JP2002124648A - Magnetoresistive memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetoresistive memory in which the oxidations of its magnetic layers are eliminated, i.e., magnetic deteriorations of its magnetic layers caused by their oxidation are not generated, and even if its elements are made fine, the good magnetic-resistance changes of its elements are obtained. SOLUTION: The magnetoresistive memory has insulators 7 made of a nitride formed on the side surface of a magneto-resistance film, where first an second magnetic layers 3, 5 are laminated via a nonmagnetic layer (an insulation layer 4).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetoresistive memory using a magnetoresistive film in which two magnetic layers are stacked via a nonmagnetic layer.

[0002]

2. Description of the Related Art Hitherto, the development of magnetic heads utilizing the anisotropic magnetoresistive effect (AMR effect) of soft magnetic materials has been promoted, and high-density recording on hard disks has been achieved. The AMR effect is a phenomenon in which a current flows in a magnetic material such as a permalloy alloy in an arbitrary direction, and the resistance of the magnetic material changes depending on the angle between the current direction and the magnetization direction of the magnetic material. Other than the head, it is also used for a magnetic sensor, for example.

A magnetic head or a magnetic sensor using a magnetic material having the AMR effect has a characteristic that it has good temperature stability and can be used in a wide range of equipment applications. Furthermore, this AMR
A solid-state memory device using an effect film has been proposed by LJSchwee (Proc. INTERMAG Conf. IEEE Tran
s. Magn., Kyoto, p.405). Unlike conventional semiconductor solid-state memory devices such as DRAMs and SRAMs, which use the electric charge of electrons, the memory devices utilize the spin of electrons, so that the stored information has high preservability and high-speed recording. And can be erased.

However, the rate of change in magnetoresistance due to the AMR effect is as small as about 6% at room temperature. For example, when the recording density of a hard disk is further increased, there is a problem that a sufficient detection output cannot be obtained.

In recent years, a giant magnetoresistive effect (GMR effect) has been applied to the magnetic head of a hard disk having a higher recording density.
Effect) is being used. This GMR
The effect is a phenomenon reported by Baibich et al. In 1988, and its magnetoresistance ratio is about 20% at room temperature.
Shows a value larger than the MR effect (MNBaibich, JMBro
to, A. Fert, F. Nguyen van Dau, F. Petroff, P. Etienn
e, G. Greuzet, A. Friederich and J. Chazelas: Phys. R
ev. Lett., 61, 2473 (1988)). In this report, a magnetic metal thin film and a non-magnetic metal thin film are alternately stacked in multiple layers, and the magnetic moments of the magnetic layers arranged side by side through the non-magnetic layer are magnetically coupled in an antiparallel state. A metal artificial lattice film is used.

There are various materials exhibiting the GMR effect. For example, Fe / Cr metal artificial lattice films and Co /
Cu metal artificial lattice films and the like have been found. Also, GM
The mechanism of developing the R effect is different from that of the AMR effect, and it is considered that the main factor is that the scattering of conduction electrons at the interface between the magnetic layer and the nonmagnetic layer depends on the spin direction of the magnetic layer.

However, in order to obtain the GMR effect in such a metal artificial lattice film, several hundred Oe (Oersted) are required.
Since the above-mentioned saturation magnetic field is required and a large number of laminations are required, it is unsuitable as a material for a magnetic head or the like.

As a material exhibiting the GMR effect, a spin valve film has been further proposed. This is the ferromagnetic layer /
A multilayer film composed of a nonmagnetic layer / a ferromagnetic layer / an antiferromagnetic layer, wherein the magnetization of one ferromagnetic layer is fixed by the antiferromagnetic layer;
The magnetization of the other ferromagnetic layer can be easily inverted by an external magnetic field. As the nonmagnetic layer, a conductor such as Cu is used. The spin valve film is characterized in that the resistance is low when the spins of both ferromagnetic layers are parallel and high when the spins are antiparallel. The saturation magnetic field of this spin valve film is as small as several Oe, and the GMR effect can be obtained without applying a large magnetic field unlike a metal artificial lattice film. However, the magnetoresistance ratio is relatively small at room temperature, about 10%.

In the spin valve film, the magnetization direction of one of the magnetic layers is fixed. However, the state in which the magnetization directions of the two magnetic layers are parallel and anti-parallel is achieved without fixing the magnetization direction. Can be created, the GMR effect appears. Therefore, for example, without providing an antiferromagnetic layer,
The magnitude of the coercive force of the two magnetic layers may be different, and the magnitude of the applied magnetic field may be adjusted. A GMR film having such a film configuration is used as a coercive force difference type GMR film or a weakly coupled GMR film.
It is called a membrane.

