High-peak power laser system used in Yb doped LMA fiber Institute of Laser Engineering, Osaka University, Suita, Osaka, Japan YOSHIDA Hidetsugu, TSUBAKIMOTO Koji, FUJITA Hisanori, NAKATSUKA Masahiro, MIYANAGA Noriaki, IZAWA Yasukazu 2007 International Extreme Ultraviolet Lithography (EUVL) Symposium 29-31 October, 2007 Sapporo Convention Center, Sapporo, JAPAN 1
Contents Generation of optional pulse shape by Yb doped fiber laser system for EUV lithography laser (1) Introduction (2) Development of optional electrical pulse circuit. (3) Generation of optional laser pulse. (4) PM-Yb Large Mode Area fiber amplifier. (5) Conclusion. Electrical pulse shape PM-Yb:SMF PM-Yb:LMA-F Single-mode Yb oscillator LN modulator 2
Optional pulse generation by fiber couple LN-modulator < EO first pockels cell> PC < Fiber couple LN modulator > CW laser High voltage(3-4kv) H. V. pulser < Pulse stacker> LN-EO modulator 1-2V Electric pulse generator P.C. Low voltage Optional pulse shape Stable 3
Front-end laser system of single-mode and polarization-maintain Yb fiber laser 1030 nm FBG-FL 1053 nm FBG-FL 1064nm FBG-FL 1080 nm FBG-FL LN Modulator 20 ns µ Pulse shape control 13 GHz 100-ps step Yb:fiber 20m µ 980 nm LD 325 mw Output 15.6nJ @5 khz Power monitor Temp. control. 980 nm LD 200 mw Yb:fiber 20m Yb:fiber 20m Power monitor 980 nm LD 325 mw 980 nm LD 325 mw 980 nm LD 325 mw 4
Principle of electrical pulse generation Trigger CH1 CH 2 400ps FWHM 250ps ATT CH 3 500ps ATT Output pulse ATT CH40 9750 ps ATT Combined pulse Optional pulse 5
Generation system of optional pulse shape Generation system of optional pulse shape Yb:fiber laser system Output 6
Generation of optional laser pulse corresponding to electrical pulse shape PC Electrical pulse Laser pulse (a) (b) (c) 7
Regenerative amplifier replace to Yb fiber laser for high average Nd:YAG laser. Reg.Amp+ Pre Amp Fiber Amp. 2 x 4 mm Rod, 2 pass 5W Fiber Osc. (Regen. Amp) Fiber Front-end 50 W 200 W 2 x 6 mm Rod, 2 pass 5000 W /SBS Pulse Compression /Higher Harmonic Gen. /Control of Focus Pattern 8 x 12 mm Rod, 2 pass to Target Chamber SBS PC Mirror 8
Comparison with regenerative amplifier and Yb LMA fiber laser Regenerative amplifier Output 5W(1mJ, 5kHz) Repetition rate 5kHz (PC limit) Pulse duration 3 ns (cavity length) Beam quality good(m 2 =1.5-2) Efficiency low Yb:fiber(LMA) amplifier Now : Output 6.6W (66µJ, 100kHz) In future: Output 30-50W (3-5mJ, 10kHz) 1-100kHz (Repetitious) Optional pulse shape and width (1-100ns) Excellent (M 2 =1.1) High 9
Experimental layout of PM-Yb LMA fiber amplifier Yb fiber laser system Isolator Isolator Input power 4mW(4nJ, 1-50kHz) t=13, 30 ns Optical stage H.W. Plate PM-Yb fiber LMA 30µm/400µm,L=4 m Absorption 4dB/m @975nm Optical stage Output Dichroic Beam-splitter Mirror (980nm T=95%,1064nm R=95%) LD 978nm 30 W 10
Output power depend on bending radius for PM-Yb LMA fiber amplifier Amplified output power (W) 7 6 5 4 3 2 1 PM-Yb fiber LMA, 30µm/400µm, L=4m Input 14mW 0 0 5 10 15 20 25 30 35 LD power (W) R 50mm(10kHz) R=100mm(10-100kHz) R 75mm(10-100kHz) Max.6.6W(@ 100kHz) Max.0.66mJ(@10kHz) R Bending radius 11
Propagation loss and output beam quality depend on bending radius for PM-Yb LMA fiber amplifier X -1.1 D.L. X 1.1 D.L. X 1.15 D.L. Propagation loss [db] 1000 100 10 1 0.1 LP 01 LP 11 LMA, 30µm/400µm,NA 0.06 R Bending radius 0.01 0 20 40 60 80 100 120 140 160 Bending radius [mm] 12
High power operation for PM-Yb LMA fiber amplifier Output power (W) 30 25 20 15 10 1054 nm 1064 nm 1080 nm Max.output 30W t=10 ns 300µJ / pulse 100kHz X 1.1 D.L. 5 0 0 20 40 60 80 100 LD input power (W) 13
Experimental layout for PM-Yb LMA fiber amplifier(50 W, 0.5mJ, 100kHz) Yb fiber laser system Isolator Input power 4mW(4nJ, 1-50kHz) t=13ns PM-Yb fiber LMA 30µm/400µm L=4.3m 5W(0.5mJx10kHz Optical stage Optical stage H.W. Plate LD 978nm 30 W Isolator LD 978nm 100 W (a) LMA-50/350 L=3.4 m (b) PCF-MMA50/390 L=3 m 50W(0.5mJx100kHz 14
Photograph for PM-Yb LMA fiber amplifier (50 W, 5mJ, 10kHz) 1st fiber amp. LD 30W 5W Output 2nd fiber amp. 600mm LD 100W 600mm 50W Output 15
Laser output power and gain characteristics(1) Core 50µm Clad 350µm NA 0.06, 12dB/m L=3.4m Near-field pattern 50 Max. 40W, Efficiency 54% 10000 G=1500, g=0.022/cm Output power (W) 40 30 20 10 Input power 0. 035 W 1.50 W 3.70 W 5.20 W Gain 1000 100 10 0 0 10 20 30 40 50 60 70 80 LD pump power (W) 1 0 10 20 30 40 50 60 70 80 16 LD pump power (W)
Conclusion Generation of optional pulse shape by Yb doped fiber laser system for EUV lithography laser The optional pulse shape generator by Yb doped fiber laser system. Yb fiber laser system operated the polarization-maintained pulsed for single transverse and -longitudinal mode using fiber Bragg grating (FBG). The laser oscillator can be tuned at four wavelengths of 1030, 1053, 1064 and 1080 nm. This system generates optional pulse shapes that sliced up the Yb fiber oscillator by a LN (LiNbO3) intense modulator with 12.5-GHz bandwidth. The several output waveforms were obtained including rectangular pulse from 1ns to 12.5 ns with a 500-ps rise time, and Gaussian pulse from 1 to 25 ns. The highest output energy of about 250 nj for 10-ns Gaussian pulse was achieved at 100-kHz repetition rate. The output power has been increased over 30W (300µJ, 100kHz) by a 30-µm core Yb double-clad polarization-maintained LMA fiber and 57W (570µJ, 100kHz) by a 50-µm core MMF fiber 17