Compositions – Magnetic – Flaw detection or magnetic clutch
Reexamination Certificate
2000-05-04
2002-06-11
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
Flaw detection or magnetic clutch
C051S307000, C051S308000, C051S309000, C451S036000, C451S037000
Reexamination Certificate
active
06402978
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to magnetic polishing fluids useful for polishing metallic surfaces, particularly metal surfaces in the microelectronic industry.
BACKGROUND OF THE INVENTION
Chemical-mechanical polishing is a commonly used technique for planarization of bare silicon, silica and other ceramic wafers. In chemical-mechanical polishing, the wafers are held against a rotating polishing pad wetted by a slurry consisting of colloidal abrasive particles (silicon dioxide, alumina, cerium oxide, etc.) and specific additives to enhance the rate and quality of polishing. When silica is used, a high pH is required. An oxide or hydroxide surface layer forms on the wafer and the reaction products are removed by mechanical action of the pad and the colloidal silica slurry. Similar processes occur when other abrasives are used.
Copper interconnects in ultra-large scale integrated (ULSI) circuit layouts were introduced relatively recently into the semiconductor industry. They became possible as a result of improvements in chemical-mechanical planarization (CMP) technology developed during the last two decades. The adoption of CMP for polishing or removing thin metal layers, such as copper, aluminum, tungsten, titanium and tantalum layers, has enabled their commercial use and markedly changed semiconductor processing. The CMP techniques presently used for metals are very similar to those used for polishing ceramics described above.
The use of CMP has led to a large increase in the amount of metal being polished in the semiconductor industry. Only ten years ago, the polishing of dielectric ceramics constituted more than 90% of semiconductor materials being polished. The current volume of metal being polished in the industry exceeds by several hundred percent that polished formerly.
The bending and stresses of the rotating polishing pad used in convential CMP polishing, strongly influence the quality of planarization. The adverse effects of a polishing pad can be avoided, or at least mitigated, by using a magnetic polishing fluid which forms a plasticized mass in an a inhomogeneous magnetic field.
Magnetorheological fluids (MRFs) for polishing ceramics and optical materials are known in the art. With MRFs, the polishing pad common to conventional polishing is dispensed with entirely.
The viscosity of magnetorheological fluids increases in a magnetic field and the fluids, which contain magnetic particles, acquire the characteristics of a plasticized solid, that is one exhibiting Bingham properties, forming an abrasive mass with a viscosity and elasticity suitable for polishing.
Typical MRF formulations are discussed in U.S. Pat. Nos. 5,804,095, 5,795,212, 5,525,249, 5,449,313, and 4,821,466. These references when mentioning polishing, do so only in the context of polishing ceramic or optical materials. They do not discuss polishing metal surfaces.
Polishing machines used with prior art MRF compositions causes them to acquire viscous, plasticized properties known as Bingham properties, when under the influence of magnetic forces. When in a magnetic field, the MRF is hard enough to be used as a polishing tool. However, these polishing fluids reach their fully developed Bingham state only at the outset of the polishing process. Once the substrate being polished begins to move relative to the MRF, the shear stress of the abrasion process causes the MRF to lose its Bingham properties and its plasticized characteristics. The MRF remains viscous throughout the process but returns to a liquid, non-plasticized state almost immediately after abrasion begins, reducing polishing efficiency.
The magnetorheological fluids in the above-cited compositions usually provide a mechanical mechanism for the polishing process. In addition, these fluids generally contain magnetic and/or abrasive particles with sizes in excess of 1 &mgr;m. These large size particles, and especially their agglomerates, introduce defects, scratches and non-uniformities onto the surface being treated.
Finally, because of the large size magnetic or abrasive particles used, these fluids have a tendency to settle due to gravitational forces. Because of their size, the abrasive particles act as agglomeration centers, contributing to the aggregation of magnetic particles and to the instability of the magnetic fluid. Any use of such fluids requires prior agitation.
SUMMARY OF THE INVENTION
The present invention relates to magnetic polishing fluid compositions suitable for polishing metal surfaces. In particular, it is suitable for polishing metal interconnects, vias and layers used extensively in current ULSI manufacturing.
One embodiment of the present invention teaches a magnetic polishing fluid composition comprising colloidal size magnetic particles with a mean particle size range from about 0.01 &mgr;m to about 0.15 &mgr;m, colloidal size polishing particles with a mean particle size range from about 0.01 &mgr;m to about 0.1 &mgr;m, at least one stabilizer for stabilizing the colloidal size particles, at least one oxidizer, at least one inhibitor for controlling the rate of oxidation of the oxidizer, and a carrying fluid where the pH of the composition is in the range from between about 0.5 to about 5.5.
In another embodiment based on the above, the magnetic polishing fluid composition does not include the colloidal polishing particles. In yet another embodiment based on the above, the polishing fluid does not contain an inhibitor.
A method for preparing the above compositions includes the steps of preparing a colloidal size magnetic particle dispersion with a stabilizer in a carrying fluid, preparing a colloidal size polishing particle dispersion in a carrying fluid, adding to the colloidal size polishing particle dispersion at least one oxidizer and at least one inhibitor, mixing said colloidal size magnetic particle dispersion and said colloidal size polishing particle dispersion to form a mixture, and adjusting the mixture to a final pH of about 0.5-5.5, if not already at the pH.
In yet another embodiment, a multi-phase magnetic composition, a magnetic polishing fluid composition contains both colloidal and non-colloidal magnetic particles. The non- colloidal magnetic particles have a mean particle size range from about 0.15 &mgr;m to about 3.0 &mgr;m and the colloidal magnetic particles have a mean particle size range from about 0.01 &mgr;m to about 0.15 &mgr;m. The composition also contains at least one oxidizer, at least one inhibitor for inhibiting the rate of oxidation of the oxidizer, at least one stabilizer for stabilizing said colloidal particles, an additive for adjusting viscosity, and a carrying fluid. The pH of the final composition is in a range from about 0.5 to about 5.5.
Yet another embodiment based on the embodiment discussed immediately above, does not include an inhibitor. A second multi-phase embodiment does not require colloidal polishing particles.
The invention also teaches a method for producing the above composition comprising the steps of preparing a non-colloidal size magnetic particle dispersion by adding the particles to a mixture of a viscosity additive in a carrying fluid. This is followed by preparation of a colloidal size magnetic particle dispersion with a stabilizer in a carrying fluid. This is further followed by preparing a colloidal size polishing particle dispersion in a carrying fluid and adding to the colloidal size polishing particle dispersion at least one oxidizer and at least one inhibitor. The colloidal size magnetic particle dispersion and the colloidal size polishing particle dispersion are mixed to form an intermediate mixture, which is then mixed with the non-colloidal size magnetic particle dispersion. Finally, the pH of the composition is adjusted to a pH in the range of about 0.5 to about 5.5, if the composition is not already at the proper pH in that range.
In yet another embodiment, a magnetic polishing fluid composition is taught which comprises magnetic particles having a mean particle size range from about 0.15 to about 3.0 &mgr;m, colloidal siz
Eitan Pearl Latzer & Cohen-Zedek
Koslow C. Melissa
MPM Ltd.
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