Hui-Gon Chun

Amorphous hydrogenated carbon films deposited by a closed-drift ion source

The general possibility of the extended (∼30 cm) closed-drift ion source application for deposition of wear-resistant amorphous hydrogenated carbon (a-C:H) films on large-area dielectric substrates, in particular, on carbon-fiber plastic, is shown. Parameters of the “ion” and the “plasma” regimes of the ion source operation in argon and methane are defined. It is shown that the ion current nonuniformity is in the range of ±5–15% depending on the operation mode. Optimum conditions for the substrate precleaning in argon and hard, well-adhered a-C:H films deposition from methane are determined. The films are characterized by high hardness (∼11 GPa) and low surface roughness (∼0.13 nm) that leads to a several times lower friction coefficient (0.05) and wear rate (0.001 μm 3 m −1 N −1 ) compared to glass and carbon-fiber plastic substrates.

A study on the removal of silicon native oxide for ULSI devices

In UV-excited F/sub 2/+H/sub 2/ dry cleaning, the etching mechanism and selective etching of silicon native oxide were investigated using PSG, BSG, TEOS and thermal oxide film on silicon wafers. Also, the removal of silicon native oxide in contact holes after UV-excited F/sub 2/+H/sub 2/ dry cleaning, was defined by confirming the reduction of Kelvin resistance.

Improving the Properties of Magnetic Bearing Shaft Material by HVOF Coating of WC-Metal Powder and Laser Heat Treatment

Abstract. Micron-sized WC-metal (WC-0.6%C-21%Cr-6%Ni) powder was coated onto the substrate of magnetic bearing shaft material Inconel718 (substrate or In718) using JK3500 HVOF thermal sprayer for the improvement of the surface properties of the substrate. The optimal coating process for the highest surface hardness was obtained using the Taguchi experimental program. The coating was laser heat-treated (LH) by CO2(g) laser for further improvement of the properties. During the thermal spraying, a small portion of metal carbides of powder decomposed to W2C, metals and free carbon. The free carbon reacted with excessively sprayed oxygen, and formed carbon oxide gases, forming porous coating. By laser-heating, porosity decreased and the porous strips at the interface of coating and substrate (coat/sub) compacted. At the interface, the precipitated graphite concentration decreased and the metal elements diffused from both the coating and substrate increased, enhancing the functions as buffer zone and increasing adhesion of coating. The surface hardness of substrate increased by coating and further increased by laser-heating from 410±30 Hv to 983±101 Hv and 1425±94 Hv respectively. Porosity of coating decreased by laser-heating from 2.6±0.4% to 0.35±0.06%, and coating thickness shrank from 280㎛ to 200㎛. Friction coefficients of substrate decreased from 0.52±0.02 to 0.36±0.04 by coating, because the free carbon formed by decomposition of WC to W2C functioned as a solid lubricant. By increasing sliding surface temperature from 25°C to 450°C, the friction coefficients of substrate and coating were decreased from 0.52±0.02 to 0.31±0.02 and from 0.36±0.04 to 0.23±0.04 respectively, because of easy formation of free carbon and metal oxides which functioned as solid lubricants. Wear depth of surface was decreased by coating and by LH coating from 55µm to 32 µm and to 12 µm respectively. HVOF coating of WC-metal powder on In718 surface and laser heat-treatment of the coating are highly recommended for the improvement of the properties of magnetic bearing shaft.

Effect of Substrate Bias Voltage on the Growth of Chromium Nitride Films

Chromium nitride (CrN) films were deposited on silicon substrate by RF magnetron sputtering assisted by inductive coupled nitrogen plasma without intentional substrate heating. Films were deposited with different levels of bombarding energy by nitrogen ions (N + ) to investigate the influence of substrate bias voltage (Vb) on the growth of CrN thin films. XRD spectra showed that the crystallographic structure of CrN films was strongly affected by substrate bias voltage. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) results showed that surface roughness and grain size of the CrN films varied significantly with bias voltage. For -80 Vb depositions, the CrN films showed bigger grain sizes than those of other bias voltage conditions. The lowest surface roughness of 0.15 nm was obtained from the CrN films deposited at -130 Vb.

