WO2014044120A1 - Polymer material and bonding method - Google Patents

Abstract

The present invention provides a polymer material. The polymer material comprises SU8 and a surfactant. The SU8 is a hydrophobic material, and therefore needs to be heated first to above 130°C to make the SU8 reflux during bonding, such that the bonding of two silicon slices (glass sheets) can be completed in cooperation with a certain pressure. By adding a small amount of the surfactant to the SU8, the SU8 can be changed to a hydrophilic material, so that the surface viscosity of the SU8 is very good, photo-etching and curing enable the SU8 to still reflux slightly at a high temperature, and the bonding can be completed in cooperation with a certain pressure and has a low pressure. Also disclosed is a bonding method using the polymer material.

Description

Polymer materials and bonds and methods

[Technical Field]

The invention belongs to the field of semiconductor manufacturing, and in particular relates to a polymer material and a bonding method using the same.

【Background technique】

In MEMS (Micro-Electro-Mechanical Glue Bonding (Adhesive) In the bonding process, the bonding process has a low process temperature (<250 ° C) but a high bonding strength. Typically used in MEMS devices requiring low temperature processes and glass to glass bonding. At Adhesive Usually, BCB or SU8 glue is used for bonding. BCB can be patterned and then bonded (250 ° C), but requires a very high pressure (> 2 bar), which is not enough for MEMS devices that require low voltage bonding. The SU8 can perform low pressure bonding (1 bar). However, SU8 is solid at room temperature, similar to photoresist, so it cannot be bonded to another silicon wafer. The characteristics of SU8 are to start reflow at 130-150 °C, which is similar in this case. The glue is glued to another piece of silicon. Therefore, it is necessary to reflow, and if there is no reflow, it cannot be bonded. For some special structures, such as wedge-shaped structures (forming the iris with the upper silicon wafer/glass sheet during bonding, see Figure 1), SU8 will flow and accumulate in the wafer and glass during the bonding process due to the iris effect. Between, affecting the bonding effect. However, before the bonding, the effect of curing or partially curing the SU8 by exposure is not good. If SU8 is cured, it cannot be bonded because it cannot be reflowed. SU8 is partially cured and still exhibits strong reflow characteristics during bonding. The process window is small and difficult to control.

[Summary of the Invention]

In view of the deficiencies of the prior art, the technical problem solved by the present invention is to provide a polymer material which can not only solve the backflow problem of SU8 but also reduce the bonding pressure of SU8 when applied to the glue bonding process. .

In order to solve the above technical problem, the technical solution of the present invention is implemented as follows:

The present invention discloses a polymeric material wherein the polymeric material comprises SU8 and a surfactant.

In one embodiment, the mass ratio of the surfactant in the polymeric material is from 9% to 11%.

In one embodiment, the mass ratio of the surfactant in the polymeric material is 10%.

In one embodiment, the hydrophilic group of the surfactant is a carboxylic acid, a carboxylate, a sulfonic acid, a sulfonate, a sulfuric acid, a sulfate, an amino, an amine, a hydroxyl, an amide or an ether linkage.

In one embodiment, the surfactant is Silwet 618 or GE.

The present invention also discloses a bonding method using the polymeric material.

In one embodiment, the bonding temperature is 170 to 200 °C.

In one embodiment, the bonding pressure is from 0.5 to 1 bar.

In one embodiment, the bonding comprises glass/glass bonding, silicon/glass bonding, silicon/silicon bonding, or wafer/silicon bonding.

In contrast to the prior art, the present invention provides a polymeric material comprising SU8 and a surfactant. SU8 is a hydrophobic material. Therefore, when bonding, it needs to be heated to 130 ° C or higher to reflow, and with a certain pressure, the two silicon wafers (glass sheets) are bonded. By adding a small amount of surfactant to SU8, SU8 is changed to a hydrophilic material, which reduces the surface tension of SU8 and strengthens its viscosity, making it easier to adhere. The lithography cure makes SU8 still very hot at high temperatures. A small amount of reflux, with a certain pressure, can complete the bonding, and the bonding pressure is low.

[Description of the Drawings]

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and other drawings can be obtained from those skilled in the art without any creative work.

Figure 1 shows the prior art application of SU8 glue in silicon/glass bonding;

2 is an electron micrograph of a polymer material applied to a silicon wafer/wafer bonding according to an embodiment of the present invention;

Figure 3 is an enlarged view of A in Figure 2.

 【detailed description】

Programs that choose bonding techniques typically rely on a range of requirements, such as temperature limits, containment requirements, and the required alignment accuracy after bonding. Bonding options include standard industrial processes such as anodic bonding, glass paste bonding and adhesive bonding, as well as newly developed low temperature eutectic bonding, metal diffusion (eutectic) bonding and silicon melting in specific applications. Bond.

