METHOD AND APPARATUS FOR RECOVERY OF WATER AND SLURRY ABRASIVES USED FOR CHEMICAL AND MECHANICAL PLANARIZATION

Abstract: A method of recovering liquid and abrasives from an aqueous slurry containing finely divided, suspended solids comprising at least one filtering step utilizing a sintered metal membrane and/or ceramic membrane in conjunction with a method of measuring specific gravity or density, physically concentrating and separating the abrasive particles from the effluent allowing disposal through the normal industrial waste system or reuse of the supernatant liquid. The method is further used for recovery of solids for reuse in other, less critical applications thus reducing or eliminating the waste by-products of the polishing process.

Description: METHOD AND APPARATUS FOR RECOVERY OF WATER AND SLURRY ABRASIVES USED FOR CHEMICAL AND MECHANICAL PLANARIZATION BACKGROUND OF THE INVENTION Related Applications: This is a continuation in part of Serial No. 08/870,082, filed June 5, 1997. 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 and mechanical abrasive slurry containing finely divided, suspended particles following their use in processing of semiconductor wafers. 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 chips, 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 on such semiconductor devices has continually increased as trace line widths and element sizes on such semiconductor devices have narrowed. At one time, for example, trace line widths on such devices typically ranged from lμm to 4μm. However, in recent years, the industry has made significant advances in reducing trace line widths used in integrated circuits to less than lμm. Currently, trace line widths of 0.5 to 0.35 μm are common, and research is being conducted to achieve trace line widths of from 0.25 μm to 0.18 μ . In addition, the demand for increased memory and computing power has driven 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 numbers of 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 action. Abrasive agents that can be used in the chemical mechanical slurry include particles of fumed silica, cesium and alumina. The chemical mechanical slurry can also include stabilizer or oxidizer agents. Fumed 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. Cesium 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% of the raw waste stream, with the remainder constituting other chemical agents such as stabilizer or oxidizer agents, and water. The raw waste stream is typically diluted with rinse water to yield a final solids concentration of approximately 1% to 1.5% 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 deionized water; it would also be desirable to reclaim the waste stream supernatant liquid to permit reuse of the supernatant liquid in the chemical mechanical planarization process. Ideally, this process would occur at the polisher tool in order to effectively reuse the deionized 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 peφendicular 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 based on the current chemistries and are relatively inflexible to handle future slurry requirements. It is therefore desirable to have a process which treats the primary- suspended particles problem, 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 and other needs. SUMMARY OF THE INVENTION Briefly, and in general terms, the present invention provides for the separation and recovery of abrasive components and fluids from an aqueous chemical mechanical slurry used for planarization of semiconductor materials, to permit the reuse of the 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. The invention accordingly provides for a method and apparatus for recovering clear liquid from an aqueous slurry waste stream and for concentrating and recovering particles of abrasive materials from the same aqueous solution. In the method and apparatus for the invention, an aqueous slurry waste stream which, on an irregular basis, contains an abrasive component is introduced into a particle detection device which used one of several technologies to detect the presence of abrasive particles. The detection device may use optical, ultrasonic or other similar detection techniques to measure the density of the abrasive solids in the effluent stream or the turbidity of the effluent stream. Based on the measurement made by the detection device, when solids concentrations below a desired threshold are indicated, the effluent stream is diverted to one or more small collection tanks. The collected liquid is pumped back to the polisher through an apparatus which provides non-process water to the polisher for reuse as rinse water. Alternatively, when a solids concentration over the desired threshold is detected, the entire waste stream is diverted to an apparatus that separates the solids from the liquid component of the waste stream using an ultrafiltration device. The clear liquid is collected in one or more collection tanks and used variously for return to the polisher as non-process rinse water; backflush water for the ultrafiltration device; or diverted to the facility industrial waste treatment system for disposal. With additional treatment (ion-exchange or elutriation for copper removal, for example) this liquid may be used for gray-water applications such as cooling water or irrigation or as feed water to the facility reverse osmosis system for further water usage reduction. The apparatus of this invention further provides for recirculating