Surface chemistry in the initial stages of TiN ALD using operando APXPS

Studies of the surface chemistry of the first few cycles of atomic layer deposition (ALD) using in situ and time-resolved operando techniques are attractive for realizing, understanding and obtaining true mechanistic information during the deposition. However, the latter techniques are yet to be applied to ALD of metal nitrides. Here we present a surface-chemistry investigation through a time-resolved ambient pressure X-ray photoelectron spectroscopy (APXPS) study of the initial growth of titanium nitride. The Ti 2p, O 1s, N 1s, C 1s and Si 2p core-level spectra recorded at different stages during the deposition show that chemisorption occurs immediately on the silicon dioxide surface due to the interaction of tetrakis(dimethylamido)titanium(IV) (TDMAT) with the surface. A delay in nucleation on the TDMAT-terminated surface was observed during the NH3 pulse. The intensity of the Ti 2p and N 1s core levels began to increase after four ALD cycles, showing that the surface was coated with Ti and N atoms and no Si signals were observed with time. The results show that ligand exchange reactions take place before transamination reactions. This was verified using the periodic changes in the intensity and peak positions of the above-mentioned spectra and complemented by residual gas analysis using mass spectrometry. These results can provide insights into the ALD surface growth of not only TiN but also other metal nitrides.