High Aspect-ratio Holographic Photoresist Gratings

Holographic gratings with periods as small as 700 nm, rectangular profiles with linewidths of <120 nm, and depths of 1.2 microm (aspect ratio of 10) have been formed using positive photoresist on Si substrates and visible laser exposure (488 nm). Similar aspect ratios have been achieved at a 400-nm period using 334-nm exposing radiation. A simple exposure and development model, which accounts for the large aspect ratios and predicts the grating fabrication limits, is presented.