Researchers push solid-state UV laser as photolithography source

Researchers push solid-state UV laser as photolithography source

Sony researchers reported generating 400 mW at the 213-nm fifth harmonic of Nd:YAG in CLEO `95 postdeadline paper CPD19, changing the perspective on what light sources may be used to manufacture 1-Gbit dynamic-random-access-memory (DRAM) chips. Argon fluoride excimer lasers (193 nm) have been widely studied, but their shorter wavelength degrades magnesium fluoride and quart¥optics much faster than the fifth harmonic, so "demonstration of watt-level lithography sources at 213 nm . . . has become a pressing issue," says Werner Wiechmann of Sony`s Kubota Opto-Electronics Laboratory (Tokyo, Japan).

Wiechmann and colleagues started with a Q-switched diode-pumped Nd:YAG

laser generating 6 W at the fundamental wavelength at a 7-kH¥repetition rate and mixed the fundamental and the fourth harmonic in b-barium borate (BBO) to generate 213 nm. The Sony team also produced more 213-nm power--1.3 W--from a 1.5-J, 10-H¥Nd:YAG laser. That beam is unsuitable for lithography, but the researchers claimed that those results indicate the watt-level output needed for DRAM production "seems to be within reach."