Laser-cleaning techniques for removal of surface particulates

Abstract

Flash laser heating using short-pulsed laser irradiation of a surface is demonstrated to be a promising new approach for effective removal of particulate contaminations of sizes as small as 0.1 μm. This is very useful because micron- and submicron-sized particulates adhere tenaciously onto a solid surface, and conventional cleaning techniques are inadequate for removal. Several varieties of the new laser-cleaning techniques have been developed by us as well as by others. For example, the pulsed laser irradiation can be used with or without the simultaneous deposition of a thin liquid film on the surface to be laser cleaned. The laser wavelength can also be chosen so that absorption occurs mainly at the sample surface, or in the liquid, or in the particulate, or in a combination of these. In this paper, we discuss and compare examples of these different approaches. We find that laser cleaning with highest efficiency is achieved by choosing a laser wavelength that is strongly absorbed by the surface together with pulse depositing a water film of thickness on the order of microns on the surface momentarily before the pulsed laser irradiation. This permits the effective removal of particles smaller than ∼20 μm, down to as small as 0.1 μm, from a solid surface using a modest ultraviolet laser fluence of ∼0.1 J/cm2.

The effects of short pulse laser surface cleaning on porosity formation and reduction in laser welding of aluminium alloy for automotive component manufacture

“…2Al + 3H2O  Al2O3 + 3H2 (8) Although laser cleaning helped to significantly reduce porosity in the studied Al alloys, there is still a very small percentage of porosity in both types of welds after cleaning. This can be attributed to many sources 5,39,40 :…”

“…According to the laser wavelength and the type of the substrate material, the irradiation energy is absorbed by the surface, a particle or the contaminated film 7 . Tam et al found that the ejection acceleration (~10 10 cm/s) given to a particle by the laser radiation is much greater than gravitational acceleration 8 . This results in particles ejection without melting the surface.…”

Continuous-wave laser particle conditioning: Thresholds and time scales

“…A CW laser system that could self-clean and condition with a low power initial start-up shot would be highly desirable. Pulsed lasers have long been studied and used for laser cleaning [6], though less research has been focused on continuous-wave laser cleaning.…”

Near field induced defects and influence of the liquid layer thickness in Steam Laser Cleaning of silicon wafers

“…In this case, the rise of the scattered light was caused by these redeposited partially agglomerated particles. This result indicates that uncontrollably deposited films with thicknesses on the order of micrometers, as were used in [6] and [16], may be far from optimal in terms of particle redeposition.…”

“…Already some of the first publications on laser cleaning [2,3] have reported an enhancement of the particle removal efficiency in SLC compared to Dry Laser Cleaning (DLC), for which no ETM is used and the cleaning relies on thermal substrate expansion or local ablation [4,5]. The capabilities of SLC have been demonstrated in a variety of experiments [6][7][8][9][10]. However, so far the amount of liquid on the surface has not been controlled very precisely in any of the measurements.…”