Development of reticle-free exposure method with LCD projection image

Liquid crystal display (LCD) in place of the conventional reticles for optical projection lithography is proposed, in order to minimize the turn-around-time and production cost. The transmittance ratio between the two modes of the LCD, such as transparent and opaque ones, is approximately a several dozen depending on the wave length of the light source. In this study, the Nikon g-line stepper was modified to apply the LCD on its reticle stage. The minimum resolution of this proposal projection system is quite similar to the one of the conventional reticle method. The exposure time is approximately 10 times longer compared to the conventional method. It has been proven that the LCD has the potential to be replaced for the conventional reticles in the optical stepper lithography that is applicable for devices with relatively large fabrication rules and low production amount.