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Grain enlargement is a crucial requirement to synthesizing two-dimensional (2D) metal chalcogenides because it can minimize the effects of carrier scattering at the grain boundaries. To this end, r...

The synthesis of a continuous and high-quality large-area layer is a key research area in the field of two-dimensional (2D) metal chalcogenides. To date, several techniques, including chemical vapo...

Two-dimensional (2-D) metal chalcogenides have received great attention because of their unique properties, which are different from bulk materials. A challenge in implementing 2-D metal chalcogenides in emerging devices is to prepare a well-crystallized layer over large areas at temperatures compatible with current fabrication processes. Tin monosulfide, a p-type layered semiconductor with a high hole mobility, is a promising candidate for realizing large-area growth at low temperatures because of its low melting point. However, tin sulfides exist in two notable crystalline phases, SnS and SnS2. Therefore, it is imperative to control the oxidation state of Sn to achieve a pure SnS film. Here, the synthesis of SnS thin films by atomic-layer-deposition (ALD) is demonstrated using bis(1-dimethylamino-2-methyl-2-propoxy)tin(II) and H2S as Sn and S sources, respectively, over a wide temperature window (90–240 °C). Impurities such as carbon, oxygen, and nitrogen were negligibly detected. The morphological evol...

An atomic layer deposition (ALD) process for SrTiO3 (STO) thin film growth was developed using a newly designed and synthesized heteroleptic Sr-precursor, {Sr(demamp)(tmhd)}2 (demampH = 1-{[2-(dimethylamino)ethyl](methyl)amino}-2-methylpropan-2-ol, tmhdH = 2,2,6,6-tetramethyl-3,5-heptanedione), which offered an intermediate reactivity toward oxygen between Sr(tmhd)2 and Sr(iPr3Cp)2. Because of the appropriate reactivity of {Sr(demamp)(tmhd)}2 toward oxygen, the abnormal initial growth behavior (due to interaction between the Sr-precursor and active oxygen contained in the underlying oxidized Ru layer) became negligible during the growth of the SrO and STO films on the Ru electrode, which allowed the growth of the SrO and STO films to be highly controllable with a moderate growth rate. Using Ti(CpMe5)(OMe)3 as the Ti-precursor and O3 as the oxygen source in the TiO2 ALD subcycle, the ALD process of the STO film revealed a growth rate of 0.05 nm/cycle and ∼85% of step coverage in terms of the thickness and ...

The reaction chemistry during the atomic layer deposition (ALD) of Sc2O3 and Gd2O3 from Sc(MeCp)3, Gd(iPrCp)3, and H2O was investigated by in situ time-resolved quadrupole mass spectrometry. Despite the similarity of the ligands of the Sc and Gd precursors, the growth characteristics and ligand dissociation patterns of the Sc2O3 and Gd2O3 ALD processes showed considerably different behavior. For both processes, the precursors reacted with the hydroxylated surface by proton transfer and release of the protonated ligand. The remaining ligands were then removed by hydrolysis during the H2O pulse. However, for the Sc(MeCp)3/H2O process, ∼56% of MeCpH was released during the Sc(MeCp)3 exposure, whereas in the case of the Gd(iPrCp)3/H2O process, as much as 90% of iPrCpH was released during the Gd(iPrCp)3 pulse. The observation that almost all iPrCp ligands were removed during the initial Gd(iPrCp)3 absorption step can be ascribed to CVD-like reactions between the Gd(iPrCp)3 precursor and excess hydroxide or phy...

The characteristics of the atomic layer deposition (ALD) of SrTiO3 (STO) films were examined for metal–insulator–metal capacitors, with Cp-based precursors Sr(iPr3Cp)2 and Cp*Ti(OMe)3 [Cp* = C5(CH3)5] employed as the Sr and Ti precursors, respectively. While the Sr precursor has a higher reactivity toward oxygen on the Ru substrate compared with another Ti precursor, with a 2,2,6,6-tetramethyl-3,5-heptanedionato ligand, which results in the highly Sr excessive STO film, the enhanced reactivity of the present Ti precursor suppressed the unwanted excessive incorporation of Sr into the film. A possible mechanism for the Sr overgrowth and retardation is suggested in detail. By controlling the subcycle ratio of SrO and TiO2 layers, stoichiometric STO could be obtained, even without employing a deleterious reaction barrier layer. This improved the attainable minimum equivalent oxide thickness of the Pt/STO/RuO2 capacitor to 0.43 nm, with acceptable leakage current density (∼8 × 10–8 A/cm2). This indicates an im...

