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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.
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