Development Update of High Index Lens Material LuAG - Sematech

SCHOTT Lithotec 

1 5 th Intern. Immersion Symposium 

22-25.9.2008, The Hague, NL, 

High Index Lens Material LuAG 

´ 

Development Update of High Index Lens 

Material LuAG for 

ArF Hyper NA Immersion Systems 

Lutz Parthier, Gunther Wehrhan, Frank Seifert, Marcus Ansorg, 

Tilo Aichele, Christoph Seitz, Martin Letz 

SCHOTT AG, Division Schott Lithotec

SCHOTT Lithotec High Index Lens Material LuAG 

Outline 

� Absorption 


22-25.9.2008, The Hague, NL, 

� Zone Refining 

� Transmission Growth 

� Intrinsic Absorption 

� Laser durability 

� Roadmap 

� Summary and Outlook

SCHOTT Lithotec 


22-25.9.2008, The Hague, NL, 

High Index Lens Material LuAG 

Absorption target is the most critical challenge for LuAG 

All activities focused on absorption improvement and addressed: 

� Raw materials purity at supplier 

� Lu 2O 3 ⇒ Stable quality with ppb level available, 

� Al 2O 3 ⇒ Reduction of impurity level by half, but 5x above Lu 2O 3 

� Installation of Continuum Source Atom Absorption Spectrometer AAS 

(Detection limit - 1ppb) at Schott Lithotec´s own invest 

� Implementation of an additional purification step for Al 2O 3 at Schott 

⇒ Installation of Zone refining machine 

� Optimization of growth conditions to control the impurity incorporation 

⇒ Valence engineering


Outline 



22-25.9.2008, The Hague, NL, 





� Roadmap 



Zone refining machine : 

Trial production run (3 weeks) � equipment works! 


22-25.9.2008, The Hague, NL, 

70 cm 

5 cm


First production run: 

After 10 zone passes no purification effect achieved 

relative purification 

2,0 

1,5 

1,0 

0,5 

0,0 

� Neither significant trend nor visible purification due too high zone pass 

velocity 

⇒ Zone speed too high (super-cooling effects) 


22-25.9.2008, The Hague, NL, 

E1 

E2 

Start End 

relative position 

Starting 

concentration


Zone refining pre-tests: proofs purification potential 

relative concentration 

3,5 

3,0 

2,5 

2,0 

1,5 

1,0 

0,5 

0,0 


22-25.9.2008, The Hague, NL, 

Gas atmosphere 1 Gas atmosphere 2 

E1 

E2 

V 1 < V 2 < V 3 

Start End 


relative concentration 

13 

11 

9 

7 

5 

3 

1 

E1 

E2 

Start End 


� Purification effect dependent on zone speed and atmosphere 

� Purification for impurity E2 more efficient than for E1 

⇒ Zone speed reduction by 50% - run currently ongoing! 

⇒ Design of Experiments (DoE) needed for optimization


Outline 



22-25.9.2008, The Hague, NL, 





� Roadmap 



New 80mm dia crystal shows homogenous low 

absorption of 0.062 to 0.068 

� Very homogeneous transmission 

� Variation top – bottom below 10% 


22-25.9.2008, The Hague, NL, 

sample position as grown 

K ini @ 193nm 

cm -1 

(bulk + surface) 

1 cone 0.062 

2 

3 

4 

5 

top 

top 

bottom 

bottom 

0.062 

0.062 

0.066 

0.068


Variation of k-value over diameter within accuracy of 

measurement ! 

� Scan of blank from top shows an average k-value of 0.063 

� Maximum value of 0.064 within accuracy of measurement 

� No distinct features (e.g. core – outer part) visible 

k [1/cm] 

0,070 

0,065 

0,060 

0,055 

0,050 


22-25.9.2008, The Hague, NL, 

0 10 20 30 40 50 60 70 80 

position [mm] 

80 mm


New Champion data: Induced Absorption k 0 = 0.035 cm -1 


22-25.9.2008, The Hague, NL, 

k 0 = 0.0356 cm -1 

dk/dH = 1.2x10 -4 cm/mJ 

� Laser Induced Absorption were measured by extrapolation of 

absorption during low fluence ArF Laser irradiation 

� Laser irradiation causes an effective surface cleaning


LIF (Laser Induced Fluorescence) shows improvement on 

crystal quality and confirm the reduction of impurities 

May 08 


22-25.9.2008, The Hague, NL, 

LIF signal normalized to STE 

10 

9 

8 

7 

6 

5 

4 

3 

2 

1 

0 

New Champion 

May 08 

150 250 350 450 550 650 750 850 

Lambda [nm] 

� Reduction of high background between ~300 and ~550 nm – attributed to 

improved crystal perfection 

� LIF is used for the optimization of the growth atmosphere 

Sept 08


Outline 



22-25.9.2008, The Hague, NL, 





� Roadmap 



Temperature dependent transmission measurements of 

LuAG carried out at Synchroton BESSY 

Transmission 

1 

0,1 

0,01 

T = 80 °C 

0,001 

170 175 180 185 190 

Sample thickness: 0.4mm ! 


