High transmission EUVL pellicle development - Sematech

High transmission EUVL 

pellicle development 

Yashesh A. Shroff, Pei-Yang Yan, 

Farhad Salamassi*, Eric Gullikson* 

2008 EUVL Symposium, Lake Tahoe 

Intel Corporation 

*Lawrence Berkeley Lab

Overview 

• Motivation & 

specs 

• Thermal modeling 

• High transmission prototype development 

– Illumination non-uniformity 

• Full-scale pellicle HVM mechanical test 

• DUV/AIMS study 

• Summary & 

future work 

"EUVL Pellicle Development", Yashesh Shroff, Pei-Yang Yan, F. Salamassi, Eric Gullickson 

EUVL Symposium 2008, Lake Tahoe 2

Concept 

Square cell mesh 

Hexagonal cell mesh 

•The Concept 

– Thin film mounted on a wire-mesh 

– Mesh located “far” from reticle plane to defocus defects 

– Transmission requires a high percentage open area 

– Illumination uniformity requires partial coherence 


Stand-off height = 6 mm 

Mesh pitch 

• Mesh apodizes 

the illuminator 

exit pupil and 

PO entrance 

pupil. 

• Mesh film 

absorbs with 

both passes. 


Motivation & Goal 

• The The aim aim of of this this research is is to to 

create create an an EUV EUV pellicle as as a 

backup to to pellicle-less operation 

– Operating Operating within within litho litho tool tool 

without without added added particles particles 

• Mesh Mesh based based pellicle’s target target 

performance: 

– EUV EUV transmission: transmission: double-pass 

double-pass 

loss loss < 30% 30% 

– Robustness: Robustness: HVM HVM capable capable 

operation operation 

– Imaging: Imaging: minimal minimal contrast contrast and and 

uniformity uniformity loss loss 


EUV Pellicle Specifications 

Frame 

length/width 

Height 5 mm 

149/122mm 

Transmission >70% 

Film thickness 50nm ± 2nm 

Illumination 

non-uniformity 

±0.6% 

Film stress Tensile ( 2000 

Stiffness 193nm frame 


Overview 


specs 






• Summary & 

future work 



Thermal model 

Pellicle 

(25% EUV absorbed) 

Entrance 

Plane of PO 

Reticle: 5-20W* 

• Instantaneous power at slit can result in high thermal load. 

• Transient model is developed to calculate peak rise in pellicle 

temperature 

* OoB power & IU transmission of EUV + OoB spectrum dependent 


Illuminator 

exit plane 

IF: 

180W 


Cooling time 

Membrane Parameters: 

• Pellicle thickness, d = 50nm 

• Exposure slit area, A = 10cm 2 

• Exposure slit time, t = 10ms 

Constants 

• Si specific heat, c = 0.7J/g-k 

• Emissivity, ε 

= 0.5 

• Radiative loss, σ = 5.67e-12 

• Si density, ρ 

= 2.33g/cm3 

ΔT=0 cooling time (ms) 

Pellicle temp stabilization v/s input radiation 

40 

800 

0 

0 5 10 15 20 25 

Reticle incident power (W) 

0 

Q= c⋅m⋅ΔT 

∂Q 

= A⋅ε 

⋅σ⋅ 

dt 

4 4 ( T − ) 

env TSi 


35 

30 

25 

20 

15 

10 

5 

∂T ⎛ A⋅ε 

⋅σ⎞ 

= ⎜− 

⎟T 

dt ⎝ c⋅m 

⎠ 

Assumes 25% reticle incident power absorption by pellicle 

EUVL Symposium 2008, Lake Tahoe 7 

Si 

4 

700 

600 

500 

400 

300 

200 

100 

ΔT initial temp rise (K)

Overview 


specs 






• Summary & 

future work 



Requirements for reaching pellicle 

transmission limits 

•GOAL: total 2-pass transmission: 70% 

– Mesh transmission: 97% 

– Membrane transmission: 93% 

•Improving the mesh 

– Reduce linewidth: 1-3um 

– Increase pitch: 70-100um 

•Improving the membrane 

– Reliable membrane thickness of 50nm 

Lithographically define the line 

– Commercially available mesh min LW only ~10um 

– Improve robustness by increasing aspect ratio of mesh wires 

– Use Si: better thermal stability with membrane 



Pellicle Process at LBNL 

1. Spin release layer on Si wafer. 

2. Deposit Si + Ru capping layer using 

magnetron sputtering. 

3. Spin on photoresist. 

4. Pattern mesh using contact 

lithography. 

5. Electroplate Ni mesh. 

6. Remove resist. 

7. Attach to frame and release from 

substrate. 


