Fabrication method to produce pit-free polysilicon buffer local oxidation isolation

Claim 3

The method of claim 1 in which, during patterning of said silicon nitride layer, a portion of said polysilicon thickness is etched into, leaving a thickness of polysilicon.

Claim 4

The method of claim 1 wherein said phosphoric acid is comprised of a solution of water and phosphoric acid.

Claim 5

In the manufacture of very large scale integrated circuit device, a method for forming an isolation region on a portion of a planar silicon surface comprising: forming an oxidation mask structure on a silicon oxide layer, said structure consisting of a layer of doped polysilicon, said doped polysilicon having been doped by ion implanting into undoped polysilicon with an impurity with a concentration greater than about 5 E 15 atoms/cm 3 to form a doped polysilicon layer, and without annealing the doped polysilicon, over said silicon oxide and a layer of silicon nitride over said doped polysilicon layer; said mask structure covers the surface regions that are intended to be isolated from other such surface regions; forming said isolation region by oxidation of said portion of said planer silicon surface; and removing said oxidation mask structure by etching with phosphoric acid (H 3 PO 4 ) at a temperature of between about 150° and 180° C., that selectively etches silicon nitride and doped polysilicon at substantially the same rate, wherein the etching rate of said silicon nitride and doped polysilicon are closer because of said not annealing the doped polysilicon.

Claim 6

In the manufacture of very large scale integrated circuit device, a method for forming an isolation region on a portion of a planar silicon surface comprising: forming an oxidation mask structure on a silicon oxide layer, said structure consisting of a layer of doped polysilicon, said doped polysilicon having been doped by ion implanting into undoped polysilicon with an impurity with a concentration greater than about 5 E 15 atoms/cm 3 to form a doped polysilicon layer, and without annealing the doped polysilicon, over said silicon oxide and a layer of silicon nitride over said doped polysilicon layer; said mask structure covers the surface regions that are intended to be isolated from other such surface regions; forming said isolation region by oxidation of said portion of said planer silicon surface; and removing said oxidation mask structure by etching with phosphoric acid (H 3 PO 4 ) at a temperature of between about 150° and 180° C., that selectively etches silicon nitride and doped polysilicon at substantially the same rate, wherein the etching rate of said silicon nitride and doped polysilicon are closer because of said not annealing the doped polysilicon.

Claim 7

The method of claim 4 in which, said doped polysilicon layer is also present on the unmasked portions of said silicon oxide layer, wherein said thickness is less than the doped polysilicon layer which is a part of said oxidation mask structure.

Claim 8

The method of claim 5 wherein said thickness of said doped polysilicon layer in said mask structure is between about 1200 to 4000 Angstroms and the thickness of said doped polysilicon layer not part of said mask structure has a thickness of between about 1000 to 3500 Angstroms.

Claim 9

The method of claim 6 wherein said phosphoric acid is comprised of a solution of water and phosphoric acid.

Claim 10

The method of claim 4 wherein said polysilicon is doped with an phosphorus impurity greater than about 1 E 19 atoms/cm 3 which have been ion implanted into undoped polysilicon.

Claim 11

The method of claim 4 wherein said polysilicon is doped with an arsenic impurity greater than about 1 E 19 atoms/cm 3 which have been ion implanted into undoped 10 polysilicon.

Claim 12

The method of claim 4 wherein said polysilicon is doped with an boron impurity greater than about 1 E 19 atoms/cm 3 which have been ion implanted into undoped polysilicon.

Claim 13

The method of claim 1 wherein said undoped polysilicon is doped with an impurity greater than about 1 E 19 atoms/cm 3 .