Processing of a CMP slurry for improved planarization of integrated circuit wafers

Abstract

The disclosure is directed to a system that processes chemical mechanical planarization (CMP) slurries to reduce or eliminate large particles in the slurries, which can scratch integrated circuit wafers without substantially altering a percentage of solids in the CMP slurry by weight. In particular, the system breaks up particles of a CMP slurry using an intensifier pump system and a fluid processing device. The techniques have proven much more effective than conventional filtering techniques in reducing or eliminating scratches to integrated circuit wafers when a processed CMP slurry is used in a CMP process.

Description

TECHNICAL FIELD

The invention relates to chemical mechanical planarization (CMP) and, more particularly, processing techniques for CMP slurries.

BACKGROUND

Chemical mechanical planarization (CMP) is commonly used during the fabrication of integrated circuit wafers, e.g., silicon wafers. During integrated circuit wafer manufacture, CMP is typically used to make the surface of the wafers both flat (i.e., planar) and smooth (i.e., polished) by removing excess materials, such as copper or other conductors or insulators, that are deposited and etched on the integrated circuit wafer. CMP is typically performed multiple times, e.g., after each successive layer is applied in the formation of an integrated circuit wafer.

In the CMP process, CMP slurries, which include hard particles in a carrier solution, may be deposited onto a rotating polishing pad. The integrated circuit wafer is then placed into contact with the polishing pad and typically rotates in the same direction as the polishing pad, but at a different rotational rate. The CMP slurries deposited onto the polishing pad are used to polish and planarize the integrated circuit wafer as part of the fabrication process.

During the integrated circuit wafer fabrication process, several CMP steps may be performed. Typically, each layer of the integrated circuit wafer may be fabricated using lithography, deposition, etching and then CMP. After one layer is formed, the next layer is formed using similar processes. Unfortunately, CMP can sometimes introduce scratches into the integrated circuit wafers. These scratches are highly undesirable and can undermine the fabrication of integrated circuit wafers.

SUMMARY

In general, the invention is directed to a system that processes chemical mechanical planarization (CMP) slurries to reduce or eliminate large particles in the slurries, which can scratch integrated circuit wafers. In particular, the system breaks up particles of a CMP slurry using an intensifier pump system and a fluid processing device. In this manner, the system can reduce the number and size of large particles that otherwise exist in a CMP slurry without substantially altering a percentage of solids in the CMP slurry by weight. The techniques can be more effective than conventional filtering techniques in reducing or eliminating scratches to integrated circuit wafers when processed CMP slurries are used in a CMP process.

In one embodiment, the invention provides a method comprising processing a CMP slurry via an intensifier pump system and a fluid processing device that breaks up at least some particles of the CMP slurry to reduce particle size. The method may further include planarizing an integrated circuit wafer using the processed CMP slurry. Alternatively, the processed CMP slurry may itself be sold for use by another entity in planarizing integrated circuit wafers.

In another embodiment, the invention provides a planarization system for integrated circuit wafers comprising a CMP slurry processing system that processes a CMP slurry to break up at least some particles of the CMP slurry to reduce particle size, and a CMP unit that planarizes an integrated circuit wafer using the processed CMP slurry. In some cases, the CMP slurry processing system includes an intensifier pump system and a fluid processing device that breaks up at least some of the particles of the CMP slurry. In this manner, the system can reduce the number and size of large particles that otherwise exist in a CMP slurry.

The invention may provide one or more advantages. For example, the invention may reduce the number and size of the large particle size tail in CMP slurries that cause scratches in integrated circuit wafers during CMP without substantially altering a percentage of solids in the CMP slurry by weight. In this manner, the techniques can improve the efficiency and yield of integrated circuit wafer fabrication by reducing or eliminating such scratches. As noted above, the techniques described in this disclosure may be more effective than conventional filtering techniques in reducing or eliminating scratches to integrated circuit wafers when the processed CMP slurries are used in a CMP process.

In an added embodiment, the invention may comprise a chemical mechanical planarization (CMP) slurry comprising water, and particles dispersed in the water. Substantially all of the particles have a diameter less than approximately 1 micron and the particles comprise at least one of alumina (Al₂O₃), cerium oxide (CeO₂) and silicon dioxide (SiO₂).

Additional details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an exemplary system that can implement chemical mechanical planarization (CMP) slurry processing techniques according to the invention.

FIG. 2 is a block diagram of an exemplary intensifier pump system that may be used according to the invention.

FIG. 3 is a cross-sectional side view of an exemplary fluid processing device that may be used according to the invention.

FIG. 4 is a cross-sectional side view of a portion of the fluid processing device shown in FIG. 3.

FIG. 5A is a simplified top view of a CMP unit that may be used to planarize integrated circuit wafers according to the invention.

