Understanding Multi Scale Pad Effects in Chemical Mechanical Planarization
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1157-E02-01
Understanding Multi Scale Pad Effects in Chemical Mechanical Planarization Abhijit Chandra1,2 and Ashraf. F. Bastawros2,1 Mechanical Engineering, 2Aerospace Engineering, Iowa State University, Ames, 50011, USA.
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Pavan K. Karra1 Mechanical Engineering, Iowa State University, Ames, IA 50011, USA.
ABSTRACT A multi-physics model encompassing chemical dissolution and mechanical abrasion effects in CMP is developed. This augments a previously developed multi-scale model accounting for both pad response and slurry behavior evolution. The augmented model is utilized to predict scratch propensity in a CMP process. The pad response delineates the interplay between the local particle level deformation and the cell level bending of the pad. The slurry agglomerates in the diffusion limited agglomeration (DLA) or reaction limited agglomeration (RLA) regime. Various nano-scale slurry properties significantly influence the spatial and temporal modulation of the material removal rate (MRR) and scratch generation characteristics. The model predictions are first validated against experimental observations. A parametric study is then undertaken. Such physically based models can be utilized to optimize slurry and pad designs to control the depth of generated scratches and their frequency of occurrence per unit area. Keywords Planarization, Agglomeration, Defectivity 1 INTRODUCTION Chemical mechanical planarization (CMP) has grown rapidly during the past decade as a necessary process step in submicron integrated circuit (IC) manufacturing because of its ability to achieve global or near-global planarization [1]. Currently, CMP is widely used for interlevel dielectrics and metal layer planarization. CMP is performed by sliding the wafer surface on a relatively soft polymeric porous pad which is flooded with a chemically active slurry containing abrasive particles of sub-micron diameter. The chemical properties of the slurry interact with the mechanical properties of the abrasive particles at the nano-scale. It also affects the mechanical macro-scale properties of the polishing pad and the wafer, as well as their surface morphologies at the micro-scale. As a result, the wafer surface, the pad surface and the slurry characteristics change. This evolution controls the quality and effectiveness of the CMP process. The finished wafer surface, however, is prone to CMP process induced scratches. Existence of a single scratch whose depth is greater than a critical threshold can render the chip unusable, and this threshold continues to decrease with successive generations of IC manufacturing. A wide range of studies on the CMP process have been reported. For example, previous work investigated the material removal rate (MRR) [2,3] and the effects of the pad and slurry properties on the process. Wang et al. [4] introduced the effects of pad wear and its evolution in an effort to extend the pad response model developed by Bastawros et al. [5], and Luo and Dornfeld [6] examined the effects of slurry properties focusing on the distrib
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