Mechanical and chemical polishing method and polishing apparatus therefor

Abstract: The invention provides a novel method of supplying a polishing liquid onto a surface of a polishing pad (6) through which a surface of a film (9) be polished wherein a solution (4) including an aggregation agent and a slurry (3) into which fine polishing particles (7) were already dispersed are separately supplied onto the polishing surface so that the slurry is mixed with the solution to thereby cause an aggregation of the fine polishing particles (11) to form aggregated particles to be used for polishing.

Description: The present invention provides a method of polishing a film by supplying a liquid on a surface of a polishing pad, and apparatus for polishing the film, and more particularly to a method of adding a polishing liquid on a surface of the polishing pad. The formation of the three-dimensional multilevel interconnections requires a planerization of the surface of the inter-layer insulator such as silicon oxide film. An aluminium wiring layer as a first bottom layer is formed thereafter a silicon oxide film is deposited by a chemical vapor deposition on the first layer. As a result, the silicon oxide film has an irregularity due to the aluminium wiring layer. When forming a second aluminium wiring layer on the irregular surface of the silicon oxide film through a photo-lithography and dry etching processes, problems are raised as to difficulty in focusing for exposure to be used for photo-resist pattern and as to difficulty in removal by dry etching of unnecessary part of the aluminium layer to form the second aluminium wiring layer. To settle this problems, it was proposed to conduct a polishing a surface of the silicon oxide film before the aluminium wiring layer is formed thereon. This is disclosed in the Japanese Patent Application No. 4-94677. The polishing of the silicon oxide film is carried out by a chemical etching function and a mechanical friction function of polishing particles. As disclosed in the Japanese laid-open patent publication No. 4-75338, a polishing liquid is used wherein silica particles having a diameter of 20 nanometers are dispersed into an ammonium solution at 10 to 30 wt%. Shortening the polishing time requires a high polishing speed which further requires a large size silica particle. The use of the large size silica particles may result in providing a damage to the surface of the film polished. Further, as illustrated in FIG. 1, the large silica particle is engaged with the problem in a high speed precipitation thereof thereby a continuous stirring of the liquid is required. The continuous stirring of the liquid requires the polishing apparatus to be provided with a stirring system thereby resulting in a complicated structure of the polishing apparatus. On the other hand, as disclosed in the Japanese laid-open patent publication No. 51-28295, when fine silica particles are used for polishing, it is permitted to suppress any damage to the polishing surface, but results in a problem as to a low speed of the polishing. A method of increasing a polishing speed without use of a large size polishing particle was proposed wherein an aggregation agent of an electrolytic salt is added into a slurry to cause an aggregation of silica particles to form a large size aggregated particles to be used for polishing as illustrated in FIG. 2. This method is, however, engaged with the disadvantages in necessarily to conducting a continuous stirring of the polishing liquid. Accordingly, it is a general object of the present invention to provide a novel method of polishing a film by supplying a polishing liquid free from any problems or disadvantages as described above. It is a further object of the present invention to provide a novel method of polishing a film at a high speed. It is a furthermore object of the present invention to provide a novel method of polishing a film without stirring a polishing liquid. It is a moreover object of the present invention to provide a novel method of polishing a film without providing any damage to the film. It is another object of the present invention to provide a novel apparatus of polishing a film by supplying a polishing liquid free from any problems or disadvantages as described above. It is a further object of the present invention to provide a novel apparatus of polishing a film at a high speed. It is a furthermore object of the present invention to provide a novel apparatus of polishing a film without stirring a polishing liquid. It is a moreover object of the present invention to provide a novel apparatus of polishing a film without providing any damage to the film. These objects can be achieved by a method and an apparatus according to claims 1, 12 and 23 respectively. The invention provides a novel method of supplying a polishing liquid onto a surface of a polishing pad through which a surface of a film be polished, wherein a solution including an aggregation agent and a slurry into which fine polishing particles were already dispersed are separately supplied onto the polishing surface so that the slurry is mixed with the solution to thereby cause an aggregation of the fine polishing particles to form aggregated particles to be used for polishing. The present invention also provides a novel apparatus for polishing a film wherein the apparatus comprises a polishing unit having a plate being provided thereon with a polishing pad on which the film is polished, a slurry supplying system for storing and supplying a surface of the polishing pad with a slurry into which fine polishing particles are dispersed and an aggregation agent solution supplying system for storing and supplying a solution including an aggregation agent on the surface of the polishing pad so that the slurry is mixed with the solution to thereby cause an aggregation of the fine polishing particles to form aggregated particles to be used for polishing. Preferred embodiments of the present invention will hereinafter fully be described in detail with reference to the accompanying drawings. FIG. 1 is a view illustrative of the convention polishing method by use of large size silica particles. FIG. 2 is a view illustrative of the other convention polishing method by use of the aggregated silica particles. FIG. 3 is a view illustrative of a novel method and apparatus of polishing a film in a preferred embodiment according to the present invention. FIG. 4 is a diagram illustrative of polishing speeds in the conventional and novel methods. The invention provides a novel method of supplying a polishing liquid onto a surface of a film to be polished by a