TWI677050B - Carrier for temporary bonded wafers - Google Patents

Abstract

The invention discloses a carrier on which a wafer can be temporarily bonded. The carrier includes a plate-like laminate. The plate-like laminate includes a first layer. The first layer includes a foil, sheet or plate. The plate-like laminate includes a second layer including a porous metal medium having three-dimensional open pores. The first layer is permanently bonded to the porous metal medium, thereby closing the pores of the porous metal medium at the side where the first layer is positioned. The second layer includes a contact layer for bonding on a wafer. The contact layer includes a mixture of metal fibers and metal powder. The metal fiber and the metal powder are permanently bonded to each other at their contact points.

Description

Carrier for temporarily bonding wafers

The invention relates to the field of carriers for wafers. The carrier can be used for temporary bonding of wafers during its processing (for example, when the wafer is thinning).

The use of temporary bonding of a wafer to a carrier to allow processing of the wafer is conventional. One challenge is to subsequently peel the wafer from the carrier. Different carriers have been described to allow peeling with solvents. In this procedure, the adhesive used for temporary bonding is chemically dissolved.

US patent US2009 / 197070A describes a support plate that is bonded to a substrate in order to support the substrate. In the support plate, a plurality of openings penetrate from the joining surface to the non-joining surface. The bonding surface faces the substrate, and the non-bonding surface faces the bonding surface. A porous region including a first region and a second region surrounding the first region is formed on the bonding surface; and the first region has an opening ratio larger than that of the second region. In this way, a support plate can be realized, which can be borrowed during the processing operation on the semiconductor wafer. It is easily peeled from the semiconductor wafer by the solvent, but does not easily fall off the substrate.

The US patent US2005 / 0173064A1 provides a supporting plate having a structure in which a solvent can be supplied to the supporting plate and the substrate in a short period after the substrate (such as a semiconductor wafer) is thinned. Between adhesive layers. The document also discloses a method for peeling the support plate. The support plate may have a larger diameter than the semiconductor wafer, and a penetration hole is formed in the support plate. The outer peripheral portion of the support plate is a flat portion in which no penetration hole is formed. When the ethanol is poured from above the support plate, the ethanol passes through the perforation holes to reach the adhesive layer, dissolves and removes the adhesive layer.

US patent US8882096B2 discloses a perforated support plate for supporting the surface of a wafer by inserting an adhesive layer. The perforated support plate has a permeation hole. A solvent used to dissolve the perforated support plate through the perforation of the support plate through the adhesive of the adhesive which is adhered to the wafer. The perforated support plate includes a reinforced portion for preventing deflection.

US2004 / 0231793A1 discloses the use of a porous sintered metal as a temporary carrier for wafers. The carrier can be released by passing a solvent through the thickness of the temporary carrier through its pores to dissolve the adhesive used to adhere the wafer to the temporary carrier.

A procedure is described in US patent US2009325467A, in which a wafer can be thinned without waviness. A support plate has a plurality of perforations. The circuit-forming surface of a wafer is adhered to one surface of a supporting plate by an adhesive member, and has a thickness of 100 micrometers or more and an A corrugation preventing member having an adhesive layer on the face is adhered to the other surface. The openings at the two ends of the perforation are therefore closed. The support plate is vacuum-sucked to a support table via the ripple prevention member, and the wafer is ground / polished to thin the wafer. The corrugation preventing member is peeled off, and the solvent penetrates into the adhesive member through the perforation to separate the wafer from the supporting plate.

US patent US2001005043A discloses a technique that has a high yield and can perform thinning of a wafer and separate it from a supporting substrate in a short time. A non-porous support substrate is bonded to the second surface of the support substrate with holes, which is achieved by using an adhesive layer that is melted by heating to plug the holes. A wafer is bonded to a first surface of the support substrate having a hole using an adhesive layer which is dissolved by a solvent. The wafer is thinned by grinding and etching. The adhesive layer is melted by heating, so that the support substrate with holes slides relative to the non-porous support substrate to thereby separate the support substrate with holes from the non-porous support substrate. The adhesive layer is then dissolved through the hole defined in the support substrate having the hole by a solvent. As a result, the wafer is separated from the supporting substrate having holes. Since no load is applied to the wafer, damage to the wafer can be avoided.

