UC San Diego

With continued scaling of transistors in integrated circuits to smaller dimensions for denser chips, demands rise for a conductive back end of the line (BEOL) interconnect metal in confined dimensions. The current interconnect, copper, requires an additional liner layer to prevent diffusion into low-k dielectrics, which increases the overall resistivity. In contrast, ruthenium metal has been seen as a promising candidate to replace copper due to its competitive resistivity in confined dimensions as well as its resistance to electromigration thus not needing a liner layer. Atomic layer deposition (ALD) as a growth method is of particular interest due to its ability to deposit conformal films. In this work, variations of ALD processes were developed for the growth of low-resistivity Ru metal using various precursor chemistries. In Chapter 1, the role of dose optimization in ALD process development for low resistivity Ru was investigated. Ru ALD using the dicarbonyl-bis(5-methyl-2, 4-hexanediketonato) Ru(II) precursor, Ru(IHD)2(CO)2 (“Carish”) precursor with O2/He as a co-reactant was performed. Dose optimization beyond growth saturation was done to optimize for the lowest resistivity metal film around 9.9 µΩ·cm. This study demonstrated that lower resistivity values can be achieved for metal films grown with dose conditions past the saturation point. Chapter two describes atomic layer deposition of Ru metal with the Ru(CpEt)2 precursor in combination with O2/He as co-reactant to achieve near bulk-like resistivity values as low as 6.5 µΩ·cm. However, this process showed a large nucleation delay on SiO2 , which results in a large interfacial roughness making XRR film thickness quantification difficult. To ameliorate this issue, a seed layer of RuC was first deposited via another ALD process using the Ru(DMBD)(CO)3 precursor with TBA as the co-reactant. The RuC can then be converted to Ru metal after forming gas anneal (FGA). Following that, Ru ALD via the Ru(CpEt)2 precursor could be performed for a low resistivity film. The composite films after deposition, however, require another post-deposition forming gas anneal to lower resistivity values close to bulk values at 6.9 µΩ·cm. ` Chapter three describes using a sputtered Ru seed layer instead of the RuC layer via ALD. The reverse-templating effects of growing ALD Ru on top of a sputtered Ru layer is investigated. A resistivity value as low as 7.1 µΩ·cm was achieved for a 2nm sputtered Ru film with 500 cycles of ALD Ru on top. Varying ratios of sputtered Ru to ALD Ru were tested across different samples to combine both the smooth interface of a sputtered Ru film with the low resistivity of an ALD Ru film.