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  Polishing medium for chemical-mechanical polishing, and polishing methodUSPTO Application #: 20070190906Title: Polishing medium for chemical-mechanical polishing, and polishing method Abstract: This invention provides a polishing medium for CMP, comprising an oxidizing agent, a metal-oxide-dissolving agent, a protective-film-forming agent, a water-soluble polymer, and water, and a polishing method making use of this polishing medium. Also, it is preferable that the water-soluble polymer has a weight-average molecular weight of 500 or more and the polishing medium has a coefficient of kinetic friction of 0.25 or more, a Ubbelode's viscosity of from 0.95 mPa·s (0.95 cP) to 1.5 mPa·s (1.5 cP) and a point-of-inflection pressure of 5 kPa (50 gf/cm2). (end of abstract)
Agent: Antonelli, Terry, Stout & Kraus, LLP - Arlington, VA, US Inventors: TAKESHI UCHIDA, Yasuo Kamigata, Hiroki Terasaki, Yasushi Kurata, Tetsuya Hoshino, Akiko Igarashi USPTO Applicaton #: 20070190906 - Class: 451036000 (USPTO) Related Patent Categories: Abrading, Abrading Process, Utilizing Fluent Abradant The Patent Description & Claims data below is from USPTO Patent Application 20070190906. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This application is a Divisional application of application Ser. No. 10/069,404, filed May 6, 2002, the contents of which are incorporated herein by reference in their entirety. Ser. No. 10/069,404 is a National Stage application, filed under 35 USC 371, of International (PCT) Application No. PCT/JP00/05765, filed Aug. 25, 2000. TECHNICAL FIELD [0002] This invention relates to a polishing medium for chemical-mechanical polishing, especially suited for polishing in the step of forming wirings of semiconductor devices, and a polishing method making use of the same. BACKGROUND ART [0003] In recent years, as semiconductor integrated circuits (hereinafter "LSI") are made high-integration and high-performance, new techniques for fine processing have been developed. Chemical-mechanical polishing (hereinafter "CMP") is also one of them. The CMP is often used in LSI fabrication steps, in particular, in making interlaminar insulating films flat in the step of forming multilayer wirings, in forming metallic plugs and in forming buried wirings. This technique is disclosed in, e.g., U.S. Pat. No. 4,944,836. [0004] Recently, in order to make LSIs high-performance, it is also attempted to utilize copper alloys as wiring materials. It, however, is difficult for the copper alloys to be finely processed by dry etching often used in forming conventional aluminum alloy wirings. Accordingly, what is called the damascene method is chiefly employed, in which a copper alloy thin film is deposited on an insulating film with grooves formed previously and is buried therein, and the copper alloy thin film at the part except the grooves is removed by CMP to form buried wirings. This technique is disclosed in, e.g., Japanese Patent Application Laid-open No. 2-278822. [0005] In a common method of polishing metals by the CMP, a polishing pad is fastened onto a circular polishing roller (platen), and the surface of the polishing pad is soaked with a polishing medium for chemical-mechanical polishing, where a substrate with a metal film formed thereon is pressed against the pad on the former's metal film side and a stated pressure (hereinafter "polishing pressure") is applied thereto on the back thereof, in the state of which the polishing platen is turned to remove the metal film at the part of its hills by mechanical friction acting between the polishing medium and the metal film. [0006] The polishing medium used in such CMP is commonly comprised of an oxidizing agent and solid abrasive grains, to which a metal-oxide-dissolving agent and/or a protective-film-forming agent are optionally added. The basic mechanism of CMP making use of this polishing medium for CMP is considered to be that the metal film surface is oxidized with the oxidizing agent and the resultant oxide layer is scraped with the solid abrasive grains. The metal surface oxide layer at the part of dales does not come into contact with the polishing pad so much and the effect of scraping attributable to the solid abrasive grains does not extend thereto. Hence, with progress of the CMP, the metal layer becomes removed at its hills and the substrate (with film) surface become flat. Details on this matter are disclosed in Journal of Electrochemical Society, Vol. 138, No. 11 (published 1991), pages 3460-3464. [0007] In order to make higher the rate of polishing by CMP, it is considered effective to add the metal-oxide-dissolving agent. It can be explained that this is because the effect of scraping attributable to the solid abrasive grains comes higher where grains of metal oxide scraped off by the solid abrasive grains are made to dissolve in the polishing medium. However, the addition of the metal-oxide-dissolving agent makes the metal film surface oxide layer dissolve (hereinafter "etching") also at the part of dales, and the metal film surface becomes uncovered, so that the metal film surface is further oxidized by the oxidizing agent. With repetition of this, the etching of the metal film may proceed at the part of dales, resulting in a damage of the effect of flattening. [0008] In order to prevent this, the protective-film-forming agent is further added to the metal-polishing medium for CMP. Thus, adding the metal-oxide-dissolving agent and protective-film-forming agent adds the effect of chemical reaction, and this brings about the effect that the CMP rate (the rate of polishing by