Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
2000-12-07
2001-12-11
Smith, Matthew (Department: 2825)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298190, C204S298120, C118S900000, C427S533000, C427S534000, C427S535000, C438S478000
Reexamination Certificate
active
06328865
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a thin film of a composite metal compound and an apparatus for carrying out the method. More particularly, the invention relates to a method for forming through sputtering a thin film of a composite metal compound on a substrate in a stable manner and at a high rate of deposition and to an apparatus for carrying out the method.
2. Description of the Related Art
Conventionally, when optical thin films for various groups of products are formed through use of only existing vapor deposition materials, satisfactory performances required of the products are very difficult to obtain. That is, designing optical thin films through use of mere substances existing in the natural world has proved difficult in terms of attaining optical spectral characteristics as required by a certain group of products.
For example, configuration of wide-band antireflection films requires materials having an intermediate refractive index (between 1.46 and 2.20), which materials rarely exist in the natural world.
Generally, in order to decrease the reflectance of, for example, glass, over the entire wavelength range of visible light, glass must be coated with a vapor deposition material having a refractive index of 1.46-2.20, called an intermediate refractive index. Materials having an intermediate refractive index are limited, and the refractive index cannot be selected as desired. Accordingly, the following techniques are known as alternative techniques for obtaining an intermediate refractive index in the above-mentioned range.
(1) A low-refraction material (e.g. SiO
2
(refractive index: 1.46)) and a high-refraction material (e.g. TiO
2
(refractive index: 2.35)) are concurrently evaporated from respective evaporation sources, and an intermediate refractive index (1.46-2.40) is obtained by virtue of their mixing ratio; (2) a low-refraction material and a high-refraction material are concurrently evaporated from a single evaporation source in the form of a mixture, and an intermediate refractive index is obtained by virtue of their mixing ratio; (3) an intermediate refractive index (1.46-2.40) is equivalently obtained through the combination of a low-refraction material and a high-refraction material (called the equivalent film technique); and (4) a composite target material is used in sputtering.
However, the above-mentioned techniques suffer from the following disadvantages.
In the above-mentioned technique (1), wherein a low-refraction material (e.g. SiO
2
(refractive index: 1.46)) and a high-refraction material (e.g. TiO
2
(refractive index: 2.35)) are concurrently evaporated from respective evaporation sources and an intermediate refractive index (1.46-2.40) is obtained by virtue of their mixing ratio, the stable deposition of a film through the simultaneous control of the rates of deposition from the two evaporation sources is difficult to achieve, and thus a desired refractive index is difficult to obtain with good reproducibility.
In the above-mentioned technique (2), wherein a low-refraction material and a high-refraction material are concurrently evaporated from a single evaporation source in the form of a mixture and an intermediate refractive index is obtained by virtue of their mixing ratio, when evaporation continues for a long period of time, the refractive index changes due to differences in melting point and vapor pressure between the low-refraction material and the high-refraction material. As a result, a desired refractive index is difficult to obtain stably.
In the above-mentioned technique (3), wherein an intermediate refractive index (1.46-2.40) is obtained through use of an equivalent film formed from combined use of low-refraction and high-refraction materials, a given refractive index requires the formation of a very thin layer; thus, the control of film thickness becomes difficult and complicated.
As mentioned above, the conventional techniques fail to concurrently implement a high, stable deposition rate, a wide range of refractive index variation, and a simple control system.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for forming a thin film of a composite metal compound capable of controlling the refractive index of a thin film as desired, forming an ultra-thin film while subjecting the ultra-thin film to oxidation, nitriding, fluorination, or a like reaction, and forming on a substrate a thin film of a metallic compound having stable optical characteristics, dynamic characteristics, and like characteristics without increasing the substrate temperature and at a high rate of deposition as well as to provide an apparatus for carrying out the same.
Another object of the present invention is to provide a method for forming a thin film of a composite metal compound capable of obtaining a wide range of refractive index variation through use of a simple control system and to provide an apparatus for carrying out the same.
The above objects are achieved by the method and apparatus according to the present invention. Herein, the expression “ultra-thin film” is used to distinguish between a final thin film and the plurality of ultra-thin films which are deposited to become the final thin film, and describes each of the ultra-thin films as being substantially thinner than the final thin film. The expression “activated species” refer to radicals, radicals in an excited state, atoms in an excited state, molecules in an excited state, and the like. A “radical” refers to an atom or molecule having at least one unpaired electron. An “excited state” denotes the state in which the energy level is higher as compared to the stable ground state having the lowest energy.
The embodiments of the present invention will next be described in detail.
First Embodiment
According to a first embodiments of the present invention, there is provided a method for forming a thin film of a composite metal compound in which first, independent targets formed of at least two different metals are sputtered so as to form on a substrate an ultra-thin film of a composite metal or an incompletely-reacted composite metal. For example, one of two targets is formed of Si, while the other target is formed of Ta.
Next, the thus-formed ultra-thin film (e.g. Si+Ta) on the substrate is irradiated with the electrically neutral, activated species of a reactive gas (e.g. activated species of oxygen gas) so as to convert the composite metal or the incompletely-reacted composite metal to a composite metal compound (e.g. a composite of SiO
2
and Ta
2
O
2
) through reaction of the ultra-thin film with the activated species of the reactive gas. The above-mentioned steps of forming an ultra-thin film and converting the ultra-thin film to a composite metal compound are sequentially repeated so as to form on a substrate a thin film of a composite metal compound having a desired thickness.
In a reactive film deposition step in which a composite metal compound is obtained from a composite metal or an incompletely-reacted composite metal, a reactive gas enriched in activated species is used for the following reason. For the chemical reaction in the film deposition step, chemically active, electrically neutral, activated species, such as radicals and excited species, are more decisively important than are charged particles, such as ions and electrons.
Activated species are generated through use of a plasma source for generating high-density plasma connected to a radio-frequency power source. Specifically, the plasma source is an inductively-coupled or capacitively-coupled plasma source or a helicon wave plasma source having an external or internal coil. As to the capacitively-coupled plasma source, it has an external or internal coil as the case may be. In order to obtain high-density plasma, a magnetic field of 20-300 gauss is generated in a plasma generation unit.
A voltage (usually a negative voltage) applied to each of the targets is inverted at 1-200 kHz intervals to a positive volta
Kikuchi Kazuo
Matsumoto Shigeharu
Ogura Shigetaro
Tang Qi
Yamasaki Masafumi
Lee Granvill
Lorusso & Loud
Shincron Co., Ltd.
Smith Matthew
LandOfFree
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