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