JP5394552B2 - Substrate for perpendicular magnetic recording medium and magnetic recording medium - Google Patents

Description

  The present invention relates to a method for inspecting a perpendicular magnetic recording medium substrate, a method for producing a perpendicular magnetic recording medium substrate, and a method for producing a perpendicular magnetic recording medium.

In recent magnetic recording apparatuses represented by HDD (Hard Disk Drive), a 2.5-inch diameter magnetic disk is required to have an information storage capacity exceeding 80 GB per sheet. In order to meet these requirements in a magnetic disk that is a magnetic recording medium for HDD, it is required to realize an information storage density exceeding 100 Gbits (100 Gbit / inch ² ) per square inch. In order to perform stable recording and reproduction at such a high recording density, it is considered desirable to adopt a perpendicular magnetic recording system as a magnetic recording and reproducing system. In a perpendicular magnetic recording medium used in the perpendicular magnetic recording system, for example, a magnetic layer such as a soft magnetic layer and a magnetic recording layer is formed on a substrate.

  In the perpendicular magnetic recording medium, it is necessary to control the magnetic anisotropy of the magnetic particles contained in the magnetic layer in order to improve the electromagnetic conversion characteristics. For example, giving magnetic anisotropy in the circumferential direction of the substrate to the magnetic particles in a plane parallel to the main surface of the substrate is not preferable because it causes noise. Further, for example, in the soft magnetic layer, it is not preferable that the magnetic anisotropy is directed in the circumferential direction because it causes noise.

  Here, it is considered that the magnetic anisotropy of the magnetic particles in the magnetic layer is influenced by the fine structure on the substrate surface. Therefore, in order to reduce the magnetic anisotropy in the in-plane direction, it is desired to appropriately control the fine structure of the substrate surface. Further, in order to control the fine structure of the substrate surface, it is necessary to evaluate the surface shape of the substrate using an appropriate index.

  2. Description of the Related Art Conventionally, there is known a method for evaluating the surface shape of a magnetic recording medium substrate that performs magnetic recording in the longitudinal recording method, using an index called linear density or line density (hereinafter referred to as LD) (for example, LD). Patent Documents 1 and 2). The LD is the number of texture peaks (or valleys) present per 1 μm in a cross-sectional view in the radial direction depth direction of the substrate obtained by measuring the substrate main surface with an AFM (atomic force microscope), for example. Number), or half the number of times it intersects the reference line. In a magnetic recording medium that performs magnetic recording for the longitudinal recording method, it is considered that the higher the LD of the substrate, the better the electromagnetic conversion characteristics.

  However, the evaluation by LD is used when an infinite number of minute grooves called textures are formed on the main surface of the magnetic recording medium substrate. This texture facilitates crystal growth along the grooves, thereby making it easy to orient the easy axis of magnetization of the magnetic particles in the circumferential direction.

  In contrast, in a perpendicular magnetic recording medium in which it is desirable to reduce the magnetic anisotropy in the in-plane direction, it is not always necessary to form a texture on the substrate. Therefore, when LD is used as an index, there is a possibility that the perpendicular magnetic recording medium substrate cannot be properly evaluated.

  Further, the cross section of the surface of the substrate is not composed of simple peaks and valleys, and the height depth and width are not uniform. Therefore, the value of LD changes depending on how high, deep, or width the shape is determined as a mountain or a valley. Therefore, it can be said that the definition of LD includes ambiguity. Also, if the LD value itself changes depending on the definition, it is difficult to use as an absolute index.

  For this reason, it is desired to evaluate the surface shape of the perpendicular magnetic recording medium substrate using a more appropriate index. It is also desirable to provide a perpendicular magnetic recording medium substrate or a perpendicular magnetic recording medium that has been inspected by evaluation using an appropriate index. An object of the present invention is to provide a method for inspecting a perpendicular magnetic recording medium substrate, a method for producing a perpendicular magnetic recording medium substrate, and a method for producing a perpendicular magnetic recording medium that can solve the above-described problems.

