Thin Film Quantitation of Chemistry and Thickness Using EPMA John Donovan Micro Analytical Facility CAMCOR (Characterization of Advanced Materials in Oregon) University of Oregon Eugene, OR (541) epmalab.uoregon.edu

Electron-Solid Interactions

Beam Penetration Beam penetration decreases with Z Beam penetration increases with energy Electron range ~ inelastic processes Electron scattering (aspect) ~ elastic processes

X-ray Generation From Wittke,

Phi-Rho Z or  (  z)

X-ray Emission-Absorption

Accuracy in “Thick” Films?

The Future? Monte-Carlo calculations (using an iterative geometric model) Will require computations roughly 10 6 faster than current processors

What is a Thin Film (for EPMA)? Films greater than 5-10 um can be considered “infinitely thick” Treat it like a “rock” (just kidding) Films less than 500 angstroms are “ultra-thin” Use MVA (and take special precautions: surface contamination, plasma cleaning prior to analysis) Films between angstroms are “normal” Use MVA (multi-voltage analysis) and model geometry John Donovan: always measure oxygen hydrocarbon contamination plasma cleaning prior to analysis John Donovan: always measure oxygen hydrocarbon contamination plasma cleaning prior to analysis

Theory of Thin Film Calculations Figure 4 - Flow charts of the iteration methods used (a) when no element with an unknown concentration is present in several layers; (b) when such an element is present in several layers. From Thiot (a)(b)

How is it done in practice? Multi-Voltage Analysis (MVA) How accurate is it?

NIST Thin Film Standard SRM 2135c

NIST Thin Film Standard SRM 2135c Certified Thickness Measurements Cr ~56 nm Ni ~57 nm John Donovan: cost of SRM $900 RF Magnetron sputtered at COMSAT Lab John Donovan: cost of SRM $900 RF Magnetron sputtered at COMSAT Lab

What if we “treat it like a rock”? Thick (Bulk) Analysis of SRM 2135C Results in weight % Not even close (enough for government work) ! John Donovan: Even calculating the ratio without Si doesn’t work John Donovan: Even calculating the ratio without Si doesn’t work

NIST Thin Film Standard SRM 2135c Thin Film (traverse 1)- homogeneous model (all elements in one layer on Si) 10, 15, keV Results in weight fraction John Donovan: Measured using 4 accelerating voltages using PFW and calculated using StrataGem with a PAP correction model Iterated on “composition” of single layer Oxygen analyzed at.5 wt.%, ~2% atom Total: wt.% No Si signal below keV John Donovan: Measured using 4 accelerating voltages using PFW and calculated using StrataGem with a PAP correction model Iterated on “composition” of single layer Oxygen analyzed at.5 wt.%, ~2% atom Total: wt.% No Si signal below keV

NIST Thin Film Standard SRM 2135c Thin Film (traverse 1)- homogeneous model (all elements in one layer on Si) 15, keV (same as above but without 10 keV data) John Donovan: Total wt.% John Donovan: Total wt.%

Actual Simple Example Johnson Lab (UofO) John Donovan: Unnormalized data is given (not shown here) John Donovan: Unnormalized data is given (not shown here) 2:1 attempted ratio

A Little More Complicated Johnson Lab (UofO) Note 4% atomic oxygen

Insulating Substrate (carbon coated) Keszler Lab (OSU) John Donovan: Carbon layer absorption and stopping power is included John Donovan: Carbon layer absorption and stopping power is included 1:1:1:1 attempted ratio

Complex substrate (Corning 1737 glass) Keszler Lab (OSU) 1:1:1 attempted ratio

Multiple Substrates Keszler Lab (OSU) Nominal Thickness

Duplicate Elements Johnson Lab (UofO) John Donovan: Constrain thickness from x- ray diffraction John Donovan: Constrain thickness from x- ray diffraction Fixed Thickness

Duplicate Elements By Stoichiometry to Obtain Mass Thickness Johnson Lab (UofO)

Conclusions A variety of substrates can be measured with accuracy approaching normal “thick” samples John Donovan: EPMA of thin film samples on a variety of substrates can be measured with an accuracy approaching that of normal “thick” or “bulk” samples Thickness can be calculated along with chemistry, provided that the same element is not in both the film and substrate, or can be confined by difference, stoichiometry or other considerations. Samples with multiple substrates can be analyzed quantitatively. X-ray diffraction data can be used in conjunction with EPMA to confine thickness and allow composition to be calculated for “duplicated” elements in multiple layers or substrates John Donovan: EPMA of thin film samples on a variety of substrates can be measured with an accuracy approaching that of normal “thick” or “bulk” samples Thickness can be calculated along with chemistry, provided that the same element is not in both the film and substrate, or can be confined by difference, stoichiometry or other considerations. Samples with multiple substrates can be analyzed quantitatively. X-ray diffraction data can be used in conjunction with EPMA to confine thickness and allow composition to be calculated for “duplicated” elements in multiple layers or substrates X-ray diffraction data used in conjunction with EPMA allows composition to be calculated for “duplicated” elements. Samples with multiple substrates can be analyzed quantitatively. Thickness can also be calculated, given density and provided that the element is not in the film and substrate, or can be confined by stoichiometry.