High-vacuum MEMS device packaging process

Abstract

The invention relates to the field of MEMS device packaging, in particular to a high-vacuum MEMS device packaging process, which comprises the following steps: after bonding of an MEMS device is completed, pre-fixing a getter into a tube shell, so that the getter is at least electrically connected with a pair of pins on the tube shell; configuring a power supply plugging assembly and an activation tool in the vacuum chamber; the vacuum degassing tube shell is assembled on the activation tool, the pair of pins, electrically connected with the getter, on the tube shell is electrically connected with the power supply plug-in assembly, the getter is electrified and activated through the power supply plug-in assembly, and compared with a traditional high-temperature heating mode for the whole packaging device, the whole packaging device can be prevented from being heated, and the packaging efficiency is improved. Getter activation and seam welding procedures are completed at a time, and a high vacuum environment and good sealing performance of a device in the packaging process are ensured.

Description

Technical Field

[0001] The present invention relates to the field of MEMS device packaging, and in particular to a high vacuum MEMS device packaging process. Background Art

[0002] Micro-electromechanical systems (MEMS) vacuum packaging technology plays a vital role in many application fields, especially in high-performance devices such as infrared detectors, inertial sensors, pressure sensors, magnetometers and miniature microphones. Since MEMS devices usually have tiny sizes and high performance requirements, they often need to operate in a vacuum environment. Therefore, MEMS vacuum packaging technology is crucial to ensure device quality and long-term stability.

[0003] In the existing MEMS vacuum packaging technology, getters are widely used in the packaging cavity to absorb residual gas that cannot be completely discharged during the packaging process, thereby maintaining a long-term vacuum environment. Getters reduce the gas pressure in the cavity to ensure that the device can work stably. However, the effect of getters is easily affected by external gas contamination or self-oxidation reactions. Therefore, how to effectively activate getters and prevent them from oxidation during the packaging process has become an important challenge in current technology.

[0004] Ceramic packaging is a common form of MEMS packaging, usually including a ceramic shell, a cover plate and a getter; traditionally, the activation of the getter is completed through high-temperature treatment. The usual method is to expose the entire device and package to a high-temperature vacuum environment, and activate the adsorption capacity of the getter through long-term heating. However, the disadvantage of this method is that high temperature may have an adverse effect on MEMS devices and their other components. Some devices need to avoid the direct impact of high temperature on the entire packaging system; in addition, the activation method and sequence of the getter will also affect the packaging effect of the MEMS device. The industry generally believes that activating the getter in a vacuum environment before packaging is more conducive to maximizing the efficiency of the getter and achieving high-vacuum MEMS packaging.

[0005] In order to solve the above problems, some researchers in the industry have proposed using special tooling to fix the getter on the cover plate, pre-separate the cover plate and the tube shell in a vacuum environment, and only heat the cover plate to activate the getter. When the required activation temperature and time are reached, the cover plate is moved down to make close contact with the tube shell, and then welded and packaged to reduce the impact on other components. This method activates the getter by heating the cover plate, ensuring that the getter can fully play its role without affecting other components. Taking China's patent application CN102275863B as an example, it grows a getter film on the capping wafer, uses bonding equipment to heat and activate the getter, and then packages it.

[0006] However, most of these reported methods or processes are for eutectic welding packaging process, and their applicability in parallel welding process is limited. As a commonly used MEMS device packaging method, the parallel welding process itself does not directly support the heating of the getter or cover plate, and due to the differences between the parallel welding method and the eutectic welding packaging, these special tools cannot be directly applied to the parallel welding process. Summary of the invention

[0007] In order to solve the deficiencies in the prior art, the present invention provides a high vacuum MEMS device packaging process, which ensures a high vacuum degree inside the device by completing the seam welding and getter activation processes at one time.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions: a high vacuum MEMS device packaging process, comprising, after completing the bonding of the MEMS device, pre-fixing the getter into the tube shell, so that the getter is electrically connected to at least a pair of pins on the tube shell; providing a packaging device, the packaging device includes a vacuum chamber, and a power connector and an activation tool are arranged in the vacuum chamber; assembling the tube shell after vacuum degassing on the activation tool, so that a pair of pins on the tube shell that are electrically connected to the getter are electrically connected to the power connector; controlling the vacuum chamber to be evacuated to a target vacuum degree, energizing the getter through the power connector assembly to activate the getter, and gradually increasing the current to heat the getter until it reaches the activation temperature and maintains it for a period of time; gradually reducing the power supply voltage after the getter is activated, and maintaining the vacuum degree in the vacuum chamber until the packaging device completes the packaging of the high vacuum MEMS device.

