JP2000285415A - Manufacture for ferromagnetic tunnel junction magnetoresistive element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an insulating layer in a short time and obtain an MR ratio with a higher performance stability by forming an aluminum layer as an insulator layer through vapor deposition and oxidizing the layer by plasma in an ambience including oxygen. SOLUTION: In a method for forming an insulator layer, a film of metallic aluminum is formed by vapor deposition and is plasma oxidized. A first ferromagnetic layer as a face of the insulator layer where the film is to be formed is more preferably formed by sputtering than the vapor deposition. When the vapor deposited aluminum is oxidized to be the insulating layer, plasma oxidation is used for the oxidation, so that the aluminum can be oxidized to an equal level in a short time as compared with natural oxidation, and the insulating film can be obtained with a resistance value approximately in an equal level in a short time. Particularly when the plasma oxidation is applied to the vapor deposited aluminum layer to obtain the insulating film, a tunneling element of a superior stability and a larger MR ratio can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk device, a magnetic encoder device, etc.
The present invention relates to an element using a magnetoresistance effect used for reading information recorded on a magnetic recording medium. More specifically, the present invention relates to a magnetoresistive element using a magnetoresistance effect by a ferromagnetic tunnel junction.

[0002]

2. Description of the Related Art There is a hard disk as a magnetic recording device capable of recording and reading a large amount of information at high speed. The recording density of hard disks used in personal computers and the like has been rapidly increasing in a short period of time, and this trend is expected to continue in the future. As a head element for reading information recorded on a magnetic medium of a hard disk, a magnetoresistive element is often used.

[0003] The magnetoresistance effect is an effect in which the electric resistance changes when a magnetic field is applied to a conductive magnetic material. A change in the magnetic field is detected using an element having this effect, and information recorded on a magnetic medium is read. Read. This magnetoresistance effect (MR-
The magnetoresistance element is not affected by the moving speed of the magnetic recording medium and can be miniaturized by thinning. Information recorded on the magnetic medium with extremely high surface density can be easily identified and read. There are advantages that can be done. As such an element, a magnetic anisotropic element that detects a resistance change ratio (MR ratio) according to an angle between a current direction of a ferromagnetic material and a magnetization axis has been conventionally used. On the other hand, a non-magnetic conductive layer is sandwiched between two ferromagnetic layers, and the antiferromagnetic layer is in contact with the outside of one of the ferromagnetic layers. With the development of a valve element, the MR ratio, which was at most about 2%, was improved to 6 to 7%, and practical use of a magnetic head using the same has been promoted. However, with the increasing trend of magnetic recording density,
There is a demand for a device having an even higher MR ratio, and a magnetoresistive effect device utilizing the ferromagnetic tunnel effect has been responded to.

Normally, almost no current flows between two conductors separated by an insulator. However, when the insulator is extremely thin, current flows when a voltage is applied.
In the classical mechanical interpretation that the electric current is caused by the movement of an electron particle, this is a very unlikely phenomenon, but according to quantum mechanics that the electron motion is a wave, the barrier of a finite width insulator Electrons can pass through at a certain probability. This is called a tunnel effect, and the current flowing therethrough is called a tunnel current. Then, when a tunnel current is detected between the two conductive ferromagnetic materials separated by the thin insulator layer, the magnetization of the ferromagnetic materials on both sides of the insulator layer becomes
It has been clarified that there is a difference in the tunnel effect between the case where the directions are the same and the case where the directions are different from each other, and this is detected as a change in the electric resistance value. Initially, this phenomenon and its large MR ratio were found in a very low temperature range, but it was found that by selecting a combination of a ferromagnetic material and an insulator, a sufficient effect could be obtained even at room temperature. Furthermore, it has been theoretically predicted that the MR ratio due to the ferromagnetic tunnel effect will reach several tens of percent, and the possibility of a magnetoresistive effect element has been attracting attention.

The structure of a magnetoresistance effect element (tunneling element) using a ferromagnetic tunnel junction is such that one of two conductor layers sandwiching a thin non-magnetic insulator layer has a ferromagnetic material whose magnetization direction changes easily by an external magnetic field. The other layer is composed of a ferromagnetic layer whose magnetization direction is hard to move or is fixed, but the performance of the insulator layer is extremely important here. The insulator layer must first obtain a practicable tunnel current, and even if a tunnel current is obtained, the applied frequency is limited if the electric resistance is high, so the resistance must be as low as possible. For that purpose, the thickness of the insulator layer must be as small as possible. However, when the thickness is reduced, short-circuit occurs due to slight inhomogeneity or defect, and when short-circuited, the device cannot be used as an element.

