Huge Temperature-Induced Increase in Chemical Resistance of Solution-Processed Amorphous Thin Films along the As₃S₇–MoS₃ Tie-Line and Its Structural Explanation

Amorphous chalcogenide thin films have been widely studied for use in lithography as a photoresist due to significant changes in etching rates caused by photoinduced structural changes upon exposure to light. Here, we report on the role of the transition metal molybdenum contained in MoS₃ on the significantly enhanced thermal stability and chemical resistance of As₃S₇-MoS₃ thin films deposited by a sol-gel method. We demonstrate that the dependences of etching rates of As₃S₇-MoS₃ thin films in a solution consisting of 1 vol % <i>n</i>-butylamine in dimethyl sulfoxide on the annealing temperature exhibit two linear regimes with a sudden change of their slopes at 160 °C. The first regime, below 160 °C, is characterized by a significantly lower chemical resistance of As₃S₇-MoS₃ thin films in comparison with As₃S₇ thin films, while the second regime manifests a gradual decrease in etching rates by 4 orders of magnitude in a range of annealing temperatures from 160 to 200 °C. We explain both trends using optical properties, differential scanning calorimetry, and attenuated total reflection results. We propose that the vast, 4-orders-of-magnitude difference in the etching rate between as-deposited As₃S₇-MoS₃ and annealed thin films at 200 °C can be successfully applied as a resist layer in wet lithography.