JP2010027142A - Method for manufacturing substrate for information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a substrate for an information recording medium which satisfies requirements of contradictory thermal characteristics of low effective thermal conductivity upon temperature increase and high effective thermal conductivity upon temperature decrease, and static and dynamic mechanical strength of high resistance to circular transverse rupture and high resistance to impact and drop. <P>SOLUTION: The method for manufacturing a substrate for an information recording medium includes: (a) a step of preparing a silicon single crystal support which has a disk shape having a central hole and which includes a main flat surface, a substrate inner circumference part adjacent to the central hole, and a substrate outer circumference part positioned at the opposite side of the main flat surface with respect to the substrate inner circumference part; and (b) a step of supplying an oxidizing gas to the substrate inner circumference part, heating the silicon single crystal support in a state where an inert or reducing gas is supplied to the main flat surface and the substrate outer circumference part, and selectively forming a SiO<SB>2</SB>film on the substrate inner circumference part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing an information recording medium substrate. The substrate for an information recording medium manufactured by the method of the present invention is used for a magnetic recording medium mounted on various magnetic recording devices including an external storage device of a computer.

  With the recent increase in recording density of magnetic disks, the magnetic recording method has shifted from the conventional in-plane recording method (longitudinal recording method) to the perpendicular recording method. With the development of the perpendicular recording method, the recording density has been dramatically improved. In the in-plane recording method, the recording density peaked at 100 gigabits (Gb) / in 2, but now it exceeds 400 Gb / in 2. Yes. However, the first generation simple perpendicular recording method has a limit of 400 Gb / in 2. This is because, in order to increase the recording density, the bit size must be made smaller. On the other hand, if the bit size is made smaller, bit deterioration due to thermal fluctuation, that is, random magnetization reversal tends to occur. It is. In order to avoid the deterioration of the bit due to such thermal fluctuation, it is an essential condition to satisfy the following expression (1).

In equation (1), _Ku is the magnetocrystalline anisotropy energy constant, V is the volume per bit of the magnetic recording layer, k is the Boltzmann constant, and T is the absolute temperature. The left side of equation (1) is called the thermal stability index.

When the bit size is reduced, the volume V inevitably decreases. In order to overcome the instability of thermal fluctuation, it is necessary for the thermal stability index to satisfy equation (1) against the decrease in volume V. If the working temperature is constant, in order to increase the thermal stability index, it is necessary to increase the value of the magnetocrystalline anisotropy energy constant K _{u. Ku} is a constant depending on the substance, and has a relationship as shown in equation (2).

In formula (2), H _c represents coercive force, Ms represents saturation magnetization, and N _z and N _y represent demagnetizing field coefficients in the z direction and y direction, respectively.

From equation (2), it can be seen that the coercive force _{H c} is proportional to _{K u.} That is, when selecting a substance having high K _u trying overcome the thermal fluctuation as described above, also increases the holding force H _c representing the intensity of the reversal magnetic field of the magnetization, magnetization reversal due Thus the magnetic head is difficult Become. That is, a phenomenon that makes it difficult to write information occurs. Thus, it provided by reduction in volume accompanying the densification, for the trade-off relationship of the "long-term stability of the recording by the thermal fluctuation" and "difficulty in recording due to high H _c of" conventional efforts As a result, it was not possible to find a solution for further increasing the recording density.

  Recently, methods for overcoming the aforementioned trade-off relationship have been proposed. Among them, there is a heat assist recording method as an effective method. (See Patent Documents 1 and 2).

The heat-assisted recording method solves the problem of “long-term stability of recording due to thermal fluctuation” by using the above-mentioned trade-off state as a breakthrough for solving “recording difficulty due to high Hc”. Specifically, when writing information to a magnetic recording medium using a high _Ku material by a magnetic head, the magnetic recording medium is heated by irradiating light for a short time, and the Hc of the recording medium is reduced for a short time. By doing so, writing is possible even in a low magnetic field. Long-term stability due to thermal fluctuation can be ensured by cooling to the reading temperature again in a short time so that the bit does not deteriorate due to thermal fluctuation.

  As described above, research and development of a prototype heat-assisted recording method as a next-generation perpendicular recording method has started, and it is suggested that the recording density may exceed 1 terabit (Tb) / square inch in principle (non-patented). Reference 1). Thus, the heat-assisted recording method has a great potential in principle, and has been positioned as a promising candidate for the next-generation perpendicular recording method. However, various problems have been found as detailed investigations toward practical application have progressed.

  One problem is the substrate. At present, substrates actually used as substrates for magnetic recording media are aluminum substrates and glass substrates. The aluminum substrate has a surface of an aluminum base material plated with about 10 μm of NiP, and is mainly used for a desktop PC or a stationary HDD recorder. Glass substrates include amorphous substrates and crystallized glass substrates, both of which are used for mobile applications such as notebook PCs. In addition, a silicon single crystal substrate has been proposed (see Patent Documents 3 and 4), although the practical use is not progressing.

  When writing with a magnetic head in the heat-assisted recording method, the desired recording area is instantaneously and locally heated by light irradiation, and light irradiation is terminated simultaneously with the end of writing, and then the recording area is rapidly cooled to the operating temperature. It is desirable that In order to establish such a behavior, the characteristics required of the substrate when the temperature is raised are required to have low thermal conductivity. That is, in order to achieve a local and rapid temperature increase with a small amount of energy when the temperature is raised, it is desirable not to raise the temperature as much as possible except for the intended location. For this reason, it is desirable that the thermal conductivity is small. On the other hand, the characteristics required of the substrate during cooling are required to have high thermal conductivity. In other words, during cooling, it is desirable to cool down to the operating temperature as quickly as possible so that the information written in the minute part of the temperature rise can exist stably. A material with high conductivity is required.

