TiSixOy as an absorptive shifter for embedded phase-shifting mask in 248 nm and the modification of R-T method for the determination of shifter's n and k

Abstract

TiSixOy as an absorptive shifter (embedded layer) for attenuated phase-shifting mask (APSM) in 248 nm wavelength is presented. TiSixOy thin film was formed by plasma sputtering of Ti (25 similar to 55 W) and Si (200 similar to 250 W) under Ar (30 seem) and oxygen (0.1 similar to 0.4 sccm). For required phase shift degree theta=180 degrees, calculated thickness d(180) of TiSixOy Film is within the range of 87 similar to 120 nm depending on its reflectivity R, transmittance T, refractive index n and extinction coefficient k. Taguchi design of experiment has been applied to study the plasma etching selectivity of TiSixOy over APSM's substrate quartz (SiO2), under Cl-2:NF3=20:30 seem; 50 W and 60 mtorr, selectivity of 10:1 similar to 35:1 was observed. Modifications of reflectivity-transmittance (R-T) method have been developed for the determination of this absorptive shifter's n and k.