Inficon XTC/3, Operating Manual, Page: 188 / 210

7 - 4
XTC/3 Operating Manual
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]
where:
T
f
= thickness of deposited film (kÅ)
F
co
= starting frequency of the sensor crystal (Hz)
F
c
= Final frequency of the sensor crystal (Hz)
F
q
= Nominal blank frequency = 6045000 (Hz)
z = Z-Ratio of deposited film material
Z
q
= Specific acoustic impedance of quartz = 8765000 (MKS units)
p = density of deposited film (g/cc)
7.5 Estimating Z-Ratio
For multiple layer deposition (for example, two layers), the Z-value used for the
second layer can be estimated based on the relative thickness of the two layers.
For most applications the following three rules will provide reasonable accuracies:
 If the thickness of layer 1 is large compared to layer 2, use material 1 Z-value
for both layers.
 If the thickness of layer 1 is thin compared to layer 2, use material 2 Z-value for
both layers.
 If the thickness of both layers is similar, use a value for Z-Ratio which is the
weighted average of the two Z values for deposition of layer 2 and subsequent
layers.
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
---------
 
 
 
 
–
 
 
 
=