FIG. 5B is a simplified side view of the CMP unit shown in FIG. 5A.

FIG. 6 is a flow diagram illustrating a technique according to the invention.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of an exemplary system 10 that can implement chemical mechanical planarization (CMP) slurry processing techniques according to the invention. In accordance with the invention, system 10 may incorporate a CMP slurry processing system 6, which breaks up at least some particles of the CMP slurry to reduce particle size without substantially altering a percentage of solids in the CMP slurry by weight. In this manner, the system can reduce the number and size of large particles that otherwise exist in a CMP slurry. As described in greater detail below, slurry processing system 6 may include an intensifier pump system 8, which uses two or more intensifier pumps that operate in a complementary fashion. In addition, slurry processing system 6 may include a fluid processing device 12 with opposing annular flow paths, as further described herein.

As shown in FIG. 1, a CMP slurry container 2 stores a CMP slurry (sometimes referred to as a “dispersion”). The slurry stored in container 2 may comprise any slurry commonly used for integrated circuit wafer planarization and polishing. For example, the slurry may comprise one or more types of hard particles in a carrier solution, such as water. The hard particles may include one or more of alumina (Al₂O₃), cerium oxide (CeO₂), silicon dioxide (SiO₂), or other hard particles used in CMP slurries. Following the processing described herein, the vast majority of particles (i.e., substantially all of the particles) exhibit a diameter of less than approximately 1 micron, which is highly desirable to reduce or eliminate undesirable scratching during the planarization process. In some cases, the CMP slurry may also include chemicals or additives, such as oxidizers, that can soften the material to be removed during the planarization process and thereby help ensure consistent removal rates during the planarization process.

One or more pumps 3 can serve to draw the CMP slurries from container 2 and deliver the CMP slurries to a mixer 4. Mixer 4 is an optional component. Mixer 4 receives the CMP slurries pumped from container 2 and mixes the CMP slurries, e.g., to achieve uniform distribution of the hard particles in the carrier solution. Mixer 4 may comprise a high-shear mixer or the like, and is optional for system 10. Additional materials, such as additives or the like, may also be added in one or more stages using mixer 4 or additional mixers. Accordingly, CMP slurry container 2 may or may not contain all of the ingredients of a final CMP slurry mixture.

As mentioned above, system 10 includes a CMP slurry processing system 6, which breaks up at least some particles in the CMP slurry to reduce particle size to a size more desirable for the planarization application. System 6 can do so without substantially altering a percentage of solids in the CMP slurry by weight. As shown in FIG. 1, slurry processing system 6 may include an intensifier pump system 8, and a fluid processing device 12.

Intensifier pump system 8 may include one or more intensifier pumps, and may be capable of generating approximately 5,000 to 60,000 psi (34.5 MPa to 413 MPa) of fluid pressure. Fluid processing device 12, as described herein, may be capable of handling pressures greater than approximately 10,000 psi (68,950 kPa), greater than approximately 30,000 psi (207 MPa), greater than approximately 50,000 psi (345 MPa), or greater than approximately 60,000 psi (413 MPa). Following pressurization by intensifier pump system 8, the CMP slurry is delivered to fluid processing device 12. Fluid processing device 12 generates intense shear and extensional forces that reduces the size of the particles in the CMP slurry. In particular, fluid processing device 12 serves to break up any large particles of the CMP slurry into smaller-sized particles, and thereby produce a finely dispersed solution of particles in the processed CMP slurry having a more desirable size range without substantially altering a percentage of solids in the CMP slurry by weight. Heat exchangers (not shown) may be used to dissipate excess thermal energy generated during processing and generally control the temperature of the processed slurry as desired. The shear and extensional forces are specifically useful in breaking up such large particles and may help to substantially eliminate any particles larger than approximately 1 micron.

One or more filters 14 may also be used to filter particles from the processed CMP slurry. For example, filters 14 may comprise one or more porous membranes, mesh screens, or the like, to filter the processed CMP slurry. Filters 14, however, are optional, and may be eliminated from some embodiments. In some cases, filtered portions of the processed CMP slurry (or, more generally, any unused portions of CMP slurry) may be recycled back to intensifier system 8 via a feedback loop 19.

The output of filters 14 (or the output of fluid processing device 12 if filters 14 are not used) may then be delivered to a CMP unit 16. If desired, a back pressure regulator (not shown) may be added downstream of filters 14 to help maintain constant pressure in system 10 and provide a return path to supply CMP slurry container 2.

CMP unit 16 planarizes and polishes an integrated circuit wafer using the processed CMP slurry. Since the CMP slurry is processed by CMP slurry processing system 6, scratches to the integrated circuit wafers may be reduced in the processing stage relative to conventional techniques that rely solely on filtering to remove large particles from the CMP slurry. In particular, CMP slurry processing system 6 can reduce the number and size of large particles, such as particles larger than 1 micron in diameter, by breaking up such particles into smaller more desirable particle size without substantially altering a percentage of solids in the CMP slurry by weight. In some cases, such particles can be completely eliminated.

