Precursor selection for plasma deposited fluorinated amorphous carbon films

Abstract

PECVD fluorinated amorphous carbon (FlAC) has shown promise as a low-k, intermetal dielectric (IMD) material. It has been demonstrated that electrical, thermal, and mechanical performance may be tailored by adjusting the amount of fluorine present in the film. There are a wide variety of fluorocarbon precursors available for the deposition of these films, each with a characteristic fluorine/carbon ratio. Additionally, hydrogen and/or various hydrocarbons can be included to lower the effective F/C ratio. The resulting film fluorine content is almost entirely dependent on this input chemistry. In this study, we examine films deposited from a number of different input chemistries; with F/C ratios ranging from 3:1 to down below 1:1. The properties of FlAC depend strongly on the amount of fluorine present in the film. In general, films with lower fluorine content exhibit better thermal stability and mechanical strength, but tend to be higher in dielectric constant and give greater current leakage. We also found film performance to be influenced by deposition temperature, particularly thermal stability. The best case films were deposited at high temperature (400°C) such that they could withstand prolonged exposure to high temperature. Fluorine content was low (<45 at.%) and the dielectric constant ranged from 2.7 to 2.9. Characterization was not limited to the FlAC material itself, but also included interactions with other dielectric films (e.g. amorphous carbon, silicon nitride, silicon dioxide, and silicon carbide).