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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
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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)
– Mechanical action
• polisher rotation and pressure
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
• Metal CMP
• Repeat for multiple levels of metal
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 10
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
• Gain experience in setting new, more environmentally sound polishing practices
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
– A combination of chemical and physical effects removes features from the wafer surface.
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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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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?
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
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CMP Basics
• What is CMP? – CMP is a physico-chemical process used to make wafer surfaces locally and globally flat.
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 11
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
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NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing 12
• How is CMP described? – key parameter: post-polish nonuniformity (NU)
• NU = ratio of the standard deviation of the post-polish wafer thickness to the average post-polish wafer thickness
Hale Waihona Puke 1• CMP Basics
Outline
• CMP Process Optimization
• Environmental Issues in CMP
Beaudoin, et al.
NSF/SRC Engineering Research Center for Environmentally Benign Semiconductor Manufacturing
• caused by variations in local removal rate
– important parameter is removal rate (RR)
• RR = average thickness change during polishing divided by polishing time
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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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.
• alumina-peroxide – 1 part slurry, 1 part 50% H2O2, pH 3.7-4.0
• alumina-ferric nitrate – 6% alumina solids, 5% ferric nitrate, pH 1.5
• alumina-potassium iodate – 6% alumina solids, 2-8% potassium iodate, pH 4.0