[0006] The thickness of the insulating layer of this tunneling element was initially about 10 nm. For example, in the invention disclosed in JP-A-4-103014, a 10-nm layer of Al ₂ O ₃ is sandwiched between _two 100-nm-thick Fe-1.0 atomic% C ferromagnetic layers.
One of the ferromagnetic layers has a structure in which the magnetization direction is fixed by an Fe-Mn antiferromagnetic layer, and each layer is formed by an ion beam sputtering apparatus. Japanese Patent Application Laid-Open No. 6-244477 discloses an invention in which a 15-nm aluminum film is deposited as an insulating layer and the surface is oxidized by being left in the air. The MR ratio of these ferromagnetic tunnel junctions is
It was not as large as about 1%, and had a high resistance value. If the film thickness is reduced, the resistance value can be reduced, but a defect due to a short circuit is liable to occur, and it is not easy to manufacture a stable element.

However, since then, bonding techniques have been improved, and an MR ratio exceeding 10% has been realized with an insulating layer thickness of 1 to 2 nm. In this case, in order to stably obtain an extremely thin insulating layer, for example, as in the invention disclosed in Japanese Patent Application Laid-Open No. 9-198622, an aluminum layer of about 1 nm is formed on a layer containing Fe ₂ O _3. There is a method in which a film is formed, and a plurality of layers are formed thereon, and then heated in a vacuum. Then, Fe ₂ O ₃ is reduced to Fe ₃ O ₄ and aluminum is oxidized to Al ₂ O ₃ . However, in many cases, a 1-2 nm thick metal aluminum film is formed on the ferromagnetic layer by a sputtering method or the like, and then is oxidized by natural oxidation by leaving it in the air to form an insulating film. A method of forming a ferromagnetic layer on the substrate is adopted. This is because it is considered that a dense oxide film with few defects such as pinholes can be formed by natural oxidation in the atmosphere.

In this natural oxidation method, if the oxidation time is short, the performance of the obtained device is unstable such as a change during use or a short circuit, and if a stable one is to be obtained, the oxidation takes several hundred hours or more. Time consuming, and the resulting junction is MR
The ratio variation is large. Prolonged oxidation has poor productivity,
Also, mere exposure to room temperature tends to result in inadequate control of temperature, humidity, atmosphere, etc., which may cause variations.Therefore, after aluminum deposition, oxidation by plasma discharge in an oxygen atmosphere has been attempted. (Journal of the Japan Society of Applied Magnetics: Vol. 22 (1998), No. 4-2, p. 557, or Bulletin of the Japan Institute of Metals: Vol. 37 (1998), No. 9, p. 736). According to this, a tunnel effect junction equivalent to long-time natural oxidation in the atmosphere can be obtained by oxidation treatment for about 60 seconds, and an MR ratio of up to 16% with the tunneling element formed as it is, if appropriate heat treatment is applied. It is stated that an MR ratio as high as 24% can be obtained. However, it is said that the magnitude of the variation in the MR ratio of the obtained junction is almost the same as that in the case of natural oxidation.

As described above, since the tunneling element has a possibility of obtaining a high MR ratio, it is strongly required that the performance is further improved, such as lowering the resistance, that the stable performance is ensured, or that the tunnel element can be manufactured with a high yield. Requested.
However, at present, it cannot be said that these problems have been addressed to a level sufficient for practical use.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetoresistive element using a ferromagnetic tunnel junction, that is, a tunneling element, in which an insulating layer, which has conventionally required a long time, can be formed in a short time. Moreover, it is an object of the present invention to provide a method capable of manufacturing an element having a high MR ratio with good performance stability.

[0011]

The biggest problem in putting a tunneling element into practical use is that the characteristics of the manufactured element vary greatly and it is difficult to obtain a stable and high-performance element. Most of the insulator layer for obtaining the tunnel effect uses an Al ₂ O ₃ (alumina) film, and its desirable thickness is as small as about 1 to 2 nm. The formation of this insulator film is generally performed by oxidizing metal aluminum after forming it.
A method of forming an alumina film is employed.

