Abrasive tool making process – material – or composition – With inorganic material – Clay – silica – or silicate
Reexamination Certificate
2003-02-05
2004-07-27
Marcheschi, Michael A. (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Clay, silica, or silicate
C106S003000, C428S404000, C438S692000, C438S693000
Reexamination Certificate
active
06767377
ABSTRACT:
CROSS REFERENCE TO RELATED CASES
The present application claims priority to German Application No. DE 102 04 471.6, filed on Feb. 5, 2002, which is hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aqueous dispersion containing a silicon dioxide powder coated with cerium oxide. In addition, the present invention provides a method of producing an aqueous dispersion containing a silicon dioxide powder coated with cerium oxide and methods of using this aqueous dispersion for chemical-mechanical polishing.
2. Discussion of the Background
Cerium oxide dispersions obtained by calcining a cerium compound and subsequently grinding the oxides have been used for a long time for glass polishing. These dispersions typically have particle sizes of more than 1000 nm and large impurity contents. These dispersions are suitable for a coarse polishing of surfaces, but not for polishing of sensitive optical surfaces, semiconductor substrates, or integrated circuits (i.e., chemical-mechanical polishing, CMP).
Smaller cerium oxide particles may be obtained from a process, which has been denoted hydrothermal synthesis. In this process a cerium (III) salt is oxidatively converted, under the influence of temperature and pressure, to cerium oxide, which crystallizes out in the form of fine particles. The particle sizes of the cerium oxide obtained by this process are 80-100 nm (EP-A-947 469), 7-50 nm (U.S. Pat. No. 5,389,352), or less than 30 nm and greater than 60 nm (U.S. Pat. No. 5,772,780). A disadvantage of this method is that it requires the use of very dilute cerium (III) solutions as the starting material.
U.S. Pat. No. 5,891,205 discloses mixtures of silicon dioxide and cerium oxide, which has been produced by hydrothermal synthesis. In the process disclosed in this reference, the cerium oxide must first by deagglomerated using a mill and subsequently the resultant cerium oxide dispersion is mixed with a silicon dioxide dispersions based on silica sol. The mixture can then be used for planarising silicon discs. The disadvantages associated with this process include the high complexity and costs for the production of the fine-particle dispersion. In addition, the deagglomeration of the cerium oxide by using a mill carries a risk of impurity transfer into the dispersion. Furthermore, it is readily appreciated in the art that silicon dioxide dispersion based on silica sol have a higher proportion of impurities than those based on silicon dioxide produced pyrogenically.
U.S. Pat. No. 5,382,272 discloses the activation of silicon dioxide particles by adsorption of a few percent by weight, preferably 2% by weight, of a cerium or zirconium oxide dispersion. The special feature of this process is that the activating effect is accomplished by grinding a silicon dioxide dispersion with a commercially available cerium or zirconium oxide dispersion. The resultant mixed dispersion behaves like pure cerium oxide dispersions in polishing of semi-conductor substrates with a high removal rate, but without leaving any scratches on the surface to be polished. This method has an advantage over other common methods in that the costs associated therewith are reduced and implementation is relatively simple. However, this method also harbors distinct disadvantages, which are described in detail in WO 00/17 282 A1, such as the production of a dispersion with a narrow particle size range and difficulties in achieving reproducible polishing results.
U.S. Pat. No. 5,697,992 discloses the production of a powder containing abrasive particles and aqueous dispersions produced therefrom. The abrasive particles consist of silicon dioxide or aluminum oxide and a coating of cerium oxide. In this reference, the abrasive particles have an average particle size of 2 &mgr;m or less. However, based on this disclosure, it is unclear whether the stated particle size refers to the powder or the dispersion. For silicon dioxide particles coated with cerium oxide a particle size of 0.6 &mgr;m is given in one example. The metal oxides come from either a sol-gel or a pyrogenic process. A disadvantage of the process employed in this reference is caking of the metal oxide particles, particularly those of pyrogenic origin, when being coated with a cerium compound. As such, this leads to the formation of hard aggregates that are difficult to disperse. In the dispersion, this can lead to a very broad particle size distribution and occasionally to the detachment of parts of the coating in the form of cerium oxide during dispersion. Accordingly, the dispersion obtained by the disclosure of U.S. Pat. No. 5,697,992 are non-uniform and, with the continuing miniaturization in the semi-conductor industry, accordingly are of only limited suitability for reproducible polishing of oxide surfaces.
Accordingly, there remains a critical need in the area of chemical-mechanical polishing (CMP) for extraordinarily high activity of cerium oxide compared to silicon dioxide and other dielectric oxides.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an aqueous dispersion containing cerium oxide, which is simple to produce, has only a small proportion of impurities and has a reproducibly adjustable particle size.
This object may be achieved by an aqueous dispersion containing a powder obtained from a core of doped, pyrogenically produced silicon dioxide with a low structure, by mixing, preferably spraying, with a cerium salt solution or suspension, forming a cerium oxide coating, wherein the powder does not exceed an average secondary particle size of 0.2 &mgr;m in the dispersion.
The above objects highlight certain aspects of the invention. Additional objects, aspects and embodiments of the invention are found in the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Unless specifically defined, all technical and scientific terms used herein have the same meaning as commonly understood by a skilled artisan in the field of semi-conductors.
All methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, with suitable methods and materials being described herein. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. Further, the materials, methods, and examples are illustrative only and are not intended to be limiting, unless otherwise specified.
The present invention is based in part on the Inventor's surprising discovery that an extraordinarily high activity cerium oxide possessing high removal rates and good selectivities, which are useful in chemical mechanical polishing can be achieved by employing an aqueous dispersion comprising a powder having an average secondary particle size of 0.2 &mgr;m obtained by a process comprising mixing a core consisting of doped, pyrogenically produced silicon dioxide having a low structure with a cerium salt solution or suspension to form a cerium oxide shell.
“Aqueous dispersion” as used herein means a dispersion in which the main component of the liquid phase is water.
“A core consisting of a doped, pyrogenically produced silicon dioxide” as used herein means a core in which the doping is introduced by means of an aerosol of a salt solution or suspension containing the doping component. For an example of the production of such cores the artisan is referred to DE-A-196 50 500.
“Low structure” as used herein means that the core consists of many individual spherical primary particles that are fused together only to a small extent. A measure of the low structure is the DBP absorption (dibutyl phthalate absorption). This is less than 100 g DBP/100 g powder, the term powder here referring to the doped core. It is also possible for the end point to be undetectable in the DBP absorption. In a pyrogenically produced, undoped sili
Batz-Sohn Christoph
Lortz Wolfgang
Mangold Helmut
Meyer Juergen
Schumacher Kai
Degussa - AG
Marcheschi Michael A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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