JPH0914947A - Carbon film thickness measurement method - Google Patents

Abstract

(57) [Summary] [Construction] Observation by X-ray photoelectron spectroscopy is performed on a magnetic recording medium in which a metal magnetic thin film and a carbon film having an unknown film thickness are formed on a non-magnetic support. Then, the step of measuring the peak area intensity I _C of the carbon atom and the peak area intensity I _M of the metal atom constituting the metal magnetic thin film, and the peak of the carbon atom from the magnetic recording medium in which the carbon film is formed to 20 nm or more. Measuring the area intensity I _C 0,
Through the steps of measuring the peak area intensity I _M 0 of the metal atoms forming the metal magnetic thin film from the magnetic recording medium on which the carbon film is not formed and the step of calculating the value of the constant λ, _The unknown film thickness d _C of the carbon film is obtained by substituting the measured values of _C , I _M , I _C 0, and I _M 0, the calculated value of the constant λ, and the value of the photoelectron escape angle α. d _C = λ sin α · ln [(I _C / I _M ) / (I _C 0 / I
_M 0) +1] [Effect] The film thickness of the carbon film in the magnetic recording medium can be properly controlled, and a carbon film having a practically necessary durability can be obtained even if it is thin.

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 on a so-called metal thin film type magnetic recording medium in which a metal magnetic thin film and a carbon film are formed on a non-magnetic support. Regarding

[0002]

2. Description of the Related Art Conventionally, as a magnetic recording medium, a powder magnetic material such as an oxide magnetic powder or an alloy magnetic powder is coated on a non-magnetic support with a vinyl chloride-vinyl acetate copolymer, polyester resin, urethane resin, A so-called coating type magnetic recording medium, which is prepared by coating and drying a magnetic coating material dispersed in an organic binder such as a polyurethane resin, is widely used.

On the other hand, with the increasing demand for high-density recording, Co--Ni alloys, Co--Cr alloys, Co--
A so-called metal magnetic thin film type magnetic recording medium in which a metal magnetic material such as O is directly deposited on a non-magnetic support by plating or vacuum thin film forming means (vacuum deposition method, sputtering method, ion plating method, etc.) It has been proposed and attracts attention.

This metal magnetic thin film type magnetic recording medium is excellent not only in coercive force and squareness ratio but also in electromagnetic conversion characteristics at short wavelengths, and the magnetic layer can be extremely thin,
There are many advantages such as remarkably small thickness loss during recording demagnetization and reproduction, and higher packing density of the magnetic material because there is no need to mix the binder, which is a non-magnetic material, into the magnetic layer. Have

Further, in order to improve the electromagnetic conversion characteristics of this kind of magnetic recording medium and to obtain a larger output, the magnetic layer is obliquely vapor-deposited when forming the magnetic layer of the magnetic recording medium. The so-called oblique vapor deposition has been proposed and put to practical use.

By the way, it is said that the magnetic recording medium as described above has problems in durability and rust resistance, and in order to solve these problems, the surface of the magnetic layer is oxidized or vacuum film formation is performed. Method, a protective film is provided on the metal magnetic thin film, and a lubricant is further applied thereon.

At present, as this type of protective film,
A carbon film formed by a sputtering method and a diamond-like carbon film formed by a chemical vapor deposition (CVD) method using a hydrocarbon-based gas are considered promising.

In order to obtain a practical level of durability by directly forming a carbon film on a metal magnetic thin film such as a Co thin film or a Co-Ni thin film, it is necessary to make this carbon film thick to some extent. However, in view of the fact that the output reduction due to spacing loss cannot be ignored as the wavelength becomes shorter with higher density in the future, the thickness of the carbon film cannot be excessively increased.
That is, it is desirable that the carbon film be formed as thin as possible within the range where durability can be maintained, and the film thickness needs to be appropriately controlled.

