The novel plasma etching process for defect reduction in photomask fabrication

As the device design rule shrinks, photomask manufacturers need to have advanced defect controllability during the Cr and MoSi etch in the process of phase shift mask(PSM). In order to decrease the number of defects, which may be originated from the mechanical transferring, plasma ignition and cross-contamination of resist stripping or cleaning process, a novel plasma etching process was developed in a commercial photomask etcher. In this process named as the "In-situ. etching", Cr and Mosi is etched stepwise in a chamber. The In-situ. etching processes produce better defect level than that of the conventional process without deteriorating other mask quality such as CD performance, profile and process reproducibility. Particle generated by plasma ignition in in-situ. etching lead to defect which is an obstacle in Cr etch. Because plasma is stable from Cr etch to Mosi etch, no defect is added in Mosi etch. Furthermore quantitative analysis of by-products deposited and eroded by the chamber position shows that by-products are comprised of Al, chlorine, carbon. These byproducts can be removed by fluorine-containing plasma.