  The thermal conductivity is a numerical value specific to the material, the thermal conductivity of glass is 1.8 W / (m · K), the thermal conductivity of aluminum is 230 W / (m · K), and the thermal conductivity of NiP. The rate is 5.0 W / (m · K), and the thermal conductivity of the silicon single crystal is 126 W / (m · K). Thus, since the thermal conductivity of NiP and glass is very small compared to a metal such as aluminum, the NiP plated aluminum substrate and the glass substrate show excellent performance when the temperature of the heat-assisted recording method is raised, and the recording density Shows a temperature rise performance such that exceeds 1 Tb / square inch. However, since both the NiP film and the glass substrate have a low thermal conductivity, the desired performance cannot be exhibited during cooling by the heat-assisted recording method. Specifically, when writing / reading was continued, the temperature of the magnetic recording layer could not be lowered sufficiently, and the written information became unstable over time.

  Also, mechanical strength is one of important characteristics required for an information recording medium substrate. A NiP-plated aluminum substrate conventionally used as an information recording medium substrate is not easily broken because aluminum has high strength. For glass substrates that are susceptible to brittle fracture, mechanical strength can be obtained by using (1) a method using crystallized glass or (2) a method called chemical strengthening to induce compressive stress on the substrate surface. Is ensured.

  On the other hand, the silicon substrate is also a brittle material like glass, and is particularly a single crystal, so that cracks are likely to occur along the cleavage plane. One of the mechanical strengths of an information recording medium substrate is called ring bending strength. The ring bending strength simulates the mechanical strength when the inner periphery of the medium is clamped when the information recording medium is incorporated into a hard disk drive (HDD). In the HDD, the information recording medium is clamped on the inner periphery, and therefore, when an excessive force is applied to the medium, destruction proceeds from the inner peripheral end surface. When a stress is applied to a brittle material such as a glass substrate and a silicon substrate, the stress is concentrated on the tip of a crack existing on the surface. Therefore, the degree of cracks formed in the coring process of making holes in the substrate affects the ring bending strength, and there is a possibility that a substrate with extremely weak strength can be obtained according to the crack depth distribution. In order to avoid this, the annular bending strength has been enhanced by polishing the inner and outer peripheral end faces of the substrate and removing cracks after the coring and end face chamfering steps.

  Recently, HDDs are increasingly used for mobile applications such as notebook computers. For this reason, it is demanded that the HDD is not easily destroyed even when it is dropped, and the information recording medium substrate is also required to have high impact drop strength in addition to the above-mentioned annular bending strength. Yes. In the impact drop strength test, an HDD incorporating an information recording medium is fixed to a drop impact test apparatus, and an acceleration of a peak value of 1000 G is usually applied for a duration of about 1 ms to check whether the substrate is destroyed. The aforementioned annular bending strength test is a quasi-static destructive test in which a force is slowly applied to the inner periphery of the substrate to check that the substrate is broken. On the other hand, the drop impact test is a dynamic destructive test in which the substrate vibrates and the force is applied to the inner peripheral clamp portion over multiple times within about 1 ms when acceleration is applied. Accordingly, a material having a high annular bending strength does not necessarily have a high drop impact strength. For example, a silicon substrate with a nominal value of 2.5 inches has an annular bending strength of 280 N, which is higher compared to 150 N of a glass substrate with a nominal value of 2.5 inches. However, in the drop impact test with an acceleration of 1000 G × 1 ms, the fracture probability of the glass substrate is zero, whereas the silicon substrate has a high fracture probability of 30%. Therefore, improvement of impact drop strength is one of the problems of the silicon substrate.

JP 2006-12249 A Japanese Patent Laid-Open No. 2003-4504 JP 59-8141 A JP 59-96539 A FUJITSU, Vol. 58, No.1, pp.85-89 (2007) Jpn. J. Appl. Phys. Vol.42, No.12, pp.7250-7255 (2003)

  As described above, in realizing the magnetic recording medium of the heat-assisted recording system, (a) in order to achieve both the ease of recording and the stability of the recorded bit, the low effective thermal conductivity at the time of temperature rise and Requirement to have contradictory thermal properties of high effective thermal conductivity when the temperature is lowered, and (b) to achieve both static and dynamic mechanical strength of high annular bending strength and high impact drop strength There is a need for an information recording medium substrate that satisfies the above requirements.

  Furthermore, when forming the constituent layers of the magnetic recording medium, a bias voltage may be applied for the purpose of ensuring the adhesion strength of the constituent layers and improving the magnetic characteristics of the magnetic recording medium. Therefore, the information recording medium substrate is also required to have (c) a configuration and conductivity capable of freely applying a bias voltage.

  The subject of this invention is providing the manufacturing method of the board | substrate for information recording media which satisfy | fills all the characteristics of above-mentioned (a)-(c).

