The incorporation of nitrogen in silicon has been shown to retard the oxidation growth rate. The present study produced aluminum gate PMOSFETs with varied gate oxide thickness on the same chip through selective nitrogen ion implantation. The nitrogen implant dose of 4x1014 ions/cm2 at 35 keV prior to gate oxide growth reduced the oxidation rate between 10% and 60% at the oxidation schedules employed. This active area N-implant led to no degradation in electrical parameters such as gate delay, mobility, or subthreshold swing. MOSFETs with different gate oxide thicknesses allow for different threshold voltages on the same chip and increased nonminimum channel length MOSFET reliability.
"MOSFETs with Variable Gate Oxide thickness by Selective Nitrogen Ion Implantation,"
Journal of the Microelectronic Engineering Conference: Vol. 10
, Article 6.
Available at: http://scholarworks.rit.edu/ritamec/vol10/iss1/6