Laser lithography quality alarm system

摘要

An electric discharge laser with an associated programmable controller which (1) will permit an operator to specify beam quality parameters based on historical data (2) will monitor those parameters and (3) will provide a notification signal to the operator informing him when the beam quality is adequate for integrated circuit fabrication. The controller is programmed to indicate an out-of-control condition when one or more quality parameters exhibit certain specified non-random behavior such as two out of three quality measurements deviating by more than 4 standard deviations and/or three out of four quality measurements deviating by more three standard deviations. In a preferred embodiment the program is designed to detect poor quality by looking for these "runs" of bad quantity data and to produce false indication of system out of control, on the average, no more than once each two months.