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2018 DXC
Micro X-Ray Fluorescence Workshop
Introduction to Micro XRF
Mary Ann Zaitz
IBM–STG
EDXRF Spectrum
Micro X-ray Fluorescence Spectrometry Workshop Agenda
Introduction to EDXRF Micro X-ray Fluorescence and
Applications M. Zaitz IBM-STG
Introduction to Capillary Optics Dr. N. Guo XOS Albany NY
Confocal XRF Spectrometry Prof Tusji Osaka University
Osaka Japan
Micro X-ray Fluorescence Spectrometry
1895 X-rays were discovered by Roentgen
1913 Bragg built first spectrometer
1928 Secondary Fluorescence was used
1950's First commercial XRF Spectrometer
1966 Introduction of the first SiLi detector
1969 First commercial EDXRF spectrometer
1987 First commercial Micro XRF
1992 First commercial TXRF
1990’s Multilayer crystal optics
2000’s Miniaturization of x-ray tubes & detectors leading to handheld systems
Micro X-ray Fluorescence Spectrometry
uXRF spectrometers are energy dispersive type
Basic physics of X-ray Fluorescence apply
Three requirements for XRF analysis
Samples should be smooth
Samples should homogenous
Samples should be infinitely thick
Micro X-ray Fluorescence Spectrometry
Micro X-ray Fluorescence Spectrometry Bulk uXRF Analysis Depth of penetration depends on incident angle and
x-ray tube KV x-rays out of sample depends on the energy of analyte
energy line e = 1/ R²
Sample backside of Si chip
Optical image of area measured Sn- Ka 25.27 keV Sn–La 3.44 keV
green rectangle
background
Micro X-ray Fluorescence Spectrometry
Optical Cu K-a K-b 3D-Xray Image
Micro X-ray Fluorescence Spectrometry
Micro XRF small spot size on a sample
Spot size 10 um – 2mm
Measures small areas or small amounts of
sample
Elemental mapping
Qualitative Analysis
Quantitative Fundamental parameters
including standardless
Micro X-ray Fluorescence Spectrometry
Micro XRF Spectrometers
Energy Dispersive X-ray Fluorescence spectrometer
Solid state ( silicon based) detector with electronics
Absorbed x-ray photon produces free electrons
Bias Voltage extracts free electrons from crystal as a charge
FET (Field Effect Transistor) collects charge, integrates to produce voltage
pulse
Silicon diode with large 'intrinsic' region- PIN
Height of pulse is proportional to energy of original photon
Liquid Nitrogen or Peltier cooling used to reduce thermal noise
Peaks produced in spectrum are approximately Gaussian
Resolution of peaks increases with energy
Micro X-ray Fluorescence Spectrometry SSD Silcon Drift Detector
SSD is a type of photodiode similar to PIN
Operates at lower capacitance than conventional diode of the same area .
Has a unique electrode structure which guides electrons to a very low small capacitance anode
This reduces electronic noise short time constants or shaping times
Micro X-ray Fluorescence Spectrometry EDXRF detector
Micro X-ray Fluorescence Spectrometry
Energy dispersive spectrum has
Background substract not?
peak artifacts Si escape, sum, diffractions peaks,
scatter peaks Compton and Rayleigh
analyte peaks elements in samples
May have all peaks in spectrum
Micro X-ray Fluorescence Spectrometry
background
Micro X-ray Fluorescence Spectrometry
Resolution of SSD
- Separation of peaks depends on quality of
and type crystal material intrinsic noise
Preamplifier short time constants high
electronic noise longer better resolution
Reference specification is full-width –at-half-
maximum or FWHM Mn Ka 150 eV
Micro X-ray Fluorescence Spectrometry
Overlap of Neighboring Peaks
• Enabling Technology for micro-XRF
– Simple apertures for beam “collimation” – wide bandpass
– Mono and Polycapillary lenses – rel. wide bandpass
– Curved Mirrors/Curved Crystals – narrow bandpass
(monochromatic)
Formed and Graded Multilayers – rel. narrow bandpass
• True micro-XRF systems require micro-spot x-ray tubes with
beam size on tube target <100 micron (ideally <10) to obtain
analytical beam sizes on the sample in the range 10-100 um
• Larger target beam sizes best limited to use w/apertures for
x-ray beam sizes in the range ~0.1–5 mm on sample
•
Micro X-ray Fluorescence Spectrometry
Micro X-ray Fluorescence Spectrometry
Capillary Optics
Micro X-ray Fluorescence Spectrometry
Teflon sample background with capillary optic and
collimator
Rh anode
35 kV 249 uA 20
um spot size
W anode
40 KV 249 uA
1000 um spot size
Micro X-ray Fluorescence Spectrometry
Advantages of EDXRF
Non destructive
Multielement spectrum with in same analysis time
combined with a either a standardless or other
fundamental parameter model gives good information
in a relative short period of time
Micro X-ray Fluorescence Spectrometry EDXRF Micro XRF Multi elements qualitative and Semi quantitative
analysis
Micro X-ray Fluorescence Spectrometry
XRD collected by Madhana Sunder
Micro X-ray Fluorescence Spectrometry
0
10
20
30
