Abrading – Abrading process
Reexamination Certificate
2002-01-22
2003-03-04
Morgan, Eileen P. (Department: 3723)
Abrading
Abrading process
C451S041000, C451S036000
Reexamination Certificate
active
06527622
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to a method of polishing a substrate comprising a noble metal.
BACKGROUND OF THE INVENTION
Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the slurry composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing slurry comprising high purity fine metal oxide particles in an aqueous medium. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No. 5,958,794 discloses a fixed abrasive polishing pad.
Conventional polishing systems and polishing methods typically are not entirely satisfactory at planarizing semiconductor wafers. In particular, polishing compositions and polishing pads can have less than desirable polishing rates, and their use in the chemical-mechanical polishing of semiconductor surfaces can result in poor surface quality. Because the performance of a semiconductor wafer is directly associated with the planarity of its surface, it is crucial to use a polishing composition and method that results in a high polishing efficiency, uniformity, and removal rate and leaves a high quality polish with minimal surface defects.
The difficulty in creating an effective polishing system for semiconductor wafers stems from the complexity of the semiconductor wafer. Semiconductor wafers are typically composed of a substrate, on which a plurality of transistors has been formed. Integrated circuits are chemically and physically connected into a substrate by patterning regions in the substrate and layers on the substrate. To produce an operable semiconductor wafer and to maximize the yield, performance, and reliability of the wafer, it is desirable to polish select surfaces of the wafer without adversely affecting underlying structures or topography. In fact, various problems in semiconductor fabrication can occur if the process steps are not performed on wafer surfaces that are adequately planarized.
Various metals and metal alloys have been used to form electrical connections between interconnection levels and devices, including titanium, titanium nitride, aluminum-copper, aluminum-silicon copper, tungsten, platinum, platinum-tungsten, platinum-tin, ruthenium, and combinations thereof. Noble metals present a particular challenge in that they are mechanically hard and chemically resistant, making them difficult to remove efficiently through chemical-mechanical polishing.
The following patents disclose polishing compositions for noble metals. U.S. Pat. No. 5,691,219 discloses a semiconductor memory device comprising a noble metal conductive layer and a polishing composition comprising a halo-compound for polishing the noble metal. U.S. Pat. No. 6,274,063 discloses polishing compositions for nickel substrates comprising a chemical etchant (e.g., aluminum nitrate), abrasive particles, and an oxidizer. U.S. Pat. No. 6,290,736 discloses a chemically active polishing composition for noble metals comprising an abrasive and a halogen in basic aqueous solution. JP 63096599 A2 discloses a method of dissolving metallic ruthenium. JP 11121411 A2 discloses a polishing composition for platinum group metals (e.g., Ru, Pt) comprising fine particles of an oxide of the platinum group metal. JP 1270512 A2 discloses a dissolving solution for noble metals comprising hydrogen peroxide, alkali cyanide, and phosphate ion and/or borate ion. WO 00/77107 A1 discloses a polishing composition for noble metals (e.g., Ru, Rh, Pd, Os, Ir, Pt) comprising abrasive, a liquid carrier, an oxidizer, and a polishing additive including EDTA, nitrogen-containing macrocycles (e.g., tetraazacyclotetradecanes), crown ethers, halides, cyanides, citric acid, phosphines, and phosphonates. WO 01/44396 A1 discloses a polishing composition for noble metals comprising sulfur-containing compounds, abrasive particles, and water-soluble organic additives which purportedly improve the dispersion of the abrasive particles and enhance metal removal rates and selectivity.
A need remains, however, for polishing systems and polishing methods that will exhibit desirable planarization efficiency, uniformity, and removal rate during the polishing and planarization of substrates, while minimizing defectivity, such as surface imperfections and damage to underlying structures and topography during polishing and planarization. Improved polishing systems are particularly needed for the polishing of chemically stable and mechanically hard noble metal-containing substrates.
The present invention seeks to provide such a chemical-mechanical polishing system and method. These and other advantages of the invention will be apparent from the description of the invention provided herein.
BRIEF SUMMARY OF THE INVENTION
The invention provides a method of polishing a substrate comprising (i) contacting a substrate comprising a noble metal with a chemical-mechanical polishing system comprising (a) an abrasive and/or polishing pad, (b) a liquid carrier, and (c) one or more polishing additives selected from the group consisting of diketones, diketonates, urea compounds, heterocyclic nitrogen-containing compounds, heteroclclic oxygen-containing compounds, heterocyclic phosphorus-containing compounds, nitrogen-containing compounds that can be zwitterionic compounds, salts thereof, and combinations thereof, wherein the chemical-mechanical polishing system has a pH of about 2 to about 12, and (ii) abrading at least a portion of the substrate to polish the substrate. The invention further provides a method of polishing a substrate comprising (i) contacting a substrate comprising a noble metal with a chemical-mechanical polishing system comprising (a) an abrasive and/or polishing pad, (b) a liquid carrier, (c) at least one polishing additive selected from metal compounds with two or more oxidation states, wherein the metal compound is soluble in the liquid carrier, and (d) a peroxy-type oxidizer, wherein the chemical-mechanical polishing system has a pH of about 2 to about 12, and (ii) abrading at least a portion of the substrate to polish the substrate. The invention additionally provides a method of polishing a substrate comprising (i) contacting a substrate comprising a noble metal with a chemical-mechanical polishing system comprising (a) &agr;-alumina and fumed alumina, (b) a polishing pad, and (c) a liquid carrier, wherein the weight ratio of &agr;-alumina to fumed alumina is about 0.6:1 to about 9:1.
DETAILED DESCRIPTION OF THE INVENTION
The invention is directed to methods of polishing a substrate comprising a noble metal. The substrate is contacted with a chemical-mechanical polishing (“CMP”) system comprising (a) an abrasive and/or polishing pad, (b) a liquid carrier, and optionally (c) at least one polishing additive (i.e., one or more polishing additives). The polishing additive can be any suitable compound that desirably increases the rate at which the system polishes at least one noble metal layer of the substrate. At least a portion of the substrate is abraded so as to polish the surface of the substrate. The abrasive (when present and suspended in the liquid carrier), the liquid carrier, and optional polishing additive(s), as well as any other components suspended in the liquid carrier, form the polishing composition of the CMP system.
The CMP systems described herein comprise an abrasive, a polishing pad, or both. Preferably, the CMP systems comprise both an abrasive and a polishing pad. The abrasive can be fixed on the polishing pad and/or can be in particulate form and suspended in the li
Brusic Vlasta
Cherian Isaac K.
De Rege Francesco M.
Moeggenborg Kevin J.
Zhou Renjie
Cabot Microelectronics Corporation
Morgan Eileen P.
Shakeri Hadi
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