1. Field of the Invention
The present invention relates to a magnetic recording medium and a production method thereof, and particularly, to a magnetic recording medium whose ferromagnetic metal layer has a high coercive force Hc, a high anisotropic magnetic field Hkgrain, and a high normalized coercive force (Hc/Hkgrain). The magnetic recording medium of the present invention can be suitably applied to a hard disk, a floppy disk, a magnetic tape, and the like.
2. Description of the Related Art
As the conventional magnetic recording medium and its production method, the following is known.
FIG. 17 is a schematic view illustrating a hard disk as an example of a magnetic recording medium. In FIG. 17, FIG. 17(a) is a perspective view of the whole magnetic recording medium, and FIG. 17(b) is a cross section along the A-Axe2x80x2 line of FIG. 17(a).
A substrate body 1 consists of an Al substrate 2 and a non-magnetic (Nixe2x80x94P) layer 3 provided on a surface of the Al substrate 2. On this substrate body, are laminated a Cr underlying layer 4, a ferromagnetic metal layer 5, and a protective layer 6.
The non-magnetic (Nixe2x80x94P) layer 3 is formed by plating or sputtering, on the surface of the disk-shaped Al substrate 2 of 89 mm (3.5 inches) in diameter and 1.27 mm (50 mil) in thickness, to form the substrate body 1. Further, on the surface of the non-magnetic (Nixe2x80x94P) layer 3, are provided concentric scratches (hereinafter, referred to as texture) by a mechanical grinding process. Generally, surface roughness of the non-magnetic (Nixe2x80x94P) layer 3, i.e., a center line average height Ra is in the radial direction 5 nm to 15 nm.
Further, the Cr underlying layer 4 and the ferromagnetic metal layer 5 (generally, a magnetic film of Co alloy family) are formed on the surface of the above-mentioned substrate body 1 by sputtering, and, lastly, the protective layer 6 comprising carbon and the like is formed by sputtering to protect the surface of the ferromagnetic metal layer 5. Typical thicknesses of respective layers are 5 xcexcm to 15 xcexcm for the non-magnetic (Nixe2x80x94P) layer 3, 50 nm to 150 nm for the Cr underlying layer 4, 30 nm to 100 nm for the ferromagnetic metal layer 5, and 20 nm to 50 nm for the protective layer 6.
The conventional magnetic recording medium having the above-described layer structure has been manufactured under the condition that back pressure of the deposition chamber is at the level of 10xe2x88x927 Torr before the sputter deposition and impurity concentration of Ar gas used for film formation is 1 ppm or more.
In the magnetic recording medium obtained by the above-described manufacturing method, and particularly in the case of a ferromagnetic metal layer 5 containing Ta element (for example, CoCrTa alloy magnetic film), it is reported by Nakai et al. that, between crystal grains forming the ferromagnetic metal layer, exists a grain boundary layer of amorphous structure, and that this grain boundary layer has a non-magnetic alloy composition (J. Nakai, E. Kusumoto, M. Kuwabara, T. Miyamoto, M. R. Visokay, K. Yoshikawa, and K. Itayama, xe2x80x9cRelation Between Microstructure of Grain Boundary and the Integranular Exchange in CoCrTa Thin Film for Longitudinal Recording Mediaxe2x80x9d, IEEE Trans. Magn., vol. 30, No. 6, pp. 3969, 1994). However, in the case of a ferromagnetic metal layer that does not contain Ta element (for example, CoNiCr or CoCrPt alloy magnetic film), the above-mentioned grain boundary layer has not been found. Further, the above report describes that, when a ferromagnetic layer contains Ta element, a normalized coercive force (expressed as Hc/Hkgrain) of the magnetic recording medium is as large as 0.3 or more, and when a ferromagnetic metal layer does not contain Ta element, its value is less than 0.3.
