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Shock Pressure Measurements for the Removal of Particles
of Sub-micron Dimensions from Silicon Wafers

21st International Congress on Applications of Lasers and Electro-Optics, Scottsdale, October 14-17, 2002 (ICALEO 2002) ISBN 0-912035-72-2

C.Curran, K.G.Watkins, J.M.Lee
Laser Group, Department of Engineering, The University of Liverpool, United Kingdom

Abstract: Laser Shock Cleaning (LSC) is a new mechanism of laser cleaning recently proposed and investigated at University of Liverpool. By aligning the incoming laser beam to be horizontal to the surface to be cleaned but close to it and selecting operating parameters that lead to a breakdown of the air above the object to be cleaned, a laser induced shock wave is produced that is very much more effective than conventional normal incidence cleaning in removing surface pollutants. However, because the laser does not come into contact with the substrate, this method significantly minimises the potential for substrate damage. Experimental work has been carried out to investigate the use of LSC in the removal of micron and sub-micron size particles from silicon wafers, a significant problem in the fabrication of microprocessors and associated components. In this paper, typical shock pressures induced at the particle/substrate interface have been measured using calibrated piezo-ceramic sensors and the values compared with typical adhesion forces to predict success in the removal of particles of sub-micron dimensions effectively. The process mechanism is discussed by considering adhesion forces at the particle/substrate interface and the pressure generated as gap distance from the surface is increased.

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