WO2017221896A1

WO2017221896A1 - Tunnel magnetoresistance element and method for manufacturing same

Info

Publication number: WO2017221896A1
Application number: PCT/JP2017/022551
Authority: WO
Inventors: 康夫安藤; 幹彦大兼; 耕輔藤原; 純一城野; 匡章土田
Original assignee: 国立大学法人東北大学; コニカミノルタ株式会社
Priority date: 2016-06-20
Filing date: 2017-06-19
Publication date: 2017-12-28
Also published as: JPWO2017221896A1; CN109314181A; JP6923881B2; CN109314181B

Abstract

The present invention improves the structure of a free magnetic layer of a tunnel magnetoresistance element, and achieves magnetoresistance characteristics having high linearity. A tunnel magnetoresistance element comprises a fixed magnetic layer 10, an insulation layer 20, and a free magnetic layer 30 which are stacked in that order from the side closer to a substrate 2, wherein the free magnetic layer includes a ferromagnetic layer 31 with a lower surface bonded to the insulation layer, and a soft magnetic layer 33 stacked in contact with an upper surface of the ferromagnetic layer. Axes of easy magnetization (A2) of the ferromagnetic layer and the soft magnetic layer constituting the free magnetic layer are in the same direction as one another and in a different direction to an axis of easy magnetization (A1) of the fixed magnetic layer.

Description

Tunnel magnetoresistive element and manufacturing method thereof

The present invention relates to a tunnel magnetoresistive element and a manufacturing method thereof.

A tunnel magnetoresistive element (TMR (Tunnel Magneto Resistive) element) includes a pinned magnetic layer whose magnetization direction is fixed, a free magnetic layer whose magnetization direction changes under the influence of an external magnetic field, and a pinned magnetic layer And an insulating layer disposed between the magnetic layer and the free magnetic layer to form a magnetic tunnel junction (MTJ (Magnetic Tunnel Junction)). The resistance of the insulating layer is changed by the tunnel effect according to the angular difference between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. Examples of using the tunnel magnetoresistive element include a magnetic memory, a magnetic head, and a magnetic sensor. (Patent Documents 1-5).
In addition, a soft magnetic layer (NiFe, CoFeSiB, etc.) that easily reacts to an external magnetic field is disposed in the free magnetic layer, and a structure in which a free magnetic layer, an insulating layer, and a fixed magnetic layer are stacked in this order from the side close to the substrate. By performing heat treatment in a magnetic field, high linearity is achieved by utilizing the resistance change of the insulating layer by the tunnel effect according to the angular difference between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer caused by an external magnetic field. There is a technology for producing a sensitive magnetic sensor (Patent Document 6).
In the free magnetic layer, a soft magnetic layer (NiFe, CoFeSiB, etc.) that easily reacts to an external magnetic field is disposed, and a magnetic coupling layer (Ta) is interposed between the ferromagnetic layer and the soft magnetic layer that are joined to the insulating layer. And Ru), a synthetic bond that generates only a magnetic bond is used while eliminating a solid physical bond between the magnetic tunnel junction and the soft magnetic material (Patent Documents 1-6).

Japanese Patent Laid-Open No. 9-25168 JP 2001-68759 A JP 2004-128026 A JP 2012-221549 A JP2013-48124A JP 2013-105825 A

However, according to the study by the present inventors, in the configuration described in Patent Document 6, if the shape of the free magnetic layer is increased (expected that Hk is improved and noise is reduced) in order to further increase the sensitivity, the upper insulating layer In addition, the fixed magnetic layer is adversely affected (presumed to be caused by deterioration of uniformity and crystallinity), and it is difficult to improve the performance as a magnetic sensor.
On the other hand, in order to increase the shape of the free magnetic layer without adversely affecting the insulating layer and the pinned magnetic layer, the pinned magnetism is started from the side close to the substrate as in the configurations of

Patent Documents

1, 2, 4, and 5. A layer, an insulating layer, and a free magnetic layer may be stacked in this order. However, in the case of this structure, a highly accurate magnetic sensor with high linearity has not been realized by heat treatment. In order to use the magnetoresistive element as a magnetic sensor that accurately measures the strength of the magnetic field, the resistance changes proportionally up and down according to changes in the positive magnetic field and the negative magnetic field from the zero detection magnetic field (neutral position). The property (linearity) to cause is required.

