Thin films of molybdenum carbonitride, MoCxNy, are deposited by low temperature chemical vapor deposition from Mo(CO)6 and NH3 in the temperature range 150–300 °C. At a substrate temperature of 200 °C and Mo(CO)6 pressure of 0.01 mTorr, the composition varies from MoC0.48N0.20 to MoC0.36N0.33 (i.e., greater nitrogen and less carbon content) upon increasing the ammonia pressure from 0.3 to 3.3 mTorr. At a constant Mo(CO)6 pressure of 0.01 mTorr and an NH3 pressure of 2 mTorr, the composition varies from MoC0.50N0.30 to MoC0.12N0.40 with increasing substrate temperature from 150 to 300 °C. Selected films grown at substrate temperatures of 150, 200, and 250 °C are superconducting with critical temperatures of 4.7, 4.5, and 5.2 K, respectively. Grazing incidence x-ray diffraction data indicate that the films are crystalline and isomorphous with the cubic phases of Mo2N and Mo2C. With a forward-directed flux of precursors toward the surface, film growth is highly conformal in microtrenches of aspect ratio 6, with step coverages of ∼0.85 and 0.80 at growth temperatures of 150 and 200 °C, respectively.
Three-dimensional nanodevice architectures require the coating and filling of deep vias and trenches, leading to an ongoing demand for dry processes with step coverages equal to or greater than one. We describe a new superconformal chemical vapor deposition process based on the use of two precursors: The first precursor readily deposits to afford film growth, but it cannot fill trenches when used alone because the coating is subconformal. The second precursor inhibits the deposition rate of the first precursor, and it grows film relatively slowly so that the overall film growth rate decreases when both precursors are present. In a trench, the inhibitor significantly suppresses the growth rate at the trench opening, but its pressure declines with depth due to consumption (film growth on the sidewalls) and the suppression effect weakens. Near the opening of the trench, where the inhibitor pressure is high, the consumption rate of the first precursor is small; it, therefore, diffuses deep into the trench to afford a growth rate that increases toward the bottom. If the flux of the inhibitor is not too high and the uninhibited growth rate of the first precursor is larger than that of the inhibitor, then the resulting film will be superconformal. We demonstrate this superconformal process for the growth of a metallic ceramic alloy, Hf1−xVxBy, in which the vanadium-bearing precursor serves as the consumable inhibitor. A continuous, single-step process is used to fill trenches with aspect ratios up to 10 with no void or seam along the centerline. We develop a model that captures the trench filling kinetics using Langmuirian growth kinetics, in which the two precursors compete for available adsorption sites and have different reaction rates. Calculations using physically plausible model parameters agree well with measured results and can be used to predict filling as a function of the aspect ratio. The model also indicates why filling fails at very high aspect ratios. In principle, a superconformal film of constant composition could be obtained using two precursors that each afford the same material.
We describe a convenient and broadly applicable method that affords the superconformal growth of films in trenches and other recessed features by chemical vapor deposition, here applied to the growth of the metal diborides CrB2 and HfB2. A flux of atomic hydrogen or nitrogen, generated by a remote plasma source, strongly inhibits growth near the feature opening, possibly by tying up dangling bonds. In a trench, the flux of atomic species declines rapidly with depth due to wall reactions, either by recombination to afford inactive H2 or N2 or incorporation into the film. As a result, the inhibition effect decreases with depth, and the growth is almost uninhibited toward the bottom of the feature. These circumstances produce a superconformal, “V-shaped” growth profile with the vertex toward the bottom. With continued deposition, the vertex moves up and out of the feature without pinch-off, i.e., no void or seam. The use of atomic hydrogen as the inhibitor of the CrB2 growth introduces no significant impurities and does not alter the film stoichiometry, in contrast, atomic nitrogen becomes incorporated into the HfB2 film. A model of the trench filling is developed, which uses lumped kinetic parameters to calculate the film growth rate and the Knudsen diffusion to calculate transport down the axis of the trench. Model calculations agree well with experimental film thickness profiles as a function of growth time, showing that the model can be used to determine the optimal inhibitor flux as a function of the trench aspect ratio. This method should be applicable to the superconformal growth of a wide variety of film compositions as well.
Ultrathin, pinhole-free, and atomically smooth films are essential for future development in microelectronic devices. However, film morphology and minimum thickness are compromised when growth begins with the formation of islands on the substrate, which is the case for atomic layer deposition or chemical vapor deposition (CVD) on relatively unreactive substrates. Film morphology at the point of coalescence is a function of several microscopic factors, which lead to measurable, macroscopic rates of island nucleation and growth. To quantify the effect of these rates on the morphology at the point of coalescence, we construct two models: (1) a Monte Carlo simulation generates the film height profile from spatially random nucleation events and a constant island growth rate; simulated films resemble AFM images of the physical films; (2) an analytical model uses Poisson point statistics to determine the film thickness required to cover the last bare site on the substrate as a function of the nucleation rate and growth rate. Both models predict the same maximum thickness required to reach 99% coverage and reveal a power law relationship between the maximum thickness and the ratio of the nucleation rate divided by the growth rate. The Monte Carlo simulation further shows that the roughness scales linearly with thickness at coverages below 100%. The results match well with experimental data for the low-temperature CVD of HfB2 on Al2O3 substrates, but there are significant discrepancies on SiO2 substrates, which indicate that additional surface mechanisms must play a role.
Although it has long been known that metal-containing compounds can serve as catalysts for chemical vapor deposition (CVD) of films from other precursors, we show that metal-containing compounds can also inhibit CVD nucleation or growth. For two precursors A and B with growth onset temperatures TgA < TgB when used independently, it is possible that B can inhibit growth from A when the two precursors are coflowed onto a substrate at a temperature (T) where TgA < T < TgB. Here, we consider three precursors: AlH3⋅NMe3 (Tg = 130 °C, Me = CH3), Hf(BH4)4 (Tg = 170 °C), and AlMe3 (Tg = 300 °C). We find that (i) nucleation of Al from AlH3⋅NMe3 is inhibited by Hf(BH4)4 at 150 °C on two oxide surfaces (Si with native oxide and borosilicate glass), (ii) nucleation and growth of HfB2 is inhibited by AlMe3 at 250 °C on native oxide substrates and on HfB2 nuclei, and (iii) nucleation of Al from AlH3⋅NMe3 is inhibited by AlMe3 at 200 °C on native oxide substrates. Inhibition by Hf(BH4)4 is transient and persists only as long as its coflow is maintained; in contrast, AlMe3 inhibition of HfB2 growth is more permanent and continues after coflow is halted. As a result of nucleation inhibition, AlMe3 coflow enhances selectivity for HfB2 deposition on Au (growth) over Al2O3 (nongrowth) surfaces, and Hf(BH4)4 coflow makes it possible to deposit Al on Al nuclei and not on the surrounding oxide substrate. We propose the following criteria to identify candidate molecules for other precursor–inhibitor combinations: (i) the potential inhibitor should have a higher Tg than the desired film precursor, (ii) the potential inhibitor should be unreactive toward the desired film precursor, and (iii) at the desired growth temperature, the potential inhibitor should adsorb strongly enough to form a saturated monolayer on the intended nongrowth surface at accessible inhibitor pressures.
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