Effects of laser bandwidth on OPE in a modern lithography tool

Abstract

The OPE signature of a lithographic stepper or scanner has become a very important characteristic of the tool, as it determines the OPC correction to be applied to reticles exposed on that tool. The signature depends on a variety of detailed information about the scanner lens and illuminator, which in turn depend on the characteristics of the illumination light from the laser. Specifically, changes in the laser bandwidth should impact OPE as the lens exhibits some chromatic aberration. Tool-to-tool differences and time fluctuation of the laser bandwidth could cause variations in OPE tool matching and stability. To assess this, a detailed study of laser bandwidth effects on OPE was performed. A sensitive spectrometer was connected to a litho laser, allowing careful measurements of both the FWHM and <i>E</i>₉₅ parameters of the laser spectral profile. Lithographic modeling using the chromatic response of the lens was run in order to predict effects. Exposures of CD through pitch were made to test the modeling. Finally, the bandwidth data was correlated with litho sensitivity to create a "bandwidth effect", put in context with the other common scanner parameters affecting OPE.