To achieve surface roughness and flatness requirements, EUV mask substrates made out of low thermal expansion material (LTEM) such as quartz, should undergo chemical mechanical polishing (CMP). This process can generate surface defects such as pits and embedded particles. Megasonic cleaning is widely preferred as the post-polish cleaning technique but must be practiced such that it does not create additional pits. Pit defects are commonly generated by transient cavitation near the surface. This work compares a conventional megasonic nozzle system with a proximity-type radially uniform megasonic system with respect to pit creation. The results show that with the nozzle system, the pits generated are generally located toward the center of the substrate. While the radially uniform proximity system creates a lesser number of pits that are more uniformly distributed.
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