Ocean Optics ElliCalc - Manual (Page 55)

Ocean Optics Germany GmbH Thin Film Metrology
54
11 Physical explanations
11.1 Refraction index and absorption indices
The refraction index n of a substance is defined as
with c = speed of light
The absorption index k of a substance describes the absorption behavior of materials. Glasses and
photoresists have negligible absorption in the visible range.
n and k are a function of the wavelength lambda: n = n(λ). This phenomenon is called „dispersion“.
n(λ) and k(λ) are closely interrelated via the complex dielectric function ε(λ).
11.2 Cauchy coefficients
These coefficients empirically describe dispersion as a function lambda
3 2
1 2 4
n n
n n
λ λ
= + + 3 2
1 2 4
k k
k k
λ λ
= + +
In many cases the 6 Cauchy coefficients are sufficient to describe the spectral behavior of resists, glasses
etc. Normally ElliCalc uses „nanometers“ as a unit dimension. If you add your own cauchy parameters in a
.dat-file, pay attention on the correct dimension !! It is possible to use other dimensions within the software
but not in the .dat-files.
Structure of a .dat-file:
SiO2_(therm) name of the material
# this is my own comment 1 arbritrary comment (beginning with #)
# this is my own comment 2
633,1.4570,0
lambda, n and k at 633 nm
150,900 measured data between these limits
Table (or CAUCHY)
150,1.5510,0
n and k at 150 nm
151,1.5504,0 n and k at 151 nm
152,1.5491,0 n and k at 152 nm
153,1.5477,0 n and k at 153 nm
154,1.5464,0 n and k at 154 nm
and so on......
The first lines are not used by the software for calculation.
ATTENTION: Do not use any blanks in the name of the file !
The third line (150,900) means that measured data are measured (=available) between these limits
(LowerLimit=150 nm and UpperLimit=900 nm) and all extracted and displayed data (drawn in light Grey
instead of black) between 900-1100 nm have NO meaning !!
v a c u u m
m a t e r i a l
c
n
c
=