MODEL 2010/M PRISM COUPLER
APPLICATION NOTES
The Model 2010/M can be used to measure thickness and index for
one or both films of a dual film structure (as many as four
film parameters) provided the top film has a higher
refractive index than the lower film. Dual film measurements
on transparent substrates or underlying (third layer) films
are even possible in many cases. Detailed specifications for
dual film measurements depend on the thickness and index of
each layer, but the following rough guidelines apply:
Minimum upper/lower film index difference required: The Model
2010/M's dual film measurement works well even when index
differences are slight (.03 or less) between the upper and
lower films. However, as the difference between upper and
lower film index gets smaller, the upper film thickness must
become larger for the measurement to be feasible. See below
for examples of minimum upper film thickness required for
dual film measurements.
Minimum measurable thickness: For silicon nitride (n =
2.05) or oxynitride (n = 1.80) over oxide (n = 1.46),
thickness and index of the upper film is measurable if the
upper film thickness exceeds 3500 Å (nitride) or 5000 Å
(oxynitride). For the underlying oxide to be measurable, the
oxide thickness should exceed 4000 Å and the total thickness
of both layers should exceed one micron. For polyimide (n =
1.70) or resist (n = 1.63) over oxide, the upper layer is
measurable if its thickness exceeds 6500 Å or 8000 Å,
respectively. For polyimide or resist over oxide, the
underlying oxide is measurable if its thickness exceeds 4000
Å. Thinner upper films are often measurable with option
2010/M-TM (see below). For other film combinations, or
applications in which there is a small difference between
upper and lower film indices, please consult Metricon.
Press on chart for larger view
TE/TM measurements of thin upper
films: The 2010/M's TM option (option #2010/M-TM) can reduce
the minimum measurable upper film thicknesses described above
by a factor of two. With this approach, both upper film
parameters (thickness and index) are measured using one TE
and TM mode, rather than two TE modes. The only requirement
for this approach to be successful is that the film not be
birefringent, i.e., that the index of the film is isotropic.
Minimum measurable thickness limits for lower films are not
affected by the TE/TM analysis.
Accuracy: Measurement accuracy and resolution for the
top film of a dual film structure meet, and often exceed, all
of the specifications which apply to single film measurements
(see Model 2010/M specifications sheet). Measurement accuracy
for the lower film is typically better than ±0.3% for index,
and ±2% for thickness.
Advance knowledge of film required: The only advance
knowledge required for dual film measurements is an
approximate starting value for the refractive index of the
lower film. Ideally, the lower film index should be known in
advance to an accuracy of ±.03, but incorrect measurement
results for the lower film are highly unlikely unless the
error in assumed lower film index is .06 or greater.
Prism selection for dual film measurements: 200-P-3 and
200-P-4 prisms are recommended for nitride and oxynitride
applications, while the 200-P-1 prism is optimum for resist,
polymer, polyimide or low index oxynitride measurements over
oxide. Please consult the factory for detailed prism
recommendation for your application.
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MONITORING
OF PHOSPHORUS AND OTHER DOPANT CONCENTRATIONS IN SILICON
DIOXIDE
HIGH ACCURACY MEASUREMENT OF RESISTS,
POLYIMIDES, AND POLYMERS
DUAL FILM MEASUREMENTS
OPTICAL WAVEGUIDE CHARACTERIZATION
BULK MATERIAL OR THICK FILM
INDEX/BIREFRINGENCE MEASUREMENT
MEASURING INDEX ANISOTROPY/BIREFRINGENCE OF FREE-STANDING POLYMER FILMS
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Copyright © 2006 Metricon Corp. All rights reserved.
Last revised:
11/8/06