Development of X-ray Stepper With High Overlay Accuracy for 100-Nm LSI Lithography

X-ray lithography using synchrotron radiation (SR) is a promising tool for fabricating large-scale integrated circuits (LSIs) with device feature sizes as small as 100 nm. The making of 100-nm devices requires both a high overlay accuracy and a printing resolution of less than 35 nm. We have developed an SR x-ray stepper meeting this requirement that utilizes air-bearing lead screws, an optical heterodyne detection system, and magnification correction by means of thermal stress control. Exposure results demonstrate that the exposure system achieves a total overlay accuracy of better than 30 nm, including stepper, mask and wafer errors.