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Shot Noise, LER and Quantum Efficiency of EUV Photoresists Robert L. Brainard,a Peter Trefonas,a Jeroen H. Lammers,b Charlotte A. Cutler,a Joseph F. Mackevich,a Alexander Trefonas and Stewart A. Robertsona • Introduction • EUV and DUV Base Titration Experiments • Poisson Statistics of LER vs. Esize • LER Simulation Model • Quantum Efficiency • New Resist Systems • Conclusions Partial Support by DARPA and EUV-LLC a. Rohm and Haas Microelectronics b. Philips Research Brainard EUV 2004 1 I. Introduction The 45 nm Node will require EUV Resists with Low LER and Esize: LER = 2 nm Esize = 2-15 mJ/cm2 Number of Photons / mJ 140 Shot Noise Limit1 = x 10 13 120 100 Limit imposed by 80 statistical probability of 60 underexposing a pixel 40 20 0 DUV Brainard EUV 2004 193 nm EUV (1) Neureuther & Wilson J. Vac. Sci. Tech. 1988. 2 Shot Noise Limits In 1998, John Hutchinson2 compared Shot Noise Limits of 193 nm and EUV resists using a theoretical model of LER. 193 nm Shot Noise Limit (10 mJ/cm2): 1 nm (1 mJ/cm2): 5 nm 13 nm (EUV) 8 nm LER 25 nm LER Without considering secondary electrons or acid diffusion effects. More recently,3 several excellent papers considered role of shot noise in limiting the ability to print contact hole arrays. (2) Hutchinson, SPIE 1998 Brainard EUV 2004 (3) O'Brien SPIE 2001, Cobb SPIE 2003, Lee SPIE 2003 3 Shot Noise Limits In 2002, Dentinger et. al.4 compared the LER of 25 resist formulations using DUV and EUV exposures. Ratio of LEREUV vs. LERDUV showed no statistically significant increase in EUV LER as photospeed is increased. EUV LER / DUV LER Ratio of EUV LER/DUV LER vs. Esize Dentinger et. al. Authors' Reasoning: Since DUV has 12X more absorbed photons than EUV and the LER ratios do not change with Dose: 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 5 10 15 EUV E size 20 25 2 (mJ/cm ) 30 35 Shot noise does not effect LER down to 3 mJ/cm2 Absorbed Photons = Esize x Abs x Photons/mJ Brainard EUV 2004 (4) P. M. Dentinger, et. al. SPIE 1998 4 Materials Experimental Resists based on EUV-2D R2 O O R3 OH Inhibiting Onium PAG Base Titration Study of EUV-2D 30 ArnE+ X- Non-Nucleophilic Base [Base]/[PAG] = 0 to 75% 3-Sigma LER (nm) R1 Polymer 100 nm LER 150-200 nm LER DUV 300-500 LER 25 20 DUV Exposure 15 Increasing Base 10 5 EUV Exposure 0 0 O 20 40 60 80 100 2 Esize (mJ/cm ) Ethyl Lactate Solvent O 100 nm Dense for EUV and 200 nm Dense for DUV OH Brainard EUV 2004 5 II. Base Titration Allowed Us to Study: Relationship between LER and Esize for Both EUV and DUV Statistical Analysis of LER vs. Esize Poisson Statistics Acid - Base Simulation Program Written for this Paper Quantum Efficiency C-Parameter (Szmanda Method) OD (2004 SPIE Paper) 3-Sigma LER (nm) 30 EUV Exposure 100 nm Lines EUV Exposure 150-200 nm Lines DUV Exposure 300-500 nm Lines 25 20 EUV-2D 15 10 5 0 0 20 40 60 80 100 2 Esize (mJ/cm ) 100 nm Dense for EUV and 200 nm Dense for DUV Other Resist Systems Brainard EUV 2004 6 III. Poisson Statistics of LER vs. Esize σN = Poisson Statistics Apply to Absorption of Incident Photons: N N = number of absorbed photons per volume element ∝ dose. Side wall roughness ∝ relative variation Base titration curves show the statistics of shot noise. Why do both EUV and DUV show the same linear behavior? 