METHOD FOR MANUFACTURING METAL LAMINATED SUBSTRATE FOR SEMICONDUCTOR ELEMENT FORMATION AND METAL LAMINATED SUBSTRATE FOR SEMICONDUCTOR ELEMENT FORMATION
Disclosed is a metal laminated substrate for forming an epitaxial growth film for forming a semiconductor element having high biaxial crystal orientation on a surface of a metal substrate and a method of manufacturing the metal laminated substrate. The manufacturing method includes the steps of activating at least one surface of a metal plate T1 by sputter etching or the like; activating at least one surface of a metal foil T2 made of Cu or a Cu alloy which is cold-rolled at a rolling reduction of 90% or more; laminating the metal plate and the metal foil such that an activated surface of the metal plate and an activated surface of the metal foil face each other in an opposed manner and applying cold rolling to the metal plate and the metal foil which are laminated to each other at a rolling reduction of 10% or less, for example; and biaxially orienting crystals of the metal foil by heat treatment at a temperature of not lower than 150° C. and not higher than 1000° C.
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The present invention relates to a method of manufacturing a metal laminated substrate for forming an epitaxial growth film for forming a semiconductor element, and a metal laminated substrate for forming an epitaxial growth film for forming a semiconductor element.
BACKGROUND ARTTo obtain an excellent semiconductor element, it is necessary to form an epitaxial growth film having high orientation on a substrate.
For this end, conventionally, as a substrate for an epitaxial growth film, a monocrystalline wafer made of monocrystalline silicon (Si), monocrystalline GaAs, monocrystalline sapphire (Al2O3) or the like having an excellent crystal orientation has been used.
However, the monocrystalline wafer made of these materials is a cut plate having a size of approximately 300 mmφ at most, and such a monocrystalline wafer cannot be formed by a continuous manufacturing method such as a reel-to-reel method. Further, also the strength of Si or the like is small and hence, the handling of the monocrystalline wafer made of Si or the like during the conveyance of the wafer is not easy whereby the careful handling of the wafer is necessary.
Besides the above-mentioned monocrystalline wafer, as a substrate for forming an epitaxial growth film thereon, there has been known a metal substrate having the high biaxial crystal orientation which is formed such that cold rolling is applied to Ni, Cu, Ag or an alloy of these materials at a rolling reduction of not less than 90% thus imparting a uniform strain to the whole material and, thereafter, the material is recrystallized.
Although a substrate made of Ni or an Ni—W alloy whose crystals are oriented is used as a substrate for an oxide superconductor, the substrate is provided in the form of a crystal-oriented metal tape having a narrow width of 4 to 10 mm, and there has been no substrate which is provided as a wide and long substrate with high crystal orientation.
Further, the above-mentioned Ni—W alloy has drawbacks that the Ni—W alloy is not a material which is used popularly in general so that a cost of the Ni—W alloy is high, the Ni—W alloy exhibits poor workability so that the manufacture of the substrate having a large width becomes difficult.
Further, as disclosed in patent documents 1, 2 and 3, as a material for forming a metal substrate which can overcome drawbacks in securing strength, there has been proposed a clad material which is formed by laminating a metal core layer and an Ni alloy layer by cold drawing or by a cold rolling method (patent documents 1, 2, 3).
- Patent document 1: JP-A-2006-286212
- Patent document 2: JP-A-2007-200831
- Patent document 3: JP-A-2001-110255
However, to laminate different kinds of metals with favorable adhesion by a cold rolling method, it is necessary to bond different kinds of metals to each other by diffusion bonding (diffusion heat treatment) as the pretreatment and, thereafter, to apply cold rolling to the bonded metals. Although it has been known that working efficiency of 90% or more is necessary to impart the high crystal orientation to an Ni layer after diffusion heat treatment, when strong rolling is applied to the different kinds of metals in a bonded state, due to the difference in mechanical properties between both materials, the difference in elongation occurs between the materials and hence, a large warp occurs. Accordingly, it is difficult to manufacture a wide and long material.
Further, in the above-mentioned clad material, materials to be bonded constrain each other on a bonding interface so that rolling is performed while causing the non-uniform deformation of the clad material whereby the uniform strain cannot be induced in the thickness direction.
