INFICON XTM/2 Thin Film Deposition Monitor - Manual (Page 91)

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XTM/2 Operating Manual
Chapter 5
Calibration and Measurement
5.1 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. The instrument's
knowledge of the density of this added material (specified by the film’s 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 5.2 .
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 by the film’s tooling parameter. The
tooling factor can be experimentally established by following the guidelines in
section 5.3 on page 5-2 .
Z-ratio is a parameter that corrects the frequency change to thickness transfer
function for the effects of acoustic impedance mismatch between the crystal
and the coated material.
5.2 Determining Density
NOTE: The bulk density values retrieved from Appendix A, Table of Densities
and Z-ratios , 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).
5 After deposition, remove the test substrate and measure the film thickness
with either a multiple beam interferometer or a stylus-type profilometer.