INFICON Guardian EIES Controller User Manual
Page 130
6 - 6
IP
N 07
4-
51
7-
P1
D
Guardian Co-Deposition Controller Operating Manual
Z-Ratio can be calculated using the Shear Modulus of quartz (U
q
) and the
deposited material (U
m
):
[10]
where:
U
q
= 32 Gpa
Unfortunately, Z-Ratio and Shear Modulus are not readily available for many
materials. Z-Ratio can also be calculated empirically using this method:
1
Deposit the material until Crystal Life is near 50%, or near the end of life,
whichever is sooner.
2
Place a new substrate adjacent to the used quartz sensor.
3
Set QCM Density to the calibrated value; Tooling to 100%. Zero thickness.
4
Deposit approximately 1000 to 5000 Å of material on the substrate.
5
Use a profilometer or interferometer to measure the actual substrate film
thickness.
6
Adjust the Z-Ratio (ZFactor) of the Guardian until the correct thickness reading
is shown.
Another alternative is to change crystals frequently. The graph in
shows
the % Error in Rate/Thickness from using the wrong Z-Ratio. For a crystal with 90%
life, the error is negligible for even large errors in the programmed versus actual
Z-Ratio.
Figure 6-4 % Error vs Z-Ratio
Z
D
q
* U
q
D
m
* U
m
1 2
=
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5
0
5
10
15
20
25
30
90% Life
75% Life
50% Life
Z-Factor
%
Error