First-principles predictions of ruthenium-phosphorus and ruthenium-boron glassy structures and chemical vapor deposition of thin amorphous ruthenium-boron alloy films

First-principles density-functional calculations are presented revealing 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. 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) alloys is examined along with local atomic ordering in the amorphous alloys. The growth of ultrathin (3 nm) amorphous Ru(B) alloy films of varying B concentration via chemical vapor deposition is explored using Ru₃(CO)₁₂ and B₂H₆ as the Ru and B sources, respectively. Experiments reveal the films grown at 250 °C are amorphous at B contents in excess of 15 at.% and polycrystalline below 10 at.% B, consistent with first-principles predictions. Amorphous Ru(B) films remain amorphous following annealing at 450 °C and become polycrystalline at 500 °C. Film resistivity ranged from 40 to 120 μΩ-cm and was independent of B loading. Electric field stress tests to failure for Cu/3-nm Ru(B)/SiO₂/Si stacks are used to indicate suitability of Ru(B) as a copper diffusion barrier layer.