The present inventors considered that the greatest cause of the characteristic variation of the tunneling element was the instability of the quality of the film, and made various studies on the influence of the film manufacturing conditions. Since the thickness of the film is extremely thin as described above, it is not easy to form a uniform and sound layer, and it is difficult to form a film due to variations in film thickness, short-circuits due to slight defects such as pinholes, and irregularities in the film formation substrate. It is presumed that the potential as a barrier to the tunnel effect is not stable due to uniformity and the like. Therefore, a first magnetic layer is formed on a substrate, a thin aluminum layer is formed on the first magnetic layer, and oxidation conditions such as temperature, oxygen concentration, and time are changed, or aluminum is oxidized using oxygen plasma to form an insulator. A layer was formed, a device was fabricated, and its performance was examined. However, it has been difficult to stably obtain a device of a specific quality due to a large variation in the resistance value of the junction and a large variation in the MR ratio of each product, and also due to a short circuit or the like.

In these investigations, the conditions which seemed to be preferable for the purpose of obtaining a higher MR ratio relatively stably were (a) forming an aluminum layer before oxidation by vapor deposition, (b) The oxidation was plasma oxidation rather than natural oxidation, and (c) the first magnetic layer for forming the aluminum layer was formed by sputtering. Therefore, the inventors further studied the combination of these methods and the optimum conditions thereof, and reached the present invention. That is, the gist of the present invention is to (1) manufacture a magnetoresistive element using a tunnel effect of an insulator layer junction composed of a first ferromagnetic layer, an insulator layer, and a second ferromagnetic layer. A method for producing a ferromagnetic tunnel junction magnetoresistive element, wherein an aluminum layer is formed by vapor deposition as an insulator layer, and this is oxidized by plasma in an atmosphere containing oxygen (2). The method for manufacturing a ferromagnetic tunnel junction magnetoresistance effect element according to the above (1), wherein the first ferromagnetic layer is formed by a sputtering method.
For the formation of the aluminum layer, a sputtering method is usually used in many cases in view of the adhesion and uniformity of the film. In contrast,
It was found that a film formed by vapor deposition can provide a tunneling element having more stable performance.

In the sputtering method, when a film is formed, particles collide with a surface to be formed with high energy and are deposited. For this reason,
Rearrangement of the colliding particles occurs on the deposition surface, and a flat and uniform layer can be obtained. However, on the other hand, it is speculated that this has the effect of hitting the surface on which the film is to be formed because the energy of the particles is large, and that the surface is roughened. It is also conceivable that it is in a state. As the film thickness increases, the surface roughness improves the adhesion of the film, and aluminum particles deposited thereafter eliminate initial defects, and an excellent film is formed by uniformizing the film surface.
However, in the case of a thin insulating film required for a tunneling element, the effect of roughening the surface on which the film is formed and defects due to entrainment of gas particles affect the aluminum layer before oxidation, which causes instability of the insulating layer. I think it will be.

[0015] In the case of vapor deposition, the deposition is almost solely thermal energy of the particles, so that the surface on which the film is to be formed is rarely roughened and gas particles are not involved. However, rearrangement and the like of the deposited particles hardly occur on the film formation surface, and there is a problem that the uniformity is poor. However, the uniformity can be greatly improved by a method such as increasing the degree of vacuum to suppress the entrapment of gas particles and uniforming the energy of the vapor-deposited particles, such as electron beam heating vapor deposition in an ultra-high vacuum.

After the aluminum layer is formed, it is oxidized to form an insulating layer. In this case, a case where natural oxidation is performed for a long time and a case where plasma oxidation is performed in a short time in an atmosphere containing oxygen are compared. As a result, it has been found that, particularly when the aluminum layer is formed by the vapor deposition method, the variation is smaller in the short-time plasma oxidation. In long-term natural oxidation, the chance of impurity contamination increases, and slight fluctuations in atmosphere and temperature are expected to have a cumulative effect over a long period of time. In some cases, conditions can be easily managed. However, when aluminum formed by the sputtering method is oxidized, there is not much difference in the performance of the obtained element between the long-time natural oxidation and the short-time plasma oxidation. When aluminum is oxidized, there is a large difference in the dispersion between the two oxidation methods. The reason why the vapor deposition film, which is presumed to be a little lacking in density, is formed in the film by rapid oxidation by plasma oxidation. It is thought that this is because it is likely to reduce the easy defects, but it is not clear.

