Abrading – Machine – Combined
Reexamination Certificate
2000-05-16
2002-08-06
Mills, Gregory (Department: 1763)
Abrading
Machine
Combined
C451S064000, C451S065000
Reexamination Certificate
active
06428399
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a hard-material coated wafer, a method of coating a substrate with hard material, a polishing apparatus and a polishing method. The hard-material wafer can be utilized for SAWs (surface acoustic wave devices), thermistors, substrates for semiconductor devices, protecting films of discs, and X-ray windows. Here “hard materials” generally indicate diamond, c-BN, or diamond-like carbon. All the hard materials cited herein have a Vickers hardness of more than Hv3000 in the state of bulk materials. The hard materials are endowed with high sound velocity which is determined by the ratio of Young modulus divided by density. Therefore, the velocity of the surface acoustic wave is extremely high. In particular, such hard material-coated wafers now attract attention as a material for the substrates of SAW devices. Suitable applications of SAWs include filters, phase shifters or convolvers. Diamond and c-BN which are intrinsically insulators can be converted to semiconductors by doping them with some impurity.
This invention further relates to a polishing method and a polishing apparatus for polishing surfaces of hard-material coated wafers which can be utilized in the technical fields of electronics, optics or optoelectronics. The hard-material coated wafer is referred to herein as a complex wafer. The wafer has a hard film which is made of a material selected from the group of diamond, diamond-like carbon and c-BN (cubic boron nitride), and a substrate base wafer. The base wafers are made of a softer material than the hard film. For example, Si or Mo is adopted as the base substrate. In particular, this invention is directed to a method and apparatus of polishing diamond-coated wafers which have been synthesized by the vapor phase CVD methods.
BACKGROUND OF THE INVENTION
This application claims the priority of Japanese Patent Application No. 165914/1994 filed Jun. 24, 1994 and No. 133773/1994 filed May 23. The above-mentioned hard materials are favored with excellent physical and chemical properties. However, these materials have not been utilized in various fields for practical uses, since fabrication of wide and inexpensive plates or wafers of the materials has not been accomplished to date. Since the hard materials are provided with several physical and chemical advantages, actual applications of the hard materials to various objects are earnestly desired and have been attempted by applying the technology of silicon semiconductor devices to the hard materials. The object has been produce wide plates (or wafers) of the hard materials.
Technologies have already ripened into a definite level capable of producing films of diamond, c-BN (cubic boron nitride) or diamond-like carbon by vapor phase deposition methods. The vapor phase deposition method makes a hard-material of the material by supplying a material gas to a pertinent substrate heated at a suitable temperature, letting the gas react with the hot substrate and depositing a film of the hard material on the substrate in vapor phase. A film of diamond or c-BN is produced by introducing a material gas including hydrogen gas and hydrocarbon gas, or another material gas including hydrogen gas, boron-containing gas and nitrogen-containing gas in the reaction chamber, supplying the material gas on the heated substrate, synthesizing diamond or c-BN by chemical reaction and depositing the synthesized material as a film on the substrate.
There are some methods for exciting the material gas, including, for example, a hot filament CVD method, a microwave plasma CVD method, a radio wave plasma CVD method or a DC plasma jet CVD method. Some methods are capable of making a wide film of hard materials on a substrate. However, the speed of synthesis is so slow that the methods cannot easily make a thick film at present. In accordance with these methods, a long for deposition is needed to make a considerably thick film on the substrate.
Nevertheless, there are still no pure wafers consisting only of a hard material free from a substrate. In other words, at present, there are no diamond wafers or c-BN wafers in their true meanings, because prior technology has not been able to produce a pure diamond wafer or a pure c-BN wafer.
The application of the hard materials, i.e., diamond, c-BN or diamond-like carbon to electronics technology requires wide area wafers of the hard materials. While surface acoustic wave devices on very small diamond substrates have been produced, larger substrates have not.
However the fact that a new device was fabricated on a quite small diamond substrate, e.g., from 5 mm square to 10 mm square, was rather insignificant from an industrial standpoint, even if the device itself exhibited an excellent performance. Since the small substrate allowed only a small number of devices to be made on it, the productivity was poor. The devices made on the small substrate had little practical significance due to the poor productivity.
What brought about the success of silicon semiconductor devices is the ability to treat a wide area Si wafer by the same wafer processes at the same time and make several equivalent devices in a short time. It has been believed that the same would perhaps hold for the hard materials. If diamond, c-BN or diamond-like carbon is to obtain a practical importance as substrates, the material should be formed into wide, round thin plates (wafers). The advent of the wide wafers will enable manufacturers to apply the technology which has been developed by the silicon semiconductor industry to the hard materials.
In the case of silicon, big single crystals with a wide section can easily be grown by Czochralski methods, and mainly 8-inch wafers are produced for making devices at present. 12-inch wafers also can be produced now for silicon.
However, a diamond or c-BN single crystal cannot be grown by the conventional methods, e.g., Czochralski methods, at present. Thus, it is still not promising to produce homogeneous wafers consisting only of a single material of the hard materials, unlike silicon (Si) or gallium arsenide (GaAs). In fact, it is impossible to make wide, homogeneous diamond wafers or c-BN wafers by conventional methods.
This invention gives up the attempt of making a homogeneous wide wafer consisting only of a single material of diamond, c-BN or diamond-like carbon. Instead of starting from the premise of making a homogeneous bulk single crystal, this invention employs a substrate of a different material than the film for making complex wafers containing a non-hard material substrate and hard material films formed on the substrate. The present invention intends to make a hard material film on a commonplace material, e.g., Si, GaAs or so, which can easily be produced or obtained. The complex wafter having a substrate plus a hard material film provides the possibility of making a wide hard material wafer by employing a wide base wafer as a substrate. The base wafer of non-hard material plays the role of the base mount on which the hard material film is deposited. The film on the base wafer is the principal portion of the wafer which will contribute to the production of semiconductor devices or SAWs.
A homogeneous wafer consisting only of pure diamond or c-BN, made by forming a very thick film on the substrate and eliminating the substrate by etching, is still unpractical, because it takes very long time and very much material to deposit such a thick layer. Further, a large inner stress would break the film when the substrate is etched away. Therefore, the production of a freestanding film remains an unpractical object.
This invention is directed to the complex, non-homogeneous wafer having a non-hard material wafer as the substrate of the wafer. The substrate of the wafer does not cause a problem in application, since almost all the devices make use only of the surface of the wafer. This invention employs a non-homogeneous, complex wafer having a Si or GaAs surface on the bottom and a diamond or c-BN surface on the top. The adoption of the complex wafer can
Fujimori Naoji
Ikegaya Akihoko
Seki Yuichiro
Tanabe Keiichiro
McDermott & Will & Emery
Mills Gregory
Sumitomo Electric Industries Ltd.
Zervigon Rudy
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