CN100494046C - Structure and manufacturing method of micromechanical system device with bump connection and hermetic packaging - Google Patents

Abstract

The invention relates to a structure and a manufacturing method of a bump connection hermetic package MEMS device, which is characterized in that a silicon chip containing a MEMS chip and a silicon chip containing a cavity pattern are bonded together by silicon-silicon bonding to form a MEMS device Then, the back side of the silicon chip containing the cavity pattern is thinned, and the back side of the silicon chip containing the MEMS chip is etched. Then use silicon glass anode bonding to bond the glass sheet on the back of the silicon sheet containing the MEMS chip to form the upper cavity of the MEMS device. The formed silicon/silicon/glass triple-layer structure encapsulates the movable parts of the MEMS device in a cavity with reliable airtight characteristics. The invention organically combines the manufacture of the movable parts of the MEMS device with the hermetic package of the MEMS device, which can not only improve the airtight characteristics of the hermetic package of the MEMS device and the electrical performance of the output, but also reduce the cost of the hermetic package; and the fabricated device Compatible with existing advanced IC packaging technology.

Description

Structure and manufacturing method of micromechanical system device with bump connection and hermetic packaging

technical field

The invention relates to a structure and a manufacturing method capable of realizing hermetic packaging of a micro-electromechanical system (MEMS) device, more precisely, to a structure and a manufacturing method of a bump-connected hermetic packaging micro-mechanical system device, belonging to the field of MEMS device packaging .

Background technique

MEMS (microelectromechanical system) refers to a system made of micro-fabrication technology, integrating micro-sensors, micro-components, micro-actuators, signal processing, and control circuits. MEMS devices have very broad application prospects in many fields. However, in MEMS devices, there are movable parts. These movable parts are very fragile and are easily affected by factors such as dust, air flow, humidity, machinery and other factors in the scribing and assembly process, thereby causing damage to the device or the overall damage of the device. Therefore, hermetic packaging measures must be taken to protect these critical parts.

In order to realize the hermetic packaging of MEMS devices, a variety of methods for hermetic packaging of MEMS devices have been proposed. moving parts. Nowadays, the bonding methods for hermetic packaging of MEMS devices mainly include: silicon-glass anode bonding, silicon-silicon bonding, glass direct bonding, low-temperature glass bonding, organic adhesive bonding, and solder bonding. At present, silicon-glass anode bonding and silicon-silicon bonding are developed based on wafer bonding technology, and are two commonly used methods to achieve hermetic packaging of MEMS devices. Silicon-glass anodic bonding is also called field-assisted thermal bonding. Its principle is to generate a strong electric field at the interface between silicon and glass. Under the action of the strong electric field, sodium ions in the glass leave the interface, resulting in a sodium ion dissipation zone and leaving oxygen molecules. At its interface, oxygen molecules diffuse into the silicon surface to form an amorphous silicon dioxide layer, enabling silicon-glass bonding. Silicon-silicon bonding is the use of high-density OH groups adsorbed on the silicon surface to remove a water molecule, forming a Si-O-Si bond on the surface of two silicon wafers, and bonding the two silicon wafers together. Silicon-glass anode bonding and silicon-silicon bonding can realize wafer-level hermetic packaging, so the cost of hermetic packaging is relatively low. These two types of bonding do not use adhesives and solders, and can obtain compact, firm and complex hermetically sealed MEMS devices. Low-temperature glass bonding, organic adhesive bonding, and solder bonding require adhesives and solders, and some additional processes are required, which is extremely detrimental to fragile MEMS devices and will increase the cost of hermetic packaging of MEMS devices. the cost of.

The output signal (current or voltage) of the MEMS device is very small, if it is connected to the peripheral circuit, if the connected impedance, parasitic effect and noise are high, the useful output signal of the MEMS device will be completely covered. At present, the electrical connection of MEMS devices mainly adopts the method of wire bonding, which will undoubtedly make the electrical connection have higher impedance and parasitic effects. Flip-chip connection has many advantages such as low connection resistance, low signal crosstalk and high power dissipation. Therefore, flip-chip connection will improve the performance of MEMS devices.

