Laser assisted removal of micron and sub micron particulate contamination from semiconductor and optically transparent substrate

The removal of particles, on the order of a micrometer - nanometer in size, adhered to surfaces poses a challenge to Integrated Circuit (IC) fabrication, space optics, high resolution and high power optics, large area displays, magnetic storage device and other critical surfaces. The existing cleaning processes are unable to clean particulate contamination at the sub-micron level. Laser Assisted Particle Removal (LAPR) is a novel technique to remove micron and submicron particulate contamination from the solid surface. In LAPR, a vapor of an Energy Transfer Medium (ETM) is condensed on the Si substrate. The vapor forms a uniform film on and around the particles. After a short time lag a KrF laser beam is used to irradiate the Si substrate which causes explosive evaporation of the ETM and propels the particle off the substrate. The ETM film thickness should be a critical factor in the LAPR process. In our experiments KrF (at 248 nm) and CO2 laser (at 10.6 mum) is used to remove polystyrene, alumina and fused silica particles of from a Si substrate using 2-propanol and water as the ETM. The Cleaning threshold fluence for these particles at varying ETM film thicknesses and dosing times is measured. The interaction between substrate/particle/ETM system plays a critical role in LAPR process and it is studied by monitoring the process under the microscope.