CMP unit 16 may include a polishing pad and the processed CMP slurry may be deposited onto the polishing pad. The polishing pad may rotate as another mechanism rotates the integrated circuit wafer relative to the rotating polishing pad in order to cause the integrated circuit wafer to be planarized. This planarization step may be performed many times in the fabrication of an integrated circuit wafer, e.g., with respect to multiple different layers fabricated into the integrated circuit wafer. In some systems, multiple CMP units 16, all of which may be supplied with CMP slurries via the same CMP slurry processing system 6 described herein.

FIG. 2 is a diagram of an exemplary intensifier system 8 in accordance with an embodiment of the invention. Intensifier system 8 may be particularly useful in the delivery of a continuous, steady, high pressure flow of CMP slurries to fluid processing device 12. Typical fluid pressure may range from 0 psi to 40,000 psi (276,000 kilopascals), or greater, during each intensifier cycle. System 8 includes two different intensifier pumps 80 and 85 that operate in a complementary fashion to achieve the continuous, steady, high pressure flow of CMP slurries to fluid processing device 12. Additional intensifier pumps, however, could also be included in system 8. Also, a single intensifier pump could be used, but this embodiment might be less effective in achieving continuous, steady, high pressure.

Intensifier system 8 may be a hydraulic system that includes a low pressure supply pump 15. Supply pump 15 is used to deliver a CMP slurry into intensifier system 8 from a supply or reservoir (not shown in FIG. 2). Supply pump 15 may be a diaphragm pump, or other suitable pump, capable of delivering an appropriate volume of the CMP slurry. Supply pump 15 may deliver the CMP slurry at about 60-100 psi, although this can vary from system to system. Referring back to FIG. 1, in an alternative configuration, supply pump 15 (FIG. 2) could be used as pump 3 (FIG. 1) with intensifier system 8 (FIG. 1) including the remaining components of FIG. 2. In that case, mixer 4 (FIG. 1) could be eliminated, or possibly included after supply pump 15 (FIG. 2).

Referring again to FIG. 2, supply pump 15 feeds into inlet 20 of a check valve, hereinafter referred to as a “smart” valve 25. Smart valve 25 may comprise a controllable valve that can be actively opened and closed by a controller 30. Smart valve 25 may include a valve poppet (not shown) that is coupled to an actuator (not shown) that is, in turn, coupled to air cylinder 35. Air cylinder 35 (or another type of actuator) is controlled by controller 30 and can quickly and efficiently open or close smart valve 25 through the actuation of the valve poppet.

When smart valve 25 is opened, a CMP slurry is delivered through inlet/outlet 40 of a charge intensifier pump 45. More specifically, the CMP slurry is delivered into an intensifier barrel 50. Charge intensifier pump 45 includes a hydraulic actuator 55 having a hydraulic piston 60. As hydraulic piston 60 is caused to move back and forth, it causes product intensifier piston 65 to move back and forth as well. More specifically, as hydraulic piston 60 and product intensifier piston 65 retract, the CMP slurry is able to fill intensifier barrel 50. As hydraulic piston 60 advances, product intensifier piston 65 advances and the CMP slurry is expelled through inlet/outlet 40 at the appropriate intensified pressure. Hydraulic piston 60 is caused to advance by introducing hydraulic fluid under pressure through hydraulic fluid supply inlet (advance) 52 and retracted by introducing hydraulic fluid under pressure through hydraulic fluid supply inlet (retract) 54. An LVDT 70 (linear variable displacement transducer) or other type of position sensor can be coupled with hydraulic piston 60 so as to provide an indication of the piston's position to controller 30. Thus, controller 30 causes smart valve 25 to open when hydraulic piston 60 is ready to begin its retraction cycle.

Each time supply intensifier piston 65 advances, the CMP slurry is moved through inlet/outlet 40 at a relatively high pressure into supply line 75. While actual pressures will vary depending upon the configuration of the system, in one embodiment the CMP slurry enters the supply line at between 700-2000 psi (4830-13,800 Kilo Pascals). The CMP slurry is then delivered to either a first product intensifier pump 80 or a second product intensifier pump 85 (each of which has the same components in the same configuration). It should be noted that more product intensifier pumps could be incorporated into the system and the illustrated embodiment having two such pumps is for illustrative purposes only. Also, in simpler embodiments, an intensifier system could include a single intensifier pump, although this would typically not provide continuous, steady, high pressure.

