Extreme ultraviolet lithography (EUVL) is one of the promising candidates for patterning process to achieve technology nodes of 50 nm or below. In order to fabricate low-defect EUVL mask blank, two kinds of cleaning technique have to be developed. One is for the substrate before Mo/Si multi-layer coating, another is for finished masks. Particles on the substrate induce phase defects by altering the periodicity of the multi-layer. This makes it essential to remove particles from the substrate. Since EUV light is not expected to transmit materials for a pellicle, the mask of EUVL will be without a pellicle. The mask without a pellicle needs to keep the surface clean, because particles on the mask are easily focused on the wafers. ASET has developed a supersonic hydrocleaning (SHC) technique, which uses twin fluid jet nozzles designed for supersonic flow. Until now, the efficiency with which SHC removes particles below 100 nm in size was unclear because of the resolution limit of current optical inspection tool. In this paper, the particle removal efficiency at that level was assessed using a highly sensitive particle inspection system co-developed by the ASET SPC Laboratory and Hamamatsu Photonics K.K. © 2002 Published by Elsevier Science B.V.
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