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

Abstract

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 % n-butylamine in dimethyl sulfoxide on the annealing temperature exhibit two linear regimes with a sudden change of their slopes at 160 degrees C. The first regime, below 160 degrees 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 degrees 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 degrees C can be successfully applied as a resist layer in wet lithography.