JPH087257A - Method for evaluating film quality of carbon film and magnetic recording medium - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a new evaluation method for the quality of carbon film,
The DLC film formed as the protective film of the magnetic recording medium is evaluated and controlled by this method to obtain a magnetic recording medium excellent in abrasion resistance. [Configuration] measured Raman spectrum with argon ion laser excitation wavelength 515.7nm carbon film, and the main peak intensity including the fluorescence spectrum in the range of wave number 900 cm ^-1 in 1800 cm ^-1 B, the background due to fluorescence Intensity ratio B / A with main peak intensity A subtracted
The film quality is evaluated by (Raman fluorescence intensity ratio). By using a DLC film having a B / A value of 2 or more as a protective film by this evaluation method, a magnetic recording medium having excellent abrasion resistance can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium such as a magnetic disk mounted in a fixed magnetic disk device or the like, and more specifically, a method for evaluating the quality of a carbon film used as a protective film for the magnetic recording medium and its evaluation The present invention relates to a magnetic recording medium provided with a protective film having a film quality specified by the method.

[0002]

2. Description of the Related Art A fixed magnetic disk device is often used as an external storage device of an information processing device such as a computer. In a fixed magnetic disk device, information is recorded / reproduced by a magnetic head while rotating a magnetic disk, which is a magnetic recording medium. In that case, the magnetic head is normally operated when the device for recording / reproducing information is in operation. The magnetic head runs slightly above the rotating disk, and when the apparatus is stopped, the magnetic head comes into contact with the surface of the stopped disk to stop the CSS (Contact Start).
The Stop method is adopted.

In this system, the disk surface and the magnetic head are in a transient sliding state when the disk starts rotating and when the disk stops rotating. By repeating such sliding, the surface of the disk is abraded, and if the degree of abrasion is severe, the magnetic layer is damaged and a crash occurs. As a countermeasure, a protective film is formed on the magnetic layer for the purpose of improving the wear resistance of the disk, and a lubricating layer is provided on the protective film for the purpose of improving the lubricity. That is, as shown in FIG. 2, a magnetic disk is generally a thin-film magnetic layer made of a nonmagnetic metal underlayer such as a Cr underlayer 2 and a ferromagnetic alloy such as a Co alloy on both sides of a disk-shaped nonmagnetic substrate 1. 3, a protective film 4, and a lubricating layer 5 are sequentially formed and configured.

In a magnetic disk having an alloy thin film magnetic layer produced by a sputtering method, an amorphous carbon (aC) film formed by sputtering carbon in a pure Ar gas atmosphere is widely used as a protective film for the magnetic layer. Came. a-C
The protective film has sufficient abrasion resistance against a conventional Mn-Zn ferrite head (Vickers hardness of about 650),
It had good CSS resistance. However, recently, there is an increasing demand for higher recording density in fixed magnetic disk devices, and thin film heads and MIG heads have been used instead of Mn-Zn ferrite heads. Al ₂ O ₃ -TiC and Ca are used for the sliders of these heads.
Hard ceramic such as TiO ₃ (Vickers hardness about 2
However, since the a-C protective film has a lower hardness than these hard ceramics, it easily causes abrasion in a thin film head or a MIG head, and has a higher abrasion resistance. Has come to be required.

On the other hand, as an alternative to the aC protective film, carbon is sputter-deposited in a gas atmosphere in which CH ₄ or the like is mixed with Ar gas, and hydrogen is contained in the film to impart diamond property. Diamond-like carbon (D
It has been proposed to form an iamond Like Carbon (hereinafter referred to as DLC) film and use this film as a protective film, and its practical application is being promoted.

The DLC film exhibits various film qualities depending on the film forming conditions. When the DLC film has a certain specific film quality (film quality in which the proportion of the diamond-bonded state and the polymer-bonded state is higher than that of the graphite-bonded state), it is higher than that of the aC film. Since it has excellent abrasion resistance, it exhibits sufficient abrasion resistance even for thin film heads and MIG heads. However, in the case of other film quality, on the contrary, the abrasion resistance is lower than that of the aC film,
When the DLC film is used as a protective film for a magnetic recording medium because of its poor CSS resistance, the film quality is accurately evaluated.
It is necessary to manage the film quality properly.

