JP2001119082A - Magnetoresistive element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetoresixtive element, which is small in a static magnetic connecting force of a magnetic layer as roughness of a lower electrode, a lower wiring, or the like is very low, and can obtain a superior output signal within the range of a desirable magnetic field. SOLUTION: This magnetoresistive element has an electrical conductor (a lower element 14, a lower wiring, or the like) of an AlCu alloy having composition of Cu of 20 at.% to 90 at.% on a substrate 16, and a multilayered film in which at least a first ferromagnetic layer 11, a nonmagnetic layer 12 and a second ferromagnetic layer 13 are sequentially formed thereon. It is more preferable that the composition of Cu of the AlCu alloy be 40 at.% to 60 at.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AlC having a small surface roughness as an electric conductor such as a lower electrode or a lower wiring.
The present invention relates to a magnetoresistive element capable of easily realizing an antiparallel state of magnetization of a magnetoresistive effect film by using a u alloy and obtaining a good output signal.

[0002]

2. Description of the Related Art As shown in FIG.
0 is basically two ferromagnetic layers (first ferromagnetic layer 11,
It is composed of a multilayer film having a sandwich structure having the nonmagnetic layer 12 between the second ferromagnetic layers 13). These two ferromagnetic layers 1
The coercive forces 1 and 13 are different. Therefore, by applying an appropriate magnetic field from the outside, the magnetization directions of the two ferromagnetic layers 11 and 13 become parallel or antiparallel.
The resistance of the element changes depending on the magnetization state. When the magnetization directions are parallel, the resistance of the element is small, and when the magnetization directions are antiparallel, the resistance of the element is large. That is, when a constant current is applied to the element and the magnetization is changed from a parallel state to an anti-parallel state, the voltage of the element increases, and conversely, when the magnetization is changed from anti-parallel to parallel, the voltage decreases.

Various film configurations have been conventionally proposed for the magnetoresistive film 10, but when the above-mentioned intermediate layer (nonmagnetic layer 12) is an insulator and electrons tunnel through the intermediate layer. The magnetoresistive film is called a spin tunnel film. An insulator generally used for the spin tunnel film is alumina. Many studies have reported that the thickness of the spin tunnel film is preferably about 1 nm to 3 nm in view of the energy barrier width. On the other hand, when the intermediate layer (nonmagnetic layer 12) is a conductor, the magnetoresistive film is called a spin scattering film. In the case of the spin scattering film, the current may flow parallel or perpendicular to the film surface.

[0004] The magnetoresistive film 10 can be used as a memory element. In this case, the application of the magnetic field is performed, for example, by arranging orthogonal upper and lower conductors 21 and 22 as shown in FIG. 16 and causing currents Is and Iw to flow through the wires 21 and 22 to generate a magnetic field. Since the magnetization reversal of the magnetoresistive film 10 occurs only when a current flows simultaneously in the upper and lower conductors 21 and 22, the magnetization direction of one element of the plurality of magnetoresistive films 10 formed on a plane is selectively changed. Can be changed to Upper and lower conductors 21, 2
2 when currents Is and Iw flow through them, respectively.
The magnetic field generated by w is applied in parallel to the film surface of the magnetoresistive film 10, but the magnetic field generated from the upper conductor 21 and the magnetic field generated from the lower conductor 22 act in directions different from each other by 90 °.

Further, when the lower magnetic layer (first ferromagnetic layer 11 in FIG. 15) of the magnetoresistive film 10 is not used as an electrode or wiring, it is necessary to provide an electrode or wiring below the lower magnetic layer. .

[0006]

SUMMARY OF THE INVENTION In the case of a spin scattering film,
The change in magnetoresistance is determined by the intermediate layer (nonmagnetic layer 12) and the magnetic layer (first layer).
This occurs at the interface between the ferromagnetic layer 11 and the second ferromagnetic layer 13) and inside the magnetic layer, and does not occur inside the intermediate layer. Therefore, the smaller the thickness of the intermediate layer, the higher the ratio of electrons involved in the resistance change, and the higher the magnetoresistance change rate. But,
As the thickness of the intermediate layer decreases, the magnetostatic coupling force acting between the two magnetic layers increases, and the magnetization does not become antiparallel. One of the causes is an orange peel effect. That is, if the interface between the magnetic layer and the nonmagnetic layer is curved, it is difficult to realize the antiparallel state of magnetization. The same applies to a spin tunnel film having a thin intermediate layer of 1 nm to 3 nm.