the waste solids stream from the ultrafiltration device in order to further concentrate the solids and effect maximum removal of clear liquid from the waste stream. This apparatus is capable of concentrating the solids from as little as 0.2% solids by weight to as high as 50% solids by weight. When the solids content reaches the preferred concentration level, the solids waste is diverted to an apparatus where the solids are collected in containers for off-site disposal or reclamation for reuse in other industries. These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram of the method and apparatus of a first embodiment of the invention for recovering liquid and slurry abrasives that have been used for chemical mechanical planarization of semiconductor wafers; Fig. 2 is a sectional view of a separation column of Fig. 1 ; Fig. 3 is a schematic diagram of the method and apparatus of a second embodiment of the invention for recovering water and slurry abrasives that have been used for chemical and mechanical planarization of semiconductor wafers; Fig. 4 is a sectional view of the shock tank of Fig. 3; Fig. 5 is a schematic view of the filter assembly of Fig. 3; Fig. 6 is a sectional view of the filter of the filter assembly of Fig. 5; Fig. 7 is a sectional view of a separation column of Fig. 3; Fig. 8 is a schematic diagram of the method and apparatus of a third embodiment according to the principles of the invention for recovering liquid and slurry abrasives that have been used from chemical mechanical planarization of semiconductor wafers; Fig. 9 is a schematic diagram of an apparatus according to the principles of the invention for detecting solids concentration in the effluent stream and diverting the clear liquid stream to the interface apparatus and back to the polisher; Fig. 10 is a perspective view of an ultrafiltration device for use in the apparatus of Fig 9 or Fig. 11 ; and Fig. 11 is a schematic diagram of an apparatus according to the principles of the invention for recovering clear liquid from a slurry abrasive waste stream and concentrating the waste stream to maximize the recovery of clear liquid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As the density of electrical components and wiring in semiconductor devices have increased, such devices have become increasingly susceptible to failure due to surface irregularities on semiconductor wafers. Conventional methods utilized in the industry for chemical mechanical planarization of the surface of semiconductor wafers to address this problem commonly result in a wasteful disposal of the abrasive agents and water in the slurry used for polishing the various layers of the semiconductor wafers. As is illustrated in the drawings, the invention is accordingly embodied in a method and apparatus for recovering particles of abrasive material from an aqueous slurry of the particles of abrasive material. Referring to Fig. 1, in a first presently preferred embodiment, an apparatus 10 for recovering particles of abrasive material from an aqueous slurry of the particles of abrasive material typically receives raw waste from inlet line 12 including the aqueous chemical and mechanical slurry containing abrasive particles and materials removed from planarization of semiconductor materials in a slurry waste collection tank 14. The quantity of flow of the slurry waste can be measured by a flow meter 16 connected to the raw waste inlet line. The slurry waste in the slurry waste collection tank is preferably maintained under conditions of ambient temperature and pressure, and is preferably maintained at approximately a neutral pH. The acidity or basicity of the slurry waste is preferably monitored by a pH meter 18 connected to the slurry waste collection tank. Electrical signals indicative of the pH of the slurry waste in the collection tank can be received by a controller 19 for controlling the introduction into the slurry waste collection tank of pH neutralizing agents that are selected depending upon the pH of the slurry effluent. Neutralizing agents can include, for example, an acid from an acid reservoir 20 dispensed through acid valve 24 controlled by the controller, or a base from a base reservoir 22 through base valve 26 controlled by the controller, or pH buffer agents, all of which are well known to those skilled in the art. The slurry waste in the collection tank is typically stirred by a stirrer (not shown) in the collection tank that is driven by motor 27. The mixture of slurry effluent and any neutralizing agents can be held in the slurry collection tank for a period of time for treatment as desired, and then discharged for further processing through the collection tank outlet 28. Alternatively, the treated slurry effluent can be discharged continuously through the collection tank outlet 28. Flow of the treated slurry effluent from the collection tank can be facilitated by pump 29 connected between the collection tank outlet and the treated slurry effluent line 30 leading to further processing of the slurry effluent. A pressure meter 32 and total dissolved solids meter 34 can be connected to the treated slurry effluent line for monitoring the condition of the treated slurry effluent. The treated slurry effluent carried by the effluent line is preferably drawn by vacuum into one or more process chambers or separation columns 36 for separating the treated slurry effluent into a portion containing a greater proportion of the abrasive particles, and a supernatant portion containing a