When a voltage is applied in the thickness direction of a thin insulating film, electrons flow by tunneling. If the insulating thin film is sandwiched between magnetic materials, the tunneling phenomenon depends on the direction of magnetization of the magnetic layer. This phenomenon is called a ferromagnetic spin tunnel effect (TMR effect), and is a type of magnetoresistance effect. The film structure is basically a sandwich structure of a ferromagnetic layer / insulating layer / ferromagnetic layer as described above, and is the same as the above-described GMR film except that the nonmagnetic layer is an insulator. Of course, the film structure may be a spin valve type. The TMR film has a feature that a high magnetoresistance ratio of 40% or more can be obtained at room temperature.

Recently, researches on memories using the TMR film have been actively conducted. Although a memory using the magnetoresistance effect has been proposed before, it was not sufficient in terms of the output signal size and the recording density due to the use of the GMR film. In the past, there was a technical problem of controlling the composition, shape, and thickness of an insulating film formed between ferromagnetic layers as extremely thin as about 2 nm in a TMR film, but this problem has been gradually solved. Is being done.

[0012]

A memory using a magnetoresistive film has a large number of magnetoresistive films on a substrate, a circuit for passing a current through the magnetoresistive film, and a magnetic field applied to the magnetoresistive film. Are formed, and an insulator is formed to electrically insulate them. An insulator is formed to protect the magnetoresistive film. An oxide such as SiO or Al ₂ O ₃ is generally used as the insulator.

This oxide is formed while supplying oxygen gas at the time of film formation in order to obtain sufficient insulation or pressure resistance. In such a film formation method, the oxide used in the magnetoresistive film is used. Even the body is oxidized. Therefore,
In particular, as the size of the magnetoresistive film is reduced, the ratio of oxidized magnetic atoms to all magnetic atoms increases, so that desired magnetism cannot be obtained, and insufficient information recording or detection is performed. The recorded signal becomes small, and the recorded information cannot be read accurately. This phenomenon is particularly remarkable when an easily oxidizable element such as a rare earth metal is used for the magnetic material.

The present invention has been made in view of these problems of the prior art, and there is no oxidation of the magnetic layer by an insulator formed on the side surface of the magnetic layer, that is, no magnetic deterioration of the magnetic layer due to the oxidation occurs. It is an object of the present invention to provide a magnetoresistive memory capable of obtaining a favorable magnetoresistance change even when the element is miniaturized.

[0015]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventor has found that the use of an insulator made of a nitride prevents the magnetic layer from deteriorating in magnetism and allows fine processing. The inventors have found that the characteristics can be sufficiently maintained even in such a case, and have completed the present invention.

That is, the present invention is characterized in that an insulator made of a nitride is formed on a side surface of a magnetoresistive film in which a first magnetic layer and a second magnetic layer are laminated via a nonmagnetic layer. It is a resistance memory.

[0017]

FIG. 1 is a schematic sectional view showing an embodiment of the element of the magnetoresistive memory of the present invention. In the example shown in this figure, a metal electrode 2 (lower electrode) is disposed on a substrate 1, a first magnetic layer 3 is formed thereon, and an insulating layer 4 (non-magnetic layer) is formed thereon. ing. A second magnetic layer 5 is formed on the insulating layer 4, and a metal electrode 6 (upper electrode) is formed thereon. And
An insulator 7 made of a nitride is formed between the element and the electrode 2.

The substrate 1 preferably has a smooth surface. For example, a silicon wafer or the like having a surface having a crystal orientation (1.0.0) subjected to a thermal oxidation treatment can be suitably used.

As the material of the metal electrode 2 (lower electrode),
It is preferable that the upper surface of the electrode 2 be smooth, have a low electric resistance, and be easily processed. Examples of such a material include metals such as Al, Cu, Ta, and W and alloys thereof. Among them, an AlCu alloy is particularly preferable because its upper surface is smooth.

As the first magnetic layer 3 and the second magnetic layer 5,
It is preferable to use a ferromagnetic layer sufficiently exhibiting the desired effects as the magnetoresistive memory. Specifically, transition metals such as Ni, Fe, and Co and alloys thereof, or Gd, Tb, D
An alloy of a rare earth metal such as y or Nd and a transition metal can be used. In particular, it is preferable to be composed of an alloy of a transition metal and a rare earth metal. However, the first magnetic layer 3 and the second
The magnetic layer 5 is only required to have a difference in coercive force between the two ferromagnetic layers so that a desired function and effect as a magnetoresistive memory can be obtained, and the magnetic material is not particularly limited.

