Amorphous carbon covered member

Details Amorphous carbon covered member Amorphous carbon covered member

2001-02-23

2004-11-23

Turner, Archene (Department: 1775)

Stock material or miscellaneous articles

Self-sustaining carbon mass or layer with impregnant or...

C428S216000, C428S217000, C428S336000, C428S698000, C051S307000, C204S192100, C204S192110, C204S192160, C204S192320, C204S192340, C429S532000, C429S507000

Reexamination Certificate

active

06821624

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an amorphous carbon covered member used for machine parts, molds, cutting tools, sliding parts, etc. to improve wear resistance, sliding properties and surface protective function.
Amorphous carbon films are carbon films or hydrogenated carbon films which are amorphous and also called diamond-like carbon (DLC), carbon hard films, a-C, a-C:H, or i-C. Since amorphous carbon films have excellent characteristics such as high hardness, high plane evenness and low friction coefficient, application to machine parts, molds, cutting tools, sliding parts, etc. for which wear resistance and low friction coefficient are required is expected. They are actually used for some of them.
As methods of forming amorphous carbon films, plasma CVD using a hydrocarbon gas such as CH
4
, sputter deposition, ion plating, vacuum arc deposition, etc. are used. But since adhesion between the substrate and the amorphous carbon film is poor, various methods for improving adhesion have been proposed. As a general way of improving adhesion of amorphous carbon films, forming an interlayer of various structures between the substrate and the amorphous carbon film have heretofore been tried. For example, in Japanese patent publication 64-79372, a method is disclosed in which after a 50-1000 nm thick interlayer of titanium carbide has been formed on a substrate by vapor phase synthesis, an amorphous carbon film is formed by vapor phase synthesis.
Also, Japanese patent publication 5-82472 discloses a structure in which an interlayer 0.1-10 &mgr;m thick comprising at least one of carbides, carbonitrides, carbooxides, carbooxinitrides, carboborides of metals in the IVa, Va and VIa groups in the periodic table, carbides or carbonitrides of Si, or mutual solid solutions thereof is formed on a sintered alloy comprising at least one of carbides, nitrides or mutual solid solutions of metals in the IVa, Va and Via groups in the periodic table, and an amorphous carbon film is formed thereon.
Heretofore, the thickness of the interlayer was usually 50 nm or over. If an amorphous carbon film was formed on such a thick interlayer, adhesion was insufficient for machine parts, cutting tools and molds that are used under extremely high contact pressure. Fields were limited to which an amorphous carbon film was applicable.
SUMMARY OF THE INVENTION
After studying various structures to improve adhesion of an amorphous carbon film, it has been found out by the applicant that the following structure makes it possible to realize an amorphous carbon covered member which has such a high adhesion as to be applicable to machine parts, cutting tools, molds, etc.
Specifically, it has been found out that by forming on a substrate an interlayer comprising at least one element selected from the group consisting of elements in the IVa, Va, VIa and IIIb groups in the periodic table and elements in the IVb group except carbon, or carbides of at least one element selected from the abovesaid groups, and forming on the interlayer an amorphous carbon film so that the thickness of the interlayer will be 0.5 nm or over and less than 10 nm, it is possible to markedly improve the adhesion of the amorphous carbon film to the substrate.
As a structure for obtaining an amorphous carbon covered member that is superior in the adhesion to the substrate, the present invention is characterized by the material, film thickness and forming method of the interlayer.
As the material for the interlayer, at least one element selected from the group consisting of elements in the IVa, Va, VIa and IIIb groups in the periodic table and elements in the IVb group except carbon can be used. Since these elements react with carbon and form carbides, by forming an amorphous carbon film on the interlayer comprising one of these elements, a bond of such an element and carbon is formed at the interface between the interlayer and the amorphous carbon film, so that a high adhesion is achieved.
Otherwise, carbides of these elements may be used as the material for the interlayer. By forming an amorphous carbon film on the interlayer of such a carbide, a bond between the carbon in the carbide and the carbon in the amorphous carbon, or a bond between one of the elements in the IVa, Va, VIa and IIIb groups in the periodic table or one of the elements in the IVb group except carbon and the carbon in the amorphous carbon is formed at the interface between the interlayer and the amorphous carbon film, so that a high adhesion is obtained. These carbides may be of a composition within or out of a stoichiometric ratio.
Among these materials, it is especially preferable to use for the interlayer at least one element selected from the group consisting of Ti, Zr, Hf, v, Nb, Ta, Cr, Mo, W and Si, or a carbide of at least one element selected from the group. Since these elements are substances that can easily form carbides, by forming an amorphous carbon film on an interlayer of one of these elements or a carbide of one of these elements, a stable and rigid bond is formed at the interface between the interlayer and the amorphous carbon film, so that an extremely high adhesion is achieved.
In the present invention, the thickness of the interlayer is preferably 0.5 nm or over and less than 10 nm. By making it thinner than the thickness of interlayers used in the prior art, it is possible to obtain a high adhesion that was impossible in the prior art. If the thickness of the interlayer is thinner than 0.5 nm, the interlayer cannot perform functions as the interlayer because it is difficult to form a continuous film that is uniform in thickness over the entire surface of the substrate. If the thickness of the interlayer is over 10 nm, no sufficient adhesion is obtainable because the adhesion at the interface between the substrate and the interlayer or at the interface between the interlayer and the amorphous carbon film decreases. More preferably, the thickness of the interlayer is 2 nm or over and 7 nm or under.
As a method of forming the interlayer, a known method can be used such as vacuum deposition, sputter deposition, vacuum arc deposition, ion plating or various CVD. Among them, ion plating, sputter deposition and vacuum arc deposition are especially preferable because of high ionization rate of the raw material, and because due to the effect of driving ions into the substrate, a high adhesion between the interlayer and the substrate is obtained.
If the interlayer is formed on the substrate after contamination and an oxide layer on the substrate surface have been removed by irradiating the substrate surface with ions, a higher adhesion is obtained. Thus doing so is preferable. As a method of cleaning the substrate surface by ion irradiation, a known technique may be used.
According to the method of ion irradiation to the substrate surface, it is possible to simultaneously carry out the cleaning of the substrate surface by etching and the formation of the interlayer. Since a DLC film formed on the interlayer by this method is especially superior in adhesion, it is preferable.
Ion irradiation is carried out by applying a negative bias voltage to the substrate at least in the presence of ions of elements forming the interlayer. As a method of producing ions, a known technique may be used. But the use of a sputter evaporation source or a vacuum arc evaporation source is desirable because of high ionization rate and a fast etching speed.
In this case, the element forming the interlayer is used as a target. For example, if such a metal as Ti, Cr and Si is used for the interlayer, these metals can be used for targets. If a metallic carbide is used for the interlayer, the metallic carbide may be used for targets. If a metal is used for the target, hydrocarbon gas such as CH
4
is supplied into the chamber as a carbon source, or using the metallic target, a metallic layer is formed on the substrate surface during ion irradiation and the metallic layer is carbonized during formation of the amorphous carbon film as described below to form a metall

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