The above-mentioned normalized coercive force (Hc/Hkgrain) of the ferromagnetic metal layer is a value obtained by dividing a coercive force Hc by an anisotropic magnetic field Hkgrain of a crystal grain, and expresses degree of increase of magnetic isolation of the crystal grain. Namely, when normalized coercive force of a ferromagnetic metal layer is high, it means that magnetic interaction between respective crystal grains constituting the ferromagnetic metal layer decreases, and high coercive force can be realized.
Further, an international patent application PCT/JP94/01184 discloses a technique relating to a cheap high-density recording medium whose coercive force is increased without using an expensive ferromagnetic metal layer, and its manufacturing method. According to PCT/JP94/01184, regarding a magnetic recording medium which has a ferromagnetic metal layer formed on a surface of a substrate body via a metal underlying layer and utilizes magnetic reversal, Ar gas whose impurity concentration is 10 ppb or less is used for film formation, so that oxygen concentration of the metal underlying layer and/or ferromagnetic metal layer is made 100 wtppm or less. Further, it is also reported that, the coercive force is further increased when Ar gas of 10 ppb or less impurity concentration is used in a cleaning process by high frequency sputtering on the surface of the above-mentioned substrate body to remove the surface of the substrate body by 0.2 nm to 1 nm, before forming the above-mentioned metal underlying layer. Further, in this report, it is described that there is a correlation between a normalized coercive force of a magnetic recording medium and its medium noise, and, in order to obtain a low noise medium, its normalized coercive force should be more than or equal to 0.3 and less than 0.5.
Further, an international patent application PCT/JP95/00380 discloses a magnetic recording medium and its manufacturing method, in which, when oxygen concentration of a ferromagnetic metal layer consisting of CoNiCr or CoCrPt is 100 wtppm or less, a grain boundary layer of amorphous structure can be formed between crystal grains constituting the ferromagnetic metal layer, and, as a result, a signal-to-noise ratio of electromagnetic transduction characteristics is high, and a stable coercive force can be obtained in mass production.
However, it is still obscure how various magnetic characteristics (coercive force: Hc, anisotropic magnetic field: Hkgrain, and normalized coercive force: Hc/Hkgrain) of a ferromagnetic metal layer or to composition distribution in a grain boundary layer of amorphous structure existing between the crystal grains constituting the ferromagnetic metal layer as high values in all the coercive force, anisotropic magnetic field and normalized coercive force, and which is adaptable to promotion of high recording density.
An object of the present invention is to provide a magnetic recording medium whose ferromagnetic metal layer has high coercive force, high anisotropic magnetic field and/or high normalized coercive force, so that it is adaptable to promotion of high recording density.
A magnetic recording medium of the present invention comprises a ferromagnetic metal layer that contains at least Co and Cr, and is formed on a base body via a metal underlying layer having Cr as its main component, and is characterized in that, the surface roughness of the base body is less than 1 nm when measured as a center line average height Ra, and, between crystal grains constituting the ferromagnetic metal layer, the magnetic recording medium has a first region in which Cr segregates, the first region penetrating the ferromagnetic metal layer, and that, in the first region, Cr concentration is lower in the neighborhood of the middle in the thicknesswise direction of the ferromagnetic metal layer than in the neighborhood of the surface and in the neighborhood of the metal underlying layer.
Film formation is performed under extra clean atmosphere to form a magnetic recording medium comprising a ferromagnetic metal layer which contains at least Co and Cr and is formed on a base body via a metal underlying layer containing Cr as its main component. Surface roughness of the base body is less than 1 nm when measured as a center line average heigh Ra. In that case, there is obtained the magnetic recording medium having a high coercive force, high anisotropic magnetic field and/or high normalized coercive force without depending on film thickness of the metal underlayer containing the main component Cr, by employing such construction that a first region in which Cr segregated and which penetrates the ferromagnetic metal layer exists between crystal grains constituting the ferromagnetic metal layer and, in that first region, Cr concentration is lower in the neighborhood of the middle in the thicknesswise direction than in the neighborhood of the surface and in the neighborhood of the metal underlying layer. In particular, even if the film thickness of the metal underlying layer is 10 nm or less, this effect can be maintained, and accordingly, it is possible to construct a magnetic recording medium which has a small surface roughness and can also be adaptable to lowering of the flying height of a head.