Conventionally, in order to measure the film thickness of the carbon film, calculation has been performed from an enlarged photograph of about 300,000 times obtained by a cross-section observation method called a microtome TEM method. Here, the TEM (transmission electron microscope) is to obtain a magnified image of a substance by irradiating a sample with an electron beam emitted from an electron gun in a vacuum and magnifying the transmission image with a magnetic field lens. The microtome is a sample preparation method for preparing a slice having a thickness that allows an electron beam to pass therethrough.

[0010]

By the way, in consideration of the allowable range of output reduction due to spacing loss when the recording wavelength is 0.5 μm, the thickness of the carbon film needs to be controlled to several nm. Therefore, the measurement of the thickness of the carbon film requires resolution at the nm level.

However, the above-mentioned microtome TE
The M method can measure the film thickness for a film having a thickness of 5 nm or more, but the resolution is not sufficient for a film thinner than this.

Therefore, a carbon film having a thickness of 5 nm or less is empirically derived from the relationship between the feeding speed of the support and the thickness of the carbon film to be formed in a continuous winding type sputtering apparatus or a continuous winding type CVD apparatus. The film thickness has been controlled.

However, the relationship between the feeding speed of the support and the thickness of the carbon film is different between the film forming methods such as the sputtering method and the CVD method,
It is difficult to control the film thickness accurately by the feeding speed of this non-magnetic support, because it varies depending on the size of the film forming chamber, the degree of vacuum, the difference in various film forming conditions such as introduced gas, etc. Met.

Therefore, the present invention has been proposed in view of such a conventional situation, and in order to obtain a carbon film capable of reducing spacing loss and ensuring sufficient durability, nm An object of the present invention is to provide a film thickness measuring method capable of measuring the film thickness of a carbon film having a level of thickness.

[0015]

The method for measuring the thickness of a carbon film according to the present invention has been proposed to achieve the above-mentioned object, and a metal magnetic thin film and an unknown thickness are formed on a non-magnetic support. When a film thickness d _C of the carbon film is formed on a magnetic recording medium formed with a carbon film having a carbon atom, the magnetic recording medium is observed by X-ray photoelectron spectroscopy to determine whether the carbon atom The peak area intensity I _C corresponding to the 1s level and 2 of the metal atoms constituting the metal magnetic thin film
The step of measuring the peak area intensity I _M corresponding to the p level and the observation by X-ray photoelectron spectroscopy on a magnetic recording medium having a carbon film of 20 nm or more,
The step of measuring the peak area intensity I _C 0 corresponding to the 1 s level of carbon atoms and the observation by X-ray photoelectron spectroscopy on the magnetic recording medium on which the carbon film is not formed are carried out to detect the metal magnetic thin film. The step of measuring the peak area intensity I _M 0 corresponding to the 2p level of the constituent metal atom, and the X-ray photoelectron spectroscopy were performed on a plurality of magnetic recording media on which a carbon film having a known film thickness was formed. After the observation and the step of calculating the value of the constant λ, the measured values of I _C , I _M , I _C 0, and I _M 0 are added to the following formula (1):
The film thickness d _C is calculated by substituting the calculated value of the constant λ and the value of the photoelectron escape angle α.

D _C = λ sin α · ln [(I _C / I _M ) / (I _C 0 / I _M 0) +1] (1) Here, X-ray photoelectron spectroscopy (hereinafter, ESCA: Electron
It is called Spectroscopy for Chemical Analysis. ) Is a method of identifying the constituent atoms and detecting the bonding state by utilizing the photoelectric effect of the substance. When a certain substance is irradiated with X-rays having a narrow energy width (for example, MgK _a , AlK _a, etc.), the electron e is knocked out by the photoelectric effect, but the kinetic energy Ek of the hit electron e and the energy hν of the irradiated X-ray. , Work function φ, and electron binding energy Eb have the relationship shown in the following equation (2).

Eb = hν-Ek-φ (2) Since the binding energy Eb of the electron is unique to each atom, it is possible to identify the atom and detect the binding energy. .