30 3-Sigma LER (nm) σN 1 1 = ∝ LER ∝ N N dose 25 20 2 DUV r = 0.94 15 10 2 EUV r = 0.97 5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1/2 Brainard EUV 2004 1/(Esize) 7 IV. LER Simulation Model (6 0 00 n gr m id un its ) 15 Exposed sk Ma EUV Light Unexposed Output of Model Schematic of Model 12.5 nm (50 grid units) 100 nm (400 grid units) Brainard EUV 2004 8 Simulation Steps Aerial Image Unexposed Exposed 10 mJ/cm2 exposure 1 Photon = Brainard EUV 2004 9 Simulation Steps Acid & Base Positions 10 mJ/cm2 exposure Unexposed Exposed 2.5Å film slice 1 Acid = 1 Base = Brainard EUV 2004 10 Simulation Steps Acid Latent Image After Base Quench Unexposed Exposed 10 mJ/cm2 exposure 2.5Å film slice 1 Acid Brainard EUV 2004 = 11 Simulation Steps Deblocked Latent Image, After acid diffusion 1.5 mJ/cm2 exposure Unexposed Exposed 2.5Å film slice Rdiffusion = 32Å Brainard EUV 2004 12 Simulation Steps Deblocking Density by Overlapping Spheres Unexposed Exposed 1.5 mJ/cm2 exposure 2.5Å film slice Rdiffusion = 32Å Brainard EUV 2004 13 Simulation Results 8 5.4 nm 2.9 nm 27 mJ/cm2 LER: 9.3 nm exposed 3 unexposed Dose: 1.5 1.6 nm Increasing Base Brainard EUV 2004 14 Simulated LER Results Excellent Fit of (Dose)-1/2 Simulation LER (nm) 10 8 Simulated Results in 2 r = 0.95 Agreement with Experimental Work 6 4 Number and Distribution of Acids Define LER vs. 2 (Dose)-1/2 Behavior 0 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 (Dose)-1/2 Brainard EUV 2004 15 V. Quantum Efficiency 3-Sigma LER (nm) 30 25 20 Why do both EUV and DUV show the same linear behavior? 2 DUV r = 0.94 15 10 2 EUV r = 0.97 5 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1/2 1/(Esize) Quantum Efficiency Brainard EUV 2004 Number of Acids Generated = Number of Photons Absorbed 16 V. Quantum Efficiency # Photons Absorbed Need to Know: • Absorption 125 nm • Number of EUV Photons / mJ/cm2 0.1 mJ/cm2 EUV Photons (41%) (6.7 x 1013) # Photons = (0.1 mJ/cm2)(0.41)(6.7 x 1013 mJ/cm2) Absorbed 1 cm x 1 cm x 125 nm EUV-2D 0.5 Need to Know: • C-Parameter • [PAG] • Avogadro's Number 0.4 [base]/[PAG] # Acids Generated 0.3 0.2 0.1 C-Parameter = 0.051 cm2/mJ 0 -0.1 0 = [PAG](1 – e(-CE))(6.02 x 1023) Brainard EUV 2004 2 4 6 8 10 12 14 Eo Szmanda's Base Titration Method 17 Quantum Efficiency of EUV-2D at DUV and 193 nm Φ OD (1/um) C-Parameter DUV 0.37 0.037 0.33 193 nm 24.5 0.12 0.14 PAG H+ hν 92.5 eV EUV Photon PAG C, H & O Polymer eee- In principal, there is enough energy in an EUV photon to activate ~20-30 PAGs Brainard EUV 2004 PAG PAG H+ H+ H+ 18 Quantum Efficiency of EUV-2D is 2.1! Wavelength Esize 2 (mJ/cm ) EUV DUV 6.7 9.7 # of Photons 2 in 1 mJ/cm 13 x 10 Absoption of 125 nm Quantum Efficiency 6.7 125 0.41 0.10 2.08 0.33 Number of Acids Generated @ Esize x 10 13 38.2 40.6 The number of acids generated at EUV and DUV are the same! The LER vs. Esize Curves for both EUV and DUV are described by Shot Noise (Poisson) Statistics: Brainard EUV 2004 LER ∝ Dose-1/2 19 VI. Is EUV Limited by LER (3-Sigma, nm) 14 Shot Noise? 12 EUV-2D 10 8 No Hard Barrier Yet Resist Improvements 6 4 Although EUV-2D 2 0 10 20 30 40 50 60 70 80 2 14 LER (3-Sigma, nm) follows a LER vs. Esize pattern Esize (mJ/cm ) 12 defined by EUV-2D shot noise statistics, 10 8 New improved resists show 6 Resist Improvements 4 that performance is not r2= 0.95 - 0.97 2 0 0.2 Brainard EUV 2004 0.4 0.6 0.8 (Esize)-1/2 1 1.2 1.4 limited by shot noise 20 VII. Conclusions Shot Noise observed at DUV and EUV for all resist systems LER follows Poisson Statistical Rules: LER ∝ Dose-1/2 Although EUV-2D follows a LER vs. Esize pattern defined by shot noise (Poisson) statistics, resists can be made with better LER/Sensitivity performance Earlier studies of shot noise and LER either predicted: • Catastrophic LER failure, or • Shot noise barrier not yet encountered We conclude that shot noise statistics have been with us all along in DUV and EUV Brainard EUV 2004 21 What Don't We Know? How are multiple acids from a single photon arranged? Will this arrangement affect LER? hν H+ H+ Brainard EUV 2004 hν hν H+ H+ hν hν hν hν H+ + + H+ + HH H H+ + + H H H+ H+ 22 VII. Acknowledgements DARPA/SPAWAR David Patterson Cynthia Hanson Donald Mullin Sandia National Laboratories Kevin McDonald Jerry Sledge Chip Stein Dan Folk John Goldsmith Donna O’Connell Shipley Kathleen Spear Kathleen O’Connell Pramod Kandanarachchi Doris Kang Tom Penniman Bob Blacksmith Chuck Szmanda Brainard EUV 2004 23