The method for manufacturing a substrate for an information recording medium of the present invention includes: (a) a disk shape having a center hole, a main plane, a substrate inner peripheral end surface adjacent to the center hole, a main plane, and a substrate inner peripheral end surface. A substrate inner peripheral chamfer portion adjacent to the substrate, a substrate outer peripheral end surface located on the opposite side of the main plane with respect to the substrate inner peripheral end surface, and a substrate outer peripheral chamfer portion adjacent to the main plane and the substrate outer peripheral end surface. A step of preparing a single crystal support; and (b) supplying an oxidizing gas to the inner peripheral edge surface of the substrate and the inner peripheral chamfer portion of the substrate, and inert or reducing to the main plane, the outer peripheral edge surface of the substrate and the outer peripheral chamfer portion of the substrate. And heating the silicon single crystal support in a state in which the gas is supplied to selectively form a SiO ₂ film on the inner peripheral end surface of the substrate and the inner peripheral chamfer portion of the substrate. The SiO ₂ film formed in the step (b) has a film thickness of 50 nm or more at the substrate inner peripheral end face and the substrate inner peripheral chamfer portion, and has a film thickness of 10 nm or less at the main plane and the substrate outer peripheral end face. Is desirable.

The method for manufacturing a substrate for an information recording medium of the present invention having the above configuration selectively performs thermal oxidation on the substrate inner peripheral end face and the substrate inner peripheral chamfer portion that require a SiO ₂ film having a thickness of 50 nm or more. By doing so, it is possible to efficiently provide a SiO ₂ film having a required film thickness as compared with the conventional method. Further, by performing thermal oxidation on the entire surface of the silicon support as necessary, a SiO ₂ film having a film thickness of 10 nm or less, which is required in the main plane, the substrate outer peripheral end surface and the substrate outer peripheral chamfer portion, is highly efficient. Can be produced.

These features eliminate the need for a SiO ₂ film etching process to obtain a desired film thickness, and at the same time facilitate post-processing processes such as a lapping process and / or a polishing process. Can be supplied at low cost and with high reproducibility.

  In addition, the information magnetic recording medium produced using the information recording medium substrate obtained by the method of the present invention is capable of high-density recording by the heat-assisted recording method, and at the same time sufficient for mobile applications. Has static and dynamic mechanical strength.

An outline of an information recording medium substrate manufactured by the method of the first embodiment of the present invention is shown in FIG. FIG. 1A is a top view of the information recording medium substrate, and FIG. 1B is a cross-sectional view of the information recording medium substrate taken along the cutting line Ib-Ib. The information recording medium substrate of the present invention has a disk shape having a center hole 8 and has a main plane 2 that serves as a surface for recording information on the information recording medium. In the substrate inner peripheral portion, the substrate inner peripheral end surface 4 that is adjacent to the central hole 8 and is perpendicular to the main plane 2 and located between the main plane 2 and the substrate inner peripheral end surface 4, And a substrate inner peripheral chamfer portion 6 which is a truncated conical surface inclined with respect to the main plane 2. In the substrate outer peripheral portion, a substrate outer peripheral end surface 5 that is a cylindrical surface that is positioned on the opposite side of the main plane 2 with respect to the substrate inner peripheral end surface 4 and perpendicular to the main plane 2, and the main plane 2 and the substrate outer peripheral end surface 5 And a substrate peripheral chamfer portion 7 which is a truncated conical surface inclined with respect to the main plane 2. The information recording medium substrate of the present invention includes a silicon single crystal support 10 and a SiO ₂ film 20 formed thereon.

The inventor forms an SiO ₂ film 20 having a low thermal conductivity on the main plane 2 of the silicon single crystal support 10 having a high thermal conductivity instead of an aluminum substrate or glass substrate with a NiP film having a low thermal conductivity. It has been found that the inconsistent thermal properties of low effective thermal conductivity during temperature rise and high effective thermal conductivity during temperature drop can be realized. Specifically, assuming a recording density of 2 Tb / square inch or more, by setting the thickness of the SiO ₂ film 20 formed on the main plane to 10 nm or less, the temperature increase rate and the high temperature rate are balanced. Found satisfaction.

In addition, the present inventor thermally compresses the substrate inner peripheral end face 4 and the substrate inner peripheral chamfer portion 6 adjacent thereto to form a SiO ₂ film having a thickness of 50 nm or more to induce compressive stress. The present inventors have found that both static and dynamic mechanical strengths such as a high ring bending strength and a high impact drop strength can be achieved (see Non-Patent Document 2).

Furthermore, the present inventors have discovered that by setting the thickness of the SiO ₂ film on the substrate outer peripheral edge surface 5 and 10nm or less, by applying a bias voltage to the substrate for information recording medium, the securing and magnetic properties of the adhesion strength of the magnetic film I found that I could achieve improvements.

Here, an information recording medium substrate having a nominal value of 2.5 inches is used as a magnetic recording layer at 5 × 10 ⁷ erg / cm ³ (5 × 10 ⁶ J / m ³ ) at room temperature (25 ° C.). high K _u value material (e.g., CoPt alloy) having a reach with film recording medium was formed of, a case of performing recording by driving at a rotational speed of 4200 rpm. As an example, consider raising and lowering the temperature of a bit existing at a radius of 20 mm from the center of the recording medium. Assuming a recording density of 2 Tb / square inch, the bit size is about φ18 nm. In order to raise the temperature by selectively irradiating the bit with light from the laser mounted on the magnetic head, the laser irradiation time can be regarded as effectively stopping the bit of φ18 nm. It is necessary to make such a short time. Considering that the recording medium is rotating at 4200 rpm, it is necessary to set the laser irradiation time to about 2 nanoseconds. On the other hand, it is desirable that the time required for the bit heated by the laser irradiation to be lowered to a certain temperature is also a short time. However, considering the stability of the magnetization of the bit in the temperature rising state, the thermal influence on the adjacent bit, and the heat resistance of the surface protective film and the lubricating film, the cooling is performed in 2 nanoseconds as in the temperature rising process. It is desirable. The aforementioned temperature rise time and temperature fall time can be realized by setting the thickness of the SiO 2 film 20 on the main plane 2 to 10 nm or less.