Further, the degree of roughness of the bonding interface is also increased so that the thickness of the Ni layer in which crystals are oriented also becomes non-uniform. Accordingly, in the heat treatment after bonding, the stable manufacture of the substrate having the uniform and high crystal orientation in the longitudinal direction becomes difficult.
DISCLOSURE OF THE INVENTION Problems that the Invention is to SolveIt is an object of the present invention to provide a method of manufacturing a metal laminated substrate for forming an epitaxial growth film for forming a semiconductor element having high biaxial crystal orientation on a surface of a metal substrate.
Further, it is another object of the present invention to provide a metal laminated substrate provided with a biaxial crystal orientation metal foil for forming an epitaxial growth film made of a semiconductor compound.
Means for Solving the Problems(1) A method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention includes the steps of: activating at least one surface of a metal plate; activating at least one surface of a metal foil made of Cu or a Cu alloy which is cold-rolled at a rolling reduction of 90% or more; laminating the metal plate and the metal foil such that an activated surface of the metal plate and an activated surface of the metal foil face each other in an opposed manner and applying cold rolling to the metal plate and the metal foil which are laminated to each other; and biaxially orienting crystals of the metal foil by heat treatment.
(2) The method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention is, in the above-mentioned (1), characterized in that the activation treatment is performed by sputter etching.
(3) The method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention is, in the above-mentioned (1) or (2), characterized in that the cold rolling is performed at a rolling reduction of not more than 10% at the time of lamination.
(4) The method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention is, in any one of the above-mentioned (1) to (3), characterized in that the metal foil made of Cu or the Cu alloy has a thickness of not less than 7 μm and not more than 50 μm.
(5) The method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention is, in any one of the above-mentioned (1) to (4), characterized in that the metal foil made of the Cu alloy contains not less than 0.01% and not more than 1% of Ag, Sn, Zn, Zr, O and N in total.
(6) The method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention is, in any one of the above-mentioned (1) to (5), characterized in that the heat treatment after the lamination is performed at a temperature of not lower than 150° C. and not higher than 1000° C.
(7) The method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention is, in any one of the above-mentioned (1) to (6), characterized in that before the heat treatment, a polish treatment is applied to the metal plate such that the surface roughness of a metal-foil-side surface of the metal plate becomes not less than 1 nm and not more than 40 nm by Ra.
(8) The method of manufacturing a metal laminated substrate for forming a semiconductor element according to the present invention is, in any one of the above-mentioned (1) to (7), characterized in that a protective film having a thickness of not less than 1 nm and not more than 10 μm is further formed on the metal laminated substrate which is manufactured by the method of manufacturing a metal laminated substrate.
(9) A metal laminated substrate for forming a semiconductor element according to the present invention is manufactured by any one of the manufacturing method described in (1) to (8).
Advantageous Effects of the InventionAccording to the method of manufacturing a metal laminated substrate for forming a semiconductor element of the present invention, a metal plate and a Cu alloy foil rolled at a high rolling reduction for obtaining a metal crystal orientation surface which are manufactured with high thickness accuracy respectively in advance can be laminated to each other at a low rolling reduction with high accuracy and with a smooth interface.
The metal laminated substrate for forming semiconductor element which is manufactured by this manufacturing method can possess a high-accuracy biaxial crystal orientation on a surface of the substrate and hence, the semiconductor element can be formed on the substrate by an epitaxial growth with high accuracy.
BEST MODE FOR CARRYING OUT THE INVENTIONAs shown in
The metal plate T1 is selected depending on a purpose of use. When the metal plate T1 is a metal plate for a solar cell on which a polycrystalline silicon film is grown epitaxially, since it is necessary to impart proper strength to the metal plate T1, a thin plate made of Fe, Al, Ni, Cr, Ag, Cu, W, or an alloy of these materials (stainless steel, for example) is given as an example.
It is preferable to set a thickness of the metal plate T1 to not less than 0.05 mm and not more than 0.2 mm.
The reason the thickness of the metal plate T1 is set to not less than 0.05 mm is to secure strength of the metal plate T1, and the reason the thickness of the metal plate T1 is set to not more than 0.2 mm is to secure workability.
As the metal foil T2, a Cu foil or a Cu alloy foil (both the Cu foil and the Cu alloy foil also referred to as a Cu alloy foil in this specification) are given as examples. The metal foil T2 is required to possess the high crystal orientation in a state where a metal laminated substrate is formed.
