257 nm Laser Exposure System

An exposure system based on a Coherent frequency doubled (FreD) argon ion laser exposure system has been developed to study the photokinetics and dissolution properties of resist components at 257 nm. The Sabre FreD laser is the same laser intended for the full-scale 257 nm optical pattern generator. Expansion and collimating optics have been designed to provide uniform exposure intensity incident on the resist. A uniform intensity profile is created by sending the light through a 1 mm diameter aperture (pin hole) to spatially filter the gaussian-shaped laser beam. The pin-hole cuts out a small portion of the expanded beam to create a uniform intensity. The spatial coherence of the beam is destroyed with a fused silica spinning diffuser to remove speckle and diffraction patterns from the pin-hole. The beam is finally expanded to around 8 mm in diameter for exposure of resist located on a vertical stage. The stage is designed to hold 4 inch diameter AR3 coated mask substrates and 4 inch diameter transparent quartz substrates. A PM3 Molectron thermopile power meter is used to measure the intensity of the beam. The uniformity of the exposure intensity has been indicated through uniform development rates over the exposure area in the resist.