| CMP slurry flow measurement
Slurry can clog up a filter pretty quickly, a system using
patented non contact concurrent transit time flow technology
(CTT flowmeter) has been devised that can help determine
filter life and avoid process interruptions. Point-of-use
(POU) slurry filtration in chemical-mechanical polishing
(CMP) applications is essential for preventing agglomerated
slurry particles, which cause scratch defects and lower
yields, from reaching the wafer surface. Preventing slurry-based
wafer contamination will become increasingly important as
device geometries shrink, because the presence of even very
small particles on the wafer can cause terrible defects
in very small line widths.
Slurry flow is a key parameter in achieving a successful
CMP process.1 POU filters are used to remove agglomerated
and oversized particles and gels that form inadvertently,
while allowing desirable slurry particles to pass through.2
The loss of slurry flow can occur at any time during the
process if particulates accumulate and clog up the filter
element.3 When POU filters are used in chemically dominant
processes such as shallow trench isolation and metal polishing
involving tungsten and copper, an unanticipated reduction
of slurry flow can be highly detrimental to wafer integrity.
Previously an ultrasonic flowmeter, although easy to install
since it mounts outside the slurry-transport tube and does
not contact the slurry, had functional velocity requirements
that do not meet the operating flow rates required to perform
the CMP process. This is no longer true with Concurrent
transit time flowmeters which have an uncanny ability to
measure ultra low flow with unsurpassed linearity and repeatability.
Slurry flow is relatively slow can not only be picked up
but measured accuractely - see
http://www.eesiflo.com/non-contact-flow-sensing-units-for-small-line-ultra-low-flow.html
A ball-float meter is designed to work only with transparent
fluids, since readings are obtained by visually observing
the ball position in the fluid medium through clear, marked
tubing. The instrument's accuracy is lower than desired,
and the position of the ball fluctuates.
A paddle-wheel meter, although commonly used to measure
slurry flow, contains parts that move in the slurry medium,
posing a risk of particle generation. The instrument is
unreliable because it can become clogged with slurry. |
