Showing papers by "Minghui Hong published in 1998"

Automatic Control and Real-Time Monitoring of Laser Cleaning and Laser Ablation

Abstract: Closed-loop control and real-time monitoring of pulsed excimer laser cleaning and ablation have been realised by software and hardware design and development. The audible acoustic wave generated during excimer laser surface cleaning and ablation has been used as the feedback signal for the automatic control system of laser-surface interaction. Man–machine interface for laser operation and acoustic monitoring has been developed with LabVIEW 4.1 under Windows 95 environment. This system has been used to control and monitor laser cleaning and ablation processes in real-time and proven to successfully meet the requirements in our study. By database exchange, this automatic control system can also be applied to control drilling and materials removing.

Plasma diagnostics in KrF excimer laser deposition of Ti thin films

Abstract: Pulsed laser deposition of Ti thin films for wafer metallization is investigated by optical spectroscopy. Ti plasma emission spectra are captured to study plasma generation, expansion and recombination during the thin film deposition. Ti plasma has a very rich emission spectrum in a region from 180 to 650 nm. There exist two phases of plasma characterization. The first phase is plasma ionization by the laser heating near the target surface. Gate delay is up to 200 ns at this phase. There is continuum emission resulted from free-free and free-bound transitions. The second phase is plasma recombination in its propagation process. The dependence of Ti spectral line intensities on gate delay, laser fluence and chamber pressure is also studied. The intensities decrease with gate delay, but increase with laser fluence and tend to saturate at laser fluence higher than 4.6 J/cm 2 due to the plasma shielding effect. The spectral line intensities do not vary with chamber pressure up to 0.1 Torr. At the higher pressure, plasma is confined by air molecules and the intensities increase greatly with the chamber pressure. Plasma electron density is calculated as the functions of gate delay, laser fluence and chamber pressure from the Stark broadening of the spectral lines. Electron temperature is also estimated as 1.5 eV from the local thermodynamic equilibrium (LTE) assumption. Fast time-resolved photography is applied to analyze the plasma plume evolution in its propagation. The plasma expands outwards and flies from target to substrate at speeds up to 10 6 cm/s.

Laser cleaning of magnetic disks

Abstract: Laser cleaning of disk surfaces was investigated both experimentally and theoretically. It was found that laser cleaning efficiency increases with increasing laser fluence and pulse number. The optimal cleaning conditions can be selected between the two boundaries of damage thresholds and critical cleaning thresholds (100% cleaning). A cleaning model was established for laser-induced removal of particles from substrate surfaces by taking Van der Waals force and cleaning force into account. The theoretical analysis shows that the cleaning force (per unit area) increases with increasing laser fluence, which leads to a higher cleaning efficiency for removing particles from disk surfaces. The experimental results can be explained by the model and simulation.

KrF excimer laser deposition of titanium thin films on silicon substrates

Abstract: Pulsed laser deposition (PLD) of titanium thin films on p-type (100) silicon substrates by KrF excimer laser ablation is investigated by changing the deposition parameters during the thin film deposition. The influence of target-to-substrate distance, laser fluence and substrate temperature is studied for high quality titanium thin films. Energy dispersive x-ray (EDX) spectrum analysis of the thin films is also carried out. The surface texture of the titanium target after the laser irradiation is studied by scanning electron microscope (SEM) images. It is found that the most important deposition parameters which affect the thin film quality are target-to- substrate distance and laser fluence. A suitable target-to- substrate distance and laser fluence can minimize the deposition of micro-sized particulates on the thin films. By optimizing the deposition parameters, the less particulate, higher deposition rate and more uniform titanium thin films are grown on the silicon substrates for wafer metallization.

Spectroscopic Study of Pulsed Laser Induced Plasma from Aluminum Surface

Abstract: Optical emission spectrum of aluminum plasma induced by a 1064 nm Nd:YAG laser is investigated by an Optical Multichannel Analyzer (OMA). Spectroscopic study shows that more number of Al, Al+, and Al++ spectral lines can be observed with increasing the incident laser fluence. Al, Al+, Al++ spectral lines are also observed successively with high fluence. The atomic spontaneous radiation is analyzed to interpret the calibrated plasma spectrum. The laser energy threshold for the appearance of excited Al, Al+, and Al++ spectral lines are about 0.8, 1.0 and 1.5 J/cm2 respectively. Assuming LTE (Local Thermodynamic Equilibrium) conditions, the plasma density is derived to be in the range of 0.7×1017 to 2×1017 cm-3 from the profiles of Al+ (358.7 and 286.1 nm) spectral lines with different gated times and incident laser fluences. The plasma temperature is also estimated to be 4000 ~ 8000 K, from relative intensities of two different Al I spectral lines (309.2 and 396.2 nm) with different fluence.

Real-time monitoring of indium tin oxide laser ablation in liquid crystal display patterning

Abstract: Audible acoustic wave detection is applied to investigate KrF excimer laser ablation of Indium Tin Oxide (ITO) thin film layer for Liquid Crystal Display (LCD) patterning. It is found that there is no acoustic wave generation if laser fluence is lower than ITO ablation threshold. For laser fluence higher than the threshold, audible acoustic wave will be detected due to shock wave generation during ITO laser ablation. The amplitude of the acoustic wave is closely related to the laser ablation rate. With more laser pulse applied, the amplitude is dropped to zero because the ITO layer is completely removed. However, if laser fluence is increased higher than ablation threshold for glass substrate, the amplitude is also dropped with pulse number but not to zero. It is due to laser ablation of ITO layer and glass substrate at the same time. Since the thickness of ITO layer is in a scale of 100 nm, laser interaction with glass substrate will happen even at the first pulse of high laser fluence irradiation. Laser ablation induced ITO plasma emission spectrum in visible light region is analyzed by an Optical Multi-channel Analyzer (OMA). Specific spectral lines are In I (325.8, 410.2 and 451.1 nm) and In II 591.1 nm. Spectral intensities of 410.2 and 451.1 nm lines are selected to characterize the evolution of ITO plasma intensity with laser fluence and pulse number. It is found that the spectral intensities are reduced to zero with laser pulse number. It is also found that spectral lines other than ITO plasma will appear for laser fluence higher than ablation threshold for glass substrate. Threshold fluences for glass and ITO ablation are estimated for setting up a parameter window to control LCD patterning in real-time.