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) AlOx and HfOx. Both kinds of high-k GIs 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 AlOx GI, the 4-nm HfOx enables a larger GI capacitance, while the HfOx-gated TFT suffers the 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/HfOx interface further causes the noticeable positive bias stress (PBS) instability. Both ALD AlOx and HfOx were 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 HfOx gives 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.
High-quality SnO2:Si films and SnO2:10 at.% Ga films were prepared by the solution method. The roughness of films is below 1.08 nm, and possess exceptional transparency (>75%) and decent semiconductor properties. Based on this, the SnO2:Si/SnO2: Ga homojunctions with different Si doping concentrations were prepared. It is found that the conductivity of the SnO2:Si thin film gradually increases, and the rectification characteristics of the homojunction are optimized with increasing Si doping content. The SnO2:15 at.% Si/SnO2:10 at.% Ga homogeneous junction has the best performance, the turn-on voltage is as low as 5.6 V, and it also exhibits good unidirectional conductivity. The photoresponse of the SnO2:15 at.% Si/SnO2:10 at.% Ga homojunction under the lights of red, yellow, and purple was explored respectively. The result shows that the device responds strongly to purple light. Compared with the test results in the dark environment, the device current increases by two orders, which is expected to be applied in the field of near-ultraviolet detection.
Atomic layer deposition (ALD) has become an indispensable thin-film technology in the contemporary microelectronics industry. The unique self-limited layer-by-layer growth feature of ALD has outstood this technology to deposit highly uniform conformal pinhole-free thin films with angstrom-level thickness control, particularly on 3D topologies. Over the years, the ALD technology has enabled not only the successful downscaling of the microelectronic devices but also numerous novel 3D device structures. As ALD is essentially a variant of chemical vapor deposition, a comprehensive understanding of the involved chemistry is of crucial importance to further develop and utilize this technology. To this end, we, in this review, focus on the surface chemistry and precursor chemistry aspects of ALD. We first review the surface chemistry of the gas-solid ALD reactions and elaboratively discuss the associated mechanisms for the film growth; then, we review the ALD precursor chemistry by comparatively discussing the precursors that have been commonly used in the ALD processes; and finally, we selectively present a few newly-emerged applications of ALD in microelectronics, followed by our perspective on the future of the ALD technology.
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 an in situ X-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/SiOx interface immediately after the first Al2O3 layer 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 Al2O3 ALD growth, which suggests the formation of Si−CH3 on the surface. These findings can provide useful routes and insights toward interface engineering by ALD.
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