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  Method and apparatus for forming interconnectsUSPTO Application #: 20060086618Title: Method and apparatus for forming interconnects Abstract: An interconnects-forming method can form a film of interconnect material, having a sufficient adhesion, by electroplating uniformly on an entire surface of a substrate and thus can form highly-reliable embedded interconnects even when the design rule is strict, and which can remove an extra interconnect material at a lower pressure. The interconnects-forming method, including: forming a conductive film on a surface of a substrate having interconnect recesses formed in an insulating film, said conductive film being insoluble in an electrolytic plating solution for the formation of a film of an interconnect material; forming a film of the interconnect material by electroplating on a surface of the conductive film serving as a seed film while filling the interconnect recesses with the interconnect material; and removing an extra interconnect material of the film formed on the conductive film, thereby forming interconnects of the interconnect material embedded in the interconnect recesses. (end of abstract)
Agent: Wenderoth, Lind & Ponack, L.L.P. - Washington, DC, US Inventors: Akira Fukunaga, Manabu Tsujimura USPTO Applicaton #: 20060086618 - Class: 205122000 (USPTO) Related Patent Categories: Electrolysis: Processes, Compositions Used Therein, And Methods Of Preparing The Compositions, Electrolytic Coating (process, Composition And Method Of Preparing Composition), Coating Selected Area, Specified Product Produced The Patent Description & Claims data below is from USPTO Patent Application 20060086618. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a method and an apparatus for forming interconnects, and more particularly to a method and an apparatus for forming interconnects which are useful for embedding a conductive material (interconnect material), such as copper or silver, into interconnect recesses provided in a surface of a substrate, such as a semiconductor wafer, to thereby form embedded interconnects, and selectively covering surfaces of the embedded interconnects with a metal film (protective film) to provide a multi-level structure. [0003] 2. Description of the Related Art [0004] As an interconnect formation process for semiconductor devices, there is getting employed a process (so-called damascene process) in which metal (interconnect material) is embedded in interconnect recesses composed of trenches and contact holes. This process includes embedding aluminum or, recently, interconnect material (metal) such as copper or silver into interconnect recesses such as trenches or contact holes, which have previously been formed in an interlevel dielectric film, and then removing excessive metal by chemical mechanical polishing (CMP) for planarization. [0005] In the production of such interconnects, for example, copper interconnects using copper as an interconnect material, a barrier film containing tungsten, tantalum or titanium is formed on a surface of an interlevel dielectric film for the purpose of preventing diffusion of copper into the interlevel dielectric film, and then a seed film of copper, which serves as an electric supply layer during electroplating, is formed on a surface of the barrier film by PVD or ALD. Thereafter, a copper film is formed on the entire surface of the substrate (barrier film), for example, by copper sulfate electroplating, followed by removal of extra copper and barrier films formed in the substrate surface, for example by CMP, thereby forming interconnects composed of the interconnect material embedded in interconnect recesses. [0006] As is widely practiced, the surfaces of the thus-formed interconnects are selectively covered with a film of a cobalt alloy or a nickel alloy formed by electroless plating or with a film of a vanadium compound formed by CVD to provide a multi-level interconnect structure. SUMMARY OF THE INVENTION [0007] As the design rule becomes stricter, a thinner seed film is required to be formed on a surface of a barrier film. As the thickness of a seed film becomes smaller, however, it is becoming increasingly difficult to form such a thin seed film with a uniform thickness. Should a uniform seed film be formed, the seed film can be dissolved in an acidic plating solution on its immersion in the plating solution, leading to difficulty in stably forming a plated film. Therefore, in the interconnects-forming technology of the 45 nm-node or later generation, the possibility of directly forming a copper film by electroplating without forming a seed film on a surface of a barrier film is envisaged. However, when forming a copper film by electroplating directly on a conventional barrier film which is generally formed of a tungsten, tantalum or titanium-based material, because of the too high electric resistance of the barrier film, a copper film can be formed uniformly over the entire substrate surface with difficulty. Further, an oxide film can be present on a surface of a barrier film. In such a case, a sufficient adhesion between the barrier film and copper (plated film) may not be obtained. [0008] On the other hand, the use of a low-k material for an interlevel dielectric film is contemplated in the 45 nm-node or later generation in order to improve the so-called RC delay. However, low-k materials are generally weak, and therefore it is difficult to use the conventional CMP technology as it is when employing a low-k material for an interlevel dielectric film. A CMP technique that enables a lower-pressure polishing is now in demand. [0009] The present invention has been made in view of the above situation in the related art. It is therefore an object of the present invention