Sub-nanometer broadband measurement of elastic displacements in optical metrology frames and other critical elements

Abstract

This paper presents the outline for a real-time nano-level elastic deformation measurement system for high precision optical metrology frames. Such a system is desirable because elastic deformation of metrology frame structures is a leading cause for performance degradation in advanced lithography as well as metrology and inspection equipment. To date the development of such systems was thwarted by the unavailability of sufficiently sensitive and cost effective strain sensors. The recent introduction to the market of the IntelliVibe(TM) S1 strain sensors with sub nanostrain sensitivity makes it possible to develop a real-time nanometer level elastic deformation monitoring system. In addition to the sufficiently sensitive and cost-effective strain sensor it is necessary to develop the analytical foundation for the measurement system and use this foundation for the development of a signal processing algorithm that will enable the real-time reconstruction of the elastic deformation state of a metrology frame at any given time from data transmitted by a reasonable number of properly placed S1 strain sensors. The analytical foundation and the resulting algorithms are demonstrated in this paper.