Robust TaNx diffusion barrier for Cu-interconnect technology with subnanometer thickness by metal-organic plasma-enhanced atomic layer deposition

Abstract

Ta N x diffusion barriers with good barrier properties at subnanometer thickness were deposited by plasma-enhanced atomic layer deposition (PE-ALD) from pentakis(dimethylamino)Ta. Hydrogen and/or nitrogen plasma was used as reactants to produce TaNx thin films with a different nitrogen content. The film properties including the carbon and oxygen impurity content were affected by the nitrogen flow during the process. The deposited film has nanocrystalline grains with hydrogen-only plasma, while the amorphous structure was obtained for nitrogen plasma. The diffusion barrier properties of deposited TaN films for Cu interconnects have been studied by thermal stress test based on synchrotron x-ray diffraction. The results indicate that the PE-ALD TaN films are good diffusion barriers even at a small thickness as 0.6nm. Better diffusion barrier properties were obtained for higher nitrogen content. Based on a diffusion kinetics analysis, the nanocrystalline microstructure of the films was responsible for the better diffusion barrier properties compared to polycrystalline PE-ALD TaN films deposited from TaCl5.

Synthesis and in situ characterization of low-resistivity TaNx films by remote plasma atomic layer deposition

“…4,36 They calculated the growth rate ͑0.03 nm/ cycle͒ from RBS measurements using the bulk mass density of cubic TaN ͑15.9 g cm −3 ͒, 37 which is expected to be a higher limit for thin TaN x films deposited by ALD. Assuming a similar mass density for their films as obtained by our work ͑see Table I͒ leads to growth rates per cycle for their experiments that are in good agreement with our results.…”

“…Due to its layer-by-layer growth, atomic layer deposition ͑ALD͒ is believed to be the method of choice for deposition in demanding 3D features. 4,[8][9][10] Sequentially employing two self-limiting surface reactions, a submonolayer of material is deposited per ALD cycle and the process is proven to yield excellent uniformity and conformality. [11][12][13] Since different TaN x crystal phases exist including low-resistivity cubic TaN and very-high-resistivity Ta 3 N 5 , 14 successful integration of TaN x films synthesized by ALD requires control over film stoichiometry and composition.…”

“…Several precursors are commercially available for ALD of TaN x films, such as Ta͓N͑CH 3 ͒ 2 ͔ 5 ͑PDMAT͒, 4 Ta ͓N͑C 2 H 5 ͒ 2 ͔ 3 NC͑CH 3 ͒ 3 ͑TBTDET͒, 15 Ta͓NC͑CH 3 ͒ 2 C 2 H 5 ͔ ͓N͑CH 3 ͒ 2 ͔ 3 , 16 TaCl 5 , 10,17 and TaF 5 . 18 For many applications metal-organic precursors are preferred over metal-halide precursors due to potential problems in reliability posed by halide impurities in the film.…”

“…18 For many applications metal-organic precursors are preferred over metal-halide precursors due to potential problems in reliability posed by halide impurities in the film. 4 In order to deposit the conductive TaN x phase, the oxidation state of the Ta atom in the precursor ͑+5 in most precursors͒ has to be reduced to oxidation state +3. Using the PDMAT precursor with NH 3 in a thermal ALD process, Travaly et al observed that the high-resistivity Ta 3 N 5 phase was deposited.…”

“…TaN is considered as a candidate to replace the poly-Si gate in metal-oxidesemiconductor field effect transistors, 1 as metal electrode in high-density three dimensional ͑3D͒ capacitors, 2 and as Cu diffusion barrier [3][4][5] and possible liner material for interconnect technology. 6,7 In addition to a high level of growth control, several applications require conformal deposition in high-aspect ratio structures, which is a requirement beyond reach of current physical vapor deposition ͑PVD͒ techniques.…”