Glass paste bonding is widely used in the manufacture of accelerometers and in the production of MEMS. The glass paste is a slurry material composed of lead silicic acid glass particles, cerium silicate filler, slurry and solvent. A common application method is through screen printing technology. Typically, the patterned paste covers a 30-200 micron wide annular region around each chip and has a thickness of 10-30 microns. The excess solvent is removed by baking the slurry after patterning. Hot press bonding is performed after wafer alignment. During the actual glass paste bonding process, the glass melts and fuses with the filler therein, thereby forming a void-free seal with excellent airtightness.

The advantage of glass paste bonding is its familiarity with the process flow and bonding interface characteristics. The initial state of the melted slurry and slurry allows the process to allow for particulate or other minor surface defects. The compression of the slurry line can be controlled by the difference in force applied to the bonder, typically 40%. The two biggest disadvantages of slurry bonding are lower cleanliness and larger seal footprint. Perhaps the most important disadvantage of slurry bonding is that high precision alignment cannot be achieved because during the bonding process, the glass paste softens and begins to flow viscously causing the wafer to slip.

Anodic bonding and glass paste bonding are two methods, accounting for 80% of the MEMS application in production. The mechanism of anodic bonding determines that it can only be applied to glass and wafer bonding. The mechanism is that ions diffuse toward the interface under the electric field assist through the interface between the glass and the silicon wafer. This technique can be applied to substrates whose surface is a polysilicon layer or a glass layer. Some bonding devices also support three layers of laminated bonding. Advantages of anodic bonding include proven processes and acceptable seal life. Glass can be thermally matched to a wide variety of substrates for vacuum or pressure packaging of devices and can accept 5nm Or worse micro roughness. Its disadvantage is that the process uses voltage and is not compatible with CMOS circuits, and has a movable Na+ The use of ions, when sodium accumulates on the anode and its outer surface, can contaminate other circuits that are sensitive to ions. Metal bonding is a diffusion-based and eutectic based method. Diffusion bonding is accomplished at temperatures between 390 and 450 ° C, requiring relatively large pressures to achieve intimate contact of the surface. In metal bonding, the roughness of the surface and the warpage of the wafer must be controlled. The metal alloy melts during the bonding process and planarizes the interface. The liquid interface allows eutectic bonding to apply relatively small but consistent pressures. In different metallurgical systems, such as copper-tin, gold-tin or gold-silicon, eutectic alloys are formed between 280-390 °C.

Adhesive bonding can use many polymer materials, including BCB, SU8, WL5300 And most common photoresist materials. As a special application, the temporary bonding uses a polymer to achieve a medium bond strength bond, and the wafer is bonded to a support substrate, such as glass or sapphire, to effect processing of the back side of the device wafer. After the back side processing, the bonding of the interface can be released by ultraviolet light, thermal decomposition or solvent. The adhesive bonding polymer is either applied to the surface by spin coating or spray coating at room temperature, or directly as a dry film. Adhesive bonding has a good tolerance to particles, surface thickness deviations and surface roughness. This bonding is not sealed and thus has no high temperature shrinkage.

SU8 adhesive is a negative, epoxy type, near-ultraviolet photoresist. It is suitable for making ultra-thick, high aspect ratio MEMS microstructures. SU8 The gel has a low light absorption in the near-ultraviolet range, so that the exposure amount obtained by the entire photoresist layer is uniform, and a thick film pattern having vertical sidewalls and a high aspect ratio can be obtained; It also has good mechanical properties, chemical resistance and thermal stability; SU8 adhesive is non-conductive and can be used directly as an insulator during electroplating. Due to its many advantages, it is gradually applied to MEMS Multiple research areas.

The SU8 can be pressed at a low pressure (1 bar). However, SU8 usually begins to reflow at 130 ° C. For some special structures, such as wedge-shaped structures (forming the iris with the upper wafer/glass sheet during bonding, see Figure 1), SU8 is in the bonding process because of the iris effect. Will flow and gather between the silicon wafer and the glass sheet, affecting the bonding effect. However, before the bonding, the effect of curing or partially curing the SU8 by exposure is not good. If SU8 is cured, it cannot be bonded because it cannot be reflowed. SU8 is partially cured and still exhibits strong reflow characteristics during bonding. The process window is small and difficult to control.

In view of the above problems, the present invention provides a polymer material comprising SU8 and a surfactant.

