INFICON Q-pod Thin Film Deposition Monitor User Manual
Page 53
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Q-pod Operating Manual
[3]
[4]
where:
d
f
= density (g/cm
3
) of deposited film
µ
f
= shear modulus (dynes/cm2) of deposited film
d
q
= density of quartz (crystal) (2.649 gm/cm
3
)
µ
q
= shear modulus of quartz (crystal) (3.32 x 10
11
dynes/cm
2
)
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
2
Install a new crystal and record its starting frequency, F
co
. The starting
frequency will be displayed on the main screen.
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 F
c
.
5
Remove the test substrate and measure the film thickness with either a multiple
beam interferometer or a stylus-type profilometer.
6
Using the density value from step 1 and the recorded values for F
co
and F
c
,
adjust the Z-ratio value in thickness
equation [5]
to bring the calculated
thickness value into agreement with the actual thickness. If the calculated value
of thickness is greater than the actual thickness, increase the Z-Ratio value. If
the calculated value of thickness is less than the actual thickness, decrease the
Z-Ratio value.
[5]
Z
d
q
q
d
f
f
------------
1
2
---
=
Z
9.378 10
5
d
f
f
-
1
2
---
=
T
f
Z
q
10
4
2
zp
--------------------
1
F
co
--------
ATan zTan
F
co
F
q
-----------
1
F
c
-----
ATan zTan
F
c
F
q
---------
–
=