A laser beam of a pulse width 10 to 20 nanoseconds is irradiated and scanned relatively and two-dimensionally on a metal thin film formed on a transparent substrate from the transparent substrate side and through the transparent substrate with a superposition number of laser beam spots set up to at most...http://www.google.ca/patents/US4190759?utm_source=gb-gplus-sharePatent US4190759 - Processing of photomask
