Study of the interaction between molten indium and sub-atmospheric pressure hydrogen glow discharge for low-temperature nanostructured metallic particle film deposition

Abstract

Indium (In) evaporation is enhanced by high-pressure hydrogen glow plasma, and a sponge-like In film containing submicron pores is prepared on the substrate. The glow plasma is generated at a total pressure of 13.3 kPa (100 Torr) as a capacitively coupled plasma. When the process atmosphere is diluted by He and Ar, the In evaporation rate increases by increasing the hydrogen concentration and no evaporation is observed without H2 gas. The In deposition rate exhibits no dependence on the In temperature in the range from 300 °C to 600 °C. However, the In deposition rate increases linearly by increasing the input power. The obtained deposition rate reaches 7.5 mg/s with an input power of 800 W even at an In temperature of 450 °C. The obtained weight deposition rate is equivalent to the thickness deposition rate of 1.6 μm/s. The prepared In film on the Si substrate is composed of a porous foam-like structure. The particle diameter distributes from 40 nm to a few tens of micrometers. The particles with diameters above a few micrometers reveal a porous structure with a pore size of less than 100 nm. The obtained In film consists of crystalline In. Thermal desorption measurements of the prepared In film reveal that a large amount of H2 gas is confined in the In film relative to the hydrogen solubility in solid In. The obtained results suggest that the excess hydrogen solubility in the liquid metal induced by H2 plasma is an important factor for the enhancement of In evaporation.