JPH04125817A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease the fluctuations in coercive force within the plane of a magnetic layer by subjecting the sputtered film of a specific metal to constitute a magnetic film t two stages of annealing at a required temp. relation. CONSTITUTION:The sputtered film essentially consisting of Fe3O4 is formed on a rigid substrate by a reactive sputtering method using a target essentially consisting of Fe in an oxidative atmosphere. The magnetic layer of the gamma-Fe2O3 having the uniform coercive force distribution within the plane is formed if the magnetic layer of a continuous thin film type essentially consisting of the gamma-Fe2O3 is formed by subjecting this sputtered film to two stages of the annealing at the treating temp. lower in the 2nd stage than in the 1st stage in the oxidative atmosphere.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a method of manufacturing a magnetic recording medium having a continuous thin film type magnetic layer mainly composed of γ-Fezes, and in particular, relates to a method for manufacturing a magnetic recording medium having a continuous thin film type magnetic layer mainly composed of When forming by the method, Fe3O<
The present invention relates to annealing for oxidizing γ-Fe2rs to γ-Fe2rs.

<Prior Art> A hard type magnetic disk in which a magnetic layer is formed on a rigid substrate and a floating magnetic head are used in magnetic disk drives used in computers and the like.

Conventionally, coated magnetic disks have been used in such magnetic disk drive devices, but as the capacity of magnetic disks has increased, sputtering methods have been used because they are advantageous in terms of magnetic properties, recording density, etc. 2. Description of the Related Art Thin-film magnetic disks having a continuous thin-film magnetic layer formed by a vapor deposition method or the like have come into use.

Thin-film magnetic disks are made by plating an N1-P underlayer on an Aβ-based disk-shaped metal plate, or by oxidizing the surface of this metal plate to form alumite. It is generally constructed by sequentially depositing a Cr layer, a metal magnetic layer such as Co--Ni, and a protective lubricant film such as C by sputtering.

However, a metal magnetic layer such as Co--Ni has low corrosion resistance and low hardness, causing problems in reliability. On the other hand, Japanese Patent Application Laid-Open Nos. 62-43819 and 63-17521
The magnetic thin film mainly composed of iron oxide as described in Japanese Patent No. 9 is chemically stable, so there is no fear of corrosion, and it also has sufficient hardness.

Magnetic thin films whose main component is iron oxide are γ-Fears and C.
The main component is O-γ-Fe3Oi, and usually
It is formed by the so-called direct method or indirect method.

The direct method is a method in which a Fe504 film is first formed by sputtering and then oxidized to obtain a γ-Fears film.

Direct methods include direct oxidation, direct reduction, and direct neutralization.

Among these, the direct oxidation method is preferably used because sputter control is easy and the film formation rate is high.

In the direct oxidation method, a target containing Fe as a main component is used, and a target of 0. A Fe5O4 film is formed by performing reactive sputtering in an Ar gas atmosphere containing gas. Next, this FeJ4 film is oxidized to γ-Fe*Os by annealing in an atmosphere containing O3.

<Problems to be Solved by the Invention> As a result of studying the continuous thin film type γ-Fears magnetic layer manufactured by such a direct oxidation method, the present inventors found that the 01 gas concentration near the substrate during reactive sputtering Due to various reasons such as non-uniformity, Fe5 after sputtering
It has been found that variations occur in the degree of oxidation within the plane of the O4 film, and as a result, variations in coercive force occur within the plane of the γ-Fe*Oa magnetic layer after annealing, causing reproduction output modulation.

The present invention was made under these circumstances, and
An object of the present invention is to provide a method for forming a continuous thin film magnetic layer containing -Fails as a main component by a direct oxidation method, which can reduce variations in coercive force within the plane of the magnetic layer.

<Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (5).

(1) A sputtered film mainly composed of Fe1o4 is formed on a rigid substrate by a reactive sputtering method using a target mainly composed of Fe in an oxidizing atmosphere, and then the sputtered film is coated on the sputtered film in an oxidizing atmosphere. A method for manufacturing a magnetic recording medium comprising the step of forming a continuous thin film type magnetic layer mainly composed of γ-Fetus by annealing, the annealing comprising a first annealing and a step after the first annealing. 1. A method for manufacturing a magnetic recording medium, the method comprising multi-stage annealing comprising a second annealing and a heat treatment temperature in the first annealing being lower than that in the second annealing.

