Surface profile determination of phase shift masks by inverse scatterometry

This report describes research conducted by Research Associate Jeffrey A. Reed and graduate student Rayan AI Assaad under the direction of Dr. Dale M. Byrne, at the University of Texas at Dallas. The period of investigation extended from September 1, 2002 to January 15,2003. The research and results reported here were directed toward the problem of determining the surface relief profile of phase-shift masks using the analysis technique that was developed by Byrne et al.1 The goal was to determine the accuracy that resulted when scatterometric data were processed using the above stated technique. Further investigations were made into the effect of "second surface interactions"; specifically how the second surface interactions affected the data collected by a scatterometer. These investigations were quite enlightening in that they produced rather negative results; hence further investigations were undertaken to develop methods to circumvent the problems created by the second surface interactions. In Section II we describe the general scatterometric configuration and provide an overview of the analysis technique of Byrne et a1. 1 We illustrate the technique using simulated scatterometric data derived from a structure that represents a phase-shift mask. At the conclusion of Section II we simulate the effect of a "second surface interaction." In Section III we discuss one method to eliminate the effects of "second surface interactions" so that their effect on scatterometric data is removed. We then consider the consequences of this method as they relate to some basic design parameters of scatterometric instrumentation.