[0009] As a preferred embodiment, the vacuum degassing of the tube shell includes: assembling the tube shell onto an electric heating tool and placing it in a vacuum environment, wherein the vacuum environment can provide at least 10 -1 Pa, the heating unit dries and degases the tube shell by conductive heating.

[0010] As a preferred embodiment, the activation tool includes a base for stably loading the tube shell, and at least one pair of through holes for leading out a pair of the pins is formed on the base, and the power connector is electrically connected to the pins on the tube shell through the through holes.

[0011] As a preferred embodiment, the pre-fixing of the getter into the tube shell includes: forming a device area and a support area in the tube shell, so that a gap or cavity is formed between the getter pre-fixed in the support area and the MEMS device in the device area.

[0012] As a preferred embodiment, the pre-fixing of the getter into the tube shell includes: forming a supporting device in the supporting area, wherein the supporting device allows the getter to be suspended in the air without contacting the inner surface of the tube shell.

[0013] As a preferred embodiment, forming a supporting device in the supporting area includes: forming a block in the supporting area in surface contact or line contact with the getter, including at least a first end and a second end, at least including a first end and a second end, and the getter is overlapped between the first end and the second end.

[0014] The method of pre-fixing the getter into the tube shell includes: providing a substrate with a heating function to form the getter on the surface of the substrate; welding the two ends of the substrate to the first end and the second end respectively, and electrically connecting them to a pair of pins on at least one pair of tube shells.

[0015] As a preferred embodiment, the pre-fixing of the getter into the tube shell includes: providing a substrate with a heating function so that the getter is formed on the surface of the substrate; welding the two ends of the substrate to the first end and the second end respectively, and electrically connecting them to at least one pair of pins on the tube shell.

[0016] As a preferred embodiment, the two ends of the substrate are welded to the first end and the second end respectively, and electrically connected to at least one pair of pins on the tube shell, including: providing a metal lead, the metal lead respectively connects the substrate and a pair of pins on the tube shell; or, the first end and the second end are respectively electrically connected to different pins on the tube shell.

[0017] As a preferred embodiment, the step of forming the getter on the substrate surface includes: pressing getter powder onto the substrate surface to form a strip-shaped getter; or sputtering the getter from a target material onto the substrate surface to form a thin film getter.

[0018] As a preferred embodiment, the power connector assembly is configured as a DC power supply; when the getter is powered on and activated, the activation state of the getter is detected by an infrared temperature sensor and dynamically detecting the vacuum degree in the vacuum chamber.

[0019] Compared with the prior art, the present invention has the following beneficial effects: Firstly, the process of the present invention uses special getter activation tooling and power connector components, which can avoid overall heating of the device compared to the traditional method of high-temperature heating of the entire packaging system, reducing the risk of performance degradation or failure of the MEMS device, and can complete the getter activation and seam welding processes at one time, ensuring a high vacuum environment and good sealing of the device during the packaging process.

[0020] Secondly, in the process of the present invention, the power connector is configured as a DC power supply, and the size of the current can be used to regulate the rise and fall of the getter temperature. Compared with the traditional overall heating or AC power supply, it is more stable. For the getter heating process that requires precise temperature control, it is also more convenient to monitor the getter activation state, which can effectively improve the process control accuracy and consistency during the getter activation process, and help reduce the complexity and operating costs of the heating system.

[0021] Secondly, in the process of pre-fixing and activating the getter, a specially designed supporting device is adopted in the process of the present invention. The supporting device makes the getter suspended and avoids contact with the inner surface of the tube shell or the cover plate, which can effectively reduce the transfer of heat and ensure that the heat is concentrated on the getter instead of being directly transferred to the MEMS device, thereby avoiding uneven activation caused by local overheating of the getter, ensuring that the getter is evenly heated during the activation process, facilitating the observation of the heating process of the getter, and being more conducive to maximizing the efficiency of the getter. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is a process flow chart of high vacuum MEMS device packaging in the present invention; Figure 2 A schematic diagram of the structure of one of the getters provided by the present invention after being pre-welded to the inside of the tube shell; Figure 3 for Figure 2 Sectional view at point A in the middle; Figure 4 A schematic diagram of the structure of one embodiment of the electric heating device provided by the present invention; Figure (a) is a front view of the electric heating device; Figure (b) is a top view of the electric heating device; Figure 5 It is a structural schematic diagram of a tube shell assembled on an activation tooling according to an embodiment of the present invention; Figure 6 for Figure 5 Sectional view at point A in the middle; Figure 7 A flow chart of getter activation in the high vacuum MEMS device packaging process of the present invention; Figure 8 A schematic diagram of the structure of one implementation mode of the activation tool provided by the present invention; Fig. 9A schematic structural diagram of one embodiment of the tube shell provided by the present invention; Fig.10 A schematic structural diagram of one embodiment of the support device provided by the present invention; Markings in the figure: 1-tube shell, 2-getter, 3-pin, 4-support device, 5-electric heating tool, 6-activation tool, 7-substrate, 11-device area, 12-support area, 41-first end, 42-second end, 61-groove, 62-through hole. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are directions or positional relationships in which the inventive product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0026] In addition, the terms "horizontal", "vertical" and the like do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0027] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] See also Figure 1 to Figure 10 A high vacuum MEMS device packaging process includes steps 100 to 800 in sequence. After the bonding of the MEMS device is completed in step 300, the following steps are specifically performed: Step 400, pre-soldering the getter, includes pre-fixing the getter 2 to the inside of the tube shell 1; see Figure 2~Figure 3 , Figure 2~Figure 3 A schematic diagram is shown after a getter is pre-soldered to the inside of a tube shell. After being fixed, the getter 2 is electrically connected to a pair of pins 3 on the tube shell 1.

