10 - 1
Cygnus 2 Operating Manual
Chapter 10
Maintenance and Calibration Procedures
10.1 Importance of Density, Tooling and Z-Ratio
The quartz crystal microbalance is capable of precisely measuring the mass added
to the face of the oscillating quartz crystal sensor. Cygnus 2's knowledge of the
density of this added material (specified in the density parameter in Material
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 10.2.
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 Material Set-Up.
The tooling factor can be experimentally established by following the guidelines in
section 10.3 on page 10-2.
In Cygnus 2, if the Z-Ratio is not known it could be estimated from the procedures
outlined in section 10.4 on page 10-3, or, typically, the Auto-Z function can be used
to determine the Z-Ratio.
10.2 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 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.
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