Improving Megasonic Exposure Uniformity for EUV Mask Substrate Cleaning

• Published in: ECS transactions Vol. 41; no. 5; pp. 123 - 129
• Main Authors: House, Matthew, Rastegar, Abbas, Dussault, Don, Liebscher, Eric
• Format: Journal Article
• Language: English
• Published: 01.01.2011
• ISSN: 1938-5862; 1938-6737
• DOI: 10.1149/1.3630835

To achieve surface roughness and flatness requirements, EUV mask substrates should undergo chemical mechanical polishing (CMP), These processes can generate both pit and embedded particles on the surface of low thermal expansion material (LTEM) masks. Megasonic-induced pits are one of the critical defectivity modes for EUV mask blank substrates. Pit defects are generated by cavitation collapse near the surface. This work compares a conventional megasonic nozzle system and a proximity-type radially uniform megasonic system with respect to pit creation. In typical cleaning processes used to remove particles on EUV substrates, the megasonic nozzle generates about 3 times more pits than the radially uniform megasonic system. These pits are located at the center of the plate. Distribution of pits generated by the radially uniform proximity system is uniform throughout the plate as megasonic exposure is uniform across the plate.