(Invited) Synergistic Effect of Polyvinyl Alcohol (PVA) Brush Type and Cleaning Chemistry Formulation for Copper (Cu) Post-Chemical Mechanical Planarization (p-CMP) Cleaning

Abstract

Chemical Mechanical Planarization (CMP) is a critical process step in extending Moore’s Law and must be understood at a deeper, mechanistic level to limit defects that are detrimental to shrinking feature size. Specifically, Cu CMP utilizes a nanoparticle dispersion (slurry) composed of SiO2 abrasive nanoparticles, complexing agent, oxidizer, and a corrosion inhibitor. Slurry components must work in synergy to chemically modify the Cu surface while unwanted topography is removed by mechanical abrasion. The CMP process can cause various defects, and they can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. Adsorbed particles, polish residues, pad debris, and other foreign materials can have catastrophic impacts on device performance as line width decreases to the atomic scale. Upon the completion of the CMP process, removal of unwanted particle residue/organic contaminants is achieved using oxidation/reduction reactions, etching, or encapsulation chemistry coupled with ultrasonic methods or polyvinyl alcohol (PVA) brush cleaning. The nature of the current cleaning techniques has been known to provide insufficient cleaning capacity for next generation devices. This presentation will explore two fundamentally different approaches to post-CMP cleaning for Cu processes. First, the implementation of supramolecular cleaning chemistries to traditional PVA brush scrubbing was explored for the removal of SiO2 nanoparticles from a Cu surface. This work explored a structure activity relationship between the type of supramolecular cleaning chemistry used and its ability to effectively “encapsulate” nanoparticle contaminants. Initial results indicate that the anionic and non-ionic micelle show some corrosive behavior due to non-uniform passivation layers formed at the Cu surface during cleaning. This behavior is not seen with the cationic micelle suggesting its effective surface adsorption to the contaminant particle which can ultimately be removed via brush contact. Secondly, current cleaning chemistries typically utilize an undercutting mechanism to remove organic residues (i.e., BTA), however, this requires harsh oxidation and can result in scratches/erosion. Therefore, an approach to chemically activate the residue in an “overcutting” mechanism can improve cleaning performance with reduced defectivity. More specifically, this work will explore the use of α-β-unsaturated ketones as cleaning agents to initiate the nucleophilic attack and subsequent removal of BTA via a Michael’s Addition reaction. This mechanism will be evaluated via dynamic Tafel analysis, contact angle, atomic force microscopy, and cleaning performance to correlate interfacial interactions/reactions to p-CMP performance.