From such a point, it is desirable that the interface between the magnetic layer and the intermediate layer is flat in order to obtain a large magnetoresistance change rate and an antiparallel magnetization state within a desired magnetic field range. Therefore, it is necessary to use a substrate having a small surface roughness (surface roughness Ra). In recent years, commonly used silicon wafers and glass substrates are fairly flat, with roughness less than 1 nm. In particular, roughness of about 0.1 nm is realized in a silicon wafer.

In a memory device using a magnetoresistive film,
At least a conductor for applying a magnetic field, an insulating layer, and a magnetic layer are formed between the substrate and the intermediate layer. further,
When the magnetic layer is not used as an electrode or a wiring, a metal layer is further formed between the substrate and the lower magnetic layer. Generally, Al having a small electric resistivity is used for the conductive wires and electrodes, and Ni, Fe, Co, and alloys thereof are used for the magnetic layer. It is generally known that when a film is formed by a sputtering method, the roughness of the thin film is reduced. From this point, it is considered that a sputtering method is preferable as a method of forming a conductive wire, an electrode, or a magnetic layer. Further, when the film is formed by increasing the sputtering gas pressure, the film has a columnar structure, which causes an increase in surface roughness. Therefore, it is preferable to reduce the sputtering gas pressure within a range where the discharge does not become unstable.

The present inventor has set the gas pressure at about 0.3 Pa in consideration of the above points,
Al layer, NiFe on silicon wafer or glass substrate
The layers were sequentially formed and their roughness was examined. It was found that the roughness of the surface of the Al layer was large, and the roughness of the Al layer having a thickness of 50 nm was about 3.5 nm. Further, the surface of the 25 nm thick NiFe layer formed on the Al layer
It showed almost the same value as the roughness of the layer surface. Similarly, an Al layer, a SiN layer (50 nm thick), and a NiFe layer were sequentially formed in the same manner, and the roughness was examined. The roughness of the surface of the multilayer film was not much different from the roughness of the surface of the Al layer. In other words, the SiN layer and the NiFe layer do not significantly increase the surface roughness of the multilayer film, but the surface roughness of the Al film is large, which is not preferable as the lower electrode or the lower wiring of the magnetoresistive element. is there.

The present invention has been made to solve such a problem, and the surface roughness of the electric conductor (lower electrode, lower wiring, etc.) provided on the substrate side of the magnetic layer is extremely low. The magnetic layer has a small magnetostatic coupling force,
It is an object of the present invention to provide a magnetoresistive element capable of obtaining a good output signal within a desired magnetic field range.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies to realize an electric conductive film having a small surface roughness, and have found that an alloy having a specific composition of Al and Cu is very suitable. The present invention has been completed.

That is, the present invention provides an AlCu alloy electric conductor having a Cu composition of 20 at.% Or more and 90 at.% Or less on a substrate, on which at least a first ferromagnetic layer and a non-magnetic layer are formed. And a multi-layer film in which a second ferromagnetic layer is sequentially formed.

[0013]

FIG. 1 is a cross-sectional view showing a film configuration of a spin tunnel film as one embodiment of a magnetoresistive element of the present invention. In the figure, 16 is a substrate, 14 is a lower electrode, 11
Is a first ferromagnetic layer, 12 is a non-magnetic layer (intermediate layer), 13 is a second ferromagnetic layer, and 15 is an upper electrode. Lower electrode 14
The upper electrode 15 needs to have a small electric resistivity, and Al is often used in the conventional technology. However, since the roughness of the surface of the Al layer is large as described above, it is difficult to realize an anti-parallel state of magnetization with the related art. The relationship between the roughness and the magnetic coupling of the two magnetic layers 11, 13 is understood by the topography model proposed by Nehru. According to this model, the lower the unevenness of the interface between the ferromagnetic layers 11 and 13 and the nonmagnetic layer 12 is, the smaller the magnetostatic coupling force between the ferromagnetic layers 11 and 13 is. Become. Therefore,
It is preferable that a material having a small surface roughness is used for the conductor and the electrode.

FIG. 2 is a graph showing a change in roughness with respect to the Cu composition of the AlCu alloy layer. Here, the surface roughness of a 50 nm thick AlCu alloy layer formed on a silicon wafer having a surface roughness of about 0.16 nm was measured. The roughness (surface roughness Ra) is
It is the center line average roughness (Ra) of JIS B0601,
The standard value was adopted as the cutoff value.

As can be seen from the results shown in FIG. 2, when the Cu composition is in the range of 20 at.% To 90 at.%, The roughness is a small value of 1 nm or less, and the roughness is 40 at.
% To 60 at.% Or less, the roughness is 0.2 n.
It is a very small value of about m.

