Screening of second-generation high-index liquids

Abstract

A series of experiments were designed to probe the interaction between second generation High Index Liquids (HIL, n=1.65) and the resist stack. Three different second-generation high index liquids were tested in five experiments: measurement of the contact angle of the liquid with the resist surface; leaching of Photo-Acid Generator (PAG) into the liquid; residue analysis of droplets evaporated from the resist surface; impact of liquid soaking on resist profiles; and imaging through high-index liquids at 72nm pitch. The selected liquids were the main candidates from two potential vendors. In parallel, tests have also been done for water. The tests show that one of the main differences between highindex liquids and water is their much smaller contact angles on the organic photoresist films. This contact angle can be influenced by a topcoat, but currently seen contact angles may force a new immersion hood concept. Imaging was not affected strongly by the high-index liquids. For some liquids, low evaporation rates and a tendency to leave residue on resist were observed, which may require a dedicated liquid removal strategy to reduce defectivity.