Novel shallow trench isolation method for reducing oxide thickness variations at different pattern densities

摘要

A method of reducing oxide thickness variations in a STI pattern that includes both a dense trench array and a wide trench is described. A first HDP CVD step with a deposition/sputter (D/S) ratio of 9.5 is used to deposit a dielectric layer with a thickness that is 120 to 130% of the shallow trench depth. An etch back is performed in the same CVD chamber with NF₃, SiF₄ or NF₃ and SiF₄ to remove about 40 to 50% of the initial dielectric layer. A second HDP CVD step with a D/S ratio of 16 deposits an additional thickness of dielectric layer to a level that is slightly higher than after the first deposition. The etch back and second deposition form a smoother dielectric layer surface which enables a subsequent planarization step to provide filled STI features with a minimal amount of dishing in wide trenches.