Semiconductor device manufacturing: process – Chemical etching
Reexamination Certificate
2000-03-30
2001-12-11
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Chemical etching
C438S001000, C438S687000, C438S800000
Reexamination Certificate
active
06329289
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a method and apparatus for forming copper wiring, and more particularly to a method and apparatus for forming copper wiring on a substrate such as a semiconductor wafer.
2. Description of the Related Art
Conventionally, in order to form a wiring circuit on a semiconductor substrate, a conductive film is deposited over a surface of a substrate by a sputtering process or the like, and then unnecessary portions are removed from the conductive film by a chemical dry etching process using a photoresist for a mask pattern.
Generally, aluminum or aluminum alloy has been used as a material for forming a wiring circuit. However, the higher integration of integrated circuits on the semiconductor substrate in recent years requires narrower wiring to thus increase the current density, resulting in generation of thermal stress in the wiring and increase in the temperature of the wiring. This unfavorable condition becomes more significant, as wiring material such as aluminum is thinner due to stress-migration or electromigration, to finally cause a breaking of the wire or a short circuit.
Hence, in order to prevent the wiring from generating excess heat while current flows, a material such as copper having a higher electrical conductivity is required to be used for a wiring circuit. However, since copper or copper alloy is not suited for the dry etching process, it is difficult to adopt the above-mentioned method in which the wiring pattern is formed after depositing the conductive film over the whole surface of the substrate. Therefore, one possible process is to form grooves for a wiring circuit having a predetermined pattern, and then fill the grooves with copper or copper alloy. This process eliminates the etching process of removing unnecessary portions of the film, and needs only a polishing process of removing unevenness or irregularities of the surface. Further, this process offers advantages that portions called wiring holes connecting between an upper layer and a lower layer in a multilayer circuit can be formed at the same time.
However, as the width of wiring becomes narrower, such wiring grooves or wiring holes have a considerably higher aspect ratio (the ratio of depth to diameter or width), and hence it is difficult to fill the grooves or the holes with metal uniformly by the sputtering process. Further, although a chemical vapor deposition (CVD) process is used to deposit various materials, it is difficult to prepare an appropriate gas material for copper or copper alloy, and if an organic material is used for depositing copper or copper alloy, carbon (C) is mixed into a deposited film to increase migration of the film.
Therefore, there has been proposed a method in which a substrate is dipped in a plating solution to plate the substrate with copper by an electrolytic plating or an electroless plating, and then the unnecessary portion of a copper layer is removed from the substrate by a chemical mechanical polishing (CMP) process. This formation of the film or layer by the plating allows wiring grooves having a high aspect ratio to be uniformly filled with a metal having a high electrical conductivity. In the CMP process, a semiconductor wafer held by the top ring is pressed against a polishing cloth attached to a turntable, while supplying a polishing liquid containing abrasive particles and thus the copper layer on the semiconductor substrate is polished.
However, in the CMP process described above, the pattern density dependence on the properties of the polishing cloth and the polishing liquid is large, and copper wiring portions are excessively polished in the form of a plate or a dish. This excessively polished phenomenon is called “dishing”.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above drawbacks in the CMP process. It is therefore an object of the present invention to provide a method and apparatus for forming copper wiring which can uniformly remove a copper layer formed on a substrate such as a semiconductor wafer, and form copper wiring having a flat and uniform surface in narrow grooves and/or minute holes in the substrate without forming dishing.
According to a first aspect of the present invention, there is provided a method for forming copper wiring on a semiconductor substrate, comprising: filling wiring grooves formed in a semiconductor substrate with copper and forming a copper layer on the semiconductor substrate; bringing the semiconductor substrate into contact with a culture solution containing bacteria whose size is larger than the width of the wiring grooves; and removing the copper layer on the semiconductor substrate by the bacteria while leaving the copper in the wiring grooves.
In a preferred embodiment, the semiconductor substrate is cleaned to remove the bacteria after removing the copper layer on the semiconductor substrate.
In a preferred embodiment, the bacteria comprises autotroph.
According to a second aspect of the present invention, there is provided an apparatus for forming copper wiring on a semiconductor substrate, comprising: a device for filling wiring grooves formed in a semiconductor substrate with copper and forming a copper layer on the semiconductor substrate; and a container for holding a culture solution containing bacteria therein; wherein the semiconductor substrate is brought into contact with the culture solution containing bacteria whose size is larger than the width of the wiring grooves, and the copper layer on the semiconductor substrate is removed by the bacteria while leaving the copper in the wiring grooves.
Organisms can be broadly classified into heterotroph and autotroph according to the way to obtain the carbon source. An organism which obtains the carbon source from other organic materials is referred to as a heterotroph, and an organism which obtains the carbon source by fixing carbon dioxide contained in the air is referred to as an autotroph. The autotroph includes the chemoautotroph which obtains the energy by oxidizing inorganic materials. Further, the chemoautotroph includes a bacterium, “thiobacillus ferrooxidans”. This bacterium lives by fixing carbon dioxide in the air using the energy which is generated by oxidization of iron, sulfur, or copper. The bacteria react with copper to remove copper at a rate of about 3000 Å per minute by imparting a certain vibration to a culture solution in which pure copper and the bacteria are placed. The size of this bacterium is about 0.5 &mgr;m in diameter and about 1 &mgr;m in length, and the shape of the bacterium is approximately cylindrical.
The present invention utilizes the size of bacterium and the size (width) of the wiring groove.
The width of wiring on the semiconductor substrate has been becoming narrower from 0.3 &mgr;m to 0.25 &mgr;m, 0.2 &mgr;m, and 0.17 &mgr;m in recent years. If bacteria whose size is larger than the width of such narrow wiring are adopted, a copper layer on the copper wiring can be removed, but a copper layer in the wiring groove cannot be removed because the bacteria cannot enter the copper wiring. Therefore, the copper wiring whose width is smaller than the size of the bacteria is not removed, and the copper wiring remains in a substantially flat surface.
REFERENCES:
patent: 4571387 (1986-02-01), Bruynesteyn
patent: 4822413 (1989-04-01), Pooley et al.
patent: 5030425 (1991-07-01), Bowers-Irons et al.
patent: 5462720 (1995-10-01), Aragones
patent: 406316800-A (1994-11-01), None
patent: 409302423-A (1997-11-01), None
Yoshiyuki UNO et al., “Micromachining of Metals Using Microorganism”, Materia Japan, vol. 37, No. 1, pp. 52-54, The Japan Institute of Metals, Jan. 20, 1998 (with partial English translation).
Ebara Corporation
Elms Richard
Pyonin Adam
Wenderoth , Lind & Ponack, L.L.P.
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