In the present invention, the intensity I _{M of} photoelectrons emitted from the metal magnetic thin film and the intensity I _{C of} photoelectrons emitted from the carbon film are measured.
The thickness d _{C of the} carbon film is calculated by using the fact that the amount of carbon existing in the range of m is reflected.

When the film thickness d _{C of the} carbon film is calculated by the above equation (1), it is necessary to determine the value of the constant λ. For this purpose, a carbon film having a known film thickness is formed. The plurality of magnetic recording media were observed by X-ray photoelectron spectroscopy to find the peak area intensity I _C corresponding to the 1s level of carbon atoms and the 2p level of the metal atoms constituting the metal magnetic thin film. After measuring the corresponding peak area intensities I _M respectively, ln [(I _C / I _M ) / (I _C 0 / I) using the previously measured I _C 0 and I _M 0.
_M 0) +1] is calculated, the value of λ sin α is obtained from the correlation between the calculated value and the known thickness of the carbon film, and the value of the photoelectron escape angle α is substituted.

For example, when the metal magnetic thin film is made of a metal material mainly containing cobalt, a value of 1.8 is used as the constant λ.

Here, the carbon film may be a carbon film formed by a sputtering method or a carbon film formed by a CVD method using a hydrocarbon gas. The sputtering method includes a magnetron sputtering method and a facing target method,
As the CVD method, CVD is plasma CVD method, EC
R plasma CVD method, arc jet plasma CVD method and the like can be mentioned.

The present invention is applied to a so-called metal magnetic thin film type magnetic recording medium in order to appropriately control the film thickness of a carbon film. However, a non-magnetic support or a metal magnetic thin film in a magnetic recording medium is used. There is no limitation on the constituent material.

For example, as the non-magnetic support, polyesters, polyolefins, celluloses, vinyls,
Polymer substrates formed of polymer materials typified by polyimides and polycarbonates, metal substrates made of aluminum alloys and titanium alloys, ceramics substrates such as aluminum glass, glass substrates, and the like can be given. Although not limited in any way, when applied to a magnetic tape, a polyethylene terephthalate film, a polyethylene naphthalate film, an aramid film or the like is preferably used. In addition, a filler may be internally added to these films to control the surface roughness,
A layer for controlling the surface roughness may be formed on the surface.

As the metal magnetic thin film, any conventionally known one can be used. For example, Fe, C
Ferromagnetic metals such as o and Ni, Fe-Co, Fe-Ni,
Co-Ni, Fe-Co-Ni, Fe-Co-B, Fe
-Ni-B, Fe-Cu, Co-Cu, Co-Au, C
o-Pt, Mn-Bi, Mn-Al, Fe-Cr, Co
-Cr, Ni-Cr, Fe-Co-Cr, Co-Ni-
Cr, Co-Ni-Pt, Fe-Co-Ni-Cr, F
A metal magnetic thin film for in-plane magnetization recording made of a ferromagnetic alloy such as e-Co-Ni-B, a Co-Cr alloy thin film, Co-
A metal magnetic thin film for perpendicular magnetization recording such as an O-based thin film may be used.

These metal magnetic materials include a vacuum vapor deposition method of evaporating a ferromagnetic metal magnetic material under vacuum to deposit it on a support, an ion plating method of evaporating a ferromagnetic metal material in a discharge, and argon. A thin film is formed by a so-called PVD technique such as a sputtering method in which atoms on the target surface are knocked out by argon ions generated through a glow discharge in an atmosphere containing the main component. The magnetic layer may be either a single-layer film or a multilayer film of a metal magnetic thin film formed by these methods. In order to improve the adhesive force between layers and control the coercive force between the non-magnetic support and the metal magnetic thin film, or between the metal magnetic thin films when the metal magnetic thin film is a multilayer film. A base layer or an intermediate layer may be provided. Further, the vicinity of the surface of these metal magnetic thin films may be an oxide layer for the purpose of improving corrosion resistance and the like.

