1 Results The reaction mechanisms of the atomic layer deposition (ALD) processes used for thin-film growth have been characterized by a combination of surface sensitive techniques. Our early studies focused on the deposition of TiN films from TiCl4 and ammonia,starting with the independent characterization of each of the two half steps comprising the ALD process. It was found that exposure of the substrate to TiCl4 leads to the initial deposition of titanium in the +3 oxidation state; only at a later stage most of the Ti atoms retain the +4 state expected for molecular TiCl4. The Cl:Ti final ratio at the end of the TiCl4 deposition was found to reach a value of≈3.5,indicating some chlorine removal. Subsequent treatment with ammonia removes most of the remaining Cl and deposits the required nitrogen,as expected,but some chlorine is still seen on the surface,most likely because of HCl readsorption. The buildup of thicker films was then tested by performing multiple cycles with alternating exposures to TiCl4 and NH3. Similar films could be deposited on glass and on W,Ni and Cu foils. Interestingly,depth-profiling studies show that the resulting films consist of a Ti3N4 layer on top of TiN. This suggests that the reduction of titanium takes place during the exposure of the surface to TiCl4,not NH3,and that it is the first reaction of the cycle the rate limiting in the whole ALD process. Additional work was performed aimed at identifying the origin of the oxygen contamination often seen in these films. Incorporation of water or oxygen from the background was ruled out,and diffusion of oxygen from the substrate was proposed.Similar conclusions were reached from studies with TaCl5. In particular,partial reduction of the tantalum atoms is seen in the initial stages of the TaCl5 uptake,suggesting again precursor disproportionation rather than reaction with ammonia as the mechanism for Ta3+ formation. A signal likely due to tantalum oxide is seen in the XPS spectra,but ammonia treatments do lead to the replacement of most of the chlorine by nitrogen. The oxide signal is the last to be removed upon sputtering,suggesting that the oxide layer may form at the interface between the substrate and the growing TaN film. 1 Results The reaction mechanisms of the atomic layer deposition (ALD) processes used for thin-film growth have been characterized by a combination of surface sensitive techniques. Our early studies focused on the deposition of TiN films from TiCl4 and ammonia, starting with the independent Characterization of each of the two half steps includes the ALD process. It was found that exposure of the substrate to TiCl4 leads to the initial deposition of titanium in the +3 oxidation state; only at a later stage most of the Ti atoms retain the + 4 state expected for molecular TiCl4. The Cl: Ti final ratio at the end of the TiCl4 deposition was found to reach a value of≈3.5, indicating some chlorine removal. , as expected, but some chlorine is still seen on the surface, most likely because of HCl readsorption. The buildup of thicker films was then tested by performing multiple cycles with alterna ting exposures to TiCl4 and NH3. Similar films could be deposited on glass and on W, Ni and Cu foils. Interestingly, depth-profiling studies show that the resulting films consist of a Ti3N4 layer on top of TiN. This suggests that the reduction of titanium takes place during the exposure of the surface to TiCl4, not NH3, and that it is the first reaction of the cycle the rate limiting in the whole ALD process. These films. Incorporation of water or oxygen from the background was ruled out, and diffusion of oxygen from the substrate was proposed. Synonyms were reached from studies with TaCl5. In particular, partial reduction of the tantalum atoms is seen in the initial stages of the TaCl5 uptake, suggesting again precursor disproportionation than than reaction with ammonia as the mechanism for Ta3 + formation. A signal likely due to tantalum oxide is seen in the XPS spectra, but amm onThe oxide signal is the last to be removed upon sputtering, suggesting that the oxide layer may form at the interface between the substrate and the growing TaN film.