Assuming a recording density of 1 Tb / square inch in the same information recording medium, the bit size is about φ25 nm. From the same consideration as described above, it is desirable that the temperature raising time and the temperature lowering time in this case be approximately 3 nanoseconds. In this case, the film thickness of the SiO ₂ film 20 on the main plane 2 may be set to 10 nm or more and 50 nm or less because the temperature rise time and the temperature fall time are 1.5 times that in the case of 2 Tb / square inch. desirable.

As described above, when an information recording medium substrate formed of the silicon single crystal support 10 is used for a heat-assisted magnetic recording medium capable of achieving a high recording density, the internal strength that determines the mechanical strength is determined. Requirements for the film thickness of the SiO ₂ film 20 in the peripheral portion (substrate inner peripheral end surface 4 and substrate inner peripheral chamfer portion 6), substrate outer peripheral portion (substrate outer peripheral end surface 5 and substrate outer peripheral chamfer for enabling application of a bias voltage) The requirements for the thickness of the SiO ₂ film in part 7) and the requirements for the SiO ₂ film on the main plane 2 that determine the rate of temperature rise and the rate of temperature fall differ significantly. If an attempt is made to form a SiO ₂ film that satisfies the above-mentioned remarkably different requirements by thermal oxidation of the entire surface of the silicon single crystal support, after forming a SiO ₂ film having a thickness of 50 nm or more, the SiO ₂ film other than the inner periphery of the substrate _It is necessary to reduce the thickness of the _two films by a technique such as polishing. This method is a very inefficient method. Therefore, it is desired to efficiently control the thickness of the SiO ₂ film at each site. In order to achieve this, in the present invention, selective thermal oxidation is performed on the inner periphery of the substrate that requires a film thickness of 50 nm or more. By selectively thermally oxidizing only the inner peripheral portion of the substrate, it is possible to eliminate or reduce the necessity for the step of reducing the thickness of the SiO ₂ film at other portions.

  The method for producing the information recording medium of the present invention will be described with reference to FIG. First, in step (a), the substrate has a disk shape having a center hole, a main plane, a substrate inner peripheral end surface adjacent to the center hole, and a substrate inner peripheral channel adjacent to the main plane and the substrate inner peripheral end surface. A silicon single crystal support having a fur portion, a substrate outer peripheral end surface located on the opposite side of the main plane with respect to the substrate inner peripheral end surface, and a substrate outer peripheral chamfer portion adjacent to the main plane and the substrate outer peripheral end surface is prepared. .

  First, a cylindrical silicon single crystal ingot is sliced to produce a silicon single crystal blank 11 having a disk shape shown in FIG. This step can be performed using any method known in the art.

  Next, as shown in FIG. 2B, the center hole 8 is formed at the center of the silicon single crystal blank 11 by the inner peripheral coring process, and the silicon single crystal support 10 is obtained. This step can be performed using any method known in the art.

  Next, chamfering (chambering) around the center hole 8 is performed to form the substrate inner peripheral end surface 4 and the substrate inner peripheral chamfer portion 6 around the center hole 8 as shown in FIG. Also, the outer periphery of the silicon single crystal support 10 is chamfered (chambering) to form the substrate outer peripheral end surface 5 and the substrate outer peripheral chamfer portion 7 as shown in FIG. This step can be performed using any method known in the art.

Further, the polishing process is performed on the inner peripheral portion of the substrate and the outer peripheral portion of the substrate. This step is useful for removing foreign substances or protrusions that may be present on the inner peripheral portion of the substrate and the outer peripheral portion of the substrate, and forming the SiO ₂ film 20 having a uniform film thickness in the subsequent thermal oxidation step. is there.

Optionally, the main plane of the silicon single crystal blank 11 after slicing the silicon single crystal ingot (FIG. 2 (a)), the silicon single crystal support 10 after inner peripheral coring (FIG. 2 (b)). Lapping and polishing of the main plane 2 of the main plane 2 and / or the main plane 2 of the silicon single crystal support 10 (FIG. 2C) after chamfering the inner and outer peripheries is performed. Foreign matter and protrusions on the plane 2 may be removed. The lapping and polishing process may be performed at each stage, or may be performed at some of the aforementioned stages. These treatments are useful for making the SiO ₂ film 20 formed on the main plane 2 uniform because of the residual oxidizing gas, which will be described later, in the subsequent thermal oxidation step, to a uniform film thickness.

Next, as a step (b), the substrate inner peripheral end face 5 and the substrate inner peripheral chamfer portion 6 of the silicon single crystal support 10 are selectively thermally oxidized to form the SiO ₂ film 20 as shown in FIG. Form. In this step, while maintaining the substrate outer peripheral portion and the main plane in an inert or reducing gas atmosphere, only the substrate inner peripheral portion adjacent to the center hole 8 is exposed to an oxidizing gas and heat-treated. The inner peripheral portion is thermally oxidized to form the SiO ₂ film 20.

