Effects of condensation reactions on the structural, mechanical, and electrical properties of plasma-deposited organosilicon thin films from octamethylcyclotetrasiloxane

Abstract

Organosilicon thin films were deposited from octamethylcyclotetrasiloxane and hydrogen peroxide using pulsed-plasma-enhanced chemical vapor deposition. Fourier transform infrared (FTIR) analysis shows significant organic content as well as hydroxyl and silanol moieties present in the as-deposited materials. Complete removal of the hydroxyl groups after annealing at 400°C for 1h was confirmed by FTIR and indicates that a condensation reaction between proximal hydroxyl groups occurred. This leads to the formation of additional Si–O–Si linkages, also confirmed by FTIR, and these structural changes lead to increased mechanical properties for the film. Mechanical property measurements were in accordance with this hypothesis, as the hardness increased between 46% and 125% after annealing. The structure-hardness relationship was evaluated in the framework of the continuous random network theory, and a percolation of rigidity was observed at a connectivity number of 2.35–2.4. Dielectric constants of the annealed films ranged between 2.78 and 3.20. Film structure and properties were strongly dependent on the feed rate of the oxidant relative to that of the siloxane.