lesser proportion of the abrasive particles. Alternatively, the slurry effluent can be pumped by positive pressure through the separation columns. Each separation column has an inlet 38 for receiving treated slurry effluent, a supernatant outlet line 40 for the lighter supernatant portion of the slurry effluent, and a bottom solids outlet 42 for the heavier portion of the separated slurry effluent containing a greater proportion of the abrasive particles. As is illustrated in Fig. 1, in a presently preferred embodiment, a plurality of the separation columns can be connected in series, so that the most upstream separation column receives treated slurry effluent from the slurry effluent collection tank, and subsequent downstream separation columns receive the lighter supernatant portion of the slurry effluent from an upstream separation column. The most downstream separation column supernatant outlet carries the processed supernatant for further processing. With reference to Fig. 2, each separation column preferably has a nozzle 44 for introducing the treated slurry effluent into a cooling portion 45 of the separation column, surrounded by a cooling coil 46 carrying a flow of coolant. The nozzle preferably introduces the slurry effluent into the cooling portion of the separation column in a direction tangential to the longitudinal axis of the separation column to create a helical or circular flow of the slurry effluent in the cooling portion of the separation column. The cooling coil preferably cools the slurry effluent to a temperature between about 0°C and about 15°C, facilitating agglomeration of the particles. After the slurry effluent is cooled, it passes through precision machined openings between two charged electrode plates. Passage of the cooled slurry effluent between the negatively charged electrode 48 and the positively charged electrode 50 results in a change in the electrical properties of the particles, causing them to agglomerate, causing the resultant floes of particles to separate from a supernatant liquid portion of the slurry effluent. The slurry effluent then passes through a second nozzle 52 that introduces the slurry effluent in a direction tangential to the longitudinal axis of the separation column to create a helical or circular flow of the slurry effluent, causing a portion of the aqueous slurry containing the agglomerations or floes of the particles to move to the solids settling chamber 54 of the of the separation column, while the supernatant liquid remaining in the aqueous slurry exits through the supernatant outlet 40. A solids outlet valve 56 allows control of the flow from the bottom solids outlet 42, so that the portion of the aqueous slurry in the solids settling chamber containing agglomerations of the particles can be discharged as desired from the solids settling chamber through a solids outlet line 58 to a solids collection tank 60, either periodically or continuously. In a presently preferred embodiment, a plurality of separating columns are connected in series such that the supernatant liquid from a supernatant outlet of one separating column passes to the inlet of the next separating column in sequence, while the supernatant outlet of the last separating column in the sequence carries the supernatant liquid for further processing and collection. In one currently preferred embodiment, the supernatant liquid from the separating columns passes via supernatant line 61 to one or more vacuum chambers 62 connected to a source of vacuum 64. The temperature and pressure of the supernatant liquid in the supernatant line can be monitored by temperature and pressure sensors, if desired. In one currently preferred embodiment, the aqueous slurry is introduced into the process chamber at ambient temperature and pressure. In a presently preferred embodiment, the supernatant liquid line from the separating columns is connected to the inlet 66 to a plurality of vacuum chambers, each of which has a supernatant outlet 68 to supernatant outlet line 70, leading to inlet 72 to supernatant liquid collection tank 74. When the supernatant liquid in a vacuum chamber is subj ected to a reduction of pressure, gas entrapped in the supernatant liquid bubbles to the surface of the supernatant liquid. The bubbling of gas to the surface of the supernatant liquid is believed to bring particles in the supernatant liquid into close proximity to cause further agglomeration of the particles due to van der Waals attraction among the particles. The agglomerated particles have a higher specific gravity than the water in the supernatant liquid, causing them to separate and precipitate to the bottom of the vacuum chamber. Alternatively, gas, such as clean dry air, oxygen or nitrogen, for example, can be injected in small quantities into the supernatant liquid in the vacuum chamber to further enhance the bubbling of gas through the supernatant liquid. A solids outlet line 76 leading from the bottom of each vacuum chamber is connected to a solids line 78 leading to solids collection tank. In a presently preferred embodiment, an outlet line 80 from solids collection tank is connected to carry collected solids and liquid to a centrifugal separator 82. Liquid passes from the centrifugal separator to the supernatant collection tank 74. Liquid from the solids collection tank 60 pass through the fluid line 84 to filter press 86, which also receives concentrated solids from the centrifugal separator via solids outlet line 87 from centrifugal separator. Solids