Hiden Analytical Instruments for exact science HIDEN SIMS

Hiden Analytical

Instruments for exact sciencewww.HidenAnalytical.com

HIDEN SIMS

Hiden Analytical


Hiden SIMS

Secondary Ion Mass Spectrometry

• Analysis Technique

• Instrumentation

•SIMS Workstation

•Bolt on components

•Applications

• Summary

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Sputter Erosion of the Specimen

+ve Ions

-Ve Ions

-ve Molecules

- +ve Molecules

Sputtered Neutrals

ElectronsCOLLISION CASCADEALTERED LAYER

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Static SIMS •Very low ion dose (~1E12 ions cm-2) gives surface specific measurement.

• Ideal for investigation of contamination, oxidation and monolayer coatings.

Dynamic SIMS • Higher ion dose erodes surface exposing deeper material.

• Monitoring mass resolved ion signals results in depth profile.

• Ideal for investigation of impurities (dopants) and layer structures.

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Scanning the beam across the sample

• Flat bottom crater for depth profiling

• Imaging

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SIMS Depth Profiling - Gating

For high dynamic range analysis measured signal must come only from the centre of the crater.

Hiden spectrometer interface unit and MASsoft electronically gates signal

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Anatomy of a Depth Profile

Matrix signal provides a reference for quantification and helps confirm validity of data

Pre-equilibrium region before bombardment chemistry stabilises

Usually a log scale due to the very high dynamic range of SIMS

Sharp decay shows good depth resolution / flat crater / adequate gating

Dip in matrix combined with rise in impurity indicates impurity is not dilute

Signal monitored as a function of time

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Primary ion beams

The probability of ion emission is affected greatly by the sample chemistry.

As the ion beam species becomes incorporated into the specimen it can be used to modify the surface chemistry and enhance probability of ionised emission.

• Oxygen enhances ionisation of electropositive elements

• many metals and semiconductor matrix species

• Caesium enhances ionisation of electronegative elements

• halogens, many contamination species, some metals

• Caesium can also be used to collect secondary cluster

ions (MCs+) of most species (M) at lower sensitivity.

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Sensitivity

SIMS is the most sensitive generally available surface analysis technique.

• in static SIMS <<1% monolayer concentrations are detected

• in dynamic SIMS detection limit can be ppb.

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The SIMS Workstation comprises

• MAXIM SIMS/SNMS analyser• IG20 gas ion gun and controller• IG5C Cs ion gun and controller• Charge compensation electron gun• Viewing camera and lighting• UHV multiport chamber• Fast entry loadlock and transfer mechanism• PC control software• Compact bench housing pumping• Provision for expansion

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Hiden SIMS Products – Ion GunsIG20 Gas Ion Gun

•1-5 keV, 1µA, 100µm (50µm imaging)

•Reliable, long life, electron impact ion source

•Integral bend to remove neutral particles

•May be used with reactive and inert gases (e.g. H, He, O, N, Ar, Xe, air)

•Differential pumping to preserve chamber UHV

•Bakeable to 250C

•Mounts on CF35

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Hiden SIMS Products – Ion GunsIG5C Caesium Ion Gun

•1-5 keV, 100nA, 80µm (20µm imaging)

•Miniature low power Cs Ion source (~8W), long life, easy replacement.

•Air stable

•Double bend to remove neutral particles

•Differential pumping to preserve chamber UHV

•Bakeable to 250C

•Mounts on CF35

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Hiden SIMS Products – Ion GunsIon Gun Control

PC controlled

Settings can be saved and recalled

Automatic ion source warm up / cool down

EHT ramp rate control

Gun diagnostics

Connect via TCP/IP, USB or serial

Upgradeable software and firmware

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Hiden MAXIM

Very high sensitivity

Off axis geometry

Integrated high efficiency SNMS ioniser

< 100V extraction potential

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SNMS (sputtered neutral Mass Spectrometry) – Post Ionisation

• Electron impact cell ionises the sputtered neutral material• Secondary ions deflected from analyser• Separating the sputter and ionisation events removes

most of the matrix effect associated with SIMS• Easily quantifies large changes in matrix material • Detection limit typically <0.1 atomic%• Excellent for alloy multilayers• No requirement for matrix matched reference materials• Neutral species are unaffected by surface charging

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Hiden MAXIM

For SNMS operation an electron impact cell is used at the very front of the probe.

This maximises the solid angle for the emitted neutrals that can be collected – improving sensitivity.

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Sample Viewing•Important to be able to accurately target sample areas and navigate around the specimen.

•Normal incidence USB colour camera and LED white light source.