As illustrated in FIG. 2, first product intensifier pump 80 is in a retracted position when second product intensifier pump 85 is at or near the end of an extension cycle. In this manner, first and second product intensifier pumps 80, 85 operate at least partially out of phase with one another to provide a combined output that is substantially continuous and constant. Put another way, first and second product intensifier pumps 80, 85 operate in a complementary fashion, with one providing pressure intensification of a CMP slurry while the other re-fills with the CMP slurry.

Second product intensifier pump 85 includes a hydraulic actuator 90 having a hydraulic piston 95. Hydraulic piston 95 is coupled to a product intensifier piston 100 located within an intensifier barrel 105. A linear position transmitter (LPT) 110 is coupled between hydraulic piston 95 and a controller 115 so as to provide positional information to controller 115. Controller 115 may be coupled with an air cylinder 120 or other type of actuator that actuates smart valve 125.

As hydraulic piston 95 reaches the end of its extension cycle, information indicative of this position is sent by LPT 110 to controller 115. Controller 115 then causes smart valve 125 to open. The CMP slurry enters inlet 130 of smart valve 125, passes through and enters an inlet 135 of intensifier barrel 105. Because the CMP slurry may be delivered at pressures of about 1200 psi (8270 kilopascals) by charge intensifier pump 45, product intensifier piston 100 is forced backwards (in retraction) at a relatively high speed, also forcing hydraulic piston 95 to retract. This eliminates the need to provide a mechanism to hydraulically retract piston 95, such as a hydraulic fluid inlet. LPT 110 registers when hydraulic piston 95 has fully retracted and this data is passed to controller 115.

Charge intensifier pump 45 has a larger product displacement per stroke than that of second product intensifier pump 85. Thus, charge intensifier pump 45 fully fills intensifier barrel 105 with each stroke. Furthermore, charge intensifier pump 45 fills intensifier barrel 105 without introducing air, thus aiding in the control and elimination of pulsation. Controller 115 can be configured to not immediately close smart valve 125. Instead, smart valve 125 may remain open for a predetermined period of time to permit preloading. The CMP slurry continues to be delivered by charge intensifier pump 45, thus raising the pressure within intensifier barrel 105. In one embodiment, the pressure within intensifier barrel 105 is caused to increase to between 1600-1700 psi (11,000-11,700 kilopascals). At the appropriate time, controller 115 then causes smart valve 125 to close.

Hydraulic fluid supply 140 is then caused to deliver hydraulic fluid under pressure into hydraulic actuator 90. This, in turn, causes hydraulic piston 95 to advance, which causes product intensifier piston 100 to advance. Normally, there would be a pre-compression phase where the CMP slurry within intensifier barrel 105 is caused to increase in pressure before it is expelled. However, this phase can be greatly reduced or eliminated by bringing this CMP slurry to high pressure via the charge intensifier pump 45. Of course, the desired output pressure will be determinative of whether the pressures achieved by charge intensifier pump 45 are sufficient for preloading. As product intensifier piston 100 advances, it forces the CMP slurry through outlet 145 and causes check valve 150 to open. At the same time, smart valves 125, 126 prevent backflow of the CMP slurry through fluid line 75. The CMP slurry is then delivered, at pressure, to output line 155 where it becomes intensified product outflow 160. At this point, the CMP slurry advanced into fluid processing device 12, which is discussed in greater detail below. In one embodiment, product intensifier pumps 80, 85 can deliver the CMP slurry at pressures up to or exceeding 40,000 psi (276,000 kilopascals).

As product intensifier piston 100 reaches the end of its extension cycle, smart valve 125 is again opened and the process in repeated. Likewise, the same process occurs with first product intensifier pump 80. Specifically, like product intensifier pump 85, first product intensifier pump 80 includes a hydraulic actuator 91 having a hydraulic piston 96. Hydraulic piston 96 is coupled to a product intensifier piston 101 located within an intensifier barrel 106. A linear position transmitter (LPT) 111 is coupled between hydraulic piston 96 and a controller 116 so as to provide positional information to controller 116. LPT 111 may be located anywhere along hydraulic piston 96 or intensifier piston 101. Controller 116 is coupled with an air cylinder 121 that actuates smart valve 126.

As hydraulic piston 96 reaches the end of its extension cycle, information indicative of this position is sent by LPT 111 to controller 116. Controller 116 then causes smart valve 126 to open. The CMP slurry enters inlet 131 of smart valve 126, passes through and enters an inlet of intensifier barrel 106. Because the CMP slurry may be delivered at pressures of about 1200 psi (depending upon the actual configuration of the system) by charge intensifier pump 45, product intensifier piston 101 is rapidly forced backwards (in retraction), also forcing hydraulic piston 96 to retract. LPT 111 registers when hydraulic piston 96 has fully retracted and this data is passed to controller 116. This is the position illustrated in FIG. 2.