An important technical significance of the present invention is that a film having a lower surface roughness can be obtained by using an AlCu alloy as compared with the case of using Al. It is very useful for wiring and lower wiring. In addition, since the specific numerical value of the roughness is affected by various conditions other than the material, there is no particular limitation on the specific range in the present invention. However, considering the required performance of the magnetoresistive element, generally, the roughness of the surface of the AlCu alloy film is preferably equal to or less than 1.0 nm, and is preferably 0.1 nm or less.
3 nm or less is more preferable.

In FIG. 1, the lower electrode 14 is made of AlCu.
Although the one using an alloy is shown as a preferred form. The present invention is not limited to this. For example, it is possible to use an AlCu alloy for the lower wiring and other various electric conductors located between the first ferromagnetic layer 11 and the substrate 16.

First ferromagnetic layer 11 and second ferromagnetic layer 1
For 3, various materials conventionally known as ferromagnetic layers in a multilayer film of a magnetoresistive element can be used. In particular, Ni
Fe, Fe, Co, CoFe, etc. are preferably used,
The ferromagnetic layer 11 and the second ferromagnetic layer 13 may be appropriately selected so that the magnetizations are reversed by different magnetic fields. For example, the first ferromagnetic layer 11 is a NiFe layer having a relatively small coercive force,
The second ferromagnetic layer 13 is a Co layer having a relatively large coercive force.

As the nonmagnetic layer 12 of the spin tunnel film, various insulators conventionally known as an intermediate layer of the spin tunnel film can be used. Usually, alumina is used. (1) a method of forming an Al layer and spontaneously oxidizing the same; (2) a method of forming an Al layer and oxidizing the same by applying energy with plasma or the like;
(3) a method of reactive sputtering an Al target, and (4) a method of directly forming a film using an alumina target.

FIG. 1 shows a preferred embodiment using a spin tunnel film. The present invention is not limited to this. For example, a spin scattering film may be formed using a conductor as the nonmagnetic layer 12. As the nonmagnetic layer 12 of the spin scattering film, a conductor conventionally known as an intermediate layer of the spin scattering film can be used. Usually, Cu is preferred.

[0021]

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

<Examples 1 to 4> The inside of the film forming chamber was 1 ×
After evacuating to 10 ⁻⁵ Pa or less, an Al target and a Cu target were co-sputtered by DC magnetron sputtering to form an AlCu alloy film having a thickness of 50 nm as the lower electrode 14 on the silicon wafer.

Thereafter, 25n is formed as the first ferromagnetic layer 11.
m thick Ni ₈₀ Fe ₂₀ layer, non-magnetic layer 12 is 2 nm thick alumina layer, and second ferromagnetic layer 13 is 25 nm thick C
The o layer was continuously formed without breaking vacuum. Here, the ferromagnetic layers 11 and 13 are formed by sputtering each target by a DC magnetron sputtering method and forming an alumina layer (nonmagnetic layer 1).
2) was formed by sputtering an alumina target by RF magnetron sputtering. The sputtering gas pressure of each layer is
In each case, the pressure was about 0.3 Pa.

As shown in FIG. 3, the first surface of the spin tunnel film (magnetoresistance effect film)
Of the resist 17 was formed. Next, the Co layer (the second ferromagnetic layer 13), the alumina layer (the nonmagnetic layer 12) and the NiFe layer (the first ferromagnetic layer 11) were partially removed by an ion milling device as shown in FIG. Was removed.

Next, the first resist 17 is removed, and a second resist 18 is formed as shown in FIG.
A silicon nitride film as the insulating layer 19 was formed by F magnetron sputtering. Here, FIG. 5A is a cross-sectional view, and FIG. 5B is a plan view.
(B) and FIGS. 7 (a) and 7 (b).]

After that, the second resist 18 was removed, and a third resist 20 was formed as shown in FIG. Next, an Al film having a thickness of 50 nm was formed by a DC magnetron sputtering method, and the third resist 20 was removed to form an upper electrode 15 and an electrode pad, thereby forming a spin tunnel element as shown in FIG. .

Here, the Cu composition of the AlCu alloy film as the lower electrode 14 is 20 at.% (Example 1), 40 at.% (Example 2), 60 at.% (Example 3), and 90 at. Four types of spin tunnel devices (Example 4) were produced. The measurement results of the magnetoresistance curves of the spin tunnel devices of Examples 1 to 4 are shown in FIGS.
It is shown in FIG. This measurement was performed by a direct current four-terminal method by bringing a probe into contact with each electrode pad.

