We have compared the step coverage of plasma enhanced chemical vapor deposition tetraethylorthosilicate films of microwave downstream, high frequency radio frequency (rf), and low frequency rf depositions. The microwave-downstream deposition, characterized by bimolecular surface reactions, produces a conformal step coverage. The rf depositions with ion-induced surface reactions produce a low sidewall, high bottom coverage. The chemical radical and the ion effects on the step coverage are discussed.
The effects of nitrous oxide plasma surface treatment of fluorinated silica glass (FSG) films were investigated to improve film stability and adhesion properties. FSG films with varying fluorine concentrations were deposited using plasma‐enhanced chemical vapor deposition (PECVD), then exposed to a nitrous oxide plasma to modify the surface. Treated films were boiled to study the moisture absorption, and subsequent depositions of foreign passivation films such as silicon nitride, silicon oxynitride, etc., were used to study the changes in adhesion characteristics. It was found that plasma treatments under certain conditions could enhance the adhesion characteristics of films with higher fluorine dopant levels but did not measurably change the moisture resistance of the films. The effects of the plasma treatment were confined to the surface and did not measurably effect the bulk properties of the film. The effects of the nitrous oxide plasma treatment of PECVD FSG films are presented along with proposed mechanisms to explain the effects.
The coupled effect of molecular scattering and surface-activated reactions on low-pressure chemical vapor deposition (LPCVD) film conformality is investigated. Using a single-precursor two-step surface-activated deposition as an example, film conformality can be found to depend on two first-principle dimensionless parameters-Sc, the intrinsic sticking coefficient, and Sa, the surface saturation factor. An analytical integral material balance formulation, developed for the feature-scale molecular transport, is solved numerically in a wide range ofSc and Sa. The results show that film conformality generally improves with decreasing Sc and increasing Sa. With Sc fixed in most LPCVD processes (due to the nature of the precursor species), the ability to control Sa in the process becomes the key to conformal deposition. The intrinsic surface-activated deposition rate expression shows no apparent reaction order. Therefore, previously reported Monte Carlo schemes and integral-differential models employing a single sticking parameter or a fixed reaction order to characterize LPCVD step coverage behavior are applicable only in limited cases. The two-parameter model has been found useful in understanding the H 2 -reduced tungsten CVD process, for which the first-principle parameters can be determined from kinetic data reported in the literature. 78
We have studied the chemical and physical properties of silicon oxide films plasma deposited from TEOS ( tetraethoxysilane), to gain an understanding of the origins of (1) step coverage and (2) film stability. TEOS was diluted in helium /oxygen mixtures and deposited as a function of discharge frequency (150 kHz and 14 MHz) and 02 flow in a parallel plate reactor. The typical deposition conditions were 1 torr total pressure, 320 °C substrate temperature, 1 -9% TEOS, 1 -80% 02, and -0.1 W /cm2 discharge power. Films deposited at high frequency with excess oxygen were generally oxygen -rich, chemically unstable and hygroscopic, while films deposited at low frequency were stable to moisture and slightly deficient in oxygen. However, coverage profiles of high frequency films showed an unusual degree of directionality, which could be used to advantage for the coating of high aspect ratio features. We suggest that a judicious combination of high and low frequency discharges may improve film properties while maintaining directional step coverage.Isotopic labeling experiments were performed using 1602 to gain insight into the origins of the oxygen that is contained in these PECVD films. Complete isotopic scrambling was not observed. Film composition data suggest that there is one tenacious Si -160 bond which remains with the silicon from the original TEOS molecule during the reaction to form SiO2.
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