The reaction mechanism of area-selective atomic layer deposition (AS-ALD) of AlO thin films using self-assembled monolayers (SAMs) was systematically investigated by theoretical and experimental studies. Trimethylaluminum (TMA) and HO were used as the precursor and oxidant, respectively, with octadecylphosphonic acid (ODPA) as an SAM to block AlO film formation. However, AlO layers began to form on the ODPA SAMs after several cycles, despite reports that CH-terminated SAMs cannot react with TMA. We showed that TMA does not react chemically with the SAM but is physically adsorbed, acting as a nucleation site for AlO film growth. Moreover, the amount of physisorbed TMA was affected by the partial pressure. By controlling it, we developed a new AS-ALD AlO process with high selectivity, which produces films of ∼60 nm thickness over 370 cycles. The successful deposition of AlO thin film patterns using this process is a breakthrough technique in the field of nanotechnology.

Short-chain aminosilanes, namely, bis(N,Ndimethylamino)dimethylsilane (DMADMS) and (N,Ndimethylamino)trimethylsilane (DMATMS), have been used as Si precursors for atomic layer deposition (ALD) of SiO 2 . In this work, the DMADMS and DMATMS Si precursors are utilized as inhibitors for area-selective ALD (AS-ALD). The inhibitors selectively adsorb on a SiO 2 surface but not on H− Si, so that SiO 2 becomes selectively deactivated toward subsequent ALD. The deactivation of the SiO 2 surface by the inhibitors was investigated using various experimental and theoretical methods, including surface potential measurements, spectroscopic ellipsometry, and X-ray photoelectron spectroscopy. Better inhibition was observed for ALD of Ru and Pt than for ALD of Al 2 O 3 and HfO 2 . Through quantum mechanical and stochastic simulations, the difference in the blocking ability for noble metal and metal oxide ALD by the aminosilane inhibitors could be attributed to the inherently partial surface coverage by the inhibitors at their saturation and the reactivity of the subsequent ALD precursors. As silane inhibitors can be easily integrated with vacuum-based processes to facilitate high volume manufacturing of upcoming electronic devices, the current study provides a potential approach for the utilization of AS-ALD in pattern fabrication inside 3D nanostructures.

Ni thin films were deposited by atomic layer deposition ͑ALD͒ using bis͑dimethylamino-2-methyl-2-butoxo͒nickel ͓Ni͑dmamb͒ 2 ͔ as a precursor and NH 3 gas as a reactant. The growth characteristics and film properties of ALD Ni were investigated. Lowresistivity films were deposited on Si and SiO 2 substrates, producing high-purity Ni films with a small amount of oxygen and negligible amounts of nitrogen and carbon. Additionally, ALD Ni showed excellent conformality in nanoscale via holes. Utilizing this conformality, Ni/Si core/shell nanowires with uniform diameters were fabricated. By combining ALD Ni with octadecyltrichlorosilane ͑OTS͒ self-assembled monolayer as a blocking layer, area-selective ALD was conducted for selective deposition of Ni films. When performed on the prepatterned OTS substrate, the Ni films were selectively coated only on OTS-free regions, building up Ni line patterns with 3 m width. Electrical measurement results showed that all of the Ni lines were electrically isolated, also indicating the selective Ni deposition.As scaling continues in order to improve device integration in the complementary metal-oxide-semiconductor ͑CMOS͒ process, the silicidation process becomes more essential for lowering contact resistance and increasing drive currents. 1 TiSi 2 and CoSi 2 have been extensively investigated as contact materials. However, these materials have been reported to cause increased series resistance of devices at the sub-65 nm technology node. 2 In addition, TiSi 2 exhibits the narrow line effect. 3 Although CoSi 2 lines depend less on the sheet resistance, the greater consumption of Si is a major concern in forming silicide with the decreased junction depth. Also, both materials require a two-step annealing process to form a low resistive phase. 3 Because of these problems, NiSi is being investigated as a contact material for application in nanoscale devices and shows no linewidth effects, low resistivity, low Si consumption, low process temperature, and a one-step annealing process. 4 The Ni metal deposition process is a key requirement in the formation of Ni silicide contacts. Among the various thin film deposition techniques, atomic layer deposition ͑ALD͒ is a promising method which exhibits good conformality and uniformity, atomic scale thickness controllability, and low impurity contamination at a low growth temperature due to its growth mechanism based on a self-limited surface reaction. 5-7 However, in spite of its importance in nanoscale device contact applications, there are only a few reports on the ALD of Ni films. 2,[8][9][10][11][12][13] In an early study, Chae et al. reported the formation of Ni films by H 2 plasma reduction of ALD NiO films using bis͑cyclopentadienyl͒nickel ͓NiCp 2 ͔ as a precursor and water as a reactant. 9 Later, Do et al. reported a Ni ALD process using a Ni͑dmamb͒ 2 precursor and H 2 as the reactant gas. 2 However, the Ni films deposited in these studies contain a large amount of carbon, which may have caused high resistivity. 2,9 These results suggest t...

