Development Progress of high refractive LuAG for Hyper ... - Sematech

SCHOTT Lithotec 

1 4th Int‘l Symp.Immersion Lithography 

Keystone, CO, October 9, 2007 

Status of High Index Lens Material 

´ 

Development Progress of high 

refractive LuAG for Hyper NA 

Immersion Systems 

Lutz Parthier, Gunther Wehrhan, Dietmar Keutel, 

Tilo Aichele, Marcus Ansorg 

SCHOTT Lithotec

SCHOTT Lithotec Status of High Index Lens Material 

Outline 

� Current focus areas of Development 

� Development Status 

� Absorption 

� Growth Technology 

� Stress Birefringence 

� Homogeneity 

� Roadmap 

� Summary and Outlook 


Keystone, CO, October 9, 2007

SCHOTT Lithotec 



Status of High Index Lens Material 

Objective: Provide full size LuAG-Lens Blank in 2009 

Main activities focused on critical development areas: 

� Transmission: - Raw materials purity 

- Identification and elimination of process 

and handling contaminations 

- Crucible impurities reduction 


� Czochralski Growth: - Flat Interface 

- Striation free growth 

� Alternative Growth: - Establish second growth method 

- Evaluation process window 

� Annealing Process: - Global stress relaxation


Outline 











New crucible quality meets the requirements and has no 

further considerable impact on the crystal quality 

Impurity 

E1 

Impurity 

E2 

Supplier 

1 

� The achieved purity of the crucible reduced the predominance of the crucible 

impurities on the crystal absorption! 



Supplier 

2 

Crucible Ir/Re 

Supplier 

3 

Supplier 

4 

Ir Ir Ir Re Ir 

Target 

>20x >20x >10 3.4x (0.15-0.8)x x 

>6 >6 >4 1.4 (0.05-0.2)x x


Significant Progress in Raw Material Quality achieved 

Impurity Jan. 06 Dez. 06 Feb. 07 Feb. 07 Mrz. 07 Jan. 06 Mrz. 07 Nov. 06 Jan. 07 Sep. 07 

Element 6N 6N+ 6N 6N+ 

E1 42x 16x 8.4x 4x (1.4-7)x 3.2x 1x 1.6x 1x 0.4x x 

E2 6x 6.4x


Progress in Transmission could be achieved, but 

Improvement behind Schedule 

Transmission [%] 

90 

80 

70 

60 

50 

40 

30 

20 

10 



0 

New Champion - after charge transfer 

New Champion - as grown 

Old Champion - after charge transfer 

Old Champion - as grown 

T theor. [%] 

Sample thickness 10mm! 

190 240 290 340 390 440 490 

Wavelength [nm] 

� Absorption reduced from 0.20cm -1 to 0.11cm -1 (about 80% internal 

Transmission), but not meeting target: 0.05cm -1 

� However remarkable absorption @ 256nm was still observed and is 

impacting the absorption at @193nm significantly! 

� Impurity elements causing the absorption are well known


Al 2 O 3 raw material limiting transmission currently, 

contamination sources have to be eliminated 

Crucible 

grade 

� Instead of a higher purity of both crucible and Lu 2 O 3 , the absorption of the 

crystal is not improved adequately 

� Purity level of Al 2 O 3 raw material seems to dominate the absorption loss 

� Based on high resolution chemical analysis (GDMS) a root cause analysis 

indicated further impurity sources (e.g. insulation ceramics in the hot zone 

region of the growth station) 



Raw Material Grown Crystal [ppm] 

Impact 

Absorption 

Lu 2O 3 Al 2O 3 E1 E2 E3 E4 k 0 [cm -1 ] 

2006 mid 6N+ 6N 6x 8x 3x 40x 0.2 

05/07 high 6N+ 6N+ 4x 2x x 10x 0.12 

09/07 high 6N++ 6N+ 4x 1.5x x 19x 0.10


Al 2 O 3 Impurity Analysis: Target Spec for each Process 

step at the Key Supplier will be defined soon 

Al(OH) 3 Al 2 (SO 4 ) 3 (NH 4 )Al(SO 4 ) 2 Al 2 O 3 

Status: Strong fluctuations of Fe 

New impurity target: is defined 

Improvement Potentials: 

1. Using higher purity acid 

2. Replace reaction Container by higher quality 

3. Using higher purity pre-product 

4. 2x recrystalization, 

Realization time: 3 -4 months 



1 2 3 4


Availability of high purity Materials in all process steps 

are crucial for the Reduction of LuAG Absorption 

� Raw materials 

� Despite of a tightening of the specification Lu2O3 in required 

quality and sufficient quantity is available 

� Al2O3 purity improved, but not stable and insufficient; further 

improvement required and addressed at supplier 

� Introduction of additional Al2O3 purification process at Schott 

necessary to push progress 

� Crucible 

� Quality of crucible from alternative manufacturing process fulfils 

requirements 

� Surrounding materials 

� By GDMS analysis identified potential contamination sources in 

the hot zone regions have to be replaced or eliminated 

� Handling 

� Improved cleanliness over the complete process chain to 

keep impurity level of the raw materials 




Outline 











Czochralski Growth Process - 

“Core free” growth is also demonstrated for LuAG crystal now 



 

