Controlling the Molybdenum Dissolution and Oxidation During Post-CMP Cleaning
ABSTRACT
Molybdenum (Mo) is rapidly emerging as a potential replacement for tungsten (W) in advanced semiconductor manufacturing due to its low electrical resistivity and high thermal stability. Mo is also considered a promising candidate for barrierless metallization for sub-5 nm interconnects [1]. However, during CMP and post-CMP cleaning, the corrosion and dissolution of Mo are highly sensitive to process conditions, which can lead to surface defects and performance degradation, posing a critical integration risk [2]. Generally, Mo and its oxides are relatively stable in acidic environments, while Mo oxide becomes very unstable as pH increases to alkaline, leading to higher dissolution susceptibility. Corrosion inhibitors can mitigate dissolution through adsorption-driven passivation [3], yet inhibitor chemistries specifically tailored to Mo for post-CMP cleaning are still limited in the literature.
Due to a lack of protective oxide on Mo surfaces addressing its corrosion susceptibility, there is a crucial requirement for inhibitors to control the corrosion at neutral and alkaline conditions for maximizing their effectiveness in advanced fabrication processes. This study focuses on suppressing excessive Mo dissolution during post-CMP cleaning, with particular emphasis on neutral to alkaline pH conditions. Inhibitor performance was systematically analyzed by quantifying inhibition efficiency and characterizing inhibitor adsorption on Mo surfaces. In addition, inhibitor effectiveness is evaluated in oxidizer-containing chemistries across a range of pH conditions to enable uniform and controlled Mo dissolution.
Blanket PVD Mo films (350 nm) deposited on 300 mm SiO₂/Si wafers were diced into 2×2 cm coupons to systematically examine Mo surface properties. Static etch rates were determined from sheet resistance changes measured by a four-point probe before and after 1 min immersion. Surface wettability was assessed using a contact angle analyzer. Electrochemical behavior was evaluated in a flat-plate cell using a standard three-electrode configuration coupled to a potentiostat. The inhibition efficiency for inhibitors A and B was benchmarked in the presence of various oxidizers at pH 3, 7, and 11 to enable uniform and controlled Mo dissolution.
Static etch rates (SER) of pre-treated Mo surfaces were measured at various pH with and without 0.1 wt% inhibitors (A and B) as shown in Fig. 1. Mo dissolution increased with an increase in pH, confirming higher corrosion susceptibility under alkaline conditions. In contrast, both inhibitors reduced the SER across all pH values, with the most pronounced suppression at pH 11, where the SER decreased significantly with inhibitor B. Lower SER with inhibitor B indicates stronger adsorption and surface passivation. Similarly, in the presence of oxidizers and inhibitors, whereas inhibitor B showed a significant decrease in Mo etch rate at all pH. This enhanced protection suggests formation of a more stable protective layer on Mo, which can improve surface integrity by enabling lower and more uniform dissolution during the cleaning process. A Nyquist diagram of EIS analysis was obtained at different pH conditions, and the Rp values were calculated from the electrical equivalent circuit (EEC). Rp decreases as pH increases, indicating higher Mo dissolution under alkaline conditions, as shown in Fig. 1 (b). Adding inhibitors A and B increased Rp at all pH values, confirming improved corrosion protection. Inhibitor B consistently showed higher Rp than inhibitor A, demonstrating superior passivation. The overall increase in dissolution with increasing pH was consistent with the SER results.
The addition of inhibitors increased the contact angle at all pH. Inhibitor B resulted in substantially higher contact angles. The consistently higher contact angles with inhibitor B indicate stronger and more stable adsorption on Mo surfaces relative to inhibitor A, consistent with improved surface coverage and passivation. The synergistic effects of the oxidizers and inhibitors were evaluated to determine the corrosion-inhibition efficiency.
BIOGRAPHY
Gyeongwon Lee is a graduate researcher in the integrated M.S.–Ph.D. program (second semester) in the Department of Materials and Chemical Engineering at Hanyang University, under the supervision of Professor Jin-goo Park. His research focuses on CMP and post-CMP cleaning, where he studies how process chemistries interact with metal surfaces to influence oxide formation, corrosion, and dissolution. By connecting interfacial mechanisms to measurable performance outcomes, he aims to support more reliable and controllable cleaning strategies for advanced semiconductor integration. He is especially interested in metal-related challenges in wet processing and how electrochemical perspectives can guide practical process design. At SPCC, he looks forward to sharing his work, learning from other researchers, and building collaborations across CMP and surface engineering communities.