LATERALLY SEALED LOCOS ISOLATION

A novel method of oxide isolation is proposed for VLSI to improve LOCOS. The purpose is to reduce the characteristic LOCOS bird's beak without introducing electrically active edge defects in silicon. As in SWAMI, a nitride sidewall spacer is used to block lateral oxygen diffusion under the active area perimeter. However, with the new method, the spacer is not formed over the sidewalls of a silicon mesa. Instead, a sacrificial oxide layer is deposited over the LOCOS nitride/oxide stack and patterned simultaneously to provide the vertical support for the spacer. Since the spacer is not embedded in silicon, the opportunity for defect generation is reduced and the manufacturability is improved with the elimination of the mesa silicon etch.