Appeal No. 1998-3043
Application 08/667,587
the claim term “field-shield isolation structure.” We look
first to the appellants’ specification.
In the section of the specification entitled Background
of the Invention, the appellants discuss methods for isolating
circuit elements in a semiconductor device. From page 1, line
16 to page 2, line 14, it is stated:
A so-called “field-shield isolation” method, which
isolates elements by a MOS structure formed on a
semiconductor substrate, has been proposed as an
isolation method which does not generate the bird’s
beaks.
Generally, the field-shield isolation structure
has a MOS structure in which shield gate electrodes
made of a polycrystalline silicon (polysilicon) film
are formed over a silicon substrate through a shield
gate oxide film. This shield gate electrode is
always kept at a constant potential of 0 V, for
example, as it is grounded (GND) through a
connection conductor when the silicon substrate (or
a well region) has a P type conductivity. When the
silicon substrate (or the well region) has an N type
conductivity, the shield gate electrode is always
kept at a predetermined potential (a powerful source
potential Vcc [V], for example).
As a result, because the formation of a channel
of a parasitic MOS transistor on the surface of the
silicon substrate immediately below the shield gate
electrode can be prevented, adjacent elements such
as transistors can be electrically isolated from one
another.
We then look to extrinsic evidence submitted by the appellants
in the form of an article entitled “FULLY PLANARIZED 0.5Fm
7
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