Structures and methods for low-k or ultra low-k interlayer dielectric pattern transfer

Abstract

The present invention relates to improved methods and structures for forming interconnect patterns in low-k or ultra low-k (i.e., having a dielectric constant ranging from about 1.5 to about 3.5) interlevel dielectric (ILD) materials. Specifically, reduced lithographic critical dimensions (CDs) (i.e., in comparison with target CDs) are initially used for forming a patterned resist layer with an increased thickness, which in turn allows use of a simple hard mask stack comprising a lower nitride mask layer and an upper oxide mask layer for subsequent pattern transfer. The hard mask stack is next patterned by a first reactive ion etching (RIE) process using an oxygen-containing chemistry to form hard mask openings with restored CDs that are substantially the same as the target CDs. The ILD materials are then patterned by a second RIE process using a nitrogen-containing chemistry to form the interconnect pattern with the target CDs.