The present invention has been made in view of the above problems in the prior art, and an object of the present invention is to improve the structure of the free magnetic layer of the tunnel magnetoresistive element and realize a magnetoresistive characteristic with high linearity.

The invention according to claim 1 for solving the above-described problems is a pinned magnetic layer in which the magnetization direction is fixed, a free magnetic layer whose magnetization direction changes under the influence of an external magnetic field, and the pinned layer A magnetic tunnel junction is formed by an insulating layer disposed between the magnetic layer and the free magnetic layer, and a tunnel effect is applied according to an angular difference between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer. A tunnel magnetoresistive element that changes the resistance of an insulating layer,
From the side close to the substrate supporting the magnetic layer and the insulating layer, the pinned magnetic layer, the insulating layer, and the free magnetic layer are laminated in this order.
The free magnetic layer is a tunnel magnetoresistive element having a ferromagnetic layer whose lower surface is joined to the insulating layer, and a soft magnetic layer laminated in contact with the upper surface of the ferromagnetic layer.

According to a second aspect of the present invention, the easy magnetization axes of the ferromagnetic layer and the soft magnetic layer constituting the free magnetic layer are in the same direction and are different from the easy magnetization axis of the pinned magnetic layer. The tunnel magnetoresistive element according to claim 1, wherein:

The invention according to claim 3 is the tunnel magnetoresistive element according to

claim

1 or 2, wherein the soft magnetic layer constituting the free magnetic layer is made of a ferromagnetic alloy. .

The invention according to claim 4 is characterized in that the soft magnetic layer constituting the free magnetic layer is made of an alloy of permalloy (NiFe, NiFeCuMO, NiFeCοMO) or amorphous (CoFeSiB, CoFeCrSiB, CoFeNiSiB, NiFeSiB). The tunnel magnetoresistive element according to

claim

1 or 2.

The invention according to claim 5 is the tunnel magnetoresistive element according to

claim

1 or 2, wherein the soft magnetic layer constituting the free magnetic layer is made of a ferrimagnetic alloy. .

The invention according to claim 6 is the tunnel magnetoresistive element according to

claim

1 or 2, wherein the soft magnetic layer constituting the free magnetic layer is made of a ferrite alloy.

The invention according to claim 7 is characterized in that the soft magnetic layer constituting the free magnetic layer is made of an alloy of microcrystals (NiCuNbSiB, NiCuZrB, NiAlSiNiSrB). This is a tunnel magnetoresistive element.

The invention according to claim 8 is the tunnel magnetoresistive element according to any one of claims 1 to 7, wherein the insulating layer is made of a material having a coherent tunnel effect. .

The invention according to claim 9 is characterized in that the insulating layer is formed of any one of magnesium oxide, spinel, and aluminum oxide. This is a tunnel magnetoresistive element.

The invention according to claim 10 is a method of manufacturing the tunnel magnetoresistive element according to any one of claims 1 to 9,
The laminated magnetic layer and the insulating layer are laminated on the substrate, and the ferromagnetic layer constituting the free magnetic layer is laminated, and heat treatment is performed while applying an external magnetic field to the free layer. A first heat treatment step in a magnetic field that forms the easy axis of the ferromagnetic layer constituting the magnetic layer and the easy axis of the pinned magnetic layer in the same direction;
After the first magnetic field heat treatment step, forming the soft magnetic layer constituting the free magnetic layer while applying an external magnetic field in a different direction from that in the first magnetic field heat treatment step. And a tunnel magnetoresistive element manufacturing method comprising: a film forming step in a magnetic field in which an easy axis of magnetization of the free magnetic layer is formed in a different direction with respect to the easy axis of magnetization of the pinned magnetic layer.