can ultimately be collected via solids waste line 88 from filter press 86. Supernatant liquid from the centrifugal separator flows via supernatant liquid outlet line 90 to the supernatant liquid collection tank 74. The pH of the supernatant liquid can be monitored by pH meter 92 connected to the supernatant liquid collection tank. The supernatant liquid can be collected through outlet 94, and can be pumped by a pump 96 through line 98 to one or more holding tanks 100 having supernatant outlets 102, where the quantity and quality of the supernatant liquid can be monitored, for example, by pH meter 104, total dissolved solids meter 106, turbidity meter 108, and flow meter 110. Referring to Figs. 3 to 7, in a currently preferred second embodiment of the invention, an apparatus 210 for recovering particles of abrasive material from an aqueous slurry of the particles of abrasive material typically receives raw waste from inlet line 212 including the aqueous chemical and mechanical slurry containing abrasive particles and materials removed from planarization of semiconductor materials in a slurry waste pH shock tank 214. The quantity of flow of the slurry waste can be measured by a flow meter 216 connected to the raw waste inlet line. The slurry waste in the slurry waste pH shock tank is preferably maintained under conditions of ambient temperature and pressure, and is preferably maintained at approximately a pH of about 2 to 4. The pH of the slurry waste is preferably monitored by a pH meter 218 connected to the slurry waste Ph shock tank, as is shown in Fig. 3. Referring to Figs. 3 and 4, electrical signals indicative of the pH of the slurry waste in the pH shock tank can be received by a controller 219 for controlling the introduction into the slurry waste pH shock tank of an acid, such as HC1, for example, and other pH controlling agents, in quantities depending upon the pH of the slurry effluent. The acid is dispensed from an acid reservoir 220 through acid valve 224 controlled by the controller, or a base from a base reservoir 222 through base valve 226 controlled by the controller, or pH buffer agents. The slurry waste in the pH shock tank is typically stirred by a stirrer 221 in the pH shock tank that is driven by motor 227. The mixture of slurry effluent and any neutralizing agents can be held in the slurry pH shock tank for a period of time for treatment as desired, and is typically held in the shock tank for a period of time ranging up to about 1 hour. The acidified aqueous slurry is then discharged for further processing through the pH shock tank outlet 228 to the pH balance tank 214'. As is illustrated in Fig. 4, the slurry waste pH shock tank 214 has a stirrer 221 propeller at end of a stirrer shaft 223 which also serves as a cathode for applying an electrical potential through the acidified aqueous slurry to change the electrical properties of the particles to facilitate agglomeration and flocculation of the particles. A wire mesh anode grid 225 is disposed in the shock tank around the stirrer shaft cathode, and is electrically connected with the base of the shock tank, which also serves as an anode. The voltage that is applied to the aqueous slurry in the shock tank is typically about 12 to 5,500 volts, although higher voltages may be even more effective. The shock tank also has a supernatant overflow outlet 229 for relief of excess aqueous slurry in the shock tank. A cooling jacket (not shown) typically of coils similar to those for the cooled process chamber preferably is used around the pH shock tank to cool the temperature of the aqueous slurry to a range of between about 0°C and about 15°C. Electrophoresis is accomplished in the pH shock tank radially, driving the particles through the separation anode grid. Outside the stirring zone within the mesh grid, the particles agglomerate and fall to the bottom of the tank, and are drawn to the bottom of the tank by the anode plate at the bottom of the tank. The agglomeration process is enhanced by chilling the aqueous slurry to a temperature between about 0°C and about 15°C, which decrease the effects of Joule heating and convective mixing caused by the electrophoretic process. Supernatant liquid can also be drawn off from the top of the pH shock tank to be neutralized and recycled with supernatant from other parts of the process. Referring to Fig.3, the acidified solids/fluid solution is drawn off from the bottom of the pH shock tank under vacuum to the pH balance tank 214', and is mixed with untreated waste slurry received via inlet line 212', and neutralizing agents added to the pH balance tank. Electrical signals indicative of the pH of the slurry waste in the pH balance tank can be received by a controller 219' for controlling the introduction into the slurry waste pH balance tank of pH neutralizing agents that are selected depending upon the pH of the slurry effluent. Neutralizing agents can include, for example, an acid such as HC1, for example, from an acid reservoir 220' dispensed through acid valve 224' controlled by the controller, or a base, such as sodium bicarbonate (Na 2 CO 3 ), from a base reservoir 222' through base valve 226' controlled by the controller, or pH buffer agents, all of which are well known to those skilled in the art. The slurry waste in the pH balance tank is typically stirred by a stirrer 221 ' in the pH balance tank that is driven by motor 227'. The mixture of slurry effluent and any neutralizing agents can be held in the slurry pH balance tank for