Growth inhibitor to homogenize nucleation and obtain smooth HfB₂ thin films by chemical vapor deposition

We describe an example of a new phenomenon: the use of a growth inhibitor to homogenize nucleation and improve the smoothness of a thin film deposited by chemical vapor deposition. For many film-substrate combinations, the rate of nucleation on the substrate is slow relative to the growth rate, a situation that produces a broad distribution of island sizes and a rough surface morphology. We show an example in which this outcome is avoided by directing a second component onto the substrate that has little effect on the nucleation rate but significantly retards the island growth rate. The case studied is the growth of HfB₂ films on SiO₂ substrates using the chemical vapor deposition precursor Hf(BH₄)₄ with NH₃ as the inhibitor. The addition of the inhibitor increases the island density at coalescence by 50× and decreases the roughness by 10× to the subnm range. We suggest that the use of inhibitors to homogenize nucleation may be applicable to other film-substrate combinations.