Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Adhesive outermost layer
Reexamination Certificate
2000-06-09
2003-08-05
Dawson, Roibert (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Adhesive outermost layer
C428S3550EP, C428S3550RA, C428S041300, C428S041500
Reexamination Certificate
active
06602599
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a technique for relieving staining on an adherend caused by re-peelable adhesive sheets to be used in manufacturing various industrial members, in particular, fine-processed parts such as semiconductors, circuits, various printed substrates, various masks and lead frames.
DESCRIPTION OF THE RELATED ART
In manufacturing, for example, a semiconductor device, a desired circuit is formed by applying a resist material onto a silicon wafer, forming a resist pattern (resist film image) by a conventional photoprocessing technique, etching by using the pattern as a mask, and then removing the resist material which is unnecessary any more. Next, the application of the resist material is repeated to form the subsequent circuit. In case of forming circuits on various substrates, unnecessary resist materials are removed after the formation of resist patterns similar to the above process.
It has been a practice that resist materials which are unnecessary any more are removed by using an asher (ashing means), a solvent or a chemical. However, it takes a long time to remove resist materials by using an asher. In this case, moreover, it is feared that impurities in resist materials are injected into wafers and semiconductor substrates are damaged. On the other hand, use of solvents or chemicals brings about a problem of the pollution of the working environment.
Accordingly, there has been recently proposed a method with the use of adhesive sheets (while the present specification sometimes uses the word “sheets” as a plurality form, what is meant by sheets herein is not just a plurality of sheets, but a genus of sheets. However, for simplification, we basically use the word “sheet” hereinafter.). In this method, an adhesive sheet provided with an adhesive layer containing a pressure-sensitive adhesive polymer as the main component formed on a base film is adhered to the upper face of a resist pattern and, after a specific treatment (for example, heating), the adhesive sheet is peeled to thereby remove the resist material together with the adhesive sheet from the substrate. In this method, however, it is sometimes observed that a large amount of organic staining matters originating in the adhesive sheet remain on the substrate after peeling the resist material and, therefore, it is needed to remove these staining matters after the completion of the peeling procedure, which makes this method not always convenient.
Although the example described above pertains to a method for removing a resist material, it has been a practice too in the fields relating to, for example, semiconductors to use a similar adhesive sheet as a means for removing foreign matters (contaminants) present on the substrate surface. Namely, the foreign matters are adhered to an adhesive sheet and then removed together with the sheet. In this case, it is sometimes observed that a large amount of organic staining matters originating in the adhesive sheet remain on the substrate, similar to the case as described above. When the adhesive sheet is employed as a re-peelable material other than those described above (for example, surface protector for metal plate, and coating mask), it is sometimes observed that a large amount of organic staining matters originating in the adhesive sheet remain on the surface of the metal plate, similar to the case as described above.
SUMMARY OF THE INVENTION
Under these circumstances, an object of the invention is to provide a low-staining adhesive sheet capable of protecting the surface of adherend (for example, substrate) from contamination with organic staining matters originating in the adhesive sheet, when employed as a re-peelable adhesive sheet, for example, for removing a resist material or foreign matters, or for use as a surface-protector, masking material or the like.
Another object of the invention is to provide a method for removing a resist material by using this adhesive sheet.
The inventors have conducted intensive studies to achieve these objects. As a result, they have clarified that these organic staining matters remaining on the surface of adherend after peeling the adhesive sheet originate in a pressure-sensitive adhesive polymer (for example, acrylic polymer) contained as the main component in the adhesive layer. That is to say, because of having a broad distribution range of molecular weight and containing a large amount of oligomeric low-molecular weight matters, this pressure-sensitive adhesive polymer is liable to undergo breakage or cohesive failure, thereby causing the adherend contamination with organic matters.
Namely, the inventors have found out that, when the adhesive layer in the adhesive sheet provided with the adhesive layer containing as the main component a pressure-sensitive adhesive polymer on a base film is substantially free from oligomeric low-molecular weight matters at least in the step of peeling the sheet, then the pressure-sensitive adhesive polymer undergoes neither breakage nor cohesive failure and thus the adherend can be protected from contamination with organic matters.
Based on this finding, the inventors have conducted further studies and, as a result, found out that the adherend contamination with organic matters can be largely relieved by reducing the content of low-molecular weight matters and narrowing the distribution range of molecular weight by, for example, reprecipitating the pressure-sensitive adhesive polymer from a poor solvent, thereby completing the invention.
The inventors have further found out that the adherend contamination with organic matters can be largely relieved by effectively crosslinking the pressure-sensitive adhesive polymer (involving the low-molecular weight matters) by blending a polyfunctional compound therewith so as to give a gel fraction of at least 90%, as another means for solving the object, thereby completing the invention.
Accordingly, the invention provides a low-staining adhesive sheet provided with an adhesive layer containing as the main component a pressure-sensitive adhesive polymer on a base film, wherein the pressure-sensitive adhesive polymer is substantially free from oligomeric low-molecular weight matters, e.g., the pressure-sensitive adhesive polymer preferably contains oligomeric low-molecular weight matters in an amount of 5 wt % or less, more preferably 3 wt % or less (first aspect of the invention); in particular, the low-staining adhesive sheet wherein the pressure-sensitive adhesive polymer is substantially free from low-molecular weight matters having a molecular weight of 5,000 or less (second aspect of the invention); the low-staining adhesive sheet wherein the pressure-sensitive adhesive polymer has a degree of molecular weight distribution (weight-average molecular weight
umber-average molecular weight) of 10 or less (third aspect of the invention); the low-staining adhesive sheet wherein the pressure-sensitive adhesive polymer has been reprecipitated from a poor solvent (fourth aspect of the invention); and the low-staining adhesive sheet wherein the adhesive layer contains, in addition to the pressure-sensitive adhesive polymer, a polyfunctional compound for crosslinking the pressure-sensitive adhesive polymer (fifth aspect of the invention).
The invention further provides the low-staining adhesive sheet wherein the pressure-sensitive adhesive polymer has been crosslinked so as to give a gel fraction of at least 90% and is substantially free from oligomeric low-molecular weight matters (sixth aspect of the invention); and the low-staining adhesive sheet which have been designed to give a gel fraction of at least 95% (seventh aspect of the invention).
As more particular embodiments of such a low-staining adhesive sheet, the invention further provides the low-staining adhesive sheet wherein the pressure-sensitive adhesive polymer is an acrylic polymer containing as the main monomer an alkyl (meth)acrylate (eighth aspect of the invention); the low-staining adhesive sheet wherein the adhesive layer contains, in addition to the pressure
Namikawa Makoto
Terada Yoshio
Toyoda Eiji
Dawson Roibert
Keehan Christopher M
Nitto Denko Corporation
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