  An example of an apparatus that can be used in this step is shown in FIG. The apparatus shown in FIG. 3A has an installation table 303 having a gas flow hole in the center, a heater 302, an oxidizing gas inlet 306, an oxidizing gas exhaust for installing a silicon substrate in the chamber 301. It has an outlet 307, an atmospheric gas inlet 304, and an atmospheric gas outlet 305. The stacked body 308 of the silicon single crystal support 10 obtained in the step (a) is installed on the installation table 303, and the weight plate 309 is installed on the stacked body. The weight plate 309 has a through hole at the center, and a gas conduit extending from the oxidizing gas inlet 306 is fitted into the through hole. Then, the oxidized portion 320 is formed by the mounting table 303, the silicon single crystal support laminate 308, and the weight plate 309. FIG. 3B is an enlarged view of the region IIIb and shows an outline of the oxidation unit 320. In the oxidation part 320, the substrate inner peripheral end face 4 and the substrate inner peripheral chamfer part 6 of the silicon single crystal support 10 are exposed, and only thermal oxidation of these parts selectively proceeds.

  In the apparatus shown in FIG. 3, the gap between the installation base 303 and the silicon single crystal support laminate 308, the gap between adjacent silicon single crystal supports 10 constituting the silicon single crystal support laminate 308, and the silicon single crystal Since the gap between the support laminate 308 and the weight plate 309 is not completely sealed, the oxidizing gas may flow out to the main plane of the silicon single crystal support 10 and the outer periphery of the substrate. In order to reduce this possibility, it is effective to apply a load to the silicon single crystal support laminate 308 by the weight plate 309. Alternatively, the pressure of the atmospheric gas may be slightly higher than the pressure of the oxidizing gas to suppress the outflow of the oxidizing gas from the oxidation unit 320.

  Another example of an apparatus that can be used in this step is shown in FIG. The apparatus of FIG. 4 has the same configuration as the apparatus of FIG. 3 except that a gas conduit extending from the oxidizing gas inlet 406 communicates with the weight plate 409 via the bellows 410. The chamber 501, installation table 403, heater 402, oxidizing gas outlet 407, atmospheric gas inlet 404, and atmospheric gas outlet 405 in the apparatus of FIG. 4 are the same elements as the corresponding elements of the apparatus of FIG. 3. It is.

  Another example of an apparatus that can be used in this step is shown in FIG. In the apparatus of FIG. 5, the silicon single crystal support 10 is stacked in the horizontal direction to form a silicon single crystal support stack 508. Then, instead of the weight plate 309, a support plate 511 is included, and the support plate 512 is fixed by a support bar 512 that is fixed to the chamber 501 via a gas seal 513. The installation table 503, the heater 502, the oxidizing gas inlet 506, the oxidizing gas outlet 507, the atmospheric gas inlet 504, and the atmospheric gas outlet 505 in the apparatus of FIG. 5 correspond to corresponding elements of the apparatus of FIG. Is equivalent to

When the apparatus shown in FIGS. 3 to 5 is used, the gap between the installation base 303 and the silicon single crystal support laminate 308, the adjacent silicon single crystal support constituting the silicon single crystal support laminate 308 are used. 10 and the gap between the silicon single crystal support laminate 308 and the weight plate 309 are not completely sealed, so that a small amount of residue remains on the main plane 2 of the silicon single crystal support 10 and the outer peripheral portion of the substrate. Oxidizing gas is present, whereby a SiO ₂ film having a thickness of about _{1 to 5} nm is formed.

The oxidizing gas contains an oxidizing agent such as water vapor, oxygen, N ₂ O, and an inert gas as a carrier as required. When using water vapor as the oxidant, water vapor supplied from outside the apparatus may be used. Alternatively, water vapor generated in situ by supplying H ₂ and O ₂ using an inert gas as a carrier may be used. Here, the ratio of the supply amounts of H ₂ and O ₂ is not limited to the stoichiometric ratio, and may be any ratio that allows efficient thermal oxidation. N ₂ O is suitable as an oxidizing gas because it decomposes at a high temperature of 300 ° C. or higher to generate N ₂ and atomic oxygen (O) having a strong oxidizing power.

  Inert gases that can be used include nitrogen and noble gases such as He, Ar, Kr and Xe. The reducing gas that can be used includes hydrogen. An inert gas and a reducing gas may be mixed and supplied into the chamber 301 from the atmospheric gas inlet 304.

The heat treatment in this step can be performed by heating the silicon single crystal support 10 to a temperature of 800 to 1000 ° C. In this step, the film thickness of the resulting SiO ₂ film 20 can be controlled by controlling the heating time. The heating time is set so that a film thickness of at least 50 nm or more can be obtained at the inner peripheral portion of the substrate.

Next, as an optional step (c), the silicon single crystal support 10 having the SiO ₂ film 20 formed on the inner peripheral portion of the substrate is heated in an oxidizing gas to heat the main plane 2 and the outer peripheral end surface of the substrate. 5 and the substrate peripheral chamfer portion 7 may be formed with an SiO ₂ film to form an information recording medium substrate as shown in FIG. In this step, the heating time is controlled so that the thickness of the SiO ₂ film formed on the main plane 2 and the outer peripheral portion of the substrate is 10 nm or less. The heating temperature is desirably in the range of 800 to 1000 ° C. In this step, an SiO ₂ film 20 is further formed on the substrate inner peripheral end face 4 and the substrate inner peripheral chamfer portion 6. However, since the SiO ₂ film 20 has already been formed in the step (b), the formation speed of the SiO ₂ film in the inner peripheral portion of the substrate is smaller than the speed in the main plane 2 and the outer peripheral portion of the substrate.