Contents of the invention

In order to avoid damage to the movable parts of MEMS devices by the additional process of hermetic packaging of MEMS devices, improve the yield of hermetic packaging of MEMS devices, reduce the impedance, parasitic effects and noise of electrical connections of MEMS devices, and improve the output signal of MEMS devices quality, the present invention proposes to realize the hermetic packaging structure of the bump connection MEMS device and the manufacturing method thereof. The structure can make full use of the existing IC technology to realize the hermetic packaging of the MEMS device, which can not only effectively reduce the cost of the hermetic packaging of the MEMS device, but also improve the quality of the output signal of the MEMS device.

The technical solution adopted in the present invention is: use silicon-silicon bonding to bond the silicon chip containing the MEMS chip and the silicon chip containing the cavity pattern together to form the lower cavity of the MEMS device, and then, the silicon chip containing the cavity pattern The backside of the silicon wafer is thinned and the backside of the silicon wafer containing the MEMS chip is etched. The purpose of thinning the back of the silicon wafer with a cavity pattern is to facilitate the production of through holes in the next step, and the purpose of etching the back of the silicon wafer containing the MEMS chip is to facilitate the formation and release of the movable parts of the MEMS device. Using the principle of silicon-glass anode bonding, the glass sheet is bonded to the back of the silicon sheet containing the MEMS chip to form the upper cavity of the MEMS device. The formed silicon/silicon/glass triple-layer structure can enclose the movable parts including the MEMS device in a reliable airtight cavity. After thinning the back side of the silicon chip containing the cavity pattern, reactive ion etching and corrosion can be effectively used to form openings for drawing out electrodes. After depositing aluminum film, photolithography mask and other processes, MEMS electrode block can be produced, then coated with polyimide dielectric film, photolithographic aluminum electrode is opened and UBM (underball metallization, underball metallization) is deposited ), thick photolithography to form electroplating openings, electroplating solder, removing photoresist, wet etching UBM, and reflowing into balls. A photoresist is applied to protect the solder balls, and then diced into individual hermetically packaged MEMS devices. (see embodiment for details).

To sum up, the present invention introduces a structure of a bump-connected hermetically sealed micromechanical system device, which is characterized in that:

(1) The structure of the device is silicon/silicon/glass three-layer bonding, which is the silicon wafer of the chip containing the micromechanical system device and the silicon wafer of the lower cover plate containing the cavity pattern are bonded to form a micromechanical system The lower cavity of the device, and then the glass sheet is bonded on the back of the silicon chip containing the micro-mechanical system chip to form the upper cavity of the micro-mechanical system device, and the movable part of the micro-mechanical system device is encapsulated on the upper and lower cover silicon In the cavity formed by the chip and the glass cover, the devices of the micromechanical system are connected by bumps.

(2) Each cavity on the lower cover silicon wafer corresponds to the position of the micromechanical system in the silicon wafer containing the micromechanical system device chip.

The method for making the bump-connected hermetically sealed micromechanical device structure is characterized in that:

(a) Using silicon-silicon bonding, the silicon chip containing the MEMS chip and the silicon chip containing the cavity pattern are bonded together to form the lower cavity of the MEMS device;

(b) Thinning the back side of the silicon chip containing the cavity pattern, and etching the back side of the silicon chip containing the MEMS chip;

(c) Bond the glass sheet on the back of the silicon chip containing the MEMS chip to form the upper cavity of the MEMS device, forming a three-layer structure of silicon/silicon/glass, and enclose the movable parts of the MEMS device in a reliable airtight In the cavity of the characteristic;

(d) Thinning the back side of the silicon wafer containing the cavity pattern, and forming openings for drawing out electrodes by wet method and reactive ion etching. Deposit aluminum film, photolithography mask, and produce MEMS electrode blocks;

(e) Coating polyimide dielectric film, photoetching aluminum electrode openings to deposit UBM, coating thick glue, photolithography forming electroplating openings, electroplating solder, removing photoresist, reflowing into balls, coating photolithography glue, diced and cut into discrete hermetically packaged MEMS devices.

