Publication

Abstract : The role of several factors influencing the chemical mechanical planarization (CMP) of oxide dielectric films was studied. The global effects of pad conditioning namely the removal rate and uniformity enhancements, the degradation in the film surface quality due to conditioning were examined. Detailed investigation uncovering the role of pad surface properties on the polishing performance was carried out using physical, optical and chemical characterization techniques. Tribological evaluation of porous and non-porous pads was performed by computing the surface roughness, bearing ratio curves and power spectra of conditioned and unconditioned pad surfaces. The formation and evolution of pad surface mesas on unconditioned porous pads were captured pictorially using confocal microscopy. The effects of mesa formation on polish characteristics of pads were determined by polishing blanket and patterned oxide films. The presence of mesas showed an adverse effect on removal rates, however, an improvement in the die level total indicated range (TIR) was observed due to their presence. Conditioned pad surfaces, on the other hand, exhibited poor planarization performance, although pad conditioning stabilized the removal rates. The surface modulus of non-porous polish pads was found to be sensitive to their exposed environment. Soaking the polish pads in aqueous or heated environment caused a decrease in surface modulus of the polish pads. Correspondingly, raising the process temperature during polishing was found to jeopardize the die level planarity across the wafer. Soaking the polish pads in slurries also had a detrimental effect on the blanket removal rates. Apart from surface level properties, the bulk properties and composite nature of the pad stack was found to impact the polishing performance. The different factors investigated included the top pad specific gravity and curing characteristics. Some of the key results obtained in this study included: (1) dependence of blanket removal rates on the surface roughness of pads, (2) improved die level planarity demonstrated by high specific gravity and highly cured hard pads, (3) clouding of polishing effects due to the presence of the softer underpad (for composite pad stacks). Hard pads used in combination with softer underpads were found to decrease the post polish within wafer uniformity, but significantly improved the die level planarity by approximately 50%.