JP2000251250A - Carbon film thickness measuring method and method of manufacturing magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable high precision, simplified and low cost measurement of film thickness by measuring reflectivity of light beam in the wavelength in the particular range for the film surface of carbon formed on a metal magnetic film, and then measuring a carbon film thickness from the liner relative correlation of the wavelength of light beam where the reflectivity becomes minimum and the carbon film thickness. SOLUTION: In the section of wavelength of light beam of 300 to 500 nm, as the film thickness of DLC protection film increases, the wavelength of optical beam that provides the minimum reflectivity becomes larger. From the figure indicating the relationship between the thickness of DLC protection film and the wavelength of light beam providing the minimum reflectivity measured in the range of wavelength of 300 to 550 m, it can be understood that the linear relationship exists between the thickness of DLC protection film and wavelength of light beam that provides the minimum reflectivity. In comparison with the figure indicating the relationship between the wavelength of light beam that provides the minimum reflectivity of the DLC protection having unknown thickness and the wavelength of the beam that provides the minimum thickness of the DLC protection film and reflectivity, the unknown DLC protection film thickness can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the thickness of a carbon film used as a protective film for a magnetic recording medium such as a magnetic tape, and a method for manufacturing a magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, a so-called coating type magnetic recording medium produced by applying a magnetic paint in which a magnetic powder is dispersed in a binder made of a resin or the like on a non-magnetic support and drying it. Widely used.

With the demand for higher density of the magnetic recording medium, a metal thin film type magnetic recording medium in which a magnetic film is formed of a metal thin film has been used. O (oxide of cobalt and nickel)
The metal deposited thin film is Co in DV format magnetic tape.
-O (cobalt oxide) metal deposited thin film as a magnetic material,
It is used.

As the recording density increases, the relative speed between the magnetic head and the magnetic recording medium tends to increase. When the relative speed between the magnetic head and the magnetic recording medium increases, the sliding speed increases, and the wear resistance of the magnetic recording medium becomes a problem. As a solution, use of a protective film has been proposed and put into practical use, and in particular, a carbon protective film has been put into practical use.

[0005] In the case of a vapor-deposited magnetic tape for an 8 mm video deck, a carbon protective film was not required because the sliding speed between the magnetic head and the magnetic recording medium was not high. A diamond-like carbon (hereinafter referred to as DLC) film is used as a protective film.

If the thickness of the carbon film, which is the protective film, is too small, the sliding durability decreases. If the thickness is too large, the distance between the magnetic film and the magnetic head increases, so that the spacing loss increases and the reproduction output decreases. descend. Therefore, the thickness of the carbon protective film must be as thin as possible in order to increase the reproduction output within a range in which the sliding durability can be increased, and must be strictly controlled. In a DV-format deposited magnetic tape, the thickness of the DLC protective film must be controlled to ± 1 nm.

As a method for measuring the thickness of the carbon protective film for controlling the thickness of the carbon protective film, the following method has been conventionally proposed. A method of measuring the thickness of the carbon protective film by observing the cross section of the magnetic tape with a transmission electron microscope (cross-sectional TEM method), and a method of measuring the carbon film thickness by X-ray electron spectroscopy (Japanese Patent Application Laid-Open No. 9-14947) ),
A method of measuring the thickness of a carbon protective film based on the degree of light transmission (Japanese Patent Laid-Open No. 6-150309) has been proposed.
Japanese Patent Application Laid-Open No. 6-150309 discloses a method for manufacturing a magnetic tape in which a protective film is formed while measuring the thickness of the protective film according to the degree of light transmission.

[0008]

As described above, the thickness of the carbon protective film of the magnetic recording medium is as thin as possible in order to increase the reproduction output within the range where the sliding durability can be increased as described above. There is a need to. Therefore, the thickness of the carbon protective film must be strictly controlled, and for that, an accurate method for measuring the thickness of the carbon protective film is required.

