Chemical routes to ultra thin films for copper barriers and liners

Ruthenium shows considerable potential as a seed layer and adhesion layer in advanced metallization schemes and may also function, alone or in concert with an under layer, as a copper diffusion barrier. Microstructure and thickness uniformity are key film parameters. This talk describes the use of alloying constituents to force the growth of amorphous ruthenium films and to stabilize the amorphous films that are grown, and describes the surface chemistry that controls film growth on amorphous and polycrystalline substrates. In general, Ru films are polycrystalline because of Ru's high surface energy, which results in a 3D, Volmer-Weber growth mode. Extending insight into amorphous structure gained from the bulk metallic glass literature one can anticipate that Ru will form various coordination polyhedra with metalloids, such as boron and phosphorus. Provided these polyhedra form during atomic layer deposition or chemical vapor deposition, an amorphous thin film should grow. This talk presents the growth and stability of amorphous Ru-P alloy films through the use of single source precursors, such as cii-ruthenium(II)dihydridotetrakis- (trimethylphosphine), cis-RuH₂(PMe₃)₄ [1] and dual sources such as Ru₃(CO) 12 and P(C₆H ₅)₃ or PMe₃ [2]. The films contain zero-valent Ru and P. Ab initio molecular dynamics calculations show that Ru-P alloys with moderate P content (∼20%) can result in a glassy structure exhibiting topological and strong chemical short-range order. In the RU₈₀P ₂₀ structure, the P-centered polyhedra prefer the tri-capped trigonal prism packing phase with Veronoi index <0,3,6,0> [1]. In addition, the Ru-P system shows the medium-range order arising from packing the "quasi-equivalent" P-centered Ru clusters in three-dimensional space. The structural model based on melt-quenching simulations support the experimental results that find ~ 13-15 % P is required to produce an amorphous film. Surface studies suggest the trimethylphosphine ligands from cis-RuH ₂(PMe₃)₄ undergo demethylation and desorb at the growth conditions and readsorb, and subsequently incorporate the P into the Ru film [1]. These studies led to an exploration of dual sources, Ru ₃(CO)₁₂ for Ru and P(CH₃)₃ for P that reinforced the results that about 15% P is required to form the amorphous microstructure. Carbon levels are difficult to establish with Ru and high resolution X-ray photoelectron spectroscopy studies with a monochromatic source and fitting routines that lead to zero percent carbon in a Ru standard, result in the C levels in listed Table 1. Film properties, such as resistivity, are related most to the C level and secondarily to the crystallinity. Resistivity increases with C content. Calculations suggest less boron (∼10%) than phosphorus (&sim20%) would be required to form a stable amorphous alloy with ruthenium.