Scanning overlapped phase interference lithography system for manufacturing optical waveguide combiner

We have been developing Scanning Overlapped Phase Interference Lithography (SOPHIL) system which can provide an excellent grid pitch uniformity, 380 nm+-0.005 nm over the entire 200 mm diameter substrate. The SOPHIL method consists of two steps. As the first step, a spot fringe pattern generated by two-beam interference is scanned direction along the grid on the wafer. As the second step, the spot is moved just the integer multiple length of its fringe period, then the spot is exposed again over the 1st fringe pattern. We achieved the pitch uniformity of +-0.002%, and also 180 nm pitch pattern was confirmed.