Method of distortion compensation by irradiation of adaptive lithography membrane masks

Abstract

Techniques are disclosed to compensate for distortions in lithography by locally heating the membrane in a lithographic mask. The techniques may be used both to shrink and to expand areas of the mask locally, in order to adjust for varying magnitudes and signs of distortion. In one embodiment the correction method comprises two steps: (1) A send-ahead wafer is exposed and measured by conventional means to determine the overlay errors at several points throughout the field. (2) During exposure of subsequent wafers, calibrated beams of light are focused on the mask. The heating from the absorbed light produces displacements that compensate for the overlay errors measured with the send-ahead wafer. Any source of distortion may be corrected—for example, distortion appearing on the mask initially, distortion that only develops on the mask over time, or distortion on the wafer. In another embodiment, a reference pattern is formed on the membrane as a means of measuring mask distortion, and the heat input distribution needed to correct distortion is determined by subsequent measurements of the reference pattern. In this alternative embodiment, any source of distortion in the mask may be corrected.

Dependencies are inferred from the claim text.