A multi-layer wafer level glass paste bonding process

Abstract

The application relates to a multilayer wafer-level glass paste bonding process, belongs to the technical field of micro-electro-mechanical system (MEMS) packaging, and particularly relates to a multilayer wafer-level layer-by-layer bonding process based on glass powder. The material of the wafer can include silicon, quartz, silicon carbide, piezoelectric ceramic and the like. The multilayer structure of MEMS can be realized, the requirement of layer-by-layer bonding of elements due to the specific structure needs is met, the problem of bubbles generated by multiple sintering of glass powder is overcome, the air tightness of the multilayer structure packaging is ensured, wafer-level packaging is ensured, the consistency of devices between wafers is ensured, and the production efficiency of the devices in the MEMS processing field is improved.

Description

Technical Field

[0001] This invention relates to a multilayer wafer-level glass paste bonding process, belonging to the field of microelectromechanical systems (MEMS) packaging technology, specifically a multilayer wafer-level layer-by-layer bonding process based on glass powder. The wafer material may include silicon, quartz, silicon carbide, piezoelectric ceramics, etc. Technical Background

[0002] With the development of MEMS technology, MEMS devices have evolved from initial micro-parts to sensors capable of various detection applications, and are now expanding into many more areas. This development has also created a demand for multilayer bonding and hermetic packaging. The quality of the bonding result is crucial for MEMS device packaging. Currently, there are various vacuum bonding methods. Traditional wafer vacuum bonding methods include anodic bonding, glass paste bonding, eutectic bonding, and fusion bonding. Different bonding technologies have their own limitations. Glass paste is widely used in hermetic bonding due to its advantages such as good hermeticity, high strength, low bonding temperature, wide range of thermal expansion coefficients, low requirements for surface flatness, and the ability for electrodes to penetrate the bonding layer. However, current glass powder bonding processes are used for single-pass bonding of two or more layers, and are not suitable for layer-by-layer bonding of multilayer structures. After the first bonding is completed, if a second bonding is performed under the same conditions (sintering temperature and isothermal time), the first bonding surface will experience bubbling and a decrease in bonding force due to the renewed high temperature. Therefore, a new bonding method must be adopted to achieve multi-layer successive bonding of glass powder. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of bubbles appearing on the bonding surface and reduced bonding strength in glass slurries due to multiple sintering processes, and to propose a multi-layer wafer-level glass slurry bonding process.

[0004] The objective of this invention is achieved through the following technical solutions.

[0005] This invention discloses a multilayer wafer-level glass paste bonding process, employing glass powder as the bonding medium between wafers. The glass powder is dissolved in an organic solvent and then screen-printed onto the bonding surface. Pre-sintering in the atmosphere removes organic matter from the paste and solidifies it. During the layer-by-layer, multiple bonding processes, different bonding temperatures and times are used to prevent bubbles and reduced bonding strength on the bonding surface due to repeated sintering. Before bonding, the bonding surface is treated with an etchant to increase its roughness. The etchant increases the hydrophilicity of the wafer surface and reduces the wetting angle. Increased roughness increases the actual contact area of ​​the bonding surface, improving bonding strength and airtightness. The steps are as follows:

[0006] 1) Glass paste is applied to the upper and lower cover discs using screen printing.

[0007] 2) The upper cover plate and the lower cover plate from step 1) are sintered in atmospheric air to pre-sinter the glass paste coated on the upper cover plate and the lower cover plate into a glassy state.

[0008] 3) The upper cover plate disc and the component layer disc are bonded using an upper and lower pressure fixture. The bonding temperature is lower than the optimal bonding temperature of the glass powder, and the bonding time is shorter than the optimal bonding time of the glass powder.

[0009] The purpose of this step is to bond the top cover plate disc to the component layer disc, but the bonding strength does not reach the optimal bonding strength of the glass powder.

[0010] 4) Use an upper and lower presser to bond the bonded upper cover plate disc, the component layer disc, and the lower cover plate disc obtained in step 3). The bonding temperature is the optimal bonding temperature of the glass powder, and the bonding time is the optimal bonding time of the glass powder.

[0011] The purpose of this step is to bond the bonded upper cover plate wafer to the component layer wafer and the lower cover plate wafer together, so that the bonding strength reaches the optimal bonding strength of the glass powder.

[0012] If more component wafer layers are required to be bonded between the upper and lower cover wafers, one side of the component wafer is coated with glass paste and pre-sintered into a glassy state under atmospheric conditions; then bonding is performed sequentially.

[0013] Beneficial effects

[0014] It can realize multi-layer MEMS structures, meet the requirements of layer-by-layer bonding of components due to specific structural needs; overcome the problem of bubbles appearing during multiple sintering of glass powder, and ensure the hermeticity of multi-layer structure packaging; wafer-level packaging ensures the consistency of devices between wafers and improves the device production efficiency in the field of MEMS processing. Attached Figure Description

[0015] Figure 1 The upper and lower cover discs are coated with glass slurry and pre-sintered.