As described above, there is a difference in stability such as a variation in characteristics of an insulating film after oxidation depending on a method of forming an aluminum film before oxidation. Regarding the film forming method, the vapor deposition method and the sputtering method were compared. As a result, it was found that the sputtering method was clearly superior. This is different from the case of the aluminum layer, where the thickness of the layer to be formed is sufficiently large, so that the sputtering method in which the moving distance from the surface is large due to the large energy of the deposited particles is smoother. It is presumed that a simple surface is obtained. That is, a uniform aluminum layer is formed on the surface by the smoother sputtering method by the evaporation method with less roughening of the surface,
This is considered to result in a sound oxide film obtained by rapid oxidation in a short time and an excellent insulating layer with little variation.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a method of manufacturing a tunneling element of the present invention, a thin film forming method such as a vapor deposition method or a sputtering method which is generally used can be applied as it is. Further, even if the main constituent element has a three-layer structure including the first ferromagnetic layer, the insulator layer, and the second ferromagnetic layer, the main component may be positioned outside the first or second ferromagnetic layer. The structure may be like a spin valve element in which the ferromagnetic layers are adjacent to each other. Furthermore, a structure in which a layer that performs some function such as a shield or the like may be stacked between the substrate and the first ferromagnetic layer. The materials of the first ferromagnetic layer and the second ferromagnetic layer are not particularly limited, and may be any as long as a magnetoresistance effect by a ferromagnetic tunnel junction can be obtained. In any case, as a method of forming the insulator layer, metal aluminum is formed by a vapor deposition method, and this is subjected to plasma oxidation.

It is desirable that the first ferromagnetic layer, which is the surface on which the insulator layer is to be formed, be formed by sputtering rather than vapor deposition. This is because the energy of the particles at the time of film formation is large, the surface smoothness after film formation is good, aluminum as an insulator layer is uniformly formed, and the characteristics of the obtained tunneling element are stable. .

The deposition of aluminum to be an insulator layer is performed by a vapor deposition method. This is because when the sputtering method is used, the variation in the electric resistance value and the MR ratio of the obtained element becomes large. The method is not particularly limited as long as it is a vapor deposition method, but an ultra-high vacuum electron beam vapor deposition method is desirable in order to obtain stable performance. The thickness of the aluminum layer that is oxidized into an insulator layer is preferably 0.5 to 2.0 nm. This is 0.5nm
This is because a short circuit of the insulating layer is apt to occur when the temperature is less than the above, and the insulating layer becomes unstable. If the thickness is more than 2 nm, a practical tunneling element cannot be obtained due to an increase in electric resistance.

The deposited aluminum is oxidized to form an insulating layer, and plasma oxidation is used for the oxidation. This is because aluminum can be oxidized to a similar degree in a short time as compared with natural oxidation, and a resistance value of an insulating film can be substantially the same in a short time. Further, when the insulating film is applied particularly to a vapor-deposited aluminum layer, it becomes possible to obtain a tunneling element having excellent stability and a high MR ratio. The oxidation may be performed under a condition that a stable plasma can be obtained at an oxygen pressure of 0.1 to 10 Torr, and it is sufficient that the deposited aluminum can be almost completely oxidized.

After the aluminum is oxidized to form an insulator layer, the second ferromagnetic layer, the antiferromagnetic layer, and other film forming methods may be any of vapor deposition, sputtering, and the like. May be used.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described with reference to specific examples.

FIG. 1 schematically shows the shape of the first ferromagnetic material, Co on a glass substrate 1 using a metal mask.
_A cross-shaped tunneling element was fabricated by sequentially forming a layer 2 of ₉₀ Fe ₁₀ (subscripts indicate atomic concentration%), an insulator layer 3 and a layer 4 of Fe of the second ferromagnetic material. Ferromagnetic layers 2, 4
Each had a width of 0.3 mm and a thickness of 20 nm. The insulator layer 3 is formed from metal aluminum as a raw material by the following method (1) formed by vapor deposition and plasma oxidized in an oxygen atmosphere, and (2) formed by sputtering for comparison. Film and left for 24 hours in the air to be naturally oxidized.
It was changed in the range of nm. The area of the joint is 0.09mm ² (= 0.3mm
× 0.3 mm).

The conditions for forming each layer are as follows.