The invention according to claim 11 is a second heat treatment step in a magnetic field in which, after the film formation step in the magnetic field, heat treatment is performed while applying an external magnetic field in the same direction as in the film formation step in the magnetic field,
11. The third magnetic field heat treatment step of performing heat treatment while applying an external magnetic field in the same direction as in the first magnetic field heat treatment step after the second magnetic field heat treatment step. It is a manufacturing method of a tunnel magnetoresistive element.

According to the present invention, it is possible to realize magnetoresistance characteristics with high linearity.

It is a schematic diagram which shows the direction of magnetization of the tunnel magnetoresistive element in the state of the position P0 on the graph of FIG. 1D. It is a schematic diagram which shows the direction of magnetization of the tunnel magnetoresistive element in the state of the position P1 on the graph of FIG. 1D. It is a schematic diagram which shows the direction of magnetization of the tunnel magnetoresistive element in the state of the position P2 on the graph of FIG. 1D. It is a graph which shows the ideal magnetoresistive characteristic which this invention tends to implement | achieve. It is sectional drawing which shows the laminated structure of the example of a conventional tunnel magnetoresistive element. It is a graph which shows the magnetoresistive characteristic which expresses in the prior art example of FIG. The horizontal axis represents the external magnetic field (H (Oe)), and the vertical axis represents the rate of change in resistance of the tunnel magnetoresistive element (TMR ratio (%)). It is sectional drawing which shows the laminated structure of the tunnel magnetoresistive element of another conventional example. It is sectional drawing which shows the laminated structure of the tunnel magnetoresistive element which concerns on one Embodiment of this invention. It is sectional drawing of the laminated structure which shows the manufacturing process of the tunnel magnetoresistive element based on one Embodiment of this invention. It is sectional drawing of the laminated structure which shows the manufacturing process of the tunnel magnetoresistive element based on one Embodiment of this invention following FIG. 6A. FIG. 6B is a cross-sectional view of the multilayer structure showing the manufacturing process of the tunnel magnetoresistive element according to the embodiment of the present invention following FIG. 6B. It is a graph which shows the magnetoresistive characteristic of the tunnel magnetoresistive element which concerns on one Embodiment of this invention. The horizontal axis represents the external magnetic field (H (Oe)), and the vertical axis represents the rate of change in resistance of the tunnel magnetoresistive element (TMR ratio (%)). It is a graph which shows the magnetoresistive characteristic of the tunnel magnetoresistive element which concerns on one Embodiment of this invention, and shows the thing after implementing the 2nd, 3rd heat processing process in a magnetic field. The case where the heat treatment temperature of the second heat treatment step in the magnetic field is 200 ° C. and the heat treatment temperature of the third heat treatment step in the magnetic field is 180 ° C. is shown. The horizontal axis represents the external magnetic field (H (Oe)), and the vertical axis represents the rate of change in resistance of the tunnel magnetoresistive element (TMR ratio (%)). It is a graph which shows the magnetoresistive characteristic of the tunnel magnetoresistive element which concerns on one Embodiment of this invention, and shows the thing after implementing the 2nd, 3rd heat processing process in a magnetic field. The case where the heat treatment temperature in the second magnetic field heat treatment step is 200 ° C. and the heat treatment temperature in the third magnetic field heat treatment step is 200 ° C. is shown. The horizontal axis represents the external magnetic field (H (Oe)), and the vertical axis represents the rate of change in resistance of the tunnel magnetoresistive element (TMR ratio (%)). It is the surface view and sectional drawing of a laminated structure which show the manufacturing process of the tunnel magnetoresistive element based on one Example of this invention. FIG. 9B is a surface view of the multilayer structure showing the manufacturing process of the tunneling magneto-resistance element according to one example of the present invention following FIG. 9A. FIG. 9B is a cross-sectional view of the multilayer structure showing the manufacturing process of the tunnel magnetoresistive element according to one example of the present invention, following FIG. 9A. FIG. 9B is a surface view of the multilayer structure showing the manufacturing process of the tunneling magneto-resistance element according to one example of the present invention following FIG. 9B. FIG. 9B is a cross-sectional view of the stacked structure showing the manufacturing process of the tunnel magnetoresistive element according to one example of the present invention following FIG. 9B. FIG. 9D is a surface view of the multilayer structure showing the manufacturing process of the tunnel magnetoresistive element according to the example of the present invention following FIG. 9C. FIG. 9C is a cross-sectional view of the multilayer structure showing the manufacturing process of the tunnel magnetoresistive element according to the example of the present invention following FIG. 9C. FIG. 9D is a surface view of the multilayer structure showing the manufacturing process of the tunneling magneto-resistance element according to one example of the present invention following FIG. 9D. FIG. 9D is a cross-sectional view of the multilayer structure illustrating the manufacturing process of the tunnel magnetoresistive element according to the example of the present invention following FIG. 9D. FIG. 9E is a surface view of the multilayer structure showing the manufacturing process of the tunnel magnetoresistive element according to the example of the present invention following FIG. 9E. FIG. 9E is a cross-sectional view of the multilayer structure showing the manufacturing process of the tunnel magnetoresistive element according to the example of the present invention following FIG. 9E. FIG. 9F is a surface view of the laminated structure, following FIG. 9F, showing the manufacturing process of the tunnel magnetoresistive element according to one example of the present invention. FIG. 9F is a cross-sectional view of the multilayer structure illustrating the manufacturing process of the tunnel magnetoresistive element according to the example of the present invention following FIG. 9F.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The following is one embodiment of the present invention and does not limit the present invention.

