2007 International EUVL Symposium, Japan Surface Properties of EUVL Mask Layers after High Energy Laser Shock Cleaning (LSC) Tae-Gon Kim, Young-Sam Yoo, Il-Ryong Son, Tae-Geun Kim *, Jinho Ahn *, Jong-Myoung Lee **, Jae-Sung Choi **, Ahmed A. Busnaina ***, and Jin-Goo Park Department of Materials Eng., Hanyang University, Ansan, Korea * Advanced Materials Sci. and Eng., Hanyang University, Seoul, Korea ** Laser Engineering Group, IMT Co., Inc., Uiwang, Korea *** NSF Center for Microcontamination Control, Northeastern University, Boston, MA, USA Contact Information of Corresponding Author Tel: +82-31-400-5226 E-mail: jgpark@hanyang.ac.kr
Introduction to Laser Cleaning The Field of Laser Cleaning Types of Removal Cleaning Methods Cleaning Principles i Contaminated Layers Ablative Cleaning Direct Ablation to Surface Particulates Dry Laser Cleaning (DLC) Steam Laser Cleaning (SLC) Wet Laser Cleaning (WLC) Laser Shock Wave Cleaning (LSC) Thermal Expansion of Materials Momentum Transfer from Vaporized Thin Liquid Layer Combined the advantages of DLC and SLC Propagation of Shock Wave Reference: C. Phipps, et al, Laser Ablation and Its Application, p. 37, Springer, New York (2006). Steam Laser Cleaning Wet Laser Cleaning 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 2
Introduction to LSC Focused laser generates plasma and shock wave (Laser-Induced Laser Shock Wave). High pressure shock wave pushes particles away from surface. Shadowgraphy of Shockwave Local and global dry cleaning method Performed under atmospheric pressure Non-contact cleaning Controllable cleaning forces Possible to remove down to 60 nm of particle size Shock Wave Front 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 3
Simple Model for Laser-Induced Shock Wave The pressures of shock waves were calculated from propagation speed of shock wave based on the Blast-wave theory. Effective for Predicting Pressure Temperature Energy-conversion efficiency Shock Wave Pressure P = P + (1 ρ / ρ ) ρ ( U a ) 0 0 0 Density Jump in the Compressed Air Layer 2 ρ/ ρ 0 = ( γ + 1)/( γ 1+ 2 M s ) where P 0 : The ambient pressure. γ: The adiabatic coefficient ( γ=1.4 for air) ρ 0 : The density of air (ρ 0 =1.169 g/l for air) U: The shock wave propagation speed a: sound speed M s : The Mach number Reference: A. M. Azzeer, et al, Applied Physics B 63,, 307 (1996) Density of gas and shock wave speed are key parameter to improve shock wave pressure. 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 4
Motivation In this presentation, to understand Propagation Speed and Pressure of Shock wave by High Laser Energy (> 1 J) Surface Topography p Change due to Shock Wave Thermal Effects due to Shock Wave Adhesion Property of EUVL surface Change due to Shock Wave 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 5
Experimental Setup Laser System for Characterization of Laser Shock Wave and Its Cleaning Performance Laser Source Q-switched Nd:YAG laser (1800E, IMT Inc., FWHM=10 ns) Wavelength: 1064 nm Maximum Energy: 2.0 J Repetition Frequency: up to 10 Hz Focal Lens: 150 mm focal length with an anti-reflection coating Motion of Wafer Scan: Spiral scan (r-θ-z axis) Probe Laser for Characterization CW He-Ne Laser (1.5mW, Thorlabs) Wavelength: 632.8 nm Samples Ru (2 nm)on MoSi 40 paris Al 2 O 3 (20 nm)/tan (27 nm)/ru (2 nm) on MoSi 40 pairs Laser Shock Cleaning System, 1800E, IMT Inc 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 6
Characterization Method Use Probe Beam Deflection Method When shock wave propagates, density of air will be changed. It follows refraction of probe beam and signal changes in photo detector. 1 st Peak due to high intensity of plasma 2 nd Peak Due to shock wave It is effective and easy to set up with advantages including a relatively wide bandwidth, dynamic range, and negligible influence on the probe wave field. 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 7
