ToF-SIMS

Overview

Time of Flight Secondary Ion Mass Spectroscopy or ToF-SIMS is an technique performed in a FIB to analyze the composition of surface layers. During analysis, a primary ion beam is rastered across the surface of a specimen to sputter atoms, molecules, and ions from the surface. Sputtered ions are attracted to and collected by a detector as they leave the specimen, which can identify ions or other charged particles according to charge and mass.

Operation Bullet Points

• Tilt to 55 degrees
• Launch ToF-SIMS Explorer (TSE)
• Pump system below 7e-4 torr
• Turn off E-beam on FIB (in case of vacuum burp from SIMS vacuum chamber)
• Open SIMS gate valve in TSE (Hardware control tab)
• Ensure stable vacuum
• Turn E-beam back on
• Load set point voltages (Acquisition > Open TOF Instrument Control)
• Wait for voltages to stabilize
• Set field of view on I-beam (100 um for unknown)
• Set current on I-beam (100 pA for unknown)
• Acquisition > Acquisition Settings
  • FIB image: 256 x 256 for unknown
  • Binning: 2 x 2 for unknown
  • Number of frames: 500 for unknown
  • Group delay: 0
  • Pulse width: 1000
  • Choose output directory
  • Choose file name (VERY SENSITIVE TO SPECIAL CHARACTERS! Underscores and spaces are ok. Filename MUST end in .h5).
  • Store SEM Data: Dealer's choice but having extra data never hurt anyone
• Start acquisition (Triangle in circle button between Wrench and Stopsign)
• Beam will raster over field of view for specified number of frames (above)
• Live data in "Mass Spectra" tab and "Depth Profile" tab
• Ctrl-left click on peak in Mass Spectra to load into Depth Profile (can also pick a nominal m/Q value from dropdown next to Stopsign)
• Large ringing peak ~ m/Q=2
• Right-click to select Y log scale
• cts/TOF-Extraction should not exceed 0.7 for measured peaks. If so, stop acquisition, reduce I-beam current, restart acquisition.
• After 500 frames, measure trench depth. If shallower than expected, reduce FoV or increase I-beam current. If deeper, increase FoV or reduce current.
• Lather
• Rinse
• Repeat
• When finished, zero voltages (Acquisition > Open TOF Instrument Control)
• Close valve (Hardware control tab)
• Close TSE

Equipment

Focused Ion Beam Microscopes

• TESCAN S8000X FIB/SEM (EDAX)