In particular, in the case of a metal magnetic thin film for in-plane magnetization recording, Bi, Sb, Pb, Sn and G are previously formed on a non-magnetic support.
A base film of a low melting point non-magnetic material such as a, In, Ge, Si, Ti is formed in advance, and a metallic magnetic material is vapor-deposited or sputtered from the vertical direction to diffuse the low melting point non-magnetic material into the metallic magnetic thin film. However, the orientation may be eliminated to secure the in-plane isotropy and improve the coercive force.

However, in the present invention, as described above, when measuring the thickness of the carbon film, the peak area intensity I _M corresponding to the 2p level of the metal atom contained in the metal magnetic thin film is measured. Since the result is used, the value to be substituted into the equation (1) varies depending on the constituent material of the metal magnetic thin film.

Further, in the magnetic recording medium in which the thickness of the carbon film is controlled by applying the present invention, a back coat layer is formed on the surface of the non-magnetic support opposite to the side on which the metal magnetic thin film is formed. May be formed, or a top coat layer made of a lubricant, an anticorrosive, or the like may be further applied on the protective film. As a material used for these layers, any conventionally known material can be used. For example, the back coat layer is a non-magnetic layer in which a non-magnetic powder having an antistatic effect and a friction reducing effect, such as carbon black formed in a normal magnetic recording medium, is dispersed in a binder. Good.

[0029]

Function The principle of the film thickness measuring method by ESCA will be briefly described.

First, consider the case where a layer having a depth z and a thickness dz from the sample surface is irradiated with uniform X-rays. The photoelectrons excited from the target atom a undergo a strong interaction with the substance. Among these, the photoelectron intensity dIa emitted in a vacuum without energy loss is the X-ray intensity irradiated by F
0, the effective area of the sample where the photoelectrons to be detected are generated is S0,
The photoionization cross-section is σ a, the number density of the atom a of interest at the depth z is na, the emission angle represented by the angle between the plane parallel to the surface and the analyzer axis is α, and the inelastic scattering mean free path is λ _a. Then, it is shown by the following formula (3).

DI _a = F 0 S 0 σ _a n _a exp (−d z / λ _a sin α) (3) In general, in the area of ESCA, λ _a is several tens nm to several hundreds nm, and strictly. Depends on the kinetic energy of the matrix and photoelectrons.

The above equation (3) is a basic equation relating to photoelectron intensity. As can be seen from equation (3), as the photoelectrons pass through the thin film, a certain probability exp (-dz / λ
_It decreases according to _a sin α). Further, it is said that 95% of the photoelectrons emitted in vacuum are from the region up to the depth 3λ _a . At the depth λ _a , 63.2
%, And 86.5% at _a depth of 2λ _a . Therefore, E
In film thickness measurement by SCA, the thickness of 3λ _a is generally the limit.

Photoelectron intensity I _a ∞ for a uniform sample
Is expressed by the following expression (4) by integrating the above expression (3).

I _a ∞ = F 0 S 0 σ _a n _a λ _a (4) Next, as shown in FIG. 1, a simple film 2 having a thickness d is formed on the substrate 1. Consider the layered model.

Photoelectron intensity I _s from substrate 1 and thin film 2
The photoelectron intensity I _{o from} is the subscript indicating the substrate 1 is s, the subscript indicating the thin film is o, the mean free path of the photoelectrons of the substrate material in the substrate 1 is λ _ss , and the photoelectron thin film 2 of the substrate material is Where λ _so is the mean free path and λ _oo is the mean free path of the photoelectrons of the thin-film material in the thin film 1,
And equation (6).

[0036] _{I s = F0 S0 σ s n} s λ ss exp (-d / λ so sinα) = I s ∞exp (-d / λ so sinα) ··· (5) I o = F0 S0 σ o n _o λ _oo [1-exp (-d / λ _oo sin α)] = I _o ∞ [1-exp (-d / λ _oo sin α)] (6) In addition, the above formula (5) and formula (6) in), a _{I s ∞ = F0 S0 σ s} n s λ ss I o ∞ = F0 S0 σ o n o λ oo.

