Method of forming a narrow self-aligned, annular opening in a masking layer

Abstract

A process for forming within a masking layer a self-aligned annular opening having a width that is substantially narrower than the space width that can be created directly using the maximum resolution of available photolithography. The process involves the following steps: creation of a mask island using conventional photomasking and etching techniques, the perimeter of said island defining the inner perimeter of the perimetric annular opening; blanket deposition of a spacer layer, the thickness of which is equal to the desired width of the annular opening; a blanket deposition of a thick protective layer that is independently etchable over the spacer layer; planarization of the protection layer to or below the top of the spacer layer; and isotropically etching the exposed spacer layer to form a narrow annular opening exposing the substrate. At this point the exposed substrate may be trenched in order to isolate the area definedd by the island, or it may be fabricated in some other configuration. This method of forming an annular opening within a mask region results in a narrow annular opening that is self-aligned with the mask island and the non-etched spacer layer. Subsequent trench fabrication has the self-alignment features of the narrow annular opening. Both the position and width of the narrow annular opening, and therefore the trench, are highly predictable and the method requires minimum masking steps. The narrowness of the annular opening also maximizes die space.

Dependencies are inferred from the claim text.