WISE 2000, International Workshop on Spectroscopic Ellipsometry, 8 9 May 2000 DUV (150 350nm ) Characterization of Materials: A new instrument, the Purged UV Spectroscopic Ellipsometer, Pierre BOHER,, SOPRA S.A., 26 rue Pierre Joigneaux, 92270 Bois-Colombes, France, 1
Outline of the talk: Introduction. Presentation of the purged UV spectroscopic ellipsometer. Experimental results: CaF 2 substrate LaF 3 film on CaF 2 substrate Photoresists and antireflective coatings Cr and CrOx layers on glass Transmittance of SiOF substrate Extended PUV range Conclusion 2
introduction: 157nm lithography successor of 193nm generation. Need to characterize accurately new materials (resists, ARC) and optics at this new wavelength. Strong correlation between thickness and indices due to low thickness values. Good candidate --> spectroscopic ellipsometry Need of additional photometric measurements (transmittance of the optics for example). New instrument: Purged UV ellipsometer 3
SE Basic theory Ellipsometry determines and analyzes the change of the polarization state of light after reflection on a sample incidence plan S elliptical polarization s θ0 E Ep rp Es rs E Ep Es surface N = n - jk ρ rp = = r s tan ψ e j 4
Advantages of ellipsometry Ellipsometry is an absolute technique ( no need of reference spectrum or reference sample ) Ellipsometry gives twice more informations than reflectometry ( ψ and instead of R ) The phase is very sensitive to surface layers As ellipsometry measures the polarization state and not the intensity, it is less sensitive to light intensity fluctuations. Ellipsometry allows to characterize directly the optical indices (n,k) of bulk materials : 2 2 2 N = ( n jk) = sin θ0 1 + 1 ρ 1 + ρ 2 tan 2 θ0 5
Ellipsometer setup Minimized beam path. Deuterium lamp as source. Double monochromator included in the polariser arm (avoid photobleaching) MgF 2 Rochon polarizers on stepper motors. Detection by a photomultiplier in photon counting mode. 6
Ellipsometer characteristics Rotating analyser instrument. Spectral range 145-350nm extendable in the visible range. 3 measurement modes possible: >variable angle spectroscopic ellipsometry >Photometry (reflectance or transmittance) >Scatterometry 7
Goniometer Analyser arm Mapping stage Polariser arm + spectrometer Purged UV spectroscopic ellipsometer 8
PM tube in photon counting mode Fixed polariser Rotating analyser Retarder Sample Prism Grating Deuterium lamp Schematic view of the purged UV spectroscopic ellipsometer 9
Purged glove box SE system is installed inside a glove box with continuous H 2 O and O 2 purification. Dry nitrogen is injected continuously with automatic pressure adjustment. Filters can be regenerated automatically every 3- month. 10
Purged glove box One working face with three gloves to adjust sample and replace deuterium lamp. Samples up to 200mm diameter introduced with load lock Residual H 2 O and O 2 measured continuously (in the ppm range during normal working conditions ). 11
Purged Glove Box 12
1 0.95 Transmission 0.9 0.85 0.8 Experiment Simulation CaF2 0.75 150 175 200 225 250 Wavelength (nm) Transmittance measurement on a CaF 2 substrate 13
0.4 1 0.3 Experiment Simulation 0.6 Tan Psi 0.2 0.2-0.2 Cos Delta 0.1 Wavelength 157.6nm Roughness 5.4nm -0.6 CaF2 n=1.600±0.001 0-1 50 52 54 56 58 60 62 64 66 68 70 Angle of incidence (deg) Analysis of the SE measurement at 157.6nm on the CaF 2 substrate 14
1.64 1.6 Refractive index n 1.56 1.52 1.48 1.44 140 190 240 290 340 Wavelength (nm) Refractive index of the CaF 2 substrate compared to the literature 15
0.6 Tan Psi 0.5 0.4 0.3 157nm 193nm 227nm 262nm 298nm 0.2 0.1 0 40 45 50 55 60 65 70 Incidence angle (deg) SE measurements on LaF3/CaF2 sample 16
Cos Delta 1 0.8 0.6 0.4 0.2 0-0.2-0.4-0.6 157nm 193nm 227nm 262nm 298nm -0.8-1 40 45 50 55 60 65 70 Incidence angle (deg) SE measurements on LaF3/CaF2 sample 17
