Plasma-enhanced chemical vapor deposition of organic particle thin films

Five organic precursors, 2,5-dimethyl-2,4-hexadiene, 2,5-norbornadiene, α-terpinine, limonene, and styrene have been studied as precursors for plasma deposition of low-k films. The films have been produced under particle-forming conditions in the plasma. Accordingly, films have a granular structure with grain sizes in the range 40-400 nm, as determined by AFM. Annealing at 400°C preserves the granular structure of the films while the grain size decreases. Of the five precursors examined, 2,5-dimethyl-2,4- hexadiene and 2,5-norbornadiene produce films with the lowest dielectric constant, with a value of 3.3. While the dielectric constant varies with deposition conditions (pressure, flow rate, concentration of precursor), we find that the grain size of the films correlates most closely with the dielectric constant and conclude that the lowest value of the dielectric constant are obtained under conditions that promote the formation of particles larger than about 200 nm.