First, a basic structure of a tunnel magnetoresistive element and ideal magnetoresistive characteristics to be realized by the present invention will be described with reference to FIGS. 1A to 1D.
As shown in FIGS. 1A-1C, the tunnel magnetoresistive element 1 includes a fixed magnetic layer 10 whose magnetization direction is fixed, a free magnetic layer 30 whose magnetization direction changes under the influence of an external magnetic field, and a fixed magnetic layer A magnetic tunnel junction is formed by the insulating layer 20 disposed between the magnetic layer 10 and the free magnetic layer 30, and tunneling is performed according to an angular difference between the magnetization direction of the pinned magnetic layer 10 and the magnetization direction of the free magnetic layer 30. The resistance of the insulating layer 20 is changed by the effect.
1A to 1C show the magnetization direction 10A of the pinned magnetic layer 10 and the magnetization direction 30A of the free magnetic layer 30 in each magnetic field state shown in FIG. 1D. 1A shows a state in which the detected magnetic field is zero (neutral position, position P0 on the graph of FIG. 1D), and FIG. 1B shows a state in which a predetermined plus magnetic field is loaded (position P1 on the graph of FIG. 1D). FIG. 1C shows a state in which a predetermined negative magnetic field is loaded (position P2 on the graph of FIG. 1D).
In FIG. 1A, in the state where the detection magnetic field is zero (neutral position P0), the magnetization direction 10A of the pinned magnetic layer 10 and the magnetization direction 30A of the free magnetic layer 30 are stable at a twist position of approximately 90 degrees. This is because each magnetized in the direction of the easy axis. That is, the tunnel magnetoresistive element 1 shown in FIGS. 1A to 1C is formed at a position where the easy magnetization axis of the free magnetic layer 30 is twisted by approximately 90 degrees with respect to the easy magnetization axis of the pinned magnetic layer 10. An arrow 10A shown in 1A indicates the direction of the easy axis of magnetization of the pinned magnetic layer 10, and an arrow 30A indicates the direction of the easy axis of magnetization of the free magnetic layer 30.
As shown in FIGS. 1A to 1C, the magnetization direction 10A of the pinned magnetic layer 10 is constant without being affected by the change of the external magnetic field, and the magnetization direction 30A of the free magnetic layer 30 is the external magnetic field (H1, H2). Changes under the influence.
As shown in FIG. 1B, when an external magnetic field H1 in the opposite direction to the magnetization direction 10A of the pinned magnetic layer 10 is applied to the tunnel magnetoresistive element 1, the magnetization direction 30A of the free magnetic layer 30 changes to the pinned magnetic layer. 10 spins in the direction opposite to the magnetization direction 10A, and the resistance of the insulating layer 20 increases due to the tunnel effect (the resistance increases from R0 to R1 in FIG. 1D). The change in resistance is schematically shown by the thickness of the arrows of the currents I0, I1, and I2 in FIGS. 1A-1C.
As shown in FIG. 1C, when an external magnetic field H2 having the same direction as the magnetization direction 10A of the pinned magnetic layer 10 is applied to the tunnel magnetoresistive element 1, the magnetization direction 30A of the free magnetic layer 30 changes to the pinned magnetic layer. 10 spins in the same direction as the magnetization direction 10A, and the resistance of the insulating layer 20 decreases due to the tunnel effect (the resistance decreases from R0 to R2 in FIG. 1D).
As shown in FIG. 1D, the property (linearity) that causes a resistance change proportional to the strength of the external magnetic field (the graph is linear) in both the direction in which the resistance (vertical axis) increases and the direction in which it decreases. We want to realize a tunnel magnetoresistive element 1 having

