Suppression of parasitic BJT Gain in BCD Power ICs Using Metal-Schottky Barrier MOS

The optimization of a metal-Schottky source-drain NMOS structure and it’s underlying parasitic lateral BJT has been performed on a 0.18 um feature size BCD power IC process. The metal-Schottky structure is fabricated using an ultra-shallow ion implantation which is capable of modifying the barrier height without the need for introduction of non-standard metal systems into the CMOS fab.

By substituting Schottky source/drain contacts for PN junctions and properly adjusting the barrier height of the Schottky-type contact, minority injection from the source can be dramatically reduced while still maintaining good ohmic contact to the MOSFET inversion layer. This reduces the gain of the parasitic n-p-n transistor by up to two orders of magnitude and thus will reduce susceptibility to latch-up while still maintaining high NMOS drive currents.