Comparative Example 1 A spin tunnel device was manufactured in the same manner as in Examples 1 to 4, except that the lower electrode 14 was formed of Cu alone. FIG. 12 shows the measurement results of the magnetoresistance curve.

Comparative Example 2 A spin tunnel device was manufactured in the same manner as in Examples 1 to 4, except that the lower electrode 14 was formed of Al alone. FIG. 13 shows the measurement results of the magnetoresistance curve.

Comparative Example 3 AlCu as Lower Electrode 14
Spin tunnel devices were fabricated in the same manner as in Examples 1 to 4, except that the Cu composition of the alloy film was changed to 10 at.%. FIG. 14 shows the measurement results of the magnetoresistance curve.

<Evaluation Results> In Examples 1 to 4, an AlCu alloy film having a Cu composition of not less than 20 at.% And not more than 90 at.% Is used for the lower electrode 14, and therefore, as shown in FIGS. The magnetic field range where the magnetoresistance change rate of the effect film is large and the resistance is high is wide. Particularly, in Examples 3 and 4, since the Cu composition is 40 at.% And 60 at.%, The magnetic field range where the resistance is high is particularly wide as shown in FIGS. 9 and 10.

In Comparative Examples 1 to 3, since a Cu film, an Al film, or an Al ₉₀ Cu ₁₀ film is used for the lower electrode 14,
As shown in FIGS. 12 to 14, the magnetoresistance ratio is low and the magnetic field range in which the resistance is high is narrower than in each embodiment.

[0033]

As described above, according to the present invention,
A magnetoresistive element having a small magnetostatic coupling force of a magnetic layer and capable of obtaining a good output signal within a desired magnetic field range can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a film configuration of a spin tunnel film as one embodiment of a magnetoresistive element of the present invention.

FIG. 2 is a graph showing a change in roughness with respect to a Cu composition of an AlCu alloy.

FIG. 3 is a cross-sectional view of a spin tunnel film after forming a first resist.

FIG. 4 is a cross-sectional view of the spin tunnel film after removing a Co layer, an alumina layer, and a NiFe layer.

5A and 5B are views showing a spin tunnel film after forming a second resist, wherein FIG. 5A is a cross-sectional view and FIG. 5B is a plan view.

6A and 6B are diagrams showing a spin tunnel film after forming a third resist, wherein FIG. 6A is a cross-sectional view and FIG. 6B is a plan view.

FIG. 7 is a view showing a spin tunnel device after processing;
(A) is a sectional view, and (b) is a plan view.

FIG. 8 is a graph showing a magnetoresistance curve of the spin tunnel device of Example 1 using an Al ₈₀ Cu ₂₀ lower electrode.

FIG. 9 is a graph showing a magnetoresistance curve of a spin tunnel device of Example 2 using an Al ₆₀ Cu ₄₀ lower electrode.

FIG. 10 is a graph showing a magnetoresistance curve of a spin tunnel device of Example 3 using an Al ₄₀ Cu ₆₀ lower electrode.

FIG. 11 is a graph showing a magnetoresistance curve of a spin tunnel device of Example 4 using an Al ₁₀ Cu ₉₀ lower electrode.

FIG. 12 is a graph showing a magnetoresistance curve of the spin tunnel device of Reference Example 1 using a Cu lower electrode.

FIG. 13 is a graph showing a magnetoresistance curve of a spin tunnel device of Comparative Example 2 using an Al lower electrode.

FIG. 14 is a graph showing a magnetoresistance curve of a spin tunnel device of Comparative Example 1 using an Al ₉₀ Cu ₁₀ lower electrode.

FIG. 15 is a sectional view of a basic film configuration of a magnetoresistive film.

FIG. 16 is a layout diagram of a magnetoresistive film and a conductive wire.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Magnetoresistive film 11 1st ferromagnetic layer 12 Non-magnetic layer 13 2nd ferromagnetic layer 14 Lower electrode 15 Upper electrode 16 Substrate 17 1st resist 18 2nd resist 19 Insulating layer 20 3rd resist

Claims (2)

[Claims] 1. An AlCu alloy electric conductor having a Cu composition of not less than 20 at.% And not more than 90 at.% On a substrate, and at least a first ferromagnetic layer, a non-magnetic layer and a second A magnetoresistive element having a multilayer film in which ferromagnetic layers are sequentially formed. 2. The magnetoresistive element according to claim 1, wherein the composition of Cu in the alloy is 40 at.% To 60 at.%.