Generally, X-ray photoelectron spectroscopy (XPS: X-ray)
Relative intensity is used for quantitative treatment in photoelectron spectroscopy. The relative intensity I _o / I _s can be expressed as the following formula (7) from the above formulas (5) and (6).

I _o / I _s = (I _o ∞ / I _s ∞) × [1-exp (−d / λ _oo sin α)] × exp (d / λ _so sin α) (7) The film thickness d of the thin film 2 can be obtained from the equation (7).

When the kinetic energies of the photoelectrons of interest are close to each other, λ _oo = λ _so = λ can be approximated.
The formula (7) is further simplified, and the film thickness d is expressed by the following formula (8).
Can be represented by

D = λ sin α · ln [(I _o / I _s / I _o ∞ / I _s ∞) +1] (8) In this equation (8), I _o , I _s , I _o ∞, Since I _s ∞ is a measured value and α is determined by the measurement conditions, if the value of λ is determined, the film thickness d can be obtained. The value of λ can be calculated by observing a plurality of samples on which a thin film having a known film thickness is formed by X-ray photoelectron spectroscopy.

Therefore, also for a magnetic recording medium in which a carbon film is formed on a metal magnetic thin film, the observed electron energy spectrum is analyzed and I _o in the formula (8) is set to the 1s level of C atom. the peak area intensity I _C of a corresponding spectrum, replacing I _s the peak area intensity I _M of spectra corresponding to the 2p level of the metal atoms in the metal magnetic thin film, similarly, the I _o ∞ to I _C 0, I _s ∞ to I _M 0
If replaced with, the film thickness d _{C of the} carbon film can be known from the above-mentioned formula (1).

D _C = λ sin α · ln [(I _C / I _M ) / (I _C 0 / I _M 0) +1] (1)

[0043]

EXAMPLES Specific examples to which the present invention is applied will be described below, but it goes without saying that the present invention is not limited to these examples.

First, a magnetic tape having a metal magnetic thin film and a carbon film formed on a non-magnetic support was prepared.

Specifically, a metal magnetic thin film having a thickness of 200 nm was formed on a polyethylene terephthalate (PET) film having a thickness of 6 μm by vacuum vapor deposition using Co as a vapor deposition source. The film forming conditions for the metal magnetic thin film are as follows.

Film-forming conditions of metal magnetic thin film Film-forming apparatus: Continuous winding type vapor-depositing apparatus Vapor-depositing source: Co100% Incident angle of vapor-deposited particles: 45 to 90 ° Deposition rate: 5000 nm · m / min Oxygen introduction amount: 500 sccm Co was partially oxidized by the introduction of oxygen.

Next, a carbon film was formed under the following film forming conditions.

Carbon Film Forming Conditions Film forming apparatus: Continuous winding type sputtering apparatus target: Carbon applied power: 10 kW Sputtering gas: Ar 75 sccm The feeding speed of the non-magnetic support on which the metal magnetic thin film is formed is 4 m. The thickness of the carbon film was variously changed by changing the thickness in the range of / min to 16 m / min.

Then, by cutting to a width of 8 mm,
Four types of magnetic tapes (sample tapes 1 to 4) having different carbon film thicknesses were completed.

Here, in order to investigate the film thickness of the carbon film in each of the sample tapes 1 to 4, ESCA was used to obtain the peak area intensity I _{Co of} the spectrum corresponding to the 2p level of Co atom in the sample tapes 1 to 4. , 1s of C atom
The peak area intensity I _C of the spectrum corresponding to each level was measured. The measurement conditions are shown below.

