HIGH-PERFORMANCE SYNCHROTRON ORBITAL RADIATION X-RAY STEPPER

A newly designed synchrotron orbital radiation x-ray stepper system has been developed to establish practical quarter-micrometer x-ray lithography and installed in the Tsukuba Research Laboratory for SORTEC Corporation, Japan. This stepper features the newly devised high-precision real-time full-closed alignment system and the ultraprecision vertical wafer stage which can be operated at an atmospheric helium pressure. In order to realize precision positioning of the wafer stage, we developed a 10-axis stage by combining a coarse XY positioning stage guided by hydrostatic air bearings and a fine positioning stage driven by six piezoelectric actuators. We also developed holographic alignment error detection optics, which consists of a three-axis Fourier transform lens system. Alignment error between the mask and the wafer can be detected during exposure and is fed back to the servo control system. By this real-time alignment error correction, an alignment precision of 0.06-mu-m (3-sigma) was successfully achieved.