The removal mechanism for interlevel dielectric ͑ILD͒ chemical mechanical polishing ͑CMP͒ with fumed silica abrasive slurry was studied by measuring silicon dioxide wafer removal rates as a function of abrasive concentration and pH and also by examining the surface charges of the abrasive particles at different pH's. The interfacial removal kinetics indicates that the wafer removal rate is consistent with a first-order reaction and is proportional to the concentration of surface silanolates on the abrasive particles. The actual removal is proposed to be achieved by a direct nucleophillic attack of the silica particle silanolates on the wafer Si-O bond. Pad surface texture provides the means to transport the slurry to the contact zone and the effective concentration of abrasive particles doing actual removal is greatly influenced by the pad surface macrotexture by grooving design and the microtexture by conditioning. The observed correlation between the pad surface parameters that are used to characterize the pad microtexture and the removal rate highlights the importance of the pad surface texture to ILD CMP.For the past 20 years, silica-based slurries have been used for chemical mechanical polishing ͑CMP͒ of interlevel dielectrics ͑ILDs͒. 1 These slurries achieve a near-perfect global planarization in manufacturing ultralarge scale integrated devices. 2 In a typical ILD CMP, the surface topography of the silicon oxide dielectric is planarized by polishing a rotating wafer that is pressed facedown on a rotating polyurethane pad in the presence of an abrasive slurry. CMP is an interfacial chemical mechanical phenomenon 3 and a better understanding of the interfacial interactions among the slurry, pad, and wafer is needed to improve the pad and the slurry performance.Most of the fundamental understanding of ILD CMP is derived from glass polishing. The widely accepted chemical mechanism is the "chemical tooth" model proposed by Cook in 1990 4 and this model was further refined by Osseo-Asare in 2002. 5 A high removal rate ͑RR͒ can be obtained when the slurry pH is close to the point of zero charge of the abrasive particles ͑e.g., ceria͒. In the model, the material removal during CMP is viewed as an adsorptive process involving release of substrate-derived species into a solution ͑disso-lution͒ followed by the adsorption of these species by abrasive particles. This model predicts that the highest oxide RR occurs at pH 9 for Al 2 O 3 . This has not been experimentally observed in normal CMP; further fundamental understanding of the interfacial chemical process in ILD CMP is needed.There is a large body of work exploring the mechanical contributions from the pad on ILD RRs. 6 The generic mechanistic framework for silicon oxide removal involves Preston's empirical equation, which states that RR is proportional to polishing down force and speed. 7 Unlike copper CMP, the material RR in ILD CMP follows Preston's equation fairly well, although some modifications have been proposed. 8 So, the CMP community views ILD polishin...

The influence of pad intrinsic properties on the removal rate profiles of ILD CMP with fumed silica abrasive slurry was studied by changing pad's polymer hardness, porosity, and pore size. Of these intrinsic properties, pore size is found to be most critical to removal rate profiles. By systematically changing the pore size from <1 μm to >100 μm, with porosity from 5% to 50%, of pad made of thermal-plastic urethane (TPU), removal rate profile of oxide polishing was studied. A flat removal rate profile cross wafer is desired for ILD CMP. It was found that when the pore size was larger than a certain threshold, flat removal rate profiles could be achieved. Below the threshold, severe edge-fast/center-slow removal rate profiles were observed and such profiles cannot be remedied by changing pad's other properties like porosity or polishing process conditions. A model is proposed to explain the non-flat removal rate profiles associated with the small pore size (<20 μm).

No abstract