JPS5952810A - Manufacture of iron-oxide magnetic thin film - Google Patents

Abstract

PURPOSE:To reduce reduction processing temperature and realize the manufacture of iron-oxide thin film with increased saturated magnetization by forming a foundation layer which promotes a deoxidizing reaction between a substrate and a magnetic thin film. CONSTITUTION:As a foundation layer which promotes reduction, a thin film, made of at least one of Ag, Au, Pd, Pt, Rh, Ir, Ru or Os, is formed between a substrate and a thin film whose main component is alpha-Fe2O3 while another thin film whose main component is the same as the latter is formed on the substrate. This thin film is heated in a reducing atmosphere and a thin film whose main component is Fe3O4 is formed. In order to form the foundation layer on the substrate, thin film forming technique such as plating, vacuum deposition or sputtering can be used. In case of sputtering, for instance, metal foil or metal powder for the foundation layer is put on a high frequency sputtering electrode and a high frequency power of 100W is applied in an Ar atmosphere of 2X10<-2> Torr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an iron oxide magnetic thin film suitable as a high:qr ty magnetic recording medium, particularly as a magnetic disk medium.

Iron oxide I-1 strong thin films are used as composite materials for magnetic disks and are manufactured using conventional methods.

First, a groove film containing α-Fe and O as main components is formed on a substrate to a thickness of 1 μm or less by a known method such as a reactive sputtering method. Next, this thin film mainly composed of α-Fe203 is heated to about 300° C. in a reducing atmosphere such as 112, and is heated to about 300° C. to reduce Fe, 0. The main component is reduced to a thin film. Subsequently, this thin film mainly composed of Fe3O4 is heated to about 300 DEG C. in an oxidizing atmosphere in the air to obtain a thin film mainly composed of r-Fe103.

When using this γ-Fez03 thin [1-magnetic disk], the above substrate is made of A with an alumite-treated surface.
A large number of t-alloy substrates are currently in use. The purpose of alumite treatment is to harden the surface and improve head crush resistance. When this alumite-covered At alloy substrate is heated, distortion occurs due to the difference in thermal expansion between the alumite layer and the At alloy base. The roughness of the disk surface caused by this strain increases rapidly at temperatures above 320° C., and in the worst case, cracks occur in the alumite coating. Defects on the disk surface such as cracks can cause missing recording signals or signal 8
, resulting in a deterioration of the t/IL sound ratio. Therefore, in order to obtain a uniform and high quality iron monoxide magnetic thin film, it is necessary to maintain the entire manufacturing process at a temperature of at least 300° C. or lower. During the media manufacturing process, the substrate temperature can be maintained at 300 DEG C. or lower by using magnetron sputtering or high-speed film formation at 150 A/- in the sputtering process. In addition, in the oxidation process, J) r -F'e20. It is possible to convert it into a thin film. However, in a reduction step different from these cases, the conventional heating temperature is close to the heat resistance limit of the substrate. For example, α-Fet added with co
The heat treatment temperature when reducing the O@ thin film is around 310°C. The purpose of adding Co to the magnetic thin film is to increase the coercive force, and the amount of Co added is usually 6 atoms or less. Similarly, in order to improve the squareness ratio of the magnetic thin film, Ti is sometimes added, usually 5 atoms or less, and the reducible temperature range in this case is 320° C. or higher. Since reducing a thin film at a high temperature of 320° C. or higher causes the above-mentioned problems, a technique has been developed to lower the reducible temperature by adding 5 atoms or less of Cu.

(J, Appl, Phys, vol, 53
, N13.1982. PP, 2556-2560.

Special Publication Showa 55-14522. % Kosho 55-14523. Tokuko Sho 56-33850. Special Publication Showa 56-17818. Special Publication No. 56-23296, etc.). However, the lowering of the M source temperature by adding Cu is limited to 225°C, and conversely, when Co + Ti
+ When the addition −° of additive elements such as Cu is increased, r
-Fe! A new problem arises in that the saturation magnetization of the 01 coating decreases and the reproduction output decreases. For example, r -Fe201 with several atoms of Co, Ti, and Cu added together
In M, the saturation magnetization decreases to 3300 Gauss. Therefore, the amount of Cu added must be reduced as much as possible, and the reduction treatment temperature could not be lowered sufficiently.

In this way, in the conventional manufacturing method of iron oxide magnetic film, the reduction must proceed at a high temperature of around 300°C.
There was a risk that cracks would occur in the alloy substrate, resulting in missing recorded signals and poor signal-to-noise ratios.

On the other hand, when a thin film mainly composed of 1ids04 is obtained by reducing a thin film mainly composed of α-1i''e203, the Dogen reaction proceeds from the membrane surface rijj, so if the thin film is thick, the crotch area will be ', , and this unreduced portion remains in the final thin film mainly composed of γ-Fe2O3.For this reason, as the thickness of the iron-resistant magnetic thin film increases, s , 1.11 There was a drawback that the magnetization decreased (bli:I had a large saturation magnetization, and a thick iron oxide magnetic thin film could not be obtained.

