Characterizing photomask etch processes by phase component analysis (PCA)

One of the most important parameters of Attenuated Phase Shift Masks (APSM) is the uniformity of the phase over the active area of the mask. Phase uniformity is an important component of lithographic process window stability. Typically, an APSM blank consists of a quartz substrate upon which a Molybdenum Silicide (MoSi) attenuating film and a Chromium (Cr) film have been deposited to act as a hard mask for the MoSi etch. There are many factors that contribute to phase non-uniformity of the final mask: thickness non-uniformity of the films, non-uniformity of the Cr etch and MoSi etch, and non-uniformity of the MoSi overetch into the quartz substrate. Phase of a completed mask is routinely measured, but quantifying how these individual components contribute to the overall phase non-uniformity is challenging. This report focuses on understanding how MoSi etch contributes to phase non-uniformity. Phase uniformity is compared for three different MoSi etch processes.