ANJUR SRIRAM
WO2000012264A1 | 2000-03-09 |
US5725420A | 1998-03-10 |
1. Calculate the flow necessary to renew the composition film at the area of interaction between the substrate and the polishing pad: Wafer area = ϋ*(10 cm)2 = 314 cm2; Film Vol. (assuming 1 μm film thickness) = 314 cm2 * 0.0001 cm = 0.0314 cm3; Flow Rate = 1.4 cm3/sec (to renew the composition every second) (note: flow rate for typical CMP apparatus is approximately 1.67 cm3/sec.)
2. Calculate the number of pores necessary to provide the 0.0314 cnrVsec flow rate (assuming 100 μm diameter pores (i.e., 7.9e"5 cm2) and 0.15 cm thick polishing pad): No. of Pores Required = 0.0314 cm3/ (7.9e"s cm2 * 0.15 cm) = approx. 2650 pores;
3. Calculate the total area of the pores required: Area of pores required = 2650 * 7.9e'5 cm2 - 0.20935 cm2; Area of 200 mm substrate = 314 cm ; % of wafer corresponding to pores = 0.20935 cm 27M3I 14 A c «~m-2 _ - , 0.067%;
4. Calculate the pressure drop (ΔP) generated by pores: (note: use Hagen-Poisseulle law: ΔP = q * 8 * n * L/(Rc)**2; where ΔP = pressure drop; q = flow volume; n = fluid viscosity; L = pad thickness; Rc = pore radius) ΔP from pores = 0.0314 cm3/sec. * 8 * 1.0 cp * 0.15 cm / (0.005 cm)**2 = 1507 dynes/ cm2; (assuming additional pressure drop from gravity = 147 dynes/ cm2) total ΔP = 1507 dynes/cm2 + 147 dynes/cm2 = 1654 dynes/cm2 = 165.4 N/m2 «* 0.001654 atm (or 0.168 kPa)
[0030] From the foregoing, 0.001654 atm (which is 0.168 kPa) is a minimal pressure drop for a polishing system to overcome, thereby indicating that the pores can adequately renew the polishing composition at the area of interaction between the substrate and the polishing pad. [0031] The pores of the first and second pluralities need not be tapered in shape to have a unidirectional effect on fluid communication. For example, in the embodiment of the polishing pad 160 illustrated in FIG. 4, at least one of the pores of the first plurality 162, and preferably more than one pore (e.g., 5 % or more of the total first plurality of pores, 10 % or more of the total first plurality of pores, 25 % or more of the total first plurality of pores, 50 % or more of the total first plurality of pores, 75 % or more of the total first plurality of pores, or 90 % or more of the total first plurality of pores), are formed as a series of frusto-conical sections 165 arranged in axial alignment as disposed between the bottom surface 168 and the top surface 166. A base portion of each frusto-conical section 165 of the first plurality of pores 162 is aligned toward the bottom surface 168 while a topmost portion of each frusto-conical section is oriented toward the top surface 166. At least one of the pores of the second plurality 164, and preferably more than one pore (e.g., 5 % or more of the total second plurality of pores, 10 % or more of the total second plurality of pores, 25 % or more of the total second plurality of pores, 50 % or more of the total second plurality of pores, 75% or more of the total second plurality of pores, or 90 % or more of the total second plurality of pores), are similarly formed by a series of similar frusto- conical sections 165 arranged in an opposing alignment. Preferably, the larger second and fourth apertures 172, 176 are formed by a base portion of a frusto-conical sections 165 while the smaller first and third apertures 170, 174 are formed by a topmost portion of a frusto-conical sections. As will be apparent to those of skill in the art, the arrangement of the frusto-conical sections in the first pores 162 encourages flow from the bottom surface 168 to the top surface 166 while substantially impeding flow in the opposite direction. The arrangement of the frusto- conical sections in the second pores 164 similarly encourages flow from the top surface 166 to the bottom surface 168. Thus, the pores of the first and second pluralities formed with the frusto-conical sections promote renewal of the polishing composition at the top surface. [0032] In the embodiment of the polishing pad 180 illustrated in FIG. 5 at least one of the pores of the first plurality 182 and at least one of the pores of the second plurality 184, and preferably more than one pore of each of the first and second pluralities (e.g., 5 % or more, 10 % or more, 25 % or more, 50 % or more, 75 % or more, or 90 % or more of each of the respective total first and second pluralities of pores), are formed as helixes disposed between the bottom surface 188 and the top surface 186. The helical first pores 182 intersecting with the top surface 186 forms the smaller first apertures 190 while the helical first pores intersecting with the bottom surface 188 forms the larger third apertures 194. Likewise, the intersection of the helical second pores 184 with the top surface 186 forms the larger second apertures 192 while the intersection of the helical second pores 184 with the bottom surface 188 forms the smaller fourth apertures 196. The combination of helical paths and the location of the larger and smaller apertures provides the unidirectional character of the pores. [0033] The polishing pad can be made from any suitable material. Typically, polishing pads are made from a polymer resin. Preferably, the polymer