Dust cover superior in transparency for photomask reticle use an

Details Dust cover superior in transparency for photomask reticle use an Dust cover superior in transparency for photomask reticle use an

1985-06-13

1987-04-14

Buffalow, Edith

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

428422, 355 30, 352130, B32B 702

Patent

active

046578056

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a dust cover superior in transparency for photomask reticle use. More particularly, the invention relates to such a dust cover comprising a film having at least thin outermost layers of a specific fluoropolymer, the film being bonded to a supporting frame.


BACKGROUND ARTS

With the densification of integrated semiconductor circuits in recent years, printed wires in the circuits have been extremely fined to widths of from 1 to 3 .mu.m and the lithographic technique of forming images of such wires on wafers are being changed from the projection system to the stepper system.
When dust is present on a photomask reticle in the lithographic process, images of dust particles will also be formed, resulting in short circuits and defects in the produced circuit, and this will lower the yield of the LSI. Specially in the stepper system, several images on a reticle are successively projected on a reduced scale to a wafer. Hence one dust particle on a reticle may make defective all the resulting LSI's. Thus it is getting very important to reduce the dust to zero.
Thereupon, a method for preventing dust adhesion onto photomask reticles (hereinafter abbreviated occasionally as "mask") has been proposed (U.S. Pat. No. 4,131,363). The method comprises arrangement of a transparent film or films over one or both sides of the mask with a space left between the film and the mask surface. According to this method, since dust adheres only to the transparent film, defects due to dust can be prevented by focussing projecting rays on the image prepared on the mask and bringing the dust adhering onto the film out of focus, so that the image of the dust is not formed on the wafer.
The dust cover, applied to the mask, is set in an exposer. The film, which is the principal part of the dust cover, is disposed in the optical path of exposure light.
Consequently, the film needs to transmit light without causing the distortion or disorder of image, have a uniform thickness, and be free of foreign matter, fault, and internal strain.
The transparency of the film to the exposure light is also important. That is, when the transparency is low, the exposure needs to be the longer and therefore the throughput will be the less. In the production of LSI, it is very important to raise the throughput since LSI's in many cases are produced in extremely large volumes. Specially in the stepper system, the exposure in some cases is repeated hundreds of times per one wafer and the improved transparency of the dust cover film hence contributes greatly to the rise in the throughput.
For the film of the dust cover, nitrocellulose is in use. Although nitrocellulose is used because of the high film strength thereof and the capability thereof to give very uniform films, the light transmittance of these films is about 92% at wavelengths of from 350 to 450 nm which are of the exposure light used today. Thus nitrocellulose films as such are insufficient in light transmittance for use as the film of the dust cover. In consequence, a method has been proposed, in which the interference of two light waves reflected from the front and rear surfaces of the film is utilized, that is, the film thickness is chosen so that these reflected waves will cancel each other (U.S. Pat. No. 4,378,953). According to this method, the light transmittance rises to 99% while the film thickness becomes 0.865 .mu.m, being extremely thin. Hence this method has the drawback of requiring the exercise of sufficient care in handling such a dust cover. On the other hand, the increase in the film thickness will extremely narrow the tolerance of the thickness in order to achieve a light transmittance of 98% or more, thus making the film production very difficult. In addition, if the film thickness is increased to 6 .mu.m or more, the light transmittance thereof will be lowered on account of minute dimensional roughness of the film surface.
Another method is to prevent the reflection with an inorganic compound layer formed by vapor deposition or t

REFERENCES:
patent: 4131363 (1978-12-01), Shea et al.
patent: 4444826 (1984-04-01), Sasaki et al.
patent: 4465759 (1984-08-01), Duly et al.
"Pellicle Protection of IC Masks", Ron Hershel, Hershel Consulting, Inc., Aug. 1981, pp. 97-106.
"Pellicle Mask Protection for 1:1 Projection Lithography", T. A. Brunner, C. P. Ausschinitt and D. L. Duly, Solid State Technology, May 1983, pp. 135-143.

Affiliated with

Also associated with

Rating

Dust cover superior in transparency for photomask reticle use an does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dust cover superior in transparency for photomask reticle use an, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dust cover superior in transparency for photomask reticle use an will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1784824