CHARACTERISTICS OF ION EMISSION FROM CO 2 /Nd:YAG LPP WITH TIN TARGET Akihiko Takahashi 1, Hiroki Tanaka 2, Atsushi Matsumoto 2, Yuuki Hashimoto 2, Kiichiro Uchino 3, Tatsuo Okada 2 1 Department of Health Sciences,, 3-1-1, Maidashi, Fukuoka 812-8582, Japan 2 Graduate School of Information Science and Electrical Engineering,, 6-1-1, Hakozaki, Fukuoka 812-8581, Japan 3 Interdisciplinary Graduate School of Engineering Sciences,, Kasuga, Fukuoka 816-858, Japan
Abstract The emission of ions from the target plasma is the crucial issue for extreme ultra-violet lithography. In order to investigate the behavior of ion emission, we measured the ion current from the laser-produced plasma (LPP) with tin solid target, tin foil target, SnO 2 solid target, and lithium target, irradiated by a Nd:YAG laser. In this experiment, a Faraday-cup detector was settled at the angle or 45 degree with the target normal. The distribution of the ion signal for the Nd:YAG LPP had the peak around the target normal. The ion energy for the tin target was about 8 kev in maximum, and 1 kev for the lithium target. We are now preparing the same experiment with CO 2 LPP.
Introduction - CO 2 LPP vs. Nd:YAG LPP TARGET: Solid Tin (Tin plate) EUV-filter & Transmission grating (φ 5μ m1/1mm) f=15mm CO2: LUMONICSTEA-61 5-1 J / 5 ns FWHM Nd:YAG: SPECTRA-PHYSICS Quanta-Ray PRO 2-12 mj /8 ns FWHM CO 2 laser/yag laser Xray CCD Camera
CO 2 LPP vs. Nd:YAG LPP - EUV Spectrum 3 1 4 CO 2 LPP 7 Nd:YAG LPP 6 1.E11 W/cm2 2 1 4 2.E1 W/cm2 1.E1 W/cm2 5 4 6.6E1 W/cm2 1.9E1 W/cm2 1 1 4 4.E9 W/cm2 3 2 1 5 1 15 2 25 Wavelength [nm] 5 1 15 2 25 Wavelength [nm] (a) (b) EUV spectra with tin solid target: (a) CO 2 LPP (b) Nd: YAG LPP Input energy is transferred to higher excited levels
CO 2 LPP vs. Nd:YAG LPP - Conversion Efficiency 1.5 1 5 CO 2 LPP 1.5 1 5 Nd:YAG LPP Spot size 1 1 5 2% 2.5X1 1 W/cm 2 1 1 5.442mm.494mm.546mm.468mm.494mm Underestimated? Spot size 5 1 4.727mm.883mm 1.1mm 1.22mm 1.53mm 1 9 1 1 1 11 CO INTENSITY [W/cm 2 ] 2 (a) 5 1 4 1 1 1 11 YAG INTENSITY [W/cm 2 ] (b) Conversion efficiencies of 13.5nm-light with tin solid target as a function of laser intensity: (a) CO 2 LPP (b) Nd: YAG LPP The maximum C.E. of CO 2 -LPP was almost same as that of YAG-LPP
Detection of Ion Current from Nd:YAG LPP - Ⅰ In order to investigate the behavior of ion emission, we measured the ion current from the Nd:YAG/CO 2 laser-produced plasma (LPP). : 19 mm Tin solid Tin foil SnO 2 solid Lithium Faraday-Cup f=15mm Faraday-cup detector was settled at the angle degree with the target normal. Nd:YAG: SPECTRA-PHYSICS Quanta-Ray PRO 2-12 mj /8 ns FWHM
Faraday-Cup Detector We used a hand-made Faraday cup detector.
Result Ⅰ- Ion Signal with Tin Solid.5 Tin Solid.4.3 Nd:YAG Energy.7 J.56 J.46 J Faraday Cup 45.34 J Laser.2.1 1 1-6 2 1-6 3 1-6 4 1-6 5 1-6 6 1-6 time [sec]
ResultⅠ- Tin Foil.4 Tin Foil.3.7 J.56 J.46 J.34 J Faraday Cup 45.2 Laser.1 1 1-6 2 1-6 3 1-6 4 1-6 5 1-6 6 1-6 time [sec]
ResultⅠ- SnO 2.7 SnO 2.6.5.4.3.7 J.56 J.46 J.34 J Faraday Cup 45 Laser.2.1 1 1-6 2 1-6 3 1-6 4 1-6 5 1-6 6 1-6 time [sec]
ResultⅠ- Lithium 1.2 Lithium 1.8.6.7 J.56 J.46 J.34 J Faraday Cup 45 Laser.4.2 1 1-6 2 1-6 3 1-6 time [sec]
Detection of Ion Current from Nd:YAG LPP - Ⅱ : Tin solid SnO 2 solid Lithium 19 mm Faraday-Cup f=15mm Faraday-cup detector was settled at the angle 45 degree with the target normal. Nd:YAG: SPECTRA-PHYSICS Quanta-Ray PRO 2-12 mj /8 ns FWHM
Result Ⅱ- Tin Solid.2 Tin Solid 45.15.1.5.7 J.56 J.46 j.18 J Faraday Cup Laser The signals became rather small and unstable. 51-6 1 1-5 1.5 1-5 2 1-5 time [sec]
Result Ⅱ- SnO 2.14 SnO 2.12.7 J Faraday Cup 45.1.8.56 J.46 J.18 J Laser.6.4.2 2 1-6 4 1-6 6 1-6 8 1-6 1 1-5 time [sec]
Result Ⅱ- Lithium.35 Lithium.3.25.2.7 J.56 J.46 J Faraday Cup 45 Laser.15.18 J.1.5 11-6 2 1-6 3 1-6 4 1-6 time [sec]
Ion Velocity/Energy Maxwell distribution of particle flax Example: Result I - Tin solid target YAG:.7 J 1.2 1.8.6 Faraday Cup Signal Distribution I(t) I () t = Kz t exp 2 5 / ( z t v ) 2 v p K: Constant Z: Distance between the target and detector V p : Average velocity on the target V : Collective velocity of particles 2.4.2 1 2 3 4 time [μsec] V p =7.x1 3 m/s V =1.1x1 5 m/s E ion =7.7 kev
Ion Energy Result I 1 Result I 8 6 Tin Bulk Tin Foil SnO2 Lithium Sn ~8 kev Faraday Cup 45 Laser 4 2.1.2.3.4.5.6.7.8 Nd:YAG Energy [J] Li ~1 kev
Ion Energy Result II 1.6 Result II 1.4 1.2 Tin Bulk SnO2 Lithium Faraday Cup 45 1.8.6.4.2.1.2.3.4.5.6.7.8 Nd:YAG Energy [J] Ion energy from Li target was almost same as that of Result-I On the other hand, Sn ion energy was rather smaller than Result-I Laser
We measured the ion current from the Nd:YAG LPP with tin targets and lithium target. The ion energy for the tin targets was about 8 kev in maximum, and 1 kev for the lithium target. The results suggests that the angular distribution of the ion energy from tin targets concentrates around the target normal, while for the lithium target the distribution was rather isotropic, for the Nd:YAG LPP. However, the experiments in this article are on the midway. Our remained plan is Measurements of the ion signal with CO 2 LPP Measurements of the angular distribution of the ion signal