In the cross-sectional TEM method, an ultra-thin section of a section of a magnetic tape is prepared, and the section is magnified to about 500,000 times, which is close to the limit of the magnifying ability of a transmission electron microscope, and observed. This is a method of calculating the thickness of the carbon protective film from the following equation. In a DV format evaporated magnetic tape, the thickness of the carbon protective film is approximately 10 nm, and the cross-sectional TEM
Even if it is magnified 500,000 times by the method, the carbon protective film thickness is observed only at 5 mm. Then, the boundary line in the thickness direction of the carbon protective film becomes considerably vague at 500,000 times, and a considerably large measurement error occurs in the cross-sectional TEM method as compared with the thickness control width of ± 1 nm which must be controlled. Was.

[0010] In addition, the preparation of ultrathin sections requires considerable skill, and the preparation of cross-sectional samples and the observation with a transmission electron microscope have taken a very long time. Further, since the transmission electron microscope is a very expensive device and large in size, it has not been possible to install this transmission electron microscope in a carbon protective film forming apparatus.

The method of measuring the carbon film thickness by X-ray electron spectroscopy is disclosed in Japanese Unexamined Patent Application Publication No. 9-14947, which has a considerably high accuracy. It takes a lot of time. Further, since the X-ray electron spectrometer is considerably expensive and large in size, it cannot be installed in a carbon protective film forming apparatus.

The method of measuring the thickness of the carbon protective film based on the degree of light transmission is simple and the apparatus is inexpensive.
Since it is possible to install the measuring device in the carbon protective film forming device, it was considered to be a good method and the measurement was performed. However, it was found that the DLC film could not be measured and that there was a problem in the measurement accuracy. In the case of a DV format vapor-deposited magnetic tape, the transmittance of light at 910 nm at the stage when a Co—O vapor-deposited magnetic film is formed on a base film is about 2.
5% (the ratio before the magnetic film was formed)
Even when a film was formed to a thickness of 10 nm, the transmittance did not change. It is presumed that the DLC film has a high light transmittance unlike the sputtered carbon film, so that the transmittance does not change.
A sputtered carbon film having poor light transmittance was formed to a thickness of 10 nm, and the transmittance was measured. As a result, there was a transmittance change of about 0.5%, but the reproducibility of repeated measurement was poor, and ± 1 n
It has been found that there is a problem in the measurement accuracy in controlling the film thickness of m.

[0013] In view of the above problems, an object of the present invention is to provide a method capable of measuring the thickness of a carbon film on a magnetic recording medium with high measurement accuracy, easily and inexpensively. Still another object of the present invention is to provide a method of manufacturing a magnetic recording medium capable of measuring and managing the thickness of a carbon film in a carbon film forming apparatus.

[0014]

In order to solve the above-mentioned problems, the present invention comprises a metal magnetic film formed on a nonmagnetic support and a carbon film formed on the metal magnetic film. Measuring the thickness of the carbon film of the magnetic recording medium, wherein the wavelength of the carbon film is 300 to 5 with respect to the carbon film surface.
The reflectance of 50 nm light is measured, and from the linear correlation between the wavelength of light at which the reflectance is a minimum and the carbon film thickness,
A carbon film thickness measurement method characterized by measuring the carbon film thickness, and

As a carbon film forming apparatus for forming a carbon film on a metal magnetic film formed on a non-magnetic support, a reflectivity measurement for measuring a reflectance of light having a wavelength of 300 to 550 nm with respect to the carbon film surface. 2. A method for manufacturing a magnetic recording medium, comprising: measuring and managing the thickness of a carbon film by the method for measuring the thickness of a carbon film according to claim 1 using a carbon film forming apparatus provided with a device. Is what you do.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The method for measuring the thickness of a carbon film according to the present invention relates to a magnetic recording medium comprising a metal magnetic film and a carbon film having an unknown thickness formed on a non-magnetic support. When measuring the thickness of the carbon film, the reflectance of the carbon film surface at a wavelength of light of 300 to 550 nm is measured, and the wavelength of the light at which the reflectance has a minimum value between 300 and 550 nm is determined. From this, the carbon film thickness is measured.

The reflectance of the carbon film surface is 300 to 550 n
The method of converting the wavelength of light having a minimum value between m and m to a carbon film thickness is a method in which, for a plurality of magnetic recording media on which a carbon film having a known film thickness is formed, the light wavelength The reflectance of 300 to 550 nm is measured, and the correlation between the wavelength of light having a minimum reflectance between 300 and 550 nm and the carbon film thickness is determined. The carbon film thickness is converted from the wavelength of the light having the minimum value.