SU8 is a hydrophobic material. Therefore, when bonding, it needs to be heated to 130 ° C or higher to reflow, and with a certain pressure, the two silicon wafers (glass sheets) are bonded. SU8 is changed to a hydrophilic material by adding a small amount of surfactant in SU8, so that the surface viscosity of SU8 is very good. By photolithography curing, SU8 still has a small amount of reflow at high temperature, with a certain amount of coordination. The pressure is sufficient to complete the bonding, and the bonding pressure is low.

The technical solutions in the embodiments of the present invention are described in detail below. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

Embodiments of the invention disclose a polymeric material comprising SU8 and a surfactant.

SU8 glue can be selected from SU8 series photoresist produced by Microlithography Chemical Company of the United States. Such as SU8-5 and SU8- 50, or SM series photoresist produced by Sotec Microsystems, Switzerland.

Surfactant refers to a substance having a fixed hydrophilic lipophilic group, which is oriented on the surface of the solution and which can significantly reduce the surface tension. The molecular structure of the surfactant is amphiphilic: one end is a hydrophilic group and the other end is a hydrophobic group; the hydrophilic group is often a polar group such as a carboxylic acid, a sulfonic acid, a sulfuric acid, an amino group or an amine. The base and its salt may also be a hydroxyl group, an amide group, an ether bond or the like; and the hydrophobic group is often a non-polar hydrocarbon chain, such as a hydrocarbon chain of 8 or more carbon atoms. The surfactant is classified into an ionic surfactant, a nonionic surfactant, and the like. The surfactant in this embodiment may be selected from any active agent which can change the surface from hydrophobic to hydrophilic, and preferably, the surfactant is Silwet 618. GE.

SU8 glue is a hydrophobic material, the surfactant is a hydrophilic substance, and the surfactant is combined with SU8 for rubber bonding, and SU8 can be changed to a hydrophilic material. So the surface of the SUB is very sticky, and the bonding can be completed at a certain temperature and pressure. The bonding effect is shown in Figure 2 and Figure 3. Preferably, the mass ratio of the surfactant is 9% to 11%, more preferably 10%; the temperature at which the bonding is completed is 170 to 200 ° C; and the bonding pressure is 0.5 to 1 bar.

The above polymeric materials can be applied to glass/glass bonding, silicon/glass bonding, silicon/silicon bonding or wafer/silicon bonding.

During the bonding process, the polymer material may be first applied to the surface of the glass or silicon by spin coating or spray coating at room temperature, and then the glass, silicon or wafer is aligned and placed over the glue.

In summary, the present invention provides a polymeric material comprising SU8 and a surfactant. SU8 is a hydrophobic material. Therefore, when bonding, it needs to be heated to 130 degrees or more to reflow. With a certain pressure, the two silicon wafers (glass sheets) are bonded. SU8 is changed to a hydrophilic material by adding a small amount of surfactant in SU8, so that the surface viscosity of SU8 is very good. By photolithography curing, SU8 still has a small amount of reflow at high temperature, with a certain amount of coordination. The pressure is sufficient to complete the bonding, and the bonding pressure is low.

It is apparent to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, and the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the present embodiments are to be considered as illustrative and not restrictive, and the scope of the invention is defined by the appended claims instead All changes in the meaning and scope of equivalent elements are included in the present invention. Any reference signs in the claims should not be construed as limiting the claim.

In addition, it should be understood that although the description is described in terms of embodiments, not every embodiment includes only one independent technical solution. The description of the specification is merely for the sake of clarity, and those skilled in the art should regard the specification as a whole. The technical solutions in the respective embodiments may also be combined as appropriate to form other embodiments that can be understood by those skilled in the art.

Claims (9)

1. A polymeric material characterized in that the polymeric material comprises SU8 and a surfactant.
2. The polymeric material according to claim 1, wherein the surfactant has a mass ratio of 9% to 11% in the polymeric material.
3. The polymeric material according to claim 2, wherein the surfactant has a mass ratio of 10% in the polymeric material.
4. The polymer material according to claim 1, wherein the hydrophilic group of the surfactant is a carboxylic acid, a carboxylate, a sulfonic acid, a sulfonate, a sulfuric acid, a sulfate, an amino group, an amine group, Hydroxyl, amide or ether linkage.
5. The polymeric material of claim 1 wherein the surfactant is Silwet 618 or GE.
6. A bonding method, characterized in that the bonding method employs the polymer material according to any one of claims 1 to 5.
7. The bonding method according to claim 6, wherein the bonding temperature is 170 to 200 °C.
8. The bonding method according to claim 6, wherein the bonding pressure is 0.5 to 1 bar.
9. The bonding method according to claim 6, wherein the bonding comprises glass/glass bonding, silicon/glass bonding, silicon/silicon bonding, or wafer/silicon bonding.

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