a period of time for treatment as desired, and then discharged for further processing through the pH balance tank outlet 228'. Alternatively, the treated slurry effluent can be discharged continuously through the pH balance tank outlet 228'. A cooling jacket (not shown) typically of coils similar to those for the cooled process chamber and the pH shock tank preferably is used around the pH balance tank to maintain the temperature of the pH neutralized aqueous slurry within a range of about 0°C to about 15°C for increasing the rate of agglomeration. Outside the agitation zone of the stirrer, agglomerated particles fall to the bottom of the pH balance tank. The effluent from the pH balance tank then preferably is preferably drawn under vacuum to a first self-cleaning reversible gross particle filter assembly 230 and then to a second self-cleaning reversible filter assembly 230' which is substantially identical to the filter assembly 230, as is illustrated in Figs. 3 and 5. The filter assemblies 230 and 230' will be described in detail with reference to the filter assembly 230 shown in Fig. 5. The self-cleaning gross particle filters operate by forcing a fluid flow through the filter containing a multi-layered filter material that traps gross particles. After a timed interval, the flow can be reversed through the filter, causing the gross particles previously captured in the filter media to flow out and to drop into a collection chamber. By repeating this process, the filters collect gross particles, and reduce the need for frequent filter replacement. The effluent from the pH balance tank outlet 228' is thus connected to filter assembly inlet 256 of the filter assembly, which includes a series of flow control valves 23 la-23 If connected to the inlet 256 that can be opened and closed to direct the flow of pH neutralized slurry through the filter 232 connected between the two filter manifolds 233a,b. As is shown in Fig. 6, in a currently preferred embodiment, the filter contains a sequence of symmetrically arranged layers of filter media 234a-g, with the gradation of the filter media being from coarsest to finest from the outside layers to the inside layer. Thus, the filter contains two outside gross filter media 234a,g respectively adjacent to a medium filter media 234b,f, followed respectively by an adjacent medium/fine filter media 234c,e, on either side of the innermost fine filter media 234d. Other similar arrangements of filter media may also be suitable. Thus, in operation, the filter assembly can be operated in either of two configurations allowing the direction of flow through the filter to be reversed periodically to flush gross particles from the filter, allowing the gross particles to be discharged through the filter assembly solids outlet 258. In an exemplary first configuration, valves 23 la, b, d, f are closed and valves 231c and e are open, allowing flow from right to left through the filter. Filtered supernatant flows up through the supernatant liquid outlet 235. After aperiod of time for collecting gross particles on the right side of the filter, the valve configuration can be changed to a reversed flushing configuration in which valves 231 a, c and e are closed, and valve 231 d is temporarily opened and valve 231 f temporarily closed to allow gross particles to be flushed to the right through to the solids outlet 258. Thereafter, valve 23 Id can be closed, and valve 23 If opened, to allow flow in a normal second flow configuration from left to right through the filter and up through the supernatant liquid outlet 235. After a period of time for collecting gross particles on the left side of the filter, the valve configuration can be again changed back to the original flow configuration for flushing of the filter, in which valves 231 b, d, f are closed, valve 231c is open, allowing flow from right to left through the filter, and valve 231a is temporarily opened and valve 23 le temporarily closed to allow gross particles to be flushed to the left through to the solids outlet 258. Thereafter, valves 231a, b, d, f are closed and valves 231c and e are open, in the normal first flow configuration, allowing flow from right to left through the filter, and filtered supernatant flows out through the supernatant liquid outlet 235. The treated slurry effluent carried by the effluent line is preferably drawn by vacuum through an inlet 238 into one or more process chambers or separation columns 236 for separating the treated slurry effluent into a portion containing a greater proportion of the abrasive particles, and a supernatant portion containing a lesser proportion of the abrasive particles. As is illustrated in Fig. 3, in a presently preferred embodiment, a plurality of the separation columns can be connected in series, so that the most upstream separation column receives treated slurry effluent from the slurry effluent collection tank, and subsequent downstream separation columns receive the lighter supernatant portion of the slurry effluent from an upstream separation column. The most downstream separation column supernatant outlet carries the processed supernatant for further processing and collection. Each separation column has an inlet 238 for receiving treated slurry effluent, a supernatant outlet line 240 for the lighter supernatant portion of the slurry effluent, and a bottom solids outlet 242 for the heavier portion of the separated slurry effluent containing a greater proportion of the abrasive particles. With reference to Fig. 