Appeal No. 2002-0453
Serial No. 08/686,229
According to a feature of the invention, by
knowing when certain remaining film thicknesses occur,
the overall etching process can be calibrated on-the-
fly. In this manner, by knowing etch rate and
remaining thickness, etch endpoint can be closely
predicted, and overetch can be more carefully
controlled.[1]
Schoenborn’s procedure includes calculating the etch rate
uniformity, u, based upon variables including the initial film
uniformity, Un (col. 4, lines 44-45; col. 12, lines 6-7).
Schoenborn teaches that if the initial film is very uniform, the
film uniformity does not need to be measured (col. 11, lines 1-
4).
Schoenborn exemplifies the etch rate uniformity as <±3.8%
(col. 12, line 7). The examiner argues that “[i]f this
measurement ‘u’ is etch rate uniformity as interpreted by
Appellants which is the rate of disappearance of film on top of
the waver [sic, wafer], then, there could be only one direction,
the % of decreasing thickness of the film. On the contrary, if
this measurement is the uniformity of thickness across the
surface of the wafer, i.e. the variation from a mean thickness,
1 Stated in different terms, “endpoint traces can reveal
interference effects caused by plasma emission being absorbed by
the etched film. An absorption minima corresponds to a known
remaining thickness, and could therefore be used for endpoint
before uncovering the underlying material (before ‘clearing’).
This would enable a switchover to a more selective or less
damaging process at a known thickness before clearing” (col. 6,
lines 46-53).
4
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