It is an object of the present invention to provide a carrier for temporarily bonding wafers. The object is to provide such a vehicle with improved properties. It is an object of the present invention to provide a carrier which makes the wafer easy to peel by dissolving the adhesive through the pores of the carrier by diafiltration with a solvent. from. It is an object of the present invention to provide a carrier which allows a wafer to be thinned and further processed to obtain a required quality specification.

A first aspect of the present invention is a carrier to which a wafer can be temporarily bonded (eg, to allow wafer thinning). The carrier includes a plate-like laminate. The plate-like laminate includes a first layer. The first layer includes a foil, sheet or plate. The plate-like laminate includes a second layer including a porous metal medium having three-dimensional open pores. The first layer is permanently bonded to the porous metal medium, thereby closing the pores of the porous metal medium at the side where the first layer is positioned. The second layer includes a contact layer for bonding on a wafer. The contact layer includes a mixture of metal fibers and metal powder. The metal fiber and the metal powder are permanently bonded to each other at their contact points.

Preferably, the carrier has a shape of a disc that is deviated from a circular circumference by a straight side. The straight sides exist to match the shape of the wafer to be bonded to the work carrier. Preferably, the diameter of the circular section of the disc is suitable for 6-inch, 8-inch or 12-inch wafers. This means that the diameter of the disk is equal to or slightly larger than the diameter of the wafer.

The carrier has the advantage that the stripping solvent can flow through the three-dimensional open pores of the porous metal medium, from the side edges of the carrier bonded to the wafer, through the entire volume of the porous metal medium. In this way, the stripping solvent can quickly reach the adhesive layer that attaches the wafer to the carrier. The carrier has sufficient hardness to transport the bonded wafer through different process steps without bending or other mechanical deformation or stress. The carrier has a further advantage in that it has sufficient mechanical properties (such as hardness) to allow the dimensional properties (such as total thickness difference (TTV), bow and warpage) required for the thinned wafer to be achieved. A further advantage of the invention is that the carrier can be used multiple times. A further advantage of this carrier of the invention is that the corrugations present on the thinned wafer are reduced or even completely eliminated. It is believed that this surprisingly beneficial effect is produced by the powder particles existing in the pores between the fibers in the contact layer, thereby reducing the size of the pores, resulting in the lower surface of the contact layer Roughness. A further advantage of the carrier of the present invention is that less adhesive is used to bond the wafer to the carrier; this also results in faster peeling.

In a preferred embodiment, the first layer comprises or consists of metal or glass or silicon or ceramic.

In a preferred embodiment, the porous metal medium includes an additional porous layer. The additional porous layer is provided between the first layer and the contact layer. The additional porous layer includes a metal fiber, a metal powder, or a metal foam. Specific examples of the additional porous layer include a sintered or welded metal fiber nonwoven fabric, a sintered powder, and a metal foam.

Preferably, the first layer comprises or consists of a metal. Preferably, the first layer includes or consists of a metal foil, a metal plate or a metal sheet. Preferably, the first layer includes the same metal or alloy as the porous metal medium.

Preferably, the porous metal medium comprises or consists of stainless steel, titanium, palladium or tungsten; or it comprises or consists of an alloy comprising more than 50% by weight of titanium, palladium or tungsten. More preferably, for implementations in which the first layer includes or consists of a metal foil, a metal plate, or a metal foil For example, the first layer system includes the same metal or metal alloy as the porous metal medium.

In a preferred embodiment, the first layer comprises a metal and the first layer is permanently bonded to the porous metal medium by a metal bond, preferably by diffusion bonding such as sintering or by welding ( And preferably by welding, where no additional filler material is used in the welding procedure). An example of a welding procedure that can be used is capacitor discharge welding (CDW).

