Photodensification in amorphous P-Se thin films

Abstract

The photoinduced shift in the absorption edge, changes in optical constants, film thickness contraction and rate of chemical dissolution were investigated for P-Se thin films deposited under normal (0°) and oblique (80°) incidence. These studies confirm our view that a variety of photoinduced phenomena observed earlier in germanium- and arsenic-based chalcogenides are primarily due to the chalcogen sulphur and/or selenium and that the role of germanium, arsenic or phosphorus is to act as matrices to stabilize a low density glassy structure. An irreversible thickness contraction of about 5% was found in films of P₄Se₁₀ deposited at 80° and is due to the decrease in the void volume on band gap irradiation. The thickness contraction was used for the generation of high resolution relief patterns. Photoinduced effects on the wet and dry etching behaviour of films, with and without an overlayer of silver, suggest the suitability of these films for positive and negative resist applications. Typical values of the contrast and the sensitivity for positive resist application are 2.6 and 10²³ photons m^-2 respectively.