(2) The heat treatment temperature in the first annealing is 150 to 25
The method for manufacturing a magnetic recording medium according to (1) above, wherein the heat treatment temperature in the second annealing is in the range of 0°C and 270 to 320°C.

(3) The method for manufacturing a magnetic recording medium according to (1) or (2) above, wherein the temperature is maintained within a fluctuation range of 20° C. in each of the first annealing and the second annealing.

(4) The magnetic recording according to any one of (1) to 3) above, wherein after the first annealing, the temperature is lowered to a temperature lower than the holding temperature in the first annealing, and then raised to the holding temperature in the second annealing. Method of manufacturing media.

(5) The method for manufacturing a magnetic recording medium according to any one of (1) to 3) above, in which the temperature is continuously raised to the holding temperature in the second annealing after the first annealing.

<Function> In the present invention, a continuous thin film type magnetic layer containing γ-Fears as a main component is formed by a direct oxidation method.

That is, by forming a sputtered film mainly composed of Fe5O4 by a reactive sputtering method using a target mainly composed of Fe in an oxidizing atmosphere, and then annealing this sputtered film in an oxidizing atmosphere, γ-F
The magnetic layer is a continuous thin film type mainly composed of ears.

In the present invention, the annealing in such a direct oxidation method is a multi-stage annealing including a first annealing and a second annealing, and the heat treatment temperature in the first annealing is set lower than the heat treatment temperature in the second annealing.

By performing such multi-stage annealing, a γ-Felon magnetic layer with a uniform in-plane coercive force distribution can be obtained.

Specific composition> Hereinafter, a specific configuration of the present invention will be explained in detail.

In the present invention, firstly, Fe3 is sputtered by a reactive sputtering method using a target containing Fe as a main component in an oxidizing atmosphere.
A sputtered film containing Oa as a main component is formed.

It is preferable to use DC sputtering for reactive sputtering when forming the Fe104 film.

By using the DC sputtering method, the spread of plasma is suppressed, and when sputtered films are formed on both sides of the substrate at the same time, mutual interference of high-frequency electric fields on both sides of the substrate does not occur, which reduces the non-uniformity of magnetic properties within the plane of the magnetic layer. It is possible to reduce the

However, RF sputtering may also be used.

Furthermore, it is preferable to use magnetron sputtering because it has high productivity. When magnetron sputtering is performed, the eroded region of the target gradually expands as sputtering progresses. The parts that are not eroded are oxidized and become blackened parts, but as the sputtering progresses, these blackened parts are also eroded, and tend to adhere to the substrate and become defects in the sputtered film. In order to prevent such film defects by expanding the erosion area of the target, it is preferable to set the leakage magnetic flux density from the target to 200 to 600G, particularly 200 to 500G.

Here, the leakage magnetic flux density is the maximum value of the component of the leakage magnetic flux density in a direction parallel to the target surface, and is a value measured on the target surface. Note that repeated sputtering erodes the target and creates recesses on the surface, but in such a case, the magnetic flux density is measured on the surface of the recesses. Further, the magnetic flux density can be measured using a Gaussmeter using a Hall element or the like.

The gas pressure in the sputtering chamber is 5.0 x 10-2 to 3.
It is preferable that Qx is 10-'Pa. When the sputtering pressure is reduced in this way, the erosion area on the target surface is further expanded, and the contamination of foreign matter into the Fe504 film is significantly reduced. If the sputtering pressure is less than this range, magnetron discharge will hardly occur, and if it exceeds this range, further expansion of the eroded region cannot be expected.

The Fe50+ film formed by reactive sputtering is annealed in an oxidizing atmosphere to form a NiFe*Os film.
oxidized to.

In the present invention, this annealing is a multi-stage annealing including a first annealing and a second annealing after the first annealing, and the heat treatment temperature in the first annealing is set lower than the heat treatment temperature in the second annealing.

In the present invention, the heat treatment temperature in the first annealing is preferably in the range of 150 to 250C, and the heat treatment temperature in the second annealing is preferably in the range of 270 to 320C.