Hydraulic fluid supply 141 is then caused to deliver hydraulic fluid under pressure into hydraulic actuator 91. This, in turn, causes hydraulic piston 96 to advance which causes product intensifier piston 101 to advance. As product intensifier piston 101 advances, it forces the CMP slurry through outlet 146 and causes check valve 151 to open. The CMP slurry is then delivered, at pressure, to output line 155 where it becomes intensified product outflow 160. At this point, the CMP slurry is then delivered to fluid processing device 12. Thus, first product intensifier pump 80 and second product intensifier pump 85 are configured so that one is always delivering product while the other is retracting. In this manner, substantially consistent and uniform intensified product outflow 160 is achieved without significant pressure pulses.

FIG. 3 is a cross-sectional view of an exemplary fluid processing device 12 suitable for use in CMP processing system 6 of the larger system 10 described above. Fluid processing device 12 may be capable of handling pressures up to or greater than approximately 60,000 psi (413 MPa). As described herein, fluid processing device 12 receives a highly pressurized CMP slurry from intensifier system 8. The CMP slurry is separated into two separate initial flow paths 225, 226. Flow paths 225 and 226 feed into opposing sides of flow path cylinder 230, which defines annular flow paths.

In particular, the inner diameter of flow path cylinder 230 defines an outer diameter of annular flow paths that feed toward one another to meet at the center of cylinder 230. Rod 232 is positioned inside flow path cylinder 230. For example, rod 232 may define first and second ends. A first end of rod 232 extends into annular flow path 233 and a second end of rod 232 extends into second annular flow path 234. The outer diameter of rod 232 defines the inner diameter of the annular flow paths. Accordingly, flow paths 225 and 226 respectively feed into annular flow paths 233, 234 defined by flow path cylinder 230 and rod 232.

The CMP slurry flows down annular flow paths 233, 234 and collides at or near outlet 236 formed in flow path cylinder 230, e.g., approximately at the lateral center of cylinder 230. The shear forces, extensional forces, and impact forces of the collision of the CMP slurry flowing down the annular flow paths 233, 234 causes particles in the CMP slurry to be broken into smaller, more desirable sized particles. Moreover, annular flow paths 233, 234 may enhance wall shear forces in fluid processing device 12 by increasing surface area associated with the flow paths. In this manner, fluid processing device 12 can be used to generate intense shear and extensional forces that act on the particles in a CMP slurry. After processing, the CMP slurry is expelled through outlet 236 and exits fluid processing device 12 (as indicated at output 238).

As further shown in FIG. 3, fluid processing device 12 may include pressure sensors 241, 242 to measure pressure within fluid processing device 12, as well as temperature sensors 243, 244 to measure the input temperature of the CMP slurry. A controller (not shown) may receive the pressure and temperature measurements, and adjust the pressure via one or more regulator valves (not shown) to maintain a desired pressure within fluid processing device 12. Similarly, one of the controllers associated with the intensifiers may receive temperature measurements, and cause adjustment of the temperature of the CMP slurry, as needed, to maintain a desired input temperature for the CMP slurry into fluid processing device 12. In particular, it is generally desirable to maintain substantially identical CMP slurry flows down the respective annular flow paths 233, 234 to ensure the desired impingement energy dissipation.

Substantially identical flows of the CMP slurries down the respective annular flow paths 233, 234, e.g., in terms of pressure or temperature, is indicative of a non-clogged condition. Temperature monitoring, in particular, can be used to identify when a clogged condition occurs, and may be used to identify when an anti-clogging measure should be taken, e.g., application of a pulsated short term pressure increase in the input flow to clear the clog.

Gland nuts 247, 248 may be used to secure flow path cylinder 230 in the proper location within fluid processing device 12. Moreover, gland nuts 247, 248 can be formed with channels (indicated by the dotted lines) that allow fluid to flow freely through flow paths 225, 226 and into annular flow paths 233, 234.

Rod 232 may be cylindrically shaped. However, other shapes of rod 232 may further enhance wall shear forces in the annular flow paths. Rod 232 may be free to move and vibrate within the flow path cylinder 230. In particular, rod 232 may be unsupported within flow path cylinder 230. Free movement of rod 232 relative to flow path cylinder 230 can provide an automatic anti-clogging mechanism to fluid processing device 12. If particles in the CMP slurry become clogged inside the fluid processing device 12, e.g., at the edges of annular flow paths 233, 234, rod 232 may respond to local pressure imbalances by moving or vibrating. In other words, a clog within cylinder 230 or in proximity of annular flow paths 233, 234 may result in a local pressure imbalance that causes rod 232 to move or vibrate. The movement and/or vibration of the rod 232, in turn, may help to clear the clog and return the pressure balance within fluid processing device 12. In this manner, allowing rod 232 to be free to move and vibrate within the flow path cylinder 230 can facilitate automatic clog removal.