Further, in the above characteristics, a crystal grain of the ferromagnetic metal layer consists of a second region in which Cr concentration increases toward the grain boundary and, in the central part of the crystal grain, a third region in which Cr concentration is lower than the neighborhood of the grain boundary. The maximum Cr concentration in the third region is smaller than the maximum Cr concentration in the second region, and it is possible to obtain a magnetic recording medium which has a higher coercive force than the conventional magnetic recording medium which does not have the third region.
Further, in the above characteristics, when the maximum Cr concentration in the above-mentioned third region is less than or equal to 0.75 times the maximum Cr concentration in the above-mentioned second region, it is possible to obtain a magnetic recording medium which has high and stable values in all the magnetic characteristics (i.e., coercive force, anisotropic magnetic field, and normalized coercive force). This effect can be obtained even with the Cr underlying layer having such an ultrathin thickness as 2.5 nm.
Further, in the above characteristics, when Cr concentration gradient in the above-mentioned second region is 4 at % or more, it is possible to obtain a magnetic recording medium having superior magnetic characteristics in comparison with the conventional magnetic recording medium in which an average of Cr concentration gradient is less than 4 at %.
Although the layer structure of the magnetic recording medium according to the present invention is same as the layer structure of the conventional medium shown in FIG. 17, the ferromagnetic metal layer constituting the magnetic recording medium of the present invention differs from the conventional medium in the following two points.
1. Between the crystal grains constituting the ferromagnetic metal layer, there is a first region in which Cr segregates and which penetrates the ferromagnetic metal layer, and, in the first region, Cr concentration is lower in the neighborhood of the middle in the thicknesswise direction of the ferromagnetic metal layer than in the neighborhood of the surface and in the neighborhood of the metal underlying layer.
2. A crystal grain of the ferromagnetic metal layer consists of the second region in which Cr concentration increases toward the grain boundary and the third region in the central part of the crystal grain, in which Cr concentration is lower than the neighborhood of the grain boundary, and the maximum Cr concentration in the third region is lower than the maximum Cr concentration in the second region.
In the following, embodiment examples of the present invention will be described referring to the drawings.
As the substrate body in the present invention, are listed aluminum, titanium and its alloys, silicon, glass, carbon, ceramics, plastic, and resin and its complexes, or these material may be used being processed on their surfaces to be provided with surface coating of a non-magnetic film of different material, by means of sputter technique, evaporation method, plating, or the like. It is preferable that the non-magnetic film provided on the surface of this substrate body is not magnetized at high temperature, is electrically conductive and easy to machine, and, on the their hand, has appropriate surface hardness. As a non-magnetic film satisfying such requirements, an (Nixe2x80x94P) film formed by sputter technique is particularly preferable.
With regard to a shape of the substrate body, when it is to be used as a disk, a doughnut-shape disk is employed. A substrate body provided with a below-mentioned magnetic layer etc., namely, a magnetic recording medium is used being rotated at a speed of, for example, 3600 rpm about a center of the disk as an axis of rotation, at the time of magnetic recording and reproduction. At that time, a magnetic head flies at a height of about 0.1 xcexcm over the magnetic recording medium. Accordingly, with regard to the substrate body, surface flatness, parallelism of both top and under surfaces, waving in the circumferential direction of the substrate body, and surface roughness should be suitably controlled.
Further, when the substrate body starts or stops rotating, the surfaces of the magnetic recording medium and magnetic head contact with and slide on each other (referred to as Contact Start Stop, CSS). As a measure against this, concentric slight scratches (texture) may be provided on the surface of the substrate body.
