Low loss optical coat for 157 nm lithography

The authors are aiming to develop an optical coating which has low optical loss at 157 nm; the loss should be <0.3% under our criteria. The optical loss of the optical coating consists of scattering, absorption, and reflection losses. We have provided newly developed instrumentation to measure the optical loss: a scatterometer, absorption measurement, and a VUV spectrometer. Using these measurement systems, we have investigated the transmittance (T), reflectance (R), absorptance loss, and scattering loss of five coating materials (AlF/sub 3/, Na/sub 3/AlF/sub 6/, MgF/sub 2/, LaF/sub 3/, GdF/sub 3/) and three deposition processes (resistive heat evaporation, electron beam heat evaporation, ion beam sputter). In this paper, we introduce the scatterometer, absorption measurement, and VUV spectrometer. We also discuss the measurement results of the test samples.