22-25.9.2008, The Hague, NL, 

Wavelength / nm 

T = -50 °C 

T = -20 °C 

T = 5 °C 

T = 25 °C 

� Band Gap at room temperature (300K) = 7.08 eV = 175nm 

(old value: 178nm) 

Cooling 

increases the 

bandgap by 

1.75 meV/K 

= 7.08 eV


Improved LuAG quality allows a precise determination of 

the intrinsic absorption limit (Urbach edge) 

� Transmission and reflection measurements were carried out on synchrotron 

May 08 

193.39nm 

-> 6.41 eV 


22-25.9.2008, The Hague, NL, 

A = 0.20cm -1 

Urbach edge @ 193nm: 

T= 24°C: 0.0026 cm -1 

0.005 cm -1 

See also: Poster V. Liberman 

Sept 08 

� Cooling can decrease the intrinsic part of the 

absorption by 4.6 E-5 (cm K) -1 

A = 0.088cm -1 

Urbach edge @ 193nm: 

T= 24°C: 0.0013 cm -1 

193.39nm 

-> 6.41 eV 0.005 cm -1


Outline 



22-25.9.2008, The Hague, NL, 





� Roadmap 



High laser durability at high fluence for LuAG shown 

Transmission [%] 

73,0 

72,9 

72,8 

72,7 

72,6 

72,5 


22-25.9.2008, The Hague, NL, 

k0=0.0358cm -1 

32mJ/cm 2 , 1000Hz, 1.77Mio pulses 

y = 0.0148x + 72.74 

0,00 0,20 0,40 0,60 0,80 1,00 1,20 1,40 1,60 1,80 

Puls number [Mio] 

k0=0.0355cm -1 

� Neither degradation of transmission nor coloration was observed during 

laser irradiation at 32mJ after 1.77 Mio pulses


Long term laser durability for LuAG shown 

Absorption k0 [cm -1 ] 

0,14 

0,12 

0,10 

0,08 

0,06 


22-25.9.2008, The Hague, NL, 

12mJ/cm 2 , 1000Hz, 1.5 G pulses 

y = -3E-06x + 0,0997 

0 200 400 600 800 1000 1200 1400 1600 

Pulise Number [Million] 

� Neither degradation of transmission nor coloration was observed during 

laser irradiation at 12mJ after 1.500 Mio pulses


Outline 



22-25.9.2008, The Hague, NL, 





� Roadmap 



Absorption Roadmap LuAG 9/08 

Absorption [cm -1 ] 

10 

1 

0,1 

0,01 

0,001 

3,7 

2,5 

1,5 

0,9 

0,63 


22-25.9.2008, The Hague, NL, 

Feasibility 

Crystal dia < 50mm 

0,2 

Demonstrator 

Crystal dia 80mm 

0,12 

Lab Scale 

Crystal dia 22mm 

0,1 

Experimental data Step 1 

Experimental data Step 2 

0,05 0,05 

0,035 

Mai-05 Dez-05 Jul-06 Jan-07 Aug-07 Feb-08 Sep-08 Mrz-09 Okt-09 

Target 

Final Target 

A


Summary and Outlook 

� Champion Absorption actually at k 0= 0,035 cm -1 (bulk + surface !) 

homogenous in the whole volume of 80mm dia crystal 

� Growth run with higher quality Al 2O 3 purified by zone refining 

scheduled for end October (last step AIP) 

� Potential of zone refining method not developed yet. 

� DOE started 

� Next production run ongoing 

� Optimization of zone refining needs 4 month 

� Next improvement step towards absorption target 0.005cm -1 required 

upscaling of growth machine 

� How to go ahead with the LuAG program? 


22-25.9.2008, The Hague, NL,


Acknowledgements 

LuAG Development at SCHOTT Lithotec - Participation and Funding 

� Canon Inc. 

� Carl Zeiss SMT AG 

� Nikon Corporation 

� SEMATECH 

Special thanks for many discussions and measurements also to: 

� John Burnett, NIST 

� Vlad Liberman, MIT 


22-25.9.2008, The Hague, NL,

Development Update of High Index Lens Material LuAG - Sematech

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