Mosfet fabrication using ion beam nitridation

Abstract

Ion beam nitridation has been suggested as an alternative to the conventional local oxidation process which is used in the fabrication of most metal-oxide-semiconductor (MOS) integrated circuits. The implantation of 2 keV nitrogen ions in doses of up to 8 x 10¹⁷ cm^-2 results in the formation of a silicon nitride layer approximately 10 nm thick. Herein we describe the electrical characteristics of n-channel silicon gate metal-oxide-semiconductor-field-effect-transistors (MOSFETs) fabricated using this modified local oxidation process, and compare them to devices fabricated simultaneously but using the conventional local oxidation technology. The effective device channel lengths and widths are determined from the electrical characteristics of devices with mask (ideal) dimensions of 4, 6, 8 or 10 μm. The ion beam nitrided devices exhibit a significant reduction in the lateral oxidation effect. A 1.3 μm increase in channel width relative to conventional processing is observed for the ion beam nitrided devices with a 690 mm thick field oxide. On the other hand, fixed oxide charge densities are found to increase by a factor of about two due to the nitrogen implantation, and device channel mobilities are reduced by about 25%.