Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1999-12-30
2002-04-23
Nguyen, George (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S053000, C451S067000, C134S022140
Reexamination Certificate
active
06375548
ABSTRACT:
TECHNICAL FIELD
This invention relates to chemical-mechanical polishing methods.
BACKGROUND OF THE INVENTION
Chemical-mechanical polishing (CMP), also known as chemical-mechanical planarization, is widely used in a variety of industries, including the semiconductor processing industry. CMP can remove unwanted material from a substrate, planarize a substrate, and/or create a desired finish on a substrate. All of such intentions may be generically termed “polishing.” Generally, the technology involves pressing some sort of solid abrasive material against the substrate to accomplish the polishing and/or planarization. The solid abrasive material may be applied in a CMP slurry of such material and liquid carriers and/or chemically active components as desired. Alternatively, abrasive material may be carried within a polishing pad. Still other techniques are encompassed within the technology.
One common byproduct of CMP is that abrasive material residues often remain on the substrate. In some applications, residual abrasive material can negatively influence subsequent processing and/or result in defective products. Accordingly, a variety of approaches have been attempted to resolve the problem of residual abrasive material.
One conventional approach is to use hydrofluoric acid-based chemistries to undercut particles attached to a silicon oxide substrate. A problem with hydrofluoric acid-based chemistries is that microscratches formed in the substrate as a result of CMP may be aggravated in the acidic conditions. Further, insoluble fluoride compounds may be formed from reactions of hydrofluoric acid with the abrasive material.
Another conventional approach includes application of ammonium hydroxide or tetramethylammonium hydroxide (TMAH) to disperse residual abrasive material. At a high pH, a silicon oxide surface and most abrasive material particles, including ceria, alumina, and silica exhibit a negative surface charge. Such charge characteristics provide electrostatic repulsion. Experimentally, such a method has produced limited benefits and appears to work much better for aluminum oxide particles in comparison to cerium oxide particles.
Still another conventional technique involves etching and/or dissolution of abrasive particles. For cerium oxide particles, such may be accomplished with the application of a mixture of hydrogen peroxide and sulfuric acid. While this method exhibits some effectiveness experimentally, it is incompatible with any surface structures featuring exposed metal.
Accordingly, it is desired to provide a new method for removing CMP residual abrasive material from a substrate.
SUMMARY OF THE INVENTION
In accordance with an aspect of the invention, a chemical-mechanical polishing (CMP) method includes applying a solid abrasive material to a substrate, polishing the substrate, flocculating at least a portion of the abrasive material, and removing at least a majority portion of the flocculated portion from the substrate. Such a method can include polishing with a CMP slurry or polishing pad. It may further include applying a surfactant-comprising material to the substrate to assist in effectuating flocculation of the abrasive material. Such surfactant comprising material may be cationic which includes, for example, a quaternary ammonium substituted salt. Also, for example, the surfactant-comprising material may be applied during polishing, brush scrubbing, pressure spraying, or buffing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).
One aspect of the present invention provides a chemical-mechanical polishing (CMP) method which involves applying a solid abrasive material to a substrate. Such substrate can include a semiconductor substrate. In the context of this document, the term “semiconductor substrate” or “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.
Applying a solid abrasive material can include applying a CMP slurry of substantially dispersed, solid abrasive material or applying a polishing pad comprising solid abrasive material. A variety of CMP slurries and polishing pads are conceivable that can include a variety of components. Examples of solid abrasive material include cerium oxide, aluminum oxide, mixtures thereof, and combinations thereof with other materials. Preferably, the solid abrasive material comprises ceria. Accordingly, ceria-based abrasive material is also preferred. The solid abrasive material may be substantially dispersed within the CMP slurry, that is, the solid abrasive material is not entirely agglomerated into floccule comprising multiple solid abrasive particles. Depending on the application, some agglomeration of abrasive material particles may be tolerated. However, substantial dispersion alleviates the problem of unnecessary scratching or other similar damage to a substrate from oversized floccule.
The method next comprises polishing the substrate. The parameters under which such polishing is to occur may be established according to the knowledge of those skilled in the technology at the time the method is being practiced. That is, it is contemplated that the present method is applicable both to currently available CMP parameters as well as others that may be later developed.
The method further includes flocculating at least a portion of the abrasive material on the substrate. Such flocculating may occur by a variety of means and at a variety of points within the CMP method. One means for flocculating abrasive material includes applying a surfactant comprising material. A variety of surfactant comprising materials are suitable and may -be characterized in a variety of ways.
One such suitable surfactant comprising material exhibits the characteristic of decreasing a settling time for the abrasive material in an aqueous dilution of the slurry. The CMP slurry may be diluted in water, such as de-ionized water, to produce an aqueous dilution of the CMP slurry having a desired concentration of the CMP slurry. For example, the aqueous dilution may comprise 0.1 weight percent (wt %) CMP slurry, 1 wt % slurry, or some other dilution level. The aqueous dilution of the CMP slurry will exhibit a settling time. That is, after a desired amount of time passes, analysis can be conducted to determine the extent to which solid abrasive particles have settled within the aqueous dilution. For example, analysis could occur on 24-hour cycles, or some other duration.
Settling time may vary depending upon a variety of factors, including the dilution level of the CMP slurry (i.e. initial particle concentration in the dilution), pH, and the temperature of the aqueous dilution. It is expected that the most significant decreases in settling time compared to an aqueous dilution without a surfactant comprising material will occur when the temperature of the aqueous dilution does not exceed about 40° Celsius (°C.). A variety of settling times may also be used to measure the effectiveness of a surfactant comprising material. One example of a settling time is the elapsed time beginning from the mixing of a surfactant comprising material with the aqueous dilution up to the time when a designated percentage of the abrasive material has settled from the supernatant of the aqueous dilution. Settling time is considered to decrease if such elapsed time is less for a dilution with the surfactant comprising material.
Another way to characterize settling time is to compare the percentage of abrasive material that has settled from an aqueous d
Micro)n Technology, Inc.
Nguyen George
Wells St. John P.S.
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