[0029] Step 500, vacuum baking includes vacuum degassing the tube shell after completing step 400; see Figure 4 , Figure 4 The electric heating tool 5 is shown to be used for baking the tube shell. After the tube shell 1 is assembled on the electric heating tool 5, the tube shell 1 is placed on the electric heating tool 5. -1 Under the condition of Pa, the tube shell is heated to 120° C. by using the electric heating tool 5 and baked for 24 hours to remove the gas molecules adsorbed inside the tube shell material.

[0030] Step 600, perform getter activation 600; add a power plug assembly (not shown in the figure) inside the vacuum chamber of the vacuum parallel sealing machine, and after reaching the target vacuum degree, use the activation tool 6 to activate the getter 2 to be activated; see Figure 5~Figure 7 , Figure 5~Figure 7 A schematic diagram of a structure in which a tube shell 1 is assembled on an activation tool 6 is shown. After the tube shell 1 is assembled on the activation tool 6, the pin 3 electrically connected to the getter is electrically connected to the power plug assembly, and the getter 2 is activated by energizing the power plug assembly; More specifically, see Figure 7 , the energizing and activating the getter 2 specifically comprises: Step 610, preset the vacuum degree; including, evacuating; starting the vacuum pump: gradually extracting the gas in the vacuum chamber to make the chamber reach the preset vacuum degree (5*10 -3Pa ), to avoid contamination of the getter by oxygen or other gases; and vacuum monitoring: During the vacuuming process, a vacuum gauge is used to monitor the vacuum level in the chamber to ensure that the vacuum level meets the process requirements. After reaching the target vacuum level, this state is maintained to ensure the stability of subsequent operations.

[0031] Step 620, power on activation; including, gradual heating: start by powering the getter at 1.5A, gradually increase the current to slowly heat the getter to avoid local overheating or unevenness caused by rapid heating; and temperature monitoring: monitor the temperature of the getter in real time through an infrared temperature sensor to ensure that the temperature rise is in line with the process curve until the getter reaches the required activation temperature of 300°C.

[0032] Step 630, maintaining activation conditions, including: temperature constant: when the getter reaches the activation temperature, maintaining the temperature for 30 minutes. During this period, the surface and internal structure of the getter will change, thereby enhancing its ability to adsorb gas; and process monitoring: during the activation process, continuously monitoring the vacuum and temperature to ensure that there is no air leakage or temperature fluctuation, and to prevent the getter from being oxidized or contaminated by other gases at high temperatures.

[0033] Step 640, monitoring the environment: including, dynamically monitoring the vacuum degree: in order to ensure that the environment in the chamber always remains in an oxidation-free state during the activation process, the vacuum degree of the chamber needs to be continuously monitored by a vacuum sensor; and adjusting the vacuum degree: if the vacuum degree fluctuates, it needs to be adjusted in time, and if necessary, a supplementary vacuum pump is started to maintain a stable high vacuum environment.

[0034] Step 700, vacuum flat sealing is performed. After the getter is activated, the power supply voltage is gradually reduced to control the cooling rate of the getter to avoid excessive cooling that may cause stress concentration or damage to the material. Under the premise of maintaining vacuum in the chamber, the flat sealing machine is started to perform the packaging operation to ensure that the packaging process is smooth and the environment in the chamber is non-oxidizing.

[0035] Step 800, inspecting the packaging quality; performing appearance inspection and air tightness test on the packaged components to ensure that the packaged equipment can operate stably for a long time.

