Jae-Min Park

Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride Using a Novel Silylamine Precursor

We report the plasma-enhanced atomic layer deposition (PEALD) of silicon nitride thin film using a silylamine compound as the silicon precursor. A series of silylamine compounds were designed by replacing SiH3 groups in trisilylamine by dimethylaminomethylsilyl or trimethylsilyl groups to obtain sufficient thermal stability. The silylamine compounds were synthesized through redistribution, amino-substitution, lithiation, and silylation reactions. Among them, bis(dimethylaminomethylsilyl)trimethylsilyl amine (C9H29N3Si3, DTDN2-H2) was selected as the silicon precursor because of the lowest bond dissociation energy and sufficient vapor pressures. The energies for adsorption and reaction of DTDN2-H2 with the silicon nitride surface were also calculated by density functional theory. PEALD silicon nitride thin films were prepared using DTDN2-H2 and N2 plasma. The PEALD process window was between 250 and 400 °C with a growth rate of 0.36 Å/cycle. The best film quality was obtained at 400 °C with a RF power of 100 W. The PEALD film prepared showed good bottom and sidewall coverages of ∼80% and ∼73%, respectively, on a trench-patterned wafer with an aspect ratio of 5.5.

Reactivity of different surface sites with silicon chlorides during atomic layer deposition of silicon nitride

We studied the reactivity of different surface sites of β-Si3N4 with silicon chlorides during the first half reaction of an atomic layer deposition (ALD) process using ab initio density functional theory calculations to understand the underlying reaction mechanism. We considered three types of surface sites, NH*/SiH*, NH*/SiNH2*, and under-coordinated bare SiN–. The reactions of the silicon chlorides with NH*/SiNH2* and SiN– are energetically favorable, whereas the reactions are endothermic with NH*/SiH*. On SiN–, the silicon and chlorine atoms of the precursors easily react with the unsaturated nitrogen and silicon atoms, respectively, resulting in very low energy barriers for the reaction. However, on NH*/SiH* and NH*/SiNH2*, the reaction undergoes high energy barriers due to the dissociation of a hydrogen atom from the surface or a chlorine atom from the precursor. We further found that Si2Cl6 shows energies of reaction lower than those of SiCl4 on SiN–. By discovering the influence of surface reaction sites on ALD reactions, we designed a new 3-step ALD process to obtain the most effective surface sites for the first half reaction, and confirmed this with deposition experiments. The N2 plasma steps, prior to the introduction of a silicon precursor, reduced the saturation dose of Si2Cl6 from 107 L to <106 L and increased the growth rate from 0.59 A per cycle to 1.1 A per cycle, which agrees with our calculations. These results show that the reactivity of the surface sites plays a very important role to determine the thermodynamics and kinetics of ALD processes.

TiO2 photocatalyst film using circulating fluidised bed–chemical vapour deposition

Abstract TiO2 photocatalyst beads were synthesised using the circulating fluidised bed–chemical vapour deposition (CFB-CVD) method. Their photocatalytic activity was compared with the TiO2 photocatalyst balls synthesised using the conventional CVD (C-CVD) method. The TiO2 film synthesized by CFB-CVD showed (110) oriented anatase crystal structure. Compared to the film synthesised by C-CVD, the CFB-CVD synthesised film had much less dense crystal structure owing to TiO2 powders precipitated during the film growth. When the CFB-CVD synthesised TiO2 beads were used in the photocatalytic decomposition of RhB in a fluidised bed reactor, the decomposition rate increased with increasing UV intensity and circulating flowrate and with decreasing initial RhB concentration. One important shortcoming of the TiO2 photocatalyst beads synthesised by CFB-CVD turned out to be that the photocatalytic activity was decreased significantly by repeated reuse, calling for further investigation to improve the durability.

Plasma-enhanced atomic layer deposition of nickel thin film using bis(1,4-diisopropyl-1,4-diazabutadiene)nickel

