Alignment accuracy evaluation of X-ray lithography system SR-1.

In order to evaluate the aligner of X-ray lithography system SR-1 developed for the replication of submicron features, mark detecting characteristics and overlay accuracy have been investigated. The results are summarized as follows : (1) The detecting characteristics of the wafer marks under transparent layers are affected by interference, which depends on the refractive index and thickness of the layers. Improvements for the mark detecting characteristics have been investigated. (2) Overlay accuracies of less than 0.08 μm (σ) have been achieved for various conditions of the wafer marks. (3) From the differences in overlay accuracy between the center and the edge of the exposure site, the standard deviations of the runout error and the proximity gap change have been estimated to be less than 0.037 μm (σ) and 0.65 μm (σ), respectively.