Development of Slurry Formulations for Molybdenum-Chemical Mechanical Planarization (Mo-CMP)

Abstract

As integrated circuit (IC) technology continues to advance, the challenge to extend Moore’s law without sacrificing power density and energy efficiency is critical. One method of achieving these goals is through the utilization of Chemical Mechanical Planarization (CMP) to achieve surface planarity down to angstrom level uniformity. Current IC architecture relies on the integration of Cu wiring into Si (i.e., TEOS) substrates to provide effective power transfer. However, this traditional design is limited in efficiency for smaller, high-powered devices which require increased insulating properties. To combat these limitations, low resistivity metals (i.e., Ta, TaN, Mo, etc.) are incorporated for their inherent resistance to electromigration. More specifically, Mo has become increasing attractive due to the metal’s thermal stability and compatibility with Cu to serve as an efficient diffusive barrier. These ideal characteristics ultimately lead to the challenge of increased hardness resulting from inherent inert properties leading to the inhibition of effective CMP processes. To overcome this challenge, Mo-CMP involves the use of harsh polishing conditions consisting of high pressure-velocity coupled with complex slurry dispersions containing aggressive redox chemistry (i.e., KMnO4, KIO3, APS, etc.) and high abrasive nanoparticle content (i.e., Al2O3, SiO2, etc.). More specifically, the utilization of harsh oxidizers and alkaline conditions results in a metal oxide film ideal for effective material removal rate (MRR). However, it is with the implementation of these conditions that ultimately results in the generation of surface defects (i.e. scratching, pitting, etching, organic residues, galvanic corrosion, etc.) which are detrimental to the performance (i.e., power efficiency, operating frequency, etc.) for next generation IC devices. This work will focus on the investigation into conditions leading to effective MRR in Mo-CMP. More specifically, this work will utilize a suite of dynamic analytical techniques (i.e. atomic force microscopy, scanning electron microscopy, quartz crystal microbalance, contact angle, electrochemical analysis, etc.) to evaluate interfacial reaction mechanisms that lead to the productive modification for the reduction of shear force during polishing. It has been shown that the incorporation of tailored chemistries and the addition of “softer” passivating agents (i.e., polyamines) can result in the formation of surface-active complexes that trigger rapid interfacial redox reactions in H2O2 environments at a more amenable pH. Increasing the chemistry’s surface activity to Mo will result in a decreased Ea limiting the effects of nanoparticle adsorption to reduce CMP induced defectivity without the expense of corrosion events necessary for MRR. Furthermore, the implementation of “softer” passivating agents can reduce the galvanic corrosion effects with Cu which significantly reduce secondary defectivity.