  Finally, optionally, the main surface 2 of the information recording medium substrate obtained in the step (b) or the step (c) may be polished to adjust the substrate surface shape.

  An information magnetic recording medium compatible with the heat-assisted recording method can be formed by forming at least a magnetic recording layer on the main plane 2 of the information recording medium substrate manufactured by the above method. If necessary, an underlayer, a soft magnetic layer, a seed layer, an intermediate layer, or the like may be formed between the information recording medium substrate and the magnetic recording layer. If necessary, a protective layer and a lubricant layer may be formed on the magnetic recording layer.

  The optional nonmagnetic underlayer can be formed using a nonmagnetic material containing Cr, such as Ti or CrTi alloy.

  The optional soft magnetic layer includes a crystalline material such as FeTaC, Sendust (FeSiAl) alloy; a microcrystalline material such as FeTaC, CoFeNi, CoNiP; or a Co alloy such as CoZrNd, CoZrNb, CoTaZr. It can be formed using an amorphous material. The film thickness of the soft magnetic layer is a layer for concentrating the perpendicular magnetic field on the magnetic recording layer, and the optimum value varies depending on the structure and characteristics of the magnetic head used for recording, but is generally about 10 nm to 500 nm. This is desirable from the viewpoint of productivity.

  A seed layer that may be optionally provided is a permalloy material such as NiFeAl, NiFeSi, NiFeNb, NiFeB, NiFeNbB, NiFeMo, NiFeCr, etc .; Further, it can be formed by using an added material; Co; or a Co-based alloy such as CoB, CoSi, CoNi, CoFe or the like. The seed layer desirably has a film thickness sufficient to control the crystal structure of the magnetic recording layer. In general, the seed layer desirably has a film thickness of 3 nm to 50 nm.

  The optionally provided intermediate layer can be formed using Ru or an alloy containing Ru as a main component. The intermediate layer usually has a thickness of 0.1 nm to 20 nm. By setting the film thickness within such a range, it is possible to impart characteristics necessary for high-density recording to the magnetic recording layer without deteriorating the magnetic characteristics and electromagnetic conversion characteristics of the magnetic recording layer.

  The underlayer, the soft magnetic layer, the seed layer, and the intermediate layer are formed by any method known in the art such as sputtering (including DC magnetron sputtering, RF magnetron sputtering) and vacuum deposition. Can be implemented.

  The magnetic recording layer can be preferably formed using a ferromagnetic material of an alloy containing at least Co and Pt. In order to perform perpendicular magnetic recording, the easy magnetization axis (c-axis of the hexagonal close-packed (hcp) structure) of the material of the magnetic recording layer is perpendicular to the surface of the recording medium (that is, the main plane 2 of the information recording medium substrate). It must be oriented in the direction. The magnetic recording layer can be formed using an alloy material such as CoPt, CoCrPt, CoCrPtB, or CoCrPtTa. The film thickness of the magnetic recording layer is not particularly limited. However, from the viewpoint of improving productivity and recording density, the magnetic recording layer preferably has a thickness of 30 nm or less, more preferably 15 nm or less. The formation of the magnetic recording layer can be performed using any method known in the art such as sputtering (including DC magnetron sputtering, RF magnetron sputtering, etc.), vacuum deposition, and the like.

  The protective layer that may be optionally provided can be formed using carbon (amorphous carbon or the like) or various thin film materials known as materials for a magnetic recording medium protective film. The protective layer is a layer for protecting each constituent layer below the magnetic recording layer below it. The protective layer can be generally formed using a sputtering method (including a DC magnetron sputtering method, an RF magnetron sputtering method, etc.), a vacuum deposition method, a CVD method, or the like.

  The optional lubricant layer is a layer for providing lubrication when the recording / reading head is in contact with the magnetic recording medium. For example, a perfluoropolyether liquid lubricant Or a variety of liquid lubricant materials known in the art. The liquid lubricant layer can be formed using any coating method known in the art such as a dip coating method or a spin coating method.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, it should be understood that these examples do not limit the present invention and can be variously modified without departing from the gist of the present invention.

Example 1
An information recording medium substrate was produced according to the manufacturing method illustrated in FIG.

  First, a single crystal silicon ingot was sliced to obtain a silicon single crystal blank 11 having a diameter of 65 mm and a thickness of 0.675 mm. The blank 11 was cored and a center hole 8 having a diameter of 20 mm was formed at the center of the blank 11 to obtain a silicon single crystal support 1. A lapping and polishing process was applied to the main plane 2 of the obtained silicon single crystal support 1 to smooth the main plane 2 and remove foreign matters and protrusions.

  Next, chamfering was performed on the inner peripheral portion and the outer peripheral portion of the substrate of the silicon single crystal support 1 to form the inner peripheral chamfer portion 6 and the outer peripheral chamfer portion 7. Subsequently, polishing of the substrate inner peripheral end surface 4, the substrate outer peripheral end surface 5, the substrate inner peripheral chamfer portion 6 and the substrate outer peripheral chamfer portion 7 was performed to remove foreign matters and protrusions at these portions.