The abrasion resistance of a film is mainly determined by its hardness and flexibility. The film quality of the DLC film as the protective film of the magnetic recording medium must also have appropriate values. The hardness of the film is measured by microhardness measurement with an indenter. On the other hand, the flexibility of the DLC film is related to the amount of hydrogen in the film, and it is known that the flexibility increases as the amount of hydrogen increases, and the amount is usually measured by IR spectrum analysis or the like.

DL as a protective film of the magnetic recording medium
As a method of evaluating the film quality of the C film, a method of directly measuring the friction coefficient after CSS is performed 20,000 times is used as an index for evaluating the CSS resistance. Further, as a film quality evaluation method of the DLC film, a method using Raman spectroscopy of the film is known. Figure 3 is a diagram showing an example of a Raman spectrum of DLC film, DLC wavenumber 900cm ^-1 ~1800cm ^-1
A peak peculiar to the film (DLC peak) is seen. FIG. 4 is an enlarged diagram showing the peak portion. For this peak portion, as shown in FIG. 5, the background due to fluorescence (fluorescence intensity) is removed by linear approximation for correction, and the Gaussian function is used. Waveform separation into two peaks, a graphite peak (G-peak) and a diamond peak (D-peak), using Raman shift of G-peak which is a high frequency side peak, intensity I _{g of} G-peak and low frequency. peak intensity to be at the peak of the side D- peak intensity I _d ratio I _d /
It is a method of compositionally evaluating the film quality based on I _g .

Further, by measuring the specific resistance of the film,
A method of compositionally evaluating the film quality is also known.

[0010]

The protective film of the magnetic recording medium is formed as a thin film having a film thickness of several hundred Å or less. Accurate micro hardness measurement of such a thin film is technically difficult. Further, the measurement of the amount of hydrogen in the film requires a large-scale device and requires a lot of time and cost. Therefore, it is not a good idea to evaluate and control the film quality based on the micro hardness and hydrogen content. Also, evaluation and management by measuring the friction coefficient require CSS 20,000 times each time, which is not preferable.

The method of compositionally evaluating the film quality by Raman spectroscopy of the film is highly accurate, and it is effective if it can be controlled by this method. However, between the Raman shift of the G-peak, which is an index for evaluating the film quality in terms of composition, and the hydrogen content, micro hardness, and friction coefficient of the film, which is an index for evaluating the film quality in terms of abrasion resistance. As shown in the relationship diagram with the friction coefficient in FIG. 6A, the relationship diagram with the minute hardness in FIG. 6B, and the relationship diagram with the hydrogen content in FIG. There is no relationship of one-to-one correspondence or monotonous increase / decrease,
Further, the index for evaluating the film quality in terms of the peak intensity ratio I _d / I _g and the wear resistance is also shown in FIG. 7 (a), which is a relational diagram with the friction coefficient, and FIG. 7 (b), the micro hardness. Relationship diagram, Fig. 7
As shown in the relationship diagram with the hydrogen content in (c), 1: 1
There is no correspondence or monotonous increase / decrease relationship. Therefore, G
Raman shift of the peak, or peak intensity ratio I _d /
It is not possible to maintain the wear resistance of the DLC protective film within an appropriate range by evaluating and managing I _g .

Conventionally, the evaluation and management of the film quality of the DLC protective film have been used as an index for evaluating the film quality compositionally with the amount of supplied CH ₄ (determined by the CH ₄ concentration, gas flow rate and discharge power density) during the protective film sputter deposition. , And the correlation between the amount of supplied CH ₄ and the index for evaluating the film quality in terms of abrasion resistance, and the appropriate range is defined from the correlation of both via this CH ₄ amount. The film quality control was difficult and complicated.