A conventional tunnel magnetoresistive element 101 shown in FIG. 2 is of the kind described in Patent Documents 1-5, in which a pinned magnetic layer 10 is formed below the insulating layer 20 and a free magnetic layer 30 is formed on the top. The layer 30 has a laminated structure in which a magnetic coupling layer (Ru) 32 is interposed between a ferromagnetic layer (CoFeB) 31 and a soft magnetic layer (NiFe or CoFeSi) 33.
Specifically, in the conventional tunnel magnetoresistive element 101, a base layer (Ta) 3 is formed on a substrate (Si, SiO ₂ ) 2 and an antiferromagnetic layer (from the bottom) is formed as a pinned magnetic layer 10 thereon. IrMn) 11, ferromagnetic layer (CoFe) 12, magnetic coupling layer (Ru) 13, and ferromagnetic layer (CoFeB) 14 are laminated, and a free magnetic layer 30 is formed thereon via an insulating layer (MgO) 20. The laminated structure includes a ferromagnetic layer (CoFeB) 31, a magnetic coupling layer (Ru) 32, and a soft magnetic layer (NiFe or CoFeSi) 33 laminated from below.
In such a conventional tunnel magnetoresistive element 101, the direction of the easy axis of magnetization of all the magnetic layers can be obtained even if the heat treatment in the magnetic field is performed a plurality of times while applying the external magnetic field while changing the direction each time. As a result, the magnetoresistive characteristics have a high hysteresis as shown in FIG. 3, and the above-described linearity cannot be realized. The arrow A1 shown in FIG. 2 is the direction of the easy axis of magnetization of the magnetic layer.

On the other hand, the conventional tunnel magnetoresistive element 102 shown in FIG. 4 is of the kind described in Patent Document 6, and has a laminated structure in which the fixed magnetic layer 10 and the free magnetic layer 30 are turned upside down with respect to FIG. . In the conventional tunnel magnetoresistive element 102, the direction of the easy magnetization axis (arrow A1) of the free magnetic layer 30 is formed in a direction different from the direction of the easy magnetization axis of the pinned magnetic layer 10 (arrow A2). In addition, the shape of the free magnetic layer 30 can be increased (Hk is improved and noise is expected to be reduced), but the upper insulating layer 20 and the fixed magnetic layer 10 are adversely affected (because of deterioration of uniformity and crystallinity). It was difficult to improve the performance as a magnetic sensor.

Therefore, as shown in FIG. 5, the tunnel magnetoresistive element 1A of the present invention is fixed from the side close to the substrate 2 that supports the

magnetic layers

10 and 30 and the insulating layer 20, similarly to the conventional tunnel magnetoresistive element 101. The magnetic layer 10, the insulating layer 20, and the free magnetic layer 30 are stacked in this order, and the magnetic coupling layer (Ru) 32 is removed from the conventional stacked structure of the tunnel magnetoresistive element 101. A laminated structure having a ferromagnetic layer 31 bonded to the insulating layer 20 and a soft magnetic layer 33 laminated in contact with the upper surface of the ferromagnetic layer 31 is employed.
According to such a laminated structure, the easy magnetization axes of the ferromagnetic layer 31 and the soft magnetic layer 33 constituting the free magnetic layer 30 are in the same direction, and are different from the easy magnetization axis of the pinned magnetic layer 10 ( It can be formed to have a magnetization characteristic at a twisted position (for example, a direction twisted approximately 90 degrees), and the linearity described above can be realized.

