Optical path and image performance monitoring of a full-field 157-nm scanner

Abstract

Designing and operating exposure tools with a stable imaging performance becomes increasingly challenging as the exposure wavelength is decreased to improve resolution capabilities. At a wavelength of 157 nm, light is highly absorbed by most materials. In addition, the high photon energies readily induce photochemical degradation of the majority of organic materials. As a result many of the materials in the optical path of 157 nm exposure tools have been replaced and more stringent controls on the purge gas quality have been introduced. As the recipient of the first full field 157 nm scanners to be installed in the field, IMEC has implemented a tool-monitoring program to assess the performance of the exposure tool. The assessment includes characterization of the baseline operating conditions of the scanner and the evaluation of any potential trends in performance related to environmental interactions. This paper describes the techniques used to monitor the tool and reports on the results obtained during the initial months of tool operation.