Choosing the right EDS detector - Thermo Fisher Scientific · Choosing the right EDS detector Keith Thompson April 28 2014 . 2 Proprietary & Confidential ... • The technology for

Choosing the right

EDS detector Keith Thompson

April 28 2014

2 Proprietary & Confidential

EDS and SEM go hand-in-hand

Electron Microscopy provides the imaging

EDS provides the “chemistry”


EDS provides a look at material composition

Point & Shoot, Line Scan and Mapping


Electron Microscopes

• Material Science

• Electronics

• Petrochemical

• Mining

• Metals

• Semiconductor

• Life Science

Many options for

electron microscopes

Many options for EDS


EDS detector: many features to consider

Many active areas Various tube size… even oval tubes

Ever Faster Acquisitions



• There are 3 main drivers in specifying an EDS

detector

• Energy resolution @ Mn k-alpha

• Sensitive to: “Xx”

• Solid angle

• How relevant are these specifications in determining

the performance of an EDS detector?

• How to choose the right EDS detector

Energy Resolution

Which detector is right for my application?


Energy resolution

Measured:

Width of the Mn k-alpha peak @

half the peak height

- Why does this spread occur?

- What is good enough?

- Is this a valuable metric?


Energy resolution

System noise drives uncertainty

in the measured energy of the

incident X-ray.

This uncertainty creates a

natural variation in the energy

histogram


System noise drives energy resolution

• In a SiLi-based EDS, the capacitance is directly related to the active

area of the device.

• Capacitance starts as BIG

• As active area increases, capacitance increases

Needs LN


SDD crystals change the equation on resolution

Get much smaller

And have potential to get smaller still.



Longer integration times result in superior energy resolution

Shorter integration times are required for high count rates


What does high count rate resolution look like?

123 eV @ 6.4 msec

183 eV @ 0.2 msec

EDS detectors are routinely specified @ 2,000 – 3,000 cps


Take-away points

• Energy resolution

• Speed matters: faster acquisition = worse resolution

• Detectors are specified at slow rates



Often-times 185 eV is just fine

2000 eV

peak-to-peak

2000 eV

peak-to-peak


Point & Shoot analysis of a geological sample

Qualitative Identification

Often-times higher energy

resolution is just fine



Mapping

Fast mapping higher resolution

is just fine on this sample.



Sometimes no resolution

is ever good enough.


Take-away points




• Sometimes poor resolution is just fine

• Other times even really good resolution will never be good enough


What does high count rate look like?

128 eV @ 6.4 msec

160 eV @ 0.4 msec

How about down here?

(input cps)

(standard EDS)


What does high count rate look like?

Difficult to even define resolution

@ 1,000,000 cps

(input cps)

(standard EDS)


Can we improve on this?

It is possible to design an SDD with excellent low energy performance

76 eV

78 eV

114 eV

66 eV

67 eV

90 eV

55 eV

61 eV

114 eV

(input cps)

(Extreme EDS)


Can we improve on this?

It is possible to design an SDD with excellent low energy performance

57 eV

67 eV

50 eV

62 eV

50 eV

62 eV

(input cps)

(Extreme EDS)


A look at the numbers

Group 1 = Extreme EDS

Group 2 = standard EDS Study involved over 300 detectors



A look at the numbers

All “129 eV” detectors ~ 10 eV difference in light element

Group 1 = Standard EDS

Group 2 = Extreme EDS


How much of an impact?

Extreme detector, 10 kcps

Standard detector, 10 kcps

Standard detector, 1 Mcps


Take-away points





• Other times the resolution will never be good enough

• Low energy part of the spectrum is affected more dramatically than the

moderate to higher part of the spectrum

• Some detectors hold it together

• Other detectors falls apart

• Specifications at Mn-ka (5.9 keV) are not reflective of low energy

performance.

Light element sensitivity

“Sensitive to:” Which detector is right for my application?


Light element sensitivity: “Sensitive to”

•EDS detectors often carry a light element

sensitivity specification termed as:

• “Sensitive to”

•Why this specification?

•What does it really indicate?



