Abrading – Abrading process
Reexamination Certificate
2000-07-10
2004-06-29
Eley, Timothy V. (Department: 3724)
Abrading
Abrading process
C051S298000, C051S307000, C451S072000, C451S443000
Reexamination Certificate
active
06755720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a vitrified bond tool, and more particularly to such a vitrified bond tool including super abrasive grains and used as a dressing tool for dressing a polishing tool such as a polishing pad which is used for a chemical mechanical polishing of a semiconductor wafer.
2. Discussion of the Related Art
In a process of manufacturing a semiconductor, there is commonly practiced a chemical mechanical polishing (herein after referred to as “CMP”) operation. In recent years, since a larger number of sheets of wafers are laminated with a larger scale of integration of electronic circuit, CMP operation is widely practiced for flattening surfaces of the wafers. In CMP operation, a polishing pad and a semiconductor wafer are rotated relative to each other, with application of a polishing fluid including fine abrasive grains to the polishing pad, for polishing the semiconductor wafer. In CMP operation for a semiconductor wafer, a high degree of flatness in the polished surface of the wafer is required by polishing a considerably small amount of the surface of the wafer. For satisfying this requirement, the polishing pad has to be dressed very frequently. The polishing pad has been conventionally dressed by using an electro-deposited diamond tool, which includes a base metal made of stainless or other metallic material, and diamond abrasive grains bonded to the base metal with Ni metal (electro-deposition bond).
JP-A-10-71559 discloses a dresser for dressing a polishing pad used for polishing a semiconductor wafer. This dresser includes a base metal and a diamond thin film. The to base metal has, in its working surface, a multiplicity of protrusions formed by using a wire-EDM (electro-discharge machining) or a metallic mold. The diamond thin film is formed on the working surface of the base metal by a vapor phase synthetic method.
JP-A-10-193266 discloses a method of a vitrified bond tool, which was proposed by the present inventors. This method is characterized by including the step of positioning a screen having a predetermined printing pattern, on a support body; the step of applying a paste including abrasive grains and vitrified bond which are dispersed in the paste, onto the support body through the screen; and the step of sintering the applied paste.
However, the operation for dressing the polishing pad with the electro-deposited diamond tool, in which the diamond abrasive grains are bonded to the base metal by Ni metal as an electro-deposition bond, suffers from elution of Ni metal into the polishing fluid whereby the workpiece is contaminated by Ni metal, particularly, where the polishing fluid is a strong-acid fluid. Further, the electro-deposited diamond tool has a drawback that all of the abrasive grains are not bonded to the base metal with sufficiently large bonding strength, due to the random arrangement of the abrasive grains in the abrasive layer, so that some of the abrasive grains which are not firmly bonded to the base metal are removed from the base metal and accordingly stay on the polishing pad. The workpiece is scratched or damaged by the abrasive grains thus staying on the polishing pad.
The dresser disclosed in JP-A-10-71559, in which abrasive grains are not used, requires a process of forming the multiplicity of protrusions in its base metal and also a process of forming the diamond thin film by the vapor phase synthetic method, thereby resulting in a considerably increased manufacturing cost. Dressers disclosed in JP-A-10-44023 and JP-A-10-138120 are costly to manufacture, too.
In the method disclosed in JP-A-10-193266, in which the paste including the abrasive grains and the vitrified bond therein is applied onto the support body through the screen, the abrasive grains are unlikely to be sufficiently dispersed in the paste, due to possible sedimentation of the abrasive grains, where each of the abrasive grains has a diameter larger than 40 &mgr;m. Thus, the paste applied onto the support body could be fixed to the support body in the sintering step, with agglomeration of the abrasive grains.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a vitrified bond tool having a construction which minimizes removal of the abrasive grains from the support body and accordingly prevents contamination or damage of a polishing tool and a workpiece to be polished by the polishing tool, and which is inexpensive to manufacture.
A second object of the invention is to provide a method suitable for manufacturing such a vitrified bond tool.
The first object indicated above may be achieved according to a first aspect of this invention, which provides a vitrified bond tool comprising: (a) a support body; (b) a vitrified bond layer which is formed on a working surface of the support body; and (c) a plurality of abrasive grains which are held by the vitrified bond layer so as to be fixed relative to the working surface of the support body and which are spaced apart from each other with spacing between adjacent ones of the abrasive grains.
In the vitrified bond tool according to the first aspect of the invention, the abrasive grains bonded to the vitrified bond tool are positioned relative to each other so as to be spaced apart from each other, so that each of the abrasive grains is bonded at an increased area of a surface thereof to the vitrified bond layer. Thus, all of the abrasive grains are bonded to the vitrified bond layer with sufficiently large bonding strength, thereby preventing removal of the abrasive grains from the vitrified bond layer or the support body, when this vitrified bond tool is used as a polishing or grinding tool for polishing or grinding a workpiece, or as a dressing tool for dressing a polishing or grinding tool. The workpiece polished or ground by this vitrified bond tool, or the polishing or grinding tool dressed by this vitrified bond tool and a workpiece polished or ground by the polishing or grinding tool is advantageously prevented from being contaminated and damaged by removal of the abrasive grains. The vitrified bond tool maintains its cutting sharpness throughout successive polishing or grinding operations, and accordingly exhibits an excellent polishing or grinding performance with high stability. In view of these advantages, the vitrified bond tool of this invention is suitable for dressing a polishing pad which is required to assure a high degree of flatness in a surface of a semiconductor wafer by polishing a considerably small amount of the surface of the wafer.
The vitrified bond tool provides other advantages. For example, the support body constituting a part of the vitrified bond tool may consist of a conventional support body. That is, a conventional support body can be used as the support body of the present vitrified bond tool, without necessity of a particular machining to the conventional support body.
In the present vitrified bond tool, agglomeration of the abrasive grains is prevented, so that each of the abrasive grains sufficiently exhibits its own polishing or grinding capacity. This makes it possible to reduce the amount or number of the abrasive grains to be used for each vitrified bond tool of the invention, thereby leading to a reduced manufacturing cost.
In the present vitrified bond tool in which each of the abrasive grains is bonded at an increased area of its surface to the vitrified bond layer, all of the abrasive grains are bonded to the vitrified bond layer with sufficiently large bonding strength, even with a reduced thickness of the vitrified bond layer. The reduced thickness of the vitrified bond layer facilitates protrusions of the abrasive grains from the vitrified bond layer after a firing step, i.e., after the manufacture of the tool, so that the vitrified bond tool does not have to be subjected to a truing operation, prior to an initial use thereof. That is, the vitrified bond tool exhibits an expected polishing or grinding performance even in the initial use without the truing
Fujii Tsuyoshi
Ishizaki Junji
Ito Kenji
Watanabe Kimihiro
Eley Timothy V.
Noritake Co., Limited
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