An Innovative Low-Azole Metal Hard Mask Etchant with an Environmentally Sustainable Cu/Co Integration Scheme
ABSTRACT
In advanced BEOL manufacturing at the Sub-14 nm node, copper interconnects are patterned using a Trench First Metal Hard Mask (TFMHM) scheme for high-precision feature definition. A TiN hard mask protects low-k dielectrics from plasma etch damage at trench sidewalls. Post-etch TiN residues are removed using H2O2-based wet cleaning solutions. CVD TiN serves as a diffusion barrier between the dielectric and liner, ensuring interconnect integrity. A major challenge is maintaining high etch selectivity without damaging adjacent Cu, Co, and ILD films. The wet etch chemistry must suppress Cu and Co oxidation, maintain low-k compatibility, and control galvanic corrosion arising from Cu–Co contact while limiting Cu/Co loss below 10 Å/min to maintain the selectivity ratio of 1:1. Inhibitors such as BTA are common azole compounds, but azole-free alternatives are increasingly being adopted to improve sustainability and compatibility with advanced integration processes. This research addresses the need for effective Cu protection while minimizing the drawbacks associated with conventional azole inhibitors.
The goal of this research is to focus on protecting Cu/Co during metal hard mask stripping by primarily using azole-free inhibitors, while limiting azole compounds to only trace amounts. Both Cu and Co were tested in solutions containing a mixture (Chemical:H2O2 = 1:9) under
dynamic conditions at 55 °C for 5 min. The Cu/Co etch rate was quantified by ICP-MS, while surface wettability and morphology were evaluated using contact angle measurements and FESEM, respectively. The results showed that effective Cu protection during metal hard mask
stripping was achieved using a low-azole inhibitor approach. Trace amounts of azole, combined with azole-free inhibitors, significantly reduced Cu dissolution and suppressed surface oxidation in H2O2-based solutions, as observed with the azole-free inhibitor. The resulting chemistry maintains low Cu/Co by maintaining the selectivity ratio of 1:1, which is compatible with advanced BEOL integration. This low-azole approach offers a cleaner and more sustainable direction for future wet processing.
BIOGRAPHY
Soonmin Lee is an M.S. student in the Department of Materials Science and Chemical Engineering at Hanyang University (ERICA), Republic of Korea, under the supervision of Prof. Jin-Goo Park. Her research focuses on semiconductor post-etch cleaning processes, particularly azole-free corrosion inhibitor systems and peroxide-based cleaning formulations designed to mitigate metal corrosion while maintaining effective removal of residues and metal hard mask byproducts. She has studied Cu back-end-of-line (BEOL) interconnect structures and evaluated cleaning selectivity and metal stability through quantitative dissolution analysis using inductively coupled plasma-mass spectrometry (ICP-MS) and contact angle measurements. Her current interests include environmentally benign chemistries, improving the reliability of Cu interconnects after plasma etching, and data-driven optimization of post-etch cleaning performance.