To further improve clog removal, a pulsated short term pressure increase in the input flow can be performed upon identifying a clog. For example, as mentioned above, temperature sensors 243, 244 may identify temperature changes in flow paths 225, 226, which may be indicative of a clogged condition. In response, a short term pressure increase, e.g., a two-fold pressure increase for approximately five seconds, can cause more substantial movement and/or vibration of the rod 232 to facilitate clog removal. The pulsated short term pressure increase in the input flow can be performed in response to identifying a clogged condition, or on a periodic basis. For example, intensifier pump system 8 (FIG. 2) can be used to adjust the input pressure to fluid processing device 12. A short term pressure increase may be particularly useful in clearing clogs that affect both annular flow paths 233, 234. In that case, the temperature of both input flow paths may be similar, but may increase because of the clog that affects both annular flow paths 233, 234.

The components of fluid processing device 12, including flow path cylinder 230 and rod 232 may be formed of a hard durable material such as stainless steel or a carbide material. As one example, flow path cylinder 230 and rod 232 can be formed of tungsten carbide containing approximately six percent tungsten by weight. As another example, flow path cylinder 230 and rod 232 may comprise so-called “non-corroding” stainless steel that will not corrode in the presence of an aqueous CMP slurry, such as 316 or 304 stainless steel.

FIG. 4 is a cross-sectional side view of a portion of a fluid processing device 12 that incorporates annular flow paths. Gland nuts 247, 248 may be used to secure flow path cylinder 230 in the proper location within fluid processing device 12. Moreover, gland nuts 247, 248 can be formed with channels (indicated by the dotted lines) that allow fluid to flow freely into annular flow paths 233, 234. The ends of flow path cylinder 230 may be formed to mate with gland nuts 247, 248 in order to facilitate securing of cylinder 230 in a precise location.

Again, annular flow paths 233, 234 are defined by flow path cylinder 230 and rod 232. Flow path cylinder 230 may define a minimum width that remains substantially constant along the annular flow paths. Rod 232 may be cylindrically shaped, and can be free to move and vibrate within the flow path cylinder 230. Ordinarily rod 232 is concentric with the annular flow paths, having a center axis that is aligned with the central longitudinal axis of flow path cylinder 230. Fluid dynamic forces and uniform balance of rod 232 can force rod 232 toward the lateral and longitudinal center of the annular flow path. Movement and vibration of rod 232 within the flow path cylinder 230 can facilitate automatic clog removal.

The minimum width of the inner diameter of flow path cylinder 230 may be in the range of approximately 0.1 inch (0.254 cm) to 0.001 inch (0.00254 cm). For example, the width of the inner diameter of flow path cylinder 230 may be approximately 0.0290 inch (0.07366 cm). The width of the outer diameter of rod 232 may be slightly smaller than the minimum inner diameter of flow path cylinder 230. For example, if the width of the inner diameter of flow path cylinder 230 is approximately 0.0290 inch (0.07366 cm), the width of the outer diameter of rod 232 may be between approximately 0.0260 inch (0.06604 cm) and 0.0280 inch (0.07112 cm). Other sizes, widths and shapes of flow path cylinder 230 and rod 232 could also be used in accordance with the invention.

By way of example, the width of outlet 236 may be approximately between 0.0001 inch (0.000254 cm) and 0.1 inch (0.254 cm). As one example, the width of outlet. 236 at the outer diameter of flow path cylinder 230 is approximately between 0.006 inch (0.01524 cm) and 0.010 inch (0.0254 cm). Outlet 236 may extend approximately 180 degrees around cylinder 230, or may extend to a lesser or greater extent, if desired. Other sizes and shapes of outlet 236 could also be used.

FIGS. 5A and 5B are simplified top and side views, respectively, of a CMP unit 16 that may be used to planarize an integrated circuit wafer 304 according to the invention. Notably, CMP slurry 305 includes particles that have reduced particle sizes relative to conventional slurries, due to the CMP slurry processing performed by CMP slurry processing system 6. The sizes of particles in CMP slurry 305 shown in FIG. 5A are greatly exaggerated for illustrative purposes. As noted, CMP slurry 305, processed as described herein, may have substantially all particles with diameters less than approximately 1 microns.

