Photocatalytic TiO2 surface combined with lithography defined area-selective deposition of Ru: Selectivity and defect formation mechanisms

Abstract

The IC manufacturing industry faces multiple challenges when employing patterning techniques at dimensions below 10 nm, aided by concepts such as litho-etch processes and self-aligned multiple patterning. Common issues include stochastic defects, line edge roughness, overlay errors and pattern collapse of photoresists. Area-selective deposition (ASD) as a bottom-up concept, presents a promising solution to mitigate some of these challenges with atomic-level accuracy. One effective approach to achieve ASD involves patterning organic monolayers using optical lithography in conjunction with a photocatalytic underlayer. This can be employed for Ru hard mask concepts. In this study, titanium oxide (TiO2) serves as the photocatalytic layer, which is passivated with organosilane self-assembled monolayers (SAMs) featuring methyl and fluorine terminations. Upon exposure to deep ultraviolet (DUV) light, fragmentation of the SAM molecules occurs due to a mechanism involving electron-hole pair generation in the presence of photocatalytic TiO2. This fragmentation in the exposed regions facilitates selective deposition of Ru. Furthermore, the selectivity is also influenced by the choice of precursor used for the subsequent Ru ASD, as demonstrated by comparing tricarbonyl (trimethylenemethane) ruthenium (Ru(TMM)(CO)3) and (ethylbenzyl)(1-ethyl-1,4-cyclohexadienyl) ruthenium (EBECHRu) precursors. Lastly, the mechanisms of Ru defect formation on the SAM-passivated areas are discussed in detail. Vapor-phase deposition of short-chain TMOS SAM was found to provide more effective surface passivation than immersion-based methods.