Keiichi Okamoto

X-Ray Exposure System With Plasma Source For Microlithography

An x-ray exposure system with a plasma source has been developed to be applied in R & D of a deep-submicron device fabrication process. This system features high accuracy align-ment using imaging optics with high-speed signal processing, precision proximity gap control by means of a wafer surface flattening mechanism, and fine pattern replication by incorporating a plasma focus soft x-ray source. The imaging optics are arranged to be diagonally symmetric with respect to the x-ray exposure axis to perform continuous pattern detection (lateral displacement and gap) directly in an exposure field. A unique wafer chuck capable of flattening a wafer surface to within ±0.5 μm by piezoelectric actuators, supported by a six-axis, micro-motion mechanism, makes it possible to align the wafer to the mask (resolution of 0.01 μm) with a uniform gap (15=11 μm). The plasma focus source which emits x-rays with wavelengths in the range of 10 ~ 14 Å from high-temperature neon plasma using the pinch effect induced by a pulse current, has been newly developed. The pattern replication performance is thoroughly examined, showing an alignment accuracy of within ±0.1 μm (2σ), and a fine pattern replication of 0.3 μm.