INFICON XTC/3 Thin Film Deposition Controller Operating Manual - Manual (Page 193)

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XTC/3 Operating Manual
Chapter 7
Calibration Procedures
7.1 Importance of Density, Tooling and Z-Ratio
The quartz crystal microbalance (QCM) is capable of precisely measuring the
mass added to the face of the oscillating quartz crystal sensor. XTC/3 knowledge
of the density of this added material (specified in the density parameter in the
Film/Source parameters set up) allows conversion of the mass information into
thickness. In some instances, where highest accuracy is required, it is necessary
to make a density calibration as outlined in
section 7.2 .
Because the flow of material from a deposition is not uniform, it is necessary to
account for the different amount of material flow onto the sensor compared to the
substrates. This factor is accounted for in the tooling parameter in the Film/Sensor
Parameters set up. The tooling factor can be experimentally established by
following the guidelines in
section 7.3 .
If the Z-Ratio is not known, it could be determined from the procedure outlined in
section 7.4 , estimated as outlined in section 7.5 or set to the default value of 1.0.
The resulting thickness error due to an estimated value will be non-linear and
increases with the total thickness, number of layers of alternate materials and the
difference from the actual Z-Ratio. Generally, if the crystal is replaced before crystal
life reaches 10%, the size of the thickness error will be small enough to be
disregarded in most applications.
7.2 Determining Density
NOTE: The bulk density values retrieved from the Material Library are sufficiently
accurate for most applications.
Follow the steps below to determine density value:
1 Place a substrate (with proper masking for film thickness measurement)
adjacent to the sensor, so that the same thickness will be accumulated on the
crystal and this substrate.
2 Set density to the bulk value of the film material or to an approximate value.
3 Set Z-ratio to 1.000 and tooling to 100%.
4 Place a new crystal in the sensor and make a short deposition
(1000-5000 Å), using manual control.
5 After deposition, remove the test substrate and measure the film thickness with
either a multiple beam interferometer or a stylus-type profilometer.