Seamless fill of deep trenches by chemical vapor deposition: Use of a molecular growth inhibitor to eliminate pinch-off

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 HfO ₂ from the precursor tetrakis(dimethylamino)hafnium and a forward-directed flux of H ₂ O 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 HfO ₂ 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 HfO ₂ 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 HfO ₂ in trenches with aspect ratios as large as 10.