Simulation of Nanoscale Polishing of Copper with Molecular Dynamics
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SIMULATION OF NANOSCALE POLISHING OF COPPER WITH MOLECULAR DYNAMICS Y.YE 1,2, R. BISWAS 1,2, J. R. MORRIS2, A. BASTAWROS3 AND A. CHANDRA4 1 Department of Physics and Astronomy and Microelectronics Research Center 2 Ames Laboratory-USDOE, Iowa State University, Ames, Iowa 50011 3 Dept. of Aerospace Engineering and Engineering Mechanics, Iowa State University, Ames, IA 50011. 4 Dept. of Mechanical Engineering, Iowa State University, Ames, IA 50011. ABSTRACT We investigate the fundamental atomistic processes in chemical mechanical polishing of copper, by simulating the nanoscale polishing of a copper surface by a single abrasive particle. The atomistic mechanisms of an individual surface-polishing event are simulated with molecular dynamics using the embedded atom method. The nature of material removal, chip formation, material defects and frictional forces were investigated as a function of the cutting speed, depth of cut, and abrasive geometry. Nanometric cutting comprises of two steps: material removal as the tool machines the top surface, followed by relaxation of the work material to a low defect configuration, after the tool or abrasive particle has passed over the machined region. Chemical etching processes during planarization considerably improve the quality of the planarized surface and reduce defects in the bulk. INTRODUCTION There is a need to understand the fundamental atomic mechanisms underlying wear and friction between surfaces. With recent advances in nanotechnology, the wear and material removal at nanoscale dimensions involves atomic-scale properties. Chemical-mechanical planarization (CMP) of semiconductor substrates is a crucial state-of-the-art processing step in semiconductor technology. CMP allows a patterned surface to be completely planarized so that an entirely different metallization pattern can be then fabricated on it- a key requirement in threedimensional structures. Small abrasive particles from a slurry polish a copper surface in CMP [1-3]. However the underlying atomic-scale processes in CMP are not fully understood and we investigate the atomistic/microscopic processes of CMP in this paper. Nano-scale processing and patterning involve changes in only a few atomic layers at the surface. At such a small governing length scale, the continuum representation of the problem becomes questionable. Accordingly, a molecular dynamics (MD) based representation is sought in the present work. The planarization process in CMP involves complex interactions between the wafer, polishing pad, chemical slurry and abrasive particles present in the slurry. Yet the fundamental CMP process involved the wafer planarization by a single abrasive particle[3,4]. CMP may be viewed as a collection of several individual polishing events. We simulate the atomistic processes of a single polishing event in this paper. MODEL
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