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 ͑1994͔͒ 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-5͒ electron-beam system. The mask contains challenging patterns used in IBM devices with ground rules from 0.4 m down to 0.15 m. 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.
Data on image shortening effects with patterns replicated with x-ray and optical lithography are presented. The x-ray exposures were performed at the IBM Advanced Lithography Facility using the Helios superconducting storage ring and a SUSS stepper. The optical exposures were performed using SVGL Micrascan 1 and 2 tools and biased optical masks. The results indicate that the image shortening effects using x-ray lithography (XRL) are considerably less pronounced than the effects observed with the optical tools. In addition, modeling of the image shortening effects for XRL using the xmas three-dimensional program for resist patterns is presented and compared with experimental results.
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