Investigation and Control of Chemical and Surface Chemical Effects During Dielectric CMP
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Investigation and Control of Chemical and Surface Chemical Effects During Dielectric CMP J. T. Abiade1, W. Choi1, V. Khosla1, R. K. Singh2 Department of Materials Science and Engineering and Particle Engineering Research Center University of Florida, Gainesville, Florida 32611 2 Microelectronic Research Center University of Texas, Austin, Texas Abstract Due to the ever-increasing popularity of STI in microelectronic device fabrication, designer slurries must be tailored to meet increasingly stringent planarity requirements. Although dielectric polishing is primarily mechanical in nature, the chemical and surface chemical effects can be tailored to enhance selectivity and planarity. Examples of chemical and surface chemical effects in dielectric CMP include; control of slurry pH, use of reactive particles such as cerium dioxide, and addition of surfactants to modulate the particle-substrate interactions. Cerium dioxide particles are utilized due to an increase in substrate dissolution through particle-substrate bonding, which accelerates the material removal of the dielectric surface. The increased efficiency of reactive particles is largely dependent on the area of contact between particle and substrate during polishing. The chemical nature of the interaction between the particles and silica substrates has been investigated using polishing experiments, AFM, and an in-situ friction force apparatus. Both the pH and cerium dioxide particles have been found to significantly affect the near surface region of the oxide film. 1
Introduction Silica-silica CMP, a largely mechanical process, requires slurries formulated in alkaline pH regimes. Above pH 9, a small chemical component may be introduced due to an enhancement in the silica dissolution rate1. In these conditions, the softened silica surface is removed at increased rates and with improved surface finish. As device dimensions shrink, the need for global planarity increases2. To meet increasingly stringent planarity, selectivity, and removal rate specifications, polishing slurries with enhanced chemical activity are being investigated3. Recently, considerable interest has been shown in ceria-based CMP slurries. Although the advantages of ceria slurries are well known, few experimental investigations of CMP of silica by ceria slurries have been reported. Despite the lack of conclusive studies, two competing models have been proposed to explain the ceria-silica CMP process. The first, termed the chemical tooth model, was proposed for glass polishing ~15 years ago by Cook and Brown1. According to the chemical tooth model, CMP of silica is seen as a multi-step process. Initially, temporary bonding between the ceria abrasives and the silica substrate occurs. Then, dissolved silica is released into solution and adsorbed onto the abrasive particle. Adsorption of substrate-derived species was quantified by treating it (adsorption) as a surface complexation process in which the solute from the silica surface is adsorbed to the ceria abrasives4. To explain the ceria –
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