Mechanisms of Passivation of Copper in CMP Slurries Containing Peroxide and Glycine
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Mechanisms of Passivation of Copper in CMP Slurries Containing Peroxide and Glycine Ling Wang and Fiona M. Doyle University of California at Berkeley Department of Materials Science and Engineering 210 Hearst Mining Building Berkeley, CA 94720-1760
ABSTRACT Copper has been observed to passivate in CMP slurries containing glycine, when hydrogen peroxide is used as an oxidant, even under acidic conditions where no solid oxidized phases appear on the potential-pH diagram. This passivation behavior is highly desirable for effective CMP. In contrast, passivation is not seen in slurries of similar pH and complexing agent concentration, where the potential is increased electrochemically. In order to model the effects of chemistry on CMP rates, we are endeavoring to better understand the mechanisms responsible for passivation in slurries containing hydrogen peroxide. Here we report tests that characterize the development and degree of passivation seen in slurries with a reasonably wide range of compositions.
INTRODUCTION As copper replaces aluminum as the interconnect metal in integrated circuits, it is becoming increasingly important to develop a quantitative understanding of the chemical mechanical planarization (CMP) process that is key in the dual damascene method for producing devices with multilevel metallization [1,2]. Compared to CMP for silicon dioxide, copper CMP is still poorly understood, because of electrochemical interactions between the slurry and the metal film during polishing, and the coupled effect of these on the mechanical properties of the surface. Early studies on copper CMP showed the importance of oxidizers and complexing agents in successful slurries [3]. Several complexing agents have been examined, such as ammonia [4,5], ethylenediamine-tetraacetic acid (EDTA) [6], glycine [7,8,9,10] and other amino acids. Favorable copper CMP results have been obtained using mixtures of glycine and H2O2 in both alkaline [7] and neutral [8] slurries. However, neutral pH’s are more attractive, because the copper polish rate selectivity with respect to SiO2 is unfavorable under alkaline conditions, where the interlayer dielectric is susceptible to erosion. As part of an effort to develop realistic models for design and control of copper CMP, incorporating both mechanical and chemical factors, we have been seeking a deeper understanding of the material removal mechanisms during polishing. Electrochemical studies have been used to probe fundamental mechanisms in CMP [11,12,13]. However, such studies are implicitly based on the hypothesis that the behavior at a given potential is comparable with the behavior that would be exhibited if a chemical oxidizer were used to control the potential,
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since commercial practice is to use chemical oxidants rather than external electrochemical
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