In a basic study to identify low-loss optics for applications in F<sub>2</sub> lithography, five potential coating materials (AlF<sub>3</sub>, Na<sub>3</sub>AlF<sub>6</sub>, MgF<sub>2</sub>, LaF<sub>3</sub>, and GdF<sub>3</sub>) and three deposition methods (thermal evaporation by a resistance heater and by electron beam and ion-beam sputtering) were investigated in the vacuum ultraviolet (VUV) region. Samples were supplied as single-layer coatings on CaF<sub>2</sub> substrates by four Japanese coating suppliers. Refractive indices (<i>n</i>) and extinction coefficients (<i>k</i>) of these coatings at 157 nm were evaluated; the transmittance and the reflectance were measured by a VUV spectrometer and were compared. As a result, resistance heating thermal evaporation is seen to be the optimal method for achieving low-loss antireflection coatings. The relation among optical constants, microstructures, and stoichiometry is discussed.
© 2002 Optical Society of America
Shunsuke Niisaka, Tadahiko Saito, Jun Saito, Akira Tanaka, Akira Matsumoto, Minoru Otani, Ryuji Biro, Chidane Ouchi, Masanobu Hasegawa, Yasuyuki Suzuki, and Kazuho Sone, "Development of Optical Coatings for 157-nm Lithography. I. Coating Materials," Appl. Opt. 41, 3242-3247 (2002)