Ru nucleation and thin film smoothness improvement with ammonia during chemical vapor deposition

Abstract

This study reports the use of ammonia to inhibit the growth of previously nucleated ruthenium islands and force the nucleation of additional islands such that thinner films form as the islands coalesce with continued growth. Ruthenium films are grown at 448 K in a chemical vapor deposition process on SiO2/Si(001) using triruthenium dodecacarbonyl, Ru3(CO)12, with and without a constant partial pressure of ammonia. Film growth was performed at a Ru3(CO)12/Ar pressure of 47.2 mTorr. The ammonia partial pressure varied from 0 to 27.8 mTorr. X-ray photoelectron spectroscopy was used to analyze the samples in situ. Ex situ characterization included scanning electron microscopy, atomic force microscopy, and x-ray diffraction and x-ray reflectivity. Nucleation studies limited to the first 10 min of growth revealed the maximum nanoparticle (island) density of 8.1 × 1011 cm−2 occurred at an intermediate ammonia pressure (5.25 mTorr) compared to a density of 3.1 × 1011 cm−2 for no ammonia addition. Extending film growth to 120 min and varying the ammonia partial pressure during the first 10 min followed by 5.25 mTorr ammonia pressure for the final 110 min reveals the importance of nucleation on film smoothness. A model describing the inhibition effects of ammonia during nucleation and growth is presented.