FEI Quanta FEG 250, User'S Operation Manual

Page: 106 / 228

Alignments: Final Lens Aperture Strip Alignment
6-4
Final Lens Aperture Strip Alignment
This mechanical alignment eliminates an image shift when focusing.
The position of the final aperture should remain constant and should
not be changed further during the alignment procedure. When the
aperture is well aligned, the image does not rotate (at low
magnification) or move (at high magnification) during focusing.
ALIGNING PROCEDURE
1. Set the accelerating voltage = 20 kV / Spot size = 3 /
WD = 10 mm / magnification = 1000×.
2. Click the Stage menu / Beam Shift Reset (see Chapter 4).
3. Click the Stage menu / Zero Beam Shift (see Chapter 4).
4. Right-click over the Tuning module / Lens Alignment 2D control
and select Zero . (see Chapter 4).
5. Find a recognizable feature on the sample surface, center it
onscreen and optimize an image as best as possible.
6. Click the Lens Alignment toolbar icon. The scanning sets to the
fastest value, the objective lens modulation starts and the
alignment cross appears in all imaging quads center.
7. Adjust the aperture position so that the image rotation center is
under the alignment cross.
8. Increase the magnification to 20 000× (if necessary to 40 000×)
and realign.
9. When corrected, click the Lens Alignment toolbar icon to switch it
off.
Note:
After the mechanical alignment you can apply steps 5 and 6
separately for fine electrical alignment (gun shift) of the final lens.
Pressing inside image area activates a quad arrow ended cursor. Try
to achieve no image shift considering the middle alignment cross. This
alignment could be used any time.