  The inventor of the present application has intensively studied that the fine structure of the substrate surface that affects the magnetic anisotropy of the magnetic particles includes not only the number or density of peaks and valleys on the substrate surface, but also the width of the peaks and valleys. I found it important. And it discovered that it was effective to use the parameter | index which carried out the Fourier transform of the waveform of the cross-sectional shape of a board | substrate as a parameter | index reflecting the width | variety of a peak or a valley. And based on these knowledge, it came to this invention. The present invention has the following configuration.

  (Configuration 1) A perpendicular magnetic recording medium substrate inspection method for inspecting the shape of a perpendicular magnetic recording medium substrate used for manufacturing a perpendicular magnetic recording medium for recording information by a perpendicular magnetic recording method, wherein a main surface is polished. The cross-sectional waveform is measured to measure the cross-sectional shape of the disc-shaped substrate, and the waveform of the cross-sectional shape measured in the cross-sectional shape measurement step is Fourier transformed to convert the waveform of the cross-sectional shape into a relationship between wavelength and intensity. A Fourier transform stage, and a determination stage for judging pass / fail of the substrate based on the relationship between the wavelength and the intensity obtained in the Fourier transform stage. In the Fourier transform stage, for example, the Fourier transform is performed using a window function according to the necessity to multiply the waveform of the cross-sectional shape.

  The window function is a function that becomes 0 outside a certain finite interval. When another function or signal (data) is multiplied by a window function, the outside of the interval becomes 0 and only the finite interval remains, so that numerical analysis becomes easy. In Configuration 1, for example, a rectangular window function or a Hamming window function can be used as the window function.

  In this case, in the relationship between the wavelength and the intensity obtained by Fourier transform, the wavelength reflects, for example, the width of a peak or valley included in the cross-sectional shape measured in the cross-sectional shape measurement stage. The intensity reflects the number of peaks and valleys with a width corresponding to each wavelength. Therefore, for example, when there are many peaks and valleys with a small width, the intensity of the small wavelength region is increased. In addition, when there are many peaks and valleys with a large width, the intensity in a large wavelength region increases.

  Thereby, for example, as the fine structure of the substrate surface, not only the number and density of peaks and valleys but also the number and density of peaks and valleys having a specific width can be grasped. In the determination stage, evaluation based on the number and density of peaks and valleys having a specific width can be performed.

  Therefore, according to Configuration 1, the surface shape of the substrate for the perpendicular magnetic recording medium can be determined by a more appropriate index reflecting the width of the peaks and valleys of the substrate surface, and the number and density of peaks and valleys of a specific width. Can be evaluated. For example, by performing an inspection based on this evaluation, for example, a perpendicular magnetic recording medium having a magnetic recording layer with a small magnetic anisotropy in the in-plane direction can be appropriately manufactured. Thereby, the electromagnetic conversion characteristics of the magnetic recording layer can be appropriately enhanced.

  In the cross-sectional shape measurement step, the cross-sectional shape is measured by, for example, an atomic force microscope (AFM). This measurement is preferably performed with measurement accuracy including 256 or more sampling points per 1 μm. The resolution required for the measurement depends on the crystal grain size of the magnetic particles in the magnetic recording layer, but if measured with such accuracy, the measurement can be performed with sufficient accuracy without increasing the cost required for the measurement.

  The measured wavelength of the entire range is, for example, a range not less than the lower limit value of the measurable range and not more than the upper limit value that is meaningful in measurement. When measurement is performed using the AFM in the cross-sectional shape measurement stage, the upper limit value meaningful in measurement is, for example, a wavelength that is ¼ of the measurement length in the cross-section shape measurement stage. This is because in the measurement by the AFM, the wavelength component of ¼ or more of the measurement length changes depending on factors such as flatness correction and does not reflect the true surface shape.