• The detector system absorbs x-rays

• Window between SEM chamber and crystal

• Thin metal layer on detector crystal to avoid cathodoluminescence

• Some detectors use N2 backfill

window

detectorcrystal

pre-amp

cold finger

insulator

X-raysliquid Nitrogen


X-ray absorption in windows

Na

O B


X-ray absorption in windows

O

B Li Be

Li detection is not possible with a window and has challenges well beyond

window technology


Light element sensitivity: “Sensitive to Be”

Extreme EDS


Light element sensitivity: “Sensitive to BN”

Extreme EDS


Light element sensitivity: “Sensitive to B”

Compact EDS

Pure B metal


Compact EDS detector



8x sensitivity Extreme EDS

Compact EDS



0

1000

2000

3000

4000

5000

6000

0

200

400

600

800

1000

1200

1400

1600

1800

2000

80 180 280 380 480

EDS

cou

nts

WD

S co

un

ts

Energy eV)

B - WDS

B - EDS

Trace B (2% B in Fe-Cr) is harder

B

C

0

2000

4000

6000

8000

10000

0

20000

40000

60000

80000

100000

120000

80 180 280 380 480

EDS

cou

nts

WD

S co

un

ts

Energy eV)

B - WDS

B - EDS

B metal is easy for EDS/WDS

B


Take-away points






• Low energy part of the spectrum is affected more dramatically than the

moderate to higher part of the spectrum



• Specifications at Mn-ka (5.9 keV) are not reflective of low energy

performance.

• Sensitivity

• Detection to B isn’t always detection to B


•Is light element sensitivity just

about my detector and window

technology?


Light element sensitivity: Variable pressure mode





C Cu-L

Pure B metal



No VP

50 Pa

200 Pa

No VP

Extreme detector

Compact EDS detector


Take-away points






• Low energy part of the spectrum is affected more dramatically than the moderate to higher part of the spectrum



• Specifications at Mn-ka (5.9 keV) are not reflective of low energy performance.

• Sensitivity


• Variable pressure mode has a major impact on light element detection

• As do many, many other factors.

• The only good light element Quant requires full standards


Light Element Detection – Li mapping

Windowless Extreme EDS detector


Take-away points






• Low energy part of the spectrum is affected more dramatically than the moderate to higher

part of the spectrum




• Sensitivity





• The technology for light element detection exists today. You need to specifically plan for it.



•Determine what you need

• Is it important to your application? • Light element detection? Or mapping?

• Transition metals?

• Do you work in VP mode?

• How critical is quant?

•Be specific & avoid ambiguity.

What detector is best for my

application?


Transition metal: Qualitative analysis

10 mm2 active area

133 eV @ Mn k-a

Sensitive to B



Qualitative Identification



Mapping


High resolution Spectral Imaging @ low kV

3 kV, 0.5 nA

100 mm2 active area

129 eV @ Mn k-a

Sensitive to Be


Complex structures in a TEM

Quantitative element map of an advanced

semiconductor gate structure

100 mm2 active area

129 eV @ Mn k-a

Sensitive to Be


Geological mapping at 5 kV

5 kV, 2 nA

100 mm2 active area

129 eV @ Mn k-a

Sensitive to Be


Example – Multiphase sample with peak overlaps

• Detector: UltraDry 10mm2 SDD

• Resolution: 129eV MnKa FWHM

• Accelerating Voltage: 7kV

• Magnification: 500x

• Map resolution: 256x192

• Storage Rate: 107,000cps

• Acquisition Time: 5 minutes

10 mm2 detector @ high beam current (> 25 nA)

60 mm2 detector @ low beam current (< 2 nA)


Example – Multiphase Sample – Raw Count Maps

Si_K

Ta_M

W_M

Ni_L

Cu_L


Multiphase Sample – Net Count Maps

Si_K

Ta_M

W_M

Si, Ta, W: No detector can separate these peaks

Peak deconvolution algorithms cleanly separate the peaks


Example – Mo, S, Ba Multiphase Sample

• Detector: UltraDry 10mm2 SDD

• Resolution: 129eV MnKa FWHM

• Accelerating Voltage: 7kV

• Magnification: 500x

• Map resolution: 256x192

• Acquisition Time: 3 minutes

10 mm2 detector @ high beam current (> 25 nA)

60 mm2 detector @ low beam current (< 2 nA)


Example – Mo, S, Ba – Raw Count Element Maps


Example – Mo, S, Ba – Net Count Maps


Example – Mo, S, Ba – Phase Maps

Distinguishing the three main phases is not

possible without robust phase identification

involving Principle Component Analysis 2100 2150 2200 2250 2300 2350 2400 2450 2500

eV

MoLa SKa


Take-away points






• Low energy part of the spectrum is affected more dramatically than the moderate to higher part of the spectrum




• Sensitivity





• The technology for light element detection exists today. You need to specifically plan for it.

• Post-processing algorithms

• Peak deconvolution, background subtraction and matrix correction algorithms are critical to high quality mapping

• Phase mapping is even more powerful than these element mapping algorithms


Summary

• EDS detectors have made many advances over the last

several years

• Know your application

• Discern what’s really important.


• Light element / Low energy

• Algorithms and post-processing techniques

• Specify carefully.

Documents

Choosing the right EDS detector - Thermo Fisher Scientific · Choosing the right EDS detector Keith Thompson April 28 2014 . 2 Proprietary & Confidential ... • The technology for