Highly selective silicon oxide/silicon nitride etching by selective boron nitride or aluminum nitride deposition

A substrate processing method, comprising:

• providing a substrate containing a silicon oxide film and a silicon nitride film;
• a1) exposing the substrate to a BCl3 gas that forms a first BCl3 layer on the silicon oxide film and a second BCl3 layer on the silicon nitride film;
• a2) exposing the substrate to NH3 gas that reacts with the first BCl3 layer to form a first boron nitride layer on the silicon oxide film and reacts with the second BCl3 layer to form a second boron nitride layer on the silicon nitride film, wherein a thickness of the second boron nitride layer is greater than a thickness of the first boron nitride layer;
• and
• a3) exposing the substrate to plasma-excited CF4 gas that etches the first boron nitride layer and the silicon oxide film, wherein the second boron nitride layer protects the silicon nitride film from etching by the plasma-excited CF4 gas.

A substrate processing method, comprising:

• providing a substrate containing a silicon oxide film and a silicon nitride film;
• a1) exposing the substrate to a boron-containing gas that forms a boron-containing layer that is thicker on the silicon nitride film than on the silicon oxide film;
• a2) exposing the substrate to a nitrogen-containing gas that reacts with the boron-containing layer to form a boron nitride layer that is thicker on the silicon nitride film than on the silicon oxide film;
• and
• a3) exposing the substrate to an etching gas that etches the boron nitride layer on the silicon oxide film and the silicon oxide film, wherein the boron nitride layer protects the silicon nitride film from etching by the etching gas.