There are scanning laser devices that are used to measure stress and curvature.
There are long scan profilometers that can be used to measure stress and
curvature.

On the cheap / crude side, you can use a precision optical microscope with
a large quality stage.  Make a stage insert with some wafer banking pins
and three support pins near the edge of the wafer. Take care that they are
all the same height - that requires careful machining and or
lapping..  Using the short depth of focus ( .5 um) of the highest power
lens ( 100x time 10) take note of the "height" at focus of the center of
the wafer and the "height"  at focus of the three support points. You can
read off the stage z adjustment knob if you trust it  or use an alternative
indicator. Simple math will give you the curvature assuming it is uniform.
Obviously there is some limit to the accuracy of this technique- bow less
than 5 um would be difficult- but it is quick and simple.  I am assuming
here a relatively small wafer (3 or 4",) .  It would take a pretty big
stage to do a 6 or 8 inch wafer.

At 12:10 PM 6/7/2006 +0100, you wrote:
>Can anyone tell me how to measure the bow of a wafer?
>   Thanks
>   Deepasree konduparthi

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Dr. Lynn Rathbun                                        [email protected]
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