Liquid purification or separation – Constituent mixture variation responsive
Reexamination Certificate
1999-04-26
2002-04-30
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Constituent mixture variation responsive
C210S418000, C134S109000, C134S902000
Reexamination Certificate
active
06379538
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to chemical mechanical processing of semiconductor wafers, and more particularly concerns a method and apparatus for recovery of components of an aqueous chemical mechanical abrasive slurry containing finely divided, suspended particles following their use in processing of semiconductor wafers. The invention herein relates specifically to an apparatus for diverting flow in a waste stream into clean and turbid components.
2. Description of Related Art
Semiconductor components are commonly manufactured by layering electrically conductive and dielectric materials to achieve appropriate electrical characteristics for fabrication of multiple electrical components such as resistors, capacitors and transistors. Many of these discrete devices are incorporated into integrated circuits for use in creating microprocessors, memory devices, logic circuits, and the like. Many integrated circuits can be produced on semiconductor wafers by layering of dielectric and electrically conductive materials to create multiple semiconductor devices in a relatively small area.
The density of electrical components and interconnect wiring on such semiconductor devices has continually increased as trace line widths on such semiconductor devices have narrowed. At one time, for example, trace line widths on such devices typically ranged from 1 &mgr;m to 4 &mgr;m. However, in recent years, the industry has made significant advances in reducing trace line widths used in creation of integrated circuits to less than 1 &mgr;m. Currently, trace line widths of 0.18 &mgr;m to 0.25 &mgr;m are common, and research is being done to achieve trace line widths of from 0.15 &mgr;m to 0.18 &mgr;m. In addition, the demand for increased memory and computing power has driven the limits on the number of semiconductor devices per integrated circuit that are achievable ever higher, resulting in an increase in the number of layers applied to semiconductor wafers, while the typical size of the integrated circuits continues to decrease. The combination of narrower trace line widths, increased layers of materials and higher densities of semiconductor devices per integrated circuit has made such devices increasingly susceptible to failure due to inconsistencies on semiconductor wafer surfaces, and it has become increasingly important that such semiconductor wafers have surfaces and dielectric layers that are uniformly smooth.
Methods for chemical mechanical planarization (CMP) have been developed to polish the surface of semiconductor wafers, and typically involve rotating the wafer on a polishing pad, applying pressure through a rotating chuck, and supplying an aqueous chemical slurry containing an abrasive polishing agent to the polishing pad for both surfactant and abrasive processing. Abrasive agents that can be used in the chemical mechanical slurry include particles of fumed or colloidal silica, ceria, and alumina. The chemical mechanical slurry can also include stabilizer or oxidizer agents. Silica is typically mixed with a stabilizer such as potassium hydroxide or ammonium hydroxide, and is commonly used to polish dielectric or oxide layers on the semiconductor wafer. Ceria and Alumina are commonly mixed with an oxidizer agent such as ferric nitrate or hydrogen peroxide, and are typically used to polish metal layers, such as tungsten, copper and aluminum, for example.
The slurry and material removed from the various layers of the semiconductor wafer form a waste stream that is commonly disposed of as industrial waste. The abrasive components constitute approximately 8% to 15% by weight of the process CMP slurry, with the remainder constituting other chemical agents such as stabilizer or oxidizer agents, and water. The raw waste stream is typically diluted with other process deionized (DI) water in the CMP polishers to yield a final solids concentration of 0.2% to 1.0% by weight in the waste stream. However, the disposal of dissolved or suspended solids in the industrial waste stream has become a relevant issue due to strict local, state and federal regulations, and it would thus be desirable to provide a process and apparatus to remove abrasive components from the waste stream for possible removal of heavy metal components for separate disposal.
Since, for a significant amount of time, the waste stream contains only DI water containing little, in any, contaminants; it would also be desirable to recover as much of this water as possible to permit reuse of the water in the chemical mechanical planarization process. Ideally, this reclaim process would occur at the polisher tool in order to effectively reuse the DI water and simultaneously save costs. While conventional filtration technology exists for point-of-use filtration, this technology is not suited for the high probability of suspended matter in the waste stream. With conventional filtration, all effluent flow is into the filter at a perpendicular angle to the membrane element. The particles embed in the membrane media and the filter subsequently clogs. This causes high downtime and related operating costs.
Alternatives to point-of-use filtration include central plant treatments such as pH neutralization and the addition of flocculating or settling agents in conjunction with filter presses; ultrafiltration or reverse osmosis filtration systems. These systems represent a prohibitively costly system for users with just several polishing tools and continuing high operation costs. Further, these systems are gravity drain based. Because of the nature of the suspended solids in the slurry effluent, and the common practice of combining waste streams at a central point prior to treatment, any clear waste collected is sufficiently mixed with particulate bearing fluid as to require treatment of the entire waste stream. It is therefore desirable to have a process which recovers the usable water from the process and eliminates the primary suspended particles problem near the point of origination of the waste stream, yet is flexible enough to meet slurry specific problems. It is also desirable to have a process that is scalable from pilot production to full scale manufacturing. The present invention meets these needs.
SUMMARY OF THE INVENTION
Briefly, and in general terms, the present invention provides for the separation of abrasive components and clear fluids from an aqueous chemical mechanical slurry used for planarization of semiconductor materials, to permit the reuse of the clear liquid effluent in non-process applications as well as for gray water for irrigation, process cooling water, or as make-up water for a reverse osmosis system, or safe disposal in the industrial waste stream, as desired. With the additional use of continuous ion exchange, the resulting water stream can be reused in high purity water applications.
The invention accordingly provides for a method and apparatus for recovering clear liquid from an aqueous slurry waste stream and for concentrating particles of abrasive materials from the same aqueous solution. In one presently preferred embodiment, the apparatus comprises a solids detection device for detecting the concentration of abrasive solids in the aqueous waste stream. The solids detection device preferably receives raw waste including the aqueous slurry containing abrasive particles and materials removed from planarization of semiconductor materials from the polishing tool, and is preferably located in a location of close proximity to the polishing tool. The solids detection device may optionally also detect other materials, and may also optionally measure incoming flow, effluent conductivity, temperature, turbidity, and/or pH. In a presently preferred embodiment, the sensor is of the type which detects solids concentration using light scattering turbidity measurements, combined with conductivity and temperature measurements. A diverter receiving the effluent flow from the solids detection device is also provided for diverting the entire effluent stream including th
Corlett Gary L.
Ferri, Jr. Edward T.
Geatz J. Tobin
Fortuna Ana
Lucid Treatment Systems, Inc.
Ward Richard W.
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