Materials science of Ru and Ru alloy thin films for barrier applications

Abstract

We report strategies to realize ultra-thin Ru films grown by chemical vapor deposition (CVD) on oxide substrates that include incorporating amorphizing elements - boron and phosphorus - and introducing light molecules - CO and NH3 - that interact reversibly with the Ru surface and force additional nucleation events on the oxide substrate. First-principles density-functional calculations reveal that Ru(P) and Ru(B) alloys with moderate P or B content can result in a glassy structure exhibiting strong chemical short-to-medium range order. In the low P or B content region amorphous phases are predicted to be energetically more favorable than the crystalline counterparts for the Ru(P) and Ru(B) alloys above ∼20 at.% P and ∼10 at.% B. The relative stability of amorphous and crystalline Ru(B) and Ru(P) alloys is examined computationally along with local atomic ordering in the amorphous alloys. The growth of ultrathin (3nm) amorphous Ru(B) and Ru(P) alloy films of varying B and P concentration via chemical vapor deposition using Ru3(CO)12 and B2H6 or PH3 as the Ru, B and P sources, respectively, is summarized. Electric field stress tests to failure are used to evaluate Cu diffusion capabilities for 3nm amorphous Ru alloys. Chemical approaches are reported that increase island nucleation density by suppressing precursor reaction/growth on existing islands using inhibitors that can block adsorption of the metal precursor on exposed metal surfaces and thereby lead to growth of ultra-thin metal films. Film growth studies with Ru3(CO)12 and Ru(tBu-Me-amd)2(CO)2 precursors and CO and NH3 are reported on thermal oxide substrates. Carbon monoxide adsorbs reversibly to Ru surfaces in the temperature range of precursor decomposition and Ru film growth (423–673 K). By adjusting the CO pressure during nucleation and growth stages, nucleation density can be increased by a factor of two and film roughness can be reduced by a factor of two. Ammonia adsorbs dissociatively on Ru and the surface is nearly saturated with adsorbed nitrogen, Nads, which inhibits growth on nucleated islands. Nucleation density increases by nearly a factor of three and film roughness can be reduced by a factor of two depending on the partial pressure of NH3 added during nucleation and growth. Ammonia has the added benefit of reducing the crystalline nature of the Ru films.