INFICON STM-2XM 2-Channel Rate/Thickness Monitor - Manual (Page 129)

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STM-2XM Operating Manual
Chapter 7
Calibration Procedures
7.1 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. STM-2XM recognizes the density
of this added material to allow conversion of the mass information into thickness.
In some instances, where highest accuracy is required, it is necessary to make a
density calibration (see
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 is accounted for by the Tooling parameter. Tooling can be
experimentally established by following the guidelines in
section 7.3 on page 7-2 .
If the Z-Ratio is not known, it could be estimated from the procedures,
outlined in
section 7.4 on page 7-3 .
7.2 Determining Density
NOTE: The bulk density values retrieved from Appendix A are sufficiently accurate
for most applications.
To determine density value:
1 Place a substrate (with proper masking for film thickness measurement)
adjacent to the sensor, to ensure 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 to 5000 Å).
5 After deposition, remove the test substrate and measure the Film thickness
with either a multiple beam interferometer or a stylus-type profilometer.