INFICON STM-100/MF Thin Film Deposition Monitor - Manual (Page 49)

Thickness Reading Calibration
Instrument calibration is affected by three different parameters, material
density, material Z-Factor, and tooling. Tooling is a deposition system
geometry correction (location of sensor relative to substrates). Density and
Z-Factor are material factors.
Density Determination
Use of the material bulk density value will normally provide sufficient film
thickness accuracy. If additional accuracy is required, the following procedure
may be used:
Using a new sensor crystal (this eliminates Z-Factor errors) place a substrate
adjacent to the sensor so that both sensor and substrate see the same
evaporant stream. Set the instrument density to the bulk value of the material
(see the Material Reference Table in section 4.3). Set the Z-Factor to 1.000
and the tooling factor to 100%. Deposit approximately 5000 angstroms of
material on the sensor and substrate. After deposition remove the substrate
and measure the film thickness with a profilometer or multiple beam
interferometer. The correct density value may be determined by the formula:
Density
Gm
cc
=
( Density Parameter) (Reading)
(Measured Thickness)

 
 •
The calculated value may be checked by setting the STM-100 / MF density
parameter to the calculated value and observing that the STM-100 / MF
thickness display shows the corrected reading. Minor value adjustments can
be made to make the measurements and calculations exactly equal.
Z-Factor Determination
A list of Z-Factor values may be found in the material reference table in section
4.3. For other materials Z-Factor may be calculated by the following formula:
Z - Factor =
Dq Uq
Df
Uf
1
2
•










Dq = Density Of Quartz
Uq = Shear Modulus Of Quartz
Df = Density Of Film
Uf = Shear Modulus Of Film
The density and shear modulus values may be found in many material
reference handbooks. Film Z-Factor values are typically very close to bulk
Z-Factor values. High stress materials seem to have values slightly lower than
expected. For a more exact solution make a calibration deposition similar to
the density method. Use the calibrated density value, a Z-Factor of 1.000 and
a tooling of 100%. Deposit a thick film using at least 50% of the sensor crystal
SECTION 4.2
Thickness
Density
Z-Factor
Calibration and Theory Page 4 - 2