Abstract

Particulate contamination is a major yield loss factor in the manufacturing of microelectronic, data-storage, and other hi-tech devices. A single particle as small as 0.1 μm in size can cause complete micro-electronic circuit failure, or seriously degrade read/write performance of magnetic storage devices or even result in a crash of the magnetic head. Standard cleaning techniques, typically performed in liquid baths, have two major drawbacks: first, there is limited cleaning efficiency for submicron particles, and secondly, liquid baths tend to redeposit or even add new particles to the submersed surface. ‘Laser cleaning’, a technique currently being developed, appears capable of overcoming the above shortcomings. We observe that, particles of size 10 - 0.1 μm can be efficiently removed from various surfaces, and there is no need for a liquid bath. The technique we studied is based on the use of <img>-pulsed infrared or ultraviolet lasers to explode a thin liquid film which is condensed onto the surface to be cleaned. Such explosion was studied in detail with nanosecond thermometry, photoacoustic detection, and fast photography. Momentum transfer from the expanding steam to the particles on the surface is believed to be the cause for the ejection of the particles. Ejection to ‘macroscopic’ distances (exceeding a few mm) from the surface facilitates particle collection procedures and thus prevents redeposition; this is of importance for practical application of ‘laser cleaning’.

© 1993 Optical Society of America