Next, using the apparatus shown in FIG. 3, the substrate inner peripheral end face 4 and the substrate inner peripheral chamfer 6 are selectively used under various conditions shown in Table 1 (type of oxidant, heating temperature and heating time). Thermal oxidation was performed to obtain an information recording medium substrate. As the atmosphere gas, Ar gas was used as a carrier gas, and 10% oxygen gas, water vapor gas, hydrogen + oxygen mixed gas, and N ₂ O gas were used.

(Comparative Example A)
An information recording medium substrate was obtained by repeating the procedure of Example 1 except that the substrate inner peripheral end face 4 and the substrate inner peripheral chamfer portion 6 were not thermally oxidized.

(Comparative Example B)
In accordance with the procedure of Example 1, a silicon single crystal support 10 in which the substrate inner peripheral chamfer portion 6 and the substrate outer peripheral chamfer portion 7 were formed was obtained. Polishing the substrate inner peripheral end surface 4, the substrate outer peripheral end surface 5, the substrate inner peripheral chamfer portion 6 and the substrate outer peripheral chamfer portion 7 of the obtained silicon single crystal support 10 was carried out, and foreign matters and protrusions at these portions Was removed.

Subsequently, the silicon single crystal support 10 is heated to 1000 ° C. in an oxygen atmosphere for 5 minutes, thereby forming a 100 nm-thickness SiO ₂ film on the entire surface of the silicon single crystal support 10. A substrate was obtained.

(Evaluation)
For each condition (1-1 to 1-16) of Example 1 and Comparative Examples A and B, a total of 60 information recording medium substrates were prepared for each test item shown below, and these substrates were The vicinity of the inner peripheral end face 4 of the substrate was chucked, incorporated in a test HDD, and subjected to a drop impact test under the conditions of an acceleration of 1000 G and an acceleration duration of 1 ms, and a substrate destruction rate was obtained and evaluated. Moreover, the average ring bending strength was measured. Furthermore, the electrical resistance value between two points located on the diagonal of the substrate outer peripheral end face 5 was measured as the outer peripheral resistance. The results of these measurements are shown in Table 1.

As can be seen from the results of 1-1 to 1-8, 1-13 and 1-14 in Table 1, when the SiO ₂ film 20 is formed on the inner peripheral portion of the substrate using oxygen as the oxidizing agent, When the film thickness of the SiO ₂ film 20 in the part was 50 nm or more, a substrate having excellent mechanical strength such as an annular bending strength of 200 N or more and a fracture probability in a drop impact test of 0% was obtained. On the other hand, the information recording medium substrate of Comparative Example A without thermal oxidation and without the SiO ₂ film 20 on the inner periphery of the substrate has an annular bending strength as low as 160 N and has a drop impact test. The probability of destruction was as high as 30%. In addition, when the SiO ₂ film 20 is formed on the inner periphery of the substrate using oxygen, but the film thickness is less than 50 nm (1-1 and 1-2), the probability of destruction in the drop impact test is set to 0%. I couldn't.

Further, as apparent from the results of 1-9 to 1-12, 1-15 and 1-16 in Table 1, instead of oxygen, water vapor, water vapor generated in situ (H ₂ + O ₂ ), and even when forming the SiO ₂ film 20 using other oxidizing agents, such as N _{2 O} in the circumferential portion in the substrate, forming a SiO ₂ film 20 having a thickness of at least 50nm in a circumferential portion in the substrate As a result, a substrate having excellent mechanical strength such as an annular bending strength of 200 N or more and a fracture probability in a drop impact test of 0% was obtained.

Further, the information recording medium substrate of Comparative Example B in which the entire surface of the silicon single crystal support 10 is thermally oxidized has a sufficient mechanical strength, but has a large SiO ₂ film of 100 nm on the outer peripheral end surface of the substrate. The outer peripheral resistance was 10 MΩ or more. From this, it was found that it was difficult to apply a bias voltage during film formation to the substrate of Comparative Example B. On the other hand, the information recording medium substrate of 1-1 to 1-16 in which the thickness of the SiO ₂ film 20 on the outer periphery of the substrate is 1 nm or less has an outer peripheral resistance of 1 MΩ or less, and bias during film formation It was found that voltage application was possible.

(Example 2)
In this example, an information magnetic recording medium was produced using the information recording medium substrate produced under the conditions 1-4 of Example 1.

First, in order to adjust the arithmetic average roughness Ra (measured with JIS B0601, AFM, reference length 10 μm) of the _second SiO ₂ film surface on the main plane 2 to 0.2 nm, a polishing process was performed. In this example, a leaf-type surface polishing method using a tape dropped and impregnated with colloidal silica was used. In this example, an information recording medium substrate having a desired Ra was obtained by polishing for 10 seconds. In this embodiment, since the thickness of the _second SiO ₂ film 22 is as small as 1 nm, it is not necessary to perform a polishing process for reducing the thickness of the _second SiO ₂ film 22, and a relatively small, leaf-type surface is used. A polisher could be used.

  After the polishing process, on the main plane of the information recording medium substrate, by sputtering, an underlayer made of CrTi with a thickness of 2 nm, a soft magnetic layer made of CoZrNd with a thickness of 40 nm, and CoNiFeSi with a thickness of 16 nm A seed layer, an intermediate layer made of Ru with a thickness of 12 nm, a magnetic recording layer made of CoPt with a thickness of 20 nm, and a protective layer made of amorphous carbon (a-C) with a thickness of 3 nm were sequentially formed. Finally, a lubricant layer made of a lubricant having a film thickness of 2 nm was formed by using a spin coating method to obtain an information magnetic recording medium.

