Evaluation of Mechanical and Tribological Behavior, and Surface Characteristics of CMP Pads
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EVALUATION OF MECHANICAL AND TRIBOLOGICAL BEHAVIOR, AND SURFACE CHARACTERISTICS OF CMP PADS A. K. Sikder, I. M. Irfan, Ashok Kumar, A. Belyaev, S. Ostapenko, M. Calves1, J. P. Harmon1 and J. M. Anthony Center for Microelectronics Research, College of Engineering, 1 Department of Chemistry University of South Florida 4202 East Fowler Avenue, Tampa, FL-33620 ABSTRACT Chemical Mechanical Planarization (CMP) occurs at an atomic level at the slurry/wafer interface and hence slurries and polishing pads play a critical role in the successful implementation of this process. Surface roughness, visco-elastic properties, thickness and pore size also play an important role in this process. Unfortunately the mechanical properties of polyurethane polishing pads used in CMP are poorly understood. Here we have studied the mechanical and visco-elastic properties and surface morphology of CMP pads using nanoindentation and dynamic mechanical analysis along with high resolution scanning electron microscopy. A state-of-the-art Universal Micro-Tribometer was used to measure the pad deformation behavior under load. A novel non-destructive scanning ultrasonic transmission technique was also used to characterize inhomogeneity of the visco-elastic properties of full-size CMP pads. Results obtained by different techniques were analyzed to demonstrate methods for quick and reliable evaluation of pad quality for current CMP technology. INTRODUCTION In spite of being a historically ancient technology, chemical mechanical planarization (CMP) has attracted an enormous amount of attention recently because of its applicability in planarizing the dielectrics and metal films used in silicon integrated circuit (IC) fabrication [1,2]. Continued miniaturization of the device dimensions and the related need to interconnect an increasing number of devices on a chip have led to building multilevel interconnection on planarized levels. CMP has emerged as an essential process for multilevel interconnection of ULSI chip fabrication [3]. In CMP very thin materials ( P KDYH WR EH UHPRYHG YHU\ precisely, maintaining precise control of the remaining thickness. Planarization of the wafer results from the synergistic action of the mechanical shear forces and the chemical action of the slurry [2,4]. Many issues, e.g. polishing conditions, pad properties, slurry chemistry and hydrodynamics, and polishing head design, have been addressed by several researchers [1,5-7]. However, a poor understanding of complicated polishing phenomena makes it difficult to achieve local and global uniformity. Polishing pads are major consumables affecting critically the within-wafer and wafer-towafer non-uniformity (WIWNU and WTWNU respectively) in planarization technology. Polishing pads are composed of either a matrix of cast polyurethane foam with filler material to control hardness or polyurethane impregnated felts [2]. The role of the pad is to transport media of slurry to the polishing reaction point and to support polishing pressure derived from down force to M1.8.1
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