Properties of Shock Wave 3500 In ntensity (a.u.) 1 5 10 15 1 1.6 mm 2 1.8 mm 3 2.0 mm 4 2.2 mm 5 2.4 mm 6 26mm 2.6 7 2.8 mm 8 3.0 mm 9 3.2 mm 10 3.4 mm 11 3.6 mm 12 3.8 mm 13 4.0 mm 14 4.2 mm 15 4.4 mm 16 4.6 mm 17 4.8 mm 18 5.0 mm Shock Wa ave Velocity (m/s) 3000 2500 2000 1500 1000 1.2 J 1.5 J 1.8 J Shock Wave Pressure (MPa) -500 0 500 1000 1500 2000 2500 3000 3500 9.0 75 7.5 6.0 4.5 3.0 1.5 0.0 Shock Wave Propagation Time (ns) 1.2 J 1.5 J 1.8 J 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Gap Distance (mm) 500 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Gap Distance (mm) Propagation speed and pressure were measured and calculated based on the deflection signals due to propagation of shock wave front. Propagation speed of shock wave decreased rapidly as a function of gap distance. There are not much differences in shock pressures at the long gap distance. The pressure of high energy laser is almost twice larger than of low energy laser (310 mj) at same gap distance. Gap distance is more effective parameter than laser energy. 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 8
Cleaning Performance Substrate: Al 2 O 3 /TaN/Ru/ML Contaminants: Silica, 50 nm Evaluation Tool: SEM E=1.2 J, d Gap = 3 mm E=1.2 J, d Gap = 5 mm Reference E=1.5 J, d Gap = 3 mm E=1.5 J, d Gap = 5 mm E=1.8 J, d Gap= 3 mm E=1.8 J, d Gap= 5 mm Particles on Al 2 O 3 layer were removed effectively by LSC 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 9
Dimension of Laser-Induced Plasma Surface damaged due to plasma Necessary understand dimension of plasma Laser Incident Direction Reference Al 2 O 3 /TaN/Ru/ML Damaged Surface 1.2 J 1.5 mm Focal Plane R q : 0.4, R a : 0.3, R pv : 3.4 R q : 2.3, R a : 1.1, R pv : 47.9 Summary of Plume Property Laser Power 1.2 J 1.5 J 1.8 J Length of Plume 5.3 mm 6.4 mm 6.8 mm Max. Thickness of Plume 2.34 mm 2.60 mm 2.81 mm Relative Position of x axis +2 0-2 To prevent surface damage due to plasma, the gap distance should be larger than half of plasma thickness. 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 10
Topography Change after LSC Substrate: Al 2 O 3 /TaN/Ru/ML Evaluation Tool: NC-AFM 1.2 J 1.5 mm 3 mm 5 mm Scan Area: 2 x 2 µm 2 Reference R q : 2.3, R a : 1.1, R pv : 47.9 1.5 J R q : 0.3, R a : 0.2, R pv : 2.9 R q : 0.3, R a : 0.2, R pv : 2.3 R q : 0.4, R a : 0.3, R pv : 3.4 (Unit: nm) R q :3.3, R a : 1.4, R pv : 55.1 R q : 0.4, R a : 0.3, R pv : 2.9 R q : 0.4, R a : 0.3, R pv : 2.9 1.8 J No topography change over 3 mm of gap distance R q : 3.5, R a : 2.1, R pv : 74.2 R q : 0.3, R a : 0.2, R pv : 3.3 R q : 0.3, R a : 0.2, R pv : 3.2 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 11
Conclusions The propagation speed and shock wave pressure were characterized by a probe beam deflection method as a function of gap distance at different laser energies. Propagation speed, shock wave pressure and temperature decreased rapidly as a function of gap distance. There are no big differences in the propagation speed and pressure even at different laser energies. To prevent the surface damage due to plasma, the gap distance should be larger than the half of plasma thickness. No topography change was observed over 3 mm of gap distance. 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 12
Acknowledgements This work is supported by The EUV R&D Program of Ministry of Commerce, Industry and Energy (MOCIE) The fostering project of the Lab of Excellency Post BK21 program. 2007 International EUVL Symposium, October 28-31, 2007, Sapporo, Japan 13