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
Loong WA., Chen CW., Chang YH., Lin CM., Cui Z., Lung CA.
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∼55 W) and Si (200∼250 W) under Ar (30 seem) and oxygen (0.1∼0.4 seem). For required phase shift degree θ =180°, calculated thickness d180 of TiSixOy film is within the range of 87-120 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 C12:NF3=20:30 seem; 50 W and 60 mtorr, selectivity of 10:1∼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.