Section 9 CMP EE143 Ali Javey Slide 9 1 Multilevel Interconnects Nonplanar Metallization Planar Metallization EE143 Ali Javey Slide 9 2 Surface Planarization Benefits for Lithography Processes Lower Depth of Focus requirement Reduced optical reflection effects on resist profiles Reduced resist thickness variation over steps topview Benefit for Etching Processes Reduced over etch time required due to steps Benefit for Deposition Processes Improved step coverage for subsequent layer deposition EE143 Ali Javey Slide 9 3 Spin On Glass SOG EE143 Ali Javey Slide 9 4 Chemical Mechanical Polishing CMP Wafer is polished using a slurry containing silica abrasives 10 90 nm particle size etching agents e g dilute HF Backing film provides elasticity between carrier and wafer Polishing pad made of polyurethane with 1 mm perforations rough surface to hold slurry EE143 Ali Javey Slide 9 5 CMP Rate Preston Model Local Removal rate R Kp P v where P local applied pressure v relative pad wafer velocity Kp Preston coefficient unit in pressure 1 function of film hardness Young s modulus slurry pad composition and structure EE143 Ali Javey Slide 9 6 Problems encountered in CMP EE143 Ali Javey Slide 9 7
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