In situx-ray photoelectron spectroscopy analysis of the atomic layer deposition of Al2O3on SiOx/Si: Interface dipole and persistent surface groups.

Atomic layer deposition (ALD) has become an essential technology in many areas. To better develop and use this technology, it is of the pivot to understand the surface chemistry during the ALD film growth. The growth of an ALD oxide film may also induce an electric dipole at the interface, which may be further tuned to modulate the flat band voltage for electronic device applications. To understand the associated surface chemistry and interface dipole formation process, we herein employ anin situx-ray photoelectron spectroscopy technique to study the ALD growth of Al2O3, from trimethylaluminum and H2O, on the SiOx/Si surface. We find that an electric dipole is formed at the Al2O3/SiOxinterface immediately after the first Al2O3layer is deposited. We also observe persistent surface methyl groups in the H2O half-cycle during ALD, and the amount of the persistent methyls is particularly higher during the initial Al2O3ALD growth, which suggests the formation of Si-CH3on the surface. These findings can provide useful routes and insights toward interface engineering by ALD.

Ultra-thin gate insulator of atomic-layer-deposited AlOxand HfOxfor amorphous InGaZnO thin-film transistors.

To strengthen the downscaling potential of top-gate amorphous oxide semiconductor (AOS) thin-film transistors (TFTs), the ultra-thin gate insulator (GI) was comparatively implemented using the atomic-layer-deposited (ALD) AlOxand HfOx. Both kinds of high-kGIs exhibit good insulating properties even with the physical thickness thinning to 4 nm. Compared to the amorphous indium-gallium-zinc oxide (a-IGZO) TFTs with 4 nm AlOxGI, the 4 nm HfOxenables a larger GI capacitance, while the HfOx-gated TFT suffers higher gate leakage current and poorer subthreshold slope, respectively originating from the inherently small band offset and the highly defective interface between a-IGZO and HfOx. Such imperfect a-IGZO/HfOxinterface further causes noticeable positive bias stress instability. Both ALD AlOxand HfOxwere found to react with the underneath a-IGZO channel to generate the interface defects, such as metal interstitials and oxygen vacancies, while the ALD process of HfOxgives rise to a more severe reduction of a-IGZO. Moreover, when such a defective interface is covered by the top gate, it cannot be readily restored using the conventional oxidizing post-treatments and thus desires the reduction-resistant pre-treatments of AOSs.