Effect of absorber thickness on image shortening in x-ray lithography

Abstract

Image shortening effects have been shown to be a problem for pattern replication using current optical tools. However, a previous study [R. DellaGuardia, J. R. Maldonado, and H. Oertel, J. Vac. Sci. Technol. B 12, 3936 (1994)] indicated that image shortening is less pronounced when pattern replication is performed using x-ray lithography. This article describes the effect of absorber thickness on the image shortening observed in x-ray lithography. The goal is to determine the optimum absorber thickness that minimizes image shortening when replicating complex patterns with the x-ray spectrum from the HELIOS storage ring installed at the IBM Advanced Lithography Facility. To study these effects, an x-ray mask with four quadrants, each having different gold thickness, was fabricated using the IBM vector scan (VS-5) electron-beam system. The mask contains challenging patterns used in IBM devices with ground rules from 0.4 μm down to 0.15 μm. The image shortening effects for different mask/wafer gaps, various line shapes, and feature sizes will be presented in this article. In addition, experimental results with conventional and chemically amplified resists will be presented to shed light on the role of resist in image shortening.