In a preferred embodiment, the first layer is permanently bonded to the porous metal medium by an adhesive. The adhesive can be selected from a wide range of adhesives that are not corroded by the stripping liquid used when the temporarily bonded wafer is peeled from the carrier. An example of a suitable adhesive is an epoxy-based adhesive.

Preferably, the carrier has a thickness between 650 microns and 750 microns.

Preferably, the first layer has a thickness between 20 microns and 650 microns, more preferably between 150 microns and 650 microns.

Preferably, the porous metal medium has a thickness between 50 microns and 150 microns, and more preferably between 50 microns and 150 microns.

Preferably, the porosity of the porous metal medium is higher than 20% and more preferably higher than 30%, more preferably higher than 40%, optimally higher than 50%, and optimally higher. At 55%. And preferably, the porosity is less than 80%, and more preferably less than 60%. This embodiment synergistically increases and improves the mechanical properties of the carrier, so that the wafer when bonded to the carrier After processing, the requirements of dimensional characteristics can be achieved.

Preferably, the porosity of the contact layer is higher than 20% and more preferably higher than 30%. The porosity of the contact layer is preferably less than 50%, and more preferably less than 40%.

Preferably, the equivalent diameter of the metal fiber in the contact layer is between 2 and 50 microns, more preferably between 2 and 40 microns, and most preferably between 2 and 25 microns. between. Even better, it is between 10 and 25 microns. Having a considerable diameter means that the diameter of the circle has the same area as the cross-section of the fiber, and the cross-sectional shape may deviate from a circular shape.

Preferably, the metal powder in the contact layer has a diameter in the range of 2 to 30 microns, preferably in the range of 2 to 20 microns, more preferably in the range of 2 to 10 microns Inside.

In a preferred embodiment, the porous metal medium has a surface for being bonded to a wafer, wherein the surface is parallel to the first layer. The surface is polished so that the carrier has a total thickness difference (TTV) of less than 10 microns. The total thickness difference (TTV) is measured by a drop meter at five points selected arbitrarily above the surface of the material. For this test method, the diameter of the drop meter is 5.99 microns. The TTV system is defined as the difference between the maximum thickness measurement and the minimum thickness measurement.

In a preferred embodiment, the porous metal medium includes a first porous layer and a second porous layer. The first porous layer is provided between the first layer and the second porous layer. The porosity of the first porous layer is higher than the porosity of the second porous layer. In a more preferred embodiment, the first A porous layer is directly bonded to the first layer. In another embodiment, the second porous layer is directly bonded to the first porous layer. In another embodiment, the second porous layer is provided for being bonded to the wafer. In a more preferred embodiment, the first porous layer includes metal fibers of a first equivalent diameter and the second porous layer includes metal fibers of a second equivalent diameter. In a preferred embodiment, the first equivalent diameter is larger than the second equivalent diameter.

In a preferred embodiment, the side edge of the porous metal medium is permanently sealed so that no open pores exist at the side edge of the porous metal medium.

The side edge can be sealed by welding the edge, or sealed by laser cutting out the size and shape of the porous metal medium, or after the first layer is bonded to the second layer It is sealed by welding the edge or cutting the size and shape of the combination of the first layer and the second layer by laser.

Another method for producing the sealed edge is to process a plate so that the upright edge is generated, and then the porous metal medium is inserted into the cup produced by processing, and then the porous metal The medium is bonded to the first layer. When the temporarily bonded wafers are to be peeled from the carrier with permanently sealed edges, initially no capillary action of the peeling liquid occurs in the porous metal medium. Initial peeling occurs on the thin layer of adhesive located between the carrier and the wafer. When the thin adhesive layer is decomposed, the peeling liquid by having an increase in the porous metal medium passes through the openings created by the adhesive layer dissolved at the edge. Capillary action increases this peeling speed.

Preferably, the carrier is provided such that when a pressure of 4 bar is applied thereto, the permanent deformation of the carrier is less than 5% of its original thickness before the pressure is applied. This can be tested by measuring the thickness of the vehicle before and after applying a pressure of 4 bar during a period of 20 seconds. According to this embodiment, a carrier can be manufactured by pre-stressing the carrier or the porous metal layer or a porous metal layer therein, so that future permanent deformation can be limited. This embodiment can surprisingly synergistically improve the properties of the wafer after processing (such as thinning) when the wafer is temporarily adhered to the carrier.