After a metal magnetic film is formed on a base film, in a method of manufacturing a magnetic recording medium in which a carbon protective film is formed on the metal magnetic film, the reflectance of the carbon film surface at a light wavelength of 300 to 550 nm is measured. Then, when the wavelength of the light whose reflectance has a minimum value between 300 and 550 nm is determined, and the carbon film thickness is measured from the wavelength, the reflectance of the light having a wavelength of 300 to 550 nm is provided inside the carbon film forming apparatus. By installing a measuring device, the carbon film thickness can be measured with high accuracy.

For the measurement of the reflectance, for example, a spectrophotometer is used. Reflectance measuring instruments such as spectrophotometers are much cheaper and smaller than transmission electron microscopes and X-ray electron spectrometers.
The measurement is simple and the measurement time is short. The reflectometer has a sufficiently high measurement accuracy.

Even in a metal oxide magnetic film having a low reflectance, the wavelength of light is 300 to 550 nm on the carbon film surface.
Is measured, and the wavelength of light at which the reflectance has a minimum value in the range of 300 to 550 nm is obtained, and the carbon film thickness can be measured based on the wavelength, particularly when Co-O (cobalt oxide) is used. Can accurately measure the carbon film thickness.

[0021] Even if the carbon protective film is a DLC film having high light transmittance, the carbon film thickness can be measured.

The wavelength of light having a minimum reflectance with respect to light having a wavelength of 300 to 550 nm due to interference of light with a metal magnetic film as an underlayer increases as the carbon film thickness increases. growing. The thickness of the carbon film can be measured using the change in the wavelength of the light having the minimum value.

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a structure of a vapor-deposited magnetic tape which is an example of a magnetic recording medium manufactured by the manufacturing method of the present invention. In this vapor-deposited magnetic tape, a Co-O magnetic layer 2 is vapor-deposited on a 6.3 μm-thick polyethylene terephthalate (hereinafter referred to as PET) base film 1 in a thickness of 200 nm.
A DLC protective film 3 is formed thereon. Further thereon, a liquid lubricating film 4 is applied in a thickness of 1 to 3 nm. On the opposite side of the PET base film 1, a back coat layer 5 is formed to a thickness of 0.5 μm.

Next, an embodiment of the carbon film thickness measuring method of the present invention will be described. In the measuring method of the embodiment, the thickness of the DLC protective film 3 is measured by measuring the reflectance of light having a wavelength of 300 to 550 nm obtained by a spectrophotometer, and the reflectance becomes a minimum value between 300 and 550 nm. As shown in FIG. 2, a magnetic recording medium having a structure including a PET base film 1, a Co—O magnetic layer 2, and a DLC protective film 3 was used as a measurement sample for measurement by light wavelength.

On the film on which the Co—O magnetic layer 2 is formed, a DLC protective film 3 is formed by a continuous winding type plasma CVD.
(Chemical Vapor Deposition
n) The film is formed by the apparatus. At that time, samples in which the film thickness of the DLC protective film 3 was variously changed by changing the film feeding speed were produced.

Each of the film samples was cut out to a size of 7 × 20 mm and attached to a colorless and transparent slide glass such that the base film surface was in contact with the glass surface. 300-8 after setting in UV-3101PC
The reflectance of the surface of the DLC protective film was measured at a wavelength of 00 nm. For attachment to the slide glass, a small amount of water was put between the sample film and the slide glass, and the water was thinly and evenly spread with a cotton swab so that wrinkles did not enter the sample film. FIG. 3 shows the measurement results. The measurement of the reflectance is extremely simple and short.

For each sample whose reflectance was measured in FIG. 3, the thickness of the DLC protective film 3 was measured by a cross-sectional TEM method. As described above, the cross-sectional TEM method does not have very good measurement accuracy, and therefore, the average value of three measurements was taken as the measurement result, and the thickness of the DLC protective film 3 was used.

