Adjustment of ion-beam column, apertures at 20 kV and 10 kV

Anders L., 2009-02-10,
This is only for service, not for general users!

Tip! 2011-11-07
When doing "210 - ion Column Alignment", on AperPos adjustment, use the mechanical wheels on the ion-column instead of the software control.

The 24 V spupply to the high voltage unit for the columns can be unplugged to reset it. If the Temp. is not readout in one of the service mode windows, this unit may need a reset. Unplug it for five seconds. It is accessible from the backside of the tall electronics cabinet. See this picture. This is much faster than reset the whole system.

Tip! 2009-03-18
If ion source does not start, e.g. error message like "cannot maintain emission", it can be heated more.
Use procedure 253: Supervisor Ion Beam, klick on the button Heat. This will increase the heating current from 2 A to 3 A for a short time. Please note that you should only use this once, maximum twice at the same occassion, otherwise the ion-source might be damaged.

It was discovered that using other voltage than 30 kV for the ion beam resulted in very bad images (or completely black images), i.e. 20 kV, 10 kV and 5 kV.
A first trial was done with the adjustment procedure, "210 - Ion Column Alignment", see image below.

The most important parameter is "AperPos", aperture position. This was very much off for all apertures at voltages different from 30 kV. In fact it was so much off that the software did not have enough range to adjust it. The adjustment had to be made in steps or iterations.

The available range for aperture positioning was increased with a service software tool (Henrik Norell, FEI).

  1. AperPos button was activated
  2. The AperPos was set to lowest center position, since this seemed to be the main offset error for all the apertures.
  3. Stig or BShift button was activated
  4. L2_Corr was adjusted for best focus
  5. Save button was clicked
  6. Finish button at top was clicked
  7. The 210 - Ion Column Alignment procedure was started again
  8. Now the setting for the AperPos was centered again, making it possible to do further adjustments to lowest center position
  9. The steps above was repeated two to four times until the correct aperture position could be fine-tuned.
  10. The Stig button was used to fine-tune the stigmation.
Not all apertures could be adjusted this way. The bigger apertures were not possible to adjust fully. The image became darker before the AperPos was fully adjusted. This may imply that there is some other type of misalignment which is not fully corrected.
The bigger apertures are usable. The effect of remaining mis-alignment is that the image is shifting (moving laterally, translating) when adjusting the focus. However all apertures are giving a much better imaging at 20 kV and 10 kV, than before the adjustment.
The StigSin and StigCos were only adjusted for those apertures where a full AperPos adjustment could be done. The StigSin and StigCos seems to be the same for all apertures, so if they are badly adjusted they affect all apertures at the used voltage.

Adjustments have been done for 20 kV and 10 kV. Here is a table for 10 kV.

Aperture Comment
0.30 pA All OK!
3.0 pA All OK!
3.0 pA All OK!
16 pA All OK!
23 pA All OK!
50 pA All OK!
0.12 nA All OK!
0.12 nA All OK!
0.21 nA All OK!
0.41 pA Cannot go enough negative i Y direction for AperPos, due to darker image.
1.1 nA Same as above
1.8 nA Same as above
2.6 nA Same as above
2.6 nA Same as above, getting dark image already on first iteration
15 nA Same as above

 

Here is an image collected with the ion-beam at the smallest aperture, at 10 kV, i.e. 0.30 pA.
The adjustment is very difficult to do due to the low signal level and therefore the high noise level. After the adjustment the image quality is approaching that of the E-beam imaging in normal mode, i.e. not immersion mode.


Image taken with ion-beam at smallest aperture (0.30 pA). Scan-rate: 0.3 s per line.
Object is sample provided by FEI with crosses for ion-beam alignment.

Anders Liljeborg Nanostructure Physics, KTH.