Introduction and Outline A Straight Forward Path (Roadmap) to EUV High Brightness LPP Source Rainer Lebert, AIXUV Target Features of High Brightness EUV Source LPP Concept to reach Specification Target Laser Parameters Simulations of HB-LPP Tin Source Laser availability Target Issues
Target Features of High Brightness EUV Source With EUVL we got used to doses on a field of about 6 cm2 of about 6 mj with a mask illumination of NA=0.063. This leads to the convenient etendue of about 2 mm 2 sr and the inconvenient power demand of >200 W at IF. Taking a bright image with sufficient contrast on a CCD camera requires about 1.5 µj per Mega Pixel of photon flux. However, the fraction of the energy usable from the source depends on the intended resolution! For dark field defect scan on mask blanks, the resolution is targeted to about 600 nm. Hence, an image field of about 0.4 mm 2 /MPx and no tight limitation on illumination allows for still using an etendue of more than 0.03 mm 2 sr/mpx. Hence a full mask can be scanned in less than 2 hours with about 20 µw in IF. This can be achieved with 0.15 sr collection from a 100 mw/(2 pi sr) source of 0.5 mm diameter. Targeting 10 nm resolution on the mask reduces image field to 14 µm/mpx diameter
Target Features of High Brightness EUV Source A bright image with sufficient contrast requires about 1.5 µj per Mega Pixel Targeting 10 nm resolution on the mask reduces image field to 14 µm/mpx diameter The Task is increased with AIMS like illumination, which brings the etendue demand down to < 2*10-6 / MPx 2 mm 2 sr. However, some 100 mw in IF might be sufficient. With Inspection, where the etendue demand can be slightly relaxed to < 2*10-5 / MPx 2 mm 2 sr, but more than 15.000 images/mpx 2 are required for 2 h inspection. This requires already > 20 mw on the detector or (under assumptions) 0.2*MPx 2 W at intermediate focus.
Consequences from high brightness requirement 1 1000 Collection, sr 0.1 0.01 0.001 Source use efficiency is very important with HB source use! 100 10 1 inband source power, W/(2 p sr) Collection sr req. power req. Power opt. HVM Use efficiency scales with 1/(Source area), i.e. 1/(source radius)^2 0.0001 0.1 10 20 55 100 170 500 1000 Source Diameter, µm
Looking for Optima for the applications 2,500 20 2,000 Drive Power, INSPECT, W 1,500 1,000 15 10 Drive Power, AIMS, W INSP AIMS 500 16 mm, 4.6 W 5 13 µm, 467W 0 0 0 10 20 30 40 50 60 70 Source Size, mm
High brightness LPP source Process Assumption Matching source etendue to optics with intermediate collection angle of 0.2 to 1 sr and achieving best conversion efficiency leads to most economic source t, because smallest source requires smallest drive power. With maximum target collection of 1 sr, matched source diameter is in the range of 3 30 µm. < 100 µm source diameter is ineffective for discharge plasmas (reason> free path length has to be << diameter) < 10 µm source diameter is difficult to achieve with standard power laser solutions (λ, M 2 ) and focusing compatible with plasma generation (NA). Laser Produced Sources should be discussed Source Size specifications should target 10 µm and reach at least 30 µm
How to generate high brightness LPP source Focus Laser to smaller than target diameter e.g. 10 µm High NA focusing: M 2 close to 1 Achieve intensity such as to achieve sufficiently good CE Intensity in the range of 10 11 W/cm 2 Keep stable target position by stable laser pointing control and stable target position This is achieved, if laser pulse duration is short compared to plasma expansion time Is this possible?
