Sung-Soo Yim

Formation of Ru nanocrystals by plasma enhanced atomic layer deposition for nonvolatile memory applications

The formation of Ru nanocrystals is demonstrated on a SiO2 substrate by plasma enhanced atomic layer deposition using diethylcyclopentadienyl ruthenium and NH3 plasma. The island growth of Ru was observed at the initial stages of the film formation up to a nominal thickness of 11.1nm. A maximum Ru nanocrystal spatial density of 9.7×1011∕cm2 was achieved with an average size of 3.5nm and standard deviation of the size of 20%. Electron charging/discharging effect in the Ru nanocrystals is demonstrated by measuring the flatband voltage shift in the capacitance-voltage measurement of metal-oxide-semiconductor memory capacitor structure.

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 ...

Separate domain formation in Ge2Sb2Te5–SiOx mixed layer

We report separate domain formation in cosputtered Ge2Sb2Te5–SiOx mixed layer, with SiOx amount less than 10mol%. As-prepared Ge2Sb2Te5–SiOx layer exhibits amorphous phase with separate domains smaller than 20nm. The separation maintains after thermal annealing, which results in crystallization into fcc phase. The crystallization activation energies of Ge2Sb2Te5–SiOx are obtained as 4.99 and 6.44eV for mixed layers containing 5.3 and 8.4mol% SiOx, respectively. Those are larger than 2.75eV of pure Ge2Sb2Te5. Furthermore, the mixed layer exhibits sublimation at increased temperature. These are interpreted as formation of Ge2Sb2Te5-rich domains separated from each other by SiOx-rich domains.

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.

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.

Formation of Ge2Sb2Te5 – TiO x Nanostructures for Phase Change Random Access Memory Applications

Amorphous Ge 2 Sb 2 Te 5 clusters with a size of 20 nm, self-enclosed by a thin layer of TiO x , were obtained by cosputtering Ge 2 Sb 2 Te 5 and TiO 2 targets at room temperature with the aim of reducing the reset current for phase change random access memory applications. Eutectic decomposition during the deposition caused a phase separation of Ge 2 Sb 2 Te 5 and TiO x . The temperature-dependent resistance change results showed that the activation energy for crystallization increased from 2.44 ± 0.76 to 3.84 ± 1.43 eV in the Ge 2 Sb 2 Te 5 film. The set resistance can be tuned within an acceptable range, and the reliability of this microstructure during repetitive laser melt-quenching cycles was tested.

Atomic Layer Deposition of Ru Nanocrystals with a Tunable Density and Size for Charge Storage Memory Device Application

We propose a deposition method capable of independently controlling the spatial density and average size of Ru nanocrystals by using both plasma-enhanced and thermal atomic layer deposition (ALD). Plasma-enhanced ALD is used to promote the nucleation of Ru nanocrystals, while thermal ALD is used to assist their growth. By the rigorous selection of each stage, we can demonstrate the formation of Ru nanocrystals with a density variation from 3.5 X 10 11 to 8.4 X 10 11 cm -2 and sizes from 2.2 to 5.1 nm, which is in the optimum density and size range of nanocrystal floating-gate memory application.

Evaluation of integrity and barrier performance of atomic layer deposited WNxCy films on plasma enhanced chemical vapor deposited SiO2 for Cu metallization

The nucleation and growth of WNxCy films deposited by atomic layer deposition (ALD) on plasma enhanced chemical vapor deposited (PECVD) SiO2 is characterized as a function of the number of ALD cycles using transmission electron microscopy analysis. The island growth of isolated WNxCy nanocrystals is directly observed at the early stages of film growth. The nucleation of the WNxCy film can be significantly enhanced by NH3 plasma treatment before the deposition of WNxCy. The capacitance-voltage measurements conducted after bias-temperature stressing reveals that an ALD-WNxCy film deposited with a thickness of approximately 5.2nm on the NH3 plasma-treated PECVD SiO2 shows good diffusion barrier performance against Cu migration.

Diffusion Barriers Between Al and Cu for the Cu Interconnect of Memory Devices

We report a comparative study on the diffusion barrier performance of transition metal nitride thin films, including TiN x , TaN x , and WN x , between Al and Cu deposited by ionized physical vapor deposition (IPVD) or atomic layer deposition (ALD), which is particularly important for the integration of the Cu interconnect into memory devices such as dynamic random access memory and NAND Flash. Without a suitable diffusion barrier, various kinds of Al-Cu intermetallic compounds were formed, even after annealing at 200°C for 30 min. Sheet resistance measurements, X-ray diffractometry, and cross-sectional view transmission electron microscopy analysis combined with energy-dispersive spectroscopy consistently showed that the insertion of a 10-nm-thick IPVD-TiN x or IPVD-TaN x layer between the two layers retarded the interdiffusion of Al and Cu during the annealing at 400 or 450°C, respectively, for 30 min in a high vacuum (<5 × 10 -5 Torr). Noticeably, ALD-WN x prepared using a sequential supply of B 2 H 5 , WF 6 , and NH 3 , could effectively prevent the interdiffusion of Al and Cu and the formation of Al-Cu intermetallic compounds up to an annealing temperature of 550°C for 30 min.