The formation and variation of AlN, Si3N4, and nitride compositions in AlSixNy (x similar to0.31, y similar to0.51) embedded material have been shown to correlate with its optical properties. The increasing content of AIN, Si3N4, and nitrides will increase n and decrease k of AlSixNy. A simple and effective correction of measured reflectance R% and transmittance T% based on scalar scattering theory has been applied to the R-T method for determining It and k of embedded layers for 193 nm lithography masks. A 0.2 mum etched pattern of an AlSixNy embedded layer on an oxide/Si wafer substrate was successfully fabricated.