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 © 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 = 6x10 13 v 1 mm /0.1 s = 2x10 11 ions cm -2

Irganox Quadrupole Common reference in SIMS (e.g. SSIMS Library) Mass Da Quadrupole data - characteristic ions but only at low mass

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

Irganox 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 = 6x10 13 v 1 mm /0.1 s = 2x10 11 ions cm -2 Less erosion when working at small areas e.g. 50 l m /30 s = 15 nm v 50 l 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 C 2 H Si C 2 H

Higher Mass Range K9I8K9I8

H-H- Hydrogen Detection

Time of Flight Mass Analyser for the ToF MiniSIMS

Time of Flight Analyser Kinetic Energy E = ½mv 2 = ½m(L/t) 2 For ions with same energy, t = km ½ 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 ~ 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 %

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

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