  Further, the measured wavelength in the entire range may be, for example, 0.6 to 120 times the average particle diameter of the magnetic particles contained in the magnetic layer or the soft magnetic layer. Even in this case, for example, the shape of the substrate surface that is highly likely to affect the magnetic anisotropy of the magnetic particles can be appropriately evaluated. The average particle size of the magnetic particles is, for example, an arbitrary 50 nm × 50 nm region is selected from a TEM photograph taken at 2 million times, and individual magnetic particles contained in the region are extracted, and the average of the major axis and minor axis of each is selected. It can be obtained by calculating the value. The individual magnetic particles included in the region are, for example, magnetic crystal particles in which the entire particle is a single crystal.

  The average particle diameter of the magnetic particles may be a predicted value that is considered to be calculated in the magnetic layer formed on the substrate. This predicted value can be obtained, for example, by preparing a sample in which a magnetic layer is formed on a substrate and performing the above calculation.

  (Configuration 2) Based on the relationship between the wavelength and the intensity obtained in the Fourier transform stage, the entire range integrated value, which is a value obtained by integrating the intensity for the measured wavelength range, and the preset wavelength range An integration stage is further provided for calculating a set range integral value that is a value obtained by integrating the intensity with respect to. The determination stage determines pass / fail of the substrate based on a ratio of the set range integral value to the entire range integral value.

  In this case, the set range integral value is a value reflecting the number of peaks and valleys of a specific range width, for example. The ratio of the set range integral value to the total range integral value is a value reflecting the ratio of the number of peaks and valleys of a specific range width to the total number of peaks and valleys in the measurement region, for example.

  The influence on the magnetic anisotropy (orientation) of the magnetic particles is considered to be particularly large when the width of the peaks and valleys on the substrate surface is within a certain range. For example, when the width of the peaks and valleys is smaller than a certain range, the number of magnetic particles growing on the peaks and valleys is reduced, so that the contribution to the control of the magnetic anisotropy of the magnetic particles is considered to be small. In addition, when the width of the peaks and valleys is larger than a certain range, the peaks and valleys are considered to be close to a flat region for the magnetic particles, and it is considered difficult to exhibit the function of controlling the magnetic anisotropy of the magnetic particles.

  Therefore, in this way, it is possible to appropriately evaluate the ratio of peaks and valleys that have a large influence on the magnetic anisotropy of magnetic particles. This also makes it possible to more appropriately evaluate the surface shape of the perpendicular magnetic recording medium substrate.

  In addition, it is thought that the influence on the magnetic anisotropy of a magnetic particle becomes large especially when the width | variety of a peak or a valley is 1-3 times the average particle diameter of a magnetic particle, for example. Therefore, it is preferable that the integration step calculates a set range integral value for a wavelength range corresponding to 1 to 3 times the average particle diameter of the magnetic particles. In the determination step, for example, when the ratio of the set range integral value to the total range integral value is equal to or less than a preset value, it is determined that the substrate is acceptable.

  Moreover, it is preferable that the cross-sectional shape measurement step measures a cross-sectional shape along the radial direction of the substrate. In this way, it is possible to appropriately evaluate the shapes of peaks and valleys that have a large influence on the magnetic anisotropy in the circumferential direction of the substrate. Thereby, the magnetic anisotropy in the circumferential direction of the substrate can be appropriately reduced.

  (Configuration 3) A method for manufacturing a substrate for a perpendicular magnetic recording medium used for a perpendicular magnetic recording medium that records information by a perpendicular magnetic recording method, and a preparation step of preparing a disk-shaped substrate having a main surface polished; An inspection step of inspecting the substrate prepared in the preparation step by the method for inspecting a perpendicular magnetic recording medium substrate according to Configuration 1 or 2. In this way, for example, the same effects as those of Configuration 1 or 2 can be obtained. In addition, it is possible to appropriately manufacture a perpendicular magnetic recording medium substrate in which in-plane magnetic anisotropy hardly occurs in the magnetic layer formed on the main surface.

  The inspection process is not necessarily a process for inspecting all the substrates. For example, the inspection process may be a sampling inspection for inspecting a part of the substrates for every predetermined number of substrates, or an inspection step performed at regular intervals in order to maintain quality.

