INFICON STM-2 USB Thin Film Rate/Thickness Monitor - Manual (Page 89)

7 - 3
PN
07
4-
61
3-
P1
A
STM-2 Operating Manual
7.4 Laboratory Determination of Z-Ratio
A list of Z-Ratio values for materials commonly used are available in Appendix A .
For other materials, Z-Ratio can be calculated from the following formulas:
[3]
[4]
where:
d
f
= Density (g/cm
3
) of deposited film
µ
f
= Shear modulus (dynes/cm
2
) of deposited film
d
q
= Density of quartz (crystal) (2.649 g/cm
3
)
µ
q
= Shear modulus of quartz (crystal) (3.32 x 10
11
dynes/cm
2
)
NOTE: The densities and shear moduli of many materials can be found in a
number of handbooks.
Laboratory results indicate that Z-Ratio of materials in thin film form are very close
to the bulk values; however, for high stress producing materials, Z-Ratio 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, F
co
.
The starting Frequency will be displayed on the Frequency Graph tab.
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.
Z
d
q

q
d
f

f
------------
 
 
 
1
2
---
=
Z 9.378 10
5
d
f

f
 
-
1
2
---
 =