The present invention relates to the field of chemical mechanical planarization (CMP) and relates specifically to a CMP polishing pad having an optically transparent window therein.
In modern integrated circuit (IC) fabrication, layers of material are applied to embedded structures previously formed on semiconductor wafers. Chemical Mechanical Planarization (CMP) is an abrasive process used to remove these layers (or portions thereof) and polish the resulting surface to achieve a desired structure. CMP may be performed on both oxides and metals and generally involves the use of chemical slurries applied in conjunction with a polishing pad in motion relative to the wafer (e.g., the pad rotates relative to the wafer with the slurry dispersed therebetween). The resulting smooth flat surface is necessary to maintain photolithographic depth of focus for subsequent wafer processing steps and to ensure that the metal interconnects are not deformed over contour steps. Damascene processing requires metal, such as tungsten or copper, to be removed from the top surface of a dielectric to define interconnect structures, using CMP.
As discussed in U.S. patent application Ser. No. 11/576,944, the ability to monitor process conditions while a wafer is being polished is important as it can provide information on the wafer surface, which, in turn, may be utilized to change the process conditions or stop processing all together. As is known in the art, some CMP systems use optical means to monitor process conditions. In particular, a light beam is directed toward the wafer through an open aperture in the polishing pad and reflected off of the wafer surface being polished. Changes in the reflected beam can be analyzed to determine the condition of the polishing process. Examples of systems, pads and methods for such process monitoring are described in U.S. Pat. Nos. 7,264,536, 7,374,477, 7,118,450, 7,029,747, 6,884,156, 6,524,164, 6,280,290, 5,893,796, 5,609,517, and 5,433,651, each incorporated herein by reference.
The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings, in which:
In a conventional CMP apparatus, a polishing pad is disposed on a platen and a wafer or other substrate is brought into rotational contact with the polishing elements of the pad, usually in the presence of a slurry. This effects polishing of the wafer. As indicated above, some CMP systems employ process monitoring means which reflect light beams off of the wafer surface being polished and analyze the reflected beams to determine polishing process characteristics. These systems may use visible or other wavelengths of light and may be single or multi-wavelength systems. The light is usually emitted from below the platen (e.g., by a laser), directed through an opening in the platen and the polishing pad onto the wafer surface, and then reflected through a similar path towards a detector. Thus, polishing pads used in such apparatus require an opening through which the light beam may pass.
Referring now to
When the pad is in use (i.e., when it is moving relative to a wafer surface), the polishing elements may make sliding contact or rolling contact with the wafer's surface. In this latter case, one or more polishing elements may have a cylindrical body and a rolling tip. The rolling tip may be made of varying materials, such as polymeric, metal oxide or an electrically conducting material. A rolling tip polishing element may be incorporated into the pad material the same way as a sliding contact polishing element. Of course, the individual polishing elements (or tips thereof) can have a variety of shapes (e.g., circular, triangular, and/or trapezoidal cross-sectional shapes) and this is not critical to the present invention. By providing for independent movement of the polishing elements along an axis normal to a plane defined by the guide plate, the present polishing pad is able to apply uniform (or near uniform) pressure across the entire surface of the wafer. This unique ability eliminates “hot spots” on the wafer which might cause local material removal rate variations or, in case of low-K materials, initiate material or interface failure damage.
In varying embodiments of the present invention, the polishing elements of the pad may be made of any suitable material such as polymer, metal, ceramic or combinations thereof, and are capable of independent or semi-independent movement in the axis normal to the plane defined by the guide plate. The polishing elements may be of different sizes and may be positioned with varying density across the pad surface. Also in varying embodiments of the invention, a pad may be made from elements that preferentially polish copper and is used to remove copper utilizing copper slurry. Another pad may be made from elements that preferentially polish barrier materials, such as Ta/TaN or other such refractory metals, and is used to remove barrier materials utilizing barrier slurry.
A suitable material for the polishing elements of the present polishing pad is cast or molded polyurethane, such as DOW Pellethane™ 2201 65D. Other polymer materials such as Torlon™ or Delrin™ may also be used. The polishing elements may be polymeric or may contain abrasive materials such as silica or alumina. in some cases, the polishing elements. may be made of PVA to provide good cleaning ability to the pad. The compliant under-layer of the present polishing pad is selected to provide compliance of the order of wafer level bow and warpage. A suitable under-layer material may be performance polyurethane made by Rogers Corporation.
As shown in
Various configurations of the present polishing pad may be adapted for use in accordance with the present invention. For example, in the embodiment illustrated in
Overlying this aperture is an optically transparent window 316 (by transparent it is meant that the window is transparent to the wavelengths of interest). The window may be made of any of a variety of materials, including but not limited to polycarbonate, thermoplastic polyurethane (TPU), high impact polystyrene (HIPS), poly(methyl methacrylate) (PMMA), polyester, or other optically transparent material (e.g., one or more polymeric materials, such as, a polyurethane or a halogenated polymer such as polychlorotrifluoroethylene (PCTFE), perfluoroalkoxy (PFA), fluorinated ethylene propylene (FEP), or polytetra-fluoroethylene (PTFE)). The window 316 may be molded, extruded, thermo-formed or cast and may be fixed in position over the slurry distribution layer of the pad by adhesive or by a thermal bonding layer (not shown).