The present invention has been made in view of the above points, and a first object thereof is to easily evaluate the compositional quality of a carbon film and to evaluate the film quality in terms of abrasion resistance. It is an object of the present invention to provide a new film quality evaluation method having a one-to-one clear correlation with each index. A second object is to provide a magnetic recording medium excellent in wear resistance and CSS resistance, which has a carbon protective film whose range of compositional film quality evaluation index is specified from the viewpoint of wear resistance. .

[0014]

According to the present invention, the above object is to provide a method for evaluating the quality of a carbon film used as a protective film for a magnetic layer of a magnetic recording medium, wherein an argon ion having a wavelength of 514.5 nm is used for the protective film. Raman spectrum measurement by laser excitation is performed. Figure 1 is a diagram showing the range of wave numbers 900cm ^-1 ~1800cm ^-1 of the Raman spectrum obtained, fluorescence and the main peak intensity B containing the spectrum, the main peak obtained by subtracting the background by fluorescence This can be solved by evaluating the film quality of the carbon film by the intensity ratio B / A (Raman fluorescence intensity ratio) with the intensity A.

In this way, the strength ratio B / A which is a film quality evaluation index when evaluated by the above-mentioned carbon film film quality evaluation method.
By using a carbon film having a (Raman fluorescence intensity ratio) value of 2 or more as a protective film, it is possible to obtain a magnetic recording medium excellent in abrasion resistance and CSS resistance.

[0016]

The fluorescence intensity of the Raman spectrum of the DLC film is D
It depends on the size of the sp ² cluster (graphite structure portion) in the LC film or its distribution state (whether they are gathered together to some extent or individually and isolated as islands). Therefore, the Raman fluorescence intensity ratio B / A described above depends on the DLC film structure, that is, the composition, and can be an index for film quality evaluation. Further, since the micro hardness, hydrogen content, and friction coefficient of the DLC film also depend on this film structure, the Raman fluorescence intensity ratio B / A has a clear correlation with the wear resistance of the film.

[0017]

EXAMPLE In manufacturing the magnetic recording medium having the structure shown in FIG. 2, the DLC protective film is formed by sputtering a carbon target in a mixed gas atmosphere of Ar gas and CH ₄ . Supply C in the gas atmosphere during this sputtering
By controlling the amount of H _4, a magnetic recording medium was formed in which a DLC protective film having various Raman fluorescence intensity ratios B / A in Raman spectra excited by an argon ion laser having a wavelength of 514.5 nm was formed.

Regarding these magnetic recording media, Al ₂ O
The friction coefficient after CSS 20,000 times was measured using a thin film head using ₃ · TiC as a slider material, and the correlation with the Raman fluorescence intensity ratio B / A of the protective film was examined. The result is shown in the diagram of FIG. As seen in FIG. 8, a clear one-to-one correlation between B / A and the friction coefficient, which was not seen with I _d / I _g or G-peak Raman shift, is observed.
Therefore, by knowing the value of B / A as a film quality evaluation index, the friction coefficient after CSS 20,000 times can be known without performing CSS. It is understood from FIG. 8 that the friction coefficient needs to be 0.4 or less in order to obtain practically sufficient abrasion resistance, but for this purpose, the value of B / A is 2 or more.

Further, when the correlation between B / A of the protective film and the micro hardness and hydrogen content was examined, as shown in FIGS. 9 and 10, respectively, I _d / I _g and G-peak Raman shift were observed. There was a clear one-to-one correlation that was not seen between the two. Therefore, the micro hardness and the hydrogen content can be known by knowing the value of B / A as the film quality evaluation index. In order to obtain good wear resistance, a value of B / A of 2 or more is an appropriate range as described above, and the micro hardness is about 4 as shown in FIG.
It can be seen from FIG. 10 that the appropriate range is 0 GPa or less, and the hydrogen content is about 40 atomic% or more.

