The influence of chemical treatments on tungsten films found in integrated circuits

The influence of four different chemical solutions on the composition, morphology, and etch rates of thin, chemically vapor deposited tungsten films have been investigated. These films are the standard material patterned to create tungsten plugs in integrated circuits through a chemical mechanical planarization (CMP) step. The tungsten films were treated with aqueous solutions of KOH, KIO3+NaOH, H2O2+NH4OH, and H2O2+HCl. We have evaluated the resulting changes in the surface chemical composition of the tungsten film with X-ray photoelectron spectroscopy (XPS). Changes in film morphology have been recorded with atomic force microscopy and material removal rates have been determined with calibrated four-point-probe resistivity measurements. Together, these measurements demonstrate the complex manner in which chemical pre-treatments in the CMP process influence thin tungsten films.