Measurement conditions Device: ULVAC-PHI ESCA5400MC X-ray: Monochromator AlK _a (15 kV, 400 W) Measuring vacuum degree: 10 ⁻⁸ Pa level Photoelectron escape angle α: 80 ° Analysis diameter: 1.1 mm Path energy: 35 .75 In addition, the photoelectron intensity I _Co 0 of _Co was measured in advance for the magnetic tape on which the carbon film was not formed, and the photoelectron intensity of the carbon film was formed for the magnetic tape on which the carbon film was formed to 20 nm or more. Although I _C 0 has been measured, the measurement conditions are the same as those described above.

Then, by substituting these measured values into the above-mentioned formula (1), the sample tapes 1 to 4 are obtained.
The thickness d _C of the carbon film in each of the above was determined.

D _C = λ sin α · ln [(I _C / I _M ) / (I _C 0 / I _M 0) +1] (1) If the value of I _Co is substituted for I _M Of course, the value of I _Co 0 may be substituted for I _M 0.

Regarding λ, there are some calculation methods based on empirical formulas determined by using experimental data. However, since it may be affected by the state of the substance to be measured, here, a known film thickness is used. Perform measurements on the samples
It was calculated by back calculation.

FIG. 2 shows a sample in which a carbon film having a known film thickness d _C ′ is formed on a metal magnetic thin film made of Co under the condition of α = 80, ln [(I _C / I _Co ) /
(I _C 0 / I _Co 0) +1] is shown. In addition, ln [(I _C / I _Co ) / (I
_When the correlation between _C 0 / I _Co 0) +1] and the film thickness d _C ′ of the carbon film was obtained, the following equation (9) was obtained.

D _C '= 1.8 × ln [(I _C / I _Co ) / (I _C 0 / I _Co 0) +1] −0.17 (9) The correlation coefficient r is 0. It was 0.99.

Here, comparing equation (9) and equation (1), the slope 1.8 in equation (9) is λ in equation (1).
It turns out that it corresponds to sin α. And α = 80
When λ is obtained by substituting for, λ = 1.8 (nm).

Therefore, in equation (1), I _C , I _Co , I
_By substituting the measured values of _C 0 and I _Co 0 and λ = 1.8 and α = 80, the film thickness d _C of the carbon film in the sample tapes 1 to 4 can be calculated.

The durability of the sample tapes 1 to 4 for which the film thickness d _C was calculated as described above was also measured. Specifically, an 8mm VCR equipped with a sendust head with a track width of 20 μm (manufactured by Sony Corporation,
The shortest recording wavelength of 0.
Recording and reproduction were performed with a thickness of 5 μm, and still durability was measured.

Here, regarding the still durability, the signal was recorded on each sample tape under the condition of 20 ° C. and 60% RH,
Still reproduction was performed, and the time required for the reproduction output to decrease by 3 dB was evaluated. The still durability was evaluated for arbitrary 20 points of each sample tape.

Table 1 shows the calculated carbon film thickness d _{C of the} sample tapes 1 to 4 and the still durability evaluation results.

[0062]

[Table 1]

From Table 1, the thickness d _{C of the} carbon film is 2.0.
It can be seen that the sample tapes 2 to 4 having a thickness of not less than nm have sufficient durability to withstand normal use. From this, it is understood that the carbon film formed as the protective film of the magnetic recording medium needs to be controlled so that the film thickness d _C thereof becomes 2.0 nm or more.

Since such a thin film thickness d _C is in the range that cannot be measured by the microtome TEM, it is very effective to apply the present invention.

In practice, the kinetic energy of the photoelectrons of Co, which is the substrate material, and the kinetic energy of the photoelectrons of C, which is the thin film material, are not close to each other, so that the mean freedom of the photoelectrons of the substrate material in the thin film 2 is small. The process λ _so and the mean free path λ _oo of the photoelectrons of the thin film substance in the thin film 1 cannot be approximated and can be set as λ, and the above formula (7) cannot be transformed into the formula (8). . However, as shown in FIG. 2, ln [(I _C / I _Co ) / (I _C 0 / I _Co 0) +1]
Here, since the correlation between the known carbon film thickness d _C 'has a very high linearity, here,
The film thickness d _{C of the} carbon film was calculated by the above-mentioned formula (1).

