Chapter Two - Cleaning

Abstract

This chapter discusses the use of liquids in laser cleaning. Liquids may facilitate the removal of particles or surface layers from solids in several ways: by reduction of adhesion forces, by providing expanding vapors, or by acting as a medium for acoustic or shock waves. The most important application of liquid-assisted (wet) laser cleaning is the removal of particulate contamination from solid surfaces, especially from silicon wafers for semiconductor integrated circuits. Regarding other areas, liquid-assisted laser techniques have proved to be effective for removal of small particles from rotating magnetic information storage disc surfaces and from telescope mirrors. Furthermore, liquids may also be beneficial at laser removal of surface layers from solids, by lowering the thermal load on the materials and preventing the dissipation of debris into the ambient atmosphere. Laser techniques have also been considered appropriate for removal of radioactive contaminants in nuclear facilities, and for cleaning of optical surfaces in space systems from frozen water and gases. This chapter delineates the principles of liquids-assisted laser cleaning (LALP). It also deals with removal of particles on solid surfaces. Furthermore, it describes various experimental techniques in laser wet/steam cleaning research and finally sheds light on the physics and phenomenology of liquid-assisted laser removal of particles from surfaces.