[0016] Figure 2 This is a schematic diagram of the bonding process between the top cover plate wafer and the component layer wafer;

[0017] Figure 3 This is a schematic diagram of the bonding process of the upper cover plate wafer, the component layer wafer, and the lower cover plate wafer. Detailed Implementation

[0018] The specific embodiments of the present invention are described in more detail below.

[0019] Example 1

[0020] The method for multilayer successive wafer bonding using glass powder according to the present invention comprises the following steps:

[0021] 1) Preparation of glass slurry: Terpineol, butyl carbitol, tributyl citrate, and ethyl cellulose are mixed thoroughly at a mass ratio of 100:40:30:11 on a magnetic stirring plate at 85℃~95℃; the ethyl cellulose is completely dissolved in the organic solvent to obtain mixture A. After mixture A cools to room temperature, xylene is added and mixed thoroughly to obtain mixture B. The mass of xylene added is 8% of the mass of mixture A. Mixture B is then thoroughly mixed with glass powder and allowed to stand for 1 hour before use; the mass ratio of mixture B to glass powder is 100:55~70.

[0022] 2) The bonding surfaces of the upper cover plate wafer, lower cover plate wafer, and component layer wafer are etched with HF acid solution to increase the surface roughness of the bonding surfaces and clean the surface of the quartz wafer to be bonded; the component layer wafer is a quartz wafer.

[0023] 3) The glass paste obtained in step 1) is applied to the bonding surfaces of the upper cover plate and the lower cover plate using screen printing.

[0024] 4) Pre-sinter the upper cover plate and lower cover plate, which are coated with glass slurry, as shown below. Figure 1 As shown. The temperature is increased to 220℃~250℃ at 10℃ / min and held for 30min to fully remove the organic solvent. The temperature is then increased to 320℃~350℃ at 10℃ / min (at this temperature the glass slurry is in powder form and has not yet formed a glassy state), and held for 30min to fully burn off the ethyl cellulose. The temperature is then increased to 360℃~380℃ at 5℃ / min and held for 5min~10min to transform the glass powder into a glassy state, and then slowly cooled to room temperature.

[0025] 5) Use upper and lower clamps to bond the upper cover plate disc to the component layer disc, such as... Figure 2 As shown, the bonding vacuum is 1e-4 Pa; the bonding pressure is 250 mbar to 350 mbar; the upper fixture temperature is 350℃, the lower fixture temperature is 400℃, and the holding time lasts for 2 minutes. The upper cover plate disc is placed on one side of the upper fixture to place it in a low-temperature field. The component layer disc is placed on one side of the lower fixture to place it in a high-temperature field.

[0026] 6) Using an upper and lower pressure die, bond the bonded upper cover plate wafer obtained in step 5) to the component layer wafer and the lower cover plate wafer, as shown below. Figure 3As shown, the bonding vacuum is 1e-4 Pa; the bonding pressure is 250 mbar to 350 mbar; the upper fixture temperature is 350℃, the lower fixture temperature is 420℃, and the heat preservation process lasts for 6 minutes. The lower cover plate disc is placed on one side of the lower fixture to place it in a high-temperature field. The upper cover plate disc is placed on one side of the upper fixture to place it in a low-temperature field.

[0027] Example 2

[0028] The method for multilayer successive wafer bonding using glass powder according to the present invention comprises the following steps:

[0029] 1) Preparation of glass slurry: Terpineol, butyl carbitol, tributyl citrate, and ethyl cellulose are mixed thoroughly at a mass ratio of 100:40:30:11 on a magnetic stirring plate at 85℃~95℃; the ethyl cellulose is completely dissolved in the organic solvent to obtain mixture A. After mixture A cools to room temperature, xylene is added and mixed thoroughly to obtain mixture B. The mass of xylene added is 8% of the mass of mixture A. Mixture B is then thoroughly mixed with glass powder and allowed to stand for 1 hour before use; the mass ratio of mixture B to glass powder is 100:55~70.

[0030] 2) Use HF acid solution to etch the bonding surfaces of the upper cover plate disc, the lower cover plate disc, and component layer discs A and B to increase the surface roughness of the bonding surfaces and clean the surface of the quartz discs to be bonded; the component layer discs are quartz discs.

[0031] 3) The glass paste obtained in step 1) is coated onto the bonding surfaces of the upper cover plate disc, the lower cover plate disc, and the component layer disc A using screen printing.