A carbon film having a known film thickness d _C ′ prepared for calculating λ is a microtome TEM.
The film thickness was measured by. The measurement conditions by the microtome TEM at this time were as follows.

Measurement conditions Device: JEOL JEM-200CX Accelerating voltage: 200 kV Microtome setting section thickness: 100 nm However, if the film thickness is 4 nm or less, the microtome TE is used.
Since the film thickness cannot be measured by M, the microtome TEM
The film thickness was controlled by strictly setting the conditions based on the feeding speed of the carbon film having the film thickness that can be measured by, and then adjusting the feeding speed at the time of film formation.

[0068]

As is apparent from the above description, when the present invention is applied, it is possible to accurately measure the thickness of a carbon film even if the thickness is conventionally unmeasurable. Therefore, the thickness of the carbon film in the magnetic recording medium can be properly controlled.

Therefore, it is possible to obtain a carbon film having a durability required for practical use even if it is thin. And
The magnetic recording medium provided with such a carbon film has both excellent electromagnetic conversion characteristics and excellent durability, and can be used for higher density recording.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a principle of a film thickness measurement method by ESCA and showing a sample in which a thin film is formed on a substrate.

FIG. 2 ln [(I _C / I _Co ) / (I _C 0 / I _Co 0) +
1] A characteristic diagram showing the correlation between the calculated value of 1] and the known film thickness d _C ′ of the carbon film.

[Explanation of symbols]

 1 substrate 2 thin film

Claims (3)

[Claims] 1. A magnetic recording medium comprising a metal magnetic thin film and a carbon film having an unknown film thickness formed on a non-magnetic support, in measuring the film thickness d _{C of the} carbon film. The medium was observed by X-ray photoelectron spectroscopy, and the peak area intensity I _C corresponding to the 1s level of the carbon atom and the peak area intensity corresponding to the 2p level of the metal atom constituting the metal magnetic thin film were observed. I _M and a magnetic recording medium having a carbon film of 20 nm or more is observed by X-ray photoelectron spectroscopy to find a peak area intensity I _C corresponding to the 1 s level of carbon atom. For the step of measuring 0 and the magnetic recording medium on which the carbon film is not formed,
After the observation by X-ray photoelectron spectroscopy, the step of measuring the peak area intensity I _M 0 corresponding to the 2p level of the metal atoms constituting the metal magnetic thin film, and the step of calculating the value of the constant λ The film thickness d _C is calculated by substituting the measured values of I _C , I _M , I _C 0, and I _M 0, the calculated value of the constant λ, and the value of the photoelectron escape angle α into the following formula (1). A method for measuring the thickness of a carbon film, which comprises calculating. d _C = λ sin α · ln [(I _C / I _M ) / (I _C 0 / I _M 0) +1] (1) 2. The peak area intensity I corresponding to the 1s level of carbon atoms is observed by X-ray photoelectron spectroscopy on a plurality of magnetic recording media on which a carbon film having a known film thickness is formed. After measuring _C and the peak area intensity I _M corresponding to the 2p level of the metal atom constituting the metal magnetic thin film, ln was calculated using the already measured I _C 0 and I _M 0.
The value of [(I _C / I _M ) / (I _C 0 / I _M 0) +1] is calculated, and the value of λ sin α is obtained from the correlation between this calculated value and the known film thickness of the carbon film. The method for measuring the thickness of a carbon film according to claim 1, wherein the value of the constant λ is obtained by substituting the value of the photoelectron escape angle α. 3. The method for measuring the thickness of a carbon film according to claim 1, wherein when the metal magnetic thin film is made of a metal material mainly containing cobalt, a value of 1.8 is used as the constant λ.