Last message

charley charley at snf.stanford.edu
Thu Jun 26 12:34:54 PDT 2003



       Hello Sonogage fans,
    I've been told my last message, via Coral, didn't have any text in
it. So here's the deal:
I have two units, each with its' own little faults, and I will be
'blending' the two to make one
good one. It is not a high precision device, as the acoustic channelling
of the moving rack
affects the reading. You can alter the reading by several counts by
putting your hand near
the ultrasonic head. Not much of a deal for bulk resistivity
calculations.
    I have a dial-indicator and granite block and an assortment of tips
on order, so we'll
have a precision measurement tool. I plan to have enough tips so you can
have your
own clean (or not...) tip touching your wafer. Yup, contact. The
Sonogage is the only
non-contact thickness guage I've seen and it's actually making better
than a percent
error, so it's within spec. I assume (I know...) that a percent won't
drastically alter your
stress calculations-let me know if that's not true. I will resurrect the
R2T2 and put it
back in the lab soon. My repair guy, although he didn't reapair it, has
promised me some
great schematics. Techs live on this stuff-don't laugh.
    I'll get it running and do a "small writeup" on the accuracy and
limitaions. I may come
up with a way to do 6" wafers on it, too. "Small writeup" as you know,
means medium
large by most folks standards, so you are forewarned!
    chw3




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