Manual

6 - 6
IPN 074-517-P1D
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 Figure 6-4 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
ZD
q
* U
q
D
m
* U
m

12
=
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