Patent ID: 6551937
Filing Date: 2003-04-22
Classification: H01L

Abstract:
A process for forming a buried oxide layer, comprising:providing a silicon body having an upper surface and forming thereon a first layer of silicon oxide; on said first layer of silicon oxide depositing a first layer of silicon nitride; on said first layer of silicon nitride depositing a second layer of silicon oxide; patterning said second layer of silicon oxide to define at least two trenches and then, using said patterned second layer of silicon oxide as a hand mask, etching said layer of silicon nitride, said first layer of silicon oxide, and said silicon body to a first depth below said upper surface, thereby forming at (east two first trenches; depositing on all exposed surfaces a two-layer laminate that further comprises a third layer of silicon oxide on a second layer of silicon nitride; selectively removing said two-layer laminate from all horizontal surfaces; using said patterned second layer of silicon oxide and said two-layer laminate as a hard mask, fetching said silicon body to a second depth below said upper surface, thereby forming at least two second trenches having sidewalls; thermally oxidizing all exposed silicon surfaces until oxide layers growing both inwards and outwards from said sidewalls meet, thereby forming a continuous layer of silicon oxide below said first trenches and parallel to said upper surface; removing said two layer laminate; then overfilling said first trenches with polysilicon; using said patterned second layer of silicon oxide as a hard mask, using a planarizing etch to remove all polysilicon that is on said hard mask and then overetching until said polysilicon and said upper surface are co-planar; and then removing said hard mask.