Fiber Lasers for EUV Lithography

Transcription

1 Fiber Lasers for EUV Lithography A. Galvanauskas, Kai Chung Hou*, Cheng Zhu CUOS, EECS Department, University of Michigan P. Amaya Arbor Photonics, Inc. * Currently with Cymer, Inc 2009 International Workshop on EUV Lithography, Sheraton Waikiki, July 13 17, 2009

2 EUVL Source Power Requirement U. Hinze et al., Laser Zentrum Hannover e.v., EUVL Symposium 2007 ~500W EUV Power 180 W Debris Shield T~1 Collector 5sr and R=50% Spectral Purity Filter T~0.9 CE~2% Required Laser Power ~25kW

3 Advantages of Fiber Laser Technology E >O efficiency is highest Robust and compact Pulsed Laser Architecture Commercial Product Electrical-to-Optical Efficiency Q-Switched Yb:Glass fiber 25% - 30% Q-Switched DPSS or Thin Disc % RF Excited CO % Long lifetime/reliable High repetition rate capability High beam quality Superior power scalability

4 High power fiber laser revolution Historical trend in diffraction limited cw fiber laser power Commercial incoherently combined 50kW cw fiber laser system (non diffraction limited: M 2 = 33) YLR Fiber lasers constitute a new and developing technology: Continuous improvement in fiber and component technology Continuing advances in power

5 Summary of 13.4nm EUV generation results with pulsed fiber lasers First proof of principle demonstration with a solid Sn target A. Mordovanakis et al, Optics Letters 31, (2006) 2% efficient 13.4nm in band EUV generation using Sn droplet source Kai Chung Hou et al, Optics Express 16, (2008) Simi A. George et al, Opt. Express 15, (2007)

6 Main trade off for high power pulsed fiber laser drivers for EUVL Practical droplet source can not exceed certain maximum repetition rate For Sn droplet source it is considered to be at 80kHz 100kHz Maximum pulse energy from a single fiber is limited by extractable energy and fiber nonlinearities For 3ns 10ns pulses max energies are 4mJ 10mJ respectively Consequently, maximum power from single fiber EUVL driver can not exceed ~1kW Practical considerations restricts to much less (approximately to 200W 500W range)

7 Power Scaling Strategy for 25 kw Fiber Laser EUV Driver Single Emitter Fiber Integrated Module (SEFIM) W (~80 100kHz, 2 6ns) Spatially multiplexed SCM blocks >25kW Spectrally Combined Modules (SCM) 5 >10kW λ 1 λ 2 ~500W EUV λ n

8 Conventional Spectral combining using diffraction gratings Based on spatial spectral dispersion of diffraction gratings: Combined Beam Fiber Laser Channels Transform Lens λ 1 λ 2 λ n f f

9 Linewidth considerations in a MW peak power fiber amplifier SPM induced spectral broadening: δω 2π n 1 exp( gl) n 1 2 max = 0.86T0 Pi i= 1 λ Aeff () i gi i i Example: 1MW peak 1ns pulse in 100μm core PCF fiber Δω max 18 GHz* *Consistent with experimental results: Christopher D. Brooks and Fabio Di Teodoro, Appl. Phys. Lett. 89, (2006)

10 Beam size and bandwidth trade off in diffraction grating based SBC Tradeoff Linewidth and beam width requirement to retain mode quality Small beam width high power density on grating Small linewidth MW peak power can not achieved, limited by SPM Example 20GHz linewidth 1mm beam width 25kW (targeted power) 1000 kw/cm 2 Thermal distortion or damage Linewidth (GHz) Design Trade for M 2 ~ Beamwidth 1/e 2 radius (mm) Intensity (kw/cm 2 )

11 Spatial dispersion free spectral combining based on sharp edge spectral filters Initial experimental results: 2nm inter channel separation, 0.5 nm spectral linewidth 91% combining efficiency, 52 W combined Combined ns duration pulses with 4mJ output energy No trade off between beam size and channel bandwidth power scalability per channel and for total power

12 Commercially available LWP Filters No limitation on linewidth and beamwidth Sharp transition > high channel density ~0.8 nm measured on sample ~0.3 nm available from mfg Yb 3+ has 60 nm gain bandwidth Tunability Measured 50 nm shift in cut off with 28⁰ change of angle Same sharpness in broad tuning range Transmission Transmission ~0.8nm º 14º 28º Wavelength (nm) Wavelength (nm)

13 Commercially available LWP Filters % average R Overall Combining Efficiency (η) N=5 96.8% 98.6% 99.4% % 0.84 N= N=20 N= Reflectance Measured performance: Residual absorption in this type of coatings: Transmission = 95%, Reflectivity = 99.7% 2 10 ppm High damage threshold: Energy =1J/cm 2 (measured by manufacturer) Power = 100kW/cm 2

14 Combining Demonstration Setup Delay Lines Pump 1 Splitter F 1 F 2 F 3 F 4 Pump 2 Combiner Pump 3 Channel Amplifiers 80μm core Yb doped LMA fibers Combined Output Input Beam

15 Spatial Beam Overlapping Beam Profiles after Combiner Output Beam Mode Quality a b FWHM Beam Diameter (μm) Horizontal axis M 2 ~1.82 M 2 ~1.82 c Blue Channel Green Channel 0 d Red Channel Combined Beam FWHM Beam Diameter (μm) Vertical axis Position (mm) M 2 ~1.85 M 2 ~ Position (mm)

16 Normalized Amplitude (a.u.) Combined Pulses Temporal Pulse Overlap 0.1 ns = 3cm τ (ns) Seed Pulse Combined ~2ns Combined power 52 W Combined pulse energy 4 mj

17 Demonstrated Feasibility of SBC for multi kw EUVL Sources Non spatially dispersive combining scheme Combines concurrent high peak power and average power Practical scheme for fiber laser based EUVL source Current filters allow up to 40 channels combined with 90% combining efficiency >92% efficiency, 52W combined power, M 2 ~1.85 demonstrated 4.6mJ combined demonstrated λ 1 λ 2 Spectrally Combined Modules (SCM) 5 10kW λ n K. Regelskis, K. Hou, G. Raciukaitis, and A. Galvanauskas, "Spatial Dispersion Free Spectral Beam Combining of High Power Pulsed Yb Doped Fiber Lasers, in CLEO 2008, paper CMA CMA4

18 Size, Efficiency, Reliability & Cost Comparison of Continuous Wave Industrial Lasers ARBOR PHOTONICS,Inc. Powering advanced laser processing Slide 18

19 Power Scaling & Cost Projections Projected Trend for Short pulse Fiber Lasers ARBOR PHOTONICS,Inc. Powering advanced laser processing Slide 19

20 Acknowledgements This work is partially supported by SRC: Task ID Feasibility study of a compact and efficient 1 kw fiber laser source for EUV generation Task ID Demonstration of Power Scalability of LPP EUV Lithography Sources Using Fiber Laser Technology with Spectral Multiplexing