INFICON Cygnus 2 Thin Film Deposition Controller - Manual (Page 206)

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Cygnus 2 Operating Manual
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]
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)
For multiple Material deposition (for example, two Materials), the Z-value used for
the second Material is determined by the relative thickness of the two Materials.
For most applications the following three rules will provide reasonable accuracies:
 If the thickness of Material 1 is large compared to Material 2, use material 1
Z-value for both Materials.
 If the thickness of Material 1 is thin compared to Material 2, use material 2
Z-value for both Materials.
 If the thickness of both Materials is similar, use a value for Z-Ratio which is the
weighted average of the two Z values for deposition of Material 2 and
subsequent Materials.
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
---------
 
 
 
 
–
 
 
 
=