Accordingly, heavy working is applied to the Cu alloy foil at a rolling reduction of not less than 90% before and after the Cu alloy foil is bonded to the metal plate T1 thus forming a rolled texture, and the crystal orientation is imparted to the Cu alloy foil by heat treatment which is performed after surface activation bonding.
This is because when the rolling reduction is less than 90%, there exists a possibility that Cu is not oriented in the heat treatment which is performed after working.
Such a high-reduction rolled Cu alloy foil having the rolled texture formed by heavy working at a rolling reduction of not less than 90% has been developed for imparting high bending property to the foil aiming at the use in a flexible printed circuit board, has become widespread, and can be easily obtained. For example, a high-reduction rolled Cu foil (product name: HA foil) made by Nikko Materials Ltd, a high-reduction rolled Cu foil (product name: HX foil) made by Hitachi Electric Wires., Ltd and the like are given as examples.
In the present invention, it is desirable to use the above-mentioned commercially available high-reduction rolled Cu alloy foils since these foils exhibit the excellent crystal orientation.
It is desirable to use the metal foil having a thickness of not less than 7 μm and not more than 50 μm, and it is more desirable to use the metal foil having a thickness of not less than 12 μm and not more than 14 μm. The reason the thickness of the metal foil is set to not less than 7 μm is to secure strength of the metal foil T2, and the reason the thickness of the metal foil is set to not more than 50 μm is to secure workability of the metal foil T2.
Although any element may be used as an element to be added to the Cu alloy foil provided that the element allows the Cu alloy foil to easily elevate a (200) surface crystal rate to not less than 99% by heat treatment, trace amounts of Ag, Sn, Zn, Zr, O, N are added to the Cu alloy foil respectively, wherein a total amount of these elements is set to not more than 1%.
The reason the total amount of elements to be added is set to not more than 1% is that although the elements to be added and Cu form a solid solution, when the total amount of elements to be added exceeds 1%, there exists a possibility that impurities such as oxides other than solid solution are increased and the impurities influence the orientation.
Accordingly, it is preferable to set the total amount of elements to be added to not less than 0.01% and not more than 0.1%.
The metal plate and the Cu alloy foil formed by cold rolling at a rolling reduction of 90% or more which are explained heretofore are laminated to each other by a surface activation bonding method. The surface activation bonding means that surfaces of a substrate to be laminated and a metal foil to be laminated are activated by removing oxide, dirt and the like on the surfaces using a method such as sputter etching, the activated surfaces are brought into contact with each other and the laminate is subjected to cold rolling. An intermediate layer may be provided to the surface of the substrate by sputtering.
As the above-mentioned surface activation bonding method, for example, a vacuum surface activation bonding device D1 shown in
As shown in
The metal plate L1 and the metal foil L2 which are conveyed from the recoiler portions S1, S2 are continuously conveyed to a surface activation treatment step where activation treatment is applied to two surfaces to be bonded in advance and, thereafter, the metal plate L1 and the metal foil L2 are brought into pressure contact with each other by cold rolling.
In the surface activation treatment step, the surface activation treatment is performed by sputter etching treatment in an extremely-low-pressure inert gas atmosphere of 10 to 1×10−2 Pa, wherein the metal plate L1 and the metal foil L2 having bonding surfaces are used as one electrodes A (S3) which are connected to a ground respectively, a glow discharge is generated by applying an AC current of 1 to 50 MHz between one electrodes A and the other electrodes B (S4) which are supported in an insulated manner, and an area of the electrode which is exposed in plasma generated by the glow discharge is not more than ⅓ of an area of the electrodes B.
As an inert gas, argon, neon, xenon, krypton or a mixture gas containing at least one kind selected from a group consisting of these gases is applicable.
In the sputter etching treatment, surfaces of the metal plate L1 and the metal foil L2 which are bonded to each other are subjected to sputtering by an inert gas so that surface adsorption layers and surface oxide films are removed whereby the bonding surfaces are activated. During this sputter etching treatment, the electrodes A(S3) take the form of cooling rolls thus preventing the elevation of temperatures of respective materials to be conveyed.
