Operation and Maintenance Manual Model 7AA Wafer Grinder
7 - 16 Version 1.2 - April 18, 1996
between the rear foot and the grind bed will change, thus adjusting
the angle of the X-Z plane.
To make the X-Z adjustment remove the exhaust plenum by
removing the four hex head screws and sliding it out the back. The
differential screw is held in position by a jam nut on each end.
Loosen each jam nut to permit screw rotation.
With the dial indicator mounted on the wheel sweep the indicator
side to side until the measured deflection is corrected. For
example, assume that a 4" spherometer indicates a 0.0005"
negative deflection on the chuck. This indicates that the chuck is
0.0005" concave measured on a 4" diameter. As the indicator is
swept across the chuck it should indicate a constant deflection (the
indicator should be as close as possible to the wheel) since the
chuck surface and wheel rim are parallel. The spindle should be
adjusted to nullify this error. Thus a positive deflection on the
indicator from chuck center to edge is needed to correct the error.
Rotating the differential screw clockwise will tilt the spindle forward,
thus making the chuck more concave. It is important to note that
once the desired spindle adjustment has been made the jam nuts
must be re-tightened to lock the screw in position. As tension is
applied by the jam nuts the position of the spindle will change. In
order to obtain the desired final adjustment measure the deflection
caused when tightening the jam nuts and readjust the differential
screw so that the indicator deflection is correct after tightening.
Once the desired correction has been made reinstall the plenum,
remove the indicator mounting hardware and reinstall the fine
wheel mounting screw. Grind the chuck once again with the
coarse wheel and measure the surface. Repeat the above steps if
further alignment is necessary.
After grinding the chuck with the coarse wheel it is possible to
improve the flatness by grinding the chuck with the finish wheel.
There are two benefits to be realized from this extra step; 1) since
the fine wheel is a larger radius the steepness of the sphere
generated on the chuck will be less for a given angle error and 2) if
a dual grind is selected the final parallelism will be better since the
chuck surface is parallel to the finish wheel which is the last wheel
to shape the wafer. The finish wheel is not capable of grinding as
much chuck ceramic as the coarse wheel and will load up quickly.
Thus it will be necessary to dress the finish wheel after chuck
grinding.
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