If the temperature is maintained within the above temperature range in each of the first annealing and the second annealing, higher effects can be obtained, but furthermore, within each of the above temperature bands, the fluctuation range is 20°C or less, especially 10°C or less. It is preferable to maintain the temperature within the range of .

The temperature holding time in the first annealing is preferably 0.5 to 5 hours, particularly 1 to 3 hours. Also, the second
The temperature holding time during annealing is 0.5 to 10 hours,
In particular, it is preferable to set it as 1 to 5 hours. If the temperature holding time is less than the above range, the annealing effect will be insufficient,
If it exceeds the above range, the amount of non-magnetic α-Fears will increase significantly.

There is no particular limit to the average temperature increase rate from the start of annealing, that is, the start of temperature increase to the start of the first annealing, but
．． It is preferable to set it as 1-10 degreeC/min in 5-b.

In the present invention, after the first annealing, the temperature may be lowered to a temperature lower than the holding temperature in the first annealing, for example, room temperature, and then raised to the holding temperature in the second annealing.
Alternatively, after the first annealing, the temperature may be raised continuously to the holding temperature in the second annealing without lowering the temperature. In any of these cases, the effects of the present invention are achieved.

After the first annealing, if the temperature is lowered to a temperature lower than the holding temperature in the first annealing, the average temperature decreasing rate is preferably 2 to b, and then the average temperature increase when raising the temperature to the holding temperature in the second annealing. The speed is preferably 0.5 to b.

Further, after the first annealing, the average temperature increase rate when continuously increasing the temperature to the holding temperature in the second annealing without decreasing the temperature is preferably about 0.5 to b min.

After the second annealing, the rate of temperature drop when lowering the temperature to room temperature is preferably 2 to b.

Note that in the present invention, at least the first annealing and the second annealing are performed.
It is sufficient that multi-stage annealing including annealing is performed, and it is not necessarily necessary to perform two-stage annealing. That is, the first
Temperature maintenance may be performed at least once before annealing, between the first annealing and the second annealing, and after the second annealing at a temperature other than the above-mentioned temperature ranges. And, between each temperature maintenance period, there may be a continuous decrease or increase in temperature (
Alternatively, the temperature may be lowered to around -° normal temperature and then raised again.

The atmosphere during annealing was 0. An oxidizing atmosphere with a gas partial pressure of about 0.05 to 0.8 atm and a total pressure of about 0.5 to 2 atm is preferable, and it is usually preferable to perform annealing in the atmosphere.

Through such annealing, Fem0< becomes knee Fe*O
It is oxidized to s. In the present invention, the specific resistance ρ, which is an index of the degree of oxidation of iron oxide, is usually 10 −4 to 10 −1 Ω・in the FezO4 film before annealing and after the first annealing.
Cf1I, especially 10-3 to 10-1Ω・C11,
When it becomes r-FezOx after the second annealing, it is usually io-' to 10'Ω' cm, especially 10-' to 10'
°Ω” Cm. Usually, [ρ after second annealing]>[ρ before annealing]>[ρ after first annealing]
].

Note that the magnetic layer may be doped with C01Ti, Cu, etc., if necessary, and may also contain Ar, etc. contained in the atmosphere during the formation of the FeJ4 film.

CO is an effective element for adjusting coercive force. The content of CO in the magnetic layer is preferably such that it replaces Fe by 10 wt% or less. Further, in order to make the magnetic layer contain Co, a Fe target containing Co may be used.

The layer thickness of the magnetic layer is set at 20 mm in consideration of productivity, magnetic properties, etc.
The number of participants is preferably about 0 to 2,000.

A rigid substrate on which such a magnetic layer is formed does not require the formation of an underlayer (the manufacturing process is simple, and it is easy to polish and control the surface roughness). In addition, it can withstand heat treatment during magnetic layer formation.
Preferably, glass is used.

As the glass, it is preferable to use tempered glass, particularly surface-strengthened glass obtained by chemical strengthening.

Furthermore, a lubricating film containing an organic compound, an inorganic protective film, or the like may be provided on the magnetic layer.

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

By reactive sputtering, outer diameter 130mm, inner diameter 40mm
, 2000 mm thick on the surface of a 1.27 mm thick glass substrate.
A human Fe5O4 film was formed.

