Self-aligned twin well process having a SiO2 -polysilicon-SiO2 barrier mask

Abstract

Abstract A method is provided for forming planar, self aligned wells without a high temperature oxidation step to form an ion barrier. The method comprises preparing a substrate with a silicon dioxide-polysilicon-silicon dioxide barrier layer that can be etched to expose different sublayers of the barrier at selected junctures in the production process. A single masking step defines the location of a first set of wells on the prepared substrate. The outer silicon dioxide layer is etched to expose the polysilicon layer at the selected locations, and the substrate is implanted with boron ions to form the first set of wells. Following ion implantation, the substrate photo-resist is removed, and the substrate is exposed to a germanium-silicon mixture under conditions selected to preferentially deposit a germanium-silicon alloy barrier layer on the exposed polysilicon layer. The germanium-silicon alloy masks the first set of doped wells against subsequent etching and an ion implantation step that forms the second set of doped wells. Since the locations at which the germanium-silicon alloy deposits are defined by the locations of the first set of wells, the second set of wells is automatically aligned with respect to the first set of wells.

Inventors

• 👤 Ashok K. Kapoor

Bibliographic Details