Plasma deposited fluorocarbon films have received considerable attention recently as potential interlevel dielectrics for future generation integrated circuits (ICs). 1,2 Apart from their low dielectric constant (<2.6), they also possess other favorable characteristics such as low moisture absorption, high chemical inertness, and plasma-assisted conformal step coverage. In this study, the effect of applied power and substrate temperature on the chemical structure, chemical composition, and thermal stability of the plasma-deposited fluorocarbon films was investigated by means of X-ray photoelectron spectroscopy (XPS), IR spectroscopy, and thermogravimetric analysis (TGA). The monomer studied, pentafluoroethane (CF 3 CHF 2 ), was selected because of its shorter atmospheric lifetime relative to that of pure fluorocarbon gases. Experimental A parallel-plate radio frequency (rf) plasma reactor was used for the deposition of fluorocarbon films from pentafluoroethane/argon mixtures. Details of the reactor setup and operation are given elsewhere, 7 so only a brief description is presented here. The distance between the 4 cm diam, parallel-plate, stainless steel disk electrodes was fixed at 2.9 cm for all experiments. RF power at 13.56 MHz from an ENI power systems HF-300 rf generator was coupled to the top electrode using a Heathkit SA-2060A antenna tuner. Substrates were placed on the grounded electrode whose temperature was regulated with a Syskon RKC temperature controller. Depositions were carried out at substrate temperatures of 120, 180, and 210ЊC, and a constant operating pressure of 1 Torr. The flow rates of pentafluoroethane and argon were set at 20 and 75 sccm, respectively, for all depositions. In some cases, films deposited at a specific substrate or deposition temperature were heated to 200ЊC in the reactor immediately after deposition and held there for 2 h in vacuum. In the following discussions, this heat-treatment of the deposited films in vacuum is referred to as postdeposition annealing. In this study, films deposited onto both the temperature-controlled, grounded electrode and the powered electrode without temperature control, were characterized by various analytical techniques including TGA, IR, XPS, and mass spectrometry. IR spectra of the deposited films were collected in reflection mode at a grazing angle of 70Њ using a Nicolet Magna-IR 560 Fourier transform infrared (FTIR) spectrometer. All spectra were recorded at a resolution of 4 cm Ϫ1 and averaged over 512 scans. In order to improve the signal-to-noise ratio, fluorocarbon films were deposited onto silicon substrates that had been sputter coated with a 300 nm layer of aluminum. Films deposited on the powered electrode were analyzed directly on the stainless steel powered electrode. XPS was used to obtain the chemical composition and bonding structure of polymer films. Spectra were collected using a PHI model 1600 XPS system equipped with a monochromator. The sample was exposed to monochromatized Al K␣ X-rays, and the ejected photoelectrons were detected by a multichannel hemispherical detector that provided high-energy sensitivity and resolution. Chamber pressure was typically below 5 ϫ 10 Ϫ9 Torr during analysis. High-resolution spectra were collected for C 1s, O 1s, N 1s, and F 1s Fluorocarbon films were deposited from pentafluoroethane/argon mixtures in a parallel-plate reactor at a pressure of 1 Torr and substrate temperatures between 120 and 210ЊC. Films deposited on substrates placed on the heated, grounded electrode as well as films formed on the powered electrode were analyzed using infrared spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). Polymer deposition rates decreased with an increase in substrate temperature indicating that reactant adsorption is the rate-limiting step. Films deposited on the powered electrode had an O/C ratio of 0.14, which was significantly higher than that of films deposited on the grounded electrode at elevated temperatures. Likewise, IR spectra of films on the powered electrode also showed significant contributions from CϭO related groups. TGA data indicated that the powered electrode films had ϳ3% weight loss at 250ЊC, while films deposited on the grounded electrode had ϳ1% weight loss at 250ЊC. The thermal stability of films deposited on the grounded electrode was significantly enhanced when deposited at higher substrate temperatures. XPS analyses indicated a decrease in the F/C ratio of the deposited films with an increase in substrate temperature. TGA analyses indicated that weight loss below 250ЊC was due primarily to the outgassing of low-molecular weight species from the fluorocarbon films. The higher weight loss region between 320 and 425ЊC was ascribed to polymer degradation due to scission of main chain C-C bonds and to evolution of HF and CO 2