Thereafter, the metal plate L1 and the metal foil L2 are continuously conveyed to a pressure bonding roll step (S5) so that the activated surfaces are pressure-bonded to each other. When an O2 gas or the like exists in the pressure bonding atmosphere, the activation processed surfaces are oxidized again during the conveyance and hence, the pressure bonding atmosphere influences the close contact between the metal plate L1 and the metal foil L2. Accordingly, it is desirable to perform the pressure bonding roll step (S5) under a high vacuum of 1×10−3 Pa or less. Further, the lower a rolling reduction, the more excellent the accuracy in thickness becomes and hence, it is preferable to set the rolling reduction to not more than 10% for preventing the collapse of a state of the metal foil, and it is more preferable to set the rolling reduction to not more than 2%.
A laminated body formed by hermetically bonding the metal plate L1 and the metal foil L2 to each other through the above-mentioned pressure bonding step is conveyed to a winding step (S6), and is wound in the step.
Next, after laminating the metal plate L1 and the metal foil L2 to each other by the surface activation bonding method, heat treatment is applied to the laminated body so as to highly orient crystal of the high-reduction rolled Cu alloy foil.
To allow the high-reduction rolled Cu alloy foil to finish the recrystallization completely, it is necessary to set a heat treatment temperature to a temperature of not lower than 150° C.
A soaking time may preferably be set to 3 to 5 minutes, and when the heat treatment is performed using a continuous annealing furnace, a soaking time may be set to approximately 10 seconds.
When the heat treatment temperature is set to an excessively high temperature, the secondary recrystallization is liable to occur in the rolled Cu alloy foil so that the crystal orientation is deteriorated. Accordingly, the heat treatment is performed with the heat treatment temperature of not lower than 150° C. and not higher than 1000° C.
After performing the heat treatment in this manner, the metal laminated substrate having high biaxial crystal orientation can be manufactured.
As shown in
Here, in a step of growing the epitaxial growth film, there may be a case where a Cu alloy foil reacts with a film forming gas depending on a film forming condition so that an epitaxial growth film having excellent adhesiveness cannot be formed on the Cu alloy foil or the epitaxial growth is not generated.
Such a drawback can be overcome by, as shown in
The protective film T4 may be made of metal such as Ni, Mo which exhibits excellent high-temperature corrosion resistance, an oxide made of an insulation material such as MgO or ZnO, or a nitride such as AIN or InGaN.
A thickness of the protective film T4 is preferably set to not less than 0.5 μm to prevent the dispersion of Cu which is a background material. Further, to form a film used for other purpose on the protective film by an epitaxial growth, it is also necessary to form the protective film by an epitaxial growth and hence, it is preferable to set a thickness of the protective film to not more than 10 μm. This is because when the thickness of the protective film becomes more than 10 μm, the crystal orientation of the protective film is lowered.
For example, in manufacturing a semiconductor element where a GaN film is formed as an epitaxial growth film T3 so as to use the semiconductor element as a blue light emitting diode, an InGaN layer or a ZnO layer is formed on the Cu alloy foil T2 as the protective film T4, and a GaN film can be formed on the protective film T4.
As a means for forming the epitaxial growth film T3, a known means such as an electrolytic plating method, a non-electrolytic plating method, a vacuum vapor deposition method or a sputtering film forming method can be used.
It is necessary to form the epitaxial growth film T3 by an epitaxial growth and it is desirable to set a film thickness of the epitaxial growth film T3 to not less than 1 nm and not more than 10 μm.
This is because when the film thickness of the epitaxial growth film T3 is less than 1 nm, the epitaxial growth film T3 cannot impart a function necessary for a semiconductor element to the semiconductor element, while when the film thickness exceeds 10 μm, a film thickness of the epitaxial growth film T3 becomes excessively large.
Next, the explanation is made with respect to the surface roughness of a metal foil (Cu alloy foil) whose crystals are oriented on the metal laminated substrate.
The lower the surface roughness (average surface roughness) Ra of the metal foil, the more the crystal orientation is improved. Accordingly, in a case of a metal foil whose surface roughness Ra is 100 nm or more, after surface activation bonding, the treatment which adjusts the surface roughness Ra to not more than 40 nm is performed.