resin is selected from the group consisting of thermoplastic elastomers, thermoplastic polyurethanes, thermoplastic polyolefins, polycarbonates, polyvinylalcohols, nylons, elastomeric rubbers, elastomeric polyethylenes, polytetrafluoroethylenes, polyethyleneterephthalates, polyimides, polyaramides, polyarylenes, polyacrylates, polystyrenes, polymethylmethacrylates, copolymers thereof, and mixtures thereof. More preferably, the polymer resin is a thermoplastic polyurethane resin. [0034] The polishing pad can be adapted for CMP processes that utilize chemical- mechanical polishing compositions or the polishing pad can be adapted for use in ECMP processes. When used in ECMP process, the polishing pad can be made from a conductive polymer or, in some embodiments, made from a non-conductive polymer having conductive elements inner-dispersed or embedded therein. The conductive polymer and conductive elements can be formed from any suitable materials. For example, the conductive elements can take the form of particles, fibers, wires, coils, or sheets and made from materials such as carbon and conductive metals such as copper, platinum, platinum-coated copper, and aluminum. Conductive polishing pads can have a maximum resistance value of, for example, 10 ohms. [0035] To provide the pores of the first and second pluralities, any suitable formation method can be employed. For instance, the pores can be formed during the manufacturing process of the polishing pad itself, such as during the molding process of the polymer resin used to produce the polishing pad. Special blowing agents or micro-spheres may be employed to assist in the formation of the pores. The pores can also be formed by any other suitable molding or casting technique. Furthermore, the pores can be formed after molding of the polishing pad through any number of various machining processes and techniques. [0036] Referring to FIG. 2, to further improve the distribution of composition along the top surface 140 of the polishing pad 104, a groove or series of grooves can be formed into the top surface that intersects at least one of the pores. For instance, in the illustrated embodiment, a first series of grooves 158 can be formed that intersect with the first plurality of pores 146 while a second series of grooves 159 can be formed that intersect with the second plurality of pores 148. The grooves 158, 159 assist in transferring the composition to and from the pores to the area of interaction between the top surface and the substrate. [0037] The grooves 158, 159 can have any suitable cross-section, such as a V-shaped cross- section. Other possible cross-sections include U-shaped cross-sections and truncated V-shaped cross-sections. The width of the cross-section can be any suitable width and typically 0.1 mm to 2 mm. The width of the cross-section may correspond to the average diameters of the apertures with which a particular groove intersects. The depth of the groove can be any suitable depth and may be dependent upon the thickness of the polishing pan and flow rate of the composition. A typical thickness of a polishing pad between the top and bottom surfaces is 0.1 mm to 10 mm. The grooves 158, 159 can also be formed in any suitable pattern on the top surface 140, such as the alternating series of parallel grooves illustrated in FIG. 2. Other possible patterns include concentric circle patterns or curved patterns. [0038] The polishing pad can be a multi-layered pad having at least a top-layer and a bottom layer. In such an embodiment, the polishing pad of the invention, e.g., polishing pad 104 illustrated in FIG. 2, including the top and bottom surfaces 140, 142 and the first and second pluralities of pores 146, 148, corresponds to the top layer of the multi-layered polishing pad. [0039] Referring to FIGS. 6 through 8, there is illustrated an example of a polishing apparatus 200 that is designed in accordance with another aspect of the invention. The polishing apparatus 200 includes a polishing table or platen 202 and a polishing pad 204 that is supported on the platen. The polishing pad 204 has a top surface 214, an opposing bottom surface 216, and a plurality of pores 210 disposed between the top and bottom surfaces. The polishing pad and the plurality of pores can be of the same construction as the polishing pad described above or of a different construction altogether. Additionally, to communicate the polishing composition to the pores 210, the bottom surface 216 of the polishing pad is positioned next to a first surface 218 of the platen 202 thereby defining a polishing composition transfer region 220 therebetween. To introduce polishing composition to the transfer region 220, the polishing apparatus 200 also includes a delivery system 206 that delivers polishing composition to a composition inlet 222 that is disposed so as to correspond to the transfer region. For mounting a substrate to be polished, there is also included as part of the polishing apparatus 200 a carrier 208 that is supported above the polishing pad 204. To impart the motion necessary for carrying out the polishing operation, the carrier 208 may be rotated and/or orbited with respect to the polishing pad 204 or the polishing