The Surface Chemistry of Atomic Layer Deposition (ALD) Processes for Metal Nitride and Metal Oxide Film Growth

The surface and gas-phase thermal chemistry of tetrakis(ethylmethylamido)titanium (TEMAT), by itself and in the presence of water, was investigated by using transmission infrared (IR) absorption spectroscopy and tandem gas chromatographymass spectrometry (GC-MS). Using IR spectroscopy, the uptake of TEMAT was contrasted on hydrogen-terminated versus native-oxide-covered surfaces of Si(100) substrates, and the self-limiting nature of the uptake on the native oxide was assessed in the temperature range from 140 to 280 degrees C. It was found that the uptake of TEMAT is indeed partially self-limiting, but that a CVD component from precursor decomposition does contribute to the deposition of Ti, a contribution that becomes more apparent with increasing temperatures. It was also found that decomposition of the amido ligands on the surface leads to the formation of surface species containing C=N bonds, most likely imine intermediates produced by beta-hydride eliminations steps. Furthermore, it was demonstrated that a controlled thin film containing Ti species can be deposited by means of TEMAT self-limiting adsorption at 150 degrees C followed by thermal decomposition at 325 degrees C. To further understand the thermal chemistry of TEMAT, a novel approach was successfully tested where the reaction products from gas-phase reactions of TEMAT, alone and in the presence of H2O, were analyzed using tandem GC-MS. It was found that TEMAT can decompose through a reductive coupling mechanism in which N, N'-diethyl-N'N'-dimethylhydrazine is formed. In contrast, addition of water to the reaction mixture promotes a competing ligand hydrogenation reaction to form ethylmethylamine instead.