Nitridation on HDP oxide before high-k deposition to prevent oxygen ingress

1. A method of reducing a migration of oxygen into a high-k dielectric layer of a semiconducting device, comprising:

forming a substrate;

forming dummy gates on the substrate, the dummy gates separated by at least one first gap;

depositing a flowable oxide into the at least one first gap to form an oxide layer of the semiconducting device on the substrate;

altering a chemical composition of a top portion of the oxide layer by diffusing nitrogen into the top portion;

removing the dummy gates to define at least one second gap;

depositing the high-k dielectric layer on the top portion of the oxide layer and the at least one second gap to form the semiconducting device, wherein the altered chemical composition of the top portion of the oxide layer reduces migration of oxygen into the high-k dielectric layer and diffuses nitrogen into the top portion of the oxide layer;

depositing a titanium nitride layer on the high-k dielectric layer;

depositing a low resistivity metal into the at least one second gap; and

annealing the semiconductor device, wherein the top portion of the oxide layer prevents migration of oxygen from the oxide layer into the high-k dielectric layer during the annealing.