In view of the above-mentioned conventional technology, the present invention has been developed by forming an underlayer between the substrate and the magnetic thin film to promote the reduction reaction.
The purpose of the present invention is to provide a method for manufacturing an iron oxide magnetic thin film that allows reduction treatment temperature to be lowered and increases saturation magnetization.
A method for manufacturing an iron oxide magnetic thin film comprising the steps of forming a thin film containing ffi as the main component, and heating the thin film in a reducing atmosphere to form a thin film containing Fe3O4'Z'' as the main component. AJ+Au+Pd, Pt, Rh,
The method is characterized in that a base layer made of at least one of Ir, Ru, or Os is formed in advance, and a thin film containing α-FelO1 as a main component is applied on the base layer.

The present invention will be explained in detail below.

In the present invention, an underlayer that promotes reduction is provided between the substrate and the α-Fe, 0@ thin film, and AfJAu+Pd+Pt+R
A thin film of Ru or OB is used. The reason why the elements used as the underlayer promote reduction is thought to be that all of the elements belong to group I or group Ib metals, and their electronegativity is as high as h, and their affinity for oxygen is small. It will be done.

In other words, the addition of Cu, which has a large electronegativity compared to % Fe, is α
It has the effect of lowering the reduction temperature from -Fe20- to F, 04, and Fe J: , l) also has a small electronegativity T.
Addition of i has the effect of increasing the reduction temperature. Also, F
Addition of Co, which has the same electronegativity as e, had no effect on the reduction reaction. Therefore, from the above results, elements with larger electronegativity than Fe, such as group II or group Ib taken up in the present invention, are
This is because it is thought to have the effect of promoting reduction to ks04. In addition, in the present invention, the conventionally used Cu
The effect of promoting reduction is greater than the above, and this is due to the fact that the elements used in the present invention: j! This is thought to be because Cu also has a large electronegativity as shown in e-1.

In addition, after reducing cl -Fe20B to Fe3O4, 1
In the process of oxidizing to -1i'et03, relatively fine crystals of Fe304 are generated by forming the above-mentioned underlayer, which has the advantage of being convenient for oxidation to γ-Fe10B.

In the present invention, thin film forming techniques such as plating, vacuum evaporation, and sputtering can be used to form the underlayer on the substrate, but in the following examples, the underlayer was formed by sputtering. That is, i@diameter 80
Gold foil or powder for the base layer was placed on the m+ high-frequency sputtering electrode, and sputtering was performed by applying high-frequency power of 100 W in an Ar atmosphere of 2 x 10'' Torr. A correction plate was provided between the substrate and the target so that the film thickness was constant. The formation speed of the base layer produced by this method is shown in the table below. The thickness of the base film was obtained by appropriately selecting the sputtering time.

Next, Example 1 shows the actual implementation. A thickness of 0.01μI was preliminarily applied to six sides of a glass substrate with a diameter of 100m.
Formation of the PT underlayer of II, and further on top of that a thickness of 0.17
pm or 0.21 μm α-FeIOsfr-based thin 1110g-3? I made it in minutes.

Table 3 Sputtering time for two films with a thickness of 0.17 μm is 28
The sputtering time for a thin film with a thickness of 0.21 μII was 35 minutes. Subsequently, these α-Fe10-based thin films were heated in Hz air containing water vapor.
It was heated to 25° C. for 1 hour to reduce and convert it into a thin O1 film. Furthermore, the film was heated to 290° C. for 4 hours in the atmosphere to obtain an m-film containing r-Fe, O, and gold as main components. The saturation magnetization of a thin film with a thickness of 0.17 μm is 3gooaau
ss, thickness 21/jm, the saturation magnetization of the ON film is 380
(l Gauss (see curve ■ in Figure 1).

The crystal structure of the iron oxide thin film was identified to be a spinel structure by X, @ diffraction.

Also, for comparison, the same SiJ film as above was used without applying PTT ground protection to the glass substrate. α-Fe under tsuttering conditions,
0. A thin film was formed. This α-Fe20B thin film is F,0
．． In order to reduce it to a film, it was necessary to heat it to 320°C or higher, and to oxidize this F'eBO thin film to an r-Fe103 thin film, it was necessary to heat it at 310°C in the air for 2 hours. 3. The saturation magnetization of the obtained negative thin film decreases as the film thickness increases, and at 0.17 pm it is 3050 Gau
ssρ, 21 fim was 2800 Gauss (see curve q in Figure 1).

As is clear from these results, in the present invention, α-Fe
Since PT was used as the base layer for both films containing 103 as the main component, the reduction of α-Fe2O3 to Fe, 04 was promoted, and γ-Fe, which was finally oxidized as the progressive reaction proceeded at low temperature, was 0. It can be seen that the saturation magnetization of the thin film containing as the main component is high.

