Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1998-11-06
2001-02-27
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C356S394000
Reexamination Certificate
active
06194101
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and apparatus for determining whether a photomask for making semiconductor devices is good or defective.
2. Background Art
A high quality photomask is necessary for the art of transferring a circuit pattern to semiconductor wafers for use in a process of making semiconductor integrated circuits. The production of a photomask includes filming a glass substrate with chrome, coating the filmed substrate with resist to make a mask blank, and describing or forming a mask pattern in the blank.
The position on a semiconductor wafer to which the mask pattern in a photomask is transferred is determined by the position of the pattern relative to the wafer. It is therefore essential for the pattern to be formed at a correct position in the mask blank.
It is therefore necessary to position a mask blank correctly relative to the position where a mask pattern should be formed in an apparatus for forming mask patterns to make photomasks. This requires the blank to be positioned correctly on a blank holder. In practical processes, however, mask blanks may not necessarily be positioned correctly. It is therefore necessary to determine whether a mask pattern is formed correctly on a mask blank. In order to confirm the position of the pattern on the blank, a coordinate measuring machine using a laser interferometer may be used. In general, however, such a coordinate measuring machine is expensive.
OBJECT AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a photomask which can cheaply and securely be judged good or defective. It is another object to provide a process and apparatus for cheaply and securely determining whether a photomask is good or defective.
In accordance with the invention, a process and apparatus are provided for determining whether a photomask made of a glass substrate having a mask pattern of an opaque film is good or defective. The pattern includes a detection mark, which is formed in it when the pattern is described or formed in a mask blank. The mark has a predetermined positional relationship with the pattern. The apparatus includes a photomask holder having a hole formed through it. The hole is aligned substantially with the mark when the photomask is placed on the holder. The process includes placing the photomask on the holder, radiating light toward the hole, receiving the light which has passed through the hole and the photomask, converting the received light into an electric signal, and determining whether the photomask is good on the basis of the signal.
This makes it possible to determine whether a photomask is good by confirming the relative positions, that is to say, the degree of overlap between the photomask mark and the holder hole on the basis of the electric signal representing the quantity of light which has passed both of the hole and the mark.
REFERENCES:
patent: 4185298 (1980-01-01), Billet et al.
patent: 5331407 (1994-07-01), Doi et al.
patent: 5353116 (1994-10-01), Tanigawa et al.
OKI Electric Industry Co., Ltd.
Rabin & Champagne PC
Rosasco S.
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