Photoresists
Measure film thickness and refractive index (n, and k) at 157nm, 193nm, 248nm.

|
Stepper Optics
Optical elements involved in
lithography exposure tools can be
enhanced with proper optical coatings.
The coating merit will depend on
refractive index and thickness.
Fluorinated materials are candidates at
157nm, as they remain transparent into
the VUV. The graph shows the index for
various fluorides measured with VUV
ellipsometry.
|
|
|
Birefringence
Ellipsometry can measure the
orientation and retardance of
birefringent materials.
Measured retardance of a 20mm
thick CaF optic is shown.
Powerful software makes this
measurement easy to perform.
|
|
Antireflective Coatings
Resists are used in conjunction with
antireflective coatings to suppress reflections
from the underlying substrate. Bottom AR
coatings absorb light penetrating the photoresist
and minimizes reflection back into the resist
layer. The AR coating refractive index should
match the photoresist to suppress reflections
from the resist/AR interface. Convenient
materials can 'tune' refractive index for this
application.
AR performance depends strongly on index and
thickness. Ellipsometers measure both values
and are able to track changes with different
process conditions (Figure shows SiO N with
various x).
|
|
|
Reflection/Transmission
Transmission measurements are often
important for increasing sensitivity to small
values. The VUV-VASE uses a vertical
sample mount allowing easy transmission
measurements at any angle.
Reflection measurements are acquired at any
angle from 10° to 90°. |
Anisotropy
Advanced anisotropic measurements
(generalized SE) provide additional
information to help fully characterize
uniaxial (2 sets of optical constants) and
biaxial (3 sets of optical constants)
anisotropic materials.
The VUV-VASE can measure in both
reflection and transmission ellipsometry
modes. The graphs show ordinary and
extraordinary dielectric functions of 4H SiC
measured with VUV-VASE.

|
|