The interference lithography is a promising technique for waveguide combiners and distributed feedback laser diodes. However, the technology has not been applied in mass production due to three issues. The first is an insufficient fringe pitch accuracy. The second is a deterioration of patterning quality due to low exposure contrast. And, last is time consuming alignment processes.
We have developed an interference lithography system applied with technologies of a high precision wafer stage, a diode pumped solid-state laser with a wavelength of 266 nm and high accuracy actuators. The system has a patterning pitch accuracy of 0.01 nm, a patterning direction angle accuracy of 0.01 degree, an ability to form clear patterns with excellent exposure contrast and an automatical beam alignment for capability of mass production. We will present an overview of the system for achieving the specifications, and examples of processing.
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.
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