The second aspect of the present invention is an assembly (or stack) of a wafer and a carrier as in the first aspect of the present invention. The wafer is bonded to the contact layer by an adhesive. Preferably, the adhesive is an adhesive that can be removed by contacting a suitable release liquid with the adhesive.

A third aspect of the present invention is a method for processing a wafer, including the following steps: temporarily attaching the wafer to a carrier as in the first aspect of the present invention by an adhesive, and processing temporarily adhering to the carrier The wafer is, for example, thinned; the wafer is stripped from the carrier by a stripping liquid that destroys the temporary adhesive bond between the wafer and the carrier; The side edge of the assembly of the wafer bonded to the carrier by the adhesive penetrates into the porous metal medium.

During and after stripping the wafer temporarily bonded to the carrier, the first One layer remains bonded to the porous metal medium.

In a preferred method, the carrier is reused one or more times after peeling for temporarily attaching another wafer thereto. Preferably, the vehicle can be used at least 5 times, more preferably at least 10 times.

100‧‧‧ Vehicle

102‧‧‧Straight side

200‧‧‧ Vehicle

210‧‧‧First floor

226‧‧‧ Extra porous layer

260‧‧‧contact layer

301‧‧‧Assembly or stack

370‧‧‧Temporary adhesive layer

380‧‧‧ wafer

FIG. 1 is a top view showing an exemplary vehicle according to the present invention.

Figure 2 shows a cross section of an exemplary vehicle according to the present invention.

FIG. 3 shows an example of a wafer assembly temporarily bonded to a carrier of the present invention.

FIG. 1 is a top view showing a carrier 100 according to the present invention. The carrier 100 has a shape of a disc deviated from a circular circumference (having a diameter D) by the straight side 102. The straight side 102 exists to match the shape of the wafer to be bonded to the work carrier.

FIG. 2 shows a cross section of an exemplary vehicle 200 according to the present invention. The carrier 200 includes a first layer 210, wherein the first layer is a metal foil or a metal sheet. The carrier 200 further includes an additional porous layer 226 (eg, a sintered non-woven metal fiber web). The carrier includes a contact layer 260 containing a mixture of metal powder particles and metal fibers sintered at each other at the contact points.

Preferably, the metal foil or metal sheet, the metal fiber, and the metal powder are made of the same metal or alloy.

The different layers are permanently bonded to each other by sintering or by welding (such as capacitor discharge welding). Instead of the non-woven metal fiber web, a sintered porous metal powder layer and / or a metal foam layer may be used as an additional layer. For example, glass, ceramic or silicon flakes or plates can be used as the first layer instead of metal foils or metal flakes. The porous metal layers (the additional porous layer and the contact layer) are bonded to each other by metal bonds (for example, sintering), and the bonding to the first layer can then be performed by an adhesive (such as epoxy resin) carry out.

FIG. 3 shows an example of an assembly or stack 301 of wafers temporarily bonded to a carrier (eg, carrier 200 of the example of FIG. 2). The same component symbols in FIG. 2 have the same meanings as those described in FIG. 2. The temporary adhesive layer 370 is applied to the porous metal medium of the carrier 200, and the wafer 380 is temporarily bonded to the carrier 200 by the adhesive layer 370.