Pellicle 50 nm Si with 100 

micron pitch and 3 micron 

linewidth mesh. Average 

transmission at 13.5 nm is 

75.7% 


Transmission results 

Membrane: 50nm Si + 2nm Ru 

cap with transmission = 84% @ 

13.5 nm 

100 μm 

Linewidth Pitch Tmesh 

expected 

Tmesh 

measured 

Tpellicle 

measured 


Double- 

pass txm 

1 μm 35 μm 94% 94.5% 79.5% 63.2% 

1 μm 100 μm 98% 97.5% 81.9% 67.1% 

No mesh 

35 μm 

1 

0.8 

0.6 

0.4 

0.2 

0 

-4 

-2 

mm 

0 

Measured at LBNL synchtroton (λ=EUV) 

EUVL Symposium 2008, Lake Tahoe 11 

2 

100 μm 

4 -5 

35 μm 

0 

mm 

5 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0

Impact on reticle plane non-uniformity 

•Non-uniformity scales with mesh linewidth. Modeled results: 

Mesh1 Mesh2 Mesh3 

Linewidth (LW) 10u 3u 1u 

Pitch 250u 100u 35u 

Non- 

uniformity 

5mm 1.4% 0.25% 0.08% 

2mm 7.4% 0.50 0.14% 

Mesh only txm 94% 94% 98% 

•Decreasing stand-off distance dramatically impacts uniformity 

due to the severely increased apodization of the pupil by the 

mesh 

•We recommend minimum stand-off distance of 5mm, 

consistent with current DUV technologies. 


Pitch 


Pellicle transmission improvement 

1 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

80nm Si membrane on 10/250um mesh 

2007 

2008 

0.2 

11 11.5 12 12.5 13 13.5 14 14.5 15 

wavelength (nm) 


Silicon deposition process 

improvement: 

- 6% increase in 1-pass 

transmission 

- Measurement at LBNL 

synchrotron 

- Mesh linewidth/pitch: 

10μm / 250μm 


Overview 


specs 






• Summary & 

future work 



Full-size pellicle development 

• Lowest Si membrane thickness 

achieved: 70nm 

– Corresponds to 85% EUV txm 

• Mesh properties: 

– Linewidth: 10um 

– Pitch: 250um 

– Transmission: 91% 



Full-size pellicle scan test 

Mechanical stability test to 

verify robustness. 

Repeated 6g acceleration, 2m/s scan 

velocity expected in 180WPH HVM 

system. 

• Vacuum environment chamber 

• Track length 75mm 

• 50min test, ramping from 1G6G 

– Continuous scan for 10’ at 6G, 

limited by motor reliability 

concerns 

• Full-size pellicles tested: 

– 70nm membrane 

– 100nm membrane 



position (mm) 

80 

60 

40 

20 

0 

-20 

-40 

-60 

Scan profile 

Position v/s time of pellicle scan 

forward scan 

reverse scan 

-80 

0 0.05 0.1 0.15 

time (sec) 

0.2 0.25 0.3 


scan velocity (m/s) 

4 

3 

2 

1 

0 

-1 

-2 

Velocity v/s time of pellicle scan 

forward scan 

reverse scan 

-3 

0 0.05 0.1 0.15 

time (sec) 

0.2 0.25 0.3 


Scan test: 6G, continuous (100nm membrane on 

10um linewidth / 250μm pitch mesh) 



Scan test: 6G with 500ms pause every cycle 

• Two pellicles are tested: 70nm and 100nm membranes with 

10/250um (LW/pitch) supporting mesh. 

• Vacuum environmental chamber was kept at 70mT pressure 

• Reticle plate was not used (load concerns) 


Accelerometer 


Overview 


specs 



• Illumination non-uniformity 



• Summary & 

future work 



DUV AIMS test 

• 150nm 1:1 features exposed with 248nm wavelength 

AIMS tool. 

• Mesh placed 2mm above the reticle plane 

• CD variation is within measurement error of tool 

– Impact of pellicle on CD needs to be ascertained w/ a 

higher resolution tool. 

• Illumination conditions: σ 

CD (nm) 

140 

120 

100 

80 

60 

40 

20 

0 

Average linewidth 

~Pellicle wire 

location 

= 0.6; NA = 0.68 

0 20 40 60 80 100 120 140 

Field position (um) 


Field position 


Summary 

• Full-size pellicles fabricated with membrane thickness of 

70%. Expected transmission is 61% double pass 

• New process developed to achieve near-best transmission of 

67% on small-size samples with tensile membrane stress. 

• Thermal model completed & shows that CTE compatible mesh 

+ Si membrane is necessary to avoid differential thermal 

expansion related issues. 

• Scan test with in-house scanner shows pellicle robustness at 

repeated 6G acceleration with peak velocities of 2m/s. 

Future work 

• Vibration test to satisfy zero-particle adder criteria 

• Full-scale pellicle for 70% double-pass txm 



Acknowledgements 

•Bob Gunion and Paul Denham (LBNL) for writing very 

challenging device drivers for the scan test motor and flexible 

UI and device setup 

•Armando Cobarrubia (Intel), for SEM support 

•Guojing Zhang and Kangmin Hsia (Intel), for IMO support 

•Luxel Corp (OR) for fabricating full-size mesh 

•Committed support from senior management at Intel for 

funding and providing resources for the project.

High transmission EUVL pellicle development - Sematech

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