No defect propagation 

and/or generation at 

interface transition 

 

� “Core free” growth of first “flat” Czochralski grown 

LuAG crystal with dia 80 mm and 160mm length 

YAG 

02/07


Full demonstrator size LuAG crystal grown 

� Current available modified Czochralski growth station allows to grow 

crystal size up to 300mm in length and 80mm in diameter 




Status Alternative Growth Process 

� Two new growth station for alternative growth process with two 

different material combinations (crucible – heater – insulation) 

designed and installed 

� First experiments carried out at station#1 show comparable 

results regarding transmission to the Czochralski grown 

crystals (using same raw material grade). 

� Process development started and supported by simulation 

� In both growth station high purity crucible made from different 

materials were used 

� Decision for growth method end of 2007 




Outline 











SBR as grown quality at Schott (flat interface YAG) is 

close to the target specification 

145 

149 

153 

157 

161 

166 

Evalu. Diameter: 65mm Evalu. Diameter: 40mm 

RMS: 2.89 nm/cm RMS: 0.73 nm/cm 

PV: 22.15 nm/cm PV: 1.83 nm/cm 



170 

174 

178 

182 

x [mm] 

186 

190 

194 

198 

203 

207 

211 

215 

72 

68 

64 

60 

55 

51 

47 

43 

39 

35 

31 

27 

23 

18 

14 

10 

6 

2 

y [mm] 

145 

149 

9,5-10,0 

9,0-9,5 

8,5-9,0 

8,0-8,5 

7,5-8,0 

7,0-7,5 

6,5-7,0 

6,0-6,5 

5,5-6,0 

5,0-5,5 

4,5-5,0 

4,0-4,5 

3,5-4,0 

3,0-3,5 

2,5-3,0 

2,0-2,5 

1,5-2,0 

1,0-1,5 

0,5-1,0 

0,0-0,5 

-0,5-0,0 

153 

157 

[nm/cm] 

161 

166 

170 

Defect 

174 

178 

182 

x [mm] 

186 

190 

194 

198 

203 

207 

211 

215 

72 

68 

64 

60 

55 

51 

47 

43 

39 

35 

31 

27 

23 

18 

14 

10 

6 

2 

y [mm] 

9,5-10,0 

9,0-9,5 

8,5-9,0 

8,0-8,5 

7,5-8,0 

7,0-7,5 

6,5-7,0 

6,0-6,5 

5,5-6,0 

5,0-5,5 

4,5-5,0 

4,0-4,5 

3,5-4,0 

3,0-3,5 

2,5-3,0 

2,0-2,5 

1,5-2,0 

1,0-1,5 

0,5-1,0 

0,0-0,5 

-0,5-0,0 

[nm/cm] 

Polariscopic 

picture


Outline 











Enhanced growth process leads to further significant 

Improvement of Homogeneity – close to the final Spec 

� YAG flat interface dia. 80 mm – as grown (30mm thickness) 

Feb 2007 

Residuals (substr. Z36): PV = 1.16 E-6 dn 

RMS = 0.12 E-6 dn 

� Achieved 02/07: 0.12 ppm RMS @ dia. 80mm 

� Achieved 09/07 0.029 ppm RMS @ dia 45mm 



Sep 2007 

PV = 4.91E-7 dn 

RMS = 2.94E-8 dn


Outline 











Summary and Outlook 

� Drawbacks and Highlights 

� Transmission progress behind schedule - requires strong efforts to 

meet the MS in Q1/08 ( A: 0.01cm-1 ) 

� Absorption reduction requires additional measures especially for 

Al2O3 addressed at supplier 

� Additional Al2O3 purification step at Schott shall secure the 

required improvement 


� Stress birefringence and homogeneity progress is much faster 

than expected and close to the final target 

� All required equipment for yellow phase (growth and annealing) is in 

place and running or in acceptance process 




Revised LuAG Roadmap: 1st Lens Blank in Q4/09 

� Realization of required improvement measures at Al 2O 3 raw material 

supplier delayed LuAG Roadmap by 3 months 



2006 2007 2008 

Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 

Candidate LuAG found 

Feasibility Study 

Pre-Development 

Crystal ∅ 80mm 

Development Production 

Crystal ∅ ~ 250mm 

Transmission / Durability will not to be showstopper 

LLE LuAG Development possible 

First promising Demo Sample 

First suitable LuAG Blank 

Decision for 

growth method 

2009 

First good Demonstrator A=0.01 cm -1 

Optimistic 

Q3 Q4 

Realistic 

A≤0.005 cm -1


Acknowledgements 

LuAG Development at SCHOTT Lithotec - Participation and Funding 

� Canon Inc. 

� Carl Zeiss SMT AG 

� Nikon Corporation 

� SEMATECH

Development Progress of high refractive LuAG for Hyper ... - Sematech

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