Atomic layer deposition (ALD) is one of the main techniques for thin layer growth in, e.g., materials science, catalysis, and solar photovoltaics. The self-limiting nature of the growth in ALD deviates strongly from the ideal scheme and the ALD surface chemistry remains largely unknown, not least due to the lack of possibilities for true in situ and operando studies. In order to address this shortcoming we carried out Ambient pressure x-ray photoelectron spectroscopy (APXPS) to study the ALD growth of HfO2 on the clean, oxidized, and native Si(111) surfaces. Tetrakis(dimethylamido)hafnium (TDMAHf) and water were used as precursors. Both half cycles were monitored during the dosing and pumping stages. The results were combined with a post mortem investigation by transmission electron microscopy (TEM) and atomic force microscopy (AFM). We carried out APXPS at high temporal resolution and identified surface species that occur in the ALD half-cycles (figure 1). Cyclic shifts in binding energy are seen to occur between the TDMAHf and water pulses. The ALD layer grows faster on the SiO2 surfaces in comparison to the clean one. Interestingly, the oxide layer was not removed during the initial TDMAHf half-cycle exposure, which is in contrast to the ALD of HfO2 on InAs and which can be explained by the higher stability of the SiO2 layer in comparison to the HfO2 layer. AFM, carried out on the samples from the APXPS experiments, illustrates that the ALD process carried out in the APXPS instruments results in films similar to those produced in real ALD reactors. Clear differences are observed between the films grown on the oxidized, clean, and native Si(111) surfaces. The TEM analysis of sample cross sections confirms the differences in reaction speed between the surfaces which results in differences in thickness and structures of the layer.

Real-time XPS monitoring of atomic layer deposition of HfO2 on Si surfaces

253rd National Meeting (2017)

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