INFICON XTC/C Thin Film Deposition Controller - Manual (Page 133)

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XTC/C - XTC/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) 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 the Table of Densities and
Z-ratios, see Appendix A , 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.