５
MEASUREMENT OPERATION
TMPM5200-2
5-131
ation
tinuous measurement
at th
high
s
e due to thermal or, sometimes, other causes. Drift
correction is done by shifting the center point of the scanning area in the same direction
and through exactly the same distance as the drift, at the end of the scan. To implement
drift compensation, therefore, it is necessary to carry out preparatory steps (to obtain the
drift speed and direction).
In drift compensation, the amount of drift per unit of time is calculated from the distance
between a certain point observed when you scan the field of view first and the same point
observed when you scan it second. Each time the measurement ends, the field of view is
shifted automatically by the inverse amount of drift corresponding to the elapsed time.
The procedure for drift compensation is as follows.
the Advanced tab window before starting
2.
S
ox in the Scan tab
■
Drift Compens
Sample thermal drift, no matter how small, poses a problem in con
e atomic level under ultra high vacuum, as this is a procedure which requires a
ly stable field of view. The Drift Control window is used to correct such drift a
occurs in the measurement imag
1.
Click on the Advanced button in
measurement.
The Advanced Control window appears.
elect the Scan tab in the Advanced Control window.
uses the parameters in the Drift Control b
Drift compensation
window.
3.
Observe the first image and grab it.
ch as a bright point or a hole that may indicate a defect)
4.
C
The mouse cursor changes to the + mark; so specify the part of the measurement
image that you selected in advance.
5.
Observe the second image and grab it.
Confirm that the acquired image includes the selected feature.
6.
Click on Set Drift Point to specify the second reference point.
Just as you selected the first feature point, specify the same feature in the second
image (it has drifted to a different position). The drift speed and direction are
calculated from the elapsed time and from the distance between the points in the
first and second images.
7.
Select Enable Correction.
Drift compensation begins.
You can specify the point up to three images for drift calculation. When you want to
specify a third point, observe a third image and specify the point in it.
Select a feature (a place su
in the image.
lick on Set Drift Point to specify the first reference point.
