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Removal
of small particles on silicon wafer by laser-induced
airborne plasma shock waves
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JOURNAL
OF APPLIED PHYSICS VOLUME 89, NUMBER 11
1 JUNE 2001
J.
M. Lee
Manufacturing
Technology Group, Institute for Advanced Engineering, Yongin,
P.O.B. 25, Kyunggi-Do, 449-860, Korea
- K.
G. Watkins
Laser Group, Department of Engineering, University
of Liverpool Brownlow Street, Liverpool L69 3GH, United
Kingdom
It
has been found that effective removal of small particles
from silicon wafer surfaces can be achieved by laser-induced
airborne plasma shock waves initiated above the surface.
This process has demonstrated successfully the removal of
1 mm sized tungsten particles from the surface. Tungsten
is known to be one of the most difficult particles to remove
using conventional laser cleaning techniques employing direct
laser irradiation onto the surface. The area cleaned by
the shock waves was over ten times larger than that achieved
by conventional laser cleaning. This provides an advantage
in speed for cleaning large areas. The cleaning efficiency
was strongly dependent on the gap distance between the laser
focus ~where laser-induced sparking takes place! and the
surface. The particle removal began to occur with a gap
of 6 mm and the removal efficiency increased significantly
with decreasing the gap resulting in a complete removal
at 2 mm. The basic idea behind this new cleaning technique
and how to apply it for the removal of small particles from
surfaces are described. Theoretical considerations about
adhesion forces of small particles on the surface and laser-induced
shock wave generation are carried out to understand this
process.
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