Analyses of post metal etch cleaning in downstream H2O-based plasma followed by a wet chemistry

The evolution of surface chemical species on etched Al (Cu) lines and films has been investigated by X-ray photoelectron spectroscopy in a postetch cl eaning process, with the aim of understanding the role of each step on the removal of the etching residues. The results from the in situ strip in down stream H2O plasma show that most of the organic species are removed by oxid ation reactions, together with the majority of the Cl species. However, the sidewall polymer leaves a Cl-containing residual film due to its high meta llic content and oxidation reactions. Adding a small amount of CF4 to the H 2O plasma can have some advantages mainly making the residues more water so luble. Further ex sial wet chemical treatment is needed to remove the oxide /fluoride layer formed in the in situ step. Tt is argued that a clean surfa ce, consisting of Al bonded strongly to its native oxide, is essential to t he reliability of the interconnect. It is also found that after dry etching there are two kinds of Cu species present at the Al surface layers. One is a CuClx residue, which can be removed effectively by the cleaning. The oth er is elemental Cu enrichment. Rutherford backscattering spectrometry resul ts reveal that this enrichment distributes over a depth of about 40 nm in A l, with a peak concentration of two to three times the bulk value. (C) 1999 The Electrochemical Society. S0013-4651(99)03-014-1. All rights reserved.