位相差回折モアレ信号による超精密位置決め制御

Abstract

The demand for high resolution in the lithographic processes is increasing. The submicron lithography requires highly accurate alignment between the mask and the wafer. The authors have proposed an automatic and accurate alignment technique for proximity printing in X-ray lithography using two pairs of moire gratings, respective moire signals from each pair being 180° out of phase with each other. The basic characteristics of diffracted moire signals obtained by some optical basic experiments and numerical calcurations were discussed for the automatic alignment. A control reproducibility better than 32nm was obtained using the stepping moter as an actuator. Experiments for the mask alignment were carried out using two paires of quadruple gratings of 16μm pitch, a combined unit of 4 matched photodiodes and two pairs of PZT controllers. A control reproducibility better than 40nm for X-Y directions was obtained. This technique has been also applied to projection photolithography, as a part of the mix and match lithographic system to go with proximity X-ray lithography.