SrRuO3 (SRO) film was deposited by sequential executions of atomic layer deposition of SrO and chemical vapor deposition of RuO2 layers at a low growth temperature of 230 °C using Sr(iPr3Cp)2, RuO4 precursors, and O2 gas. A wide range of Sr (Ru) concentration could be obtained by modulating the SrO/RuO2 subcycle ratio, and a high growth rate of ∼2.0 nm/supercycle was achieved with the stoichiometric SRO composition. The as-deposited SRO film was amorphous, and crystallized SRO film was obtained by post deposition annealing in N2 ambient at temperatures ranging from 600 to 700 °C. Crystallized SRO film was adopted as a seed layer for the in situ crystallization of ALD SrTiO3 (STO) film for application to capacitors for next generation dynamic random access memory. Consequently, a crystalline STO film was grown on crystallized SRO in the as-deposited state, and the dielectric constant of the STO film was largely improved compared to that of the amorphous STO, from 12 to 44.

This study examined the nucleation behavior of RuO2 films grown by pulsed chemical vapor deposition (p-CVD) using a RuO4 solution and a N2(95%)/H2(5%) mixed gas as the Ru precursor and reactant, respectively, on various substrates such as Pt, TiN, TiO2, and SiO2 surfaces. In addition, highly doped and nondoped Si substrates were also used to understand the influence of the electrical conductivity of a given substrate material. Contrary to the nucleation behavior of atomic layer deposited and CVD Ru or RuO2 using metal–organic precursors, where oxygen supplying surfaces facilitate nucleation, the nucleation in this study was enhanced by oxygen consuming substrates such as TiN and Si. This is basically due to the thermal decomposition mechanism of the RuO4 precursor. This precursor showed fluent nucleation properties on a Pt substrate too, which is thought to come from the catalytic activity of the surface. The electrical conductivity and ionicity of the substrate had little relevance with the nucleation ch...

The ever-shrinking dimensions of dynamic random access memory (DRAM) require a high quality dielectric film for capacitors with a sufficiently high growth-per-cycle (GPC) by atomic layer deposition (ALD). SrTiO3 (STO) films are considered to be the appropriate dielectric films for DRAMs with the design rule of ∼20 nm, and previous studies showed that STO films grown by ALD have promising electrical performance. However, the ALD of STO films still suffers from much too slow GPC to be used in mass-production. Here, we accomplished a mass-production compatible ALD process of STO films using Ti(O-iPr)2(tmhd)2 as a Ti-precursor for TiO2 layers and Sr(iPr3Cp)2 as a Sr-precursor for SrO layers. O3 and H2O were used as the oxygen sources for the TiO2 and SrO layers, respectively. A highly improved GPC of 0.107 nm/unit-cycle (0.428 nm/supercycle) for stoichiometric STO films was obtained at a deposition temperature of 370 °C, which is ∼7 times higher than previously reported. The origin of such high GPC values in ...

The role of the interfacial reactions in the atomic layer deposition of TiO2 films was examined using titanium diisopropoxide bis(tetramethylheptadionate) (Ti(O-iPr)2(tmhd)2) as the titanium precur...

RuO2 thin films were grown on thermal SiO2(100 nm) and Ta2O5(4 nm)/SiO2(100 nm) substrates at 230 °C by pulsed-chemical vapor deposition using a RuO4 precursor dissolved in blend of chosen organic ...

HfO2/TiO2 bilayered thin films were grown on Ru and TiN electrodes at 250 °C by atomic layer deposition. The crystalline structure of the HfO2 layer was affected by the crystalline structure of the...

Ru thin films were grown on Au, Pt, TiN, TiO2, and SiO2 substrates by atomic layer deposition using 2,4-(dimethylpentadienyl)(ethylcyclopentadienyl)Ru (DER) dissolved in ethylcyclohexane at a concentration of 0.2 M as the Ru precursor and O2 as the reactant. There was a long incubation time for Ru film deposition on TiN and SiO2 due to the weak interaction between DER and the covalent bonds in TiN and SiO2. On the other hand, the Ru films on TiO2 exhibited a shorter incubation time. There was a negligible incubation time for Ru film deposition on Au and Pt due to the strong interactions between the DER precursor and metallic surfaces, resulting in a smooth surface morphology and strong c-axis texture. A continuous Ru film, not an island-shaped film, was formed on Au, which does not catalytically dissociate molecular oxygen, even at a film thickness of 1 nm. Therefore, the initial growth of Ru thin films was determined by the adsorption of the metal precursor not the catalytic dissociation of molecular oxygen.

Ru thin films were grown by pulsed chemical vapor deposition using RuO4 and 5% H2/95% N2 as the precursor and reducing gas, respectively. The film grown at 230 °C showed the best structural and electrical properties among the chemically grown Ru films ever reported.