7, each separation column typically has a solids outlet end cap 255 and a supernatant liquid outlet end cap 257. for introducing the treated slurry effluent into a cooling portion 45 of the separation column, surrounded by a cooling coil 46 carrying a flow of coolant. A nozzle 252 receiving the aqueous slurry flow from the inlet preferably introduces the slurry effluent into the cooling portion of the separation column in a direction tangential to the longitudinal axis of the separation column to create a helical or circular flow of the slurry effluent in the cooling portion of the separation column. The cooling coil preferably cools the slurry effluent to a temperature between about 0°C and about 15°C, facilitating agglomeration of the particles, causing a portion of the aqueous slurry containing the agglomerations or floes of the particles to fall out of suspension to the solids settling chamber 254 at the bottom of the separation column, while the supernatant liquid remaining in the aqueous slurry exits through the supernatant outlet 240. The accumulated solids can be either periodically purged or continuously drawn by vacuum from the separation columns to a gross solids collection tank 260. Referring to Figs. 3 and 7, a solids outlet valve 256 allows control of the flow from the bottom solids outlet 242, so that the portion of the aqueous slurry in the solids settling chamber containing agglomerations of the particles can be discharged as desired from the solids settling chamber through a solids outlet line 258 to a gross solids collection tank 260, either periodically or continuously. In a currently preferred embodiment, the effluent from solids outline 258 is drawn to the gross solids collection tank by a vacuum gravity vessel 261 connected to a vacuum source 264. The gross solids collection tank can be emptied while fluid flow continues through the separating columns. In a currently preferred embodiment, the supernatant liquid from the separating columns passes via supernatant outlet line 240 to one or more vacuum gravity vessel 262 connected to the source of vacuum 264. In one currently preferred embodiment, the aqueous slurry is introduced into the process chamber at ambient temperature and pressure. In a presently preferred embodiment, the supernatant liquid line from the separating columns is connected to the inlet 266 to a plurality of vacuum gravity vessels, each of which has a supernatant outlet 268 connected to the fine sludge collection tank 270, having an outlet 272. An outlet line 280 from solids collection tank is connected to carry collected solids from the outlet of the gross solids collection tank and fine sludge from the fine sludge collection tank outlet and liquid remaining in the gross sludge and fine sludge to a centrifugal separator 282. The lighter liquid fraction separated in the centrifugal separator is conducted to the supernatant collection tank 274. Concentrated solids are conducted to a dryer 286 via the solids outlet line 287 from the centrifugal separator. Solids can ultimately be collected via solids waste line 288 from the dryer. Supernatant liquid from the centrifugal separator flows via supernatant liquid outlet line 290 to the supernatant liquid collection tank 274. The supernatant is drawn from the centrifuge, through an optional V light source and ion exchange resin bead to remove dissolved solids, into the supernatant liquid collection tank for final processing. The pH and total dissolved solids of the supernatant liquid can be monitored by pH meter 292 and total dissolved solids metering station 293, respectively, connected to the supernatant liquid collection tank. The supernatant liquid can be collected through outlet 294, and can be pumped by a pump 296 through line 298, which can be provided with one or more filters 297. In the case of silica-based and TEOS based slurries, the flocculated material may be recovered for reuse of the silicon or TEOS in the slurries. In the case of alumina-based slurries, the flocculated material may also be recovered for reuse of the silicon in the slurries. Due to metallic impurities, it is unlikely that alumina-based slurries can be reclaimed for use in the semiconductor industry. In the case where TEOS or silica-based and alumina or cesium-based slurries are combined, then the flocculated material is treated as alumina-based solids for reuse or disposal. The reuse or disposal of the silicon, alumina and other metals and the required purity for any such reuse is well known to those skilled in the art of slurry manufacture. Referring to Fig. 8, in a currently preferred third embodiment of the invention, a method and apparatus are provided first for the recovery of clear liquid from an aqueous waste stream that may contain abrasive materials, and then for the removal of the solids from the aqueous solution. The apparatus 300 for detecting the concentration of abrasive solids in an aqueous waste stream receives raw waste from a polisher 302 including the aqueous slurry containing abrasive particles and materials removed from planarization of semiconductor materials . The apparatus 300 is located in a location of close proximity to the polishing tool, and generates a signal 304 to a control unit 306 controlling valve 308 for directing the effluent from the detector apparatus 300. When the abrasive solids concentration is below a desired threshold, the entire effluent stream is diverted by the valve 308 to an apparatus 310 for reuse in non-critical rinsing applications