As a method of lowering the surface roughness, the rolling reduction using pressure rolls, buffing, electrolytic polishing, electrolytic abrasive grain polishing and the like are considered. However, any method can be used. Although it is desirable to set the surface roughness to a mirror surface level, by taking a currently available technique and an economic aspect into consideration, it is desirable to set the surface roughness Ra to not less than 1 nm and not more than 10 nm.
By performing the above-mentioned surface roughness adjustment, it is possible to acquire the more excellent metal laminated substrate for an epitaxial growth film and hence, a high-performance functional film can be formed on the substrate.
By manufacturing the metal laminated substrate for an epitaxial growth film by surface activation bonding as described above, the Cu metal foil can be laminated to the metal substrate with an interface formed between the Cu metal foil and the metal substrate made smooth while maintaining a state where the metal foil is cold-rolled at a high rolling reduction. This is because, in biaxially orienting crystals of the metal foil by heating after such cold rolling, when a state where the Cu metal foil is cold-rolled at a high rolling reduction is not maintained, required biaxial crystal orientation is not generated. Further, when the interface is not smooth, there exists a possibility that the biaxial crystal orientation collapses.
Further, by adopting the surface active bonding method, the metal foil can be laminated to the metal substrate with favorable adhesiveness. It may be possible to laminate the metal foil on the metal substrate with favorable adhesiveness using an adhesive agent. In this case, however, there exists a possibility that the adhesive agent is deteriorated or modified due to heating after lamination leading to the collapse of the biaxial crystal orientation.
Example 1Hereinafter, an embodiment of the present invention is exemplified, wherein properties of the manufactured metal laminated substrate are explained. A high-reduction rolled Cu foil (metal foil) having a width of 200 mm and a thickness of 18 μm and an SUS316L plate (metal plate) having a thickness of 100 μm are bonded to each other by a room-temperature surface activation bonding method and, thereafter, the high-reduction rolled Cu foil and the SUS316L plate are subjected to heat treatment at a temperature of 200° C. to 1000° C. for five minutes thus acquiring the metal laminated substrate.
Table 1 shows a rate at which a Cu (200) surface is made parallel to a Cu foil surface, that is, a crystal orientation rate (a diffraction peak strength rate of a (200) surface at a θ/2θ diffraction peak measured by X-ray diffraction: I(200)/ΣI(hkl)×100(%)), and a Δφ° (φ scan peak (an average value of half value widths of 4 peaks at α=35°) obtained by an Ni (111) pole figure in accordance with X-ray diffraction) which indicates that the (200) surface is parallel to the longitudinal direction <001>, that is, a biaxial crystal orientation index.
As comparison examples, peak strength rates when the heat treatment is performed at a temperature of 130° C. and 1050° C. are also shown. Also as a comparison example, shown is a peak strength rate when a high-reduction rolled Ni foil having a thickness of 30 μm is bonded instead of the Cu foil by the above-mentioned room-temperature activation bonding method and, thereafter, heat treatment is applied to the high-reduction rolled Ni foil at a temperature of 1000° C. for 1 hour.
As can be understood from Table 1, in the high-reduction rolled Cu foil, the crystal orientation rate is 93% when the heat treatment is performed at a heat treatment temperature of 130° C. for 5 minutes and hence, the crystal orientation rate is not sufficient yet. However, when the heat treatment temperature falls within a range from 200° C. to 1000° C., the (200) surface crystal orientation rate becomes 99% or more when such heat treatment temperature is held for 5 minutes.
When the heat treatment temperature exceeds 1000° C., the uniaxial orientation of the (200) surface collapses due to the secondary recrystallization so that the strength rate is lowered to 70%.
With respect to the Ni foil which is shown as the comparison example, the recrystallization temperature is around 700° C. and the strength rate is 98% even with the heat treatment at a temperature of 1000° C. which is considered as the optimum heat treatment temperature whereby the strength rate does not reach 99% and Δφ is also 15.4°.
Here, the measured value described above is an average of values measured at three points consisting of areas in the vicinity of both ends of the plate and the center of the plate having a size of 200 mm in the widthwise direction, and no difference is substantially recognized with respect to the value among the embodiments.
As shown in Table 1, the metal laminated substrates which are manufactured by the manufacturing method of the present invention can be manufactured as an elongated coil having a large width while maintaining the uniform crystal orientation and hence, the metal laminated substrates can be used as substrates for various epitaxial growth films.