As an example, a carrier for an 8-inch wafer has been manufactured. As the first layer, a 200-micron-thick titanium foil has been used. A non-woven titanium fiber web with a thickness of 500 micrometers and a porosity of 56% (the equivalent diameter of the 22 micrometers of the titanium fiber) has been applied on top of the titanium foil. The combination of the titanium foil and the nonwoven titanium fiber web has been sintered together. A titanium powder slurry has been prepared. The slurry comprises 20% by weight of a 20 micron diameter titanium powder, and a small amount of a suitable dispersant is added to the water. A uniform slurry layer has been applied to the non-woven titanium fiber web side of the sintered fiber web / titanium sheet combination. The application can be accomplished by a screen printing stack, which utilizes a screen having openings evenly distributed over its surface. A volume of 200 mg / cm ^{3 was} applied (the volume is based on the porous non-woven fibrous medium). The powder slurry penetrates into the non-woven titanium fiber web and generates a mixture of titanium powder and fiber, thereby generating a contact layer of the carrier, whereby the contact layer includes a mixture of titanium fiber and titanium powder. The product was dried at 180 ° C for 30 minutes, and then subjected to a sintering step at 800 ° C for 1 hour under a vacuum state, thereby producing a sintered joint between the contacted titanium powder particles and the titanium fiber. The sintering is performed in a state where the thickness of the carrier remains the same. Before and after the titanium powder slurry is applied and sintered to the carrier, the distribution of the pore size is measured using a porometer (Porolux 100). Before the titanium powder was applied, the average pore size of the porous portion was 55 to 65 micrometers, and after the titanium powder mixture was applied, the average pore size was reduced to 45 micrometers.

Claims (15)

A carrier on which a wafer can be temporarily bonded, wherein the carrier includes a plate-like laminate including: a first layer, wherein the first layer includes a foil, a sheet, or a plate; and Two layers, including a porous metal medium with three-dimensional open pores; wherein the first layer is permanently bonded to the porous metal medium, thereby closing the porous metal at the side where the first layer is positioned The pores of the medium; wherein the second layer includes a contact layer for being bonded on the wafer, wherein the contact layer includes a mixture of metal fibers and metal powders, wherein the metal fibers and the metal powders are mutually Permanently engages at its point of contact. For example, the first scope of the patent application scope, wherein the first layer includes metal, glass, silicon or ceramic. For example, the vehicle of claim 1, wherein the first layer includes a metal; and wherein the first layer is provided by the same metal or alloy as the porous metal medium. For example, the carrier according to the scope of patent application, wherein the porous metal medium includes stainless steel, titanium, palladium or tungsten; or an alloy including more than 50% by weight of titanium, palladium or tungsten. For example, the vehicle of claim 1, wherein the first layer includes a metal; and wherein the first layer is permanently bonded to the porous metal medium by a metal bond. For example, the vehicle according to the scope of patent application, wherein the first layer is permanently bonded to the porous metal medium by an adhesive. For example, the carrier of the scope of application for patent No. 1 wherein the porosity of the porous metal medium is between 20 and 80%. For example, the carrier of the scope of patent application No. 1 wherein the porosity of the contact layer is higher than 20%. For example, the vehicle according to the scope of patent application, wherein the equivalent diameter of the metal fiber in the contact layer is between 2 and 50 microns. For example, the carrier according to the scope of the patent application, wherein the metal powder in the contact layer has a diameter in a range of 2 to 10 microns. For example, the carrier of claim 1, wherein the porous metal medium has a surface for being bonded on a wafer, wherein the surface is parallel to the first layer; and wherein the surface is polished and This allows the carrier to have a total thickness difference (TTV) of less than 10 microns. For example, the vehicle according to item 1 of the patent application scope, wherein the porous metal medium includes a first porous layer and a second porous layer, and the first porous layer is disposed on the first layer. And the second porous layer; and wherein the porosity of the first porous layer is higher than the porosity of the second porous layer. For example, the vehicle in the scope of application for patent No. 1 wherein the side edge of the porous metal medium is permanently sealed so that no open pores exist at the side edge of the porous metal medium. An assembly of a wafer and a carrier according to any one of claims 1 to 13, wherein the wafer is bonded to the contact layer by an adhesive. A method for processing a wafer, which includes the following steps: temporarily attaching the wafer to a carrier as in any of claims 1 to 13 by applying an adhesive; and processing temporarily adhering to the carrier The wafer; peeling the wafer from the carrier by destroying a peeling liquid temporarily bonding the adhesive between the wafer and the carrier; wherein the peeling liquid is bonded to the carrier by an adhesive The side edges of the wafer assembly of the carrier penetrate into the porous metal medium.