pad and platen 202 may be rotated and/or orbited with respect to the carrier or a combination of both elements may be rotated and/or orbited. [0040] Illustrated in FIG. 7(a) is an embodiment of the polishing pad 204 overlaying the transfer region 220. To transfer polishing composition to the pores in an organized fashion, the transfer region 220 is composed of a first plurality of channels 226 and, preferably, a second plurality of channels 228. The first plurality of channels 226 align with pores of a first type 211 that are adapted to communicate polishing composition to the top surface of the pad while the second plurality of channels 228 align with pores of a second type 212 that are adapted to remove polishing composition from the top surface. It will be appreciated that the longitudinal axis of the channels are generally parallel to the plane of the polishing pad and generally normal to the axis of the pores. The channels 226 of the first plurality are in communication with the composition inlet and, preferably, are arranged in parallel with one another. Likewise, the channels 228 of the second plurality are also preferably arranged in parallel with each other and generally normal to the channels 226 of the first plurality. [0041] Illustrated in FIG. 7(b) is another embodiment of the polishing pad 204 overlaying the transfer region 220. The transfer region 220 includes a first plurality of generally parallel channels 226 and a second plurality of generally parallel channels 228. The channels of the first and second pluralities 226, 228 are arranged perpendicularly to each other. Located proximate to and in communication with the intersections of the first and second plurality of channels 226, 228 is a pore of the first type 211 that is adapted to communicate polishing composition to the top surface of the pad. The pores of the second plurality 212, which are adapted so that they remove polishing composition from the top surface, are disposed through the pad 204 such that they are not aligned with either the first or second pluralities of channels 226, 228. [0042] Referring to FIG. 8 (a), there is illustrated in detail a channel 226 of the first plurality (corresponding in part to the transfer region) disposed between the polishing pad 204 and the platen 202. To facilitate communication of the polishing composition from the channel 226 through the pore 211 to the top surface 214 of the polishing pad 204, there is disposed within the channel a plurality of protrusions 230. Each protrusion 230 of the plurality is aligned with a pore 211 and, in the illustrated embodiment, is formed as an integral part of the platen protruding upward into the channel 226. In operation, at least a portion of the polishing composition delivered from the composition inlet is redirected by the protrusion 230 from the channel 226 into the pore 211. Redirecting the polishing composition improves the renewal of the composition at the area of interaction between the substrate and top surface of the pad and, in ECMP applications, promotes uniform ion conduction between electrodes thereby facilitating the ECMP dissolution of conductive materials from the substrate. [0043] Referring to FIG. 7(a), another advantage of redirecting the polishing composition is that, in applications in which the composition is pressurized by the delivery system, the redirected composition displaces the composition already located at the top surface of the polishing pad. The displaced polishing composition may enter the pores 212 of the second type and thereby be returned to a reservoir by the second plurality of channels 268, thus further improving renewal of the composition. [0044] Referring to FIG. 7(b) an advantage of locating the pores of the first type 211 at the intersections of the first and second pluralities of channels 226, 228 is that the amount of composition communicated to the top surface can be controlled by adjusting the composition flow rate in either of the first plurality of channels or the second plurality of channels. In essence, locating the pores of the first type 211 at the intersections of the first and second pluralities of channels 226, 228 provides for multiple degrees of control over the amount of composition communicated to the top surface. [0045] To provide the channels 226, 228 that correspond to the transfer region, referring to FIG. 8(b), there is formed into the first surface 218 of the platen 202 a plurality of ducts 240. Each duct 240 corresponds to and defines at least a portion of one channel 226, 228. Referring to FIG. 8(c), in another embodiment the channels 226, 228 are provided by forming the ducts 242 into the bottom surface 216 of the polishing pad 204. The ducts can be formed by any suitable means such as machining or, where appropriate, molding. The ducts can also be of any suitable shape and cross-section, including, as illustrated, hemispherical. [0046] Referring to FIG. 9, in another embodiment of the polishing apparatus 300, the transfer region can correspond to and be defined by a plurality of composition pipes or tubes 302 disposed between the polishing pad 306 and the platen 308. The composition tubes 302 can be formed as a hollow structure