polishing apparatus wherein a solution including an aggregation agent and a slurry into which fine silica particles were already dispersed are separately supplied onto the polishing surface so that the slurry is mixed with the solution to thereby cause an aggregation of the fine silica particles to form aggregated particles to be used for polishing. The present invention also provides a novel apparatus for polishing a film wherein the apparatus comprises a polishing unit having a plate being provided thereon with a polishing pad on which the film is polished, a slurry supplying system for storing and supplying a surface of the polishing pad with a slurry into which fine silica particles are dispersed and an aggregation agent solution supplying system for storing and supplying a solution including an aggregation agent on the surface of the polishing pad so that the slurry is mixed with the solution to thereby cause an aggregation of the fine silica particles to form aggregated particles to be used for polishing. The slurry into which the fine silica particles is stored in a slurry tank. The fine silica particles are not precipitated due to its small size. This results in no need to stir the slurry in the tank. The slurry is transmitted onto the surface of the polishing pad separately from the solution including the aggregation agent and then on the polishing pad surface the slurry is mixed with the solution including the aggregation agent to thereby cause an aggregation of the fine silica particles involved in the slurry and subsequently aggregated silica particles are formed to serve as a polishing particle for polishing the film. The aggregated silica particles have a sufficiently large diameter for achieving a high sped polishing but a flexibility capable of presenting any damage to a surface of the film to be polished. The flexibility is caused by an electric force combining the fine silica particles. By contrast, the use of the large size silica particle used in the conventional method provides a damage into the surface of the film to be polished. As illustrated in FIG. 3, the novel polishing apparatus is provided with a slurry tank 1 for storing a slurry 3 and an aggregation agent solution tank 2 for storing an electrolytic solution 4. The slurry 3 and the electrolytic solution 4 are separately supplied separately by pump onto a surface of a polishing pad 6 formed on a polishing plate 5. A silicon oxide film formed on a semiconductor substrate 9 fined on a substrate zipper 10 is polished on the surface of the polishing pad 6. In the slurry tank 1, a slurry is stored as a suspension liquid wherein 10 to 40 wt% of fine silica particles 7 is dispersed into a pure water or an alkaline solution of a 8 to 9 pH value. The silica particles has a diameter in the range from 10 to 100 nanometers to prevent precipitation of the particles into the slurry 3. Considering the alkali metal pollution to the semiconductor process line, it is not preferable to use alkali metals such as NaOH or KOH dissolved into a pure water to prepare the alkaline solution of the 8 to 9 pH vale. If anything, it is preferable to use non-alkali metals such as ammonia or amine. In the aggregation agent solution tank 2, a solution including 0.3 mol/1 of ammonium acetate is stored. It is preferable to use, as an electrolytic salt, ammonium salts such as ammonium nitrate or ammonium chloride. NaCl or KCl are also available. From the aggregation agent solution tank 2, the solution including 0.3 mol/l of the ammonium acetate is fetched to be dropped onto the surface of the polishing pad 6 at a dropping rate of 20 ml/min. The slurry including 30 wt% of fine silica particles is then adjusted with addition of ammonia to have a 9 to 10 pH value and subsequently fetched and dropped onto the surface of the polishing pad 6 at a dropping rate of 40 ml/min. As a result, the dropped slurry is mixed on the surface of the polishing pad 6 with the aggregation agent solution to thereby cause an aggregation of fine silica particles involved in the slurry and then aggregated silica particles 11 are formed to act as polishing particles with a large diameter for allowing a high speed polishing and with a flexibility allowing the surface of the film from any damage in polishing thereof. On the surface of the polishing pad 6, a silica concentration is 20 wt% and a concentration of ammonium acetate is 0.1 mol/l thereby 10 to 50 of the fine silica particles having a diameter of about 20 nanometers are aggregated an aggregated particle 11 having a diameter of 200 to 1000 nanometers. FIG. 4 illustrates a polishing rate or a polishing amount versus a polishing time under the condition of a polishing pressure of 0.4 kg/cm 2 and a rotation speed of 35 rmp. When dropping the slurry only, then a polishing speed is 300 A/min. By contrast, when the slurry is dropped together with the solution including ammonium acetate, then the polishing speed is increased up to 900 A/min. To check any generation of damage, by use of laser particle checker a micro-scratch on a polished surface is checked. The used checker is able to detect a micro-scratch with a width not less than 0.3 micrometers. Even the micro-scratch, if existing, may be detectable as a scratch like line, no micro-scratch was detected. Although in the foregoing embodiment the silica particle is used as the polishing particle, alumina particles or cerium oxide particles are also available. When the alumina particles are used by dispersing the same into a slurry, the preferable pH value is in the range from 3 to 5. In any event, the pH value has to be controlled to present any aggregation of the fine particles in the slurry in the slurry tank. The above novel method is needless to say applicable to polishing of not only the silicon oxide film but also other films such as silicon nitride film, a boron phosphate silicate glass film, aluminium film, copper film and a tungsten film. From the above descriptions, it is understood that the present invention allows a high speed polishing without providing any damage to the polishing surface of the film and a shortening of the polishing time as well as a reduction of the manufacturing cost. Whereas modifications of the present invention will no doubt be apparent to a person having ordinary skill in the art to which the invention pertains, it is to be understood that embodiments shown and described by way of illustration are by no means intended to be considered in a limiting sense. Accordingly, it is to be intended to cover by the appended claims all modifications of the present invention which fall within the scope of the invention.

