Mechanism of Cu oxidation in ashing process

Abstract

Because Cu is easily oxidized and its oxidation reaction proceeds without stopping, the oxygen ashing process causes unacceptable oxidation of the Cu surface. We investigated the chemical state and morphology of the Cu surface after the oxygen ashing process using x-ray photoelectron spectroscopy∕Auger electron spectroscopy and scanning electron microscopy, and then considered the oxidation mechanism of the Cu surface under the oxygen downstream and the oxygen reactive ion etch (RIE) ashing processes in the substrate temperature range of 35 °C to 260 °C. The Cu surface treated by an oxygen RIE ashing process at temperatures below 150 °C was found to have chiefly CuO bonds, whereas the Cu surface treated by the oxygen downstream ashing process consisted mostly of Cu2O bonds. The oxidized Cu thickness after the oxygen downstream process was thicker than that formed by the oxygen RIE ashing process. The Cu surface treated with the oxygen RIE ashing process at under 150 °C is less prone to oxidization because the Cu surface with CuO formation has a smooth surface that suppresses further oxidation.