Example 7 A Rh film with a thickness of 0.1 μm was applied as a base layer on the alumite-treated A1 alloy substrate 7, and a 0.1 μm thick Rh film was applied thereon.
．． A 17 μm α-pe,o thin film was formed under the same conditions as in Example]. Further, under the same conditions as in Example 1.

The α-Fe20BY table! The membrane was reduced and oxidized. Therefore, it was possible to reduce the heat treatment of the first generation more than before. f)) As shown in Figure 1, the saturation magnetization of the γ-F'el os# film was 3600 Gauss, which was higher than before. 111i was etched with Ar ions, and the entire composition in the thickness direction of the film was measured by Auger+lj molecular analysis. The 1ll11 constant results are shown in FIG.

In the figure, the peak of Rh gradually rises from 11J at the etching time when the peak of the package begins to decrease, and 15-ri, this is ] f iron chloride tw ++y This shows that Rh has not expanded at all within the 7
Therefore, the above-mentioned effect was not obtained due to the presence of Rh diffused in the iron oxide thin film, but the above-mentioned effect was obtained because Rh existed outside of the iron oxide thin film as an underlying layer. It turns out that.

Example 3 A St wafer with a thickness of 0.21/'ms and a diameter of 100!
Im AP, Au, Pd, Ru, Rh, Ir or O
A base layer of s was applied. On top of that is the same α-Fe as in Example 1.
A thin film containing 203 as the main component was formed under the same conditions, and then the above thin film was heated for 1 hour in an H gas stream containing water vapor to the temperature shown in the table below to reduce it to a thin film containing F+404 as the main component. . Furthermore, the Fe3O4 thin model was exposed to 29
It was heated to 0° C. for 4 hours to oxidize into a thin film containing γ-1i'e10B as a main component. The saturation magnetization of the obtained thin film mainly composed of r -Fe2O3 is shown in the table below.
At 3500 Gauss, a higher value than before was obtained.

Table 4 Example 4 An St inner disk with a radius of 100 fi was used as a substrate, and an Ir underlayer with a thickness of 1.01 μm was formed on the substrate. Furthermore, a thin film containing α-1i'e203 as the main component as in Example 1 was formed thereon to a thickness of 0.14 μm. Next, the α-FetOs''tL acid component thin film was subjected to the same reduction and oxidation heat treatment as in Example 1 to form a thin film of 11 g mainly composed of γ-Fe 20B. The saturation magnetization of the film was 3400 Gauss, and the same value as before was obtained.

Example 5 A polyimide substrate with a diameter of 100 mm, Ni-P was used as a substrate.
Using plated At alloy substrates, the surface of these substrates has a thickness of 0.
．． A Pd underlayer of 0.01 μm was applied. Furthermore, a thin film mainly composed of α-F'elOg having a thickness of 12 μm was formed thereon under the same conditions as in Example 1. Next, the thin film was heated at 150° C. for 1 hour in a humid H2 stream to reduce it to a thin film containing Fe3O4 as a main component. The saturation magnetization of both of the obtained iron oxide magnetic thin films was 3500 Gauss.

As described above in detail based on the examples, the present invention allows the reduction heat treatment temperature to be significantly lowered than in the past, and allows the reduction reaction to proceed uniformly in the film thickness direction. The saturation magnetization of the γ-FelO@ thin film increases compared to the conventional method.In addition, since the reduction heat treatment temperature has been lowered, roughness of the film surface is prevented during the heat treatment, and furthermore, Ru, 11. h, Ir or O
If a high hardness metal element such as No. 8 is used, it is also possible to manufacture a magnetic disk with improved head crush resistance.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between saturation magnetization (Gauss) and γ-Fe 203 film thickness (μm), and Figure 2 is a graph showing the relationship between composition and etching time. 1 (γ-1?620 manufactured by
3 thin film, 2 is a γ-Fe203 thin film using PT as a base layer, 3 is a γ-Fe203 thin film using R11'fr: as a base layer.
03 thin film, 4 is oxygen concentration, 5 is F'e speed, 7 is ■ζh concentration, and 6 is C concentration. Patent Applicant Nippon Telegraph and Telephone Public Corporation Agent Patent Attorney Mitsuishi Shibu (and 1 other person) Figure 1 γLFe 20 March Denoq (A%)

Claims (1)

[Claims] Forming a thin film mainly composed of α-Fe203 on the substrate,
In the method for manufacturing an iron oxide magnetic thin film, the method includes the step of heating the thin film in a reducing atmosphere to form a thin film containing Feg04 as a main component.
, Pt, Rh, Ir, Ru, or at least one citron of 08) is formed in advance on the base layer.
- A method for producing an iron oxide magnetic thin film, characterized by applying a thin film containing 20 g of F"e as a main component,