The insulating layer 4 (non-magnetic layer) is not particularly limited, but is generally a tunnel insulating layer made of Cu, Al ₂ O ₃ or the like. In particular, it is preferable to use Al ₂ O ₃ because a higher magnetoresistance ratio can be obtained. Al ₂ O ₃
Is preferred, the layer thickness is preferably about 1 to 2 nm.
A typical example of a method for forming a tunnel insulating layer is a method in which an oxide target such as Al ₂ O ₃ is directly sputtered. Also, after a film of Al or the like is first formed by sputtering, the film is allowed to stand in the air for several hours to be spontaneously oxidized, or after a film of Al or the like is formed, oxygen is introduced into the film forming apparatus and RF power is applied. Generate plasma and Al
Although there is a method of oxidizing the film, any method may be used as long as the insulating layer is sufficiently oxidized and the magnetic film is not oxidized.

In the present invention, the first magnetic layer 3 and the second magnetic layer 5 are laminated via an insulating layer 4 (non-magnetic layer), and constitute a magnetoresistive film. This magnetoresistive film is particularly preferably a ferromagnetic spin tunnel effect film. In this magnetoresistive effect film, for example, one of the two magnetic layers is fixed in magnetization direction and the other magnetic layer is oriented in an arbitrary direction so that it can be used as a magnetoresistive memory. It is also preferable to provide a protective layer on the surface of the magnetoresistive film for the purpose of preventing oxidation of the uppermost ferromagnetic layer. The material forming the protective layer is not particularly limited as long as it has such a function and is a nonmagnetic material.

As a material of the metal electrode 6 (upper electrode),
It is preferable that the material has low electric resistance and is easy to process. Such materials include, for example, Al, Cu, Ta,
W and their alloys.

For the insulator 7, an insulating material made of nitride is used. The nitride is not particularly limited, and may be any nitride that can function as an insulator provided on the side surface of the magnetoresistive film of the magnetoresistive memory. In particular, the use of AlN as the nitride is preferable because the same insulating properties as Al ₂ O ₃ can be maintained and the alkali resistance can be increased. On the other hand, the use of, for example, Si ₃ N ₄ is not preferred because the reaction with an alkali substance may cause deterioration.

A memory using such a magnetoresistive film generally has a large number of magnetoresistive films on a substrate, a circuit for passing a current through the magnetoresistive film, and a magnetic field applied to the magnetoresistive film. Wiring and the like are formed, and an insulator is formed to electrically insulate them. An insulator is formed to protect the magnetoresistive film. In the present invention, since the nitride is used as the insulator, the problem of the related art can be solved.

In particular, it is important to use a nitride as an insulator at least on the side surface of the magnetoresistive film in order to solve the problem of oxidation of the magnetic material. In other words, in the prior art,
In particular, when the element is miniaturized or when an easily oxidizable element such as a rare earth metal is used for the magnetic material, the problem of oxidation of the magnetic material may occur. The present invention solves such a problem. You can do it. Furthermore, not only the side surface of the element, but also the recording means for recording information on the magnetoresistive film and the insulator on the side surface of the reading means for reading out the recorded information (insulator between wirings) are nitrided. Object (AlN
Is a very preferred embodiment.

[0027]

The present invention will be described in more detail with reference to the following examples.

<Embodiment 1> First, TMR is performed in the following order.
A film was prepared. First, a silicon wafer (crystal orientation 1.0.0) whose surface was oxidized was used as a substrate, and an AlCu alloy was formed as a lower electrode on the substrate by sputtering to a thickness of 20 nm. The first ferromagnetic layer Ni
₈₀ Fe ₂₀ was formed to a thickness of 20 nm. Further, an Al ₂ O ₃ target was directly sputtered to form a 2 nm tunnel insulating layer (nonmagnetic layer). Subsequently, 20 nm of Co was formed as a second ferromagnetic layer. That is, in this embodiment, the first ferromagnetic layer is formed of Ni ₈₀ Fe ₂₀ , and the second ferromagnetic layer is formed of Co. Finally, as a protective layer on the surface of the laminated thin film, a Pt film was formed by 5 nm sputtering.