As the metal underlying layer in the present invention, are listed Cr and its alloys, for example. When alloy is used, combination with V, Nb, Ta, or the like is proposed. In particular, Cr is preferable, since it causes segregation action of a below-mentioned ferromagnetic metal layer. It is used frequently in mass production, and, as the method of the film formation, sputter technique, evaporation method, or the like is employed.
The role of this metal underlying layer is to promote crystal growth of the ferromagnetic metal layer in such a manner that the axis of easy magnetization of the ferromagnetic metal layer lies in an in-plane direction in the substrate body, or, in other words, in such a manner that a coercive force in an in-plane direction in the substrate body becomes large, when the Co-based ferromagnetic metal layer is formed on the metal underlying layer.
When the metal underlying layer comprising Cr is formed by sputter technique, as film formation factors that control its crystalline properties, are listed a surface shape, surface state or surface temperature of the substrate body, gas pressure at the time of film formation, bias applied to the substrate body film thickness to be realized, and the like. In particular, a coercive force of the ferromagnetic metal layer tends to be higher in proportion to the film thickness of Cr, and, accordingly, the conventional film thickness of Cr is selected in the range of 50 nm to 150 nm, for example.
Here, the film formation conditions of the conventional technique [present invention] imply that back pressure of the deposition chamber is at the level of 10xe2x88x927 Torr [at the level of 10xe2x88x929 Torr], Ar gas used for film formation is normal-Ar (impurity concentration is 1 ppm or more) [uc-Ar(impurity concentration is 100 ppt or less, and preferably 10 ppb or less)]. Further, a target used in forming the metal underlying layer and ferromagnetic metal layer is preferably 150 ppm or less.
To improve the recording density, it is necessary to lower the flying height of the magnetic head from the surface of the medium. On the other hand, when the above-mentioned thickness of the Cr film is larger, surface roughness of the medium becomes larger also. Accordingly, it is desired to realize a high coercive force with thinner Cr film thickness.
As the ferromagnetic metal layer in the present invention, preferable is material that generates Cr segregation between crystal grains of the ferromagnetic metal layer. Namely, a ferromagnetic metal layer containing at least Co and Cr is used frequently. To give examples, CoNiCr, CoCrTa, CoCrPt, CoNiPt, CoNiCrTa, CoCrPtTa etc. are mentioned.
In the present invention, by forming a metal underlying layer and ferromagnetic layer under ultra clean atmosphere, which is cleaner than the conventional film formation conditions, the following two structures are realized.
1. Between the crystal grains constituting the ferromagnetic metal layer, there is the first region in which Cr segregates and which penetrates the ferromagnetic metal layer, and, in the first region, Cr concentration is lower in the neighborhood of the middle in the thicknesswise direction of the ferromagnetic metal layer than in the neighborhood of the metal underlying layer.
2. A crystal grain of the ferromagnetic metal layer consists of the second region in which Cr concentration increases toward the grain boundary and, in the central part of the crystal grain, the third region in which Cr concentration is lower than the neighborhood of the grain boundary, and the maximum Cr concentration in the third region is lower than the maximum Cr concentration in the second region.
Here, the film formation conditions under ultra clean atmosphere in the present invention [conventional film formation conditions] implies that back pressure of the deposition chamber is at the level of 10xe2x88x929 [10xe2x88x927] Torr, and impurity concentration of Ar gas used in the film formation is 100 ppt or less and preferably 10 ppb or less [1 ppm or more]. Further, the target used in forming the ferromagnetic metal layer is preferably 30 ppm or less in its impurity concentration.
Among the above-mentioned materials, favorably used materials are CoNiCr, which is inexpensive and less susceptible to a film formation atmosphere, and CoPt type, which is used to realize a coercive force of 1800 Oe or more that is difficult in the cases of CoNiCr and CoCrTa.