having an inner surface 312 and a corresponding outer surface 314. In the illustrated embodiment, the tubes 302 are cylindrical in shape but could in other embodiments have some other suitable shape. The composition tubes 302 can be interconnected together to form a network 310 for transferring composition between the polishing pad 306 and the platen 308. For example, in the embodiment illustrated in FIG. 8, the tubes 302 are arranged in a first plurality of parallel tubes that interconnect with a second plurality of parallel tubes to generally form a grid. However, the tubes can be arranged in any suitable manner and the network 310 of tubes is not to be construed as limited to a grid. The network 310 can be formed as a separable element or can be mounted to either the platen 308 or the polishing pad 306. [0047] The tubes 302 forming the network 310 include a plurality of openings 316 disposed between the inner and the outer surfaces 312, 314 that correspond to the pores 320 in the polishing pad 306. In the illustrated embodiment, the openings 316 are formed at the interconnections between the first and second pluralities of tubes. However, in other embodiments the locations of the openings can vary depending upon the arrangement of the tubes and the network. Additionally, the plurality of pores 320 can be of the same construction as the unidirectional pores described above or a different construction altogether. [0048] To facilitate delivery of the polishing composition from the tubes 302 to the top surface 322 of the polishing pad 306, there is included within the tubes a plurality of protrusions 318. The protrusions 318 can be formed on the inner surface 312 of the tubes aligned opposite the openings 316. In operation, when polishing composition is introduced into the network, the protrusions 318 will redirect at least a portion of the composition through the openings 316 and into the pores 320. As mentioned above, redirecting the polishing composition improves the continuous renewal of the composition at the area of interaction between the substrate and top surface of the pad and, in ECMP applications, promotes uniform ion conduction between the anode and the cathode thereby facilitating the ECMP dissolution of conductive materials from the substrate. [0049] The composition tubes and protrusions can be of any appropriate size for communicating polishing composition in a polishing apparatus. For example, the tubes can have an inner diameter of 10 micrometers to 50 micrometers and the protrusions can have a height of 2 micrometers to 10 micrometers. Preferably, as a general rule, the height of the protrusions should be 25% of the width of the tubes. Additionally, in ECMP applications, the composition tubes forming the network can be made of a conductive material and can serve as an electrode for generating the electrical bias necessary for ECMP applications. CLAIMS
1. A polishing pad for use with a polishing composition, the polishing pad comprising: (a) a top surface; (b) an opposing bottom surface; (c) a first plurality of unidirectional pores disposed between the top and bottom surfaces adapted to communicate the polishing composition from the bottom surface to the top surface; and (d) a second plurality of unidirectional pores disposed between the top and bottom surfaces adapted to communicate the polishing composition from the top surface to the bottom surface, at least one of the pores of the first and the second plurality having a non-cylindrical cross-section. 2. The polishing pad of claim 1, wherein at least one of the pores of the first plurality tapers between the bottom surface and the top surface. 3. The polishing pad of claim 2, wherein at least one of the pores of the second plurality tapers between the top surface and the bottom surface. 4. The polishing pad of claim 1, wherein the intersection of the pores of the first plurality and the top surface forms a first plurality of apertures, and the intersection of the pores of the second plurality and the top surface forms a second plurality of apertures, an average diameter of the apertures of the first plurality being smaller than an average diameter of the apertures of the second plurality. 5. The polishing pad of claim 4, wherein the intersection of the pores of the first plurality and the bottom surface forms a third plurality of apertures, and the intersection of the pores of the second plurality and the bottom surface forms a fourth plurality of apertures, an average diameter of the apertures of the third plurality being larger than an average diameter of the apertures of the fourth plurality. 6. The polishing pad of claim 5, wherein the apertures of the first and third pluralities have a combined average diameter of 50 micrometers or less. 7. The polishing pad of claim 5, wherein the apertures of the second and fourth pluralities have a combined average diameter of 20 micrometers or less. 8. The polishing pad of claim 1, wherein at least one of the pores of the first plurality is helically disposed between the top and bottom surface. 9. The polishing pad of claim 1, wherein at least one of the pores of the second plurality is helically disposed between the top and bottom surface.