Thermal limitation of Silicon EUV Pellicle and possible...

Thermal limitation of Silicon EUV Pellicle and possible improvements for mass production of

EUV Lithography

Sungwon Kwon, Yongseok Jung, Hwanchul Jeon, Jinsu Kim,

Jaehyuck Choi, Byung-Gook Kim, and Chan Uk Jeon

Wednesday 7 October (2015)

Semiconductor R&D Center, Samsung Electronics Co., Ltd

Outline

Motivation – Current status of EUV pellicle development

– Prediction on the thermal stability

– Two types of Silicon

Experimental – Heat-load test on wafers

– Heat-load test on membranes

– New capping material

– Improvement of the thermal stability

Summary

2 International Symposium on Extreme Ultraviolet Lithography, 7 October 2015, Maastricht, NL. e-mail: [email protected]

Current status of EUV pellicle development p-Si pellicle with SiN capping (by ASML)

– One of the most potential candidates for the 1st generation of EUV pellicle

– The compatibility for EUV HVM is still doubtful: heat-load

A suggestion for improvement on the thermal stability

– Si-based pellicle: good alternative within a time-line

Time line 2015 2016 2017 2018

p-Si : ASML & industry

Si-based : SEC

Production: industry adoption

HVM

Pilot: complete EUV pellicle solution

Membrane

Capping

Today

Co-work with industry

Membrane w/ capping

Proto-type w/ infrastructure

3

*Poly-crystal silicon (p-Si)

International Symposium on Extreme Ultraviolet Lithography, 7 October 2015, Maastricht, NL. e-mail: [email protected]

Prediction on the thermal limitation of Si Thermal stress exceeds the yield strength (σSi) of Si thin-film.

– Si can undergo thermal softening effect during EUV exposure.

A main risk for Si pellicles: repeated heat-load

– High temperature and stress: material perspective, ‘creep deformation’

4

Region of Si transition Bulk σSi ~1GPa

App. Opt., Vol.50, No.21 (2011)


Two types of Silicon's Poly-crystal silicon (p-Si) and single-crystal silicon (c-Si)

– p-Si: grain boundaries between grains (surface-to-surface)

– c-Si: well-ordered structure (bond between atoms)

Different mechanisms of deformation against external forces

2~4GPa @fatigue

Poly-crystal Si

Surface-to-surface split at the grain boundaries

Poly-crystal Si

4~10GPa @fatigue

Single-crystal Si

Elongation with maintaining the atomic bonds

Single-crystal Si

Muhlstein et al, Sensors & Actuators, 2001


Heat-load test on wafers Si surface analysis after 532nm LASER expose on wafers

– p-Si: changing - grain growths and more number of grains

– c-Si: no changing - remains with the same orientation

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Phase p-Si c-Si (001)

Category SEM (50k) EBSD (100k) Concept SEM (50k) EBSD (100k) Concept

Ref.

<Tm

>Tm

**EBSD (Electron backscatter diffraction) ***Si thickness 50nm, SiOx thickness 100nm


Short-term heat-load test Heat-load test on Si membranes

– Continuous heating with a 355nm LASER during 30min.

– 50nm Si freestanding membrane with 20nm SiN capping

c-Si is more stable than p-Si under the same heat-load.

– Equal result with the previous on wafer tests

An window for 355nm LASER

Pyrometer or FLIR

Vacuum chamber (10-2T.)

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LASER power and peak temperature


Long-term heat-load test Methodology of quantification test

– Pulse heating with a 355nm LASER and EUV trans. measurement

– Criterion: exposure time to drop by 3% of EUV trans.

c-Si shows 50% longer exposure time than p-Si.

Mechanism of EUV trans. drop during and after heat-load

– High temperature heating induces micro-cracks within a membrane.

8

*DIC (Differential Interference Contrast) images

Scattering

Early heating

Si membrane

Long-time heating

EUV trans. drop Normal

150hrs/3%

+50% Membrane

225hrs/3%


Procedure for new capping material Categories: Optical/Mechanical/Thermal/Chemical

– Test procedure and the results of atomic H treatment

Emissivity on the 50nm films at 100℃

Mat’ls pSi SiN B4C Mo

(Pre) H plasma

(Post) H plasma

ΔThick (nm) 4.7 nm 0.5 nm 0.8 nm 1 nm

ΔThick (%) 12 % 0.9 % 1.5 % 3.8 %


Selection of new capping material Candidates of radiation emissivity enhancer against heat-load

B4C for new capping material

– Improvement of total emissivity: ~10 times higher than p-Si with SiN capping

Category SiN Mo B4C SiO2

Thermal Emissivity

On 50nm film (@100°C) 0.008 0.027 0.145 0.012

Δ (-raw Si) +0.007 -0.308 +0.208 +0.001

TEC (10-6/K) 3.58 4.8-5.1 3.0-5.0 0.56

Chemical H plasma resistance (1/Etch Rate, p-Si=1) 9.4 4.7 5.9 15.7

Mechanical

Modulus (GPa)

50nm cap. on Si wafer 166.3 168.9 170.1 170.2

Δ (-raw Si) 1.4 4 5.2 5.3

Hardness (Gpa)

50nm cap. on Si wafer 17.9 12.7 15.4 14.2

Δ (-raw Si) 5 -0.2 2.5 1.3

SiN 4nm

p-Si 25nm

SiN 4nm

ε=0.01~0.03 εt=0.01

~0.03

εt ~ x10

TSi ~x1.6 ε=0.01~0.03

B4C 4nm

c-Si 40nm

B4C 4nm

εt=0.15

~0.22

ε ~ 0.1 ε ~ 0.001


Improvement of the thermal stability Heat-load test on the c-Si membrane and new capping (B4C/c-Si)

– Exposure time to 3% EUV trans. loss: ~2 times longer than p-Si with SiN capping

– Possibility for HVM within the methodology

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150hrs/3%

+50%

>100%

Membrane

Membrane + New Capping

225hrs/3% >320hrs


Future plan Verification of the methodology in this study

– Comparison with the results from the actual EUV scanners

Compatibility of the new pellicle with other infrastructures

– EUV pellicle frame and etc.

Improvement for fabrication process

– Supplying SOI wafers is another key technology for the new pellicle.

Consideration of the next generation pellicle after Si pellicles

– Alternative solutions for the EUV 500W era


Summary p-Si pellicle might have not enough thermal stability for EUV HVM.

c-Si pellicle is more stable than p-Si pellicle, however it is still not enough for EUV HVM.

New capping material is chosen to improve the radiation emissivity.

B4C/c-Si combination shows better thermal stability than SiN/p-Si, which can be applicable for EUV HVM.


Thank you for your attention


Thermal limitation of Silicon EUV Pellicle and possible...

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