A problem to be solved in the above-mentioned materials is to develop material and a manufacturing method that are cheap in the material cost and low in medium noise, and can realize a high coercive force, to improve recording density and to decrease production cost.
The magnetic recording medium in the present invention refers to a medium (in-plane magnetic recording medium) in which recording magnetization is realized in parallel with the film surface of the above-mentioned ferromagnetic metal layer. In such a medium, it is necessary to further miniaturize recording magnetization in order to improve recording density. This miniaturization reduces leakage flux of each recording magnetization, and thus reduces output of regenerative signal at the magnetic head. Accordingly, it is desired to further reduce medium noise, which is considered as effect of adjacent recording magnetization.
In the present invention, xe2x80x9ccoercive force of the ferromagnetic metal layer: Hcxe2x80x9d implies a coercive force of the medium, obtained from a magnetization curve which is, in turn, measured using a variable sample magnetometer (referred to as VSM). xe2x80x9cAnisotropic magnetic field of a crystal grain: Hkgrainxe2x80x9d is an applied magnetic field in which rotational hysteresis loss measured by a high sensitive torque magnetometer completely disappears. Both coercive force and anisotropic magnetic field are values measured in a plane of a thin film, in the case of the magnetic recording medium in which the ferromagnetic metal layer is formed on the surface of the substrate body via the metal underlying layer.
Further, xe2x80x9cnormalized coercive force of the ferromagnetic metal layer: Hc/Hkgrainxe2x80x9d is a value obtained by dividing the coercive force Hc by the anisotropic magnetic field of a crystal grain Hkgrain, expressing degree of increase in magnetic isolation of the crystal grain, which is described in xe2x80x9cMagnetization Reversal Mechanism Evaluated by Rotational Hysteresis Loss Analysis for the Thin Film Mediaxe2x80x9d, Migaku Takahashi, T. Shimatsu, M. Suekane, M. Miyamura, K. Yamaguchi, and H. Yamasaki: IEEE TRANSACTIONS ON MAGNETICS, VOL. 28, 1992, PP. 3285.
Normalized coercive force of the ferromagnetic metal layer formed by the conventional sputter technique is less than 0.35, as far as the ferromagnetic metal layer is Co-based. According to Stoner-Wohlfarth theory, it is shown that, when crystal grains are completely magnetically isolated, normalized coercive force becomes 0.5, and this value is the upper limit of normalized coercive force.
Further, J.-G. Zhu and H. N. Bertram: Journal of Applied Physics, VOL. 63, 1988, pp. 3248 describes that, when normalized coercive force of a ferromagnetic metal layer is higher, magnetic interaction of crystal grains becomes lower, and high coercive force can be realized.
As the sputter technique employed in the present invention, are listed, for example, a transfer type in which a thin film is formed while a substrate body moves in front of a target, and a static type in which a thin film is formed while a substrate body is fixed in front of a target. The former is favorable for manufacturing a low cost medium owing to its mass-productivity, and the latter can be employed for manufacturing a medium superior in record and reproduction performance since it is stable in incident angles of sputtered particles on a substrate body.
xe2x80x9cSequential forming of the metal underlying layer and the ferromagnetic metal layerxe2x80x9d in the present invention implies xe2x80x9cafter the metal underlying layer is formed on the surface of the substrate body, it is not exposed to pressure atmosphere with higher pressure than the gas pressure at the time of film formation, before the ferromagnetic metal layer is formed on its surfacexe2x80x9d. It is publicly known that, if the surface of the metal underlying layer is exposed to the atmosphere, and thereafter, the ferromagnetic metal layer is formed on it, coercive force of the medium falls remarkably (for example, no exposure: 1500 Oexe2x86x92exposure: 500 Oe or less)
As xe2x80x9cimpurity in Ar gas used for film formationxe2x80x9d in the present invention, are listed H2O, O2, CO2, H2, N2, CxHy, H, C, O, CO, and the like. In particular, H2O, O2, CO2, O, and CO are, presumedly, impurities that affect quantity of oxygen taken into the film. Accordingly, impurity concentration in the present invention is expressed by the sum of H2O, O2, CO2, O, and CO contained in Ar gas used for film formation.
