the Invention

[0005] In view of this, the present invention provides a MEMS device based on SU8 adhesive and a packaging method to solve the above problems.

[0006] To address the above technical problems, this invention provides a MEMS device based on SU8 adhesive, comprising:

[0007] The structural substrate and the packaging wafer are anoly bonded by an SU8 adhesive bonding ring; the packaging wafer has grooves to form a moving microcavity; getter is deposited in the moving microcavity of the packaging wafer; the moving microcavity is also used to accommodate the MEMS movable structure set on the surface of the structural substrate; chip pads and metal leads are laid on the outside of the moving microcavity; the packaging wafer is also provided with an anti-reflow groove, which is located at the end of the packaging wafer near the SU8 adhesive bonding ring.

[0008] As an alternative, chip pads are positioned at both ends of the structural substrate.

[0009] As an alternative, the reflux grooves may include at least two.

[0010] As an alternative, getter is deposited at the corner of the moving microcavity near the packaged wafer.

[0011] On the other hand, the present invention also provides a MEMS device packaging method based on SU8 adhesive, which, as an optional approach, includes the following steps:

[0012] S1. Fabricate MEMS movable structures and leads on a structural substrate;

[0013] S2. Fabricate anti-reflow grooves, MEMS device motion microcavities, and dicing grooves on the packaged wafer;

[0014] S3. A hard mask is used to fabricate a getter in the microcavity of the packaged wafer movement;

[0015] S4. Apply SU8 adhesive to the packaged wafer;

[0016] S5. Expose and develop the SU8 adhesive to form SU8 adhesive bonding rings on the packaged wafer.

[0017] S6. Align and bond the packaging wafer with the SU8 adhesive bonding ring to the structural substrate for packaging.

[0018] S7. Divide along the dicing groove to form an independently packaged chip unit.

[0019] As an alternative, the structural substrate in S1 above can be a MEMS device fabricated using bulk silicon technology or a MEMS device fabricated using surface technology.

[0020] As an alternative, the packaging wafer in S2 above is a silicon wafer or a glass wafer; the anti-reflow groove and the moving microcavity are fabricated using an etching process.

[0021] As an optional method, the SU8 adhesive in S4 above is applied by a laminating machine or by a roller, with an application temperature of 50-70℃;

[0022] The SU8 adhesive consists of three layers: a PP protective film, SU8 adhesive, and a PET substrate. During coating, the PP protective film is removed first, and the exposed SU8 adhesive is then bonded to the surface of the encapsulated wafer. After coating, the PET substrate is removed.

[0023] As an alternative, in step S5 above, the coated SU8 adhesive is exposed in an ultraviolet lithography machine with an exposure dose of 50-800 mJ / cm2;

[0024] Subsequently, the SU8 adhesive is post-baked on a hot plate or in an oven at a temperature of 85-95°C for 5-40 minutes; then developed using PGMEA or cyclohexanone, ultimately forming SU8 adhesive bonding rings on the packaged wafer.

[0025] As an optional method, in the above S7, chip separation is achieved through two dicing operations;

[0026] The first dicing is along the outer edge of the bonding ring, with a dicing depth equal to the thickness of the packaged wafer; the second dicing is along the outer edge of the chip, with a dicing depth equal to the sum of the thicknesses of the structural substrate, the packaged wafer, and the SU8 adhesive.

[0027] The beneficial effects of this invention are as follows:

[0028] This invention utilizes SU8 adhesive to fabricate polymer bonding rings on complex packaging wafers with microcavities, offering a simple and flexible process. By optimizing the SU8 adhesive pretreatment process and designing an anti-reflow structure, contamination of the device due to SU8 adhesive flow is avoided. Polymer wafer-level bonding is employed for MEMS device packaging, with chip separation achieved through two dicing operations. This method offers advantages such as low temperature, low stress, process flexibility, and low cost. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a wafer-level packaging structure for MEMS devices based on SU8 adhesive, according to an embodiment of the present invention.

[0030] Figure 2 This is a flowchart of the wafer-level packaging process for MEMS devices based on SU8 adhesive, according to an embodiment of the present invention.

