Pressure sensitive adhesive sheet for wafer sticking

Details Pressure sensitive adhesive sheet for wafer sticking Pressure sensitive adhesive sheet for wafer sticking

2001-02-16

2003-02-25

Zirker, Daniel (Department: 1771)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Adhesive outermost layer

C428S345000, C428S3550AC, C428S901000

Reexamination Certificate

active

06524700

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a pressure sensitive adhesive sheet for wafer sticking. More particularly, the present invention is concerned with a pressure sensitive adhesive sheet for wafer sticking which is used to fix a wafer having circuits printed thereon at the time of dicing the wafer by each circuit.
BACKGROUND OF THE INVENTION
A semiconductor wafer of, for example, silicon or gallium arsenide is produced in a large diameter, cut and separated (diced) into elemental chips and subjected to the subsequent mounting step. In this process, the semiconductor wafer, in the state of being stuck to a pressure sensitive adhesive sheet (dicing sheet), undergoes the steps of dicing, washing, drying, expanding, pickup and mounting.
In the steps from dicing to pickup for the semiconductor wafer, it is common practice to use a pressure sensitive adhesive sheet comprising a base and, superimposed thereon, a pressure sensitive adhesive. In this pressure sensitive adhesive sheet, a base composed of a relatively soft resin is employed taking an expansibility into account, and a pressure sensitive adhesive with a relatively low elastic modulus is employed taking a stickiness into account.
For example, a polyvinyl chloride base containing a plasticizer is known as such a soft base. The polyvinyl chloride base containing a plasticizer is soft, exhibits high stiffness, is excellent in processability and is available at low cost. Therefore, the polyvinyl chloride base containing a plasticizer is used in various fields. However, in the pressure sensitive adhesive sheet including this type of base, the plasticizer may migrate into the pressure sensitive adhesive layer to thereby cause the pressure sensitive adhesive performance to deteriorate with the passage of. As a result, the pressure sensitive adhesive may be softened and no longer strippable to thereby invite the danger of staining the adherend. Accordingly, in the field of semiconductor processing wherein especially strict process control is required, the use of the polyvinyl chloride base containing a plasticizer may be refrained from, and, for example, a polyolefin film may be employed in place thereof. However, the pressure sensitive adhesive sheet for wafer sticking including the polyvinyl chloride base containing a plasticizer is highly attractive from the viewpoint that, due to its excellent processability, it is applicable to processing under widely varied conditions in even when a little variety of pressure sensitive adhesive sheet is used.
On the other hand, the pressure sensitive adhesive sheet including a pressure sensitive adhesive with a relatively low elastic modulus, although excellent in stickiness, cannot suppress minute vibrations of the wafer at the time of dicing of the wafer. Thus, the wafer may suffer from breakage (chipping) at the cut face thereof. This breakage, if extensive, may result in the damaging of circuits per se. Even if minute, the breakage may invite the danger of causing the final package to crack with the passage of time.
The present invention has been made in view of the above state of the prior art. Therefore, it is an object of the present invention to provide a pressure sensitive adhesive sheet for wafer sticking which can inhibit the vibration of the wafer at the time of dicing of the wafer so that chipping of the wafer can be minimized.
SUMMARY OF THE INVENTION
The pressure sensitive adhesive sheet for wafer sticking according to the present invention comprises a base of polyvinyl chloride containing a plasticizer and, superimposed thereon, an energy radiation curable pressure sensitive adhesive layer,
wherein the energy radiation curable pressure sensitive adhesive layer, before exposure to energy radiation (or energy beams, or energy rays), has an elastic modulus ranging from 4.0×10
4
to 5.0×10
6
Pa at 50° C.
In the present invention, it is preferred that the energy radiation curable pressure sensitive adhesive layer comprise a vinyl ester copolymer and/or an acrylic copolymer having a glass transition temperature of 0 to 40° C.
The pressure sensitive adhesive sheet for wafer sticking according to the present invention preferably has an adhesive strength to mirror-finished stainless steel plate of at least 1000 mN/25 mm before exposure to energy radiation and an adhesive strength to mirror-finished stainless steel plate of 50 to 1000 mN/25 mm after exposure to energy radiation.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
The pressure sensitive adhesive sheet for wafer sticking according to the present invention comprises a base of polyvinyl chloride containing a plasticizer and, superimposed thereon, an energy radiation curable pressure sensitive adhesive layer.
The base is composed mainly of a widely interpreted polyvinyl chloride resin, such as polyvinyl chloride, polyvinylidene chloride or a vinyl chloride copolymer. Preferably, the base is composed mainly of polyvinyl chloride.
A plasticizer is contained in the polyvinyl chloride resin. It is preferred that the plasticizer be contained in an amount, in terms of DOP, of 25 to 50 parts by weight, especially 30 to 45 parts by weight, per 100 parts by weight of polyvinyl chloride resin. The terminology “amount in terms of DOP” used herein means the amount corresponding to the amount of common plasticizer dioctyl phthalate (DOP) added to attain given properties. The plasticizer is not particularly limited, and can be, for example, any of phthalic acid ester plasticizers such as dioctyl phthalate, phosphoric acid ester plasticizers and polyester plasticizers.
The base composed of the polyvinyl chloride resin containing the above plasticizer is excellent in strength (stiffness), processability, elongation ratio, breaking strength and expansibility.
The thickness of the base, although not particularly limited, preferably ranges from about 50 to 200 &mgr;m, still preferably from about 70 to 150 &mgr;m. According to necessity, the base may be compounded with additives such as a filler, a stabilizer, an antistatic agent and a colorant.
The base side of the pressure sensitive adhesive sheet for wafer sticking according to the present invention is exposed to energy radiation after the completion of the dicing step. When ultraviolet light is used as the energy radiation, the base must be transparent.
The energy radiation curable pressure sensitive adhesive layer superimposed on the base comprises a polymer component and an energy radiation curable component as principal components thereof.
The energy radiation curable pressure sensitive adhesive layer, before exposure to energy radiation has an elastic modulus ranging from 4.0×10
4
to 5.0×10
6
Pa, preferably 5.0×10
4
to 5.0×10
6
Pa, at 50° C.
Generally, at the time of wafer dicing, frictional heat is generated, so that the temperature of the pressure sensitive adhesive layer is raised to about 50° C. When the elastic modulus at 50° C. falls within the above range, the transmission of vibration generated at the time of dicing from the pressure sensitive adhesive layer to the wafer is suppressed to thereby enable stably holding the wafer and hence enable reducing the occurrence of chipping. Even if the pressure sensitive adhesive layer has a high elastic modulus at temperatures lower than 50° C., the effect of reducing the occurrence of chipping cannot be expected when the elastic modulus at 50° C. is smaller than the above range.
As long as the energy radiation curable pressure sensitive adhesive layer satisfies the above requirement, various polymer components can be used as a main material thereof. For example, use can be made of polymer components such as vinyl ester copolymers, acrylic copolymers, rubber pressure sensitive adhesives and silicone pressure sensitive adhesives. Also, use can be made of mixtures and composites thereof. Further, for example, use can be made of copolymers of a vinyl ester monomer and an acrylic ester monomer.
In the present invention, polymer components

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