in the polishing tool. When the abrasive solids concentration is above the desired threshold, the entire effluent stream, including the aqueous slurry containing abrasive particles and materials removed from planarization of semiconductor materials, is diverted by the valve 309 to an apparatus 312 which can be the concentrator apparatus of Figs. 1 -2 or Figs.4-7, to further separate the clear liquid component from the abrasive solids and concentrates the abrasive solids for disposal. The clear liquid from the concentrator apparatus 312 is returned via line 313 to the concentration detection apparatus 300 for recycling or to the industrial waste treatment system 314 for disposal. The concentrated abrasive solids and materials removed from planarization of semiconductor materials are diverted to an apparatus 316 for alternatively filling one of several waste collection containers 317 which, when filled, are removed for off-site processing 318. Referring to Figure 9, in another presently preferred embodiment, an apparatus 320 for detecting the concentration of abrasive and other materials in an aqueous solution receives raw aqueous effluent possibly containing an aqueous slurry of abrasive particles in a solids detection device 322 where the incoming flow 324 and effluent pH 326 are also measured. The solids detection device utilizes optical, ultrasonic or similar detection techniques to detect turbidity and/or particulate density. The solids detection device generates a signal 328 to a control unit 330 controlling valve 332 for directing the effluent from the solids detection device. If the incoming effluent stream contains solids under a desired threshold, the entire effluent stream is diverted by valve 332 to one or more collection tanks 334; otherwise, the entire effluent stream containing abrasive solids is diverted by valve 332 to one or more collection tanks 336 for local filtration. From tank 336, effluent containing abrasive solids and materials from polishing semiconductor wafers is transferred by pump 338 through an ultrafiltration device 340 of either ceramic or sintered metal construction, as illustrated in Fig. 10. The ultrafiltration device is preferably manufactured from ceramic or sintered metal, although other materials of construction such as polysulfone may alternatively be used. After a single pass, the aqueous solution containing abrasive solids and materials from polishing semiconductor wafers is sent by drain 342 to a solids concentrator apparatus for further processing. The clear liquid from this ultrafiltration device is collected in the one or more collection tanks 334. An electronic interface of the control unit with the polisher indicates when non-process equipment rinse water is required by the polisher 344. Upon receipt of a signal from the polisher, pump 346 draws clear liquid from one or more collection tanks 334, and pumps the liquid through flow meter 348 and valve 350 to return to the polisher as non-process equipment rinse water. When adequate reclaimed water is not available from collection tanks 334, additional rinse water is obtained by opening the deionized water by-pass valve 352. When the supply in the collection tank 334 is sufficient to meet the demand of the polisher, the excess is diverted to the industrial waste treatment system through an overflow drain 354. Referring to Fig. 11, the apparatus 360 for concentrating the abrasive solids in the waste stream receives an aqueous solution from the solids detection apparatus 362 into one or more concentration tanks 364. The solids content in this tank is monitored on a continuous basis by a solids concentration measurement device 366 while the pH of the liquid is monitored continuously by the pH sensor 368. While the solids concentration is below a desired threshold and the fluid level in the tank is below the level sensor 370, pump 372 recirculates the aqueous solution through an ultrafiltration device 374 such as the one shown in Fig. 10. The ultrafiltration device 374 is preferably manufactured from ceramic or sintered metal, although other materials of construction such as polysulfone may alternatively be used. The retentate 375 from the ultrafilter is returned to the concentration tank 364 for re-filtration while the permeate 377 or clear liquid from the ultrafiltration device 374 is sent to either the industrial waste treatment system (not shown) or back to the solids detection apparatus 362 for use as non-process equipment rinse water, or to a backflush water collection tank 379 through valve 376. The ultrafiltration device 374 is backflushed periodically (preferably every 10 to 20 minutes) by diverting the waste stream at valve 378 to an apparatus for collection of the solids waste (not shown) and opening valve 380 for a short period of time. Backflush water is drawn by pump from the backflush water collection tank (not shown) and used to pressurize the back side of the ultrafiltration device. This causes possible embedded particles to break away from the ultrafiltration element and return to the concentration tank 364. When the solids concentration reaches the desired threshold, or when the fluid level in the concentration tank 364 reaches the level sensor 370, the flow from pump 372 is diverted by valve 378 to apparatus for collection of the solids waste (not shown). It will be apparent from the foregoing that while particular forms of the invention have been illustrated and described, various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.

