Article pubs.acs.org/est
Comparison of Ceria Nanoparticle Concentrations in Effluent from Chemical Mechanical Polishing of Silicon Dioxide Larry Zazzera,*,† Brian Mader,‡ Mark Ellefson,‡ Jess Eldridge,‡ Steve Loper,† John Zabasajja,† and Julie Qian† †
3M Company, Electronics Materials Solutions Division Laboratory, St. Paul, Minnesota 55144-1000, United States 3M Company, Environmental Laboratory, St. Paul, Minnesota, 55144-1000 United States
‡
S Supporting Information *
ABSTRACT: This work measured and compared the effluent from the chemical mechanical polishing (CMP) of silicon dioxide using ceria slurry and ceria fixed abrasive. CMP waste streams were tested for total solids, cerium, silicon, and 6 nm to 20 μm diameter particles. The concentration of cerium and total solids in the effluent were very different for the two polishes studied. The fixed abrasive polish produced 94% less CeO2 emissions per SiO2 removed. The higher ceria levels in the slurry effluent are associated with 99−279 nm particles, and attributed to ceria abrasive. The lower concentration of ceria in the effluent from the fixed abrasive process is due to the lower wear rate of mineral from the fixed abrasive, compared to the more environmentally mobile mineral in the slurry. These results support the “bonded” nature of the abrasive particles in fixed abrasive polishing and are relevant to sustainability strategies that seek to reduce particle emissions in surface conditioning technology.
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concentrations in waste and water treatment facilities.6−8 The scope of the ITRS EHS plan includes the vision of managing what can be measured, so measuring CeO2 emissions from fixed abrasive and slurry CMP is important.9 The goals of this work were to (1) develop effective monitoring tools to measure the CeO2 effluent in the waste streams of slurry and fixed abrasive CMP polishes, (2) compare CeO2 particles emitted from these two different polishes, and (3) inspire the development of sustainable surface finishing processes that can eliminate or minimize particle emissions in a broad range of applications.
INTRODUCTION Chemical Mechanical Planarization, Slurry, and Fixed Abrasives. The processing speed and memory capacity of microelectronic devices are strongly linked to Moore’s law, whereby the number of transistors that can be placed on an integrated circuit has doubled approximately every two years.1 Moore’s law has proved to be accurate, in part because the International Technology Roadmap for Semiconductors (ITRS) guides the industry’s future manufacturing practices.2 The ITRS includes Chemical Mechanical Planarization or CMP, which is a polishing process used to thin material and smooth surfaces, with a combination of chemical and mechanical forces.3,4 Removal of silicon dioxide films, using ceria abrasive, is a common CMP step. Slurry CMP uses free abrasive particles dispensed onto a pad, and fixed abrasive CMP uses particles already bonded or “fixed” into the pad. The materials and mechanics used in slurry and fixed abrasive polishes are different, so it is reasonable to expect different emissions in the polish byproducts. Potential Risks of Ceria Nanoparticles and Goal to Measure, Minimize, and Manage Emissions. Engineered nanoparticles are defined as having at least one dimension 600 nm) and Particles (
Comparison of Ceria Nanoparticle Concentrations in Effluent from Chemical Mechanical Polishing of Silicon Dioxide Larry Zazzera,*,† Brian Mader,‡ Mark Ellefson,‡ Jess Eldridge,‡ Steve Loper,† John Zabasajja,† and Julie Qian† †
3M Company, Electronics Materials Solutions Division Laboratory, St. Paul, Minnesota 55144-1000, United States 3M Company, Environmental Laboratory, St. Paul, Minnesota, 55144-1000 United States
‡
S Supporting Information *
ABSTRACT: This work measured and compared the effluent from the chemical mechanical polishing (CMP) of silicon dioxide using ceria slurry and ceria fixed abrasive. CMP waste streams were tested for total solids, cerium, silicon, and 6 nm to 20 μm diameter particles. The concentration of cerium and total solids in the effluent were very different for the two polishes studied. The fixed abrasive polish produced 94% less CeO2 emissions per SiO2 removed. The higher ceria levels in the slurry effluent are associated with 99−279 nm particles, and attributed to ceria abrasive. The lower concentration of ceria in the effluent from the fixed abrasive process is due to the lower wear rate of mineral from the fixed abrasive, compared to the more environmentally mobile mineral in the slurry. These results support the “bonded” nature of the abrasive particles in fixed abrasive polishing and are relevant to sustainability strategies that seek to reduce particle emissions in surface conditioning technology.
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concentrations in waste and water treatment facilities.6−8 The scope of the ITRS EHS plan includes the vision of managing what can be measured, so measuring CeO2 emissions from fixed abrasive and slurry CMP is important.9 The goals of this work were to (1) develop effective monitoring tools to measure the CeO2 effluent in the waste streams of slurry and fixed abrasive CMP polishes, (2) compare CeO2 particles emitted from these two different polishes, and (3) inspire the development of sustainable surface finishing processes that can eliminate or minimize particle emissions in a broad range of applications.
INTRODUCTION Chemical Mechanical Planarization, Slurry, and Fixed Abrasives. The processing speed and memory capacity of microelectronic devices are strongly linked to Moore’s law, whereby the number of transistors that can be placed on an integrated circuit has doubled approximately every two years.1 Moore’s law has proved to be accurate, in part because the International Technology Roadmap for Semiconductors (ITRS) guides the industry’s future manufacturing practices.2 The ITRS includes Chemical Mechanical Planarization or CMP, which is a polishing process used to thin material and smooth surfaces, with a combination of chemical and mechanical forces.3,4 Removal of silicon dioxide films, using ceria abrasive, is a common CMP step. Slurry CMP uses free abrasive particles dispensed onto a pad, and fixed abrasive CMP uses particles already bonded or “fixed” into the pad. The materials and mechanics used in slurry and fixed abrasive polishes are different, so it is reasonable to expect different emissions in the polish byproducts. Potential Risks of Ceria Nanoparticles and Goal to Measure, Minimize, and Manage Emissions. Engineered nanoparticles are defined as having at least one dimension 600 nm) and Particles (
