Do-Joong Lee

Sub-10-nm nanochannels by self-sealing and self-limiting atomic layer deposition.

We report on a novel fabrication method of a nanochannel ionic field effect transistor (IFET) structure with sub-10-nm dimensions. A self-sealing and self-limiting atomic layer deposition (ALD) facilitates the fabrication of lateral type nanochannels smaller than the e-beam or optical lithographic limits. Using highly conformal ALD film structures, including TiO(2), TiO(2)/TiN, and Al(2)O(3)/Ru, we have fabricated lateral sub-10-nm nanochannels with good control over channel diameter. Nanochannels surrounded by core/shell (high-k dielectric/metal) layers give rise to all-around-gating IFETs, an important functional element in an electrofluidic-based circuit system.

Nucleation kinetics of Ru on silicon oxide and silicon nitride surfaces deposited by atomic layer deposition

The nucleation behavior of Ru deposited by atomic layer deposition (ALD) using bis(ethylcyclopentadienyl)ruthenium precursor and O2 reactant is investigated as a function of the number of ALD cycles. The substrates are thermally grown SiO2, NH3 plasma-treated SiO2, and chemical vapor deposited SiNx. The nucleation of Ru strongly depends on the substrate and is much enhanced on the nitride substrates. Transmission electron microscopy analysis reveals that the maximum density of the nuclei is 5.7×1010cm−2 on the SiO2 surface at 500 ALD cycles, 1.2×1012cm−2 on SiNx at 160 ALD cycles, and 2.3×1012cm−2 on NH3 plasma-nitrided SiO2 at 110 ALD cycles. Although the kinetics of Ru nucleation is different on the various substrates, the overall nucleation process in each case consists of an initial slow nucleation stage and a subsequent fast nucleation stage before the coalescence of the nuclei occurs. Considering the adsorption of Ru precursor on the substrate and the surface diffusion of deposited Ru during an ALD ...

Low Temperature Atomic Layer Deposition of Ruthenium Thin Films Using Isopropylmethylbenzene-Cyclohexadiene-Ruthenium and O2

Ru thin films were deposited by atomic layer deposition (ALD) through alternating exposures of a metallorganic precursor, C 16 H 22 Ru [(η6-1-isopropyl-4-methylbenzene) (η4-cyclohexa-1,3-diene)ruthenium(0)] and O 2 at 220°C. The growth rate was 0.1 and 0.086 nm/cycle on TiN and thermally grown SiO 2 , respectively. On both substrates, negligible incubation cycles were observed indicating that Ru nucleation was enhanced compared to the results obtained using the cyclopentadienyl-based Ru precursors. Plan-view transmission electron microscopy analysis revealed the formation of a continuous Ru film with a thickness of ~3.5 nm after only 50 ALD cycles. The step coverage was approximately 100% over the contact holes (top opening diameter was 89 nm) with a high aspect ratio (24:1).

Frustrated antiferromagnetism at heterointerfaces in a semiconductor superlattice: MnSe/ZnSe

The role of interfaces in influencing behavior of antiferromagnetic semiconductors has been studied in the new strained layer MnSe/ZnSe superlattice system, grown by molecular‐beam epitaxy, with individual MnSe layers approaching the monolayer limit. Large paramagneticlike contributions to overall magnetization are observed at low temperatures. Such anomalous characteristics are interpreted in terms of frustration against antiferromagnetic ordering by microstructure effects at the heterointerfaces.

Effect of Al Distribution on Carrier Generation of Atomic Layer Deposited Al-Doped ZnO Films

The effect of the Al distribution on the electrical properties of Al-doped ZnO (AZO) films deposited by atomic layer deposition (ALD) is investigated. In order to control the Al distribution, the pulsing time of trimethylaluminum (TMA) is varied from 2 (within an ALD window) to 0.1 s. As a result, the areal density of Al atoms incorporated in a single dopant layer decreases from 3.3 x 10 14 to 1.2 ×10 14 cm -2 . Hall measurements reveal that the minimum resistivity of the ALD-AZO films is decreased from 3.2 x 10 -3 to 1.7 ×10 -3 Ω cm as a result of reducing the TMA pulsing time from 2 to 0.1 s. This decrease is due to the obvious increase of the carrier concentration from 1.4 x 10 20 to 4.7 x 10 20 cm -3 . It is suggested that both the improved doping efficiency (from 13 to 58%) and the insertion of more dopant layers within the ZnO matrix are responsible for the increase of the carrier concentration.

Formation of Ru Nanotubes by Atomic Layer Deposition onto an Anodized Aluminum Oxide Template

Ru nanotubes were fabricated by atomic layer deposition (ALD) using bis(ethylcyclopentadienyl)ruthenium and oxygen onto an anodized aluminum oxide (AAO) template with a diameter of 50 nm and an aspect ratio of 10. The wall thickness of the Ru nanotubes could be precisely controlled from 13 to 23 nm by adjusting the number of ALD cycles. Transmission electron microscopy analysis revealed that the maximum density of the Ru nuclei on the alumina surface was as high as 1.8 X 10 12 cm -2 at 180 ALD cycles, and was thereby responsible for the conformal deposition of Ru inside the pore wall of the AAO template.