For the sputtering method, reactive DC magnetron sputtering was used, the target was Co-containing Fe, the atmosphere was an Ar gas atmosphere containing O2 gas, and the pressure was 1.5XlO-'Pa.
And so.

The thickness of the target was 3 mm, and the leakage magnetic field strength on the target surface during sputtering (the maximum value of the component of the magnetic flux density measured on the target surface in the direction parallel to the target surface) was 350G.

Note that as sputtering progresses, the leakage magnetic flux density changes due to erosion of the target surface, but in this example, an electromagnet is used as the magnetic field generation source, and the leakage magnetic flux density is kept constant by changing the generated magnetic field strength. I kept it.

The surface of the Fe3Oa film formed in this way was viewed at a magnification of 50
Observed with a magnified optical microscope, 1 ca+X 1c11
The number of foreign particles present within the range of 2 was measured at four arbitrary locations on the membrane surface, and the total was found to be 2 or less on average.

Next, the Fe504 film was annealed in air to form γ-
A Fe2O3 magnetic layer was used as a magnetic disk sample.

Annealing was performed according to the temperature transition pattern shown in FIGS. 1 to 4, and samples Nos. 001 to 4 were obtained. Samples Nos. 081 to 3 were subjected to two-stage annealing as shown in FIGS. 1 to 3, respectively. Also, sample N
Samples o and 4 are comparative samples that do not use multi-stage annealing as shown in FIG.

The in-plane coercive force distribution of these samples was measured.

The coercive force was measured at a total of 16 points at angles of 0090° and 180'2700 at each radius of 30.40.50.60++ m, and the average value and distribution width (maximum value - minimum value) were calculated, and the results are shown in Table 1. It was shown to. The smaller the distribution width, the better the uniformity in the in-plane direction of the film.

table No.

Average value distribution width 4 (comparison) 1500 180 Furthermore, Fe5
The specific resistance ρ of the 04 film is 0.032 to 0.034Ω” cm
and the above sample No.

ρ after the first annealing of 1 to 3 is 0.025 to 0.026
Ω・am, ρ after second annealing is 0.61-0.64Ω
” cm.

The effects of the present invention are clear from the above examples.

<Effects of the Invention> If the present invention is applied to the formation of a γ-Fe2O3 continuous thin magnetic layer by a direct oxidation method, the distribution of coercive force in the plane of the magnetic layer becomes almost uniform, resulting in a magnetic recording medium with extremely low reproduction output modulation. will be realized.

[Brief explanation of drawings]

1 to 3 are graphs showing temperature transition patterns during annealing according to the present invention. FIG. 4 is a graph showing a temperature transition pattern during conventional annealing. Attorney at law, TDA-K Co., Ltd. Patent attorney Yo Ishii

Claims (5)

[Claims] (1) A sputtered film mainly composed of Fe_3O_4 is formed on a rigid substrate by a reactive sputtering method using a target mainly composed of Fe in an oxidizing atmosphere, and then,
A method for producing a magnetic recording medium comprising the step of forming a continuous thin film type magnetic layer containing γ-Fe_2O_3 as a main component by annealing the sputtered film in an oxidizing atmosphere, wherein the annealing is performed in a first step. A method for producing a magnetic recording medium, comprising multi-stage annealing including annealing and a second annealing subsequent to the first annealing, the heat treatment temperature in the first annealing being lower than the heat treatment temperature in the second annealing. (2) The heat treatment temperature in the first annealing is 150 to 25
2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the heat treatment temperature in the second annealing is in the range of 270 to 320°C. (3) The method for manufacturing a magnetic recording medium according to claim 1 or 2, wherein the temperature is maintained within a fluctuation range of 20° C. in each of the first annealing and the second annealing. (4) Manufacturing the magnetic recording medium according to any one of claims 1 to 3, wherein after the first annealing, the temperature is lowered to a temperature lower than the holding temperature in the first annealing, and then raised to the holding temperature in the second annealing. Method. (5) The method for manufacturing a magnetic recording medium according to any one of claims 1 to 3, wherein the temperature is continuously raised to the holding temperature in the second annealing after the first annealing.