INFICON Cygnus Thin Film Deposition Controller - Manual (Page 161)

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Cygnus Operating Manual
7.4 Laboratory Determination of Z-Ratio
NOTE: On Cygnus, the Auto Z function is available to automatically calculate the
Z-Ratio. Especially when precise Z-Ratio values are significant, Auto Z is
recommended. Refer to
section 9.1.6 on page 9-9 for a description of Auto
Z theory.
A list of Z-values for materials commonly used is available in the Material Library.
For other materials, Z can be calculated from the following formula:
[3]
[4]
where:
d
f
= density (g/cm3) of deposited film
µ
f
= shear modulus (dynes/cm2) of deposited film
d
q
= density of quartz (crystal) (2.649 gm/cm3)
µ
q
= shear modulus of quartz (crystal) (3.32 x 1011 dynes/cm2)
The densities and shear moduli of many materials can be found in a number of
handbooks.
Laboratory results indicate that Z-values of materials in thin-film form are very close
to the bulk values. However, for high stress producing materials, Z-values of thin
films are slightly smaller than those of the bulk materials. For applications that
require more precise calibration, the following direct method is suggested:
1 Establish the correct density value as described in section 7.2 on page 7-1 .
2 Install a new crystal and record its starting frequency Fco. It will be necessary
to send the SC 12 n command to get this information (see
section 5.4.4,
STATUS Commands, on page 5-24 ).
3 Make a deposition on a test substrate such that the percent crystal life display
will read approximately 50%, or near the end of crystal life for the particular
material, whichever is smaller.
4 Stop the deposition and record the ending crystal frequency Fc using the SC
12 n command.
5 Remove the test substrate and measure the film thickness with either a multiple
beam interferometer or a stylus-type profilometer.
Z
d
q

q
d
f

f
------------
 
 
 
1
2
---
=
Z 9.378 10
5
d
f

f
 
-
1
2
---

=