The authors report the plasma enhanced atomic layer deposition (PEALD) of a nickel thin film using bis(1,4-diisopropyl-1,4-diazabutadiene)nickel [Ni(dpdab)2] and NH3 plasma. Ni(dpdab)2 is an oxygen-free liquid Ni precursor with a vapor pressure of 0.23 Torr at 80 °C. Ni films were deposited by alternating exposures to Ni(dpdab)2 and NH3 plasma at 125–250 °C. Ni(dpdab)2 showed the atomic layer deposition (ALD) process window between 125 and 150 °C with the ALD growth of ∼2 A/cycle. The growth rate increased significantly above 200 °C, probably due to the thermal decomposition of the Ni precursor. The resistivity of the ALD thin film decreased with increasing radio-frequency (RF) power, and lower resistivities with high RF powers are due to the lower carbon concentration and larger grain size. The minimum resistivity of the PEALD film at 150 °C in the ALD process window was 146 μΩ cm, which is significantly higher than bulk Ni resistivity (7.0 μΩ cm) mainly due to the nitrogen content (∼13%) in the as-deposited film. For a lower nitrogen concentration, the PEALD film was annealed at 400 °C under 1 Torr of H2 for 30 min, resulting in the reduction of resistivity from 146 to 13.3 μΩ cm and removal of nitrogen impurities.The authors report the plasma enhanced atomic layer deposition (PEALD) of a nickel thin film using bis(1,4-diisopropyl-1,4-diazabutadiene)nickel [Ni(dpdab)2] and NH3 plasma. Ni(dpdab)2 is an oxygen-free liquid Ni precursor with a vapor pressure of 0.23 Torr at 80 °C. Ni films were deposited by alternating exposures to Ni(dpdab)2 and NH3 plasma at 125–250 °C. Ni(dpdab)2 showed the atomic layer deposition (ALD) process window between 125 and 150 °C with the ALD growth of ∼2 A/cycle. The growth rate increased significantly above 200 °C, probably due to the thermal decomposition of the Ni precursor. The resistivity of the ALD thin film decreased with increasing radio-frequency (RF) power, and lower resistivities with high RF powers are due to the lower carbon concentration and larger grain size. The minimum resistivity of the PEALD film at 150 °C in the ALD process window was 146 μΩ cm, which is significantly higher than bulk Ni resistivity (7.0 μΩ cm) mainly due to the nitrogen content (∼13%) in the as-depos...

Catalyzed Atomic Layer Deposition of Silicon Oxide at Ultralow Temperature Using Alkylamine

We report the catalyzed atomic layer deposition (ALD) of silicon oxide using Si2Cl6, H2O, and various alkylamines. The density functional theory (DFT) calculations using the periodic slab model of the SiO2 surface were performed for the selection of alternative Lewis base catalysts with high catalytic activities. During the first half-reaction, the catalysts with less steric hindrance such as pyridine would be more effective than bulky alkylamines despite lower nucleophilicity. On the other hand, during the second half-reaction, the catalysts with a high nucleophilicity such as triethylamine (Et3N) would be more efficient because the steric hindrance is less critical. The in situ process monitoring shows that the calculated atomic charge is a good indicator for expecting the catalyst activity in the ALD reaction. The use of Et3N in the second half-reaction was essential to improving the growth rate as well as the step coverage of the film because the Et3N-catalyzed process deposited a SiO2 film with a step coverage of 98% that is better than 93% of the pyridine-catalyzed process. The adsorption of pyridine, ammonia (NH3), or trimethylamine (Me3N) salts was more favorable than that of Et3N, n-Pr3N, or iPr3N salts. Therefore, Et3N was expected to incorporate less amine salts in the film as compared to pyridine, and the compositional analyses confirmed that the concentrations of Cl and N by the Et3N-catalyzed process were significantly lower than those by the pyridine-catalyzed process.

Novel Cyclosilazane-Type Silicon Precursor and Two-Step Plasma for Plasma-Enhanced Atomic Layer Deposition of Silicon Nitride

We designed cyclosilazane-type silicon precursors and proposed a three-step plasma-enhanced atomic layer deposition (PEALD) process to prepare silicon nitride films with high quality and excellent step coverage. The cyclosilazane-type precursor, 1,3-di-isopropylamino-2,4-dimethylcyclosilazane (CSN-2), has a closed ring structure for good thermal stability and high reactivity. CSN-2 showed thermal stability up to 450 °C and a sufficient vapor pressure of 4 Torr at 60 °C. The energy for the chemisorption of CSN-2 on the undercoordinated silicon nitride surface as calculated by density functional theory method was -7.38 eV. The PEALD process window was between 200 and 500 °C, with a growth rate of 0.43 Å/cycle. The best film quality was obtained at 500 °C, with hydrogen impurity of ∼7 atom %, oxygen impurity less than 2 atom %, low wet etching rate, and excellent step coverage of ∼95%. At 300 °C and lower temperatures, the wet etching rate was high especially at the lower sidewall of the trench pattern. We introduced the three-step PEALD process to improve the film quality and the step coverage on the lower sidewall. The sequence of the three-step PEALD process consists of the CSN-2 feeding step, the NH3/N2 plasma step, and the N2 plasma step. The H radicals in NH3/N2 plasma efficiently remove the ligands from the precursor, and the N2 plasma after the NH3 plasma removes the surface hydrogen atoms to activate the adsorption of the precursor. The films deposited at 300 °C using the novel precursor and the three-step PEALD process showed a significantly improved step coverage of ∼95% and an excellent wet etching resistance at the lower sidewall, which is only twice as high as that of the blanket film prepared by low-pressure chemical vapor deposition.