High-volume production stepper for x-ray lithography

The prototype of a high volume production stepper for x-ray lithography, designed and built by Suss Advanced Lithography, Inc. (SAL), has been installed for beta testing at the Center for X-ray Lithography (CXrL) at the University of Wisconsin. SAL has put substantial efforts into the design and construction of this third generation x-ray stepper in order to meet industry requirements, mainly throughput, CD-control and overlay. Several design changes -- compared to the second generation XRS200 -- have been implemented to assure those goals. This includes a scanning beamline end to achieve exposure times of 1 sec as well as a high speed xy-stage for combined step end expose times below 2 seconds. Together with an improved optical alignment system (ALX70) for overlay accuracy below 50 nm (3(sigma) ) and a state-of-the-art loading/unloading wafer handler the measured throughput is currently between 26 WLPH (32 fields/200 mm wafer). Proximity gap is controlled to an accuracy of plus or minus 0.4 micrometer while minimum proximity gap is currently at 20 micrometer. Mask and wafer chuck are mounted kinematically to avoid mechanical stress to either mask or wafer for improved distortion control. A 3-axis-state-of-the-art HP laser interferometric system with a resolution of 2.5 nm controls mask to wafer movement to better than 20 nm. While this prototype is designed for wafer sizes of 75 to 200 mm, design changes are on the way to enable 300 mm wafer handling with increased throughput. Results obtained during a GaAs based MMIC and QWIP device fabrication program with 0.2 micrometer CD, demonstrate consistency with the prototype specification. Areas have been defined to further enhance the capabilities of the production stepper XRS 2000.