Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
1998-03-26
2001-02-27
Rose, Robert A. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C451S055000
Reexamination Certificate
active
06193585
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 will 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 materials cited here 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 for the material of the substrate of SAW devices. SAWs have applications for filters, phase shifters or convolvers. Diamond and c-BN which are intrinsically insulators can be converted to semiconductor 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 now named a complex wafer. The wafer has a hard film which is made of one of diamond, diamond-like carbon and c-BN (cubic boron nitride) and a substrate base wafer. The base wafers are softer material than the hard film. For example, Si or Mo is adopted as the base substrate. In particular, this invention aims at the method and the apparatus of polishing diamond-coated wafers which have been synthesized by the vapor phase CVD methods.
BACKGROUND OF THE INVENTION
This application claims the priorities Japanese Patent Application No.165914/1994 filed Jun. 24, 1994 and No.133773/1994 filed May 23. These materials are favored with excellent physical and chemical properties. However, these materials have not been utilized in various fields for practical uses, since wide and inexpensive plates or wafers of the materials can not be fabricated so far. Since the hard materials are provided with a lot of physical and chemical advantages, actual applications of the hard materials to various objects are earnestly desired by transplanting the technology of silicon semiconductor devices to the hard materials. What should be prepared in the first place is wide plates (or wafers) of the hard materials.
Technologies have already ripened into the 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 film 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 piling the synthesized material as a film on the substrate.
There are some methods for exciting the material gas, that is, a hot filament CVD method, a microwave plasma CVD method, a radio wave plasma CVD method or a DC plasma jet CVD method. Some method is capable of making a wide film of hard materials on a substrate. However, the speed of the synthesis is so slow that the method cannot easily make a thick film at present. A long time of deposition relying on some method can make a considerably thick film on the substrate.
Nevertheless, there are still no pure wafer consisting only of a hard material free from a substrate. At present, there is not a diamond wafer or a c-BN wafer in a true meaning, 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 the electronics technology requires wide area wafers of the hard materials. Someone once produced surface acoustic wave devices on very small diamond substrates.
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 the standpoint of industry, even if the device itself exhibited an excellent performance. Since a small substrate allowed to make only small number of devices on it, the productivity was poor. The devices made on the small substrate had little practical significance owing to the poor productivity.
What brought about the success to silicon semiconductor devices is the probability of treating with a wide area Si wafer by the same wafer processes at the same time and making a plenty of equivalent devices in short time. The same matter will perhaps hold for the hard materials. If diamond, c-BN or diamond-like carbon wants to obtain a practical importance as the substrates, the material should be formed into wide, round thin plates (wafers). The advent of the wide wafers will enable manufactures to apply the technology which has been grown by the silicon semiconductor 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 can also 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). It is totally impossible to make wide, homogeneous diamond wafers or c-BN wafers even at present.
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 bulk single crystal, this invention starts from a substrate of other materials for making complex wafers consisting of 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 of a substrate plus a hard material film gives manufactures 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 result of the reaction is piled. The film on the base wafer is the principal part which will contribute to the production of semiconductor devices or SAWs.
If a homogeneous wafer consisting only of pure diamond or c-BN may be made by forming a very thick film on the substrate and eliminating the substrate by etching. However, it is still unpractical, because it takes very long time and very much material to deposit so a thick layer. A big 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 submits itself to the complex, inhomogeneous wafer having the base wafer as a non-hard material wafer. The remainder base wafer does not cause a problem, since almost all the devices make use only of the nature of the surface of the wafer. This invention employs a inhomogeneous, 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 overcome the difficulty of making a wide bulk single crystal of the hard materials, because complex wafers can be made by the thin film-formation technology. The term “hard material wafer” in the present invention is quite different from the ordinary wafers produced by slicing an ingot of bulk sin
Fujimori Naoji
Ikegaya Akihoko
Seki Yuichiro
Tanabe Keiichiro
Pillsbury Madison & Sutro
Rose Robert A.
Sumitomo Electric Industries Ltd.
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