Jong-Myoung Lee

Removal of small particles on silicon wafer by laser-induced airborne plasma shock waves

It has been found that effective removal of small particles from silicon wafer surfaces can be achieved by laser-induced airborne plasma shock waves initiated above the surface. This process has demonstrated successfully the removal of 1 μm sized tungsten particles from the surface. Tungsten is known to be one of the most difficult particles to remove using conventional laser cleaning techniques employing direct laser irradiation onto the surface. The area cleaned by the shock waves was over ten times larger than that achieved by conventional laser cleaning. This provides an advantage in speed for cleaning large areas. The cleaning efficiency was strongly dependent on the gap distance between the laser focus (where laser-induced sparking takes place) and the surface. The particle removal began to occur with a gap of 6 mm and the removal efficiency increased significantly with decreasing the gap resulting in a complete removal at 2 mm. The basic idea behind this new cleaning technique and how to apply it f...

Laser removal of oxides and particles from copper surfaces for microelectronic fabrication

Laser removal of surface oxides and small particles from copper surfaces was carried out using a Q-switched Nd:YAG laser. Oxide layers and small particles on copper surfaces should be removed for the improvement of solder quality on printed circuit boards (PCBs) and for the prevention of circuit failure or loss of production yield during the fabrication of microelectronic devices. A selective removal of surface oxides from a copper surface was achieved by the laser treatment, which was confirmed by on-line acoustic monitoring of the process. An angular laser cleaning technique in which the laser irradiates the surface at a glancing angle was used for effective removal of the particles from the surface. The unique characteristics of this technique and the cleaning mechanism are discussed.

Ultraviolet laser removal of small metallic particles from silicon wafers

Laser removal of small 1 μm sized copper, gold and tungsten particles from silicon wafer surfaces was carried out using ultraviolet radiation at 266 nm generated by Nd:YAG harmonic generation. Successful removal of both copper and gold particles from the surface was achieved whereas tungsten particles proved to be difficult to remove. The cleaning efficiency was increased with an increase of laser fluence. The optimum processing window for safe cleaning of the surface without any substrate damage was determined by measuring the damage threshold laser fluence on the silicon substrate and the required fluence for complete removal of the particles. The different cleaning efficiencies with particle type are discussed by considering the adhesion force of the particle on the surface and the laser-induced cleaning force for the three different particles.

Chromatic modulation technique for in-line surface monitoring and diagnostic

Abstract A fast and reliable surface monitoring and diagnostic technique is essential to develop a real-time automatic control system for laser cleaning of artworks. In this paper, an in-line surface monitoring and diagnostic system based on chromatic modulation using tristimulus detectors and fibre optics is presented. The system produces measurements that are dependent on the spectral signature of the incident light but are independent of intensity. In order to demonstrate its usefulness and versatility, the technique was applied to surface monitoring in the laser cleaning of metal and stone. Results show that the spectral parameters derived from chromatic detection not only provide a clear indication of the surface cleanliness and surface damage but also much surface chromatic information from its versatility. It is also shown in this paper how a chromatic modulation technique may be utilised as a robust method for monitoring and diagnosing the surface during laser cleaning.

Application Study of Dry-ice Pellet Cleaning for Removing Oil Paint and Lacquer of Outdoor Metal Artifacts

Damage of cultural properties happens variously. Particularly, the surface damage of metal cultural properties exposed outdoors lowers historical and art historical value of artifact by artificial damage such as paint, scribbling containing oily material and so on. Therefore, this study compared dry-ice pellet cleaning with poultice when clearing paint and oily material environment-friendly, harmlessly to humans and without damage of artifact. As the result of experiment, when clearing those (paint and oily material) by poultice, oily paint was cleared, but there were spots of metal surface. Also, Lacquer spray wasn`t well cleared, and resin came off the surface of artifact. When clearing those by dry-ice pellet cleaning, oil paint was cleanly cleared without surface damage of artifact according to Stereoscopic microscope observation, color-measurement, FT-IR, SEM analysis. Also, lacquer spray seemed to be cleared with the naked eye, but there were minute particles on surface according to the result of SEM observation. Consequently, we could confirm possibility of dry-ice pellet cleaning substitution.

Prediction system of surface damage

During laser cleaning, surface damage on the substrate could easily occur by overexposure to a laser pulse of high fluence. The damage is especially serious in art conservation where recently the laser has found a successful field of application. Successful cleaning without surface damage can be achieved by skilled expert operators with long experience and good technique. This paper presents a fuzzy rule-based expert system to predict surface damage during laser cleaning like a human expert. In this work, a fuzzy rule base was used to embed the acoustic information including an indication for the progress in cleaning and the result. An inference process was conducted to predict whether and how much surface damage would be induced on the substrate. In order to detect the acoustic waves a wide-band microphone was utilised. Tests of the performance of the fuzzy expert system showed that the prediction of surface damage is well correlated with the actual results independent of initial surface conditions. Finally, a process control algorithm for laser cleaning has been developed on the basis of the surface damage prediction system.

Underlying Mechanisms in Laser Techniques for Art Conservation: Two Improved Cleaning Methods

Optimization of restoration techniques employing lasers is dependent on the selection wavelength, cover fluid, pulse duration and method of application. This affects the mechanisms operating during the removal process and hence its efficiency. The risk of unwanted side effects will be more or less controllable depending on the mechanism of removal.

Laser removal of particles using tunable wavelength

Summary form only. As semiconductor and microelectronic devices are becoming increasingly smaller, contamination of these devices is becoming an increasing problem for manufacturers. Conventional techniques such as mechanical wiping, scrubbing and etching may involve chemicals and hence pose possible environmental problems as well as introducing possible changes in surface profile. Therefore steps have been taken to introduce new techniques that do not pose any of these problems, one such technique is to use lasers. Laser cleaning is versatile, controllable, selective and environmentally friendly.

Angular laser cleaning for the enhancement of cleaning efficiency

Summary form only given. Laser cleaning has begun to attract a considerable amount of interest recently as a new cleaning technique among scientists and engineers. Due to its unique characteristics as a selective, precise, controllable and environmentally-friendly process, the laser cleaning technique is finding a wide range of successful applications both in industry and in the world of art conservation. In this paper, laser removal of small particles on metal surface is carried out by changing the incidence angle of laser beam. It is found that dramatic improvement of cleaning efficiency is observed at the glancing angle of incidence on the surface compared to the perpendicular incidence of laser beam. Furthermore substrate damage is greatly reduced and probably eliminated at the glancing angle of incidence.