A Strategic Approach to Environmentally Benign Chemical Mechanical Planarization
Slurries for Advanced Cu Interconnect Applications
Ph.D. Dissertation Defense
Thi Thuy Hoang Tran
Abstract
Chemical mechanical planarization (CMP) is a critical process in semiconductor manufacturing, facilitating the planarization of metal and dielectric surfaces to ensure device functionality. Conventional CMP slurries frequently incorporate benzotriazole (BTA) as a corrosion inhibitor, particularly to protect Cu interconnects in configurations utilizing Co as the liner material. However, BTA presents significant challenges, including poor degradability in conventional wastewater treatment processes and its tendency to form hydrophobic residues on Cu films, complicating post-CMP cleaning. This research investigates the potential of aliphatic amino acids such as methionine, glutamic acid, and leucine as environmentally friendly and effective alternatives to BTA in CMP slurries designed for Cu and Co films.
The study systematically evaluated the corrosion inhibition properties of methionine, leucine, and glutamic acid by examining corrosion current densities, corrosion potential differences, and galvanic current densities during polishing. Methionine and leucine demonstrated notable efficacy, reducing Cu corrosion to icorr = 20 μA/cm2 and 17 μA/cm2, respectively, compared to 38 μA/cm2 without inhibitors. Methionine demonstrated strong corrosion inhibition for Co (icorr = 12 μA/cm2) and effectively mitigated galvanic corrosion within the Cu-Co couple (|∆Ecorr|= 8 mV, igc = 3 μA/cm2). These findings were complemented by in-situ electrochemical measurements, including open circuit potential (OCP) transients during holding and polishing phases, revealing dynamic electrochemical changes occurring in amino acid-based slurries during polishing.
Surface analysis using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) showed that methionine’s sulfur-containing side chain effectively stabilized Cu(I) species and formed a protective oxide layer comparable to that formed with BTA through a combination of physisorption and chemisorption. Leucine, with its branched hydrocarbon chain, mitigated Cu corrosion through physisorption but increased galvanic corrosion for Co. Leucine formed a thin and unstable passive layer that readily broke down during the Cu(I) to Cu(II) transition. Glutamic acid, with its additional carboxylic acid group, was not effective as a corrosion inhibitor but showed a relatively low |∆Ecorr| = 5 mV, indicating minimal galvanic interaction.
Removal rates of Cu and Co correlated with corrosion inhibition trends, with methionine achieving better selectivity for Cu barrier CMP. Increasing methionine concentration from 10 to 20 mM further enhanced polarization resistance, effectively mitigating adverse effects under high-pressure conditions and achieving saturation adsorption more rapidly than BTA. Electrochemical evaluations established a relationship between the polishing kinetics constant (K’p), adsorption energy and passive layer thickness (K’p = f(∆Gads0,δ)). In-situ measurements further demonstrated reduced Vmech/Vchem ratios with methionine and BTA, confirming their role in increasing chemical contributions through effective corrosion inhibition. The degradability of the amino acid-based polishing slurry was assessed to determine its ease of breakdown compared to BTA. An electro-Fenton process coupled with post-analysis techniques showed that methionine and leucine degraded significantly more (both exceeding 96%) than BTA (62%) after 30 minutes of treatment, with degraded products found by mass spectroscopy.
Keywords: Semiconductor, CMP, Slurry, Sustainability, Green corrosion inhibitors.
Tuesday, 12/03/2024 at 3:00 pm CAMP 372
Zoom link: https://clarkson.zoom.us/j/9262905473?omn=97613678818
Advisors:
Prof. Jihoon Seo
Prof. Elizabeth Podlaha-Murphy
Other Committee Members:
Prof. Devon A. Shipp
Prof. Sitaraman Krishnan
Prof. Ian McCrum