  Using a spin stand equipped with a laser irradiation head for forming a φ15 nm beam spot using near-field light for a thermally assisted medium and a magnetic recording head for writing information in a portion heated by the laser The TAA (Track Average Amplitude) of the obtained information magnetic recording medium was measured to evaluate the electromagnetic conversion characteristics. The TAA measurement was performed under the conditions of a recording frequency of 506 MHz using a track having a radius of 22 mm from the center at a rotational speed of 4200 rpm. This condition corresponds to a recording density of 2 Tb / square inch. The information magnetic recording medium of this example exhibited an excellent TAA value exceeding 80.

(Reference Example 3)
In this example, an information magnetic recording medium was produced using the information recording medium substrate of Comparative Example B produced by a conventional technique.

Since the information recording medium substrate of Comparative Example B has a SiO ₂ film having a film thickness of 100 nm on the main plane, in addition to the polishing process for adjusting the surface roughness, the film thickness of the SiO ₂ film is reduced. Therefore, it was necessary to perform a polishing process. The polishing process for reducing the film thickness requires a very long processing time when using a leaf-type surface polishing apparatus. Therefore, in this reference example, a large batch type polishing apparatus was used. Using a batch polishing apparatus, the main plane was polished, the thickness of the SiO ₂ film on the main plane was reduced to 10 nm or less, and the arithmetic average roughness Ra of the SiO ₂ film surface was adjusted to 0.2 nm. . The main plane polishing process required a processing time of 180 seconds.

In addition, since the information recording medium substrate of Comparative Example B has a SiO ₂ film having a film thickness of 100 nm on the outer peripheral end surface of the substrate, the substrate outer peripheral end surface is polished using a batch type polishing apparatus. The film thickness of the SiO ₂ film on the end face was reduced to 10 nm or less. The polishing process on the peripheral edge of the substrate required a processing time of 180 seconds.

  Subsequently, an information magnetic recording medium was obtained by laminating an underlayer, a soft magnetic layer, a seed layer, an intermediate layer, a magnetic recording layer, a protective layer, and a lubricant layer by the same procedure as in Example 2. The TAA value of the obtained information magnetic recording medium was measured under the same conditions as in Example 2. The information magnetic recording medium of this reference example exhibited an excellent TAA value exceeding 80.

As described above, by reducing the thickness of the SiO ₂ film on the main plane, the information magnetic recording medium of this reference example exhibited the same magnetic characteristics as the information magnetic recording medium of Example 2. However, since the large-scale apparatus is required for reducing the film thickness of the SiO ₂ film on the main plane and the outer peripheral end surface of the substrate, and a long processing time is required, the method of this reference example is in terms of manufacturing cost. It is disadvantageous.

BRIEF DESCRIPTION OF THE DRAWINGS It is a block diagram of the board | substrate for information recording media of this invention, (a) is a top view, (b) is sectional drawing along the cutting line Ib-Ib. It is the schematic explaining the process of the manufacturing method of the board | substrate for information recording media of this invention, (a)-(e) is sectional drawing which shows each process. A schematic diagram of an example apparatus used for the selective formation of SiO ₂ film in the substrate peripheral portion, (a) is a cross-sectional view, an enlarged sectional view of (b) the region IIIb. It is a schematic diagram of another example of an apparatus used for the selective formation of the SiO ₂ film on the substrate in the peripheral portion. It is a schematic diagram of another example of an apparatus used for the selective formation of the SiO ₂ film on the substrate in the peripheral portion.

Explanation of symbols

2 main plane 4 substrate inner peripheral end surface 5 substrate outer peripheral end surface 6 substrate inner peripheral chamfer portion 7 substrate outer peripheral chamfer portion 8 central hole 10 silicon single crystal support 20 SiO ₂ film 301, 401, 501 chamber 302, 402, 502 heating Heaters 303, 403, 503 installation bases 304, 404, 504 Atmospheric gas inlets 305, 405, 505 Atmospheric gas outlets 306, 406, 506 Oxidizing gas inlets 307, 407, 507 Oxidizing gas outlets 308, 408 , 508 Silicon single crystal support laminate 309, 409 Weight plate 320 Oxidizing part 410 Bellows 511 Support plate 512 Support bar 513 Gas seal

Claims (2)

(A) having a disc shape having a center hole, a main plane, a substrate inner peripheral end surface adjacent to the center hole, a substrate inner peripheral chamfer portion adjacent to the main plane and the substrate inner peripheral end surface, and the substrate Preparing a silicon single crystal support having a substrate outer peripheral end surface located on the opposite side of the main plane with respect to the inner peripheral end surface, and a substrate outer peripheral chamfer portion adjacent to the main plane and the substrate outer peripheral end surface;
(B) Supporting a silicon single crystal in a state where an oxidizing gas is supplied to the substrate inner peripheral end surface and the substrate inner peripheral chamfer portion, and an inert or reducing gas is supplied to the main plane, the substrate outer peripheral end surface and the substrate outer peripheral chamfer portion. And a step of selectively forming a SiO ₂ film on the inner peripheral end surface of the substrate and the inner peripheral chamfer portion of the substrate by heating the body. The SiO ₂ film formed in the step (b) has a film thickness of 50 nm or more at the substrate inner peripheral end face and the substrate inner peripheral chamfer portion, and has a film thickness of 10 nm or less at the main plane and the substrate outer peripheral end face. The method for manufacturing an information recording medium substrate according to claim 1.

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