development of a tof version of the desktop minisims design & applications a.j. eccles, b....

Development of a TOF Version

of the Desktop MiniSIMS

Design & Applications A.J. Eccles, B. Cliff, C. Jones, N. Long, P. Vohralik

Millbrook Instruments LimitedBlackburn Technology Centre, Blackburn, UK

www.minisims.com© Millbrook Instruments Ltd. 2005

http://www.minisims.com/

Outline of Presentation

• Brief Introduction to the MiniSIMS• Instrument design concept

• Demonstration of improved performance• Comparison with quadrupole MiniSIMS

• The ToF analyser for the new MiniSIMS• Unconventional design for ToFSIMS

• New application areas

The MiniSIMS Instrument

Design Objectives

• Increase routine use of Surface Analysis• more affordable

• more accessible

• static, imaging & dynamic SIMS in one compact unit

• Not a replacement for conventional SIMS• not state-of-the-art performance

• restricted analysis conditions

New Options for 2005

• Large Sample Handling• Up to 100 mm diameter samples

• Multiple samples (unattended operation)

• New Instrument case• Aesthetic appeal and added functionality

MiniSIMS TOF

New Options for 2005

• Large Sample Handling• Up to 100 mm diameter samples

• Multiple samples (unattended operation)

• New Instrument case• Aesthetic appeal and added functionality

• ToF version of the new MiniSIMS• Improved performance for small area analysis

• Unconventional design of analyser

Comparison of

Quadrupole MiniSIMS

and ToF MiniSIMS

Current MiniSIMS

• Based on liquid metal gallium ion source

and quadrupole mass analyser

• Low cost, stable mass spectrometry

• However there are limitations…

• limited mass resolution

• limited mass range

• sequential scanning so “throw away” much available signal

Time of Flight Benefits

• Five main improvements:

• Improved Static SIMS from smaller areas

• Retrospective Experiment

• 2D Imaging• 3D Imaging / Depth Profiling

• Higher Mass Range

• Higher Mass Resolution

• Hydrogen Detection

Parallel Mass Detection

• Faster spectrum acquisition (x300) means lower primary ion dose

• Less fragmentation of organics

• e.g. 1 mm /30 s = 6x1013 v 1 mm /0.1 s = 2x1011 ions cm-2

Irganox 1010 - Quadrupole

Common reference in SIMS (e.g. SSIMS Library)C(CH3)3

OH

C(CH3)3

CH2

CH2

O

OCH2

4

Mass 1176.78 Da

Quadrupole data - characteristic ions but only at low mass

Irganox 1010 - ToF

ToF positive ion mode - peaks up to 900 Da as library data

Irganox 1010 - ToF

ToF negative ion mode - molecular ion at m/z = 1175 Da

Parallel Mass Detection

• Faster spectrum acquisition (x300) means lower primary ion dose

• Less fragmentation of organics

• e.g. 1 mm /30 s = 6x1013 v 1 mm /0.1 s = 2x1011 ions cm-2

• Less erosion when working at small areas

• e.g. 50 m /30 s = 15 nm v 50 m / 0.1s = <0.1 nm

Effect of Decreasing Area

Analysis Area

Dimension

Mass Scale

Quadrupole Data

Effect of Decreasing Area

Analysis Area

Dimension

Mass Scale

Time of Flight Data

Identification of Contaminant

Retrospective Experiment

Mass Resolution

Al+

26.9815C2H4

+

28.0314Si+

27.9769

C2H3+

27.0236

High Mass Peaks (KI)

0

100

200

300

400

350 550 750 950 1150 1350

Mass

Inte

nsi

ty

Higher Mass Range

K9I8

Hydrogen Detection

0

50000

100000

0 1 2 3 4 5 6 7 8 9 10

Mass (Daltons)

Inte

ns

ity

(C

ou

nts

)

H-

Hydrogen Detection

Time of Flight Mass

Analyser for

the ToF MiniSIMS

Time of Flight Analyser

• Kinetic Energy E = ½mv2 = ½m(L/t)2

• For ions with same energy, t = km½

• Ion Mirror compensates for energy spread• More energetic ions follow longer path

• Detector efficiency falls with increasing mass

• Mass resolution depends on timing and dE


• Detector measures arrival times for ion packet

• Need definite start time for ion packet

• Conventionally by pulsing primary ion beam

• Flight time ~ 50 µs, Pulse time ~ 0.005 µs

• Very efficient but Duty Cycle < 0.1%

• Artificially long analysis times


• MiniSIMS uses different design• Primary beam is continuous

• Secondary ion beam is pulsed

• Less efficient, but Duty Cycle 10 - 50%

Continuous Primary Beam

• High duty cycle = Fast acquisition times• Spectrum acquisition << 1 second

• Image acquisition times < 1 minute

• Image resolution remains unchanged• No degradation of spot size on pulsing

• All sputtered material contributes to depth profiles• No alternating etch / analyse / etch requirement

Speed of Imaging

Secondary Electron Image

Secondary Ion Image (30 seconds)

New Application Areas

for the ToF MiniSIMS

TOF - Practical Advantages

• More efficient than quadrupole instrument

• Analysis of unknown samples

• Analysis of unique samples

• Improved analysis of organic materials

• Smaller area static SIMS analysis

TOF - Practical Advantages

• More information than quadrupole instrument

• Extended mass range

• Higher mass resolution to resolve common

hydrocarbon / elemental interferences

• Actually simpler instrument operation

• Retrospective experiments


• (1) Organic Materials Mol. Wt. < 1500• Polymer additives

• Biomolecules

• (2) Heavy metals• Environmental (Pb, Hg …)

• Catalysis & Electronics (Os, Pt …)


• (3) Small Area Analysis• Electronic devices

• Contaminant spots

• (4) Troubleshooting (analysis of unknowns)• 3D imaging / Depth profiling


• (5) Existing SIMS Users

• Customers using ToFSIMS contract analysis

• Static SIMS capability for DSIMS users

• Depth Profiling capability for ToF users

Conclusions

ToF MiniSIMS( v quadrupole MiniSIMS )

• Improved Static SIMS from smaller areas

• Retrospective Experiment

• 2D Imaging• 3D Imaging / Depth Profiling

• Extended Mass Range

• Higher Mass Resolution

ToF MiniSIMS( v conventional ToFSIMS )

• Use of Continuous Primary Beam

• Fast analysis (= low cost per sample)

• No loss of image resolution in pulsing

• Simplified depth profiling (single beam)

• Fast & simple static / imaging / dynamic

SIMS in one instrument

development of a tof version of the desktop minisims design & applications a.j. eccles, b....

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