Ion implant of the moat encroachment region of a locos field isolation

Abstract

A method of forming a semiconductor device and the device, the method comprising the steps of providing a silicon substrate of predetermined conductivity type having a layer of silicon oxide with a first mask thereon, implanting a first impurity of the predetermined conductivity type into the substrate in unmasked regions of the substrate, masking the substrate except for a small region immediately adjacent the first mask with a second mask, implanting a second impurity of the predetermined conductivity type into the substrate in the unmasked regions of the substrate to cause some of the impurity to extend in the substrate beneath the first mask, removing the second mask, oxidizing the substrate with the first mask thereon to form a bird's beak extending beneath the first mask with the impurities extending along the bird's beak both beneath and external to the first mask and completing fabrication of a semiconductor device on substrate. The device is a semiconductor device having a silicon substrate of predetermined conductivity type with a semiconductor device structure therein, and a bird's beak region on the substrate wherein the substrate has a higher level of impurity of the predetermined conductivity type along and directly beneath the bird's beak region than in the bulk of the substrate.