Reverse Shallow Trench Isolation Process

Abstract

A method of polishing a substrate surface containing silicon nitride and silicon oxide or silicon dioxide, comprising movably contacting the surface with a polishing pad and having a polishing composition disposed between the polishing pad and the surface, said polishing composition comprising 1) hydrous ceria abrasive; 2) polyvinylpyridine, vinyl pyridine copolymers, or both, and 3) water, wherein at 2 psi downpressure the silicon nitride removal rate is at least 500 angstroms per minute and the selectivity of silicon nitride to silicon oxide is at least 30.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This patent application claims the benefit of U.S. Provisional Patent Application Ser. No. 60 / 956,232 filed 16 Aug. 2007.BACKGROUND OF THE INVENTION[0002]The present invention is directed to a process of making a shallow-trench-isolation type structure comprising polishing a silicon nitride layer disposed over a silicon dioxide or silicon oxide film formed for example from tetraethoxysilane (TEOS) or plasma enhanced tetraethoxysilane (PETEOS) using an aqueous chemical mechanical planarization slurry comprising, or alternatively consisting essentially of or consisting of: 1) hydrous (not calcined) ceria abrasive; 2) an effective amount of vinyl pyridine polymers and / or copolymers, e.g., poly(4-vinylpyridine), poly(4-vinylpyridine co-styrene), or mixture thereof; and 3) a pH adjusting agent which is advantageously an alkyl ammonium hydroxide.[0003]Classical shallow trench isolation (STI) is a well-known method in the fabrication of IC chips...

AI Technical Summary

Benefits of technology

[0008]The invention includes the use of poly(4-vinylpyridine) and poly(4-vinyl pyridine co-styrene) for suppressing the TEOS rate with no effect on the removal rate of silicon nitride. Hence poly(4-vinylpyridine) and copolymers of 4-vinylpyridine such as poly 4-vinyl pyridine co-polystyrene are selective with respect to silicon nitride with complete suppression of oxide removal rate. The homopolymer and copolymer offer different protection profiles, and a polishing composition most preferably has both poly(4-vinylpyridine) and one or more copolymers of 4-vinylpyridine such as poly(4-vinyl pyridine co-styrene). However, the invention has additional improvements on the art. The invention is robust such that while removal rates are tunable the amount of material needed to affect tenability is sufficiently large (a difference of at least 50 ppm from high silicon nitride to silicon oxide selectivity to low silicon nitride to silicon selectivity) and the composition provides high polishing rates with low downpressure. While the system allows excellent tenability over a considerable range, advantageously the silicon nitride to silicon oxide selectivity is preferably at least 30, more preferably at least 35, most preferably at least 40. At pH 3.9 to 4.1, the selectivity of silicon nitride to silicon oxide can exceed 40, and can even be made to exceed 60 or 80. At such high selectivities, the small protruding silicon oxide layer remaining after STI will not be damaged, and can be made thinner than would be possible if the slurry had a selectivity of 25 or less, especially 10 or less. At the same time, advantageously, by only changing the amount of vinyl pyridine-based polymers, the selectivity of silicon nitride to silicon oxide can be made equal to 1 (0.8 to 1.2, preferably 0.9 to 1.1). This allows use of the base slurry in a variety of manufacturing variants where a slurry that always polishes silicon nitride at rates greater than silicon oxide can not be used.

[0009]The polishing composition advantageously comprises, consists essentially of, or consists of: A) about 0.05% to 2%, preferably 0.2% to 1%, by weight of hydrous ceria; B) about 10 to 1000, preferably about 20 to about 600, more than 50 to about 300 ppm, or 60 to 200 ppm, or 80 to 150 ppm, of one or more of poly(4-vinylpyridine), a polymer made from monomers consisting essentially of 4-vinylpyridine, poly(4-vinylpyridine co-styrene), other 4-vinylpyridine-based copolymers, or mixture thereof; C) a carrier which is preferably high purity water; D) optionally a pH adjuster, preferably a halide-free ammonium-based compound such as an tetra-alkyl ammonium compound, to adjust the pH between 3.5 and 4.5, preferably between 3.8 and 4.2, if necessary; and E) optionally between 5 and 500 ppm of nonionic surfactants including for example Zonyl FSJ® (10 to 1000 ppm) and Zonyl FSN® (5 to 50 ppm) to reduce defect counts and increase slurry stability.

Problems solved by technology

Disadvantageously, during planarization, an excess amount of the trench fill tends to be removed, resulting in the top of the trench fill being “dished” in the middle; i.e., lower than the top of the trench.

This condition complicates subsequent processing, thereby lowering manufacturing yield and increasing production costs.

Even moderately selective polishing compositions, having a selectivity of between 4 and 25, more typically between 6 and 12, will result in considerable erosion of the protruding oxide.

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