Surface reaction mechanisms during atomic layer deposition of zirconium oxide using water, ethanol, and water-ethanol mixture as the oxygen sources

The authors have investigated the surface reaction mechanisms during the atomic layer deposition (ALD) of ZrO2 from tetrakis(ethylmethylamino)zirconium (TEMAZ) with H2O, C2H5OH, and H2O-C2H5OH mixture as the oxygen sources. The ligand-exchange reactions were characterized using in situ attenuated total reflection Fourier transform infrared spectroscopy, and the film growth was recorded using in situ four-wavelength ellipsometry. In the H2O-based ALD process, as expected, surface -OH groups were the reactive sites for TEMAZ, and a growth per cycle (GPC) of similar to 1.1 angstrom was obtained at 200 degrees C. Contrary to previous reports, no film growth was observed for the C2H5OH-based ALD process. During the TEMAZ half-cycle, the -OC2H5-terminated surface obtained after the C2H5OH half-cycle simply underwent ligand exchange without any addition of Zr to the surface, most likely forming Zr[N(CH3)(C2H5)](4-)(x)[OC2H5](x) (1 <= x <= 3) as the byproduct. Film growth was observed during the ALD of ZrO2 using an H2O-C2H5OH mixture as the oxygen source. The addition of C2H5OH reduced the surface hydroxyl coverage by forming surface ethoxide sites, which did not contribute to film growth. This in turn led to a lower GPC, similar to 0.6 angstrom, compared to the TEMAZ/H2O ALD process.