2D transition metal dichalcogenides (TMDs) have attracted much attention for their gas sensing applications due to their superior responsivity at typical room temperature. However, low power consumption and reliable selectivity are the two main requirements for gas sensors to be applicable in future electronic devices. Herein, a p-type (WSe 2 /WS 2) and n-type (MoS 2 /WSe 2) photovoltaic self-powered gas sensor is demonstrated using 2D TMD heterostructures for the first time. The gas sensors are operated by the photovoltaic effect of 2D TMD heterostructures, which are uniformly synthesized by the vacuum-based synthesis. The gas sensing properties of the WSe 2 /WS 2 and MoS 2 /WSe 2 heterostructure gas sensors are investigated for NO 2 and NH 3 with changing gas concentration, and each sensor exhibits selectivity to NO 2 and NH 3. From the results, it is confirmed that the 2D TMD heterostructures can be a viable platform for highly sensitive, selective gas sensor applications without external bias due to their photovoltaic features. Further, this study contri butes toward revealing the gas sensor mechanism in 2D TMD heterostructure.

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We report the effect of YO passivation by atomic layer deposition (ALD) using various oxidants, such as HO, O plasma, and O, on In-Ga-Zn-O thin-film transistors (IGZO TFTs). A large negative shift in the threshold voltage (V) was observed in the case of the TFT subjected to the HO-ALD YO process; this shift was caused by a donor effect of negatively charged chemisorbed HO molecules. In addition, degradation of the IGZO TFT device performance after the O plasma-ALD YO process (field-effect mobility (μ) = 8.7 cm/(V·s), subthreshold swing (SS) = 0.77 V/dec, and V = 3.7 V) was observed, which was attributed to plasma damage on the IGZO surface adversely affecting the stability of the TFT under light illumination. In contrast, the O-ALD YO process led to enhanced device stability under light illumination (ΔV = -1 V after 3 h of illumination) by passivating the subgap defect states in the IGZO surface region. In addition, TFTs with a thicker IGZO film (55 nm, which was the optimum thickness under the current investigation) showed more stable device performance than TFTs with a thinner IGZO film (30 nm) (ΔV = -0.4 V after 3 h of light illumination) by triggering the recombination of holes diffusing from the IGZO surface to the insulator-channel interface. Therefore, we envisioned that the O-ALD YO passivation layer suggested in this paper can improve the photostability of TFTs under light illumination.

We investigated atomic layer deposition (ALD) of B 2 O 3 and SiO 2 thin films using trimethylborate (TMB) and bis-(diethylamino)silane (SAM-24) precursors, focusing on growth characteristics and film properties. For both cases, ALD processes using O 3 and O 2 plasma as reactants exhibited well-defined growth saturation and linear growth behavior without any incubation cycles, and produced highly pure, stoichiometric films. In the case of B 2 O 3 films, however, SiO 2 layer passivation is required onto the B 2 O 3 due to a spontaneous decomposition caused by moisture in air. On the basis of electrical characterization, the detailed dielectric properties of SiO 2 and B 2 O 3 /passivation SiO 2 films were extensively discussed including the k-value, flat band voltage, and leakage currents. Then, boron-doped SiO 2 films with different B/(B + Si) compositions were prepared by controlling B 2 O 3 and SiO 2 growth cycles, followed by drive-in annealing and a subsequent wet removal process. Based on both theoretical estimation and SIMS depth profile results, we demonstrated that the surface doping concentration is effectively modulated with controllable B doping contents in the B-doped SiO 2 films.

We fabricated metallic nanostructures directly on Si substrates through a hybrid nanoprocess combining atomic layer deposition (ALD) and a self-assembled anodic aluminum oxide (AAO) nanotemplate. ALD Ru films with Ru(DMPD)(EtCp) as a precursor and O(2) as a reactant exhibited high purity and low resistivity with negligible nucleation delay and low roughness. These good growth characteristics resulted in the excellent conformality for nanometer-scale vias and trenches. Additionally, AAO nanotemplates were fabricated directly on Si and Ti/Si substrates through a multiple anodization process. AAO nanotemplates with various hole sizes (30-100 nm) and aspect ratios (2:1-20:1) were fabricated by controlling the anodizing process parameters. The barrier layers between AAO nanotemplates and Si substrates were completely removed by reactive ion etching (RIE) using BCl(3) plasma. By combining the ALD Ru and the AAO nanotemplate, Ru nanostructures with controllable sizes and shapes were prepared on Si and Ti/Si substrates. The Ru nanowire array devices as a platform for sensor devices exhibited befitting properties of good ohmic contact and high surface/volume ratio.