Hyunchul Sohn

The electronic structure of C60/ZnPc interface for organic photovoltaic device with blended layer architecture

The interfacial electronic structures of fullerene (C60)/zinc-phthalocyanine (ZnPc) and C60/ZnPc:C60 (50 wt %) containing a blended layer were investigated by in situ ultraviolet photoelectron spectroscopy (UPS), in an attempt to understand the role of the blended layer in improving the performance of organic photovoltaic devices that contain such layers. From the UPS spectra, the band bending found to be 0.30 eV in the ZnPc layer and 0.43 eV in the C60 layer at the C60/ZnPc interface. On the other hand, the band bending was 0.25 eV in both of the organic layers at the ZnPc:C60/ZnPc interface and no significant band bending in the C60 layer at the C60/ZnPc:C60 interface was found. The observed interface dipole was 0.06 eV at the C60/ZnPc interface and 0.26 eV at the ZnPc:C60/ZnPc interface. The offset between the highest unoccupied molecular orbital of ZnPc and the lowest occupied molecular orbital of C60 was 0.75 eV at C60/ZnPc and was 1.04 eV at the ZnPc:C60/ZnPc interface. The increased offset can be a...

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).

TEM Study on Volume Changes and Void Formation in Ge2Sb2Te5 Films, with Repeated Phase Changes

Changes in volume in Ge 2 Sb 2 Te 5 (GST) films due to the density change during phase transformations between amorphous and crystallized states and consequent void formations were examined. Transmission electron microscopy (TEM) was used to measure changes in volume during laser-induced crystallization for both as-deposited and melt-quenched GST amorphous films, and changes in density were estimated. We found the formation of voids and their coalescence during repeated heat cycling by laser. A variation in chemical composition around the voids was confirmed using energy-dispersive spectroscopy analysis. The void formation and compositional changes can lead to degradation of reliability in phase-change random access memory devices.

Phase-change memory in Bi2Te3 nanowires

nanowires show considerable promise as building blocks for phase-change random access memory (PRAM). Phase-change materials are used in nonvolatile optical memory (e.g., CDs and DVDs), and are being actively inves-tigated as the media in universal solid-state memory devices that combine rapid read and write speeds, high storage density, and non-volatility.

Effects of B2H6 Pretreatment on ALD of W Film Using a Sequential Supply of WF6 and SiH4

The effects of diborane pretreatment on atomic layer deposition (ALD) of tungsten (W) thin film using a sequential supply of and on thermally grown and TiN films at 300°C were investigated. The results show that the pretreatment reduces the incubation time for film growth. X-ray photoelectron spectroscopy and scanning electron microscopy analysis suggest that elemental B on , released during pretreatment, induce rapid W nucleation. The drastically improved step coverage of ALD-W film is achieved at the ultrahigh aspect ratio contact (height: and top diameter: ) by the enhanced nucleation and growth via pretreatment. The effects of pretreatment on the properties of ALD-W films such as roughness, phase, microstructure, and resistivity are also investigated.

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.

A Comparative Study of the Atomic-Layer-Deposited Tungsten Thin Films as Nucleation Layers for W-Plug Deposition

The properties of three different kinds of atomic-layer-deposited (ALD) W thin films were comparatively characterized and investigated as nucleation layers for the W-plug process of 70 nm design-rule dynamic random access memory. ALD-W (A) film was deposited using alternating exposures of WF 6 and SiH 4 and ALD-W (B) film was treated with B 2 H 6 for 5 s prior to W ALD using WF 5 and SiH 4 . Finally, ALD-W (C) film was deposited using alternating exposures of WF 6 and B 2 H 6 . All the ALD-W films showed excellent step coverage at the contact with an aspect ratio of ∼ 14, but their resistivities were as high as 125-145 μΩ cm at the thickness of 20 nm. High resistivities of ALD-W films are discussed on the basis of impurities cooperation such as Si and B, phase (body-centered-cubic α-W or primitive cubic β-W), crystallinity (crystalline or amorphous), and grain size. It was found that ALD-W (C) film formed an amorphous phase, which was stable until 900°C annealing. This is clearly different from ALD-W (A) and ALD-W (B) with polycrystalline grains of α-W and β-W, and β-W was transformed to α-W after 800°C annealing. The formation of amorphous W resulted in the formation of large-size grains of chemical-vapor-deposited W film deposited on ALD-W (C) and the reduction in the resistivity of W-plug stack. The integration results showed that the reduced resistivity of W-plug stack with ALD-W (C) provided a significantly lower resistance at the W bit line contact. Another advantage of the integration scheme with ALD-W (C) was its stable contact resistance at the ultrahigh aspect ratio (UHAR) contact even though the step coverage of the underlayer, TiN, was poor. It was also found that the B 2 H 6 pretreatment was effective for obtaining the low and stable contact resistance at UHAR contact.

