Chemical mechanical planarization of shallow trenches in semiconductor

Abstract

A new method for planarization of shallow trenches is presented. Shallow trenches are patterned into a semiconductor substrate that has been coated with a layer of silicon nitride. A conformal coating of oxide is deposited onto the wafer to fill the trenches. A thin layer of etch-stop silicon and a second layer of oxide are then deposited. The second layer of oxide is patterned with a filler mask using conventional photolithographic techniques and etched to the silicon etch-stop layer, leaving blocks of oxide in the depressions above the trenches and oxide spacers along the sidewalls. Chemical mechanical polishing is then used to polish the oxide back to the silicon nitride. The process offers excellent global planarity, minimal variation in silicon nitride thickness across active areas of varying size and density, and relative insensitivity to chip design.