Photocopying – Projection printing and copying cameras – Detailed holder for photosensitive paper
Reexamination Certificate
1999-07-01
2001-11-13
Adams, Russell (Department: 2851)
Photocopying
Projection printing and copying cameras
Detailed holder for photosensitive paper
C355S075000, C083S870000, C029S239000
Reexamination Certificate
active
06317197
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Technical Field
This invention applies generally to methods of photo-printing microcircuit patterns on photosensitive coated substrates used in the manufacture of semiconductor slices and more particularity, to a method and apparatus for removing a pellicle frame from a surface of a photomask consisting of an array of enlarged circuit patterns.
(2) Description of the Prior Art
The following three documents relate to various methods dealing with pellicle mounting apparatus.
U.S. Pat. No. 4,637,713 issued Jan. 20, 1987 to Shulenberger et al, discloses a pellicle mounting apparatus having a pair of pellicle holder assemblies positioned on either side of a photomask holder assembly.
U.S. Pat. No. 5,311,250 issued May 10, 1994 to Suzuki et al, shows another pellicle mounting apparatus.
U.S. Pat. No. 5,422,704 issued Jun. 6, 1995 to D. Sego discloses a pellicle frame.
A wafer for the manufacture of a semi-conductive elements is subjected to numerous sequenced operations which enable the fabrication of all its circuit elements. The use of a photo resist material in conjunction with photograhic masks provides the means to transfer the various pattern layers to the semiconductor wafer. The photo mask carries an enlarged pattern which is optically reduced upon each wafer's surface by projection printing. The layers upon which these images are to be reproduced are either a semiconductor, an oxide on a semiconductor, or a metal film covering the semiconductor.
The image formed in the photo resist can not be better than the photomask used to determine the exposed and unexposed areas. The most important characteristics that the image must possess are; dimensional correctness, uniform density in both clear and opaque areas, and sharp definition between clear and opaque areas.
In most applications, thousands of images are formed on a single photomask. A sequenced series of photomasks is required to complete a given semi-conductive device. Each mask controls the exposure of window patterns on wafers coated with photo sensitive resist material. This resist material is processed (developed) to wash away the exposed resist which permits access through the windows for depositing, implanting, or etching a variety of materials.
Multiple mask images which make up a mask series are produced with a defined, closely controlled spacing. In most semiconductor manufacturing operations, a series of photomasks are required to produce finished semi-conductive devices. Since the series of masks are used sequentially, mask alignment and the center to center spacing between features produced by successive masks must conform to preceding mask images to form a coherent array of materials in the layers of the devices being built.
It is well known that during the manufacture of semiconductive devices the goal is to achieve defect free exposures of circuit patterns. As integrated circuits evolved from small scale integration to very large scale integration the need for ultra clean manufacturing space became increasingly critical. As an example, a single airborne particle landing on the photomask surface during exposure can ruin the circuit exposed on the wafer below it.
To help solve this problem, the photolithographic industry developed pellicles to intercept particulates and protect the surfaces of photomasks against all forms of contamination. Pellicles include a thin, transparent membrane stretched across a frame. The frame holds the membrane in tension and keeps it away from the mask surface by the thickness of the frame. An adhesive is used to bond the frame to a surface of the photomask.
Because of the obvious inherent simplicity of this device, it has found use over a very wide range of the electromagnetic spectrum. The pellicle concept has been used in the optical industry for many years. A transparent membrane would have the effect of increasing the number of wavelengths in an optical path, or as a beam splitter in interferometry. Its application has been extended to photolithography by intercepting dust particles and other contaminents from reaching the focal plane of photomasks.
Many difficulties have been fronted in properly removing pellicle assemblies from photomasks. This procedure is necessary when cleaning or replacing damaged pellicle membranes. Presently, this job is done manually with the aid of simple hand tools and a stereomicroscope. Techniques for removing pellicle assemblies from photomasks vary widely. Each technician developes their own procecure and craftiness therefore, at times, cause costly miscues.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide apparatus for removing pellicle assemblies from a photomask without damaging the photomask's image quality.
Another object of the present invention is to standardize the removal process of pellicle assemblies by eliminating the crafty dependance of an operator.
In accordance with the objects of this invention, a new method and apparatus is provided to standardize the removal of pellicle assemblies from photomasks. This invention describes an apparatus that requires less skill and training with little chance of damaging the photomask or producing inbedded particulates on the plane of the mask's circuit pattern causing repeating shorts or opens during a wafer's exposure process.
Briefly, the invention describes a mechanical apparatus that permits only the degrees of freedom necessary for removing the pellicle assembly from the photomask. The mechanical apparatus is positioned inline with a pellicle/photomask nesting station. A mask is placed within the nesting station, the apparatus is then moved towards the pellicle/photomask assembly until a pair of prying arms come into contact with adjacent corners of the pellicle at the bonded interface between the pellicle frame and photo mask. The materials making contact with the pellicle assembly and photomask especially in the area of prying are delicate in composition and non-obtrusive to the photomask's glass surface.
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patent: 5311250 (1994-05-01), Suzuki et al.
patent: 5422704 (1995-06-01), Sego
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patent: 5976307 (1999-11-01), Cook
Hsieh-Mei Liu
Li Meng-Chun
Ackerman Stephen B.
Adams Russell
Fuller Rodney
Saile George O.
Taiwan Semiconductor Manufacturing Company
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