CMP unit 16 includes a polishing pad 302 which rotates. Polishing pad 302 may comprise a polyurethane material or the like. As polishing pad 302 rotates, CMP slurry 305 is deposited onto polishing pad 302. A mechanism 306 holds an integrated circuit wafer 304, such as a silicon wafer, and lowers a surface of integrated circuit wafer 304 into contact with polishing pad 302. Integrated circuit wafer 304 is rotated, typically in the same direction as polishing pad 302, but at a different rotational rate. As shown, integrated circuit wafer 304 has a much smaller circumference than polishing pad 302 and is placed at an offset location relative to the center of polishing pad 302. As polishing pad 302 rotates, the CMP slurry 305 passes between co-rotating integrated circuit wafer 304 and pad 302 to planarize and polish integrated circuit wafer 304 and remove excess materials that have been previously deposited onto integrated circuit wafer 304, e.g., to define circuit traces. The processing of CMP slurry 305, as described herein, can help to reduce or eliminate scratches to integrated circuit wafer 304 during the process shown in FIGS. 5A and 5B.

The planarization/polishing shown in FIGS. 5A and 5B may be repeated for several successive layers of integrated circuit wafer 304. Each layer, for example, may be formed by lithography, deposition, etching and then the polishing/planarization shown in FIGS. 5A and 5B, which uses processed CMP slurry 305. Successive layers of integrated circuit wafer 304 may be formed in similar successive fashion to form the final integrated circuit wafer, including many integrated layers of e.g., silicon transistors, circuit traces and other circuit components.

FIG. 6 is an exemplary flow diagram illustrating a method for processing a chemical mechanical planarization (CMP) slurry via an intensifier pump system and a fluid processing device that breaks up large particles in the CMP slurry in order to reduce the number and size of undesirable large particles without substantially altering a percentage of solids in the CMP slurry by weight. As shown in FIG. 6, pump 3 delivers a CMP slurry from container 2 to CMP slurry processing system 6 (401). Mixer 4 (shown in FIG. 1) is optional.

In CMP slurry processing system 6, intensifier system 8 intensifies the pressure of the CMP slurry (402). Fluid processing device 12 breaks up particles in the CMP slurry in order to reduce particle size (403), which can help minimize or reduce scratching to integrated circuit wafers. Following the processing by CMP slurry processing system 6, the processed CMP slurry is used in CMP unit 16 to planarize an integrated circuit wafer (404).

EXAMPLE

Slurries: Commercially available alumina based first-step copper slurry (C-100), silica based copper first step slurry (C-002), ceria based Shallow Trench Isolation (STI) slurry (S-001), fumed silica based STI slurry (S-002), colloidal silica based copper barrier slurry (B-001), and fumed silica based copper barrier slurry (B-002) were used directly without any chemical alternation. A given slurry was fed through an intensifier pump system (like that illustrated in FIG. 2) and a fluid processing device (like that illustrated in FIG. 3), and the slurry was immediately directed onto a polishing pad without performing any filtration. The particle size and size distribution before and after the treatment by intensifier pump and fluid processing device were measured on a Matec Applied Sciences APS-100 Acoustic Particle Sizer. The oversized particle count was measured on a Particle Sizing Systems AccuSizer™ 780A.

Testing wafers: 8″ copper blanket wafers with 15000 A° PVD (Physical Vapor Deposition) deposited copper on a stack comprising 250 A° tantalum, 5000 A° thermal oxide and a silicon substrate were used in the investigation. Patterned wafers from SKW company of Germany (6-3 patterned wafers with 10,500 A° electroplated copper over 1000 A° copper seed layer) were deposited on SiO₂ trenches 5000 A° deep with 250 A° Ta/TaN as barrier was used. The SKW 6-3 wafers had features ranging from 100 μm to 0.18 μm with varying pattern-densities.

Wafer planarization: All wafers were planarized using the slurries mentioned above on a Strasbaugh n-Hance polisher equipped with Rohm Haas IC 1000™ pad and System Marshall Girt 100 pad conditioner. The slurry flow was set at 200 mL/min. The table/carrier speeds were set at 75/65 rpm. The thickness on the Cu wafers was measured using the RS-35 resistivity mapping tool. Measurements were carried out on two diametrically perpendicular directions before and after planarization to calculate the material removal rate (MRR) and the so called Within Wafer Non-Uniformity (WIWNU). The surface quality of the planarized wafers was examined under the Burleigh Horizon Optical profilometer. The film thickness of all non-metal wafers was measured using Filmetric optical reflectometer. For patterned wafers, step-heights, dishing and erosion values were measured using Ambios XP-2 profilometer. Planarization Efficiency (PE) was calculated for the first step of the planarization process. The defectivity count was conducted on a KLA-Tencor 7700M Inspection Station with an optical microscope for defect classification. The post CMP clean before defectivity inspection was conducted on a SSST Evergreen brush cleaner.

