A novel, borderless metal-to-diffusion contact technique

Abstract

This paper describes a borderless contact process from metal to polysilicon and diffusion regions using a unique, three-step reactive ion etch (RIE) being used on IBM's advanced semiconductor logic products at its Microelectronics Division manufacturing facility in Essex Junction, Vermont. Borderless contacts to polysilicon and diffusion allow metalization to partially spread to adjacent oxide spacer and oxide isolation regions with no adverse effects. A fast, nonselective etch begins the process by removing 8% phosphosilicate oxide (PSG) quickly for high wafer throughput. This is followed by a PSG etch that is nonselective to a nitride etch-stop layer. Optical emission at 387 nm from a nitride radical is used to endpoint this selective etch. Finally, a timed, in-situ nitride removal step opens up both polysilicon and diffusion features for metal deposition. The process window is grossly defined by over- and under-etching, resulting in junction leakage and contact opens, respectively. We will show how to predict the process window based on PSG/nitride etch rate selectivity, film thicknesses and the topography.