[0032] 4) Pre-sinter the upper cover plate, lower cover plate, and component layer plate A coated with glass paste. Increase the temperature at 10℃ / min to 220℃~250℃ and hold for 30min to fully remove the organic solvent. Increase the temperature at 10℃ / min to 320℃~350℃ (at this temperature, the glass paste is in powder form and has not yet formed a glassy state), and hold for 30min to fully burn off the ethyl cellulose. Increase the temperature at 5℃ / min to 360℃~380℃ and hold for 5min~10min to transform the glass powder into a glassy state, then slowly cool to room temperature.

[0033] 5) The upper cover plate disc and component layer disc A are bonded using an upper and lower clamping fixture. The bonding vacuum is 1e-4 Pa; the bonding pressure is 250 mbar to 350 mbar; the upper clamping fixture temperature is 350℃, and the lower clamping fixture temperature is 400℃, with the holding time lasting 2 minutes. The upper cover plate disc is placed on one side of the upper clamping fixture to expose it to a low-temperature field. Component layer disc A is placed on one side of the lower clamping fixture to expose it to a high-temperature field.

[0034] 6) Using an upper and lower pressure fixture, bond the bonded upper cover plate disc obtained in step 5) to component layer discs A and B. The bonding vacuum degree is 1e-4 Pa; the bonding pressure is 250 mbar to 350 mbar; the upper pressure fixture temperature is 350℃, and the lower pressure fixture temperature is 400℃, with the holding time lasting 2 minutes. The upper cover plate disc is placed on one side of the upper pressure fixture to place it in a low-temperature field. Component layer disc B is placed on one side of the lower pressure fixture to place it in a high-temperature field.

[0035] 7) Using an upper and lower pressure fixture, bond the bonded upper cover plate wafer, component layer wafer A, and component layer wafer B obtained in step 6) to the lower cover plate wafer. The bonding vacuum degree is 1e-4 Pa; the bonding pressure is 250 mbar to 350 mbar; the upper pressure fixture temperature is 350℃, and the lower pressure fixture temperature is 420℃, with the holding time lasting 6 minutes. The lower cover plate wafer is placed on one side of the lower pressure fixture to expose it to the high-temperature field. The upper cover plate wafer is placed on one side of the upper pressure fixture to expose it to the low-temperature field.

Claims

1. A multilayer wafer-level glass paste bonding process, characterized in that... The steps are as follows: 1) Prepare the glass slurry: Mix terpineol, butyl carbitol, tributyl citrate, and ethyl cellulose in a mass ratio of 100:40:30:11 on a magnetic stirring plate at 85℃~95℃ until fully dissolved; allow the ethyl cellulose to dissolve completely in the organic solvent to obtain mixture A. After mixture A cools to room temperature, add xylene and mix thoroughly to obtain mixture B. The mass of xylene added is 8% of the mass of mixture A. Mix mixture B thoroughly with glass powder and let stand for 1 hour before use; the mass ratio of mixture B to glass powder is 100:55~70. 2) The bonding surfaces of the upper cover plate wafer, lower cover plate wafer, and component layer wafer are etched with HF acid solution to increase the surface roughness of the bonding surfaces and clean the surface of the quartz wafer to be bonded; the component layer wafer is a quartz wafer. 3) The glass paste obtained in step 1) is applied to the bonding surfaces of the upper cover plate and the lower cover plate using screen printing. 4) Pre-sinter the upper and lower cover discs coated with glass slurry. Increase the temperature to 220℃~250℃ at 10℃ / min and hold for 30min to fully remove the organic solvent. Increase the temperature to 320℃~350℃ at 10℃ / min and hold for 30min to fully burn off the ethyl cellulose. Increase the temperature to 360℃~380℃ at 5℃ / min and hold for 5min~10min to make the glass powder become glassy. Then slowly cool to room temperature. 5) The upper cover plate disc and the component layer disc are bonded using an upper and lower pressure fixture. The bonding vacuum is 1e-4 Pa; the bonding pressure is 250 mbar to 350 mbar; the upper pressure fixture temperature is 350℃ and the lower pressure fixture temperature is 400℃, and the heat preservation process lasts for 2 minutes. The upper cover plate disc is placed on one side of the upper pressure fixture to place it in a low temperature field; the component layer disc is placed on one side of the lower pressure fixture to place it in a high temperature field. 6) Using an upper and lower pressure plate, the bonded upper cover plate wafer, component layer wafer, and lower cover plate wafer obtained in step 5) are bonded together. The bonding vacuum degree is 1e-4 Pa; the bonding pressure is 250 mbar to 350 mbar; the upper pressure plate temperature is 350℃ and the lower pressure plate temperature is 420℃, and the heat preservation process lasts for 6 minutes. The lower cover plate wafer is placed on one side of the lower pressure plate to place it in a high-temperature field; the upper cover plate wafer is placed on one side of the upper pressure plate to place it in a low-temperature field.

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