Gas-phase technology and structure of films based on C/sub 60/ fullerene

The technology of C/sub 60/ fullerite film preparation by means of gas-phase deposition and the structure of the films are described. A flow three-channel set-up was used to obtain fullerene films. The films were deposited in an inert gas flow under reduced pressure onto a cooled silicon or sapphire substrate placed inside the reaction chamber. This set-up allows one to obtain films of pure fullerenes and to synthesise films from fullerene compounds and doped fullerenes. The film structure was investigated by FESEM and SEM techniques. All samples show columnar structure with a high level of porosity. The synthesis of fullerene-based films for use in electronics is shown to be promising. For example, experiments confirm the possibility of using fullerene films to produce humidity and thermal sensors. It is also possible to employ the sensitivity of these films to isostatic pressure. Experiments with C/sub 60/-Cu-J films shown quite strong dependence on the pressure of different sorts of medium-gases that could be used as gas-sensitive sensors. The structure and preparation technology of resistive sensors based on fullerene films are described.

HVOF Coating of µ-WC-Metal Powder and Laser Heat-Treatment of the Coating for the Improvement of Turbo Shaft Material

A hybrid surface treatment was performed to improve the surface properties and the durability improvement of turbo shaft material Inconel718. A micron sized (µ) WC-metal powder (86% WC 10% Co 4% Cr) was coated onto a substrate surface using HVOF thermal spraying, and the coating was heat treated by a CO2 laser. With the HVOF coating of the powder onto the substrate, the surface hardness of substrate increased approximately 300% from 399 Hv to 1260±30 Hv, and further increase of approximately 40% from1260±30 Hv to 1820±100 Hv by laser heating the coating for 0.6 s. Porosity of coating decreased more than five times from 2.2±0.3% to 0.4±0.1% by laser heating. According to the reciprocating sliding test, friction and wear behavior of coating improved by coating for both sliding surface temperature of 25°C and 450°C. Therefore, the HVOF coating and laser heat treatment of coating are recommended for the durability improvement of turbo shaft materials.

Chromium Nitride Coating by Inductively Coupled Plasma-assisted RF Magnetron Sputtering

Chromium nitride (CrN) films were deposited by using inductively coupled plasma (ICP) assisted RF magnetron sputtering to investigate the effect of substrate bias voltage on the hardness, surface morphology roughness, and crystalline growth on Si(100) substrate. As increasing substrate bias voltage (Vb), surface hardness increased from 5 to 15 GPa. The grain size also increased proportionally as increasing Vb from -30 to -80, while beyond -80 Vb, the grain size was deteriorated by an intense N+ion bombardment.

A Study for Stable End Point Detection in 90 nm WSix/poly-Si Stack-down Gate Etching Process

The device makers want to make higher density chips on the wafer through scale-down. The change of WSix/poly-Si gate film thickness is one of the key issues under 100 nm device structure. As a new device etching process is applied, end point detection(EPD) time delay was occurred in DPS+ poly chamber of Applied Materials. This is a barrier of device shrink because EPD time delay made physical damage on the surface of gate oxide. To investigate the EPD time delay, the experimental test combined with OES(Optical Emission Spectroscopy) and SEM(Scanning Electron Microscopy) was performed using patterned wafers. As a result, a EPD delay time is reduced by a new chamber seasoning and a new wavelength line through plasma scan. Applying a new wavelength of 252 nm makes it successful to call corrected EPD in WSix/poly-Si stack-down gate etching in the DPS+ poly chamber for the current and next generation devices.

Structure and Conductivity Characteristics of Sandwich Structures with Fullerite Films

We report on the technology of formation of sandwich structures based on fullerite films and on experimental results in research of optical and conductivity properties of these sandwich samples. Single crystals of sapphire (100) or silicon were used as substrates. The sandwich specimens were based on the structure M//M (M

Surface Morphology, Microstructure and Mechanical Properties of Thin Ag Films

Thin Ag films deposited onto SiO/sub 2//Si substrates by DC magnetron sputtering and thereafter annealed at temperatures 100-500/spl deg/C are investigated by scanning tunneling and atomic force microscopy. It is shown that the film surface topography and microstructure are considerably changed as a result of annealing. To provide a quantitative estimation of the surface topography changes of Ag films the surface fractal dimension was calculated. Elasticity and hardness of the films are studied by a nanoindentation technique. The films are found to have value of elastic modulus close to that of bulk silver while their hardness and yield stress are essentially higher.