INDUSTRIAL APPLICABILITYAccording to the present invention, it is possible to provide a metal laminated substrate constituted of an elongated coil which can be continuously formed by a reel-to-reel method, and a crystal-oriented polycrystalline silicon film for a solar cell or a semiconductor compound such as a GaN element for a light emitting diode are formed on the metal laminated substrate as an epitaxial growth film. Accordingly, the metal laminated substrate can be used as a new material for an epitaxial growth film in new fields where the utilization of the metal laminated substrate has not been studied and hence, the present invention is industrially extremely useful.
BRIEF EXPLANATION OF DRAWINGA schematic cross-sectional view showing the constitution of a metal laminated substrate 5A obtained by carrying out a manufacturing method of the present invention.
A schematic cross-sectional view showing the constitution in a state 10A where an epitaxial growth film T3 is formed on the metal laminated substrate of the present invention.
A schematic cross-sectional view showing the constitution in a laminated state 10B where a Cu alloy foil T2 is laminated to a metal plate T1 by surface active bonding and, after heat treatment, a protection layer T4 is provided and, thereafter, a target epitaxial growth film T3 is formed.
A schematic view of a surface activation bonding device D1 used in the present invention.
EXPLANATION OF SYMBOLS
- T1: metal plate
- T2: Cu foil or Cu alloy foil
- T3: epitaxial growth film
- T4: protective layer
- 5A: metal laminated substrate
- 10A: cross-sectional view showing a state where epitaxial growth film T3 is formed on metal laminated substrate
- 10B: cross-sectional view showing a state where protective later T4 is formed on metal laminated substrate and, thereafter, epitaxial growth film T3 is formed
Claims
1. A method of manufacturing a metal laminated substrate for forming a semiconductor element comprising the steps of:
- activating at least one surface of a metal plate;
- activating at least one surface of a metal foil made of Cu or a Cu alloy which is cold-rolled at a rolling reduction of 90% or more;
- laminating the metal plate and the metal foil such that an activated surface of the metal plate and an activated surface of the metal foil face each other in an opposed manner and applying cold rolling to the metal plate and the metal foil which are laminated to each other; and
- biaxially orienting crystals of the metal foil by heat treatment.
2. The method of manufacturing a metal laminated substrate for forming a semiconductor element according to claim 1, wherein the activation treatment is performed by sputter etching.
3. The method of manufacturing a metal laminated substrate for forming a semiconductor element according to claim 1, wherein the cold rolling is performed at a rolling reduction of not more than 10% at the time of lamination.
4. The method of manufacturing a metal laminated substrate for forming a semiconductor element according to claim 1, wherein the metal foil made of Cu or the Cu alloy has a thickness of not less than 7 μm and not more than 50 μm.
5. The method of manufacturing a metal laminated substrate for forming a semiconductor element according to claim 1, wherein the foil made of the Cu alloy contains not less than 0.01% and not more than 1% of Ag, Sn, Zn, Zr, O and N in total.
6. The method of manufacturing a metal laminated substrate for forming a semiconductor element according to claim 1, wherein the heat treatment after the lamination is performed at a temperature of not lower than 150° C. and not higher than 1000° C.
7. The method of manufacturing a metal laminated substrate for forming a semiconductor element according to claim 1, wherein before the heat treatment, a polish treatment is applied to the metal plate such that the surface roughness of a metal-foil-side surface of the metal plate becomes not less than 1 nm and not more than 40 nm by Ra.
8. The method of manufacturing a metal laminated substrate for forming a semiconductor element according to claim 1, wherein a protective film having a thickness of not less than 1 nm and not more than 10 μm is further formed on the metal laminated substrate which is manufactured by the method of manufacturing a metal laminated substrate.
9. A metal laminated substrate for forming a semiconductor element which is manufactured by any one of the manufacturing methods according to claim 1.
Type: Application
Filed: Oct 20, 2009
Publication Date: Dec 1, 2011
Applicant: TOYO KOHAN CO., LTD. (Tokyo)
Inventors: Hironao Okayama (Yamaguchi), Akira Kaneko (Yamaguchi), Kouji Nanbu (Yamaguchi)
Application Number: 13/127,905
International Classification: C22F 1/08 (20060101); C23F 1/00 (20060101); C22C 9/00 (20060101);