Claims: A method of supplying a polishing liquid onto a surface of a polishing pad (6) through which a surface of a film (9) is polished wherein a solution (4) including an aggregation agent and a slurry (3) into which fine polishing particles (7) were already dispersed are separately supplied onto the polishing pad surface so that the slurry is mixed with the solution to thereby cause an aggregation of the fine polishing particles to form aggregated particles (11) to be used for polishing. The method as claimed in claim 1, wherein a pH value of said slurry is controlled to suppress any generation of aggregation of said fine polishing particles until the slurry is mixed with said solution on said polishing pad surface. The method as claimed in claim 1, wherein said slurry comprises a suspension liquid with a non-alkali metal compound and fine polishing particles. The method as claimed in claim 3, wherein said non-alkali metal compound comprises ammonia. The method as claimed in claim 3, wherein said non-alkali metal compound comprises amine. The method as claimed in claim 1, wherein said polishing particle comprises a silica particle. The method as claimed in claim 1, wherein said polishing particle comprises an alumina particle. The method as claimed in claim 1, wherein said polishing particle comprises a cerium oxide particle. The method as claimed in claim 1, wherein said aggregation agent comprises an electrolytic salt. The method as claimed in claim 9, wherein said electrolytic salt comprises ammonium nitrate. The method as claimed in claim 9, wherein said electrolytic salt comprises ammonium chloride. A method of polishing a film (9) with supplying a polishing liquid onto a surface of a polishing pad (6) through which a surface of a film (9) is polished wherein a solution (4) including an aggregation agent and a slurry (3) into which fine polishing particles (7) were already dispersed are separately supplied onto the polishing pad surface so that the slurry is mixed with the solution to thereby cause an aggregation of the fine polishing particles to form aggregated particles (11) to be used for polishing. The method as claimed in claim 12, wherein a pH value of said slurry is controlled to suppress any generation of aggregation of said fine polishing particles until the slurry is mixed with said solution on said polishing pad surface. The method as claimed in claim 12, wherein said slurry comprises a suspension liquid with a non-alkali metal compound and fine polishing particles. The method as claimed in claim 14, wherein said non-alkali metal compound comprises ammonia. The method as claimed in claim 14, wherein said non-alkali metal compound comprises amine. The method as claimed in claim 12, wherein said polishing particle comprises a silica particle. The method as claimed in claim 12, wherein said polishing particle comprises an alumina particle. The method as claimed in claim 12, wherein said polishing particle comprises a cerium oxide particle. The method as claimed in claim 12, wherein said aggregation agent comprises an electrolytic salt. The method as claimed in claim 20, wherein said electrolytic salt comprises ammonium nitrate. The method as claimed in claim 20, wherein said electrolytic salt comprises ammonium chloride. An apparatus for polishing a film (9), comprising : a polishing unit having a plate (5) being provided thereon with a polishing pad (6) on which the film is polished, a slurry supplying system (1) for storing and supplying a surface of the polishing pad (6) with a slurry (3) into which fine polishing particles (7) are dispersed ; and an aggregation agent solution supplying system (2) for storing and supplying a solution (4) including an aggregation agent on the surface of the polishing pad (6) so that the slurry is mixed with the solution to thereby cause an aggregation of the fine polishing particles to form aggregated particles (11) to be used for polishing. The apparatus as claimed in claim 23, wherein a pH value of said slurry is controlled to suppress any generation of aggregation of said fine polishing particles until the slurry is mixed with said solution on said polishing pad surface. The apparatus as claimed in claim 23, whereìn said slurry comprises a suspension liquid with a non-alkali metal compound and fine polishing particles. The apparatus as claimed in claim 25, wherein said non-alkali metal compound comprises ammonia. The apparatus as claimed in claim 25, wherein said non-alkali metal compound comprises amine. The apparatus as claimed in claim 23, wherein saiä polishing particle comprises a silica particle. The apparatus as claimed in claim 23, whórein said p olishing particle comprises an alumina particle. The apparatus as claimed in claim 23, wherein said polishing particle comprises a cerium oxide particle. The apparatus as claimed in claim 23, wherein said aggregation agent comprises an electrolytic salt. The apparatus as claimed in claim 31, wherein said electrolytic salt comprises ammonium nitrate. The apparatus as claimed in claim 31, wherein said electrolytic salt comprises ammonium chloride.

Inventors: HAYASHI YOSHIHIRO, HAYASHI, YOSHIHIRO
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1995
Main classification: B24B57
IPC codes: C09K3, H01L21, B24B37, B24B57