Laser-induced oxidized zinc alloy films for direct-write grayscale photomasks

Previous research showed laser-induced oxidization in Bi/In and Sn/In bimetallic films produced a large optical density change (3.00 to 0.22 OD at 365nm), making them promising in grayscale photomask application. This thesis explores Zn alloys as new bimetallic combinations. Sn/Zn, Zn/Sn, Al/Zn, Zn/Al, Bi/Zn, Zn/Bi and In/Zn were DC/RF-sputtering deposited and then exposed to an argon ion CW laser (spot size ≤ 10µm). Using a UV/Visible spectrometer, the most transparent material obtained was an exposed In/Zn film (3.20 to 0.20 OD). Zn/Sn, Zn/Al and Sn/Zn, producing a shallow OD versus laser power slope (5~9 OD/W) over a 0.4W power range while achieving a large OD range up to 3.45, gave the best results for laser direct-write grayscale photomasks. These bimetallic photomasks are able to pattern complex 3D microstructures by a single exposure. Using UV photolithography with these grayscale masks and SU-8 photoresist, 100µm high microbridges and 30°~60° V-grooves were fabricated.