INFICON Cygnus Thin Film Deposition Controller - Manual (Page 162)

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Cygnus 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 layer deposition (for example, two layers), the Z-value used for the
second layer is determined by 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.
7.5 Determining Cross Sensitivity Correction For Co-Deposition
The Cross Talk Percent correction feature of the Cygnus is beneficial to
applications involving the simultaneous deposition of two materials. When
depositing two materials it is not always possible to isolate each crystal so that it
samples material from a single source. The Cross Sensitivity feature is used to
eliminate this "cross talk" of material from the second source being deposited onto
the crystal intended to control the deposition rate from the first source.
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
---------
 
 
 
 
–
 
 
 
=