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CMP Basics (cont’d)
• How does CMP work? – A rotating wafer is pressed face-down against a rotating polishing pad; an aqueous suspension of abrasive (slurry) is pressed against the face of the wafer by the pad.
– important parameter is removal rate (RR)
• RR = average thickness change during polishing divided by polishing time
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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Metal Damascene Process
• Trenches/vias etched into ILD (interlayer dielectric)
• Metal deposition
• Metal CMP
• Repeat for multiple levels of metal
Beaudoin, et al.
– Mechanical action
• polisher rotation and pressure
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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CMP Consumables (cont’d)
• W polishing – pH 4 with H2O2 or KIO3 – pH 1.5 with ferric nitrate – pH 6 with potassium ferricyanide, potassium acid phosphate and ethylene diamine • Al polishing – peroxide or iodate-based slurries • Cu polishing – ammonia-based solutions, passivating agents
• Become aware of the processing and environmental challenges associated with CMP
• Learn how to assess the environmental consequences of manufacturing processes and how to compare the impacts of competing processes • Gain experience in setting new, more environmentally sound polishing practices
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing9Biblioteka CMP Consumables
• Slurries for oxide (SiO2) polishing – colloidal suspension of silica particles in alkaline medium – hydroxyl ions attack SiO2, causing softening and chemical dissolution (mechanism unverified) – particles range from 10 to 3000 nm, mean size 160 nm – 12% (wt) particles, KOH used to set pH ~11 – other concerns: particle size distribution (scratching), particle shape, particle agglomeration
• NU = ratio of the standard deviation of the post-polish wafer thickness to the average post-polish wafer thickness • caused by variations in local removal rate
Chemical Mechanical Polishing (CMP) Overview
Dr. Stephen Beaudoin Arizona State University Dr. Duane Boning Massachusetts Institute of Technology Dr. Srini Raghavan The University of Arizona
1999 Arizona Board of Regents for The University of Arizona
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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Learning Objectives
• Gain the ability to discuss CMP with polishing experts • Understand basic phenomena that occur during polishing and will be able to explain why these phenomena occur
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CMP Apparatus
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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CMP Basics (cont’d)
• Why do we need CMP? – for precise photolithography for advanced devices – for advanced multilevel metallization processes (Damascene) • How is CMP described? – key parameter: post-polish nonuniformity (NU)
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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CMP Consumables (cont’d)
• Polish pads – cast polyurethane or felt impregnated with polyurethane, thickness~ 1-3 mm – hardness affects planarization and nonuniformity – surface treatment (conditioning) required to control polish rate and slurry transport
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Outline
• CMP Basics • CMP Process Optimization • Environmental Issues in CMP
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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CMP Consumables (cont’d)
• Slurries for metal (W, Al, Cu) polishing – oxidants cause metal dissolution and passivation (reactions to form protective layer on metal surface) – typically alumina particles (a or g), 100 to 2000 nm in diameter, 12% (wt) particles, pH 3 to 4
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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Questions
• • • • • • • What is CMP? How does CMP work? Why do we need CMP? How do we describe CMP? What are the problems associated with the CMP process? What are the environmental impacts of CMP? How can we alter the environmental impacts of CMP?