Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1998-07-10
2001-11-13
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S667000, C210S912000
Reexamination Certificate
active
06315906
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to a process and apparatus for removing metal ions from wastewater. In one aspect, this invention relates to a process and apparatus for removing copper ions from wastewater from a chemical mechanical polishing (CMP) of integrated circuit microchips.
2. Background
Semiconductor microelectronic chip (microchip) manufacturing companies have developed advanced manufacturing processes to shrink electronic circuitry on a microchip to smaller dimensions. The smaller circuitry dimensions involve smaller individual minimum feature sizes or minimum line widths on a single microchip. The smaller minimum feature sizes or minimum line widths, typically at microscopic dimensions of about 0.2-0.5 micron, provide for the fitting of more computer logic onto the microchip.
An advanced new semiconductor manufacturing technology involves the use of copper in place of aluminum and tungsten to create a copper microchip circuitry on a silicon wafer. The copper has an electrical resistance lower than aluminum, thereby providing a microchip which can operate at much faster speeds. The copper is introduced to ULSI and CMOS silicon structures and is utilized as interconnect material for vias and trenches on these silicon structures.
ULSI silicon structures are Ultra Large Scale Integration integrated circuits containing more than 50,000 gates and more than 256K memory bits. CMOS silicon structures are Complimentary Metal Oxide Semiconductor integrated circuits containing N-MOS and P-MOS transistors on the same substrate.
For fully integrated multi-level integrated circuit microchips, up to 6 levels, copper now is the preferred interconnect material.
A chemical mechanical polishing (CMP) planarization of copper metal layers is used as a part of the advanced new semiconductor manufacturing technology. The chemical mechanical polishing (CMP) planarization produces a substrate working surface for the microchip. Current technology does not etch copper effectively, so the semiconductor fabrication facility tool employs a polishing step to prepare the silicon wafer surface.
Chemical mechanical polishing (CMP) of integrated circuits today involves a planarization of semiconductor microelectronic wafers. A local planarization of the microchip operates chemically and mechanically to smooth surfaces at a microscopic level up to about 10 microns (&mgr;m). A global planarization of the microchip extends above about 10 microns (&mgr;m) and higher. The chemical mechanical polishing planarization equipment is used to remove materials prior to a subsequent precision integrated circuit manufacturing step.
The chemical mechanical polishing (CMP) planarization process involves a polishing slurry composed of an oxidant, an abrasive, complexing agents, and other additives. The polishing slurry is used with a polishing pad to remove excess copper from the wafer. Silicon, copper, and various trace metals are removed from the silicon structure via a chemical/mechanical slurry. The chemical/mechanical slurry is introduced to the silicon wafer on a planarization table in conjunction with polishing pads. Oxidizing agents and etching solutions are introduced to control the removal of material. Deionized water rinses often are employed to remove debris from the wafer. Ultrapure water (UPW) from reverse osmosis (RO) and demineralized water also can be used in the semiconductor fabrication facility tool to rinse the silicon wafer.
INTRODUCTION TO THE INVENTION
The chemical mechanical polishing (CMP) planarization process introduces copper into the process water, and governmental regulatory agencies are writing regulations for the discharge of wastewater from the chemical mechanical polishing (CMP) planarization process as stringently as the wastewater from an electroplating process, even though CMP planarization is not an electroplating process.
The copper ions in solution in the wastewater must be removed from the byproduct polishing slurry for acceptable wastewater disposal.
The chemical mechanical polishing planarization of the microchip produces a byproduct “grinding” (polishing) slurry wastewater which contains copper ions at a level of about 1-100 mg/l. The byproduct polishing slurry wastewater from the planarization of the microchip also contains solids sized at about 0.01-1.0 &mgr;m at a level of about 500-2000 mg/l (500-2000 ppm).
An oxidizer of hydrogen peroxide (H
2
O
2
) typically is used to help dissolve the copper from the microchip. Accordingly, hydrogen peroxide (H
2
O
2
) at a level of about 300 ppm and higher also can be present in the byproduct polishing slurry wastewater.
A chelating agent such as citric acid or ammonia also can be present in the byproduct polishing slurry to facilitate keeping the copper in solution.
A chemical/mechanical slurry wastewater will discharge from the chemical mechanical polishing (CMP) tool at a flow rate of approximately 10 gpm, including rinse streams. This chemical/mechanical slurry wastewater will contain dissolved copper at a concentration of about 1-100 mg/l.
Fabrication facilities operating multiple tools will typically generate a sufficient quantity of copper to be an environmental concern when discharged to the fabrication facility's outfall. A treatment program is needed to control the discharge of copper present in the copper CMP wastewater prior to introduction to the fabrication facility's wastewater treatment system.
A conventional wastewater treatment system at a semiconductor fabrication facility often features pH neutralization and fluoride treatment. An “end-of-pipe” treatment system typically does not contain equipment for removal of heavy metals such as copper. An apparatus and method for providing a point source treatment for copper removal would resolve a need to install a costly end-of-pipe copper treatment system.
Considering equipment logistics as well as waste solution characteristics, a point source copper treatment unit is needed which is compact and which can satisfy the discharge requirements of a single copper CMP tool or a cluster of copper CMP tools.
Iron sulfate (FeSO
4
) or aluminum sulfate (Al
2
(SO
4
)
3
) can be used to co-precipitate copper ions and produce a sludge. This precipitation process raises the pH to precipitate iron hydroxide and copper hydroxide with a remainder of a silica, alumina wastewater slurry.
The byproduct polishing slurry wastewater containing copper ions from the CMP of semiconductor microelectronic chips containing copper can be passed through a microfilter to remove solids in the form of a silica, alumina wastewater slurry.
Medford et al., U.S. Pat. No. 3,301,542, disclose treating copper contaminated acidic etching solutions from the manufacture of printed circuit boards. The acidic etching solutions wastewater is neutralized with sodium hydroxide.
Leach et al., U.S. Pat. No. 4,010,099, disclose extracting copper by contacting with an organic liquid ion exchange reagent.
Stephens, U.S. Pat. Nos. 3,912,801, and Marquis et al, 5,348,712, disclose extracting metals with cyclic organic carbonates.
Spinney, U.S. Pat. Nos. 3,440,036; Swanson, 3,428,449; and Dalton, 4,231,888, disclose extracting copper using organic oximes as the extraction agent.
The permeate from the microfilter containing permeate copper ions can be reacted with sodium sulfide (NaS
2
) or an organic precipitating solution of a dithiocarbamate to precipitate the copper.
The dithiocarbamate precipitating solution is used to pull the copper ions away from the complexing agent.
Siefert et al., U.S. Pat. No. 5,346,627, disclose a method for removing metals from a fluid stream with a water soluble ethylene dichloride ammonia polymer that contains dithiocarbamate salt groups to form complexes with the metals.
If hydrogen peroxide (H
2
O
2
) is present, the dithiocarbamate reacts with the hydrogen peroxide (H
2
O
2
) before the dithiocarbamate operates to pull the copper ions from the complexing agent. Accordingly, hydrogen peroxide present in the precipitating step makes it difficult
Filson James L.
Kemp Philip M.
Sassaman, Jr. Frank L.
Cintins Ivars
Glantz Douglas G.
United States Filter Corporation
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