Overhang isolation technology

Abstract

Abstract A process for defining isolation structures between active regions of an integrated circuit is disclosed. The technique includes first forming a thermally grown silicon dioxide layer. A polysilicon layer is then deposited over the silicon dioxide layer and a silicon nitride-I layer is deposited thereon. A photo-resist mask is then formed on the top of the laminate and selective anisotropic dry etching is used to remove the unmasked silicon nitride-I and polysilicon layers. This step is followed by an isotropic dry etching to undercut the polysilicon beneath the silicon nitride-I layer. After the photo-resist masks and unmasked pad oxide are removed, a layer of silicon nitride-II is deposited. Thereafter, an anisotropic dry etching step is performed to remove the unmasked silicon nitride-II completely. An implantation step is then optionally performed. The uncovered silicon substrate is oxidized to form the isolation regions and, finally, the residual layers of silicon nitride-I, -II, polysilicon and pad oxide are removed. The silicon nitride-I and -II layers may be removed with boiling H 3 PO 4 , the polysilicon layer by using reactive-ion etching, and the pad oxide layer by using 50:1 hydrogen fluoride.

Inventors

• 👤 Fung-Ching Chao

Bibliographic Details