[0036] The above technical solution can accurately control the getter activation process through special getter activation tooling and power plug-in components. Compared with the traditional method of high-temperature heating of the entire packaged device, it can avoid heating the entire device, ensure the performance and reliability of the MEMS device, and can complete the getter activation and seam welding process at one time, ensuring a high vacuum environment and good sealing of the device during the packaging process, so that the internal vacuum degree of the MEMS device can be stabilized at 9*10 -5 Pa level.

[0037] As a preferred embodiment, see Figure 4 The electric heating tool 5 includes a heat spreader 51 and a heat source 52. The heat spreader 51 includes a heating portion (not shown in the figure) and a mounting hole matched with the pins of the tube shell. The heating portion dries and degases the tube shell by conductive heating to provide uniform heat transfer. Compared with vacuum radiation baking, it can ensure that the interior of the tube shell is heated uniformly as a whole, and ensure that the adsorbed gas molecules inside the tube shell material can be fully discharged.

[0038] As a preferred embodiment, see Figure 6 and Figure 8The activation tooling includes a base, which can be assembled in the vacuum chamber and used to stably load the tube shell 1. A pair of grooves 61 for accommodating each pin 3 are formed on the base, and a pair of through holes 62 are correspondingly arranged at one end of the groove. The pair of pins 3 on the tube shell 1 that are electrically connected to the getter 2 can be inserted into the through holes 62; it can be understood that, please refer to Figure 6 The pin 3 inserted into the through hole 62 is connected to the positive and negative terminals of the power connector respectively, forming a power supply circuit for the getter 2.

[0039] As a preferred embodiment, see Fig. 9 The pre-fixing of the getter 21 into the tube shell 1 includes: forming a device area 11 and a support area 12 in the deep cavity of the tube shell 1, so that a gap or cavity is formed between the getter 2 pre-fixed in the support area 12 and the MEMS device (not shown in the figure) in the device area 11, so as to ensure that the high temperature when the getter is activated will not cause damage or interference to the MEMS device.

[0040] As a preferred embodiment, see Figure 2 , Fig. 9 , the pre-fixing of the getter 2 into the tube shell includes: forming a supporting device 4 in the supporting area 12, wherein the supporting device 4 allows the getter 2 to be suspended in the air without contacting the inner surface of the tube shell 1, so as to form an isolation layer between the getter 2 and the inner surface of the tube shell 1, so that the heat can be more concentratedly conducted to the getter 2 instead of being dispersed to other areas, which helps to maintain the uniformity of the heating of the getter; on the other hand, in this design, the heat dispersion to other areas is reduced, so that the heating process of the getter body 2 is easier to monitor, thereby maximizing the effectiveness of the getter.

[0041] For more details, see Figure 3 , Fig. 9 and Fig.10 In order to make the getter 2 suspended, the support device 4 includes a first end 41 and a second end 42, and the getter 2 is overlapped between the first end 41 and the second end 42; see Figure 3 The first end 41 and the second end 42 may both be in a block shape, or other structures in surface contact with the getter, so as to facilitate welding and fixing of the getter; in some embodiments of the present application, see Fig.10 In order to increase the suspended area of ​​the getter, the first end 41 and the second end 42 may also be angular structures, or other structures in linear contact with the getter.

[0042] As a preferred embodiment, see Fig. 9, the pre-fixing of the getter into the tube shell includes: providing a substrate 7 with a heating function, so that the powder of the getter 2 is formed on the surface of the substrate; welding the substrate 7 to the supporting device 4, and electrically connecting it to a pair of pins 3 on at least one pair of tube shells 1; the melting point of the substrate 7 is higher than the melting point of the getter 2, ensuring that the substrate will not melt or deform due to high temperature during the heating process. Exemplarily, the substrate 7 can be a nickel strip, an iron strip with nickel plating on the surface, or a molybdenum strip. In some embodiments of the present application, in order to obtain a good heating effect, when a low-temperature getter is used, the substrate 7 can also be copper, aluminum or other composite materials, and the present application does not limit this.

[0043] As a preferred embodiment, the substrate 7 is welded to the support device 4 and electrically connected to a pair of pins 3 on at least one pair of tube shells 1, including: providing a metal lead (not shown in the figure), the metal lead is respectively connected to the substrate and a pair of pins on the tube shell, and a closed circuit is formed between the substrate and the tube shell, which can be a copper wire or an aluminum wire, and in applications under a higher temperature environment, it can also be a nickel wire or a molybdenum wire, and the present application is not limited to this. In some embodiments of the present application, the substrate is welded to the support device and electrically connected to a pair of pins on at least one pair of tube shells can also be: providing a support device 4 made of metal material, that is, the support device 4 has electrical and thermal conductivity properties in addition to bearing mechanical loads, and the first end and the second end are respectively electrically connected to different pins on the tube shell.