(Manufacturing process key points)
For this purpose, the main points of the manufacturing method will be described.
First, as shown in FIG. 6A, after laminating the layers from the substrate 2 to at least the ferromagnetic layer 31, the laminated body is subjected to a heat treatment while applying an external magnetic field in a predetermined direction (arrow A1), and free magnetic A first heat treatment process in a magnetic field is performed in which the easy axis of the ferromagnetic layer 31 constituting the layer 30 and the easy axis of the pinned magnetic layer 10 are formed in the same direction.
After the first heat treatment process in the magnetic field, as shown in FIG. 6B, it is free to apply an external magnetic field that is twisted in the direction different from that in the first heat treatment process in the magnetic field (in the direction of arrow A2). By forming the soft magnetic layer 33 constituting the magnetic layer 30, the easy magnetization axis of the free magnetic layer 30 is different from the easy magnetization axis of the pinned magnetic layer 10 (for example, a direction twisted approximately 90 degrees). A film formation step in the magnetic field to be formed is performed to obtain a stacked structure shown in FIG. 6C.
As shown in FIG. 6C, the easy axis of magnetization of the ferromagnetic layer 31 and the soft magnetic layer 33 constituting the free magnetic layer 30 are the same through the first heat treatment process in the magnetic field and the film formation process in the magnetic field. It is possible to form magnetization characteristics that are in the direction and different from the easy magnetization axis of the pinned magnetic layer 10 (preferably in a direction twisted approximately 90 degrees). That is, the easy magnetization axis of the pinned magnetic layer 10 is formed in the magnetic field direction (arrow A1) applied during the first heat treatment process in the magnetic field, and the easy magnetization axis of the free magnetic layer 30 is formed in the film formation process in the magnetic field. It is formed in the magnetic field direction (arrow A2) applied at the time.
At this point, a linear magnetoresistive characteristic as shown in FIG. 7 is obtained.

Further, it is preferable to carry out the following step after the film forming step in the magnetic field. That is, a second heat treatment process in a magnetic field is performed in which heat treatment is performed while applying an external magnetic field in the same direction (arrow A2) as in the film formation process in a magnetic field. Further, after the second heat treatment process in the magnetic field, a third heat treatment process in the magnetic field is performed in which the heat treatment is performed while applying the external magnetic field in the same direction as the first heat treatment process in the magnetic field (arrow A1). Thereby, as shown in FIG. 8, Hk and Hc can be made small and high sensitivity can be achieved.

(Example of manufacturing process)
An embodiment of a manufacturing process according to the main points of the manufacturing process will now be described with reference to FIGS. 9A-9G2. 9A-9G2, the illustration of the underlayer 3 is omitted.
A first magnetic field heat treatment step is performed on the ferromagnetic tunnel junction (MTJ) multilayer film (layers 10, 20, 31) formed on the substrate 2 (FIG. 9A). The direction of the magnetic field to be applied is the direction of arrow A1, the strength of the magnetic field is 1T, and the heat treatment temperature is 375 ° C. This heat treatment greatly improves the tunnel magnetoresistance (TMR) ratio, which is the rate of change in resistance.

A resist pattern is formed on the surface of the MTJ multilayer film subjected to the first heat treatment process in a magnetic field by photolithography or electron beam lithography (photolithography in this embodiment) (FIGS. 9B1 and 9B2). The layer 41 is a Ta layer formed on the ferromagnetic layer 31 and is formed before the first magnetic field heat treatment step. A resist pattern 42 is formed on the Ta layer 41.
Ar ion milling is performed on the MTJ multilayer film on which the resist pattern 42 is formed, and etching is performed up to the MgO insulating layer 20 (FIGS. 9B1 and 9B2). Since the MTJ multilayer film directly under the resist pattern 42 is not exposed to Ar ions, the multilayer film structure remains up to the uppermost layer, and the formed resist-shaped MTJ pillars are formed (FIGS. 9B1 and 9B2).

