Appeal No.2003-2001
Application No. 09/345,173
step to form field oxide regions (thicker silicon oxide regions).
Chung employs a wet etching step (hot phosphoric acid bath) to
remove the remaining nitride/poly stack while maintaining the
thickness and integrity of field oxide regions and a pad oxide
region. See column 2, line 46 through column 3, line 23 of
Chung.
The examiner acknowledges (answer, page 3) that Chung does
not describe using a breakthrough etch step or a descumming step
as required by appellants’ claims.
The examiner turns to Cher for allegedly teaching and
suggesting the claimed breakthrough etch step. In this regard,
the examiner (answer, page 3) takes the position that:
Cher teaches [a] method for anisotropically
etching the polysilicon having a first breakthrough
etch using a fluorocarbon etchant (col. 4, line[s] 30-
35). It would have been obvious at the time of the
invention for one skill[ed] in the art to modify Chung
in light of Cher because Cher teaches that the
breakthrough etch would remove the oxide on the poly
before the main etch.
The examiner (answer, page 6) further explains that:
[a]s described by Chung, the HF dip is done before
forming and etching the nitride layer and the
breakthrough etch, described by Cher, is done right
before the actual etching of the polysilicon is carried
out.
As for the claimed descumming step, the examiner asserts,
at pages 3 and 4 of the answer, that:
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