Initial reactions of ultrathin HfO2 films by in situ atomic layer deposition: An in situ synchrotron photoemission spectroscopy study

Abstract

An in-depth exploration of the initial reaction and interfacial characteristics of ultrathin HfO2 films was implemented using in situ atomic layer deposition (ALD) and synchrotron radiation photoemission spectroscopy (SRPES). A newly developed Hf(mp)4 [mp = 3-methyl-3-pentoxide, OC(CH3)(C2H5)2] precursor, and H2O were adopted for the ALD of ultrathin HfO2. During the ALD process, the chemical composition and energy bandgap below the Fermi level of the HfO2 thin film were investigated at each cycle of the precursors by in situ measurements of SRPES. The Hf 4f, O 1s, and Si 2p core level and valence band spectra suggested that the initial ALD reactions yielded a Si suboxide and Hf silicate over three ALD cycles. An observation of the abnormal phenomena originating from the interfacial layer between HfO2 and Si revealed that the uniform HfO2 thin films exhibited a sufficient valence band offset as an insulating layer, which ensured that the valance band offset between Si 3p and O 2p reached to 2.78 eV over three ALD cycles, which coincided with that of the typical HfO2/Si structures.