Multilayer Development for Extreme Ultraviolet and Shorter Wavelength Lithography Eric Louis 1, Igor Makhotkin 1, Erwin Zoethout 1, Stephan Müllender 2 and Fred Bijkerk 1,3 1 FOM Institute for Plasma Physics Rijnhuizen, The Netherlands 2 Carl Zeiss SMT, GmbH, Germany 3 MESA+ Institute for Nanotechnology, The Netherlands
2 ASML presentation: 2010 International Workshop on EUV Sources, Dublin, Ireland
Outline FOM, who we are 13.5 nm research Need for shorter wavelengths optics 6.x nm multilayer issues relevant for performance and choice of optimum operational wavelength Passivation of La with Nitrogen Roughness reduction B 4 C B Wavelength selection: multilayer reflectivity profile @ 6.5-6.9 nm 3
EUVL: from basic research development labs FOM pilot research on lithographic imaging using 13.5 nm (1992) Two prototype 13.5 nm wafer scanners: ASML Alpha Demo Tools, ADT, including Zeiss and FOM ML-optics 13.5 nm exposures in resist 13.5 nm NA 0.2 # Multilayer optics 10 Max diameter 45 cm Resolution ~ diffraction limited 4
14 year of research on Mo/Si optics! Optical contrast Reflectance Period change (nm) Increased thermal stability 250 C annealing (hours) Mo/Si, no barriers With barriers Bandwidth Stress [MPa] 800 600 400 200 Stress reduction 0 Coating uniformity Periodicity control FOM, Si polish Windt et al M irkarimi et al FOM, Mo+Si polish 0.2 0.4 0.6 0.8-200 Contamination Bandwidth -400-600 Mo fraction/ E. Louis et. al., Prog. Surf. Sci., doi:10.1016/j.progsurf.2011.08.001, 2011 5
Downscaling to next generation EUV: 6.x nm = 13.5 6.X nm Novel ML coatings: New materials: Mo La, Si B (B 4 C) Reduced bi-layer thickness: 6.8 3.4 nm Requirements interlayer quality scale with λ Baseline technology required: Reduction of layers intermixing Roughness mitigation Optimization of optical contrast Search for optimal ML performance Technological aspects: Additionally to coating issues More bi-layers: @13.5 nm N=50 @6.x nm N~200 Bandwidth of the optical column λσ/λ(mo/si)=2% λσ/λ(la/b)=0.6% Reflectance Reflectance 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 REALITY Mo/Si 12.8 13 13.2 13.4 13.6 13.8 14 Wavelength (nm) GOAL La/B 4 C 0.0 6.50 6.55 6.60 6.65 6.70 6.75 6.80 Wavelength (nm) 6
1 st challenge: thermodynamics @ La/B 4 C interfaces The first TEM image blurred interfaces are observed: La-B compound formation? Compound La B 4 C LaC 2 LaB 6 LaN H for (kj/mol) 0-71 -89-130 -303 At interfaces: 7 La + 6 B 4 C 4 LaB 6 + 3 LaC 2 ( H = - 305.4 kj/mole) Solution: nitride formation can prevent La-B and La-C compound formation Introduce stable nitrides by N-ion treatment: LaN can even enhance optical contrast 1 1 T. Tsarfati, E. Louis, F. Bijkerk, et. all., Thin Solid Films 518, 24, 7249-7252 (2010) 7
La distribution, arb. un. 0.12 0.08 0.04 0.00 How does LaN perform in reflectance? Reconstruction of La depth profile in La/B 4 C in LaN/B 4 C 0.0 0.5 1.0 1.5 2.0 Multilayer period Reflectance 0.35 0.30 0.25 0.20 0.15 0.10 0.05 75 period multilayers 0.00 6.4 6.5 6.6 6.7 6.8 6.9 wavelength (nm) LaN/B 4 C La/B 4 C Dramatic difference in maximum reflectance Without any process optimization (Only 75 period multilayers) X ray CBO ω 2Ѳ PSA open Soll er 5⁰ NaI Nitridation of La key to reducing layer intermixing 8
2 nd challenge: roughness reduction Optical contrast 0.020 0.015 0.010 0.005 0.000 Calculations for 200 period LaN/B 4 C multilayer: Roughness reduction from 0.4 to 0.2 nm significant reflectivity gain -0.005 0.0 0.2 0.4 0.6 0.8 1.0 Multilayer period 0.8 0.7 0.6 Roughness control is essential Reflectance 0.5 0.4 0.3 0.2 0.1 0.0 6.50 6.55 6.60 6.65 6.70 6.75 6.80 Wavelength (nm) 9
