Method of forming MOSFET devices with heavily doped local channel stops

• Main Authors: LIN; JENGPING, CHIEN; SUNIEH
• Format: Patent
• Language: English
• Published: 21.10.1997
• Edition: 6
• Subjects: BASIC ELECTRIC ELEMENTS; ELECTRIC SOLID STATE DEVICES NOT OTHERWISE PROVIDED FOR; ELECTRICITY; SEMICONDUCTOR DEVICES

Device isolation is provided for a MOSFET circuit by providing channel stop regions comprising a distribution of dopants localized beneath and adjacent to corresponding field oxide regions. Channel stop regions are not formed under the channel regions of the MOSFETs and are selectively formed under the narrower field oxide regions which are most likely to provide inadequate device isolation. The channel stop regions are formed subsequent to the formation of field oxide regions, beginning by forming polysilicon spacers so that the polysilicon spacers extend over the bird's beak regions of the field oxide regions. Next, a channel stop mask having openings over selected field oxide regions is formed. Trenches are etched near the center of the exposed field oxide regions, leaving approximately 500 ANGSTROM of oxide on the bottom of the trench. Ions are implanted through the bottom of the trenches to form channel stop regions beneath the field oxide regions.