Reflectivity reduction by oxygen plasma treatment of capped metallization layer

Oxygen plasma treatments of thin cap layers of Ti, Ta, W, or W–10% Ti deposited over Al or refractory metal silicide films can significantly reduce the optical reflectivity. The reduction is proportional to the thickness of oxide film grown on the cap layer. The oxidation occurs mostly in the first 5 min of plasma treatment and is a function of temperature. The oxide films have been characterized by Auger spectroscopy, Rutherford backscattering spectrometry, and ellipsometry. The measured reflectivities agree very well with the calculated results. This reduction in reflectivity is useful for photoresist processing as demonstrated by both computer modeling and experimental photoresist linewidth measurement.