Polishing parameter dependencies and surface oxidation of chemical mechanical polishing of Al thin films

We describe chemical mechanical polishing (CMP) of blanket and patterned al uminum films employing a polyurethane pad and a slurry based on alumina par ticles as the abrasive and hydrogen peroxide as the oxidizer. The experimen ts were conducted at pressures from 19 to 47 kPa and at linear velocities f rom 26 to 48 m/min, and yielded Al removal rates from 80 to 250 nm/min. The oxidant concentration has a weak effect on the removal rate of Al. Polishi ng selectivities of Al to silicon dioxide as high as 130:1 were obtained wi th the maximum selectivities being observed at regions of low pressures and low velocities. The Preston equation fails to describe the dependence of t he removal rate on pressure and velocity, and a power function is proposed instead. X-ray photoelectron spectroscopy was used to examine the surface o f Al before and immediately after CMP. These experiments provided informati on on the thickness of the oxidized Al layer. We found that larger removal rates correlated with a smaller AU-oxide thickness. We conclude from this t hat Al CMP proceeds by oxidation of the Al and subsequent Al-oxide removal. (C) 1999 The Eleccrochemical Society. All rights reserved.