Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
1998-08-21
2001-04-17
Ahmad, Nasser (Department: 1772)
Stock material or miscellaneous articles
Circular sheet or circular blank
C501S090000, C204S192150, C204S192230, C204S192260, C264S068000, C428S446000, C428S698000
Reexamination Certificate
active
06217969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a sputtering target disk which is made of silicon carbide and which is advantageously used for a sputtering treatment for forming thin films, which are useful as protective films and functional films in various parts of electronic devices, and thin films, which are useful for a surface treatment of various jigs and tools to improve durability.
2. Description of the Related Art
Recently, several types of thin films formed on substrate materials have been utilized in various fields, such as the electro-mechanical industry. These films exhibit various functions, such as magnetism, insulation, and dielectric property, and have various mechanical properties, such as high strength and high hardness, and various chemical properties, such as corrosion resistance.
The processes for forming such thin films are mainly classified into the following two processes: (i) the process of chemical vapor phase deposition (CVD process) in which gases of various materials are introduced into a nonoxidizing atmosphere, and a film is formed by deposition which accompanies the reaction; and (ii) the process of physical vapor phase deposition (sputtering process, or PVD process) in which a material for a film is used as a target, and ions are made to collide against a film of the material on a substrate disposed at a position opposing the target. There are two types of sputtering processes, a direct current sputtering process and a high frequency sputtering process. The sputtering process is much more advantageous than the CVD process because the sputtering process is superior from the standpoint of production cost and mass production and is less dependent on the substrate material.
The material of silicon carbide used herein exhibits the best heat resistance, heat conductivity, surface hardness, and corrosion resistance among various ceramic materials. Products having a thin film of this material formed on a substrate have been used very advantageously in parts of various electronic devices, in various jigs and tools for assembly of parts, and in molds. Particularly in parts of electronic devices, the above material is used for protective films of peripheral instruments of computers, such as heads and disk plates of hard disks and optical magnetic disks, by taking advantage of the high hardness and the excellent sliding property of the material. The material is also used for separation membranes in functional devices by taking advantage of its high heat conductivity.
It is most preferable that the silicon carbide thin film is formed in accordance with the sputtering process as described above, but a high performance sputtering target disk made of silicon carbide is required for the process.
The conventional target disk used for forming a thin film is a sintered material prepared by adding alumina or boron as the auxiliary sintering agent or is a porous sintered material prepared without adding an auxiliary sintering agent because a high density sintered material can be obtained from powder of silicon carbide. However, when an auxiliary sintering agent containing a metal, such as alumina, is added, there occurs the problem that the auxiliary sintering agent becomes impurities in the sintered material, and thus the product is not suitable for application in the electronic field. The porous sintered material has problems in that ion sputter tends to become uneven during the sputtering, and this causes uneven wear of the porous sintered material which in turn decreases its life, and in that free particles are formed by cleavage of particles forming the target, and in that cracks tend to be formed in the target when the target is attached to a packing plate because of low mechanical strengths and low impact resistance under heating, such that the target may break during attachment thereof to an apparatus.
Under the above circumstances, there is the need to provide a target disk of silicon carbide having a higher density and a smaller content of impurities. To satisfy this need, processes for obtaining a high density sintered material without using conventional metallic auxiliary sintering agents have been proposed. Examples of such processes include 1) a process in which fine powder is formed in accordance with the process of vapor phase growth (the CVD process), and a sintered material is prepared from the formed powder without using an auxiliary sintering agent, and 2) a process in which a product having a plate shape is directly prepared by the process of vapor phase growth (the CVD process). In these processes, gases or solutions containing silicon and carbon are used as the raw materials.
However, these processes also have a drawback in that productivity is very poor, and the cost of production is high. Moreover, process 1) has a drawback in that the powder is too fine, and particles tend to be formed even when the product after sintering is used in parts of electronic devices. Process 2) has a drawback in that it is difficult to prepare a molded product having a large thickness, and it is difficult to obtain an electric conductivity suitable for the direct current sputtering.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a sputtering target disk comprised of silicon carbide which is advantageously used for a sputtering treatment to form thin films having a high purity useful as protective films and functional films in various parts of electronic devices, and thin films suitable for use in the surface treatment of various jigs and tools to improve durability. The disk according to the present invention exhibits excellent mechanical properties, electric properties, and durability against uneven wear.
The present inventors found that when a sintered silicon carbide obtained in accordance with a specific process is used for the sputtering target disk, the disk can exhibit the very excellent properties.
Accordingly, the sputtering target disk of the present invention is comprised of a sintered silicon carbide which has a density of 2.9 g/cm
3
or more and which is obtained by sintering a uniform mixture of a powdered silicon carbide and a nonmetallic auxiliary sintering agent.
The nonmetallic auxiliary sintering agent is preferably an organic compound which generates carbon in the presence of heat. The nonmetallic auxiliary sintering agent may be present in such a condition that the agent covers the surface of the powdered silicon carbide during sintering.
The sintered silicon carbide may be obtained by hot pressing the above mixture in a nonoxidizing atmosphere.
The total amount of impurity elements contained in the sintered silicon carbide is preferably 1 ppm or less.
The powder of silicon carbide is obtained in accordance with a process comprising a solidifying step which comprises solidifying a mixture obtained by mixing a silicon source containing at least one liquid silicon compound, at least one liquid organic compound which generates carbon in the presence of heat, and a polymerization or crosslinking catalyst to obtain a solid material; and a sintering step which comprises carbonizing the resulting solid material in a nonoxidizing atmosphere by heating, followed by sintering the carbonized material in a nonoxidizing atmosphere. In accordance with this process, a high purity sintered material having a total content of impurities of 1 ppm or less can be obtained.
In accordance with the present invention, the sintered material has a high purity, contains little foreign substance at the crystal boundaries, and shows excellent heat conductivity, since metallic auxiliary sintering agents such as boron, aluminum, beryllium or compounds of these metals, or carbon auxiliary sintering agents such as carbon black and graphite are not used as the auxiliary sintering agent, and a nonmetallic auxiliary sintering agent alone is used. The sintered material of the present invention exhibits more excellent characteristics of silicon carbide such as resistance to contamination and wear resistance. A s
Satou Akira
Takahashi Yoshitomo
Wada Hiroaki
Ahmad Nasser
Bridgestone Corporation
Oliff & Berridg,e PLC
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