Method of forming a buried interconnect on a semiconductor on insulator wafer and a device including a buried interconnect

Abstract

A buried interconnect can be incorporated into the starting semiconductor on insulator wafer during the early stages of the circuit fabrication process flow for use with semiconductor devices. The buried interconnect provides an additional interconnect layer enabling an overall reduction in the silicon real estate occupied by interconnections. The buried interconnect has low resistance and can prevent the formation of unwanted PN junctions through the use of silicides. The buried interconnect and its fabrication method include an S0I wafer that has an oxidation layer formed on top of a semiconductor layer by oxidation, followed by an nitride layer formed on top of the oxide layer which then is selectively etched to form two trenches with regions of different depths. Some regions of the trenches are etched to remove all of the semiconductor layer in the trench to expose the buried oxide layer. In other regions, a thin layer of semiconductor is left at the bottom of the trenches. Next, all of the exposed surfaces of the trenches are oxidized and the oxide at the trench bottom is removed to expose the underlying semiconductor material. The underlying semiconductor material is then silicided to form a buried interconnect. The wafer, including the trenches, is subsequently covered with oxide and chemical-mechanical polishing is used to remove excess oxide outside the trenches.