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Thermo Fisher Scientific

Beam drifting and C1/C2 lens wobbling after normalization

Issue

Beam drift 6nm/min and C1/C2 lens wobbling after normalization

Environment

Krios G3i

Resolution

These are possible resolutions for the issue:

  • remove EMI X sensor

Cause

These are possible causes for the issue:

  • EMI effect

Details

  1. Replace C1/C2 CGNL .No effect on beam stability.
  2. Checked high tension stability using back focal plane. Stable
  3. Firmware version of CGNL correctly? Version correctly. 
  4. Does the beam drift start without normalizing the lenses?
    The beam drifts steadily at a slow, constant rate. but beam jumps strongly when normalizing C1/C2. 
  5. Environment parameters all in spec? yes, all of them are stable and within spec.
  6. Does issue occur in low mag and nanoprobe modes as well? The magnitude of the instability scales with the magnification. The higher magnification, the more strong/noticeable the beam movement becomes.
  7. What is the resistance of the C1, C2, C3 lens coils? all in a range of 8.1 to 8.3 ohms 
  8. Is the beam and image drifting together or only beam drift? beam and the image drift together.
  9. What direction is the drift and does it change with magnification changes? The direction of the drift appears to be the same at all magnifications.
  10. How long does the wobble decay take? . Wobble decays in 5-10 seconds. The direction is nonuniform.
  11. In clock terms what direction does the drift move? The direction of the passive drift seems to be changing day to day.
  12. Drift tests at 250 kX and spot size 6 in microprobe with various combinations of C2 and C3:
    1. C2 + C3 ON, drift failed in 5 minutes (to the left)
    2. C3 OFF, drift failed in 5 minutes (to the left)
    3. C2 OFF, drift passed
    4. C2 + C3 ON, reverse polarity C3, drift passed in opposite direction (to the right)
    5. C2 + C3 ON, reverse polarity C2, drift failed in 3 minutes (to the left) This seems to point to an issue with C2
  13. Teste the stability of the C2 CGNL. Found it normal, as well as the Condenser X ODDA
  14. checked the voltage on the FREF. they are solid 10V and -10V.
  15. Is there any contaminates in the chiller water or in the flow meters? The flow meters and chiller water appear to be free of contaminates.

Solution:
When Turn off EMI compensator, the beam is more stable, but still drifting. moved the X sensor so the beam is not longer wobbling, spot drift test pass.

 

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