Appeal No. 95-2413
Application 07/936,865
(col. 1, lines 16-18). Prior art magnetron sputtering
sources, as shown in figure 4(a), used an annular magnetic
field, shown as ring section 34. Suzuki recognized that
erosion is a function of exposure time of the ring over the
target (col. 3, lines 30-40):
When annular ring 34 rotates around Or, eroding the
target surface, a portion of the ring region in a
vicinity of point B sweeps much faster than that of
point A. The erosion of the target is proportional to
the exposed time of the target for the plasma, and, in
other words, is proportional to the quantity of the total
length of an arc length divided by sweep velocity. The
sweep velocity is in this case proportional to the radius
of rotation and the total arc length corresponding to
each point A, B, and C is shown as dashed curve length X,
Y, and Z+Z' respectively in FIG. 4(a).
Suzuki discloses that "an uneven erosion is caused by a
difference in the exposed time of the target for the plasma,
therefore the present invention is to find a magnet
arrangement, whereby the time of exposition is constant
everywhere over the target surface" (col. 3, line 67 to
col. 4, line 4).
Suzuki discloses a N-piece graphic method for producing
uniform erosion in connection with figure 8, where N=16 in
this case. An annular doughnut-shaped region 63 between inner
circle 62 and outer circle 61 is an erosion area to be
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