Mechanistic Understanding of Material Detachment During CMP Processing
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Mechanistic Understanding of Material Detachment During CMP Processing Wei Che1, Yongjin Guo1, Ashraf Bastawros2, Abhijit Chandra1 1 Dept. of Mechanical Engineering, Iowa State University, Ames, IA 50011 2 Dept. of Aerospace Engineering and Mechanics, Iowa State University, Ames, IA 50011
ABSTARCT A combined experimental and numerical approach has been devised to understand the abrasion aspects of material removal mechanisms of ductile copper film on silicon wafers during Chemical mechanical planarization. The experimentally observed trends of the deformation patterns and the force profiles from micro and nano-single scratch experiments are used to guide numerical simulation using finite element simulation at the continuum scale and molecular dynamics simulation at the atomistic scale. Such integrated approach has provided several plausible mechanisms for material detachments through a combination of surface plowing and shearing under the abrasive particles. The gained insights can be integrated into mechanismbased models for the material removal rate in these processes as well as addressing possible defect formation. INTRODUCTION Surface machining is becoming an integral processing step in multilevel metallization designs for integrated circuit (IC) manufacturing to ensuring local and global surface planarization. The surface machining process (industrially known as Chemical-Mechanical Polishing, CMP), employ micro and nano particle abrasives in chemically active slurry with a soft polishing pad to remove material from the surface. The chemical aspect of the process is thought to be softening and/or dissolving the top surface layer, while mechanically removing it. This work focuses on understanding the mechanical aspects of the surface material detachment mechanisms during the CMP process. The experimentally observed deformation patterns and force profiles from the micro-single scratch experiments are used to provided several plausible mechanisms for material detachments through a combination of surface plowing and shearing under the abrasive particles. The gained insights can be integrated into mechanism-based models for the material removal rate (MRR). The process of mechanical surface polishing is usually envisioned through the phenomenological Preston formula [1]; wherein MRR=C.P.U, and P is the applied down pressure, U is the relative sliding velocity and C is a proportionality constant. All the unforeseen process parameters are lumped into such constant. Detailed analysis [2-5] have shown that the pressure dependence is non linear with exponent that ranges from 0.33 to 1.2 based on the details embraced by the model. Regardless of the model details, these models approximately present the proper trend of MRR dependence on P, U and the slurry parameters (particle size and concentration). However, these models overestimate the MRR magnitude by several orders, recasting the difference into the proportionality constant of Preston formula. These models usually divide the applied down pressure between the “a
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