  (Structure 4) A method of manufacturing a perpendicular magnetic recording medium for recording information by the perpendicular magnetic recording method, wherein the perpendicular magnetic recording medium substrate manufactured by the method for manufacturing a perpendicular magnetic recording medium substrate according to Structure 3 is used. At least a magnetic recording layer is formed. In this way, a perpendicular magnetic recording medium having a small magnetic anisotropy in the in-plane direction can be appropriately manufactured. Thereby, the electromagnetic conversion characteristics of the magnetic recording layer can be appropriately enhanced.

  According to the present invention, for example, the surface shape of a perpendicular magnetic recording medium substrate can be evaluated using a more appropriate index.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the configuration of a perpendicular magnetic recording medium 10 according to an embodiment of the present invention. The perpendicular magnetic recording medium 10 is a magnetic disk used in a perpendicular magnetic recording type HDD, and includes a substrate 12, a soft magnetic layer 14, and a magnetic recording layer 16. The substrate 12 is a disk-shaped glass substrate having a circular hole in the center. This glass substrate is, for example, an aluminosilicate amorphous glass substrate. The main surface of the substrate 12 and the inner and outer peripheral end surfaces are polished to a predetermined surface roughness.

  The soft magnetic layer 14 and the magnetic recording layer 16 are magnetic layers formed on the substrate 12. The soft magnetic layer 14 is a layer that forms a magnetic circuit between the magnetic recording layer 16 and the magnetic head of the HDD, and includes, for example, magnetic particles having an average particle diameter of 7.5 to 8.5 nm. The magnetic recording layer 16 is a layer containing hard magnetic particles such as CoCrPt. The magnetic recording layer 16 may be a layer having a granular structure in which magnetic particles are dispersed in a matrix of an oxide such as TiO 2. The magnetic recording layer 16 includes, for example, magnetic particles having an average particle diameter of 7.5 to 8.5 nm.

  Although omitted for the sake of simplicity in the above description, the perpendicular magnetic recording medium 10 is provided between the substrate 12 and the soft magnetic layer 14, between the soft magnetic layer 14 and the magnetic recording layer 16, or the magnetic recording layer. Further layers may be provided on 16. For example, the perpendicular magnetic recording medium 10 may further include an orientation control layer for controlling the crystal orientation of the magnetic recording layer 16 between the soft magnetic layer 14 and the magnetic recording layer 16. Further, a protective layer, a lubricating layer, or the like may be further provided on the magnetic recording layer 16. The soft magnetic layer 14 may be amorphous.

  FIG. 2 is a flowchart showing an example of a method for manufacturing the substrate 12. In this example, the manufacturing method first prepares a disk-shaped substrate whose main surface and inner and outer peripheral end faces are polished to a predetermined surface roughness (preparation step S102).

  Subsequently, the shape of the substrate prepared in the preparation step S102 is inspected (inspection step S104). In this example, the inspection step S104 first measures the cross-sectional shape of the substrate 12 along the radial direction by, for example, an atomic force microscope (AFM) (cross-sectional shape measurement step S202).

  When AFM is used, a roughness curve for each scanning line can be obtained in accordance with, for example, JIS B0601. Therefore, if the AFM is used, the cross-sectional shape of the substrate 12 can be measured appropriately and with high accuracy. This measurement is preferably performed with measurement accuracy including 256 or more sampling points per 1 μm. If the measurement is performed with such accuracy, the measurement can be performed with sufficient accuracy without increasing the cost required for the measurement.

  The measurement of the cross-sectional shape may be a measurement performed on a partial region of the main surface of the substrate 12. In the cross-sectional shape measurement step S202, for example, the cross-sectional shape is measured for a measurement region of 500 nm extending in the radial direction of the substrate 12.

