Appeal No. 95-2454
Application No. 07/396,733
the same or opposite conductivity type as the substrate. In the case of the latter, a PN junction is directly
formed at the interface of the substrate and the epitaxial layer. In the case of the former, a region of the
opposite conductivity type is first formed in the substrate and then the epitaxial layer of the same
conductivity type as the substrate is grown on the substrate forming the PN junction. In the next part of
applicant’s process the insulating channels are formed. A layer of insulation is placed over the epitaxial
layer. The layer may be silicon nitride or any material which is unaffected by silicon etchants and masks
against thermal oxidation of the underlying semiconductor material. The portions of the insulation over
areas of the epitaxial layer to be oxidized are removed. A portion of the exposed epitaxial silicon is then
removed by etching to form channels. The exposed silicon is oxidized. The amount of epitaxial silicon
removed is controlled so that upon oxidation (1) the oxide layer reaches the PN junction and (2) fills the
grooves with oxide so that the surface of the oxide layer is substantially coplanar with the original surface
of the epitaxial layer. The oxide channels, along with the underlying PN junction, form electrically isolated
regions of semi-conductor material.
Applicant’s independent claims 14 and 25 are representative and are reproduced in the margin.2
2
14. The method of forming a plurality of electrically isolated pockets of semiconductor
material in a semiconductor structure comprising a silicon substrate of one conductivity type with an epitaxial silicon
layer of opposite conductivity type thereon, which comprises the steps of:
growing a doped epitaxial silicon layer on said silicon substrate, said doped epitaxial silicon layer having a
conductivity type relative to the conductivity type of at least a, portion of the top surface of said substrate such that
a laterally-extending PN junction is formed in at least part of said semiconductor structure;
forming a layer of insulation on said epitaxial silicon layer, said insulation having the properties that it is
substantially unaffected by at least one etchant used to remove epitaxial silicon and substantially masks the
diffusion of oxygen;
removing portions of said insulation overlying regions of said epitaxial silicon layer to be converted into
oxidized silicon;
forming depressions to a specified depth in said epitaxial silicon exposed by removal of said insulation by
removing part of said epitaxial silicon exposed by removal of said insulation; and
subdividing said epitaxial silicon layer into a plurality of electrically isolated pockets of semiconductor
material by oxidizing the silicon exposed by said depressions to form oxidized silicon extending through said epitaxial
silicon layer to said PN junction;
(continued...)
3
Page: Previous 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Next
Last modified: November 3, 2007