Alignment Pattern Detection Method Using Diagonal Imaging Optics for X-ray Exposure System

A precision alignment-pattern detection method using diagonal detection optics and twodimensional image processing technique has been developed to improve the alignment accuracy of X-ray exposure systems. This method features (1) consecutive pattern detection in an exposure field, (2) capability of detecting both lateral displacement and proximity gap between a mask and a wafer using the same detection optics, and (3) reduction of detection error caused by variations in the alignment-pattern fabrication process by using broad-spectrum (Xe light) illumination. According to the simulation of expected quantizing errors in image processing, a pixel resolution of 0.18 μm has been selected to attain a detection resolution less than 0.02 μm. The detection accuracy of an experimental apparatus was investigated, checking the expected error due to variations of wafer alignment patterns, resulting in a detection accuracy of ±0.02 μm for the lateral displacement detection and ± 0.06 μm for the gap detection, respectively.