Simulated Emission Pulses 1.06 µm, 0.7 ns, x*10 11 W/cm 2, 10 µm Focus Inband Emission, MW/(Half sphere) B6 B5 mj ns Focus Intens CE B5 1.0.7.01 18.2 1.32 B6 1.5.7.01 27.3 1.09
As expected, for small spots, CE peak at higher I and lower CE 1.6% 1.4% 1.2% Inband CE 1.0% 0.8% 0.6% 0.2 ns 0.5 ns 0.7 ns 1 ns 1 ns 0.7 ns 0.4% 0.2% 0.0% 0 5E+11 1E+12 1.5E+12 2E+12 2.5E+12 3E+12 3.5E+12 4E+12 4.5E+12 Intensity, W/cm 2
Understanding CE Only I I = 20 2.0% 1.8% 1.6% Focus Diameter and Pulse duration matched. 0.6 ns, 10µm 1.4% 0.7 ns, 20µm CE 1.2% 0.35 ns, 10µm 1 ns, 10µm Poly. 1.0% Too long pulse or focus too small for Pulse duration 0.8% 0.6% 0.2 ns, 20µm Too short pulse or too large focus for Pulse duration 0.4% 0.00 20.00 40.00 60.00 80.00 100.00 120.00 tau/d =
Variation of Intensity and Pulse Duration allows for maximizing brightness No Brightness evaluation, yet. Representative for source Size: Average Charge distribution A9, 1ns, 10.2*10 11 W/cm 2: 0.8 mj < CE = 1.21% A10, 1ns, 20.2*10 11 W/cm 2 1.59 mj; < CE = 1.18% B4, 0.7 ns, 9*10 11 W/cm 2 0.5 mj: CE = 0.89 % B5, 0.7 ns, 18*10 11 W/cm 2 01 mj: CE = 1.32 %
Minimum Spot Size with low <Z> emission A9, 1ns, 10.2*10 11 W/cm 2:v 0.8 mj ;< CE = 1.21% A10, 1ns, 20.2*10 11 W/cm 2 1.59 mj; CE = 1.18%
Path of solution Material: Tin Target Source Size: 10 µm NA and M² Best Pulse duration: e.g. 0.7 ns Best Intensity e.g. 10*10 11 W/cm² Pulse Energy Total Power M² Pulse Duration Pulse Energy Rep Rate Confidential
Laser for high Brightness X-Ray Source is available Diode 1pJ Reg. Amp. 2.33 mj PC Slab 1 25 mj Slab 2 67 mj Slab 3 ~100 mj Slab2 Pump 2b Pump 2a Slab1 Slab amplifier stages 1 and 2: experimental setup Pump 1
Beam characterization after slab 1 @ 62W M² measured with 90/10 method M²x=1.63 M²y <1,5 There is still potential for optimization of beam quality
Realization of the MOPA Prototype features housed breadboard full software control of all functions Reg. Amp. Slab I Slab III a and b Slab II
Laser Development Plan Available Regenerative amplifier meets target specs for 1 W laser Power and 1 khz repetition rate. 10 mw EUV source already close to AIMS specs. Available Lasers achieve > 200 W Could drive 2 W inband EUV LPP source and 0.25 W IF power. Laser Power Upgrade only by rep-rate increase. Target concept is independent of rep-rate and should be able to support up to MHz, which is 10 W EUV source: Target Cooling is immanent with thermalized bath. Upgrade Development of Regenerative amplifier with thin disk or Innoslab concept (potentially with one amplifier should reach target specs for > 200 W laser Power and 200 khz repetition rate. Upgrade developments and commercialization together with Trumpf, Rofin-Sinar and Edge- Wave Companies envisioned. Close collaborations exist.
Summary Laser 209 W average power, 105 mj pulse energy at 2 khz PRF demonstrated A peak power of more than 200 MW is achieved without beam distortion by nonlinear effects or optical damage Contrast ratio better than 2000 : 1 Beam quality in the range of M2 < 1.4 4 allows for efficient plasma generation Pulse length can be set from 0.3 ns to 1.5 ns INNOSLAB offers efficient single pass amplification to high average power 200 MW peak power
High brightness LPP source Target Assumption With small source demands on beam pointing control and target position increases significantly (estimated < 5 µm lateral and < 20 µm axial) Laser pulses and targets have to be matched. Liquid Jet or liquid droplet target do not achieve sufficient stability and make problems with temporal synchronization and pulse to pulse cross-talk (at 100 khz to 1 MHz) Regenerative target is required; Suggested is liquid tin target (Film target similar to Philips EUV s DPP would require > 200 m/s circ. velocity) Some innovation required for reaching low debris level
Droplet target is only stable close to Nozzle; at usable distances the budget is exceeded.
LIQUID BATH TARGET is suggested Laser EUV Level Sensor Cooling LIQUID TARGET Temp. Sensors Heating
SUMMARY A new source type dedicated for applications with high brightness demand is suggested. Source areas in the range of 10-4 mm 2 seem achievable. This allows for use of up to 1 sr emission and hence, up to 5 % extraction efficiency (0.5 W from 10 W) With available laser and target technology and a strong research and commercial network going onto a development track seems promising. With available laser technology of > 200 W power of lasers with suited parameters source powers of 3 W are in close reach. With > 50 mw of collected power, Brilliances of 500 W / mm 2 sr exceed those of future HVM sources. Development Plan for a factor of > 5 in power is envisioned.