  Next, the cross-sectional waveform is converted into the relationship between the wavelength and the intensity by Fourier transforming the measured cross-sectional waveform (Fourier transform step S204). The Fourier transform step S204 performs Fourier transform, for example, by fast Fourier transform (FFT). Fast Fourier transform is an algorithm for calculating discrete Fourier transform (DFT) at high speed on a computer. As the window function of the Fourier transform, for example, a rectangular window function or a Hamming window function is used.

  Next, with respect to the relationship between the obtained wavelength and intensity, an operation for integrating the intensity with the wavelength is performed (integration step S206). In this example, the integration step S206 includes a total range integrated value that is a value obtained by integrating the intensity over the measured wavelength range and a set range integration that is a value obtained by integrating the intensity over a preset wavelength range. Value.

  Next, the set range integral value is normalized by calculating the ratio of the set range integral value to the entire range integral value. Then, it is determined whether the substrate 12 is acceptable based on the standardized set range integral value (determination step S208). According to this example, for example, the shape of the substrate 12 can be appropriately evaluated in consideration of the ratio of peaks and valleys that have a large influence on the magnetic anisotropy (orientation) of the magnetic particles. Thereby, evaluation of the surface shape of the board | substrate 12 can be performed using a suitable parameter | index.

  In the present example, the integration step S206 has a wavelength range for obtaining the set range integral value of 1 to 3 times the average particle diameter of the magnetic particles contained in the soft magnetic layer 14 to be formed on the substrate 12. The wavelength range is used. This average particle diameter can be calculated as a predicted value of the average particle diameter by, for example, preparing a sample in which the soft magnetic layer 14 is formed on the substrate 12 in advance. When the soft magnetic layer 14 is amorphous, a wavelength range of 1 to 3 times the average particle diameter of the magnetic particles contained in the magnetic recording layer 16 can be used.

  When such a range of wavelengths is used, the ratio of the set range integral value to the total range integral value is such that peaks and valleys with a width that easily gives magnetic anisotropy to the magnetic particles of the soft magnetic layer 14 and the magnetic recording layer 16. It is thought that the ratio of For example, when this ratio is large, it is considered that the ratio of peaks and valleys having a width that easily gives magnetic anisotropy to magnetic particles is large.

  Therefore, in this example, the determination step S208 determines that the substrate 12 is acceptable when, for example, the ratio of the set range integral value to the total range integral value is equal to or less than a preset reference value. This reference value is 0.3, for example. In this way, for example, the substrate 12 having a large ratio of peaks and valleys with a width that easily gives magnetic anisotropy to the magnetic particles can be rejected. Thereby, for example, the shape of the substrate 12 can be appropriately controlled, and the magnetic anisotropy of the soft magnetic layer can be maintained in the radial direction.

(Example)
Hereinafter, an example of a method for evaluating the surface shape of the substrate 12 will be described in more detail with reference to examples. As the substrate 12 according to Example 1, an aluminosilicate amorphous glass substrate was prepared. The substrate 12 is a 2.5-inch magnetic disk substrate having a diameter of 65 mm, an inner diameter of 20 mm, and a disk thickness of 0.635 mm. Then, AFM was performed with a measurement accuracy of 256 points / 1 μm for a measurement region of 500 nm extending in the radial direction of the substrate 12. Further, Fourier transform was performed on the cross-sectional waveform obtained by this measurement using a Hamming function as a window function.

  FIG. 3 is a graph illustrating the result of Fourier transform on the substrate 12 according to the first embodiment. By comparing this result with, for example, a determination criterion prepared in advance, the surface shape of the substrate 12 can be evaluated in consideration of the widths of peaks and valleys on the surface of the substrate 12. For example, the substrate 12 can be inspected by performing the integration step S206 and the determination step S208 described with reference to FIG.

  In the first embodiment, when the integral value of the entire range is calculated in the integration step S206, the lower limit wavelength of the measured wavelength range is the distance between sampling points (3 (3 points) at a measurement accuracy of 256 points / 1 μm. .9 nm) to 4 nm. The upper limit wavelength is 125 nm (excluding 125 nm), which is a quarter of the length of the measurement region of 500 nm. This is because, in AFM measurement, a wavelength component that is ¼ or more of the measurement length varies depending on factors such as flatness correction during measurement and does not reflect the true surface shape. Therefore, it is preferable to calculate the total range integral value for a wavelength range of 4 nm or more and less than 125 nm.

