Copyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Optical Projection Printing and ModelingPurpose: Explain 8 of the top 10 phenomena and concepts key to understanding optical projection printingBasic Parameters: Resolution and Depth of FocusOptical Proximity EffectsBragg Diffraction and Image CalculationImage Characterization: I=EE* => 0.25, NL, MEEFLAVA Website: Simulation; Mask ViewerSuggested reading:Griffin: Plummer, Deal and Chapter 5Sheats and Smith: 188-196, 124-133, 148-152, 182-188, 121 Wong: 31-45, 55-58, 83Copyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006ASML 5500/90 ToolLight pathMask PortObjective LensTo WaferHexagonal Light Pipe OutputSigma ApertureFly’s EyeCondenser LensCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Projection Printer ExamplesSheats and SmithStepperMaskWaferScannerMaskWaferCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Optical Projection Printing ParametersWavelength λ = 248 nm)Partial Coherence Factor σ = (NAc/NAo) = 0.3Numerical Aperture NA = sin (θ) = 0.5#0 Key Parameters: λ, NA, σCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Parameters for Microlab Projection Printers59901253507.2300.70.250.5248ASML-DUV10350028590013190.80.50.32365GCA-i105500390125011160.80.70.28436GCA-g45500390125011160.80.70.28436405Canon-ghΜTFRnmλ/(4NA)nmk1λ/NAnmθILLdegθLENdegk1σNAλnmToolTFR = Total focus range = 2 x Rayleigh Depth of Focus = 2DOFM is the demagnification factorWorking ResolutionNAkLLINEWIDTHλ1=( )222 NAkDOFλ=Copyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Optical System Point Spread Function• The small pinhole due to its size diffracts uniformly over all angles.• This diffraction uniformly fills the lens pupil.• The lens re-phases the remaining emerging rays so that they re-converge at the wafer with the same relative phases and uniform magnitude.• The electric field at the waver is thus the inverse Fourier transform of a disk = Airy Function.• The intensity is the time average of the square of the electric field = (Airy function)2• The pattern shape is independent of the shape of the pin hole with diameter 1.22λ/NA.• The peak E is proportional to pin hole area the peak I is proportional to Area2 or (dimension)4.LensWaferMaskPin holeImage of a pin hole (Diffraction limited)Relationship for electric fieldsCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Resolution in Projection PrintingNAdfdf λλλ 61.0261.022.1 ==Minimum separation of a star to be visible.f = focal distanced = lens diameterPoint spread functionNull positionPDG Fig. Ch 5F# = f/dCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Resolution ~ Transverse Variationλ = 248 nmλTRANS= λ/sinφ = 3.22λ = 800nmφWave graphic by OngiEnglander and Kien LamThe most useful rays in forming an image are those with the same pitch as the patternLarger angles give higher resolution#1 Resolution = P/2 = λ/(2 sinφ) = 0.5(λ/NA))Assumes one wave is on-axis and the other off-axisCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Depth of Focus: Phase change on vertical axisPlane of Best Focus4.75λ5.0λPlane of Rayleigh l/4 DefocusObserve phase along a vertical lineWave graphic by OngiEnglander and Kien LamCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Depth of Focus in Projection PrintingResult must be modified fora) High NA, andb) Two waves at arbitrary angles.PDG Fig. Ch 5#2 Depth of Focus = λ/(2NA2)Copyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Normalized ParametersNAkLLINEWIDTHλ1=( )222 NAkDOFλ=λ = 365, 248,193, 157, 13.4 nmNA = 0.167, 0.38, 0.5, 0.63, 0.7, 0.75, 0.80Instead of recalculation for every new combination of λ and NA a universal catalog of image behavior can be utilized if we first determine the k1and k2factors in the actual system for the linewidth and defocus and look up results in a data based based on λ = 0.5µm and NA =0.5.mkmkNAkLLINEWIDTHµµλ1115.05.0===( ) ( )mkmkNAkDOF µµλ222225.025.02===For any wavelength λ and numerical aperture NA.Copyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Optical Proximity Effect- lateral influence functionE-field Point Spread Function for Coherent Imaging:• Finite size of projection lens (i.e. low-pass filter) images point on mask as Airy pattern on wafer.0.6 1.1λ/NA[Airy = IFT (disk) = f(l/NA)]illuminatorCondenser lensmaskProjectionlenswaferCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Various Types of Image DistortionProximity effect with neighborsCorner roundingEnd shorteningNonlinearity with sizeCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Optical Proximity Correction (OPC)Called Optical Process Proximity Correction (OPP) when compensations for other process effects are included.WongCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006waferplaneparallelopticalbeam grating withspatial frequency 1/PPP=2L...,2,1,0sin±±==nnPλφ-1-2+1+2Mask lenslmL S0Qualitative Explanation of image degradation by lenssin φ < NA of lensφθCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Bragg ConditionλϕnPn=sinPP=L+SL SChromeQuartznλφnRay of LightWavefronts#3 The Bragg condition sets the diffraction anglesIncident ray with wave frontsTransmitted rayDiffracted rayCopyright 2006, Regents of University of CaliforniaVer: 4/11/06EE 143 Optical Lithography Lecture, A.R. Neureuther, Sp 2006Pupil Wave
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