SEM Mechanical Source Condenser Realign Jan 2017

Current status

• More than one year since the last align
• Still original source, 47,244 hours
• Fill 2.330 A, Ext 5.02 kV, Current 263 uA (EHT off)
• EHT on 8 kV, 197 uA 25.7% extraction

Procedure

1. Start with 10 um grid on Si, flat calibration sample
1. note, clean it next time, lots of dust and particles
2. Delete old recipes
3. Set user and service alignments to neutral
4. record "before" emission images, 3 and 8 kV
5. clear shift relative to 11/8/13, relatively uniform illumination but way off center

3 kV after mechanical source align, all electronic corrections off

3 kV max condenser after source align, all electronic corrections off

3 kV, all electronic alignments neutral, condenser off/on

Any attempt to get closer to mechanical center strongly clips beam

Probably time for source replacement, emitter must be off center in grid cap

Condenser Align

1. Instructions say bring center aperture to mechanical center by mechanical source alignment. Not possible. Come as close as possible, 90 um not too far from center
2. Goal is to avoid image shift with condenser.
3. In Aperture Calibration, for each aperture, select "Cal Gun/Aper Align" and zero gun and aperture alignments, click OK. Now changing probe current only changes condenser. Note some controls disabled if Condenser Normal unchecked. Others disabled while in Cal mode.
4. Draw circle around 120 um aperture (only one fully on screen without electronic shift) with cond off, with 20 pA current, and with max current. Condenser at zero, low and high excitation
5. Pretty good at 3 kV. Somewhat off at 8 and 15 kV, but condenser  excitation is less, so should be less critical. 
6. NOTE: at 15 kV condenser is off for 20 pA, while it is on low excitation for 8 or 3 kV.
7. NOTE: do not change voltages in emission mode, toggle  back to normal for change in EHT so condenser settings update.

After 3 kV condenser align, circles for MAX, 20 pA and condensers off

At 8 kV, MAX off-center relative to 20 pA and OFF

At 15 kV, off-center relative to 20 pA/OFF