JEOL IT800SHL - Reduced Charging Imaging Modes

Techniques to reduce charging during your imaging session.

Samples accumulating electric charge during imaging is a common issue in the SEM. This typically manifests as the image drifting/shifting (blurring the image during slow photo acquisitions), astigmatism needing constant re-correction, and generally inability to get sharp images no matter the imaging conditions.

The first and easiest method to reduce charging is to deposit a thin layer of Au/Pd onto your sample, and use clips to provide a path to from the sample surface to the grounded stage, as described here:

• Hummer SEM Sample Coater - thin Au/Pd coating to reduce charging in SEMs

However the AuPd coating may not be acceptable for your devices (although gold etchant should be able to remove it). The following methods may work without AuPd coating, you can always add the AuPd later if needed.

Imaging conditions for reduced charging

Here are some settings to reduce charging:

• Beam Voltage (in databar on bottom of screen): 1kV
• Set "P.C." (Probe Current, in databar) to: HD/High Definition mode, and then 75% current.
  • HD mode increases resolution (smaller beam) but is lower current (higher noise), so sliding up to 75% increases SNR back to original levels.

• Adjust Wobble first. Ok to do at lower magnifications. Use X/Y knobs to make image not shift laterally when defocused.
  • Use "Lens Clear" function beforehand (right-click image and choose "Lens Clear")
  • Use "ABA" (Auto Beam Alignment) - faster than manual for low beam voltages
• Adjust Astigmatism "Stig": see this video for tips: Optimizing Astigmatism (CalTech Nanoscience Institute)
  • Adjust stig while observing an object with many angles (eg. dust/dirt) - avoid adjusting stig on an object with flat lines (eg. cleaved edge) or you will skew the image along that edge.
• Switch to [CF1] or [CF2] acquisition modes for final image (next to Scan1/Scan2 etc) - "Charge Free" mode.
  • Fast scans to reduce charging, but re-scans each line multiple times to reduce noise.
  • If you don't see these buttons, please ask the tool supervisor to add them to your user account.

During imaging

• Right-click the image and click "Lens Clear" - this removes residual magnetism in the lens and can help remove distortion, or make stig correction work better. Especially if you have trouble getting Wobble and Stig to align.
• If you have set Wobble and Stigmator to "no man's land" (you're "lost"), reset it with: Alignment > OL Stigmator > [Reset All]

• Use "RDC" for optimizing image on a small, fast scan area before acquiring entire image.
• Right-Click > [Find Focus] to auto-focus on a particular feature/location on the image.

Written by Demis D. John, 2024-11-02.