to provide a method and an apparatus for forming interconnects which can form a film of interconnect material, having a sufficient adhesion, by electroplating uniformly on an entire surface of a substrate and thus can form highly-reliable embedded interconnects even when the design rule is strict, and which can remove an extra interconnect material at a lower pressure. [0010] In order to achieve the above object, the present invention provides an interconnects-forming method, comprising: forming a conductive film on a surface of a substrate having interconnect recesses formed in an insulating film, said conductive film being insoluble in an electrolytic plating solution for the formation of a film of an interconnect material; forming a film of the interconnect material by electroplating on a surface of the conductive film serving as a seed film while filling the interconnect recesses with the interconnect material; and removing an extra interconnect material of the film formed on the conductive film, thereby forming interconnects of the interconnect material embedded in the interconnect recesses. [0011] By using a conductive film, which is insoluble in an electrolytic plating solution for the formation of a film of an interconnect material, as a seed film in electroplating and forming a film of the interconnect material directly on the conductive film, dissolution of the conductive film in the plating solution can be avoided even when the conductive film (seed film) is thin and the film of the interconnect material can be formed after a sufficient contact between the conductive film and the plating solution. This makes it possible to form an interconnect material (plated film), having a sufficient adhesion to the conductive film, by electroplating uniformly on an entire surface of a substrate (conductive film) and thus can form highly-reliable embedded interconnects with good reproducibility. [0012] Preferably, after the formation of the conductive film, the conductive film is subjected to pre-electroplating processing. [0013] As the size of a substrate becomes larger and the thickness of a conductive film becomes smaller, it becomes difficult to form a conductive film as a plating base uniformly on an entire surface of a substrate. Thus, electroplating is required to be carried out uniformly on an entire surface of a non-uniform base. It will, therefore, be necessary to carryout appropriate pre-plating processing to improve the uniformity of the plating base. Examples of the pre-plating may include water-washing, a surfactant processing, etc. to uniformize wetting, chemical processing, plasma processing, etc. to remove or chemically reduce a non-uniform oxide film, and a plating seed-forming processing to apply the same material as a plated film to the substrate surface with a thickness of not more than 10 nm e.g. by plating, PVD or CVD. [0014] Preferably, after the formation of the interconnects, the conductive film present outside the interconnect recesses is removed. [0015] Methods for removing the conductive film on an insulating film include polishing, etching with a chemical and plasma etching. An appropriate method can be selected in consideration of the properties of the conductive film, consistency with the previous or next processing, the morphology of the surface after the removal of the conductive film, etc. [0016] The present invention provides another interconnects-forming method, comprising: forming an adhesive film on a surface of a substrate having interconnect recesses formed in an insulating film; forming a conductive film on a surface of the adhesive film, said conductive film being insoluble in an electrolytic plating solution for the formation of a film of an interconnect material; forming a film of the interconnect material by electroplating on a surface of the conductive film serving as a seed film while filling the interconnect recesses with the interconnect material; and removing an extra interconnect material of the film formed on the conductive film, thereby forming interconnects of the interconnect material embedded in the interconnect recesses. [0017] By forming a conductive film on a surface of an adhesive film formed on a substrate (insulating film), it becomes possible to secure with the adhesive film a sufficient adhesion between the conductive film and the insulating film (interlevel dielectric film), thus preventing a loss of reliability due to insufficient adhesion between the conductive film and the insulating film. The adhesive film can be formed by any known method such as PVD, CVD or ALD. [0018] Preferably, after the formation of the interconnects, the conductive film and the adhesive film both present outside the interconnect recesses are removed. [0019] Methods for removing the conductive film and the adhesive film include polishing, etching with a chemical and plasma etching. As with the above-described removal of conductive film, an appropriate method can be selected in consideration of the properties of the films, consistency with the previous or next processing, the morphology of the surface after the removal of the films, etc. [0020] In a preferred embodiment of the present invention, the adhesive film contains tungsten, tantalum or titanium. [0021] In a preferred embodiment of the present invention, the conductive film contains palladium, rhodium or ruthenium. [0022] The conductive film is required to be thin film-formable, have a relatively high electric conductivity and hardly form an oxide film, a conductive one if formed, on the surface. A conductive film containing palladium, rhodium or ruthenium can meet these requirements. The conductive film can be formed by any known method such as PVD, CVD or ALD. Continue reading... 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