Results: Typical experimental results showed 30-70 percent reduction in large particle size (i.e., diameters>0.64 microns) counts in processed CMP slurries relative to unprocessed CMP slurries. Using the processing techniques described above, an approximately 25% reduction in the volume of particles in the large particle size tail of the CMP slurry was achieved. Most importantly, significant scratch reductions were observed in integrated circuit wafers that were polished/planarized using processed CMP slurries, relative to circuit wafers that were polished/planarized using control unprocessed CMP slurries. This significant reduction in scratches occurred without a significant change in MRR (Material Removal Rate).

A number of embodiments of the invention have been described. Nevertheless, it is understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A method comprising processing a chemical mechanical planarization (CMP) slurry via an intensifier pump system and a fluid processing device that breaks up at least some particles of the CMP slurry to reduce particle size.

2. The method of claim 1, wherein the processing does not substantially alter a percentage of solids in the CMP slurry by weight.

3. The method of claim 1, further comprising planarizing an integrated circuit wafer using the processed CMP slurry.

4. The method of claim 3, wherein planarizing the integrated circuit wafer includes several separate planarizing steps.

5. The method of claim 3, wherein planarizing the integrated circuit wafer includes depositing the processed CMP slurry onto a polishing pad.

6. The method of claim 5, wherein the polishing pad rotates and wherein planarizing the integrated circuit wafer includes rotating the integrated circuit wafer relative to the rotating polishing pad.

7. The method of claim 3, further comprising filtering the processed CMP slurry prior to planarizing the integrated circuit wafer.

8. The method of claim 1, wherein the intensifier pump system includes at least two hydraulic intensifier pumps, and wherein processing the CMP slurry includes operating the hydraulic intensifier pumps in a complementary fashion.

9. The method of claim 1, wherein the fluid processing device includes:

a first annular flow path for the CMP slurry;

a second annular flow path for the CMP slurry;

an outlet for the CMP slurry flowing within the first and second annular flow paths;

a flow path cylinder that defines an outer diameter of the first and second annular flow paths, the outlet being formed in the flow path cylinder; and

a cylindrical rod positioned within the flow path cylinder that defines an inner diameter of the first and second annular flow paths, wherein the cylindrical rod is not attached to any structure within the fluid processing device and is free to move under fluid dynamic force relative to the flow path cylinder.

10. The method of claim 1, wherein the CMP slurry includes particles dispersed in water.

11. The method of claim 10, wherein the particles comprise at least one of:

alumina (Al2O3);

cerium oxide (CeO2) and

silicon dioxide (SiO2).

12. The method of claim 1, further comprising adding additives to the CMP slurry.

13. A planarization system for integrated circuit wafers comprising:

a chemical mechanical planarization (CMP) slurry processing system that processes a CMP slurry to break up at least some particles of the CMP slurry to reduce particle size; and

a CMP unit that planarizes an integrated circuit wafer using the processed CMP slurry.

14. The planarization system of claim 13, wherein the CMP slurry processing system does not substantially alter a percentage of solids in the CMP slurry by weight.

15. The planarization system of claim 14, wherein the CMP slurry processing system includes an intensifier pump system and a fluid processing device that breaks up at least some of the particles of the CMP slurry.

16. The planarization system of claim 15, wherein the intensifier pump system includes at least two hydraulic intensifier pumps that operate in a complementary fashion.

17. The planarization system of claim 16, wherein the fluid processing device includes:

a first annular flow path for the CMP slurry;

a second annular flow path for the CMP slurry;

an outlet for the CMP slurry flowing within the first and second annular flow paths;

a flow path cylinder that defines an outer diameter of the first and second annular flow paths, the outlet being formed in the flow path cylinder; and

a cylindrical rod positioned within the flow path cylinder that defines an inner diameter of the first and second annular flow paths, wherein the cylindrical rod is not attached to any structure within the fluid processing device and is free to move under fluid dynamic force relative to the flow path cylinder.

18. The planarization system of claim 14, wherein the CMP unit includes a polishing pad and wherein the processed CMP slurry is deposited onto the polishing pad.

19. The planarization system of claim 18, wherein the polishing pad rotates and wherein a mechanism rotates the integrated circuit wafer relative to the rotating polishing pad.

20. The planarization system of claim 14, wherein the CMP slurry includes particles dispersed in water, wherein the particles comprise at least one of:

alumina (Al2O3);

cerium oxide (CeO2) and

silicon dioxide (SiO2).

21. The planarization system of claim 14, further comprising one or more filters to filter the processed CMP slurry prior to planarizing the integrated circuit wafer.

22. The planarization system of claim 14, further comprising a feedback loop to feed unused portions of the processed CMP slurry back to the CMP slurry processing system.

23. A chemical mechanical planarization (CMP) slurry comprising:

water; and

particles dispersed in the water, wherein substantially all of the particles have a diameter less than approximately 1 micron and wherein the particles comprise at least one of:

alumina (Al2O3);

cerium oxide (CeO2) and

silicon dioxide (SiO2).