40
50
60
Al O Si K Ca Ti Fe Cu Mg Na
M4 wt% reference wt %
Micro X-ray Fluorescence Spectrometry
Micro X-ray Stage height focus and spot
position
Need to have control of x-ray spot position on
sample especially for small amounts of sample
like particles, patterns and elemental imaging
Reference sample and procedure from vendor
Monitor routinely
Micro X-ray Fluorescence Spectrometry
Stage height; image focus; x-ray spot control
Manual focus
Auto focus
Define camera resolution for both cameras
Range of auto focus: top/bottom right/left for both
cameras
Micro X-ray Fluorescence Spectrometry
Spot Calibration capillary optic 25 um
10 X low res 100X high res
Micro X-ray Fluorescence Spectrometry
Chart for 10X low res spot calibration
-6
-5
-4
-3
-2
-1
0
0 2 4 6 8 10 12 14
10X Spot Calibration
X Y
uXRF Map Images of X-ray spot position out of
calibration
video image and elemental Ni map shifted
Optical image Video Image video Ni map
Map images post X-ray spot calibration
Video and Ni elemental map match
Otpical image Video image video Ni map
Micro X-ray Fluorescence Spectrometry
uXRF Analysis for Particles from Filter
Micro X-ray Fluorescence Spectrometry
Micro X-ray Fluorescence Spectrometry
Small Particle Analysis with Elemental Mapping
21
1
Micro X-ray Fluorescence Spectrometry
Elemental Mapping Conditions Area to be mapped
Number of measuring points
Mapping Data acquisition
Micro X-ray Elemental Mapping of Semiconductor Packaging Module
Backside corrosion on pads Ni/ Pd/ Au Cl contamination
Backside corroded pad Ni Pd Au Cl
Pad 334
Micro X-ray Fluorescence Spectrometry
Map spectrum with Regions of Interest (ROI) for mapping
Micro X-ray Fluorescence Spectrometry Spectra from Pads 3 & 4 small circle area of measurement
Pad 3
Micro X-ray Fluorescence Spectrometry
uXRF Corrosion Study Elemental Mapping
uXRF Corrosion Study Elemental Mapping uXRF detected Ag in corroded area. SEM-EDS reported AgS as corrosion product
UXRF mapping shows BaS as flame retardant across whole area
S Ba
Micro X-ray Fluorescence Spectrometry uXRF Corrosion Study Elemental Mapping 2nd Analysis
uXRF elemental map of another area on sample detected possible Ag
migration between Ag pads. XRD analysis confirmed elemental Ag . So
mechanism was electro migration of Ag not corrosion from S as
determined by SEM-EDS
Micro X-ray Fluorescence Spectrometry
Elemental Maps for Cu-La Cu-Kb
Cu
Cu
Cu
Micro X-ray Fluorescence Spectrometry
Tenets of bulk X-ray Florescence Analysis
Samples should be infinitely thick
However there is a range where intensity is
proportional to thickness.
Thin film Analysis by XRF used in may
industries
Micro X-ray Fluorescence Spectrometry
XRF Thickness for Multilayer Film Stacks for Semiconductor Chip
Carriers mico XRF analysis of choice
Metallurgical bond pad interface on the IC
Metallurgical bond pad interface on the package
Electrical interconnection between these two interfaces
Film layers have a purpose thickness must be controlled to spec limits
Au layer provides surface to bond to either chip or pins.
Ni Layer barrier layer to prevent Cu diffusion
Cu layers electrical wiring between chip and package
Micro X-ray Fluorescence Thin Film Analysis Wide dynamic thickness range: 2 Å (0.0002 um) to
60+ um
Non Linear relationship between XRF Intensity and thickness of multi layers due to absorption and enhancements effects
Fundamental Parameter model defines the layer thicknesses
Sample type: pure elemental and type standards
Two separate spectra
Blue with low Pd, high Au
Yellow with high Pd, low Au
Is Pd thickness the same?
Au
Ni
Pd
XRF Thickness for Multilayer Film Stacks for Semiconductor Chip Carriers
Capability to do multi point measurements on one pad
The small red circle shown in the right image is approximately ~ 25 um Low Res Optical Image Hi Res Optical image of individual pad
Point analysis on adjacent pads for Au/Pd/Ni thickness Yellow marker shows where measurements were taken
0
200
400
600
800
1000
1200
1 2 3 4
Au Pd Thickness in Angstrom
Au ang Pd ang
Micro X-ray Fluorescence Spectrometry
Bruker uXRF Webinar Example
Micro X-ray Fluorescence Spectrometry uXRF Mapping of Diffraction Peaks from Gold Sample
Au
Micro X-ray Fluorescence Spectrometry
Comments
uXRF Analayis is a versatile technique the
provides fast multi elemental analysis for a
wide range of materials
Elemental mapping
Micro X-ray Fluorescence Spectrometry
Comments
Micro XRF Analysis provides fast non destructive
feedback that can identify potential defects or
problems so corrective actions can be applied
quickly be it changes in the process or requiring more
advanced follow on analysis.
Micro XRF analyzes wide range of samples and
sample sizes making it an important part of a
characterization laboratory.
Micro X-ray Fluorescence Spectrometry