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Whereas electrostatic damage to reticles
used to be a catastrophic but fairly
easily detected event, the nature of the
damage is changing. Reticle damage now
builds up progressively, causing a gradual
degradation of critical dimensions (CD)
and ultimately causing the formation of
bridges across clear areas. Thus a mask
that originally produces perfect devices
can deteriorate during use and print
increasingly defective images, but the
tiny defects are highly localised and can
be very difficult to detect. This type of
fault can escape detection until the
devices fail final test, by which time the
WIP racks are full of defective wafers –
that is a yield manager’s worst nightmare.
This paper explains the changing
nature of reticle damage and why established
static control precautions used in
fabs do not adequately protect against
this risk.
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