Appeal No. 95-2454
Application No. 07/396,733
invention is not confined to substrates of silicon, to insulation by an SiO -layer and to the filling of the
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insulating grooves by polycrystalline silicon.” Frouin, col. 6, lines 48-51.
The difference between the process set out in applicant’s claims 14 and 36 and the process
disclosed by Frouin resides in applicant’s use of a combined etchant and oxidation resistant coating, etching
partially through the epitaxial layer to form a channel and oxidizing the channel to completely fill the
depressions with silicon oxide rather than using a filler.
Murphy also relates to integrated circuits having electrically isolated regions. In particular, Murphy
relates to a technique for filling depressions in epitaxial silicon layers by oxidation. Murphy, col. 1, lines
27-30. Murphy teaches
the use of a multirole mask on a semiconductor surface. In one step the mask
protects a portion of the semiconductor surface while the unmasked portions are
partially etched away. In another step the same mask prevents oxidation of the
protected portion of the semiconductor surface while the previously etched
portions are oxidized. Subsequently the mask is removed in a solution which does
not attack the oxide or the semiconductor surface.
Murphy, col. 2, lines 53-61. Thus, Murphy teaches the use of a single mask to both etch the desired
regions in the epitaxial layer and to form the oxide insulation. Silicon nitride is taught as a suitable mask
material having the characteristics of being unaffected during the etching of the epitaxial silicon and masks
the diffusion of oxygen during the oxidation step. Murphy, col. 2, line 68 - col. 3, line 8; col. 3, lines 41-
46. Murphy discloses that during the oxidation step approximately 440 angstroms of silicon is consumed
for every 1000 angstroms of silicon oxide formed. Murphy, col. 2, lines 62-65. Murphy teaches that the
epitaxial layer is etched to a predetermined depth so that during oxidation (1) the oxide extends through
the epitaxial layer and (2) the depression is filled with oxide restoring a substantially planar surface to the
device. Murphy, col. 3, lines 15-21.
Doo relates to integrated circuits electrically isolated by oxide channels. Doo, col. 1, lines 10-26.
The oxide filled channels are depicted in Doo’s Figures 1 and 6 (element 6). The oxide is preferably silicon
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