Kyoung-cheol Lee

Surface modification of silicon and PTFE by laser surface treatment: improvement of wettability

Laser surface treatment was used to modify the surface of silicon and PTFE (polytetrafluoroethylene). This method is in order to improve its wettability and adhesion characteristics. Using a 4th harmonic Nd:YAG pulse laser (λ = 266 nm, pulse), we determined the wettability and the adhesion characteristics of silicon and PTFE surfaces developed by the laser irradiation. Particularly, surface treatment of PTFE was only effective when the irradiated interface was in contact with the triethylamine photoreagent. We investigated laser surface treatment of materials by the surface energy modification. By using the sessile drop technique with distilled water, we determined that the wettability of silicon and PTFE after the irradiation showed a decrease in the contact angle and a change in the surface chemical composition. In case of the laser-treated materials surface, laser direct writing of copper lines was achieved through pyrolytic decomposition of copper formate films by using a focused argon ion laser beam (λ = 514.5 nm, cw) on silicon and PTFE substrates. The deposited patterns and the surface chemical compositions were measured by using energy dispersive X-ray, scanning electron microscopy, X-ray photoelectron spectroscopy, and surface profiler to examine cross section of the deposited copper lines.

The dry laser cleaning of photoresist residues on Si and ITO substrate

The cleaning of photoresist residues on Si and ITO substrate is necessary in electronics device fabrication in order to improve the device performance and manufacturing efficiency. This study is about the laser cleaning of the photoresist residues (AZRFP23OK2) on the substrates being able to substitute conventional photoresist ashing and wet cleaning equipment. The laser cleaning effect of Q-switched Nd:YAG laser at 266 and 532 nm in order to remove the residues on Si and ITO substrate was investigated with regard to laser fluence, shots and wavelength. The cleaning efficiency for the residues on Si substrate was higher than that of ITO at the same laser fluence and shots for both 266 and 532 nm. Much more effective cleaning of the residues on the substrate can be done with flowing assistant inert N2 gas during the laser cleaning process.

Comparison of the structural characteristics and surface morphology of ZnO thin films grown on various substrates by pulsed laser deposition

ZnO thin films on (100) p-type Si and sapphire substrates have been deposited by pulsed laser deposition technique using Nd:YAG laser with a wavelength of 266 nm. The influence of the deposition parameters such as oxygen pressure, substrate temperature and laser energy density on the properties of the grown films, was studied. The experiments were performed for substrates temperature in the range of 200 - 500°C and oxygen pressure in the range of 100 to approximately 700 sccm. All the films grown in this experiment show strong c-axis orientation with (002) textured ZnO peak. With increasing substrate temperature, the full width at half maximum (FWHM) and surface roughness were descreased. In case of sapphire substrate, the intensity of PL spectra increased with increasing ambient oxygen flow rate. We investigated in the structural and morphological properties of ZnO thin films using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Optoelectrical and optoacoustic analysis of the laser cleaning process of a photoresist on Si and ITO

By irradiating a Nd:YAG (λ=266 and 532 nm, pulse) laser beam, we investigated the cleaning process of a photoresist particles on Si and ITO substrate. The influences of laser fluence, wavelength, and substrate properties on the laser cleaning performance were investigated. The removal rate for the particles of Si substrate was higher than that of ITO at the same laser fluence and pulses for a wavelength of 266 nm. Using 2nd harmonic Nd:YAG laser (λ = 532 nm), it was found to be inappropriate for the complete particle removal and ablation of photoresist film without substrate damage. Water-condensed particles are rarely cleaned even on the laser fluence of being capable of completely removing dried sample resulting from the increase of viscosity of the particles, the scattering, and the reflection of incident laser beam.

Comparison of ITO ablation characteristics using KrF excimer laser and Nd:YAG laser

We studied to develop ITO (Indium Tin Oxide) thin films ablation with a pulsed type KrF excimer ((lambda) equals248 nm) and Nd:YAG laser ((lambda) equals262 and 532 nm) required for the electrode patterning application in flat panel display into small geometry on a large substrate area. The threshold fluence for ablating ITO on glass substrate using KrF excimer laser is about 0.1 J/cm2. In this case, through the optical microscope measurement the surface color of the ablated ITO is changed into dark brown due to increase of surface roughness and transformation of chemical composition by the laser light. And the XPS analysis showed that the relative surface concentration of Sn and In were essentially unchanged (In:Snequals5:1) after irradiating the KrF excimer laser. It has been reported that ripple like structure was by 2nd harmonic Nd:YLF laser (equals523nm). But in case of using 2nd harmonic Nd:YAG laser, in our study, the ablated films have well patterned and the shape is almost clean even though by-product exists in the vicinity of the etched surface region. But the films were damaged at the same laser fluence using 4th harmonic Nd:YAG laser. We will discuss this cause in terms of photon energy and the film thickness, used in this experiment, repetition rate and beam scan speed of each laser.

An Experimental Investigation on Mechanical Fatigue Property of Chemical Starch-Based ER Fluids

In this work, mechanical fatigue properties of a chemical starch-based ER fluid are empirically investigated. To do this, a flow-mode type electroviscometer, which has the same working mode as the cylindrical ER damper, is constructed. The linear reciprocating motion is obtained by driving a hydraulic power unit, and the number of fatigue cycle is measured by the limit switch. The field-dependent yield stress and response time to step input are evaluated as a function of the operating cycle. In addition, the vibration control performance of ER suspension for a passenger car is analyzed by incorporating the full-vehicle model with the yield stresses evaluated at different operating cycles.

Etching characteristics of the PDP barrier rib pastes by focused Ar + laser and Nd:YAG laser

The paste dried and hardened on glass substrate for fabrication of the PDP (Plasma Display Panel) barrier rib was selectively etched using focused Ar+ laser ((lambda) =532 nm), the threshold laser fluence was about 6.5 mJ/cm2 for the barrier rib samples softened at 120 degree(s)C. The thickness of 180 (mu) of the sample was completely removed without any damages on the glass substrate by laser fluence of 19.5 J/cm2. In order to increase the etch rate of the barrier rib materials, samples were heated on a hot plate during the laser irradiation. The etch rate at the hot plate temperature of 200 degree(s)C was roughly 4.2 times faster than that of room temperature.

Laser direct etching for a PDP cell using Nd:YAG laser

A photoresist films on Si and commercial glass and the paste dried and hardened for forming barrier rib of PDP were directly etched with Ar+ laser Nd:YAG laser beam. Exposing the photoresist to a fourth harmonic Nd:YAG laser beam to produce electrodes on the transparent conductive material, the etching threshold laser fluence was 25 J/cm2 and the damage of substrate was appeared over the laser fluence of 40 J/cm2. The reaction mechanism of the photoresist by the UV laser beam, compared to that by Ar+ laser, is photon-assisted ablation. A barrier rib is compared of mixtures that were made form organic gel, glass powder and ceramic powder. Using a second harmonic Nd:YAG laser the threshold laser fluence was 65 mJ/cm2 for the barrier rib samples softened at 120 degrees C. The thickness of 130 (mu) M of the samples on the glass was clearly removed without any damage on the glass substrate by laser fluence of 19.5 J/cm2. The barrier rib samples on hot plate were etched by Nd:YAG laser with increasing a temperature of the sample. The etch rate at 200 degrees C was 4 times of that at room temperature. Indium tin oxide thin films on lime glass were directly etched using the second and fourth harmonic Nd:YAG laser beam.