Method for forming an integrated circuit device

Abstract

The present invention advantageously provides a method for retaining a substantially transparent dielectric above alignment marks during polishing of the dielectric to ensure that the alignment marks are preserved for subsequent processing steps. According to an embodiment, alignment marks are etched into a semiconductor substrate. Thereafter, a pad oxide layer is deposited across the substrate surface, followed by the deposition of a first nitride layer. Isolation trenches which are deeper than the alignment mark trenches are formed spaced distances apart within the substrate. Optical lithography may be used to define the regions of the first nitride layer, the pad oxide layer, and the substrate to be etched. The isolation trenches thus become the only areas of the substrate not covered by the pad oxide layer and the first nitride layer. A substantially transparent dielectric, e.g., oxide, is then deposited across the semiconductor topography to a level spaced above the first nitride layer. In this manner, both the isolation trenches and the alignment mark trenches are filled. The dielectric is then subjected to a polish that removes the dielectric above the isolation trenches to the nitride layer and the dielectric above the alignment mark trenches to a level above the nitride layer. A slurryless fixed abrasive polishing technique may be used to planarize the dielectric. A polysilicon/nitride stack which is deposited across the topography may be patterned using lithography. Light is reflected from the alignment marks to detect their positions so that a reticle can be aligned to the polysilicon/nitride stack during the lithography process.