■
Drift compensation
5-78
TMPM5200-2
S
ous measurement
at the atomic level under ultra high vacuum, as this is a procedure which requires a
highly stable field of view. The Drift Control window is used to correct such drift as
occurs in the measurement image 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 n
y 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.
ample thermal drift, no matter how small, poses a problem in continu
ecessary to carr
The functions of the buttons an
d indications in the Drift Control window are as follows:
r computing the drift
ore reference points
ction is being checked, the
n each time measurement is performed.
least square.
Carry out drift compensation as follows:
1.
Click on the Advance button in the Advanced tab window to open the
Advance Control window.
Then click on the Scan tab.
2.
Carry out measurement of the first image, and capture the image.
Pick up features of the image such as a single bright point and hole that may
indicate defects.
3.
Click on the Set Drift Point button, and specify the first reference point.
The mouse cursor changes to a cross shape, so specify the part of the measurement
image that you picked up in advance.
4.
Carry out measurement of the second image, and capture the image.
Confirm that the picked-up part is included in the measurement image.
5.
Click the Set Drift Point button, and specify the second reference point.
Clear Oldest Point
You can erase the oldest of the set reference points.
Set Drift Point
You can set the reference points fo
speed. You can specify up to three points.
Enable Correction
You can select this item if two or m
are set. While Enable Corre
center point of measurement shifts exactly by the amount
of drift correctio
Drift Rate
The computed drift speed is displayed. The drift speed is
computed by a first order approximation based on the
