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The information that follows is the
result of many joint efforts on behalf Noah Precision
and its Plasma Etch customers who share common goals;
Improve temperature uniformity at the wafer, reduce
the temperature component of first wafer effect,
and improve overall “chiller” cost of
ownership.
Below are five (5) considerations
when selecting a Thermoelectric Temperature Control
System:
1. All Thermoelectric (TE) chillers
NOT alike
Confirmed; TEs’ represent
only one part of a chiller’s design. The switching
& control methods used by a chiller will impact
the TEs’ reliability. The TEs’ can switch
directly from heating to cooling, or visa-versa. They
can switch on & off while in the heating or cooling
more and can increase or decrease the amount of heating
or cooling without switching whatsoever…
2. TE chiller close to chamber does
NOT equate to dynamic control
The reality is; that true Dynamic
Temperature Control can only be achieved when all
five (5) of the following system design and installation
requirements are met:
- fluid set-point temperature is controlled at the return loop
- very small fluid reservoir and process fluid-loop volume (< 1 US GA.)
- heating / cooling elements with rapid ramp rates
- short hose lengths from the POU module to the chamber
- maximized process fluid flow rate
(Therefore, installing a static unit next to a chamber
will not enable it to provide dynamic temperature
control)
3. TCU's do NOT require cooling capacity
equal to the process’ RF power
Our experience shows; that RF power
coupling efficiencies for optimally designed chambers
are approximately 40 – 45% of the lower RF power
and only 5 – 15% of the upper RF power.
All static TCUs require vast cooling
& heating capacities due to their very large
process fluid reservoirs vs. Noah’s dynamic
control system has 350 to 800% less fluid volume,
thereby requiring much less cooling/heating capacity
at significantly less cost.
4. Changing TCU's does NOT force process
recipe revisions
Noah will, for a customer’s
retrofit evaluation, monitor and adjust its fluid
temperature control profiles to match an existing
TCUs’ in order to guarantee a smooth process
integration via DAQ.
The Noah POU system’s dynamic
temperature control design and software gives
it exceptional flexibility for process-matching,
independent heating/cooling, PID control parameters,
independent heat/cool spread and cross-over control
values.
5. All wafer process tools do NOT accurately
display the temperature of their chambers
More than 3000 POU installations have proven
that; temperature monitoring differs according
to tool/chamber type, and:
- TC / RTD positions relative to the
wafer vary
- tool & TCU software calibration
procedures vary
- external test equipment not
used regularly for verifying
- inline fluid sensor (high RF
power) readings displayed
- TCU reports its reservoir temperature
on the tool
- calibration and software offset
procedures vary per customer/fab
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