Transcript MKelley_FNAL_5.23.07

Overview of Characterization Methodology
Michael J. Kelley
College of William & Mary and Jefferson Lab
[email protected]
A View of Characterization Science
The materials equivalent of analytical chemistry
Product,
Microstructure
Processing
Starting
Materials
Characterization
Understanding,
Improvement
Service
Environment
Performance
End-use
What are We Looking At ?
BCP
EP
Crystallites:
size, orientation, contaminants
Topography:
average roughness, variability,
sharpest features
Chemistry:
Nb speciation, contaminants
Near-surface:
Oxide layers, adjacent metal
Effect of process changes
Variability within cavity
Can we use coupons ?
Effect of post-treatment ?
Statistics and sampling ?
Surface Morphology
Polycrystal Nb
Single crystal Nb
200 nm/div
BCP
200 nm/div
EP
Optical microscopy images
AFM images for BCP treated SC & EP treated PC
EP treated polycrystal Nb surfaces are significantly smoother than that of BCP treated,
The ridges at the grain boundaries are smaller than BCP treated surfaces;
BCP treated single crystal Nb surface is comparable to EP treated polycrystal Nb
Typical performance: vertical – few nm to several tenths mm; horizontal – 30 nm
Structure: Diffraction in the SEM
EBSD – Electron Backscatter Diffraction
Crystalline materials diffract the primary
electrons
Backscatter is slightly reduced along
major planes - pattern of dark lines
Automated systems are now available to
index channeling patterns
Useful for orientation images of flat
surfaces
Samples about 50 nm depth.
Pole
Figures
EBSD by Matt Nowell at
EDAX/TSL
1.5 x 1.5 mm field after BCP. Stereographic triangle indicates grain orientation
Black dots appear to be pits. Are they associated with grain boundaries ?
EBSD is available as a standard SEM accessory – nothing but money !
Hydrocarbons & impurities
Nb hydroxides
Dielectric Nb2O5
NbOx (0.2 < x < 2),metallic
NbOx precipitates (0.02 < x < 0.2)
Nb (Penetration depth : ~ 40 nm)
Surface
concept
Is it layers ?
What are species ?
Effect of topography
Nb2O5
Effect of treatment
X-ray Photoelectron
Spectroscopy: XPS
NbOx
Nb
Energy conservation:
hn = K.E. + B.E.
Nb species can be resolved
Lateral resolution: < 10 mm
Data acquisition and analysis
can be automated
Inelastic Mean Free Path, nm
Varying photon energy to
vary sampling depth in XPS
hn = K.E. + B.E.
B.E. of Nb 3d 5/2 = 202.2 eV
hn depth
300 1.76
550 3.31
930 5.34
1254 7.01
[Photoelectron Kinetic]
Mg Al
X1B
M.P.Seah, W.A.Dench; Surf.Int.Analy.1(1979) 1
TEM Operating Modes
Bright field - pass central beam only. scatterers
are dark
Dark field - select and pass diffracted beam
only. Only the Diffracting species is bright
High resolution - pass two beams under phasecontrast (interference) conditions
STEM - convergent (spot) beam - operate like
SEM
TEM Contrast Mechanisms-3
Phase contrast Electrons travelling different paths
experience different phase shifts
A plane wave entering becomes phase
modulated with structure information
Characteristic distances are ~ 10 nm
Combining beams creates interference
image.
Phase Contrast Development
Note: beam direction is a zone axis
Au-Pd
Would show fringes
if crystalline
Oxide
~7.0 nm
Nb
Dale Batchelor, North Carolina State University
Secondary Ion Mass Spectroscopy (SIMS)
Concepts
• Bombard with (0.5) 5 keV - 25 keV ions
• Ions penetrate the surface, displacing
atoms which in turn displace others:
Collision Cascade
• A few collision trains reach the surface
• “Entities” are ejected with near-thermal
energy
[0.5 mm vs 50 nm lateral resolution]
Ion Collision Cascade Concepts
Effect of topography, recoil implantation
D-SIMS
shallow
implant
profile
Quantification
requires standards
Sputter Profile
Issues
The ion beam unavoidably
drives some of struck atoms
deeper into the solid than
their original position (knock
-on mixing), distorting the
depth profile. A sputter
profile from the backside possible only with special
samples - reveals the size of
the effect. Spectra of B in Si.
K.L.Yeo et al.; J.Vac.Sci.Technol.
B21 (2003) 193
Summary
SEM – EBSD is effective for grain size and orientation.
AFM – Effective for topography, but scatter and rare
events are issues. Need lots of data.
XPS – Effective for Nb speciation and oxide thickness
estimation. Improved lateral resolution helps
HRTEM – Cross-sections are promising, but extensive
study is needed. $$ !!
SIMS – Sensitive, but depth profiling issues about
topography and mixing. Need standards.
“Our Best Facilities”
XPS: PHI/Ulvac “Quanterra”, NSLS X1B
SEM: Hitachi 4700 with EDS, EBSD
FIB: FEI “Helios” dual beam with SEM and EBSD
TEM: FEI “Titan”; JEOL 2100-F; Hitachi HF-2000
Dynamic SIMS: Cameca 6f, 7f
Static SIMS: PHI “Trift-II”
AES: PHI 660 SAM
“Shared courses”