Furthermore, as described above, the specific resistance of the film is known as an index for evaluating the compositional film quality of the protective film. When the correlation between this specific resistance and B / A was examined, FIG.
As shown in the diagram, a clear one-to-one correlation is recognized, and in order to obtain good wear resistance, the specific resistance is about 10 ⁸ Ω · c.
It can be seen that m or more is a proper range. As described above, there is a one-to-one clear correlation between the Raman fluorescence intensity ratio B / A as the compositional film quality evaluation index of the protective film and each evaluation index of the abrasion resistance of the protective film. Therefore, DL measurement can be easily performed by measuring Raman spectrum of DLC film and obtaining B / A value.
The wear resistance of the C protective film can be evaluated.
By controlling the quality of the protective film so that the value is in the proper range, it becomes possible to obtain a magnetic recording medium having excellent wear resistance and CSS resistance.

[0021]

According to the present invention, the Raman spectrum of the carbon film used as a protective film for the magnetic layer of the magnetic recording medium is measured by exciting the protective film with an argon ion laser having a wavelength of 514.5 nm, and the wave number is measured. 900 cm
^-1 to a 1800 cm ^-1 wavenumber, a carbon film with an intensity ratio B / A (Raman fluorescence intensity ratio) of a main peak intensity B containing fluorescence in the spectrum and a main peak intensity A subtracting the background due to fluorescence To evaluate the film quality of. According to this method, the abrasion resistance of the film can be easily evaluated without measuring the microhardness and hydrogen content of the film. By setting the B / A value of the protective film to 2 or more in such a film quality evaluation method, a magnetic recording medium excellent in abrasion resistance and CSS resistance can be easily obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of Raman fluorescence intensity ratio B / A according to the present invention.

FIG. 2 is a schematic sectional view of a magnetic recording medium.

FIG. 3 is a diagram showing an example of a Raman spectrum of a DLC protective film.

FIG. 4 Wavenumber 900 of Raman spectrum of DLC protective film
enlarged view of the range of cm ^-1 ~1800cm ^-1

FIG. 5 is an explanatory diagram of a peak intensity ratio I _d / I _g of a Raman spectrum of a DLC protective film.

6 is a diagram showing the correlation between G-peak Raman shift and each wear resistance evaluation index, FIG. 6 (a) is a relationship diagram with a friction coefficient, and FIG. 6 (b) is a relationship with micro hardness. Figure, Figure 6 (c) is the relationship diagram with hydrogen content

7 is a diagram showing a correlation between I _d / I _g and each wear resistance evaluation index, and FIG. 7 (a) is a relational diagram with a friction coefficient, FIG.
FIG. 7B is a relationship diagram with micro hardness, and FIG. 7C is a relationship diagram with hydrogen content.

FIG. 8 is a diagram showing the relationship between the Raman fluorescence intensity ratio B / A and the friction coefficient.

FIG. 9 is a diagram showing a relationship between Raman fluorescence intensity ratio B / A and micro hardness.

FIG. 10 is a graph showing the relationship between Raman fluorescence intensity ratio B / A and hydrogen content.

FIG. 11 is a diagram showing the relationship between the Raman fluorescence intensity ratio B / A and the specific resistance of the film.

[Explanation of symbols]

 1 non-magnetic substrate 2 non-magnetic metal underlayer 3 magnetic layer 4 protective film 5 lubrication layer

Claims (2)

[Claims] 1. A method for evaluating the quality of a carbon film used as a protective film for a magnetic layer of a magnetic recording medium, comprising a wavelength of 51
Raman spectrum excited by 4.5 nm argon ion laser was measured and the wave number was from 900 cm ^-1 to 180.
To evaluate the film quality of the carbon film by the intensity ratio B / A (Raman fluorescence intensity ratio) between the main peak intensity B containing fluorescence within the range of 0 cm ^-1 and the main peak intensity A from which the background due to fluorescence is subtracted. A method for evaluating film quality of a carbon film, comprising: 2. A magnetic recording having a carbon film as a protective film having an intensity ratio B / A (Raman fluorescence intensity ratio) of 2 or more when evaluated by the film quality evaluation method of the carbon film according to claim 1. Medium.