0.6 Wavelength 157.6nm 1 0.5 0.4 Experiment Simulation 0.6 Tan Psi 0.3 Roughness 3.3nm 0.2-0.2 Cos Delta 0.2 0.1 LaF3 Layer 400nm n = 1.713 CaF2 Subtrate -0.6 0 40 45 50 55 60 65 70 Angle of incidence (deg) Analysis of the SE measurement at 157.6nm on the LaF 3 /CaF 2 sample 18-1
2.9 1.5 SiO2 SiO2 Index of refraction n 2.4 1.9 SiN Extinction coefficient k 1 0.5 x100 SiN 1.4 0 150 250 350 450 150 250 350 450 Wavelength (nm) Wavelength (nm) Measured dielectric constants of SiO 2 and SiN layers 19
1 Cos Delta 0.8 0.6 0.4 0.2 0-0.2 75deg 70deg 65deg -0.4-0.6-0.8-1 140 160 180 200 220 240 260 280 300 320 Wavelength (nm) Variable angle measurement on a photoresist film 20
5 4 75deg 70deg Tan Psi 3 2 65deg 1 0 140 160 180 200 220 240 260 280 300 320 Wavelength (nm) Variable angle measurement on a photoresist film 21
2.2 F2 ArF KrF 2 Refractive index n 1.8 1.6 1.4 1.2 KrF resist ArF resist i-line resist ARC F2 resist 150 200 250 300 Wavelength (nm) Refractive index of different resists and antireflective coatings 22
1 F2 ArF KrF 0.75 Absorption k 0.5 KrF resist ArF resist i-line resist ARC F2 resist 0.25 0 150 200 250 300 Wavelength (nm) Extension coefficients of different resists and antireflective coatings 23
1.8 0.21 GESP Refractive index n 1.7 1.6 PUV 157.6nm 0.14 0.07 Extinction coefficient k 1.5 0 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 Energy (ev) Dielectric constants of photoresist 1 measured with the GESP and PUV instruments 24
2.2 1 refractive index n 1.95 1.7 1.45 GESP PUV 0.75 0.5 0.25 Extinction coefficient k 157nm 1.2 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 Energy (ev) Dielectric constants of photoresist 2 measured with the GESP and PUV instruments 25 0
Incident angle PHOTORESIST Canceled by ARC ARC SUBSTRATE * Reduction of the notching effect ---> lower line width fluctations * Reduction of the «swing» effect ---> periodic behaviour of the reflectivity 26
* Spectroscopic Ellipsometry provides : -Thickness: T - Refractive index : n(λ) - Extinction coefficient : k(λ) * The index profile : quality of the material * The knowledge of N and K allows to simulate the REFLECTIVITY of the material for any thicknesses, any angles of incidence and at any photolithographic wavelengths. The best conditions for the deposition process can be predicted 27
REFLECTIVITY SIMULATIONS Normal incidence PHOTORESIST Wavelength : 157.6 nm R ARC Ambient : Photoresist SUBSTRATE 28
Extinction coefficient 0.2 Reflectance 0.15 0.1 0.05 1.5 1.75 2.0 2.25 2.5 Refractive index Reflectivity at 157.6 nm versus n & k using photoresist 1 Thickness=150 Å 29
3.2 2.7 n (CrOx) k (CrOx) n (Cr) k (Cr) Optical indices 2.2 1.7 1.2 0.7 150 170 190 210 230 250 270 290 310 330 350 Wavelength (nm) Measured Refractive Indices of Cr oxide and Cr versus Wavelength. 30
0.4 Reflectance (%) 0.35 0.3 0.25 0.2 0.15 Simulated reflectance Measured reflectance 0.1 0.05 0 0 0.01 0.02 0.03 0.04 0.05 0.06 Thickness (µm) Measured and Simulation of reflectance of Cr Oxide on Cr on Glass at 157.6 nm. 31
100.00% Transmittance (%) 75.00% 50.00% 25.00% 0.00% 152 157 162 167 172 177 182 187 192 Wavelength (nm) Transmission of SiOF versus wavelength. 32
8 1 7 0.75 6 0.5 5 0.25 Tan Psi 4 0 Cos Delta 3-0.25 2-0.5 1-0.75 0-1 100 200 300 400 500 600 700 Wavelength (nm) SE on SiO 2/ Si samples using extended PUV range 33
1.8 0.07 1.7 0.06 1.6 PUV Database 0.05 Refractive index n 1.5 1.4 1.3 0.04 0.03 0.02 Extinction coefficient k 1.2 0.01 1.1 0 1 0 1 2 3 4 5 6 7 8 9 10-0.01 Energy (ev) Optical indices of SiO 2 compared to litterature using extended PUV range 34
Conclusion: A new purged UV spectroscopic ellipsometer has been presented. Experimental results on: CaF 2 substrate. LaF 3 layer on CaF 2 substrate CrOx/Cr/glass structures. Photoresists and antireflective coatings SiOF transmittance Now the range is extended to 145-630nm 35