[0031] Figure labels and their correspondences:

[0032] 1-Structural substrate; 2-Packaging wafer; 3-MEMS movable structure; 4-Moving microcavity; 5-Chip pad; 6-Metal lead; 7-SU8 glue bonding ring; 8-Anti-reflow groove; 9-Getting agent. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0034] Please see Figure 1 and Figure 2 The purpose of this embodiment is to provide a MEMS device based on SU8 adhesive. SU8 adhesive is applied to the surface of a packaging wafer with microcavities using a roller. Standard photolithography processes are then employed for baking, exposure, and development to remove the photoresist from non-bonded areas, forming an SU8 adhesive bonding ring. The packaging wafer with the SU8 adhesive bonding ring is then bonded to the MEMS device wafer via adhesive bonding, achieving wafer-level hermetic packaging of the MEMS device.

[0035] In this embodiment, the structure includes a structural substrate 1 and a packaging wafer 2; both the structural substrate 1 and the packaging wafer 2 are provided with SU8 adhesive bonding rings, and the two are bonded together by anodic bonding; getter 9 is deposited in the groove of the packaging wafer 2; a MEMS movable structure 3 is provided on one side of the structural substrate 1, located in the moving microcavity 4; chip pads 5 and metal leads 6 are laid on the outside of the moving microcavity 4; the packaging wafer 2 is also provided with an anti-reflow groove 8, which is located at the bonding point.

[0036] As an optional configuration, chip pads 5 are disposed at both ends of the structural substrate 1. At least two anti-reflow recesses 8 are provided; when the packaged wafer 2 and the structural substrate 1 have two bonding locations, there are four, such as... Figure 1 As shown. Furthermore, in this embodiment, getter 9 is deposited at the corner of the moving microcavity near the packaging wafer.

[0037] On the other hand, this embodiment also provides a MEMS device packaging method based on SU8 adhesive, which is implemented as follows:

[0038] S1. Fabricate MEMS movable structure 3 and leads on a structural substrate;

[0039] S2. Fabricate anti-reflow grooves 8, MEMS device motion microcavities 4, and dicing grooves on the packaging wafer 2;

[0040] S3. A getter 9 is fabricated in the moving microcavity 4 of the packaged wafer 2 using a hard mask;

[0041] S4. Apply SU8 adhesive to the encapsulation wafer 2 with grooves and microcavities using a roller;

[0042] S5. The SU8 adhesive is exposed and developed using standard photolithography to form an SU8 adhesive bonding ring on the packaging wafer 2.

[0043] S6. Align and bond the packaging wafer 2 with the SU8 adhesive bonding ring to the structural substrate to achieve hermetic packaging.

[0044] S7. Divide along the dicing groove to form an independently packaged chip unit.

[0045] Alternatively, the structural substrate in S1 can be a MEMS device fabricated using bulk silicon technology or a MEMS device fabricated using surface technology.

[0046] As an alternative, the packaging wafer 2 in S2 is a silicon wafer or a glass wafer; the anti-reflow groove 8 and the moving microcavity 4 are fabricated using an etching process.

[0047] As an optional method, SU8 adhesive in S4 is applied by a laminating machine or by a roller, with an application temperature of 50-70℃;

[0048] The SU8 adhesive consists of three layers: a PP protective film, SU8 adhesive, and a PET substrate. During coating, the PP protective film is removed first, and the exposed SU8 adhesive is then bonded to both sides of the encapsulation wafer. After coating, the PET substrate is removed.

[0049] As an optional method, in S5, the coated SU8 resist is exposed in a UV lithography machine with an exposure dose of 50-800 mJ / cm2;

[0050] Subsequently, the SU8 adhesive is post-baked on a hot plate or in an oven at a temperature of 85-95°C for 5-40 minutes; then developed using PGMEA or cyclohexanone, finally forming SU8 adhesive bonding rings on the packaged wafer 2.

[0051] As an optional method, in S6, the packaged wafer 2 with SU8 adhesive bonding ring is aligned with the structural substrate and bonded in a bonding machine; the bonding temperature is 100-150℃ and the bonding pressure is 500-3000N.

[0052] As an optional method, in S7, chip separation is achieved through two dicing processes;

[0053] The first dicing is along the outer edge of the bonding ring, with a dicing depth equal to the thickness of packaged wafer 2; the second dicing is along the outer edge of the chip, with a dicing depth equal to the sum of the thicknesses of the structural substrate, packaged wafer 2, and SU8 adhesive.