(1) Insulating layer is formed by depositing aluminum by vapor deposition and plasma oxidation. First ferromagnetic layer Film forming apparatus: DC magnetron sputtering apparatus Sputter gas: Argon (gas pressure 1.5 × 10 ⁻³ Torr) Sputtering Power: 200 W Applied magnetic field: 40 Oersted ・ Insulator layer Aluminum film deposition equipment: Vacuum electron beam evaporation equipment Beam voltage: 5 kV Beam current: 160 mA Vacuum degree: 1 × 10 ^-8 Torr (Evaporation time is 1-4 minutes) Oxidation: Plasma ashing device Plasma power: 200 W Oxidation time: 100 seconds ・ Second ferromagnetic layer Film formation device: Vacuum electron beam evaporation device Beam voltage: 5 kV Beam current: 45 mA Degree of vacuum: 2 × 10 ⁻⁸ Torr Applied magnetic field: 100 Oersted (2) The insulating layer was formed by sputtering aluminum.
Spontaneous oxidation ・ Same as the first ferromagnetic layer (1) ・ Insulator layer Aluminum film forming device: DC magnetron sputtering device (same as the first ferromagnetic material layer) Sputter gas: Argon (gas pressure 1.5 × 10 ^-3 Torr) ) Sputtering power: 200 W Oxidation: Leaving in the air for 24 hours ・ Same for the second ferromagnetic layer (1) After any film formation, the inside was sufficiently cooled, then released to the atmosphere, and the metal mask was replaced. The application of the magnetic field during the film formation was performed in a direction parallel to the length direction of each of the ferromagnetic layers. As shown in FIG. 1, the electrical resistance value and the MR ratio of the fabricated junction device at a magnetic field change of 500 Oe were measured by a DC four-terminal method. At this time, the current was adjusted so that the voltage between the terminals was about 0.5 mV.

FIG. 2 or FIG. 3 shows the electric resistance value or M with respect to the thickness of aluminum in the case of the above method (1).
The measurement result of R ratio is shown. Also, in the case of the method (2) performed for comparison, the measurement results in the same manner as in (1) are shown in FIGS. 4 and 5, respectively.

As is clear from the comparison between FIG. 2 and FIG.
In the tunneling device using the insulating layer formed by vapor-depositing and plasma-oxidizing aluminum according to the present invention, the electrical resistance tends to increase as the aluminum thickness increases. In contrast, it can be seen that there is little variation in the values. On the other hand, when aluminum is formed by a sputtering method and spontaneously oxidized, the tendency of the change in the electric resistance value with respect to the aluminum thickness is not clear, and the variation is large even with the same aluminum thickness.

From the comparison between FIG. 3 and FIG. 5, when the aluminum of the present invention is vapor-deposited and plasma-oxidized, it is found that the MR ratio is large and stable when the aluminum thickness is 1.1 nm or more. it is obvious.

[0030]

According to the present invention, a good product can be stably manufactured with a good yield with respect to a tunneling element which has been difficult to stably mass-produce due to the frequent occurrence of characteristic failures. This can greatly promote the practical use of a magnetoresistive element that can be expected to have a high MR ratio.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating a structure of a magnetoresistive element using a ferromagnetic tunnel junction and a method for measuring characteristics thereof.

FIG. 2 is a diagram showing a relationship between a film thickness of aluminum and a measured value of electric resistance of a junction in a tunneling element in which an insulating layer is formed by depositing aluminum by an evaporation method and performing plasma oxidation.

FIG. 3 is a diagram showing the relationship between the thickness of aluminum and the measured MR ratio of a tunneling element in which an insulating layer is formed by depositing aluminum by an evaporation method and performing plasma oxidation.

FIG. 4 is a diagram showing a relationship between a film thickness of aluminum and a measured electric resistance of a junction in a tunneling element in which an insulating layer is formed by forming aluminum by sputtering and spontaneously oxidizing the film.

FIG. 5 is a diagram showing the relationship between the thickness of aluminum and the measured MR ratio of a tunneling element in which an insulating layer is formed by sputter-depositing aluminum and spontaneously oxidizing it.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 First ferromagnetic layer 3 Insulator layer 4 Second ferromagnetic layer 5 Voltmeter 6 Ammeter 7 Power supply

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shuji Tanoue 1-8 Fuso-cho, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd. Electronics Technology Research Laboratory F-term (reference) 5D034 BA03 BA15 DA07

Claims (2)

[Claims] 1. A method of manufacturing a magnetoresistive element using a tunnel effect at a junction of an insulator layer comprising a first ferromagnetic layer, an insulator layer, and a second ferromagnetic layer, the method comprising: A method for manufacturing a ferromagnetic tunnel junction magnetoresistance effect element, comprising forming an aluminum layer as a body layer by vapor deposition, and oxidizing the aluminum layer by plasma in an atmosphere containing oxygen. 2. The method according to claim 1, wherein said first ferromagnetic layer is formed by a sputtering method.