CMP) is improved and also any injury (damage) of the metal layer surface to be polished by CMP may less occur. [0009] In order to obtain a flat polished surface, it is important to balance the effect attributable to the metal-oxide-dissolving agent and protective-film-forming agent used in the polishing medium for CMP. In the CMP, it is preferable to use a polishing medium which does not etch the metal film surface oxide layer so much at the part of dales, dissolves in a good efficiency the particles of the oxide layer scraped off, and has a high rate of polishing. [0010] However, the formation of buried wirings by CMP using a conventional polishing medium for chemical-mechanical polishing which contain solid abrasive grains involves the problems such that; [0011] (1) it may cause a phenomenon that the surface of the metal wiring having been buried is isotropically corroded at the middle thereof to become hollow like a dish (hereinafter "dishing"); [0012] (2) it may cause polishing mars (scratches) arising from solid abrasive grains; [0013] (3) the wash processing to remove solid abrasive grains remaining on the substrate surface after polishing is troublesome; and [0014] (4) a cost increase may arise because of the prime cost of solid abrasive grains themselves and the disposal of waste liquor. [0015] Accordingly, in order to keep the dishing from occurring or the copper alloy from corroding during the polishing, to form highly reliable LSI wirings, a polishing method making use of a polishing medium for CMP which contains a metal-oxide-dissolving agent comprised of amino acetic acid (e.g., glycine) or amidosulfuric acid and contains BTA (benzotriazole) is proposed. This technique is disclosed in, e.g., Japanese Patent Application Laid-open No. 8-83780. [0016] However, the BTA has a very high protective-film-forming effect, and hence it may greatly lower not only the rate of etching but also the rate of polishing. Accordingly, it is sought to provide a polishing medium for CMP which lowers the etching rate sufficiently but does not lower the CMP rate. DISCLOSURE OF THE INVENTION [0017] An object of the present invention is to provide a polishing medium for CMP and a polishing method which can form highly reliable buried metal film patterns in a good efficiency by making the etching rate sufficiently low while keeping a high CMP rate. [0018] As the protective-film-forming agent, a compound by which a chelate complex is readily formed with copper is used, such as ethylenediaminetetraacetic acid or benzotriazole. Such a compound has a very strong effect of forming a protective film on the surface to be polished. For example, if it is incorporated in the polishing medium for CMP in an amount of 0.5% by weight or more, the copper alloy film comes not subject to CMP, to say nothing of etching. [0019] In this regard, the present inventors have discovered that the use of the protective-film-forming agent in combination with a water-soluble polymer enables achievement of a high CMP rate while keeping a sufficiently low etching rate. They have moreover discovered that the use of such a polishing medium enables the polishing to be carried out at a practical CMP rate even without incorporating any solid abrasive grains in the polishing medium. [0020] This is considered due to the fact that the scraping by friction with a polishing pad takes place in place of the effect of scraping by the friction with solid abrasive grains in conventional cases. According to the present invention, the water-soluble polymer is added to a metal polishing medium containing an oxidizing agent for the polishing object, a metal-oxide-dissolving agent, a protective-film-forming agent and water, whereby the CMP rate can be made higher while the etching rate is kept low. [0021] As to the value of etching rate, it has been found that a preferable flattening effect can be achieved as long as the etching rate is controlled to 10 nm/minute or less. As long as the lowering of CMP rate is within a tolerable range, it is desirable for the etching rate to be much lower. As long as the etching rate is controlled to 5 nm/minute or less, the dishing can be kept to a degree not coming into question even when, e.g., the CMP is performed in excess by about 50% (i.e., CMP is performed for a time 1.5 times that necessary for removing the polishing object). As long as the etching rate can further be controlled to 1 nm/minute or less, the dishing does not come into question even when the CMP is performed in excess by about 100% or more. [0022] Accordingly, the present invention provides a polishing medium for CMP, comprising an oxidizing agent, a metal-oxide-dissolving agent, a protective-film-forming agent, a water-soluble polymer, and water, and a polishing method making use of this polishing medium. [0023] In order to achieve much higher CMP rate, higher flattening, lower dishing level and lower erosion level, the polishing medium for CMP may preferably satisfy at least one of the following (1) to (4), and may particularly preferably satisfy all of them. [0024] (1) That the water-soluble polymer has a weight-average molecular weight of 500 or more. [0025] This enables the CMP rate to be made higher while the etching rate is kept low. The water-soluble polymer may preferably have a weight-average molecular weight of 500 or more, more preferably 1,500 or more, and particularly preferably 5,000 or more. The upper limit of the weight-average molecular weight is not particularly defined. From the viewpoint of solubility, it may preferably be 5,000,000 or less. Continue reading... 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