Chemical and electrical characterization of the interaction of BCl3/Cl2 etching and CF4/H2O stripping plasmas with aluminum surfaces

In this work, the effect of BCl3/Cl-2 etching and CF4/H2O stripping plasmas on Al surfaces during patterning is investigated. The purpose is to consider the direct impact of plasma exposure on the intrinsic electrical properties of the interconnect in terms of its effectively conductive cross section. First, the origin of the plasma-transformed sidewall area is clarified. It is demonstrated by X-ray photoelectron spectroscopy that after the final dry stripping sequence, the Al sidewalls are transformed into AlFx or Al(FO)(x) due to the chemical interaction with the CF4 plasma, which degrades their metallic, conductive nature. The actual dimension of the plasma-affected region is then quantified electrically to be in the order of 20 nm and is found to increase with decreasing BCl3/Cl-2 ratio. The latter indicates that it is the structural integrity of the protecting sidewall polymer formed during the etching process which controls the degree of interaction between the interconnect sidewall and the subsequent stripping plasma. Since the CF4 plasma interaction seriously degrades the electrical performance of an Al interconnect by reducing its effective conductive area, care should be taken in general that while optimizing a plasma-stripping sequence, both stripping efficiency and sidewall interaction are considered. (C) 1999 The Electrochemical Society. S0013-4651 (99)02-043-1. All rights reserved.