Characteristics of ALD Tungsten Nitride Using B2H6, WF6, and NH3 and Application to Contact Barrier Layer for DRAM

Tungsten nitride (WN x ) thin films were grown by atomic layer deposition (ALD) within the temperature range of 200-350°C from diborane (B 2 H 6 ), tungsten hexafluoride (WF 6 ), and ammonia (NH 3 ) for application to a contact barrier layer in dynamic random access memory (DRAM). Herein, B 2 H 6 was used as an additional reducing agent to produce a low-resistivity ALD-WN x film, and its resistivity was in the range of 300-410 μΩ cm, depending on the deposition conditions for the ∼ 10 nm thick film. An increase in the growth rate was observed with increasing deposition temperature, but an almost constant growth rate of ∼0.28 nm/cycle was obtained in the temperature range from 275 to 300°C. The properties of the as-deposited film, including the resistivity, W/N ratio, density, B and F impurity content, and phase, were affected by the deposition temperature and B 2 H 6 flow rate during the process. As the deposition temperature and B 2 H 6 flow rate increased, the W/N ratio and film density increased and the impurity content decreased, leading to a reduction in the resistivity of the film. An increased W/N ratio was found to be favorable to the formation of a face-centered-cubic β-W 2 N phase. Excellent step coverage was obtained even on a 0.14 μm diameter contact hole with an aspect ratio of 16:1. The ALD-WN x film in this study was thermally stable to annealing at 800°C for 30 min, but after annealing at 900°C, it converted to body-centered-cubic α-W with the accompanying release of N. The ALD-WN x film was evaluated as a barrier layer for W-plug deposition for 70 nm design-rule DRAM. The results showed that the integration scheme with ALD-WN x showed lower contact resistance than metallorganic chemical vapor deposition TiN or TiCl 4 -based chemical vapor deposited TiN.

Atomic layer deposition of low-resistivity and high-density tungsten nitride thin films using B2H6, WF6, and NH3

Tungsten nitride thin films were grown by atomic layer deposition using alternating exposures of B 2 H 6 , WF 6 , and NH 3 at 300°C. The film thickness linearly increased with the number of the reaction cycles and the determined growth rate was ∼0.28 nm/cycle with B 2 H 6 , WF 6 , and NH 3 at pulsing times of 5, 0.25, and 2 s, respectively. The film had a resisitivity of ∼350 μΩ cm with a metallic W-N bond and density of ∼15 g/cm 3 at the thickness of 10 nm. X-ray diffractometry analysis showed that the film had nanocrystalline grains with β-W 2 N and δ-WN phase. Step coverage was approximately 100% even on the 0.14 μm diameter contact hole with a 16:1 aspect ratio.

Phase Transformation Behavior of N-Doped Ge2Sb2 + x Te5 Thin Films ( x = 0 , 0.2 ) for Phase Change Memory

Ge 2 Sb 2 Te 5 and nitrogen-doped Ge 2 Sb 22 Te 5 films were deposited by dc magnetron sputtering on Si y O 2 /Si(100) substrates and the effects of antimony (Sb) and nitrogen (N) doping on microstructure and sheet resistance were investigated. After annealing at various temperatures between 100 and 400°C, phase transformations in Ge 2 Sb 2 Te 5 and nitrogen-doped Ge 2 Sb 2 2 Te 5 films were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The sheet resistance of those samples was measured by four-point probe. XRD and plan-view TEM analysis showed that the addition of Sb and N elements to pseudo-binary Ge 2 Sb 2 Te 5 caused crystallization and phase transformation from face-centered cubic (fcc) structure to hexagonal close-packed (hcp) structure to occur at higher temperatures with grain refinement. Also, the Sb and N doping produces increased sheet resistance in Ge 2 Sb 22 Te 5 films with improved phase stability of amorphous and fcc structures up to higher temperatures. N-doped Ge 2 Sb 22 Te 5 with high sheet resistance is favored for phase-change random access memory application because of reduced writing current with increased crystallization speed and thermal stability.