Vesna Janicki, Jordi Sancho-Parramon, Olaf Stenzel, Marc Lappschies, Björn Görtz, Christoph Rickers, Christina Polenzky, and Uwe Richter, "Optical characterization of hybrid antireflective coatings using spectrophotometric and ellipsometric measurements," Appl. Opt. 46, 6084-6091 (2007)
A hybrid antireflective coating combining homogeneous layers and linear gradient refractive index layers has been deposited using different techniques. The samples were analyzed optically based on spectrophotometric and spectroscopic ellipsometry measurements under different angles of incidence in order to precisely characterize the coatings. The Lorentz–Lorenz model has been used to calculate the refractive index of material mixtures in gradient and constant index layers of the coating. The obtained refractive index profiles have been compared with the targeted ones to detect errors in processes of deposition.
V. Janicki, D. Gäbler, S. Wilbrandt, R. Leitel, O. Stenzel, N. Kaiser, M. Lappschies, B. Görtz, D. Ristau, C. Rickers, and M. Vergöhl Appl. Opt. 45(30) 7851-7857 (2006)
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Refractive indices correspond to the starting refractive index of the layers. Only the thickness of the third ramp (D) is more than 6% higher than the thickness of the original design . Average error in refractive index is 2.7%. Error of Nb2O5 refractive index is 0 because it was fixed. When allowed to optimize, the quality of the fit did not improve.
Refractive indices correspond to the starting refractive index of the layers. The thickness of the second ramp B is 8% higher than the thickness of the original design and the thickness of the layer is 27% higher (11 nm). Thicknesses of the other layers are within 3% of error to the starting thickness. Average error in refractive index is 2.2%. Error of refractive index is 0 because it was fixed. When allowed to optimize, the quality of the fit did not improve.
Thickness of each layer is within 3% of error. Thicknesses of ten layers have reached their minimum–maximum allowed value. There was no improvement to the fit when absorption was introduced. Average error in refractive index is 1.1%.
Tables (4)
Table 1
Dispersion Parameters and Material Refractive Indicesa
Material
a0
a1(nm2)
k0
k1 (nm)
n (570 nm)
k (570 nm)
Nb2O5
Data file determined from single layer
2.2838
0
Ta2O5
Data file determined from single layer
0.00093
0.013
2.1249
9.3 × 10−4
±0.9 × 10−4
TiO2
Data file determined from single layer
2.4078
0
SiO2 EBE
1.4703
2790
0
0
1.4789
0
±0.0009
SiO2 RFS
1.4852
3520
0
0
1.496
0
±0.001
SiO2 IBS
Data file determined from single layer
1.4992
0
The dispersion formula for the refractive index was and for the extinction coefficient
Refractive indices correspond to the starting refractive index of the layers. Only the thickness of the third ramp (D) is more than 6% higher than the thickness of the original design . Average error in refractive index is 2.7%. Error of Nb2O5 refractive index is 0 because it was fixed. When allowed to optimize, the quality of the fit did not improve.
Refractive indices correspond to the starting refractive index of the layers. The thickness of the second ramp B is 8% higher than the thickness of the original design and the thickness of the layer is 27% higher (11 nm). Thicknesses of the other layers are within 3% of error to the starting thickness. Average error in refractive index is 2.2%. Error of refractive index is 0 because it was fixed. When allowed to optimize, the quality of the fit did not improve.
Thickness of each layer is within 3% of error. Thicknesses of ten layers have reached their minimum–maximum allowed value. There was no improvement to the fit when absorption was introduced. Average error in refractive index is 1.1%.