MOSFET scaling limits determined by subthreshold conduction

The formulation and solution of the equations governing transistor subthreshold behavior in explicit analytical form provide quantitative predictions for minimum feature length as well as immediate information on the relative importance of all major transistor fabrication parameters. Such a formulation and a solution for subthreshold conduction are presented. The importance of gate oxide thickness, channel impurity concentration, source-drain junction depth, and applied potentials are examined. The results suggest that successful advanced process development programs must devise methods for ultrashallow (<100 Å) source-drain junction formation and ultrathin (<50 Å) gate insulators. With vanishingly small (<50 Å) junction depth, a 30 Å gate oxide dielectric and a channel acceptor concentration of 2×10¹⁸ per cubic centimeter, one can achieve acceptably low subthreshold conduction at effective channel lengths down to 0.06 μm at an operating temperature of 300 K