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of these measurements (uncorrected) and the average of these measurements
corrected for the edge sharpness (corrected).
The parameters FILT, POINT and LINESCANS must be chosen to be large
enough so that noise on the signal does not make the measurement inaccurate.
17.6.2.1.
Measure diameter using metal calibration mark
Measuring the diameter on the calibration mark is relatively quick, can be done
automatically and can be done on any holder. It is limited to spot sizes above
about 30 nm.
1. Move stage to the 10 µm octagonal calibration mark.
2. With a 16-bit pattern generator in order to be able to scan the beam in
small steps to measure the smallest spot sizes more accurately the
pattern generator resolution should be set to a small value. Set the
maximum fieldsize to e.g. 0.16384 mm:
VB_OPER> FLD 0.16384
For the 18-bit and 20-bit pattern generators this is not necessary.
3. Switch to SEM mode and graph mode.
4. Adjust gain and backoff so that the signal from the mark is a little below
the maximum level and the signal from the background is a little above the
zero level.
5. Adjust the focus and stigmation.
6. Type :
VB_OPER>QDISPLAY DIA FM / ALL / LINELENGTH=2 / EDGE=5 /
FILT=16 / POINT=8 / LINESCANS=1
17.6.2.2.
Measure diameter using knife edge
Measuring the diameter using a knife edge is a relatively long procedure, must
be done manually and usually only one holder has a knife edge loaded. It does
however allow spot sizes below 10 nm to be measured.
A fresh knife edge can be made by cleaving a piece of GaAs wafer so as to give
a smooth face normal to the wafer surface. Care must be taken to ensure the
face is smooth, has no damage to the top edge and has little debris on the edge.
The piece must be small enough to mount on the knife edge holder. The edge is
nominally in the same plane as the substrate surface in the holder but because
the knife edge is not front face referenced, the edge may be a few hundred
microns above or below the plane.
1. Load holder containing the knife edge on the stage.
2. With a 16-bit pattern generator in order to be able to scan the beam in
small steps to measure the smallest spot sizes more accurately the
pattern generator resolution should be set to a small value. Set the
maximum fieldsize to e.g. 0.16384 mm :
VB_OPER> FLD 0.16384
3. For the 18-bit and 20-bit pattern generators this is not necessary.
Part Number:878275
Vectorbeam Operator Manual