Paper TF+AS+SE+SS-MoA4
The Chemistry of the Cu(I) s-Butyl Amidinate Atomic Layer Deposition (ALD) Precursor on Ni and Cu Surfaces

Monday, October 28, 2013, 3:00 pm, Room 104 A

Thanks to the self-limiting and complementary nature of the reactions involved, atomic layer deposition (ALD) has become a promising method for making uniform and conformal thin films . Cu(I) amidinates have been introduced in recent years as promising precursors for the ALD of copper interconnects. An understanding of the surface chemistry of these copper(I) amidinates is essential to the design of the corresponding ALD processes. Here we report the results from our studies on the surface chemistry of Cu(I) s-butyl amidinate on Ni and Cu surfaces using X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD).

It was determined that, on Ni surfaces, the reduction of Cu(I) to metallic Cu happens already at room temperature. The Cu(I) s-butyl amidinate adsorbs dissociatively on those Ni surfaces, and decompose thermally to produce H₂, HCN and N₂, at about 500 K, 570 K and 830 K, respectively. After annealing to temperatures above 800 K, all N-containing species desorb as HCN or N₂, but some carbon left on the surface. It was found that Cu (I) s-butyl amidinate adsorption on Ni between 300 K and 400 K is self-limited, with an estimated Cu saturation coverage of 0.15 ML, but switches above 500 K to a behavior where continuous copper deposition occurs, as typically seen in chemical vapor deposition (CVD) processes. It was also found that surface oxygen on Ni substrates exerts a great effect on the surface chemistry of the Cu precursor. On oxygen covered Ni surface, the Cu(I) reduction to metallic Cu only happens above 500 K, at which point the Ni surface oxide is reduced by the organic surface species that result from Cu(I) s-butyl amidinate adsorption to form H₂O and CO₂. The presence of surface oxygen greatly reduces the carbon deposition in the annealing process.

On Cu surfaces, which form after several ALD cycles on any substrate, the Cu(I) s-butyl amidinate precursor shows less activity than on Ni surfaces. The molecule adsorbs molecularly on Cu at 300 K, and the Cu(I) center is reduced to metallic Cu only after annealing above 500 K. Chemisorbed Cu (I) s-butyl amidinate starts to dissociate at about 460 K, via the breaking of a C-N bond and the formation of pyrrolaminium (C₄H₇N₂) and butene. H₂ desorption is detected at about 510 K, and HCN and N₂ desorption above 800 K. As on Ni surfaces, self-limited copper uptake on Cu substrates takes place between 300 K and 400 K, with an estimated Cu saturation coverage of 0.06 ML, and changes to CVD above 500 K. On O/Cu(110), H₂O desorption peaks at 470 K and a broad CO₂ desorption feature is seen between 450 K and 600 K. H₂ desorption was detected at 595 K.