The practical effect of the present invention is that the manufacture of the movable parts of the MEMS device can be organically combined with the hermetic packaging of the MEMS device, and the reliability of the MEMS hermetic packaging can be improved by using the mature technology of silicon-silicon bonding and silicon-glass anode bonding. Sex, reduce the cost of hermetic packaging of MEMS devices; use the flip-chip bump connection method to reduce the on-resistance and signal interference of the interconnection, and improve the quality of the output signal of the MEMS device.

The device made by adopting the invention can not only improve the airtight characteristics and output electrical performance of the MEMS device hermetic package, reduce the cost of the MEMS package, but also be compatible with the existing IC packaging process in technology, and provide a hermetic package MEMS device A new method for connecting with redistributed bumps.

Description of drawings

Figure 1 is a top view of a silicon wafer containing an array of MEMS devices.

Fig. 2 is a top view of the lower cover silicon wafer containing the array cavity.

Figure 3 is a top view of the glass cover.

Fig. 4 is a cross-sectional structure diagram of a lower cavity formed by bonding a silicon chip containing a MEMS device and a silicon chip containing a cavity. (a) silicon wafer, (b) lower cover silicon wafer, (c) silicon wafer and lower cover silicon wafer are pre-bonded.

Fig. 5 is a cross-sectional structure view of a complete cavity formed by a silicon wafer and a glass cover plate of a MEMS device. (a) Schematic diagram of the thinning of the lower cover plate, (b) Schematic diagram of the cavity 501 formed on the groove, (c) Schematic diagram of the movable parts encapsulated in the cavity formed by the silicon wafer of the lower cover plate and the glass cover plate.

Fig. 6 is a flow chart of the electrical connection of the bumps of the hermetic MEMS device. (a) opening holes in the electrode area, (b) depositing aluminum film in the holes, (c) coating polyimide film, (d) making openings for aluminum electrodes with a photolithography mask, (e) depositing under bumps metal film.

Detailed ways

In order to fully demonstrate the advantages and positive effects of the present invention, the substantive features and remarkable progress of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

In FIG. 1 , on a silicon wafer 101 , MEMS devices 102 are fabricated by semiconductor technology, and each MEMS device 102 has an electrode region 103 . The electrode region 103 can be connected to the bump through the metallization of the via hole.

In FIG. 2 , the lower cover silicon wafer 201 has cavities 202 distributed in an array, and the position of each cavity 202 on the lower cover silicon wafer 201 exactly corresponds to the MEMS device 102 in FIG. 1 . In order to form the lower cavity of the movable part of the MEMS device 102 after silicon bonding.

FIG. 3 is a glass cover 301 . The glass cover 301 may contain a mask pattern or not contain a mask pattern, and is mainly used to form an upper cavity of the MEMS device 102 and support the MEMS device 102 .

In Fig. 4, firstly, the silicon wafer 101 (Fig. 4-a) and the lower cover silicon wafer 201 (Fig. Align the cavity 202 in the lower cover silicon wafer 201, complete the pre-bonding at room temperature and a certain pressure, move it to the vacuum chamber, and raise the temperature to 400°C. At this time, the OH groups on the interface of the two silicon wafers generate react, remove water, form Si-O-Si bonds, bond the silicon wafer 101 and the lower cover silicon wafer 201 together, and form the lower cavity 202 .