As xe2x80x9ccleaning process by high frequency sputteringxe2x80x9d in the present invention, is mentioned, for example, a method comprising applying AC voltage from RF (radio frequency, 13.56 MHz) power source to a substrate body placed within a space of electrically dischargeable gas pressure. This method is characterized by its applicability to a non-conductive substrate body. Generally, as effect of the cleaning process, is mentioned improvement in adherence of a thin film to a substrate body. After the cleaning process, however, there are many ambiguities in quality of a thin film itself formed on a substrate body.
As xe2x80x9cimpurity in a Cr target used in forming the metal underlying layerxe2x80x9d, are listed, for example, Fe, Si, Al, C, O, N, H and the like. In particular, it is conjectured that O is an impurity affecting quantity of oxygen taken into the film. Accordingly, impurity concentration in the present invention refers to oxygen contained in a Cr target used in forming a metal underlying layer.
As xe2x80x9cimpurity in a Co-based target used in forming the ferromagnetic metal layerxe2x80x9d, are mentioned, for example, Fe, Si, Al, C, O, N and the like. In particular, it is conjectured that O is an impurity affecting quantity of oxygen taken into the film. Accordingly, impurity concentration in the present invention refers to oxygen contained in a target used in forming a ferromagnetic metal layer.
xe2x80x9cApplication of negative bias to a substrate bodyxe2x80x9d in the present invention implies that, when a Cr underlying film or magnetic film is formed to manufacture a magnetic recording medium, DC bias voltage is applied to a substrate body. It is known that, when a suitable bias voltage is applied, coercive force of the medium is increased. It is publicly known that the above-mentioned effect of the bias application is larger when it is applied to both layers than when it is applied only in forming either of layers.
In many times, however, the above-mentioned bias application acts also on objects, i.e., substrate body supporting members and a substrate body holder, in the neighborhood of the substrate body. As a result, gas or dust is generated in a space in the neighborhood of the substrate body, and taken into a thin film being formed. Thus, it tends to cause such an inconvenient state that various film characteristics become unstable.
Further, the bias application to a substrate body gives rise to the following problems:
1. It can not be applied to a non-conductive substrate body such as glass;
2. Saturation magnetic flux density (Ms) of the formed magnetic film is decreased;
3. It is required to provide a complex mechanism inside the deposition chamber; and
4. Degree of applying bias to a substrate body is liable to change, and thus, it tends to cause variation in magnetic characteristics.
Thus, desired is a manufacturing method in which various film characteristics targeted can be obtained without applying the above-mentioned bias.
xe2x80x9cUltimate degree of vacuum of a deposition chamber in which the metal underlying layer and/or the ferromagnetic metal layer is formedxe2x80x9d in the present invention is one of the film formation factors, affecting a value of coercive force for certain material. In particular, conventionally, it has been considered that, when the above-mentioned ultimate degree of vacuum is low (for example, in the case of 5xc3x9710xe2x88x926 Torr or more), its effect is large in the case of ferromagnetic metal layer of Co-based material containing Ta In the present invention, however, it is found that, also in the cases of CoNiCr and CoCrPt, i.e., Co- based materials without containing Ta, the ultimate degree of vacuum of a deposition chamber has an effect, when seen from the viewpoint that grain boundary of amorphous structure can be formed or not between crystal grains.
xe2x80x9cSurface temperature of the substrate body at the time of forming the metal underlying layer and/or the ferromagnetic metal layerxe2x80x9d is one of the film formation factors, affecting a value of coercive force without depending on material of the ferromagnetic metal layer. Higher coercive force can be realized when film formation is carried out at higher surface temperature as long as it does not damage the substrate body. The damage of the substrate body implies external transformations such as warping, swelling, cracking, and the like, and internal changes such as development of magnetization, increase of quantity of generated gas, and the like.
