Composite metal and polysilicon field plate structure for high voltage semiconductor devices

Claim 1

A semiconductor device having a composite field plate; said semiconductor device comprising a body of semiconductor material having at least a first generally flat surface; at least one P-N junction formed in said first surface and terminating on said first surface wherein said first surface is P type on one side of said P-N junction and N type on the other side of said P-N junction; a first insulation layer on said first surface and extending over at least a part of said P-N junction; a layer of polysilicon of relatively high conductivity having a first body portion galvanically connected to said first surface on only one of said sides of said P-N junction; said layer of polysilicon having a second body portion continuous with said first portion, which said second portion is stepped up from said first surface and overlies and is supported by the upper surface of said first insulation layer; said second body portion terminating on an edge; a second insulation layer extending from an edge overlying said first body portion of said layer of polysilicon and extending to and overlying at least portions of said second body portion of said layer of polysilicon and extending across said edge of said layer of polysilicon; and a contact metal layer overlying said layer of polysilicon and overlying said second insulation layer and extending beyond said edge of said polysilicon; said composite polysilicon and said contact metal layer in surface-to-surface contact with one another only in areas on one side of said edge of said second insulation layer to define a double stepped field plate extending beyond the region of galvanic contact to said first surface by said polysilicon to reduce the curvature of the electric field equipotential lines within said body of semiconductor material during reverse bias of said P-N junction.