Appeal No. 95-2454
Application No. 07/396,733
semiconductor pockets electrically isolated from one another by the oxidized
silicon and the PN isolation junction. 11
Brief, p. 14-15. Applicant asserts that only this first step is taught by Frouin. We find Frouin to be
significantly more informing to the person having ordinary skill in the art. In addition to step (1), Frouin
at least implicitly teaches (2) forming an etch resistant coating (photo resist) or “insulation layer” on the
epitaxial silicon layer, (3) creating openings over the areas where the silicon is to be removed, (4) etching
the exposed silicon to form channels having a specified depth in the epitaxial silicon layer, and (5) thermally
oxidizing the channels to form an isolation region dividing the epitaxial layer into a plurality of semiconductor
pockets electrically isolated from one another by the oxidized silicon and PN isolation junction. Steps (2)
to (5) are at least implicit in Frouin’s disclosure at col. 5, lines 38-44:
The grooves are formed by etching in a usual manner, using a photo-resist tech-
nique. The grooves separate the islands from one another. After forming the
grooves, their walls are coated with an insulating layer 12, which in the present
example preferably consists of silicon oxide, for which process a conventional
technique can be used.
Etching using “a photo-resist technique” describes a process that was well known to those working in the
art at the time the invention was made to include applying the photoresist coating, creating openings in the
layer over the areas where the silicon is to be removed, and etching the exposed silicon. Frouin discloses
that thermal oxidation is disclosed as one technique of forming a silicon oxide layer. Frouin, col. 5, lines
62-63. Thus, the difference between Frouin’s disclosure and the claimed invention resides in the use of
a combined etch and oxidation resistant coating, etching partially through the epitaxial layer and oxidizing
the depression to completely fill the depressions with silicon oxide.
11
We note that applicant’s characterization of the steps is not entirely accurate. The claim step
corresponding to step (2) above also requires that the insulation be unaffected by the etchant used to form the
depressions.
13
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