POLYSILICON ENCAPSULATED LOCAL OXIDATION

Many different advanced isolation techniques have been suggested for the reduction of lateral oxidation of silicon (LOCOS). These advanced isolations often involve numerous additional steps requiring new deposition and etch processes. Polysilicon encapsulated local oxidation (PELOX) is proposed as an effective isolation technique that satisfies advanced device requirements without any difficult-to-control structures or processes. Simple modifications to a standard LOCOS process flow minimize encroachment without introducing defects. These modifications include an HF dip after nitride patterning to form a cavity self-aligned to the nitride edge, reoxidation of exposed silicon, and polysilicon deposition to fill the cavity. Physical (scanning electron micrographs) and electrical (gate oxide quality, diode integrity, and W(eff)) data are presented which indicate that cavity reoxidation is critical to obtaining significant bird's beak reduction without defect introduction.