Next, the TMR thin film laminated on the substrate by this sputtering was processed to a size of several μm by using the photolithography method and the lift-off method in the following order.
First, a photosensitive cured resin (photoresist) on the substrate
Was applied to a thickness of 1 μm using a spin coater. In this case, a desired film thickness was realized by controlling the spin coater at 3000 rpm using a photoresist having a viscosity of 6 cP. Next, a heater maintained at about 90 ° C.
A 0 second bake treatment was performed. After this baking, return to room temperature,
The substrate on which the photoresist was applied by the spin coater was used to form a first pattern with a metal mask made of Cr using an exposure apparatus (wavelength: 436 nm).

Next, the substrate on which the photoresist mask was formed was subjected to a first pattern cutting process by dry etching using Ar ion gas. An AlN film was formed to have a thickness equal to or several nm thick as the depth of the AlN film cut by sputtering as a formation of an insulating layer between the cut element side surface and the element and the wiring. At this time, the dimensions of the first magnetic layer and the second magnetic layer were set to 0.6 μm × 0.3 μm.

Thereafter, the wafer on which the insulating film of the AlN film was formed was lifted off by an ultrasonic cleaner.
After the resist mask is removed, a second pattern of photoresist is formed in the same procedure as when forming the first pattern,
An Al film was formed to a thickness of 50 nm by sputtering. Thereafter, lift-off was performed using an ultrasonic cleaning machine to obtain an upper electrode. Next, the obtained magnetoresistive memory element was annealed in a magnetic field in a vacuum chamber. The annealing temperature is 25
At 0 ° C., a magnetic field of 300 Oe was applied in the longitudinal direction of the magnetic layer.

FIG. 2 shows a magnetoresistive curve of the magnetoresistive memory element thus manufactured. As can be seen from FIG. 2, the magnetoresistance change rate is as large as 26%, and the change is steep.

COMPARATIVE EXAMPLE 1 A sputtering gas was used as a mixed gas of 50 sccm of argon gas and 30 sccm of oxygen gas, and a silicon target was sputtered to make Al ₂ O ₃ an insulator formed on the side surface of the element and between the element and the wiring. Except for this, a magnetoresistive memory element was manufactured in the same manner as in the example. FIG. 3 shows a magnetoresistance curve of the magnetoresistance memory element. As can be seen from FIG. 3, the rate of change in magnetoresistance is 5%, which is significantly smaller than the rate of change in magnetoresistance shown in FIG. 2 (Example 1), and the change in resistance is gradual.

[0034]

As described above, in the magnetoresistive memory of the present invention, the magnetic layer is not oxidized, that is, the magnetic layer is not degraded by the oxidation, and even if the element is miniaturized, the magnetoresistive memory is excellent. A change in magnetoresistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing one embodiment of an element of a magnetoresistive memory of the present invention.

FIG. 2 is a graph showing a magnetoresistance curve of the magnetoresistance memory of Example 1.

FIG. 3 is a graph showing a magnetoresistance curve of the magnetoresistance memory of Comparative Example 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 substrate 2 metal electrode (lower electrode) 3 first magnetic layer 4 insulating layer (non-magnetic layer) 5 second magnetic layer 6 metal electrode (upper electrode) 7 insulator

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01F 10/14 H01L 43/08 Z 10/26 H H01L 43/08 27/10 447 G01R 33/06 R

Claims (6)

[Claims] 1. A magnetoresistive memory, wherein an insulator made of a nitride is formed on a side surface of a magnetoresistive film in which a first magnetic layer and a second magnetic layer are laminated via a nonmagnetic layer. 2. A recording device for recording information on a magnetoresistive film, and a reading device for reading the recorded information, wherein the recording device and the side surface of the reading device are also made of nitride. 2. The magnetoresistive memory according to claim 1, wherein an insulator is formed. 3. The magnetoresistive memory according to claim 1, wherein the nitride forming the insulator is aluminum nitride. 4. The magnetoresistive memory according to claim 1, wherein said magnetoresistive effect film is a ferromagnetic spin tunnel effect film. 5. The magnetoresistive film can fix the magnetization direction of one of the two magnetic layers and the magnetization direction of the other magnetic layer can be directed to an arbitrary direction. The magnetoresistive memory according to any one of claims 1 to 4. 6. A magnetic layer used for a magnetoresistive film,
The magnetoresistive memory according to claim 1, wherein the magnetoresistive memory is made of an alloy of a transition metal and a rare earth metal.