Polyimide and polyphenylquinoxaline are important dielectric materials used in microelectronics fabrication. These polymers could be used even more extensively if they had greater moisture resistance. We demonstrate that plasma processing techniques can be used to improve the moisture resistance of polyimide and polyphenylquinoxaline films. Films are exposed to nitrogen trifluoride plasmas to introduce fluorine into the surface of the polymers. Fluorination is monitored with x-ray photoelectron spectroscopy and Fourier-transform infrared absorption spectroscopy. Water-contact angle measurements are used to assess the hydrophobicity of the treated surfaces. The polyimide and polyphenylquinoxaline film surfaces are quickly fluorinated during plasma exposure, and the moisture resistance improves consequently. The water-contact angle of our best film, 102°, compares favorably with polytetrafluoroethylene (109°). Plasma conditions can be controlled to minimize polymer degradation. The polyphenylquinoxaline films are etched by less than 0.01 μm/min in these experiments. Spectroscopic studies show that the aromatic carbons in the polymers are more readily fluorinated than carbonyl group carbons, and that the fluorination is restricted to the surface.

The effects of Ar, H2/Ar, 02/Ar, and H2/02/Ar downstream microwave plasmas on the surface structure and properties of polyvinyl chloride films are described. Plasma-polymer surfaces interactions are monitored using in situ infrared reflection-absorption spectroscopy. The influence of downstream microwave plasma conditions (e.g., pressure, gas composition, irradition time) on polymer surfaces are studied, in either the direct or the indirect exposure configuration. Indirect downstream microwave H2/02/Ar plasma exposures under appropriate conditions do not alter polymer surfaces to the detection limit of the infrared technique. Complementary results are provided by pressure changes in the plasma reactor system, water contact angle measurements, and surface morphology studies on polymer surfaces using atomic force microscopy. The results of similar plasma treatments on polyethylene surfaces are described briefly.

We demonstrate a means of controlling the microstructure and carbon content in amorphous hydrogenated silicon carbide (a-SiC:H) thin films prepared in a plasma-enhanced chemical vapor deposition system. The capacitively coupled, parallel-plate deposition apparatus includes provision for adjusting the potential of the powered electrode by application of an additional, independent dc voltage. This voltage affects the deposition chemistry. Films prepared when various positive and negative dc voltages are applied are studied with infrared absorption, nuclear magnetic resonance, and electron spin resonance. Their optical band gaps, electrical conductivities, and dark conductivity activation energies are also measured. The films have carbon contents ranging from 1 to 4 at. %. We find that we can alter the microstructure of a-SiC:H by adjusting the powered-electrode potential during deposition, and that these microstructural changes are reflected in the film properties. A small increase in the self-biased voltage of the powered electrode leads to a film with the least amount of infrared-observable microstructure and the highest photoconductivity. Applying an external dc voltage leads to an increase in deposition rate regardless of voltage polarity. The films prepared with externally applied voltage all have lower hydrogen contents than the film prepared with self-biased voltage, which may explain the observed property changes. The addition of an external dc voltage can have beneficial effects on the deposition rate, structure, and properties of a-SiC:H films.

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Alloying amorphous hydrogenated silicon with carbon, although increasing the optical band gap, results in a dramatic increase in the number of paramagnetic defects and subsequent deterioration of optoelectronic properties. Electron-nuclear double-resonance and electron spin resonance studies of "Cenriched materials provide a picture of how unpaired electrons, silicon atoms, and carbon atoms relate to each other in the alloys. We report the observation of weak hyperfine interactions originating from ' C and Si nuclei which are about two bond lengths away from the unpaired electrons. The absence of stronger interactions between unpaired electrons and ' C nuclei indicates that carbon dangling bonds do not exist, even in materials with a high level of paramagnetic defects. We suggest a model involving dangling-bond migration and carbon-double-bond formation to explain these results.