In a basic study to identify low-loss optics for applications in F2 lithography, five potential coating materials (AlF3, Na3AlF6, MgF2, LaF3, and GdF3) 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 CaF2 substrates by four Japanese coating suppliers. Refractive indices (n) and extinction coefficients (k) 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
[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)