PUNCHTHROUGH CURRENTS IN SUBMICRON SHORT-CHANNEL MOS-TRANSISTORS

The punchthrough current in sub-micron MOS transistors is essentially initiated at the surface near the edge of source junction. A surface d iffusion current (I-sdif) originates from the injection of minority ca rriers from the source junction due to the combined effect of drain-in duced-barrier-lowering (DIBL) and surface-band-bending (Delta phi(50)) . The DIBL effect increases with decreasing channel length. In additio n, the extracted Delta phi(50) from the punchthrough current indicates that surface space charges at the source edge shift from the accumula tion/depletion mode for long sub-micron devices (approximate to 0.62 m u m) to the strong-inversion mode for deep sub-micron devices (approxi mate to 0.12 mu m). For intermediate sub-micron devices (approximate t o 0.37 mu m), I-sdif eventually converts to the bulk space-charge-limi ted current (I-scl) as the connected source/drain depletion region exp ands with increasing drain bias. For long sub-micron devices only I-sd if dominates, while for deep sub-micron devices it converts rapidly to I-scl in the bulk depletion regions over the drain bias range investi gated. (C) 1997 Elsevier Science Ltd.