INFICON SQM-160 Thin Film Deposition Monitor - Manual (Page 102)

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SQM-160 Operating Manual
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.