INFICON XTM/2 Thin Film Deposition Monitor - Manual (Page 93)

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XTM/2 Operating Manual
5.4 Laboratory Determination of Z-ratio
A list of Z-values for materials commonly used is available in Appendix A, Table
of Densities and Z-ratios . For other materials, Z can be calculated from the
following formula:
[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 gm/cm
3
)
µ
q
= shear modulus of quartz (crystal) (3.32 x 10
11
dynes/cm
2
)
The densities and shear moduli of many materials can be found in a number of
handbooks.
Laboratory results indicate that Z-values of materials in thin-film form are very
close to the bulk values. However, for high stress producing materials, Z-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 Using the calibrated density and 100% tooling, make a deposition 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.
2 Place a new substrate next to the sensor and make a second, short
deposition (1000 - 5000Å).
3 Determine the actual thickness on the substrate (as suggested in density
calibration).
4 Adjust Z-ratio value in the instrument to bring the thickness reading in
agreement with actual thickness.
Z
d
q
µ
q
d
f
µ
f
-------------
⎝ ⎠
⎜ ⎟
⎛ ⎞
1
2
---
=
Z 9.378 10
5
d
f
µ
f
( )
-
1
2
---
Ч
=