Project Overview

Analysis of SIMS technology, science and application. Start up of a desktop SIMS tool for CBEE professor Dr. Gregory Herman. Tool will help SHARP Labs with thin film research. Tool will also be used by future grad students of Dr. Herman. Secondary Ion Mass Spectrometry Overview

•SIMS is based on secondary ion emission and the mass analysis of

charged particles from solid surfaces.

•Sample is bombarded with a beam of charged particles with

energies in the 1-25 keV range. These incoming particles are called primary ions. Common ion sources include gallium and bismuth.

•These primary ions bombard the

surface and break bonds up to 3 nm deep. This process is called sputtering.

•These charged species are called

secondary ions. Typically this ejected material has an energy of ~20 keV.

•Time of flight (TOF) relies on

analyzing the time it takes for charged species to reach a detector.

•Quadrupole mass

spectroscopy (QMS) which relies on magnetic fields to filter particles of different masses.

Secondary Ion Mass Spectrometer Start-Up Quantification Techniques Under Dynamic SIMS 1

• General Relationship

Department of Chemical, Biological, and Environmental Engineering Tyler Roberts and Jared Sherr Faculty Sponsor: Dr. Gregory Herman

 1

Y N tot p l



i l f q N

( 

l q

( 

l

) 

q

) ( 

l

) c(A) = fractional concentration of element A (#A/total#)

Y tot N p

= total sputter yield (total species sputtered/primary ion) = primary ion rate (ions/second)

l i

= number of A atoms in molecule Ω

l N q (M l

) = detection rate of molecule Ω

l

with charge q (counts/second)

f q (M l

) = instrumental transmission factor

α q (M l

) = probability of charge state q for molecule Ω

l

• Calibration Curve Method

MiniSIMS: The Chemical Microscope

The Millbrook MiniSIMS tool is a compact solution for surface, or near surface characterization of solids.

Turbomolecular pump Quadrupole mass spec

• • • Advantages Ease of use High throughput Low cost 2

Loading chamber

• • Disadvantages 2-300 amu mass range Lower mass resolution

Gallium primary ion source

I

q

I

q

 • Relative Sensitivity Factors 

r

1

For a matrix element R with constant concentration, the ratio of detected currents of element A to element R in charge state q is a function of the fractional concentration of A at or near the surface. A calibration curve must be made for different matrix type (i.e., for different chemistries). For low concentration of A, a calibration curve is approximately a straight line. The values of the relative sensitivity factors S element A for different reference elements R in a particular matrix type can be found by standard testing.

r

of

Future Projects

Tool will analyze silicon carbide films from SHARP Labs. These films have applications in multijunction photovoltaics.

The MiniSIMS may be used to assess surface contamination or differences in treatments 3 . It has been used to evaluate laser cleaning of museum objects 4 , study the structural properties of CuInSe 2 -based absorber layers for photovoltaics 5 , and monitor the effects of pre-treatment for adhesives 2 .

Determine the composition and presence of hydrogen, and the number of bonded carbon atoms in these thin films.

Acknowledgements

• • • Static SIMS mode • Used for acquiring a mass spectrum • Low primary ion dose – least • destructive Answers the question, “what is present at the surface?” Imaging SIMS mode • Used for acquiring a “chemical map” • Only one atomic mass unit considered at a • time Answers the question, “where on the surface are these chemical species located?” Dynamic SIMS mode • Used to acquire a depth profile • High primary ion dose – sputtering down into • sample, very destructive Answers the question, “how do these species compare to each other as a function of depth?” • Dr. Philip Harding • Millbrook • Dr. Greg Herman • Hewlett – Packard • University of Oregon

References

[1] Benninghoven, A, F.G. Rudenauer, and H.W. Werner. Secondary Ion Mass Spectrometry: Basic Concepts, instrumental Aspects, Applications and Trends. John Wiley & Sons: New York. 1987. [2] Eccels, A.J. and T.A. Steele. Routine problem solving with the SIMS chemical microscope. International Journal of Adhesion & Adhesives, 21 (2001), pages 281-286. [3] Eccles, A.J., T.A. Steele, and A.W. Robinson. Broadening the horizons of SIMS: the low cost Chemical Microscope. Applied Surface Science, 144 (1999), pages 106-112. [4] McPhail, D.S., et.al. Rapid characterization of surface modifications and treatments using a benchtop SIMS instrument. Applied Surface Science, 231 (2004), pages 967 971. [5] Dale, P.J., et.al. Characterization of CuInSe 2 material and devices. Journal of Physics D: Applied Physics, 41 (2008).