Patent Application
20110105000
The present disclosure relates generally to a chemical mechanical planarization pad.
An integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semiconductive, or insulative layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer until the non-planar surface is exposed. For example, a conductive filler layer can be deposited on a patterned insulative layer to fill the trenches or holes in the insulative layer. The filler layer is then polished until the raised pattern of the insulative layer is exposed. After planarization, the portions of the conductive layer remaining between the raised pattern of the insulative layer form vias, plugs, and lines that provide conductive paths between thin film circuits on the substrate. In addition, planarization is needed to planarize the substrate surface for photolithography.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that the substrate be mounted on a carrier or polishing head. The exposed surface of the substrate is placed against the polishing surface of a polishing pad, such as a rotating polishing disk or linearly advancing belt. The carrier head provides a controllable load on the substrate to push it against the polishing pad. A polishing liquid, which can include abrasive particles, is supplied to the surface of the polishing pad, and the relative motion between the substrate and polishing pad results in planarization and polishing.
One objective of a chemical mechanical polishing process is to achieve wafer to wafer polishing uniformity. If different substrates are polished at different rates, it becomes difficult to achieve a uniform target layer thickness between multiple wafers. Another objective of a chemical mechanical polishing process is to achieve within wafer polishing uniformity. If different areas on the substrate are polished at different rates, then it is possible for some areas of the substrate to have too much material removed (“overpolishing”) or too little material removed (“underpolishing”), which can result in non-uniform topography across the substrate.
In general, in one aspect, a polishing pad includes a polymer matrix and polyhedral oligomeric silsequioxane (“POSS”) molecules dispersed within the polymer matrix. This and other embodiments can optionally include one or more of the following features. The POSS molecules can be chemically linked to the polymer matrix. The POSS molecules can include a functional group, and wherein the functional group is selected from a group consisting of NH2, OH, SH, R—NH, —NCO, and COOH. The polymer matrix can include polyurethane. The polymer matrix can be porous. The pores of the polymer matrix can be filled with a gas. The gas can be nitrogen. The pores can include 15-40% of the polishing pad by volume. The hardness of the polishing pad can be between approximately 40 and 75 Shore D. The POSS molecules can include approximately 5 to 15 percent of the polishing pad by weight.
In general, in one aspect, a method of making a polishing pad includes mixing a polymer solution and polyhedral oligomeric silsequioxane (“POSS”) molecules together to form a mix and curing the mix such that a polymer matrix having POSS particles is formed.
This and other embodiments can optionally include one or more of the following features. The polymer solution can include polyurethane. The method can further include bubbling gas through the mix prior to curing. The gas can include nitrogen.
In general, in one aspect, a polishing pad includes a polymer matrix, soluble particles dispersed within the polymer matrix, and a surfactant dispersed within the polymer matrix.
This and other embodiments can optionally include one or more of the following features. The polymer matrix can be porous. The soluble particles can be chosen from a group consisting of CaCO3, K2SO4, phenolic novolac, and polyethylene glycol ether. The soluble particles can be approximately 1 to 25 micrometers in size. The soluble particles can include approximately 1 to 15% of the polishing pad by weight. The polymer matrix can include polyurethane. The surfactant can be chosen from a group consisting of copolymers, block copolymers, and nonionic surfactants. The hardness of the polishing pad can be between approximately 60 and 75 Shore D.
In general, in one aspect, a method of making a polishing pad includes casting a liquid polymer on a conveyer belt, wherein the conveyer belt comprises a casting surface with a first set of projections, and curing the liquid polymer on the conveyer belt such that a polymer matrix is formed, wherein the polymer matrix has a surface with a second set of projections, the second set of projections being complimentary to the first set of projections.
This and other embodiments can optionally include one or more of the following features. The method can further include injecting a gas through the liquid polymer prior to casting. The gas can be nitrogen. The casting surface of the conveyer belt can include a material chosen from a group consisting of stainless steel, Teflon, and silicone. The polymer can include polyurethane. The method can further include detaching the matrix from the conveyer belt.