However, to realize high surface temperature of the substrate body, it is generally necessary to perform heat treatment in the deposition chamber or in a previous chamber. Also, this heat treatment has such inconvenient aspects that gas or dust is generated in a space in the neighborhood of the substrate body, and taken into a thin film being formed, and various film characteristics become unstable.
Further, high surface temperature of the substrate body has following problems:
1. Magnetization of non-magnetic NiP layer is caused in a substrate body of NiP/Al;
2. Strain is caused in the substrate body; and
3. It is difficult to raise or maintain temperature of a substrate body, in the case of a substrate body having low thermal conductivity such as glass. Accordingly, desired is a manufacturing method in which the above mentioned heat treatment is not carried out, or various film characteristics targeted are obtained with lower heat treatment.
As surface roughness of the substrate body in the present invention is mentioned a center line average height Ra. As a measuring apparatus, is used a TALYSTEP made by RANKTAYLORHOBSON Ltd.
When the substrate body starts to rotate from a stationary state or vice versa, surfaces of the magnetic recording medium and magnetic head contact with and slide on each other (referred to as contact Start Stop, CSS). At that time, to suppress adhesion of the magnetic head or rise in friction coefficient, a larger Ra is favorable. On the other hand, when the substrate body arrives at the maximum rotational speed, it is necessary to ensure spacing between the magnetic recording medium and the magnetic head, i.e., the flying height of the magnetic head, and, accordingly, a smaller Ra is desirable.
Thus, the surface roughness of the substrate body and the maximum and minimum of Ra are suitably decided based on the above-described reasons and required specifications of the magnetic recording medium. For example, in the case that the flying heigh of the magnetic head is 2 xcexcinch, Ra=6 nmxe2x88x928 nm.
However, to realize much higher recording density, it is necessary to further reduce the flying heigh of the magnetic head (the distance between the magnetic head and the surface of the magnetic recording medium at the times of recording and reproduction). To satisfy this demand, it is important to flatten the surface of the magnetic recording medium furthermore. By reason of this, smaller surface roughness of the substrate body is favorable.
Thus, desired is a manufacturing method in which various film characteristics targeted are obtained even when the surface roughness of the substrate body is smaller.
As texture processing in the present invention, are listed, for example, a method using mechanical grinding, a method by chemical etching, a method of giving a physical concave and convex film and the like. In particular, in the case of a substrate body of aluminum alloy that is used most widely, the method using mechanical grinding is employed. For example, with regard to an (Nixe2x80x94P) film provided on a surface of a substrate body of aluminum alloy, there is a method in which a tape to which abrasive grains for grinding are adhered is pressed against the rotating substrate body so that concentric slight scratches are given to the substrate body. In this method, the abrasive grains for grinding are sometimes used being separated from the tape.
However, because of the reasons described in the above section of xe2x80x9cSurface roughness of the substrate bodyxe2x80x9d, desired is a method in which the above-mentioned texture processing is not carried out, or a method in which various fandn characteristics targeted are obtained with a slighter texture pattern.
As composite electrolytic polishing processing in the present invention, is mentioned, for example, processing of providing an oxidized passive film by producing chromium oxide as product material on an inner wall of a vacuum chamber that is used in forming a magnetic film or the like. In that case, as the material constituting the inner wall of the vacuum chamber, preferable is, for example, SUS316L or the like. This processing can reduce quantities of O2 and H2O emitted from the inner wall of the vacuum chamber, and thus, it is possible to further reduce quantity of oxygen taken into the formed thin film.
The present invention has used a magnetron sputtering system (model number ILC3013: load-lock static facing type) made by Anelva Co., Ltd., in which, the above-described processing is carried out on inner walls of all vacuum chambers (a charging/discharging chamber, a deposition chamber, and a cleaning chamber).