Testing new chemistries for mask repair with focused ion beam gas assisted etching

摘要

In modern photolithography mask repair, shorter exposure wavelengths, smaller dimensions, and tighter process latitudes pose new challenges. We have systematically investigated focused ion beam (FIB) gas assisted etching (GAE) of chrome and mask transmission at 193 nm ultraviolet (UV) irradiation for various FIB parameters. The gases, used either alone or in binary combinations, include XeF_2, Cl_2, NH_3, CO, CO_2, Br_2, H_2O, and O_2. While the bromine GAE appears to be the most effective among single gases in etching chrome, the quartz transmission after chrome removal remains ～50% compared with unexposed material, and residue is present. The gas mixtures NH_3 /Br_2 and CO_2 /Br_2 were found to reduce the amount of residue and to enhance the chromium mask etching rate compared to Br_2-only etching. This enhancement occurs in a narrow range of gas partial pressures, and the FIB process may need to be optimized further. The best transmission at 193 nm UV irradiation of the FIB GAE repaired regions achieved to date with no postprocessing is ～95% of the transmission of a blank mask. We also applied laser power to heat the area where the ion beam is incident. No increase in Cr removal rate was seen for the Br based chemistries. Some increase in removal rate was seen for Cl_2 + O_2 and XeF_2 but the overall rate with both gas and laser power was barely higher than sputtering alone.