Sub-100nm pattern transfer on compound semiconductor using sol-gel based TiO ₂ resist

The possibility to pattern III-V compound semiconductor with nanometer scale is of great interest to photonic, electronic and optoelectronic systems. Typical method for sub-micrometer compound semiconductor dry etching utilizes PMMA or other resist to transfer patterns to SiO ₂ as intermediate masks due to resist's low etching selectivity, especially for ultra-small features. This additional pattern transfer will inevitably increase the potential damage caused by plasma dry etching and the complexity of patterning process. Therefore, it is desirable to find an easier and more effective way to pattern compound semiconductor. In this paper, we report a new approach of direct pattern transfer using Ti(OBun) ₄ solgel derived TiO ₂ resist as mask. The optimal dose of TiO2 resist for e-beam lithography is ̃220mC/cm2. Thermal stability study of spin-coated TiO ₂ shows a good performance as lithography resist even at 300 °C, which will have wider applications than conventional resists. Post-annealings at different temperatures are performed to study temperature-dependence of patterned TiO ₂ resist as dry-etching mask. The etching selectivity of sample InP compound semiconductor to TiO ₂ resist is over 7:1. A variety of sub-100 dry etching patterns with good profile qualities have been obtained. The aspect ratio of etching patterns is over 20:1, and the smallest feature is as small as 20nm with over 600nm deep. This sol-gel derived TiO ₂ sipn-coatable nanolithography resist with high etching selectivity and high aspect ratio etching profile provides a novel and convenient way to directly pattern compound semiconductor material for various challenging nano sacle photonic, electronic and optoelectronic applications.