Evaluation of Copper Oxide to Copper Selectivity of Chemical Systems for BEOL Cleaning Through Electrochemical Investiga
- PDF / 139,908 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 38 Downloads / 200 Views
0990-B08-25
Evaluation of Copper Oxide to Copper Selectivity of Chemical Systems for BEOL Cleaning Through Electrochemical Investigations Nandini Venkataraman, Ashok Kumar Muthukumaran, and Srini Raghavan Materials Science and Engineering, The University of Arizona, Tucson, AZ, 85721 ABSTRACT Back End of Line (BEOL) cleaning of copper based structures requires chemical formulations that can remove copper oxide selectively without corroding copper and etching the dielectric. Many commercially available semi-aqueous and all aqueous formulations claim to meet these criteria. These include semi-aqueous fluoride strippers (SAF) and all- aqueous ammonium phosphate based chemical systems. This paper will report the results from a fundamental study undertaken to evaluate the performance of a semi-aqueous fluoride formulation in removing copper oxide films of controlled thickness grown on copper. The thickness and composition of the oxide films were determined electrochemically using cathodic reduction technique. Electrochemical Impedance spectra of samples immersed in the formulation have been measured as a function of time to follow copper oxide dissolution and the data have been analyzed to detect the transition of copper oxide to copper. Keywords: BEOL cleaning, Copper oxide removal, electrochemical impedance spectroscopy INTRODUCTION The process of fabrication of copper interconnect structures in a matrix of low-k materials involves many cleaning steps. In order to create vias and trenches for the formation of dual damascene structures, plasma etching of the dielectric is done and this process typically leaves post etch residue(PER) on the sidewalls and the bottom of the copper lines. A significant portion of the PER include oxides of copper, which need to be removed from narrow, high aspect ratio features[1]. Cleaning chemistries need to exhibit a high degree of selectivity in removing copper oxide over the underlying copper and on dielectric sidewalls. In addition, they should also leave the dielectric constant of the low k dielectric material unaltered. Several semi-aqueous fluoride based chemistries (SAF) have been developed commercially to meet this end, where the fluoride component functions as the active ingredient in removing copper oxide [2, 3]. SAF chemistries typically contain an organic solvent, a fluoride component and some amount of water. Some of the organic solvents used in these formulations include dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAC), N-methyl pyrrolidone (NMP) and ethanolamine. The fluoride component is typically an inorganic fluoride such as HF, NH4F or H2SiF6. These chemistries have the advantage of working at ambient temperature conditions and in short duration cycles. Due to the industry drive to reduce the use of organic solvents, some all-aqueous chemical systems based on ammonium phosphate[4] as well organic acids such as citric acid, oxalic acid, acetic acid etc. have also been developed [5, 6]. Due to the proprietary
nature of many of these formulations, their mechanism of
Data Loading...
