Eliminating organic contamination on oxidized Si

surfaces using atomic oxygen Liz Strein, David Allred, R. Steven

Turley, and the EUV/thin films group

Outline

• Motivation

• Techniques/Methods

• Results

J. Tveekrem, “Contamination effects on EUV optics,” NASA Technical Report TP-1999-209264, 1999. Used with permission.

0

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1

0 5 10 15 20 25 30 35 40

0.1nm organic1nm organic

angle (from grazing)

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1

0 5 10 15 20 25 30 35 40

0.1nm organic

angle (from grazing)

Calculated reflectance for 41.3nm (30 eV) light on silicon

SiO2

Si

organic

incident light reflected light

E. Gullikson, X-Ray Interactions with Matter, http://henke.lbl.gov/optical_constants Accessed 27 Feb 2008. (calculated with the bilayer program)

refle

cta

nce

Instrumentation

X-ray Photoelectron Spectrometer (XPS)

Ellipsometer

Excimer UV lamp (cleans samples)

Evactron Plasma Cleaner(cleans XPS antechamber)

Excimer Lamp

• Cleaning technique

• The excimer lamp creates ozone and oxygen radicals by exposing oxygen to 172nm photons.

•These products oxidize the adventitious carbon on the samples thus freeing the sample of its organic contamination

Adapted from http://ecl.web.psi.ch/NanoKat/Ni_Al2O3_ethanol_1.jpg

O

SiO2

organic

Ellipsometry

• Looks at how polarized light changes when it reflects from a surface.

• Used to determine the relative change in thickness for the “apparent oxide” on a sample

Adapted from http://users.aber.ac.uk/tej/ellipso5.gif

SiO2

Si Substrate

organic“apparent oxide” layer

X-ray Photoelectron Spectroscopy(XPS)

• Detects the speed of electrons ripped off from a sample’s surface by x rays.

• Used to determine the chemical composition of a sample.

http://www.almaden.ibm.com/st/scientific_services/materials_analysis/xps/XPS.gif

Need for Evactron: Deposition rate on the samples exposed to the XPS antechamber

Evactron C DeContaminator

• Plasma clean the XPS chamber

http://www.evactron.com/63193/image2.gif

Before excimer lamp

After excimer lamp

Si 2p

Si 2p

Correlation between characterization methods

how the “apparent oxide” thickness decreases with exposure time

Conclusions

• 5 min under lamp cleans off most of the last couple of angstroms of AC

• Correlation between characterization techniques (there are big problems when the characterization instruments change the nature of a sample)

• Cleanliness is important

Acknowledgements

• Amy Grigg• Mike Keenlyside at Surface Physics• Resonance LTD for the excimer lamp• Gabe Morgan and Ron Vane for their loan of the

Evactron C De-Contamination System• Dr. Matt Linford• Lei Pei• The department of Physical and Mathematical

Sciences for funding

1.7

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2.1

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2.5

0 5 10 15 20

never exposed to chamberin chamber for < 1.5 min

appa

ren

t oxi

de t

hick

ness

(nm

)

days stored in air

Storage dataStorage time: 10 min to 19 days

Most samples began with an apparent oxide layer ≤ 1.83nm