[0054] This embodiment addresses the challenges of polymer spin-coating difficulties and poor uniformity on complex microcavity wafer surfaces in current MEMS device packaging. It provides a MEMS device and packaging method based on SU8 adhesive. SU8 adhesive is applied to the surface of the packaging wafer 2 with microcavities using a roller. Standard photolithography processes are employed for baking, exposure, and development to remove photoresist from non-bonded areas, forming an SU8 adhesive bonding ring. The packaging wafer 2 with the SU8 adhesive bonding ring is then bonded to the MEMS device wafer via adhesive bonding, achieving wafer-level hermetic packaging of the MEMS device. Furthermore, to prevent contamination of the device area caused by the flow of SU8 adhesive during bonding, the SU8 pretreatment process is optimized to partially cure it, and an anti-backflow groove 8 is designed. This solution solves the problem of polymer coating on microcavity surfaces. Utilizing the good insulation and high flowability of polymers, it can simultaneously achieve hermetic packaging and wire interconnection of MEMS devices. It offers advantages such as low bonding temperature, low thermal stress, simple and flexible process, low cost, and ease of mass production.

[0055] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A MEMS device based on SU8 adhesive, characterized in that, include: The structural substrate and the packaging wafer are bonded by SU8 adhesive bonding ring anodic bonding; The packaging wafer has grooves for forming a moving microcavity; a getter is deposited in the moving microcavity of the packaging wafer; the moving microcavity is also used to accommodate a movable MEMS structure disposed on the surface of the structural substrate; Chip pads and metal leads are laid on the outer side of the moving microcavity; The packaging wafer is also provided with an anti-reflow groove, which is located at one end of the packaging wafer near the SU8 adhesive bonding ring.

2. A MEMS device based on SU8 adhesive according to claim 1, characterized in that, The chip pads are located at both ends of the structural substrate.

3. A MEMS device based on SU8 adhesive according to claim 1, characterized in that, The reflux grooves include at least two.

4. A MEMS device based on SU8 adhesive according to claim 1, characterized in that, The getter is deposited at the corner of the moving microcavity near the packaged wafer.

5. A MEMS device packaging method based on SU8 adhesive, characterized in that, Includes the following steps: S1. Fabricate MEMS movable structures and leads on a structural substrate; S2. Fabricate anti-reflow grooves, MEMS device motion microcavities, and dicing grooves on the packaged wafer; S3. A hard mask is used to fabricate a getter in the microcavity of the packaged wafer movement; S4. Apply SU8 adhesive to the packaged wafer; S5. Expose and develop the SU8 adhesive to form SU8 adhesive bonding rings on the packaged wafer. S6. Align and bond the packaging wafer with the SU8 adhesive bonding ring to the structural substrate for packaging. S7. Divide along the dicing groove to form an independently packaged chip unit.

6. The MEMS device packaging method based on SU8 adhesive according to claim 5, characterized in that, The structural substrate in S1 above is a MEMS device fabricated using bulk silicon technology or a MEMS device fabricated using surface technology.

7. The MEMS device packaging method based on SU8 adhesive according to claim 5, characterized in that, The packaging wafer in S2 above is a silicon wafer or a glass wafer; the anti-reflow groove and the moving microcavity are fabricated using an etching process.

8. The MEMS device packaging method based on SU8 adhesive according to claim 5, characterized in that, In the above S4, SU8 adhesive is applied by a laminating machine or by a roller, and the application temperature is 50-70℃; The SU8 adhesive consists of three layers: a PP protective film, SU8 adhesive, and a PET substrate. During coating, the PP protective film is removed first, and the exposed SU8 adhesive is then bonded to the surface of the encapsulated wafer. After coating, the PET substrate is removed.

9. A MEMS device packaging method based on SU8 adhesive according to claim 5, characterized in that, In step S5 above, the coated SU8 resist is exposed in a UV lithography machine at an exposure dose of 50-800 mJ / cm². 2 ; Subsequently, the SU8 adhesive is post-baked on a hot plate or in an oven at a temperature of 85-95°C for 5-40 minutes; then developed using PGMEA or cyclohexanone, ultimately forming SU8 adhesive bonding rings on the packaged wafer.

10. A MEMS device packaging method based on SU8 adhesive according to claim 5, characterized in that, In the above S7, chip separation is achieved through two dicing processes; The first dicing is performed along the outer edge of the bonding ring, with a dicing depth equal to the thickness of the packaged wafer. The second dicing is performed along the outer edge of the chip, with a dicing depth equal to the sum of the thicknesses of the structural substrate, the packaged wafer, and the SU8 adhesive.

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