In FIG. 5 , the lower cover silicon wafer 201 of the structure formed in FIG. 4 is chemically mechanically polished to reduce the thickness of the lower cover silicon wafer 201 to about 100 μm ( FIG. The purpose of thinning 201 is to facilitate the formation of electrical connection via holes and reduce the "step" covered by the film in subsequent processes. After the lower cover silicon wafer 201 is thinned, use a photoresist mask to etch silicon with KOH solution, release the movable parts of the MEMS device 102 in the silicon wafer 101, and form a cavity 501 on the groove (Fig. 5- b). In the vacuum chamber, place the glass cover 301 shown in FIG. 3 on the silicon wafer 101, heat it to 400°C, and apply a negative bias voltage to the glass cover 301 at the same time to generate a A strong electric field, under the action of the strong electric field, the sodium ions in the glass cover 301 leave the interface, resulting in a sodium ion dissipation zone, leaving oxygen molecules on the interface, and the oxygen molecules diffuse into the surface of the silicon wafer 101, forming a layer of no The silicon dioxide layer is shaped to realize the bonding of the glass cover plate 301 and the silicon wafer 101 . And obtain the upper cavity 501 . So far, the movable parts of the MEMS device 102 in the silicon wafer 101 are enclosed in the complete cavity formed by the lower cover silicon wafer 201 and the glass cover 301 ( FIG. 5 - c ).

左右，Cu为电镀的种子层，其厚度为

左右。光刻掩模制作电镀的开孔，电镀Cu/PbSn，电镀Cu膜的厚度为10μm，去胶，选择性腐蚀掉UBM605，回流形成焊球606(图6-e)。涂覆光刻胶，划片切成独立的气密封装的MEMS器件。FIG. 6 is a flow chart of making electrical connection bumps for the MEMS device 102 in the structure of FIG. 5 . In Fig. 6-a, a photoresist mask is used to etch silicon with KOH solution or reactive ions to form an opening 601 in the electrode region 103 of the MEMS device 102 in the structure of Fig. 5, considering the "step" size of the opening connection Problem, it is more preferable to use KOH solution to etch the silicon to make the opening 601 of the electrode region 103 of the MEMS device 102 in the structure shown in FIG. 5 . Deposit aluminum film with sputtering method, the thickness of aluminum film is about 1 μ m, photolithography mask and corrosion, lead the electrode area 103 of MEMS device 102 in the structure of Fig. 5 to the bottom surface aluminum electrode 602 of lower cover silicon chip 6-b). Coating a polyimide film 603 ( FIG. 6 - c ), the thickness of the polyimide film 603 is about 20 μm. The polyimide film 603 can improve the reliability of the through-hole connection and support the bumps. Make the opening 604 of the aluminum electrode 602 (Fig. 6-d) by photolithography mask, and deposit the UBM (underball metallization) 605 under the bump by sputtering method, UBM605 is Cr/Cu or Ti/Cu, Cr or Ti is the adhesive layer, its thickness is

Left and right, Cu is the seed layer for electroplating, and its thickness is

about. Make electroplating openings by photolithography mask, electroplating Cu/PbSn, the thickness of electroplating Cu film is 10 μm, remove glue, selectively etch UBM605, and reflow to form solder balls 606 (Fig. 6-e). Coating photoresist, dicing and cutting into independent hermetically sealed MEMS devices.

Claims (8)

1. the structure of an air-sealed packing micromechanical system device with convex point connection, the structure that it is characterized in that described device is three layers of bonding of silicon/silicon/glass, it is the silicon chip and the lower cover wafer bonding that contains the cavity figure that contains the chip of micromechanical system device, form the lower chamber of micromechanical system device, discharge the micromechanical system device movable member in the silicon chip then, again sheet glass is bonded in the behind of the silicon chip that contains the micro mechanical system chip, form the upper cavity of micromechanical system device, the moving part of micromechanical system device is encapsulated among the cavity that cover plate silicon chip and glass cover-plate form up and down, and the device of micro mechanical system adopts the salient point mode to connect; Each cavity is corresponding with the position that contains the micro mechanical system in the micromechanical system device chip silicon chip on the lower cover silicon chip;

It is to contain the silicon chip thinning back side of cavity figure, the perforate of extraction electrode, deposition of aluminum film that described salient point connects, mask is produced the electrode block of MEMS, coating polyimide dielectric film, mask is made the perforate of aluminium electrode, the deposit Underbump metal film, and refluxing forms welding.

