Integrated circuit with isolation of field oxidation by noble gas

Abstract

A silicon semiconductor integrated circuit includes an insulative field oxidation layer which substantially does not encroach under active circuit elements of the integrated circuit. The field oxidation layer is formed of oxidized amorphous silicon created by bombardment of a silicon substrate with noble gas ions. The amorphous silicon oxidizes at a rate much faster than crystalline silicon so that when the field oxidation layer is formed crystalline silicon foundations for the active circuit elements are left substantially intact. The crystalline silicon foundations are formed by using appropriate shield elements during the noble gas ion bombardment. This noble gas ion bombardment also has the advantage of eliminating dislocation defects which may be present in the field oxidation area so that these defects do not propagate into the crystal lattice of the silicon during subsequent heating and cooling cycles. Also, the amorphous silicon relieves surface layer stresses which may be present from prior processes or because of prior morphological structural elements formed on the silicon substrate. A boron ion bombardment may also be used to further inhibit loss of P-well dopant to the oxidant forming the field oxidation layer and preserving a desired high field threshold voltage and robust field isolation for the integrated circuit.