Contamination control in EUV exposure tools

Contamination control in EUV exposure tools Katsuhiko Murakami Noriaki Kandaka, Takashi Yamaguchi, Atsushi Yamazaki, Tsuneyuki Hagiwara, Tetsuya Oshino, Jiro Inoue and Kazuya Ota Nikon Corporation June 12, 2013

Contamination control in EUV exposure tools EUV-induced contamination Carbon contamination Surface oxidation Particles in vacuum June 12, 2013 2

Contamination control in EUV exposure tools EUV-induced contamination Carbon contamination EUV + O 2 mitigation On-body UV dry cleaning Surface oxidation Particles in vacuum June 12, 2013 3

Relative reflectance Relative reflectance Contamination study using a synchrotron facility Neutral density filter Synchrotron radiation Branch chamber Folding mirror Load rock chamber Neutral density filter Gate valve with Zr filter Rotational photo diode Transfer rod Gas inlet Sample stage Exposure chamber BL 18 at SAGA LS SR facility 1 0.95 0.9 0.85 0.8 1W/cm 2 8W/cm 2 0.1W/cm 2 0 200 400 600 Cumulative dose [J/mm 2 ] 1 0.98 0.96 0.94 8W/cm 2 1W/cm 2 0.1W/cm 2 0.01W/cm 2 0.92 0.9 0.002W/cm 2 0.88 0 2 4 6 8 10 Cumulative dose [J/mm 2 ] Contamination growth with perfluorohexane (C 6 F 14 ) June 12, 2013 4

V, contaminating/cleaning rate [nm/s] IU transmittance [arb. unit] EUV + O 2 mitigation of carbon contamination 1E-1 C6F14 (5E-5Pa) O2 cleaning (2E-2Pa) Modeled Actual 1E-2 Oxygen flow optimized 1E-3 1E-4 1E-5 1 10 100 1000 10000 E, irradiance [mw/cm2] Contamination growth rate and O 2 cleaning rate 7 8 9 10 11 12 13 14 15 16 Number of pulses irradiated to IU [billion pulses] History of IU transmittance of EUV1 O 2 cleaning rate exceeds carbon contamination growth rate in appropriate condition. Degradation of IU (Illumination Unit) transmittance of EUV1 was stopped after optimization of O 2 flow rate. EUV + O 2 mitigation is very effective to carbon contamination. June 12, 2013 5

UV dry cleaning of carbon contamination Reflectivity UV dry cleaner using a low pressure mercury lamp Before cleaning, After cleaning Position on mirror Before cleaning After cleaning Carbon contamination on a illumination optics of EUV1 can be removed with UV dry cleaning. Initial reflectivity was recovered. June 12, 2013 6

UV dry cleaning in depressurized atmosphere Vacuum 真空チェンバー chamber Low 低圧水銀ランプ pressure mercury lamp measured --- calculation 1/100 atm 1 atm Low pressure mercury 低圧水銀ランプ lamp Sample 洗浄サンプル Cleaning rate of carbon contamination with UV dry cleaning increases with reduced pressure. UV dry cleaning was applied to an on-body cleaning method in EUV1. June 12, 2013 7

On-body UV dry cleaning for IU of EUV1 Con1 FE1 FM Con2 FE2 Low pressure mercury lamps placed near each mirror enabled on-body cleaning of illumination optics. June 12, 2013 8

Contamination control in EUV exposure tools EUV-induced contamination Carbon contamination EUV + O 2 mitigation On-body UV dry cleaning Surface oxidation Metal-oxide capping layer Particles in vacuum June 12, 2013 9

Relative change of reflectivity Metal oxide capping layer Metal oxide capping layer 1 Si Mo Si Mo Si 0.95 0.9 Si 0.85 MoOx NbOx Ru 0.8 H 2 O: 1x10-3 Pa, 8 W/cm 2 0.0E+0 5.0E+4 1.0E+5 1.5E+5 2.0E+5 Dose [J/cm 2 ] Reflectivity change of Mo/Si multilayers with several different capping layer materials during EUV exposure in water vapor was measured. Metal oxide capping layers have much higher oxidation durability compared with conventional Ru capping layer. June 12, 2013 10

Contamination control in EUV exposure tools EUV-induced contamination Carbon contamination EUV + O 2 mitigation On-body UV dry cleaning Surface oxidation Metal-oxide capping layer Particles in vacuum Particle capture using silica aerogel June 12, 2013 11

Particles in vacuum: Materials Potential particle generating events Physical contact Collisions: wafer/reticle transfer, pod open/close, valve o/c, grounding pin contact, Rubbing: bearings, ultrasonic motors, Physical reaction Sputtering: corona ionizers, EUV sources, Evaporation and condensation: pumping down in load lock Electrical discharge/spark EUV sources Discharge between reticle and pod during a transitional region in load lock Micro-discharge between wafer/reticle backsides and e-chucks. Potential materials Metal/metalloid: Na, Al, Si, K, Ca, Ti, Cr, Fe, Ni, Mo, Ru, Sn, Ta, Inorganic: SiO 2, Organic: C x H y O z +V -V HEAVY! > 7 g/cm 3 cf. PSL~1 g/cm 3 June 12, 2013 12

