INFICON MDC-260 Thin Film Deposition Controller - Manual (Page 131)

MDC-260 DEPOSITION CONTROLLER
THEORY OF OPERATION 10-7
of these parameters is not necessary. A library of material names, density and
acoustic impedance of the more commonly deposited materials is stored in the
MDC-260 memory. These materials are also listed in Table 10-1.
If the values of the density and acoustic impedance are not known they can be
calibrated empirically as described below.
Calibration requires the establishment of the film density, the tooling factor and
the acoustic impedance in this order. If the approximate value of the parameters
is known they should be used initially. If the acoustic impedance is not known
use the value 8.83, the value for quartz.
10.5.1 FILM DENSITY
Establishing the film density can be accomplished by depositing a trial film on
several test substrates placed around and as close as possible to the sensor crystal
and in the same plane. The trial deposition should be thick enough to allow an
independent measurement of the film on the test substrates to be made with
adequate precision using an optical interferometer or surface-measuring device.
When making the trial deposition, use a fresh crystal and remember to write down
the final thickness reading displayed by the MDC-260, as this will be needed in
the calculation. If the acoustic impedance parameter has been accurately
established previously, a fresh crystal is not required.
Determine the average film thickness on the test substrates and use the following
equation to calculate the material's density:
Density = (Displayed Thickness/Average Measured Thickness) * Density(test)
Where Density(test) is the density parameter setting used during the calibration
run.
Once the calibration procedure is complete, the programmed film density is
correct for this particular film.
10.5.2 TOOLING FACTOR
Having established the film density, the material and the sensor tooling factors
should be established next. For the MDC-260, it is typical to keep the material
tooling factor equal to 100% and only use the sensor tooling factors to
compensate for geometric factors in the deposition system which result in a
difference between the deposition rate on the substrates and the rate on the
sensing crystal. This way, each sensor's individual rate, as displayed in the
Source/Sensor Status Screen, will represent the rate on the substrates. This will
make it easy to identify any changes in the vapor distribution since all sensors
should display the same rate once calibrated.
To do the sensor calibration, place several test substrates at representative
locations in the deposition fixture and change the crystals in the sensors head or
heads that you wish to calibrate for this material. Go to the material selection
menu and select the material you wish to calibrate. Set the material conditioning
parameters as well as the desired deposition rate if not set already. Also, enter the