Certain implementations may have one or more of the following advantages. Having POSS molecules dispersed within the polymer matrix can decrease pad wear by both making the polishing pad harder and increasing the lubrication of the surface of the polishing pad. Dispersing soluble particles within the polymer matrix can increase the polishing pad hardness, thereby reducing pad wear, and can increase surface roughness of the polishing pad, thereby increasing the removal rate of the polishing surface during CMP. Dispersing a surfactant within the polymer matrix can uniformly disperse the POSS and/or particles, thus also increasing surface roughness. Further, a pad as described herein can be made thicker than traditional pads because the polymer walls between the grooves are stronger and therefore are less likely to collapse. Curing liquid polymer on a mold having ridges can eliminate the need to put grooves in after curing, thereby saving money and time. Likewise, curing the liquid polymer on a mold having ridges can minimize pad to pad variation that can be caused by grooving knives if grooves are formed after curing.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the invention will become apparent from the description, the drawings, and the claims.
Like reference numbers and designations in the various drawings indicate like elements.
During chemical mechanical polishing, a lack of surface roughness of the polishing surface of the polishing pad can result in a low removal rate. Furthermore, polishing pads can have a high wear rate, causing short pad life and requiring frequent replacement of the polishing pads. Polishing pad surface roughness can be increased by dispersing soluble particles and/or surfactant within the polishing pad. Likewise, the wear rate of the polishing pad can be reduced by dispersing molecules, e.g., nanoparticles, that increase the hardness of the pad material, such as polyhedral oligomeric silsequioxane (“POSS”) molecules, and/or soluble particles within the polishing pad.
Referring to
In one implementation, shown in
In another implementation, shown in
Further, a surfactant can be included in the polymer matrix, which, as discussed below, can increase the surface roughness of the pad 100. The surfactant can be, for example, a copolymer, block copolymer, or nonionic surfactant.
Referring to
After mixing, the contents of the vat 406 can be poured through an ejector 502 over a mold 504, as shown in
Although not shown, once the sheet 508 has cured, a stamp can cut individual polishing pads 100 from the sheet 508. The polishing pads 100 can then be removed from the substrate 504. The substrate 504 can be made of, for example, stainless steel, a Teflon material, a silicone material, or a material coated with Teflon or silicon such that the polishing pads 100 can be easily removed from the substrate 504 after curing. The polishing pad 508 can then be placed in a CMP apparatus (not shown) for CMP polishing.
The properties of a polishing pad can affect the polishing rate of a substrate during CMP. For example, large, poorly distributed pores (as opposed to evenly spaced small pores) in the polishing pad can reduce the surface roughness of the polishing pad. Reduced surface roughness, in turn, can decrease the polishing rate by reducing polishing liquid transport during polishing and decreasing the abrasiveness of the pad. By introducing soluble particles during the production of the polishing pad, the polishing rate can be increased, as before the soluble particles on the polishing surface dissolve, they can act as abrasives, and after the soluble particles on the polishing surface dissolve, the surface roughness can be increased due to small voids left behind. Furthermore, the introduction of surfactants to the formulation can increase the polishing rate by allowing for better distribution of voids, POSS nanoparticles, or soluble particles, and can thereby increase the surface roughness.
The polishing rate can be further increased by incorporating macro-texture or grooves into the surface of the polishing pad, which can facilitate the transport of polishing liquid during polishing. However, the creation of macro-texture after curing of the polishing pad can be extremely timely and expensive. By casting the precursor polishing pad mixture onto a substrate with grooves, the pad grooves can be generated during curing, thereby reducing the cost of creating grooves after curing.
The properties of the polishing pad can also affect the wear rate of the pad itself. In particular, if a polishing pad has high porosity, the wear rate of the pad can be high. By incorporating molecular level POSS into the polishing pad, the hardness of the pad can be increased, and the surface friction can be reduced, both of which can reduce the polishing pad wear rate. Likewise, the polishing pad wear rate can be reduced by incorporating soluble organic or inorganic particles into the polishing pad, which can increase the hardness of the polishing pad.
Particular embodiments of the invention have been described. Other embodiments are within the scope of the following claims.
This application claims priority to U.S. Application Ser. No. 61/247,411, filed on Sep. 30, 2009, the entire disclosure of which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61247411 | Sep 2009 | US |
