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Laser Cleaning of a Delicate (Easily Laser Damaged) Surface

IP.com Disclosure Number: IPCOM000108668D
Original Publication Date: 1992-Jun-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 104K

Publishing Venue

IBM

Related People

Tam, AC: AUTHOR [+2]

Abstract

Recent laser cleaning has shown effective particulate removal from a surface using laser irradiation together with liquid-film deposition. This is easily done on a "robust" surface (e.g., Si wafer) which withstands relatively high laser fluence. For delicate surface (e.g., thin carbon), we show that laser damage is greatly reduced or eliminated by droplet condensation on the particulates together with large incidence-angle irradiation.

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Laser Cleaning of a Delicate (Easily Laser Damaged) Surface

       Recent laser cleaning has shown effective particulate
removal from a surface using laser irradiation together with
liquid-film deposition.  This is easily done on a "robust" surface
(e.g., Si wafer) which withstands relatively high laser fluence.  For
delicate surface (e.g., thin carbon), we show that laser damage is
greatly reduced or eliminated by droplet condensation on the
particulates together with large incidence-angle irradiation.

      With the rapid advance in miniaturization, resolution, and
performance in high-technology, the demand for effective cleaning of
even tiny submicron particles without damaging delicate parts becomes
more and more critical.  The inadequacies of existing cleaning
techniques is well summarized in a recent article (1); these
techniques including liquid rinses, ultrasound, plasmas,
electrostatics, gas jets, and other conventional cleaning techniques
are all regarded as ineffective for submicron particle removal.  To
remedy this situation, various techniques of "laser cleaning" have
recently been demonstrated, e.g., "dry laser cleaning" (2), "wet
laser cleaning" with continuous liquid-film enhancement (3), and "wet
laser cleaning" with pulsed liquid-film enhancement (4).  However,
these previous investigations required relatively large laser
fluence, e.g., about 0.3, 30, and 0.2 J/cm2 in (2, 3 and 4),
respectively.  While these work well for relatively "robust" surface,
delicate surface could be damaged by the laser pulses.  For example,
in our attempt to perform liquid-film enhanced laser cleaning of a
carbon-coated ceramic surface, we observed that even a fluence of 100
mJ/cm2 would cause removal of the thin a-carbon coating.  This
situation is observed for a carbon-coated ceramic surface being
cleaned by several pulses from a KrF laser at a fluence of 120 mJ/cm2
at normal incidence with pulsed water enhancement (4); while
particles are definitely removed, the carbon coating at the surface
is also completely removed too.  When the fluence is reduced to 100
mJ/cm2, the carbon coating at the surface is still partially removed.
At lower fluence, cleaning becomes ineffective.  Hence, this
straightforward laser cleaning cannot be simply applied to clean
delicate parts like the magnetic heads.

      The present invention shows how to overcome the difficulty
above for laser cleaning of minute particles from such delicate
surfaces that can be d...