Comparison of plasma chemistries and structure-property relationships of fluorocarbon films deposited from octafluorocyclobutane and pentafluoroethane monomers

Fluorocarbon films are deposited from mixtures of pentafluoroethane (PFE)/a rgon and octafluorocyclobutane/argon in a parallel plate reactor at pressur es of 0.75 and 1 Torr and substrate temperatures between 120 and 240 degree sC. These monomers are compared in terms of plasma dissociation chemistries as well as chemical structure and properties (electrical, thermal, chemica l, and optical) of the resulting films. Deposition rates with C4F8 are sign ificantly higher than CF3CHF2. With both monomers, the deposition rate decr eases with an increase in substrate temperature. indicative of an adsorptio n limited process. Films deposited from both monomers are analyzed using Fo urier transform infrared spectroscopy, x-ray photoelectron spectroscopy (XP S). thermogravimetric analysis (TGA), and capacitance measurements. XPS ana lyses indicate a higher flourine to carbon ratio for films deposited from C 4F8. Likewise, these films have lower refractive indices (n similar to 1.38 -1.39) and lower dielectric constants (k similar to 2.18-2.33) than PFE fil ms (n = 1.41, k = 2.23-2.55). Films deposited from both monomers exhibit hi gh dielectric losses ( similar to 10(-2) - 10(-3)) at deposition temperatur es > 200 degreesC. TGA analyses of films deposited from both monomers indic ate comparable thermal stabilities up to a temperature of 300 degreesC. How ever, the decomposition rate is much higher for C4F8 films in the temperatu re range between 300 and 425 degreesC. Thermal stability of films deposited from both monomers is enhanced at higher deposition temperatures. However, the sensitivity of thermal stability to deposition temperature is lower fo r films deposited from C4F8. A tradeoff exists between the electrical prope rties and thermal stability of films deposited from both monomers. (C) 2001 American American Society.