•Save images to other applications and documents.

•Flexible positioning to allow optimum illumination of samples (such as specula reflection for observing craters on polished surfaces).

Craters visible on silicon wafer during

analysis using specula illumination

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Sample Charging

The surface of samples, principally insulators, charges during bombardment. This is primarily due to secondary electrons leaving the surface.

To overcome this problem an electron gun is used to balance the lost electrons and maintain sample neutrality.

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Applications

•Static SIMS

•Contamination analysis

•Dynamic SIMS

•Depth profiling semiconductors and layer structures

•Imaging

•Semiconductors

•Industrial components

•SNMS

•Hard disc head

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SIMS Imaging

• SIMS signal from raster scanned ion beam is monitored and presented as an image• Chemical map shows distribution of species on the surface• Can be used to find areas for subsequent depth profile or spectrum analysis• Ideal for investigating transfer contamination, surface diffusion and cross sections• Can be used with bevelled samples for rapid assessment of depth profile

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SIMS SIMS - IMAGING

•Semiconductor bond pads must have a clean surface for successful wirebonding (ultrasonic welding).

•SIMS imaging (27Al) reveals surface of some pads (circled) obscured by contaminant.

•Real-time images can be used navigate to problem area for static SIMS analysis – identified fluorocarbon from etching process.

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SNMS Depth Profiling

Depth profile shows a NiCr/Cu/NiFe layer structure primary ions 5 keV Ar from IG20 ion gun

0.1

1

10

100

0 100 200 300 400Depth / nm

Co

ncen

trati

on

/ a

tom

ic %

Ni

Cr

Fe

Cu

Integrated electron impact ionizer

Separation of sputtering from ionization minimises matrix effects.

Easily quantified composition to 100%

Does not require matrix matched reference materials.

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• Hard disk Platter comprises magnetic and non-magnetic metal layers on aluminium substrate.

SNMS Depth Profile of Hard Disk Platter

Polymer / lubricant

Magnetic data layer

Nonmagnetic layer

Magnetic base

Substrate

‘Contact’ layer

N head S

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SNMS Depth Profile of Hard Disk Platter

0.1

1

10

100

0 1 2 3 4 5 6 7 8 9 10depth / µm

con

cen

trat

ion

/ a

tom

%

Cr

Ni

Co

Al

C

Polymer / lubricant

Magnetic data layer

Nonmagnetic layer

Magnetic base

Substrate

‘Contact’ layer

N head S

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Near Surface Detail of Hard Disk Platter

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180 200depth / nm

con

cen

trat

ion

/ a

tom

%

Cr

Ni

Co

Al

C

Polymer / lubricant

Magnetic data layerNonmagnetic layer

Magnetic base

Substrate

‘Contact’ layer

N head S

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Case Study – Contamination on Diesel Injector

After a period of intense engine running, a hard, stain like, deposit was observed on a fuel injector component.

EDX (energy dispersive X-ray) analysis in the SEM was inconclusive as the thin nature of the deposit meant that most of the excited volume was in the underlying metal.

300µm

1cm

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The flexible sample handling of the SIMS Workstation permitted mounting of the component, without further preparation. Important because cutting or grinding of the hardened steel would have exposed the component to heat and contamination.

Image from instrument camera

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56Fe SIMS images of the defective region. The right hand image shows detail in the position of the arrow, where something is blocking the iron signal from the steel.

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A localised mass spectrum from the steel shows typical constituents, • Fe at 54-58, with the major isotope at 56• Cr at 50-54 with the major isotope at 52• and Na (23) and K(39 and 41) being contaminants to which SIMS is

extremely sensitive.

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The localised mass spectrum from the defect is dominated by Ca.

The defect is Ca based and it is suggested that this is due to a bio-diesel catalytic production step. This known possible fuel contaminant is limited by EU regulations to 5mg/kg (summed with the Mg content).

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Summary

• SIMS is the most sensitive surface analysis technique with ppb detection limits in many cases. It detects across the entire periodic table and provides isotopic information unavailable with chemical, electrical or optical (incl. X-ray) techniques.

• Analysis of the uppermost monolayer (static SIMS)

• Analysis of near surface and layers structure by depth profiling

• Depth profiles may be quantified with high accuracy and sensitivity.

• Spatial distribution can be observed directly by imaging.

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Conclusion

• Bolt-on Hiden SIMS products provide a cost effective means of adding high performance SIMS to existing instrumentation.

• The Hiden SIMS Workstation is a high flexibility SIMS/SNMS tool designed specifically for ease of operation and low cost of ownership.

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Hiden Analytical Instruments for exact science HIDEN SIMS