INFICON IC/5 Thin Film Deposition Controller - Manual (Page 207)

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IC/5 Operating Manual
Chapter 10
Applications
10.1 Multiple Sensor Deposition Control
The conventional method of controlling thin film depositions is to use one crystal
sensor for each material source. In addition to this conventional method, the IC/5
can make use of multiple sensors for control of each material source.
To use multiple sensor deposition control, elect the appropriate Sensor Option for
as many sensors as desired (up to 8). The Sensor Option parameter is located on
page 3 of each Material Set-Up display (refer to
section 4.3 on page 4-5 ). For
conventional deposition control (one sensor per material source) simply select one
sensor.
The multiple sensor deposition control feature is designed to monitor a source's
flux distribution using many sensors. Multiple point sensing improves thickness
reproducibility by controlling an aggregate (averaged) deposition rate. Two
important elements of a deposition process contribute to layer-to-layer thickness
variances and cannot be addressed by a single point controller. First, a deposition
source never has the idealized (cosine) flux distribution. Also, the flux distribution
is dynamic, changing as the deposition progresses.
The IC/5, when using more than one sensor for each material, calculates an
aggregate rate and uses it for rate control and thickness termination. This
aggregate rate is comprised of rate information from up to 8 sensors, each sensor
having its own weighting and tooling factors.
As the source distribution changes, any individual sensor may detect more (or less)
of the source flux. However, the aggregate rate is held constant. Each substrate,
contained in a rotating planetary substrate holder, is then exposed to the constant
aggregate rate, eliminating thickness variations due to a change in the source's flux
distribution.
This concept is illustrated in Figure 10-1 , which also shows the preferred
placement of the Quartz Crystal sensors relative to the deposition source and
substrates.