Sub-half-micron critical dimension control in x-ray lithography mask technology

Abstract

The main problems in x-ray mask fabrication concern the defect density, the pattern placement accuracy, and the critical dimension (CD) control. To demonstrate the performance of x-ray lithography, it is necessary to fabricate sub-half-micron features with high reproducibility and small linewidth variations. This requires an absorber patterning procedure with extremely high stability and homogeneity and additionally a measuring technique with high accuracy in the sub-half-micron range in order to control the linewidth quality. It has been shown that mask fabrication can fulfill most of the requirements on x-ray mask technology using electron beam (e-beam) writing in a trilevel process with electroplated gold absorbers. Furthermore, a copying procedure was developed which multiplies an e-beam written master mask by using x-ray lithography in a single-layer resist and again gold electroplating. To characterize the linewidths and their variations, an e-beam based measuring technique is presented, which is able to measure quarter-micron CD’s with an accuracy of ∼25 nm as a 3σ value. The aim of this paper is to demonstrate the homogeneity of the running mask technology including the mask copying process and the feasibility of the applied measuring technique. Results are presented showing clearly that linewidth variations can be limited to 50 nm for both master mask and mask copy. X-ray masks with gate lengths down to a quarter-micron dimension have been fabricated in this quality. The technological ways to achieve these results are summarized in this paper.