Claims: WHAT IS CLAIMED IS: 1. A method for recovery of liquid and particles of abrasive materials used for chemical mechanical planarization from an aqueous slurry waste stream, the density of the particles of abrasive materials in the liquid of the aqueous slurry waste stream varying on an irregular basis, the method comprising the steps of: measuring the density of abrasive particles in an aqueous slurry waste stream; comparing the density of abrasive particles in the aqueous slurry waste stream with an aqueous slurry density threshold; diverting the aqueous slurry waste stream to at least one reuse collection tank based on the density measurement when the density of abrasive particles in the aqueous slurry waste stream is below said aqueous slurry density threshold; and diverting the aqueous slurry waste stream for separating the abrasive particles from the liquid of the waste stream based on the density measurement when the density of abrasive particles in the aqueous slurry waste stream is greater than or equal to said aqueous slurry density threshold to provide a waste solids stream. 2. The method of Claim 1 , wherein said step of separating the abrasive particles from the liquid of the waste stream comprises separating said abrasive particles from the liquid of the waste stream by ultrafiltration. 3. The method of Claim 1 , further comprising the step of recirculating said waste solids stream to further concentrate the abrasive particles in said waste solids stream and further remove clear liquid from said waste solids stream. 4. The method of Claim 3, further comprising the steps of: measuring the density of abrasive particles in said waste solids stream; comparing the density of abrasive particles in said waste solids stream with a waste solids stream density threshold; and diverting said waste solids stream when the density of abrasive particles in said waste solids stream is greater than or equal to said waste solids stream density threshold. 5. An apparatus for recovery of liquid and particles of abrasive materials used for chemical mechanical planarization from an aqueous slurry waste stream, the density of the particles of abrasive materials in the liquid of the aqueous slurry waste stream varying on an irregular basis, the apparatus comprising: means for measuring the density of abrasive particles in an aqueous slurry waste stream; means for comparing the density of abrasive particles in the aqueous slurry waste stream with an aqueous slurry density threshold; means for diverting the aqueous slurry waste stream to at least one reuse collection tank based on the density measurement when the density of abrasive particles in the aqueous slurry waste stream is below said aqueous slurry density threshold; and means for diverting the aqueous slurry waste stream to a means for separation of the abrasive particles from the liquid of the waste stream based on the density measurement when the density of abrasive particles in the aqueous slurry waste stream is greater than or equal to said aqueous slurry density threshold to provide a waste solids stream. 6. The apparatus of Claim 5, wherein said means for separation of the abrasive particles from the liquid of the waste stream comprises an ultrafiltration device. 7. The apparatus of Claim 5, further comprising means for recirculating said waste solids stream to further concentrate the abrasive particles in said waste solids stream and further remove clear liquid from said waste solids stream. 8. The apparatus of Claim 7, further comprising: means for measuring the density of abrasive particles in said waste solids stream; means for comparing the density of abrasive particles in said waste solids stream with a waste solids stream density threshold; means for diverting said waste solids stream when the density of abrasive particles in said waste solids stream is greater than or equal to said waste solids stream density threshold. 9. An apparatus for recovery of liquid and particles of abrasive materials used for chemical mechanical planarization from an aqueous slurry waste stream, the density of the particles of abrasive materials in the liquid of the aqueous slurry waste stream varying on an irregular basis, the apparatus comprising: a detector receiving an aqueous slurry waste stream containing liquid and particles of abrasive materials, for measuring the density of abrasive particles in an aqueous slurry waste stream; a comparator for comparing the density of abrasive particles in the aqueous slurry waste stream with an aqueous slurry density threshold; and a valve for diverting the aqueous slurry waste stream to at least one reuse collection tank based on the density measurement when the density of abrasive particles in the aqueous slurry waste stream is below said aqueous slurry density threshold, and for diverting the aqueous slurry waste stream to an ultrafiltration device for separating the abrasive particles from the liquid of the waste stream based on the density measurement when the density of abrasive particles in the aqueous slurry waste stream is greater than or equal to said aqueous slurry density threshold to provide a waste solids stream. 10. The apparatus of Claim 9, further comprising a valve for recirculating said waste solids stream to further concentrate the abrasive particles in said waste solids stream and further remove clear liquid from said waste solids stream. 11. The apparatus of Claim 10, further comprising: a detector for measuring the density of said abrasive particles in said waste solids stream; a comparator for comparing the density of said abrasive particles in said waste solids stream with a waste solids threshold; and a valve for diverting said waste solids stream when the density of said abrasive particles in said waste solids stream is greater than or equal to said waste solids threshold.

Inventors: CORLETT GARY L, FERRI EDWARD T JR, GEATZ J TOBIN, CORLETT, GARY, L., FERRI, EDWARD, T., JR., GEATZ, J., TOBIN
Applicants: LUCID TREATMENT SYSTEMS INC, LUCID TREATMENT SYSTEMS, INC.
Application year: 1999
Main classification: B01D37
IPC codes: B01D37, B01D61, B01D69, B24B37, B24B57, C02F1, H01L21