As can be seen from FIG.
In the section of 550 nm, as the thickness of the DLC protective film 3 increases, the wavelength of light at which the reflectance has a minimum value increases. DLC protective film thickness and light wavelength 30
The reflectance at 0 to 550 nm is measured and the reflectance is 300
FIG. 4 shows the relationship between the wavelengths of light having a minimum value between 550 nm and 550 nm. From FIG. 4, very clearly, DLC
It can be seen that there is a linear correlation between the thickness of the protective film and the wavelength of light at which the reflectance has a minimum value.

As described above, since there is a linear correlation between the thickness of the DLC protective film and the wavelength of the light at which the reflectance has the minimum value, the reflectance of the DLC protective film having an unknown film thickness has the minimum value. By comparing the wavelength of light to be obtained with FIG.
The C protective film thickness can be measured.

As described above, the measuring method of this embodiment is as follows.
An inexpensive and small measuring device makes it possible to measure the thickness of a carbon film on a magnetic recording medium with high measurement accuracy, easily and in a short time.

Next, an embodiment of the method for manufacturing a magnetic recording medium according to the present invention will be described. Co on PET base film 1
After the -O magnetic layer 2 is formed by vapor deposition with a thickness of 200 nm, the DLC protective film 3 is formed on the Co-O magnetic layer 2 by a continuous winding type plasma CVD apparatus. A spectrophotometer for measuring the reflectance of light having a wavelength of 300 to 550 nm is installed between the DLC forming section and the film winding section inside the continuous winding type plasma CVD apparatus, and the reflection on the DLC protective film surface is measured. Measure the rate. From the wavelength of the light at which the reflectance becomes a minimum value, D is determined by the above-described carbon film thickness measuring method.
The thickness of the LC film is measured, and the thickness of the DLC protective film in the continuous winding type plasma CVD apparatus is controlled.

On the DLC protective film 3, a liquid lubricating film 4 is applied to a thickness of 1 to 3 nm. On the opposite side of the PET base film 1, a back coat layer 5 is formed to a thickness of 0.5 μm.

As described above, according to the manufacturing method of this embodiment, in the DLC protective film forming apparatus, the thickness of the DLC protective film can be measured with high measurement accuracy, easily and in a short time. A magnetic tape whose film thickness is accurately controlled can be manufactured.

[0034]

As described above, the method for measuring the thickness of a carbon film of the present invention can measure the thickness of a carbon film on a magnetic recording medium with high measurement accuracy, easily and in a short time using an inexpensive and small measuring device. Measurement.

Further, the method of manufacturing a magnetic recording medium of the present invention can measure the thickness of a carbon film in a carbon film forming apparatus with high measurement accuracy, easily and in a short time, It enables the manufacture of well-managed magnetic recording media.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a magnetic recording medium manufactured by a method for manufacturing a magnetic recording medium according to the present invention.

FIG. 2 is a diagram showing an example of a magnetic recording medium used in the carbon film thickness measuring method of the present invention.

FIG. 3 is a graph showing the reflectance of a DLC protective film at each wavelength of light.

FIG. 4 is a graph showing the relationship between the thickness of a DLC protective film and the wavelength of light at which the reflectance has a minimum value, which is used in one embodiment of the method of measuring the thickness of a carbon film.

[Explanation of symbols]

 Reference Signs List 1 PET base film 2 CoO magnetic layer 3 DLC protective film 4 Liquid lubricating film 5 Back coat layer

Claims (2)

[Claims] 1. A method for measuring the thickness of a carbon film of a magnetic recording medium comprising a metal magnetic film formed on a non-magnetic support and a carbon film formed on the metal magnetic film, Wavelength of 300 to 550 n with respect to the carbon film surface
m is measured by measuring the reflectance of light having a minimum value of m, and measuring the carbon thickness from a linear correlation between the wavelength of the light at which the reflectance becomes a minimum value and the carbon thickness. Method. 2. A carbon film forming apparatus for forming a carbon film on a metal magnetic film formed on a non-magnetic support, a reflection measuring device for measuring the reflectance of light having a wavelength of 300 to 550 nm with respect to the carbon film surface. A method for manufacturing a magnetic recording medium, comprising: measuring and managing the thickness of a carbon film by the method for measuring the thickness of a carbon film according to claim 1 using a carbon film deposition apparatus provided with a rate measuring device.