Particle in vacuum: Velocities Interaction with surfaces bounce or stick depends on the relationship between the particle impact velocity V i and the critical velocity V c. V i < V c : stick V i > V c : bounce V i >> V c : split and stick/bounce V c is determined by the surface material, the particle material, the particle size, etc. Particles that have lower velocities than the critical velocity cannot continue to fly. FAST! Typical Vc : 100 m/s for 100-nm particles 2,000 m/s for 10-nm particles 76 m/s 457 m/s 96 m/s Critical velocity vs. particle diameter S. Wall, et al., Aerosol Science and Technology, Volume 12, Issue 4, 1990, Pages 926 946 100 nm June 12, 2013 13

Flying range (m) Particles in vacuum: Flying range Forces acting on particles in vacuum Gravity: r 3, dominant force but not decelerating force Drag force: r 2, weak, depends on the gas pressure Coulomb force: weak, depends on E and amount of electric charge Thermophoretic force: very weak, depends on the thermal gradient Flying range vs. Initial velocity 1,000,000 100,000 Particle diameter 10 nm 100 nm 1,000 nm 10,000 1,000 100 10 1 below V c 10 100 1,000 10,000 Initial velocity (m/s) LONG! > 100 m Mo particles in 0.01-Pa O 2 gas June 12, 2013 14

Particle reduction system Particle shield Particle catcher Particle catcher Shield Mask Mask Particle source at the top. Shield between the particle source and the mask. Performance of shield is insufficient. Particle source at the top. Particle catcher on the shield. Particle catcher can drastically reduce the number of flying particles. To simplify the models, gravity is neglected and the same coefficient of restitution (COR) is used for both the vertical component and the parallel component to the wall. June 12, 2013 15

Silica aerogel as particle catcher STARDUST : NASA s comet sample return mission, 1999-2011 February 7, 1999 Stardust Launch Dust Collector with aerogel Comet particles Velocity: ~ 6.5 km/s Diameter: 40-300 µm Vacuum tool particles Velocity: 10 m/s - 1 km/s Diameter: 1 µm - 10 nm Kinetic energy 10 13-15 Thinner sheet is enough for EUV tools. 1 Aerogel In Hand Photos from jpl.nasa.gov Particle Tracks in Aerogel (experiment) Comet Ejecta in Aerogel June 12, 2013 16

Structure of silica aerogels Pore network Apparent density: 0.003-0.35 g/cm Density of air: 0.0012 g/cm 3 at 20 C SiO 2 Pore size micro pores: < 2 nm mesopores: 2-50 nm macro pores: > 50 nm Silica particle diameter 2-5 nm June 12, 2013 17

Experimental setup of particle catcher MPE Tool Lead wire: V Particle generator installed in ESC chamber Lead wire: +V High voltage feedthroughs Induction coil Particles were generated by discharging (Air pressure ~5E-3 Pa) 10-20% of particles can go out through the gap Metal Plate having a through hole Cover plate Photos of aerogel tested: bare (left) and covered by a foil (right) Aerogel holding plate Aerogel Size: 100 mm (W), 100 mm (D), 15 mm (H) Density: 0.012 g/cm 3 Aerogel in ESC chamber A quarts substrate for particle adhesion evaluation (not shown in the photo) June 12, 2013 18

Experimental conditions of particle catcher #1: Aerogel sheet covered with a foil An aerogel sheet covered by a foil on the holding plate was put between the quarts substrate and the particle generator. Discharging was continuously and the total time was about 8 seconds. Particles are not captured. #2: Bare aerogel sheet The foil was removed. Discharging was continuously and the total time was about 8 seconds. Particles are captured. June 12, 2013 19

Experimental results #1: Covered with foil Up Down Particle density: 1,331 particles/cm 2 Particle density: 1,368 particles/cm 2 Almost the same density Pixel Histogram Pixel Histogram 41... 117 41... 157 40 13,266 40 20,431 20 59,354 20 83,262 10 49,915 10 53,683 7 90,868 7 79,865 5 3 2 1 4,452 16,635 19,063 29,952 Total = 283,622 26- >=300 nm 22-25 200 nm 17-21 100 nm 14-16 80 nm 11-13 70 nm 7-10 60 nm 1-6 pix =< 50 nm 5 3 2 1 22,982 3,839 13,137 14,289 Total = 291,645 June 12, 2013 20

Experimental results #2: Bare aerogel Up Down Particle density: 68 particles/cm 2 Particle density: 111 particles/cm 2 #1 1/20 #1 1/12 The aerogel sheet caught almost all particles that impacted it!! Pixel Histogram Pixel Histogram 41... 8 41... 74 40 184 40 519 20 1,456 20 3,730 10 2,285 10 4,288 7 5,546 7 8,317 5 3 2 1 274 1,201 1,414 2,119 Total = 14,487 26- >=300 nm 22-25 200 nm 17-21 100 nm 14-16 80 nm 11-13 70 nm 7-10 60 nm 1-6 pix =< 50 nm 5 3 2 1 412 2,856 1,663 1,812 Total = 23,671 June 12, 2013 21

Summary Oxygen introduction during EUV exposure effectively mitigates carbon contamination growth on optical elements in EUV exposure tools. Carbon contamination on optical elements can be removed by UV dry cleaning. It can be applied to an on-body cleaning method in EUV exposure tools. Surface oxidation of multilayer mirrors during EUV exposure can be prevented by using metal-oxide capping layer. Particles in a vacuum chamber fly very long distance. Silica aerogel is suitable material to capture such flying particles in EUV exposure tools. June 12, 2013 22

Acknowledgements EUVA NEDO METI Selete & EIDEC SAGA Light Source Chiba University Panasonic Corp. June 12, 2013 23

Thank you for your attention.