A CMP Numerical Model Combining Die Scale and Feature Scale Polishing Characteristics
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A CMP Numerical Model Combining Die Scale and Feature Scale Polishing Characteristics Stéphanie Delage, Frank Meyer1 and Goetz Springer1 Infineon Technologies AG, Memory Products, Balanstrasse 73, D-81541 Munich, Germany 1 Infineon Technologies Dresden GmbH & Co.OHG, Center for Development and Innovation, P.O. Box 10 09 40, D-01076 Dresden, Germany ABSTRACT In this paper a new numerical model combining die scale and feature scale polishing characteristics for oxide CMP is proposed. This work is based on the effective density model [1-3] which takes into account a die scale pad deformation. We have extended this model to include the description of material removal at the feature scale. A pseudo topography discretization allows us to describe the polishing in down areas more accurately depending on the down area width. The physical parameters considered include the deformation of the polishing pad (die scale and feature scale), the removal rate of a blanket wafer polished under the same process conditions, and the removal rate in down areas for small polishing times. Comparison of simulated results with MIT testreticle experiments has been performed and evaluated. MOTIVATION Chemical Mechanical Polishing (CMP) has emerged as the leading process for global and local planarization in silicon integrated circuits fabrication. However, a large number of variations and effects due to layout pattern, equipment, and process dependencies still remain poorly understood. An effective modelling methodology is needed to facilitate the assessment and reduction of such variations. Several works have proposed models for Chemical Mechanical Polishing which provide various benefits. Nevertheless most of them relate to a single scale process description (wafer/die/feature) and a lack of multiscale models remains. In this paper we propose a new numerical model which describes the pad-wafer interaction during the Chemical Mechanical Planarization of a patterned oxide layout at the die scale and the feature scale simultaneously. MODEL DESCRIPTION Background Our model is based on the phenomenological models from B. Stine et al. [1], J. Grillaert et al. [2], and T. H. Smith et al. [3] which describe the Chemical Mechanical Planarization on the die scale for a patterned wafer. The key of the first model [1] is to describe the pad bending at the die scale through the pattern density which corresponds to the volume fraction of the oxide within an infinitesimal surface. To apply this model one therefore has to determine this density window (planarization length) for each particular CMP process. The final oxide thickness is derived from Preston´s equation and is linear with time. An important assumption of this model is the negligible polishing rate from the down areas compared to the one of the up areas : the pad is assumed to be incompressible. The benefit of this model is the M5.5.1
prediction of post-CMP thickness for arbitrary layouts. The second model [2] combines two pad modes. The pad is incompressible as long as it does not touch the d
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