Highly selective etching of SnO2 absorber in binary mask structure for extreme ultra-violet lithography

Among the core EUVL (extreme ultra-violet lithography) technologies for nanoscale patterning below the 30 nm node for Si chip manufacturing, new materials and fabrication processes for high-performance EUVL masks are of considerable importance due to the use of new reflective optics. In this work, the selective etching of SnO2 (tin oxide) as a new absorber material, with high EUV absorbance due to its large extinction coefficient, for the binary mask structure of SnO2 (absorber layer)/Ru (capping/etch stop layer)/Mo-Si multilayer (reflective layer)/Si (substrate), was investigated. Because infinitely high selectivity of the SnO2 layer to the Ru ESL is required due to the ultrathin nature of the Ru layer, various etch parameters were assessed in the inductively coupled Cl2/Ar plasmas in order to find the process window required for infinitely high etch selectivity of the SnO2 layer. The results showed that the gas flow ratio and V(dc) value play an important role in determining the process window for the infinitely high etch selectivity of SnO2 to Ru ESL. The high EUV-absorbance SnO2 layer, patternable by a dry process, allows a smaller absorber thickness, which can mitigate the geometric shadowing effects observed for high-performance binary EUVL masks.