In some instances, the window 316 may have rounded or beveled edges to facilitate easy sealing against the slurry distribution layer. Preferably, all interfaces between the window 316 and the pad 300 are sealed to eliminate (or substantially reduce) leakage into aperture 314. Likewise, the edges of compressible under layer and slurry distribution layer which abut the aperture may also be sealed, for example using adhesive or a thermal bonding layer (not shown). The window thickness does not extend beyond the tips of polishing elements 302, thereby preventing scratching of a wafer or other substrate even though the window 316 is positioned above the level of the top surface of the slurry distribution layer (if present) or the top surface of the guide plate (if the slurry distribution layer is not present).
Referring now to
Fitted within the aperture 414 is a C-shaped transparent member (e.g. a C-shaped plug) 416 (the entire plug need not be transparent so long as the upper member 418 thereof is transparent to the wavelengths of interest). The transparent member 418 may be affixed to the sides of the guide plate and the compressible under layer (and the slurry distribution layer, if present) defined by the aperture 414 with any suitable adhesive or adhesively backed tape. In some embodiments, a cure in place adhesive may be used. in other cases, the C-shaped plug may be fixed in place using a thermal bonding adhesive. The edges of the C-shaped plug need not extend through the entire thickness of the guide plate and the compressible under layer and, in some embodiments, will extend only partially therethrough.
The top surface 418 of the C-shaped plug 416 may be made of any of a variety of materials, including but not limited to polycarbonate, TPU, HIPS, PMMA, polyester, or other optically transparent material (e.g., one or more polymeric materials, such as, a polyurethane or a halogenated polymer such as PCTFE, PFA, FEP, or PTFE). The C-shaped plug may be molded, extruded, thermo-formed or cast. The C-shaped plug does not extend beyond the tips of polishing elements 402, thereby preventing scratching of a wafer or other substrate even though a portion of the plug may extend above the level of the top surface of the slurry distribution layer (if present) or the top surface of guide plate (if the polishing composition distribution layer is not present).
Referring now to
Fitted within the aperture 514 is a rectangular-shaped transparent member (e.g. a plug) 516. Plug 516 is transparent to the wavelengths of interest. The plug 516 may be affixed to the sides of the guide plate and the compressible under layer (and the slurry distribution layer, if present) defined by the aperture 514 with any suitable adhesive or adhesively backed tape. In some embodiments, a cure in place adhesive may be used. In other cases, the plug may be fixed in place using a thermal bonding adhesive. The edges of the plug need not extend through the entire thickness of the guide plate and the compressible under layer and, in some embodiments, will extend only partially therethrough.
The plug 516 may be made of any of a variety of materials, including but not limited to polycarbonate, TPU, HIPS, PMMA, polyester, or other optically transparent material (e.g., one or more polymeric materials, such as, a polyurethane or a halogenated polymer such as PCTFE, PFA, FEP, or PTFE). The plug may be molded, extruded, thermo-formed or cast. The plug thickness does not extend beyond the tips of polishing elements 502, thereby preventing scratching of a wafer or other substrate even though the plug is positioned above the level of the top surface of the slurry distribution layer (if present) or the top surface of guide plate (if the polishing composition distribution layer is not present).
As indicated above, the slurry distribution layer is an optional component of the present polishing pad. In some cases, the guide plate may be used as means for polishing composition distribution during polishing operations. In such instances, a guide plate 732 may be fashioned with a series of circumferential grooves 734, as shown in
The micro-replicated posts may be any shape, including but not limited to triangular, cylindrical, square, hexagonal, conical, truncated conical, truncated pyramidal, etc. In some embodiments the micro-replicated posts may have a cross-sectional area of 50-250 microns and a height of 50-250 microns.
Thus, structural and material properties of a CMP polishing pad utilized in CMP processing have been described. Embodiments of the invention may be fashioned by (a) making an aperture in a polishing pad such as that shown in
In particular, in a polishing pad having a guide plate, a compressible foam under layer disposed adjacent to a lower surface of the guide plate, and a plurality of polishing elements that extend in a first direction substantially normal to a plane defined by the guide plate and through the guide plate, an aperture may be formed in the polishing pad, the aperture extending through the compressible foam under layer and the guide plate, and an optically transparent window may be affixed overlying the aperture, the optically transparent window being above an upper surface of the guide plate but below tips of the polishing elements, the upper surface of the guide plate being opposite the lower surface thereof. In cases where the pad further includes a slurry distribution layer disposed on the upper side of the guide plate, the aperture extends through the slurry distribution layer, and the optically transparent window overlies the aperture and is affixed to a top surface of the slurry distribution layer.
In a further embodiment, in a polishing pad having a guide plate, a compressible foam under layer disposed adjacent to a lower surface of the guide plate, and a plurality of polishing elements that extend in a first direction substantially normal to a plane defined by the guide plate and through the guide plate, an aperture is formed in the polishing pad, the aperture extending through the compressible foam under layer and the guide plate, and an optically transparent window is formed using a plug that is secured within the aperture and which protrudes above an upper surface of the guide plate but below tips of the polishing elements, the upper surface of the guide plate being opposite the lower surface thereof. In cases where the pad further includes a slurry distribution layer disposed on the upper side of the guide plate, the aperture extends through the slurry distribution layer, and the plug protrudes above a top surface of the slurry distribution layer.
This application is a NONPROVISIONAL and claims the priority benefit of U.S. Provisional Patent Application No. 61/118,431, filed Nov. 26, 2008, incorporated herein by reference.
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