Last updated Spring 2019

Oval defect sources

• Seen in Ga and In

• Causes

  • Overfilling

  • Oxygen contamination in the source charge

  • Cell PIDs are unstable (need to be retuned)

  • Unintentional nucleation sites due to scratches on the crucible lip (due to handling during maintenance)

How to measure and characterize

• Nomarski imaging (AKA phase-contrast imaging)

  • Use max exposure time (you'll miss some of the smaller defects if you don't!)

  • measure at multiple magnification levels

  • Measure at different parts of the sample

    • Defects more likely when the temperature is off, e.g. near the edge of the sample where it makes contact with metal faceplate

    • Center of the sample should be better than the edge (Spring 2019 center of AlInAsSb digital alloy samples defect count was 1 order of magnitude lower than the edge on full 2" samples)

  • measure the individual defects (include pics) b/c morphology can tell you defect source

  • Be sure to block cleanroom light out by cupping your eyes for thin samples (small not bright defects)

How to mitigate them

Rough order of debug:

1. Visually inspect cell to look for any blobs or dark regions on the cell. These are nucleation sites where(include pics)

2. Tune cell stability with PIDs (see wiki pages)

3. Adjust tip-base delta (mention the reason why)

4. Check previous samples that are comparable

   1. did this issues come from most recent maintenance?

   2. has this issue always existed but you never noticed?

References