Excitonic trapping from atomic layer epitaxial ZnTe within ZnSe/(Zn,Mn)Se heterostructures

ZnSe‐based structures have been fabricated, consisting of monolayers of ZnTe grown by atomic layer epitaxy spaced by appropriate dimensions to approximate a Zn(Se,Te) mixed crystal; this method has been used to overcome the difficulties encountered in the molecular beam epitaxy (MBE) of the alloy with a low Te concentration. Reported work has shown that blue‐blue/green luminescence, originating from exciton self‐trapping at Te sites in Zn(Se,Te) bulk crystal alloys, is significantly more intense than the light emitted from ZnSe. Luminescence originating from ZnTe‐containing ZnSe/ZnTe superlattice and ZnSe/(Zn,Mn)Se multiple quantum well structures was used to illustrate how the presence of ZnTe acts to trap excitons. Optical signatures of the MBE‐grown structures were similar to those of the random alloy, indicating that the exciton self‐trapping mechanism is important to the interpretation of recombination processes in structures containing ZnSe/ZnTe heterointerfaces.

Atomic layer deposition of Ti-doped ZnO films with enhanced electron mobility

Ti is introduced as a dopant during the atomic layer deposition (ALD) growth of ZnO for use as a transparent electrode. ALD-grown Ti-doped ZnO (TZO) films are deposited via alternate stacking of ZnO and TiOx atomic-doping layers. Their growth behavior, structural, electrical and optical properties are investigated. Macroscopic film growth and doping concentration characterization show that both diethylzinc and titanium tetrakis(isopropoxide) exhibit enhanced adsorption during the ALD of TZO films. Contrary to conventional homogeneous compounds, atomic-layer Ti doping by ALD results in a much higher electrical conductivity and doping efficiency compared to its Al counterpart. Specifically, the ALD-grown TZO films show an electrical conductivity of 951 S cm−1, nearly twice that of AZO films (591 S cm−1), thanks to the high doping efficiency of Ti (41%) and its extraordinary high mobility (>20 cm2 V−1 s−1). Such high electron mobility is likely due to a smaller concentration of inactivated dopants as scattering centers.

A Bilayer Diffusion Barrier of ALD-Ru/ALD-TaCN for Direct Plating of Cu

Diffusion barrier performances of atomic layer deposited (ALD)-Ru thin films between Cu and Si were improved with the use of an underlying 2 nm thick ALD-TaCN interlayer as diffusion barrier for the direct plating of Cu. Ru was deposited by a sequential supply of bis(ethylcyclopentadienyl)ruthenium [Ru(EtC p ) 2 ] and NH 3 plasma and TaCN by a sequential supply of (NEt 2 ) 3 Ta = Nbu t (tert-butylimido-trisdiethylamido-tantalum), and H 2 plasma. Sheet resistance measurements, X-ray diffractometry, and Auger electron spectroscopy analysis showed that the bilayer diffusion barriers of ALD-Ru (12 nm)/ALD-TaCN (2 nm) and ALD-Ru (4 nm)/ALD-TaCN (2 nm) prevented the Cu diffusion up to annealing temperatures of 600 and 550°C for 30 min, respectively. This is because of the excellent diffusion barrier performance of the ALD-TaCN film against the Cu, due to its amorphous structure. A 5 nm thick ALD-TaCN film was even stable up to annealing at 650°C between Cu and Si. Transmission electron microscopy investigation, combined with energy-dispersive spectroscopy analysis, revealed that the ALD-Ru/ALD-TaCN diffusion barrier failed by the Cu diffusion through the bilayer into the Si substrate. This is due to the ALD-TaCN interlayer preventing the interfacial reaction between the Ru and Si.

Nonvolatile memory characteristics of atomic layer deposited Ru nanocrystals with a SiO2/Al2O3 bilayered tunnel barrier

This paper reports a formation process and electrical properties of a nonvolatile memory structure with atomic layer deposited Ru nanocrystals and a SiO2/Al2O3 bilayered tunnel barrier. Al2O3 tunnel barrier/Ru nanocrystals/Al2O3 blocking barrier were deposited sequentially on a SiO2 2 nm/Si substrate by an in situ atomic layer deposition (ALD) process. Ru nanocrystals grown on the Al2O3 surface for 80 ALD cycles had a spatial density of 2.4×1012 cm−2 and an average diameter of 2.6 nm (38% standard deviation in the diameter). Charging/discharging behavior of the Ru nanocrystals embedded in the metal-oxide-semiconductor capacitor structure was examined by programming/erase operations and comprehended in terms of asymmetric barrier height of the bilayered tunnel barrier. The memory structure showed charge retention of 91% and 85% after 105 s at room temperature and at 85 °C, respectively.