INFICON MDC-360 Thin Film Deposition Controller - Manual (Page 124)

MDC-360 DEPOSITION CONTROLLER
10-4
10.4 RATE CALCULATION
The deposition rate is calculated by dividing the change in thickness between
r to filter out quantizing and sampling noise introduced by
% of the final value in 5 sec.
10.5 RATE CONTROL
0 by comparing the measured
power
r in
impedance of the more commonly deposited materials is stored in the
MDC-360 memory. These materials are also listed in Table 9.1.
Calibra
the a
. f the parameters
is known they should be used initially. If the acoustic impedance is not known
on
ugh to allow an
e test substrates to be made with
ptical interferometer or surface measuring device.
Whe sition, use a fresh crystal and remember to write down
the ustic impedance parameter has been accurately
established previously, a fresh crystal is not required.
measurements by the time between measurements. The rate is then filtered by a
three pole digital filte
the discrete time, digital nature of the measurement process. The above filter has
an effective time constant of about 2 seconds. Following a step the displayed rate
will settle to 95
Deposition rate control is achieved in the MDC-36
thickness rate with the desired thickness rate. The rate error and the rate of
change of rate error are then used to determine how much to increment the
up or down.
The amount the power is incremented is also affected by the response parameter.
The response parameter is divided by 50, squared and then used as a multiplie
the determination of delta power.
The rate error is divided by the programmed rate and multiplied by 100 to obtain
the displayed percent rate error.
10.6 EMPIRICAL CALIBRATION
For many film materials the film density and acoustic impedance is known to
sufficient accuracy that the values can be used directly, and empirical calibration
of these parameters is not necessary. A library of material names, density and
acoustic
If the values of the density and acoustic impedance are not known they can be
calibrated empirically as described below.
tion requires the establishment of the film density, the tooling factor and
coustic impedance in this order If the approximate value o
use the value 8.83, the value for quartz.
10.6.1 FILM DENSITY
Establishing the film density can be accomplished by depositing a trial film
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 eno
independent measurement of the film on th
adequate precision using an o
n making the trial depo
the final thickness reading displayed by the MDC-360, as this will be needed in
calculation. If the aco
THEORY OF OPERATION