Optical characterization of highly inhomogeneous thin films

Transcription

1 Optical characterization of highly inhomogeneous thin films D.M. Rosu, A. Hertwig, P. Petrik, U. Beck Department Surface Modification and Measurement Technique BAM - Federal Institute for Materials Research and Testing 8th Workshop Ellipsometry March 11-13, 2014

2 Outline Motivation Experimental set-up Patterned samples Spectroscopic ellipsometry large scale inhomogeneity small scale inhomogeneity Conclusions

3 Motivation quality and consistency control: defects, thickness and structural variation, optical constants thin film materials: ideal (database optical constants) real (inhomogeneity, roughness, non-stoichiometric, depolarization, anisotropy, multilayers)

4 Experimental set-ups EP 3 -SE (Accurion GmbH) Imaging- Null-Ellipsometer + Microscope Spectral range: 400 nm nm Objectives: 10x, 20x, 50x Field of view: 1 mm 2 Region of interest 5µm 2 M2000DI (J. A. Woollam Co.) Rotating compensator (RC) ellipsometer Spectral range: 192 nm nm Variable angle spectroscopic ellipsometry Spot size ~5 mm mapping ellipsometry

5 Patterned samples Fraunhofer IISB: Si(100) substrate Ø 150 mm lithographically patterned SiO 2 and photoresist(az 5214E) overview of the sample and a fraction of the patterned, obtained using a Polyvar MET metal microscope

6 SiO 2 : spectroscopic ellipsometry- visible range refractive index extinction coefficient n k / Experiment 65 Experiment 70 Experiment 75 Experiment 60 Simulations Energy/eV 50 Ψ/ Energy/eV thickness of the SiO 2 layer: optical constants of SiO 2 from C.M. Herzinger, B. Johs, W. A. McGahan and J. A. Woollam, J. of App. Phys. 83 (1998) 3323

7 SiO 2 : spectroscopic ellipsometry- visible range Spot ID Thickness/nm x y (298.3) 300.7(300.9) (299.3) (299.1) 297.2(297.3) Woollam M2000DI ellipsometer; AOI: thickness inhomogeneity: ~1.3% across the sample total uncertainty for the thickness determination: ± 2 nm

8 SiO 2 : imaging ellipsometry Image to be mapped, grabbed at λ=533 nm map, measured at λ=533 nm Ψ map, measured at λ=533 nm Imaging ellipsometry in the visible spectral range Map of a 374 µm x 289 µm area of 5 and 10µm native SiO 2 stripes 7 wavelength in the visible range were used

9 SiO 2 : imaging ellipsometry Pixel = Pixel = 1 Image to be mapped, grabbed at λ=533 nm 187 Calculated thickness map Imaging ellipsometry in the visible spectral range Map of a 374 µm x 289 µm area of 5 and 10µm native SiO 2 stripes 7 wavelength in the visible range were used Thickness determined using both Ψ and maps

10 Photoresist : spectroscopic ellipsometry- visible range Woollam M2000DI ellipsometer; AOI: thickness of the resist: Cauchy dispersion model up to 3eV multi-sample analysis (optical constants do not vary) thickness inhomogeneity: 8% across the sample thickness inhomogeneity: 1.28% (~20 nm variation inside the measured spot) Spot Thickness/nm ID x y

11 Photoresist : spectroscopic ellipsometry- visible range Middle spot on the sample total uncertainty for thickness calculation: 6 nm (middle spot: 1574 ±6 nm) e.g. experimental and simulation for the spot in the center of the sample: single spot and multispot analysis optical constants of the layers: General oscillator model with 1 Gauss oscillator up to 6 ev

12 Photoresist : spectroscopic ellipsometry- visible range Depolarization% measured 55 measured 65 measured 70 Simulation Energy/eV thickness inhomogeneity: 1.28% (~20 nm variation inside the measured spot)

13 Photoresist: local inhomogeneity 1515 Pixel = ,176 x / pixel Imaging ellipsometry in the visible spectral y /pixel range Map of a 187 µm x 184 µm area of a photoresist covered area ,52 Pixel = 1 15 wavelength used Thickness determined using a Cauchy dispersion model for the calculated map

14 Photoresist: local inhomogeneity Stripe width Thickness of SiO 2 layer/nm Measurement of the native oxide covered areas in the patterns using nulling ellipsometry with a 20X objective Structures smaller than 25 µm are difficult to measure/ analyze; any small defect strongly influences the measurement and the calculations

15 Conclusions Local and global inhomogeneity were studied using spectroscopic ellipsometry The homogeneity of the SiO 2 film qualifies it as a patterned large-area reference sample for film thicknesses Patterns with dimensions in the range of 10 µm were well resolved Imaging ellipsometry in visible spectral range detected the smallest deviations in the photoresist layer 8% inhomogeneity was calculated across the photoresist layer

16 Acknowledgments BAM Berlin Fraunhofer IISB/MTA Hungary Andreas Hertwig Matthias Weise Uwe Beck Gudrun Rattmann Schellenberger Martin Peter Petrik This work was funded through the European Metrology Research Programme (EMRP) Project IND07 Thin Films.

17 Calculation of thickness uncertainty relative error 2.0 xc = relmse thickness/nm

18 Variation of the optical constants due to thickness uncertainty single spot analysis vs. multiple spot anylysis (Gauss oscillator model) n, Gauss single spot n, Gauss - multispot k, Gauss single spot k, Gauss - multispot n Energy/eV