Laser exposure apparatus

Details Laser exposure apparatus Laser exposure apparatus

2001-11-01

2004-03-02

Adams, Russell (Department: 2851)

Photocopying

Projection printing and copying cameras

Step and repeat

C235S494000

Reexamination Certificate

active

06700642

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a laser exposure apparatus, more in details, to a laser exposure apparatus for exposing an identification code attached to a wafer for carrying out history control or quality control for respective process in semiconductor fabricating steps or the like.
BACKGROUND OF THE INVENTION
Conventionally, in fabricating steps of a liquid crystal panel, there has already been carried out history control or quality control for respective fabrication process by attaching an identification code to the liquid crystal panel. Two-dimensional codes or characters are used for the identification code and the two-dimensional codes or the characters are marked on a surface of the liquid crystal panel by exposing the surface to laser beam.
However, in the case of the liquid crystal panel, the liquid crystal panel per se is a comparatively large object and therefore, it is not necessary to reduce the identification code to be marked and the identification code does not become unreadable. However, in the case of a wafer dealt with in semiconductor fabricating steps, the wafer is a very small object and therefore, the identification code attached thereto is obliged to be very small. As a result, in reading the identification code, the identification code may become unreadable by a scanning type camera.
FIGS. 4A and 4B
are explanatory views showing a situation when an identification code marked by a conventional laser exposure apparatus is read by a scanning type camera.
As shown by
FIG. 4A
, an identification code M′ marked by a conventional laser exposure apparatus is formed by an aggregation of a number of circular dots d′. When the identification code M′ comprising the aggregation of the circular dots d′ is read by a scanning type camera, a number of scanning lines A through E are scanned to cross the identification code M′ to thereby discriminate portions of the black circular dots d′ from a white matrix portion.
However, as shown by
FIG. 4B
, although according to the scanning lines A and D searching vicinities of centers of the circular dots d′, signal levels received thereby correctly catch the identification code M′, according to the scanning lines B, C and E searching portions deviated from the centers of the circular dots d′, as shown by broken lines, there appears noise n′ caused by a clearance formed between the two contiguous circular dots d′ in signal levels and there is a concern that the noise is erroneously recognized as if the white matrix were present.
Further, in the semiconductor fabricating steps, after marking the identification code on the wafer, a metal film may further be coated in later steps. When the metal film is provided in this way, as shown by
FIG. 5A
, black and white contrast of the circular dots d′ is remarkably deteriorated and therefore, the scanning lines A through E must read to catch contours of the circular dots d′ and signal levels thereof appear as shown by FIG.
5
B. Also in this case, according to the signal levels provided from the scanning lines B. C and E, similar to the case of
FIG. 4B
, there appears the noise n′ caused by the clearance formed between the two contiguous circular dots d′ and therefore, the noise n′ similarly causes the erroneous recognition.
The noise n or n′ in
FIG. 4
or
FIG. 5
may be avoided by a filter processing or the like. However, by adding such a processing mechanism, there poses a problem that the cost is increased or a processing time period is taken.
DISCLOSURE OF THE IINVENTION
It is an object of the invention to provide a laser exposure apparatus in which even when a very small identification code is attached to a very small object such as a wafer, there is enabled marking for improving reading recognizability of the identification code.
A laser exposure apparatus of the invention achieving the above described object is characterized in comprising a laser oscillator for oscillating a laser beam having a circular section, a beam expander for enlarging the laser beam oscillated from the laser oscillator, a square mask for shaping the laser beam having the circular section enlarged by the beam expander into a square section and an optical system for contracting the laser beam formed into the square section by the square mask.
In this way, the laser beam having the circular section oscillated from the laser oscillator is shaped into the laser beam having the square section by the square mask and therefore, an identification code comprising an aggregation of dots exposed by the laser beam, is not formed with a clearance between contiguous ones of the dots as in the case of the conventional circular dots. Therefore, noise caused by the clearance is not caused in a signal searched by a scanning line of a scanning type camera and the identification code can be recognized correctly.


REFERENCES:
patent: 4794238 (1988-12-01), Hampton
patent: 4810867 (1989-03-01), Speicher
patent: 5710620 (1998-01-01), Taniguchi
patent: 6051845 (2000-04-01), Uritsky
patent: 6179207 (2001-01-01), Bossen et al.
patent: 6310680 (2001-10-01), Taniguchi

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