Direct phase measurements in phase-shift masks

Abstract

We have made direct phase shift measurements in phase shift masks using a transmission optical interferometer based upon a modification of an optical, laser scanning reflection profilometer. Measurements were carried out at 632.8 nm in transparent samples that consisted of thin films of SiO2 on fused silica substrates and thin films of SiO2 and Al2O3 on fused silica substrates. Measurements were also performed on attenuated phase shift mask blanks. The phase values measured at 632.8 nm were corrected for refractive index and wavelength for 248 nm.