  Further, when calculating the set range integral value, a wavelength range of 1 to 3 times the average particle diameter of the magnetic particles contained in the soft magnetic layer 14 to be formed on the substrate 12 is used. For example, when the average radius of the magnetic particles contained in the soft magnetic layer 14 can be predicted to be 8 nm, a wavelength range of 8 to 24 nm is used as a wavelength range for calculating the setting range integral value. In this way, it is possible to appropriately consider the ratio of peaks and valleys that have a large influence on the magnetic anisotropy of the magnetic particles in the fine structure of the surface of the substrate 12.

  When integration was performed in the above wavelength range, in Example 1, the total range integrated value was 4.14, and the set range integrated value was 1.07. As a result, the ratio of the set range integral value to the entire range integral value was 0.26.

  In the determination step S208, the pass / fail of the substrate 12 is determined by comparing this ratio with a reference value (for example, 0.3). Thereby, it is possible to appropriately determine the substrate 12 in which the magnetic anisotropy in the circumferential direction of the substrate hardly occurs in the magnetic layer formed on the main surface. Therefore, according to Example 1, the surface shape of the substrate 12 can be appropriately evaluated.

  Further, when the soft magnetic layer 14 was formed on the substrate 12 of Example 1 and the magnetic anisotropy of the soft magnetic layer was measured, it was oriented in the radial direction. For this reason, it was confirmed that the magnetic anisotropy in the circumferential direction of the substrate can be appropriately controlled by using the substrate 12 determined to be acceptable in the determination step S208.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

  The present invention can be suitably used, for example, for a perpendicular magnetic recording medium substrate.

1 is a cross-sectional view showing an example of the configuration of a perpendicular magnetic recording medium 10 according to an embodiment of the present invention. 5 is a flowchart showing an example of a method for manufacturing the substrate 12. 6 is a graph showing the result of Fourier transform on the substrate 12 according to Example 1;

DESCRIPTION OF SYMBOLS 10 ... Perpendicular magnetic recording medium, 12 ... Substrate, 14 ... Soft magnetic layer, 16 ... Magnetic recording layer

Claims (5)

A perpendicular magnetic recording medium substrate used for manufacturing a perpendicular magnetic recording medium for recording information by a perpendicular magnetic recording method,
A disk-shaped substrate whose main surface is polished,
No texture is formed on the main surface,
The cross-sectional shape of the main surface of the substrate is measured, and the waveform of the cross-sectional shape thus measured is Fourier transformed to convert the waveform of the cross-sectional shape of the main surface into a relationship between wavelength and intensity, and obtained by Fourier transform. Based on the relationship between the measured wavelength and intensity, an integrated value of the entire range, which is a value obtained by integrating the intensity with respect to the measured wavelength range, and a value obtained by integrating the intensity with respect to a preset wavelength range. When the set range integral value is calculated, the ratio of the set range integral value to the total range integral value is 0.3 or less,
The wavelength of the entire range is a wavelength in the range of 4 nm or more and less than 125 nm,
The perpendicular magnetic recording medium substrate according to claim 1, wherein the wavelength range for calculating the set range integral value is a wavelength range of 8 to 24 nm. The perpendicular magnetic recording medium substrate according to claim 1 , wherein the perpendicular magnetic recording medium substrate is used for manufacturing a perpendicular magnetic recording medium having a soft magnetic layer. The perpendicular magnetic recording medium substrate according to claim 1 or 2, wherein the material of said substrate is glass. 4. The perpendicular magnetic recording medium substrate according to claim 3 , wherein the glass is amorphous aluminosilicate glass. On the substrate for a perpendicular magnetic recording medium according to any one of claims 1 to 4, a magnetic recording medium characterized by forming at least a magnetic layer.

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