2. make the method for salient point connection air-sealed packing micromechanical device architecture as claimed in claim 1, it is characterized in that concrete steps are:

(a) utilize Si-Si bonding, the silicon chip that will contain the MEMS chip is in the same place with the wafer bonding that contains the cavity figure, forms the lower chamber of MEMS device;

(b) the silicon chip back attenuate of cavity figure will be contained, and the silicon chip back etching of MEMS chip will be contained;

(c) sheet glass is bonded in the silicon chip back that contains the MEMS chip, forms the upper cavity of MEMS device, form silicon/silicon/glass three-decker, the movable member of MEMS device is encapsulated in the cavity of reliable hermetic properties;

(d) will contain the silicon chip back attenuate of cavity figure, and utilize wet method and reactive ion etching to form the perforate of wanting extraction electrode, deposition of aluminum film, mask is produced the electrode block of MEMS;

(e) apply poly-phthalimide dielectric film, photoetching aluminium electrode deposit UBM applies thick glue, and photoetching forms electroplates perforate, electroplates scolder, removes photoresist, and the backflow balling-up applies photoresist, and scribing is cut into the MEMS device of discrete level Hermetic Package.

3. connect the preparation method of air-sealed packing micromechanical device architecture by the described salient point of claim 2, it is characterized in that the preparation method of described step (a) is:

(1) at first silicon chip (101) and lower cover silicon chip (201) are carried out chemical surface treatment:

(2) with litho machine the micromechanical system device (102) in the silicon chip (101) is aimed at cavity (202) in the lower cover silicon chip (201), at room temperature finished pre-bonding;

(3) move to vacuum chamber again and be warmed up to 400 0C, two silicon chips form the Si-O-Si key, are bonded together and form lower chamber (202).

4. connect the preparation method of air-sealed packing micromechanical device architecture by the described salient point of claim 2, it is characterized in that described step (b) and preparation method (c) are:

(1) the lower cover silicon chip (201) of the structure that step (a) is formed carries out chemical polishing, makes the lower cover wafer thinning;

(2) adopt the photoresist mask, the movable member of system device discharges the micromechanics system (102) in the silicon chip with KOH solution corrosion silicon, and forms groove upper cavity (501);

(3) in vacuum chamber, glass cover-plate (301) is placed on the silicon chip (101), be heated to 400 ℃, apply a back bias voltage for simultaneously glass cover-plate (301), realize glass cover-plate (301) and silicon chip (101) bonding, obtain upper cavity (501), form three layers of bonding structure of silicon/silicon/glass, the movable member of the micromechanical system device (102) in the silicon chip (101) is encapsulated among lower cover silicon chip (201) and the formed cavity of glass cover-plate (301).

5. connect the preparation method of air-sealed packing micromechanical device architecture by the described salient point of claim 2, it is characterized in that described step (d) is the making that is connected salient point with (e), step is successively:

(1) adopts the photoresist mask,, form the electrode district perforate (601) of micromechanical system device (102) with KOH solution or reactive ion etching silicon;

(2) use the sputtering method deposition of aluminum film, mask and corrosion make electrode district cause lower cover silicon chip basal surface;

(3) apply poly-phthalimide (603) in the bottom surface of lower cover silicon chip again, salient point is played a supportive role;

(4) photo etched mask is made the perforate (604) of aluminium electrode (602);

(5) with sputtering method deposit Underbump metal film;

(6) mask is made and is electroplated perforate, removes photoresist, and Underbump metal film is fallen in selective corrosion, refluxes to form soldered ball, applies photoresist, finishes making.

6. connect the preparation method of air-sealed packing micromechanical device architecture by the described salient point of claim 5, the aluminium film thickness that it is characterized in that described deposition is 1 micron.

7. connect the preparation method of air-sealed packing micromechanical device architecture by the described salient point of claim 5, it is characterized in that described is 20 microns to the passive poly-acid imide thickness of salient point.

8. connect the preparation method of air-sealed packing micromechanical device architecture by the described salient point of claim 5, it is characterized in that the metal film under the described deposition salient point is Cr/Cn or Ti/Cu, Cr or Ti for adhesion layer thickness are

The Seed Layer of Cu for electroplating, thickness is

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