Impact of Organic Acid and Gas Bubbling on Copper and Copper Oxide Etch-Rates in Diluted HF Solution

Abstract

In the damascene integration scheme, copper is used as an interconnect material. In a damascene integration scheme, the etch treatment by a plasma process leads to the formation of polymer residues, copper sputtered on the dielectric side wall, copper oxidation at the bottom of the via and copper precipitates at the hard mask surface. In order to remove these impurities, a post-via etch cleaning is mandatory [1]. Several aqueous cleaning solutions constituted of diluted HF and an organic acid were tested. Diluted HF was mainly used to remove the polymer residues and the organic acid to clean the copper surface. These mixtures were already studied and compatible with several porous and dense ULK materials [1]. In this paper, the impact of organic acids and gas bubbling in diluted HF solution on copper and copper oxide-dissolution rate is presented. Firslty the copper oxide and the copper etch-rates and the roughness were obtained from the kinetics of copper dissolution determined by X-ray reflectometry characterization [3]. Secondly, speciation calculations were performed in order to explain the copper etch-rates differences as a function of the solutions and gas bubbling.