A Strategic Approach to Environmentally Benign Chemical Mechanical Planarization Slurries for Advanced Cu Interconnect Applications
Thi Thuy Hoang Tran
Chemical mechanical planarization (CMP) is an integral part of semiconductor processing including the back-end-of-line (BEOL) step. A goal of CMP is to uniformly polish the metal interconnects and the liner/barrier materials while minimizing CMP-related defects such as pitting, dissolution, and galvanic corrosion. A variety of azoles are used as corrosion inhibitors such as benzotriazole (BTA) to prevent corrosion defects during polishing. These azoles work together with particles in the slurries to polish the overplated metal forming the interconnects. Spent slurries, however, pose an environmental hazard as the azole corrosion inhibitors do not readily degrade in conventional wastewater treatment processes. Also, it is known that the use of BTA leads to contamination of Cu films by forming undesirable hydrophobic organic residues (e.g., BTA and Cu-BTA complexes), making their removal very difficult during cleaning. To address these challenges aliphatic amino acids were examined as potential corrosion inhibitors to replace problematic azoles in CMP slurries.
The main objective of the research is to use more benign and easily treatable corrosion inhibitors for environmentally benign Cu CMP slurries when Co films are used as liners. The influence of three aliphatic amino acids: L-methionine, L-glutamic acid and L-leucine on Cu corrosion resistance, galvanic corrosion of Cu in contact with Co, Cu removal rates during polishing, and oxide passivation was assessed. Open circuit potential and linear sweep voltammetry were used to determine the corrosion characteristics. These parameters were determined during polishing and compared to a BTA electrolyte; and the Cu and Co removal rates in polishing experiments conducted on a polisher. A representative polishing slurry contained 35 nm colloidal silica abrasives, 1 wt% H2O2 as an oxidizer, and 10 mM amino acid at pH 8. Surface oxides were determined by X-ray photoelectron spectroscopy and morphology was examined by electron microscopy. The degradation of the amino acid-based polishing slurry was assessed to evaluate the ease of degradation of a spent slurry. A Fenton-based advanced oxidation process with post-analysis techniques was used to determine whether the amino acids could be degraded more easily compared to BTA. The degradation of methionine and leucine was considerably greater than that of BTA, with degraded products found by mass spectroscopy.
Keywords: Semiconductor, CMP, Slurry, Sustainability, Green corrosion inhibitors.
Monday, 10/21/2024 at 4:30 pm CAMP176
Hoang Tran is currently a 3rd year Ph.D. candidate who joined the Department of Chemical Engineering at Clarkson University in the spring of 2022 and is being advised by Prof. J. Seo and co-advised by Prof. Podlaha- Murphy. Her primary research area involves the development of environmentally friendly CMP slurries for metals.