Planar multi-level metal process with built-in etch stop

Claim 1

In the fabrication of an integrated circuit package comprised of a substrate having a conductive interconnected pattern on a surface thereof, the method of forming superposed levels of metallurgy comprising: (A) forming a first layer of an electrically insulating polymer on said surface, (B) coating said first layer with a second layer of silicon nitride, (C) coating said second layer with a third layer of a polymer that is selectively soluble in a solvent substantially inert to the first said polymer, (D) coating said third layer with a fourth layer resistant to reactive ion etching in oxygen, (E) forming on said fourth layer a resist mask defining at least one via opening to a portion of said conductive pattern, (F) reactive ion etching in an ambient comprised of CF 4 the exposed portion of said fourth layer in said via opening, (G) reactive ion etching in am ambient comprised of O 2 the exposed portions of said third layer in said via opening, (H) reactive ion etching in an ambient comprised of CF 4 the exposed portions of said silicon nitride in said via opening, (I) reactive ion etching in an ambient comprised of O 2 the exposed portion of said first layer in said via opening to expose said portion of said conductive pattern, (J) blanket coating said substrate inclusive of said via opening with a conductive metal layer having a thickness substantially matching the thickness of said first layer, (K) exposing said substrate to said solvent for a time sufficient to remove said third layer and all overlying layers thereon, to expose said silicon nitride second layer and said deposited metal via-connection in said via opening, (L) sequentially coating said silicon nitride second layer with fifth, sixth and seventh layers of, corresponding, respectively to the compositions of said first, third and fourth layers, (M) forming a second resist mask having openings corresponding to desired metallurgy patterns to be deposited on said silicon nitride second layer, said opening encompassing said via connector and adjacent discrete portions of said silicon nitride second layer, (N) reactive ion etching in an ambient comprised of CF 4 the exposed portions of said seventh layer in the openings of said second resist mask, (O) sequentially reactive ion etching in an ambient comprised of O 2 said sixth layer and said fifth layers in the opening of said second resist mask, to expose said via connector and adjacent portions of said silicon nitride second layer, (P) depositing a blanket coating of a conductive metal over said substrate inclusive of said via connector and said adjacent exposed portion of said silicon nitride second layer, (Q) exposing said substrate to a solvent selective to the sixth layer for a time sufficient to remove said sixth layer and all overlying layers thereon.