Transcript The New Time-of-Flight (TOF) Version of the MiniSIMS

Development of a TOF Version
of the Desktop MiniSIMS
Design & Applications
A.J. Eccles, B. Cliff, C. Jones, N. Long, P. Vohralik
Millbrook Instruments Limited
Blackburn Technology Centre, Blackburn, UK
www.minisims.com
© Millbrook Instruments Ltd. 2005
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
O
C O
H2
C C
H2 H2
Mass 1176.78 Da
OH
C(CH3)3
4
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 lm /30 s = 15 nm v
50 lm / 0.1s = <0.1 nm
Effect of Decreasing Area
Mass Scale
Analysis
Area
Dimension
Quadrupole Data
Effect of Decreasing Area
Mass Scale
Analysis
Area
Dimension
Time of Flight Data
Identification of Contaminant
Identification of Contaminant
Identification of Contaminant
Identification of Contaminant
Retrospective Experiment
Retrospective Experiment
Retrospective Experiment
Retrospective Experiment
Mass Resolution
Al+
26.9815
C2H3+
27.0236
Si+
27.9769
C2H4+
28.0314
Higher Mass Range
High Mass Peaks (KI)
400
Intensity
300
200
100
K9I8
0
350
550
750
950
Mass
1150
1350
Hydrogen Detection
Hydrogen Detection
Intensity (Counts)
100000
50000
H-
0
0
1
2
3
4
5
6
Mass (Daltons)
7
8
9
10
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
Time of Flight Analyser
• 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
Time of Flight Analyser
• 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 Ion Image
(30 seconds)
Secondary Electron
Image
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
New Application Areas
• (1) Organic Materials Mol. Wt. < 1500
• Polymer additives
• Biomolecules
• (2) Heavy metals
• Environmental (Pb, Hg …)
• Catalysis & Electronics (Os, Pt …)
New Application Areas
• (3) Small Area Analysis
• Electronic devices
• Contaminant spots
• (4) Troubleshooting (analysis of unknowns)
• 3D imaging / Depth profiling
New Application Areas
• (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