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...

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 process...

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