Scattering from interfaces As deposited Individual interface roughness: 0.3-0.6 nm No severe increase roughness with number of layers First optimization Growth optimization Smoothing mechanisms Kinetic growth manipulation Process optimization smoother interfaces 10
Reflectance 0.8 0.7 0.6 3 rd challenge: optimal optical contrast Replacement B 4 C B: enhancement of the optical contrast 200 period ML's LaN/B LaN/B 4 C 0.5 0.4 0.3 0.2 0.1 0.0 6.50 6.55 6.60 6.65 6.70 6.75 6.80 Wavelength (nm) Reflectance 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 LaN/B LaN/B 4 C 0.00 6.6 6.7 6.8 6.9 7.0 7.1 Wavelength (nm) 50 period ML s AOI=30 o Calculations on ideal multilayers using measured 1,2 optical constants: 10% reflectivity gain Measurements of pilot samples confirm reflectivity gain Deposition pure B to be optimized 1. R. Soufli et. al., Appl. Opt., Vol. 47, 25, 2008 2. M. Fernandez-Perea et. al., J. Opt. Soc. Am. A, Vol. 24, 12, 2007 Replacement of B 4 C with B reflectivity gain expected 11
Outline FOM, who we are 14 years of extensive 13.5 nm research Coating research is essential key to new generation 6.x multilayer issues (a.o. materials) to determine performance and optimum operational wavelength Passivation of La with Nitrogen Roughness reduction B 4 C B Wavelength selection: multilayer reflectivity profile @ 6.5-6.9 nm 12
Calculated multilayer reflectance Optical constants: R. Soufli et. al., Appl. Opt., Vol. 47, 25, 2008 M. Fernandez-Perea et. al., J. Opt. Soc. Am. A, Vol. 24, 12, 2007 0.9 0.20 0.8 Peak reflectance 0.7 0.6 0.5 0.4 0.3 0.2 0.1 LaN/B 4 C (Henke) LaN/B LaN/B 4 C 0.15 0.10 0.05 Bandwidth (nm) 0.0 0.00 6.50 6.55 6.60 6.65 6.70 6.75 6.80 6.85 6.90 Wavelength (nm) Perfect multilayer: LaN/B: maximum reflectance at 6.66 nm LaN/B 4 C: maximum reflectance at 6.63 nm 13
Can optical constants be trusted? R( ) measured at various angles of incidence 1.0 LaN/B 1.0 LaN/B 4 C Normalized reflectance 0.8 0.6 0.4 0.2 experiment calculation 0.0 6.50 6.55 6.60 6.65 6.70 6.75 6.80 6.85 6.90 Wavelength (nm) Normalized reflectance 0.8 0.6 0.4 0.2 experiment calculation 0.0 6.50 6.55 6.60 6.65 6.70 6.75 6.80 6.85 6.90 Wavelength (nm) Calculated maximum confirmed by measured data optical constants reliably predicts optimal wavelength! 14
What about the source? Determination wavelength 6.x nm lithography: Simultaneous optimization required: source multilayer performance optical design Candidate wavelength band: 6.5-7.0 nm S.S. Churilov et al., Phys. Scr. 80 (2009) 15
Throughput of a 10 mirror system Integrated Reflectance 1.0 0.8 0.6 0.4 0.2 Tb LaN/B LaN/B 4 C 0.0 6.50 6.55 6.60 6.65 6.70 6.75 6.80 6.85 6.90 Wavelength (nm) Gd Significantly larger throughput for LaN/B based optics! Optimal wavelength: LaN/B 4 C: =6.64 nm; LaN/B: =6.67 nm Based on 10 ML reflectivity: Tb > 6.63 nm; Gd > 6.78 nm 16
Conclusions La-B interdiffusion strongly suppressed by nitridation: La/B 4 C LaN/B 4 C LaN/B 4 C LaN/B enhanced reflectance experimentally confirmed Preferred multilayer wavelength value: 6.63 nm or higher LaN/B 10 mirror system: highest throughput at 6.67 nm Source: Tb: > 6.63 nm Gd: > 6.78 nm Choice to be made also by source arguments 17
Acknowledgements Coworkers at and and Dutch Technology Foundation The team at Berlin The team at Kurchatov Institute Moscow, Hamburg and Institute of Crystallography RAS Moscow. 18