[0044] As a preferred embodiment, the step of forming the getter 2 on the surface of the substrate includes: pressing the getter 2 powder onto the surface of the substrate 7 to form a strip-shaped getter, which can cover a larger surface area of ​​the substrate, and because of its linear shape, can form a uniform getter distribution on the contact surface of the substrate, ensuring that the function of the getter is more uniform; in some embodiments of the present application, the getter 2 can also be in the form of a thin film, and the getter is sputtered from the target material to the surface of the substrate 7 to form a thin film getter.

[0045] As a preferred embodiment, the power connector assembly is configured as a DC power supply, and the temperature can be adjusted by utilizing the size of the current. Compared with the traditional overall heating or AC power supply, it is more stable. For the process of heating the getter that requires precise temperature control, it is also easier to monitor the activation status of the getter, and can effectively improve the process control accuracy and consistency during the getter activation process, which helps to reduce the complexity and operating costs of the heating system.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high vacuum MEMS device packaging process, characterized in that: The method comprises: after completing the bonding of the MEMS device, pre-fixing a getter into the tube shell so that the getter is electrically connected to at least a pair of pins on the tube shell; A parallel welding and sealing device is provided, comprising a vacuum chamber, in which a power connector assembly and an activation tool are arranged; a tube shell after vacuum degassing is assembled on the activation tool, so that a pair of pins on the tube shell electrically connected to a getter are electrically connected to the power connector assembly; The vacuum chamber is evacuated to the target vacuum degree, the getter is powered on and activated through the power connector, and the current is gradually increased to heat the getter; after the getter is activated, the power supply voltage is gradually reduced to maintain the vacuum degree in the vacuum chamber, and the welding and sealing equipment is started to complete the packaging of the high vacuum MEMS device.

2. The high vacuum MEMS device packaging process according to claim 1, characterized in that: The vacuum degassing of the tube shell comprises: assembling the tube shell on an electric heating tool and placing it in a vacuum environment, wherein the vacuum environment can provide at least 10 -1 Pa, the heating unit dries and degases the tube shell by conductive heating.

3. The high vacuum MEMS device packaging process according to claim 1, characterized in that: The activation tooling comprises a base for stably loading the tube shell, and at least one pair of through holes for leading out a pair of the pins is formed on the base, and the power connector is electrically connected to the pins on the tube shell through the through holes.

4. The high vacuum MEMS device packaging process according to any one of claims 1 to 3, characterized in that: The pre-fixing of the getter into the tube shell includes: forming a device area and a support area in the tube shell, so that a gap or a cavity is formed between the getter pre-fixed in the support area and the MEMS device in the device area.

5. The high vacuum MEMS device packaging process according to claim 4, characterized in that: The pre-fixing of the getter into the tube shell comprises: forming a supporting device in the supporting area, wherein the supporting device allows the getter to be suspended in the air without contacting the inner surface of the tube shell.

6. The high vacuum MEMS device packaging process according to claim 5, characterized in that: Forming a support device in the support area includes: forming a block in the support area in surface contact or line contact with the getter, including at least a first end and a second end, and the getter is overlapped between the first end and the second end.

7. The high vacuum MEMS device packaging process according to claim 6, characterized in that: The method of pre-fixing the getter into the tube shell includes: providing a substrate with a heating function to form the getter on the surface of the substrate; welding the two ends of the substrate to the first end and the second end respectively, and electrically connecting them to at least one pair of pins on the tube shell.

8. The high vacuum MEMS device packaging process according to claim 7, characterized in that: Welding the two ends of the substrate to the first end and the second end respectively, and electrically connecting them to at least one pair of pins on the tube shell includes: providing a metal lead, the metal lead respectively connecting the substrate and a pair of pins on the tube shell; or, the first end and the second end are respectively electrically connected to different pins on the tube shell.

9. The high vacuum MEMS device packaging process according to claim 7, characterized in that: The method of forming the getter on the surface of the substrate includes: pressing the getter powder onto the surface of the substrate to form a strip-shaped getter; or sputtering the getter from the target material onto the surface of the substrate to form a thin film getter.

10. The high vacuum MEMS device packaging process according to any one of claims 1 to 3 or 4 to 9, characterized in that: The power connector assembly is configured as a direct current power supply; when the getter is powered on and activated, the activation state of the getter is detected by using an infrared temperature sensor and dynamically detecting the vacuum degree in the vacuum chamber.

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