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This paper provides a detailed analysis of the deposition of iron by chemical vapor deposition from the well-known precursor iron pentacarbonyl, Fe(CO)5. The authors show that at a constant temperature (e.g., 300 °C) the growth rate decreases monotonically with time. Growth eventually ceases altogether at a certain film thickness and cannot restart, even under conditions that are favorable for nucleation. The authors propose that the reduction in Fe deposition rate observed here and in previous studies results from surface poisoning: the dissociative chemisorption of CO molecules on the Fe surface at elevated temperature forms inactive surface species, especially graphitic carbon, which accumulate on the surface and eventually stop Fe growth. Remarkably, the surface poisoning effect can be inhibited, so that Fe deposition occurs at a constant rate with no self-limiting growth behavior, by coflowing NH3 along with the Fe(CO)5 precursor during growth. The adsorbed NH3 inhibits CO chemisorption by displacing CO from the growth surface and inhibiting CO chemisorption. The resulting Fe films are of high purity, i.e., carbon and nitrogen contents each below 1 at. %.

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Attempts to fill deep trenches by chemical vapor deposition often result in a “bread-loaf” profile, an overhang near the trench opening that arises whenever the growth rate is slightly higher near the opening than deeper in the feature. Continued growth leads to premature pinch-off at the opening, which leaves an undesirable void or seam along the centerline. Bread-loaf profiles can form even under superconformal growth conditions, as the authors recently found for the growth of HfO2 from the precursor tetrakis(dimethylamino)hafnium and a forward-directed flux of H2O coreactant. The current paper describes a method that can reduce or eliminate the bread-loaf problem: addition of an isotropic flow of a reactant that inhibits growth near the trench opening but leaves the growth rate unchanged deeper in the trench. A Markov chain model for ballistic transport of the inhibitor inside trenches is developed to account for this behavior: the model reveals that suppression of a bread-loaf profile is best accomplished with growth inhibitors that have a high sticking probability (>0.1 per wall collision) and that are consumed during growth. Four molecules are investigated as potential inhibitors during HfO2 growth: tris(dimethylamino)silane, 3DMAS; methoxytrimethylsilane, MOTMS; hexafluoroacetylacetone, H(hfac); and acetylacetone, H(acac). The molecules 3DMAS and MOTMS inhibit growth but do so everywhere. As a result, they improve conformality, but are unable to eliminate the bread-loaf profile. In contrast, relatively small partial pressures (fluxes) of H(hfac) or H(acac) strongly inhibit HfO2 growth and do so selectively on the upper substrate surface and near trench openings. In conjunction with the use of a forward-directed water flux that affords superconformal growth, the use of H(hfac) or H(acac) enables seamless fill of HfO2 in trenches with aspect ratios as large as 10.