Abstract: A method is provided for forming a self aligned contact by etching an opening through a low doped or undoped dielectric layer such as phosphosilicate glass. The dielectric layer may be formed on a semiconductor layer which may include regions of monocrystalline silicon and undoped silicon dioxide. A first portion of a dielectric layer may be etched with a first etch chemistry, and a second portion of the dielectric layer may be etched with a second etch chemistry. The first etch chemistry may be substantially different than the second etch chemistry. In this manner, the first etch chemistry may have a substantially different etch selectivity than the second etch chemistry. For example, in an embodiment, the first etch chemistry may be selective to silicon nitride, and the second etch chemistry may be selective to undoped silicon oxide.

Abstract: A method for etching a dielectric layer formed upon a barrier layer with an etch chemistry including CxHyFz, in which x≧2, y≧2, and z≧2 is provided. Such an etch chemistry may be selective to the barrier layer. For example, the etch chemistry may have a dielectric layer:barrier layer selectivity of at least approximately 20:1, but may range from approximately 20:1 to approximately 50:1. Therefore, etching a dielectric layer with such an etch chemistry may terminate upon exposing an upper surface of the barrier layer. As such, a thickness of a barrier layer used to protect an underlying layer may be reduced to, for example, approximately 100 angstroms to approximately 150 angstroms. In addition, critical dimensions of contact openings formed with such an etch chemistry may be substantially uniform across a wafer. Furthermore, critical dimensions of contact openings formed with such an etch chemistry may be uniform from wafer to wafer.