An interlayer insulating layer 43 is formed to electrically insulate the MTJ pillar from the soft magnetic layer 33 and the upper electrode layer formed in a later process, and to allow current to flow only in the MTJ pillar portion (FIGS. 9C1 and 9C2). As a material of the interlayer insulating layer 43, SiO ₂ or Al—Ox can be used (in this embodiment, SiO ₂ is used). As a process for forming the interlayer insulating layer 43, a lift-off method or a contact hole forming method can be used (in this embodiment, a lift-off method). In the lift-off method, an insulating film such as SiO ₂ is formed on the entire substrate while leaving the resist pattern 42 for MTJ pillar formation. A sputtering method or low-temperature CVD can be used for forming the insulating film (low-temperature CVD is used in this embodiment). After forming the insulating film, the resist 42 is removed by ultrasonically cleaning the substrate with an organic solvent such as acetone or dimethylpyrrolidone. At this time, since the insulating film formed on the resist 42 is also removed, a structure in which the multilayer film is exposed only on the upper surface of the MTJ pillar can be manufactured. In the contact hole forming method, the MTJ pillar forming resist pattern 42 is removed with an organic solvent or the like, and an insulating film is formed on the entire substrate. Thereafter, a resist pattern having openings where only electrical contacts on the MTJ pillar are required is formed, and reactive etching is performed using CHF3, CH4, or the like as a process gas, thereby forming openings in the insulating film. By removing the resist pattern for opening the contact with an organic solvent or the like, a structure in which the multilayer film is exposed only on the upper surface of the MTJ pillar can be manufactured.

A resist pattern 44 is formed on the substrate on which the interlayer insulating layer 43 is formed by photolithography using the soft magnetic layer 33 and the mask for forming the upper electrode (FIGS. 9D1 and 9D2). Pattern formation is performed using the region where the soft magnetic layer 33 and the upper electrode layer are formed as an opening.
Etching by Ar ion milling is performed on the substrate on which the soft magnetic layer 33 and the upper electrode layer forming resist pattern 44 are formed to expose the upper CoFeB ferromagnetic layer 31 in the MTJ multilayer film (FIGS. 9E1 and 9E2). . By forming the soft magnetic layer 33 on the exposed CoFeB layer 31, soft magnetic characteristics are exhibited in the magnetoresistance curve. In order to prevent the magnetic coupling between the CoFeB layer 31 and the soft magnetic layer 33 from being hindered by oxidation or the like on the surface of the CoFeB layer 31, the substrate is not exposed to the atmosphere during the Ar ion milling and the soft magnetic layer 33 deposition. It is desirable to continuously perform etching and film formation under vacuum. The soft magnetic layer 33 can be made of an amorphous material such as CoFeSiB or a soft magnetic material such as a NiFe alloy (CoFeSiB is used in this embodiment). By forming a film while applying a magnetic field in the hard axis direction (arrow A2 direction) of the MTJ multilayer film when forming the soft magnetic layer 33 (FIGS. 9F1 and 9F2), the magnetic multilayer film below the MTJ and the upper part are formed. In FIG. 7, the easy axis of magnetization of the CoFeB layer 31 and the soft magnetic layer 33 can be twisted to 90 degrees, whereby the resistance linearly changes with respect to the magnetic field component in the hard axis direction of the free magnetic layer 30. A magnetoresistive curve with linearity as shown is obtained.
In this example, the substrate 2 is made of Si, SiO ₂ , Ta is 5 nm, Ru is 10 nm, IrMn is 10 nm, CoFe is 2 nm, Ru is 0.85 nm, CoFeB is 3 nm, MgO is 2.7 nm, CoFeB. 3 nm and Ta 5 nm were stacked, the magnetic field strength was 1 T, the temperature was 375 ° C., and the first heat treatment was performed in the magnetic field. Then, after exposing the CoFeB layer 31, a soft magnetic layer (CoFeSiB) 33 was formed by sputtering in a magnetic field to a film thickness of 100 nm.

After the soft magnetic layer 33 is formed, the upper electrode layer is formed (FIGS. 9G1 and 9G2). As the upper electrode layer material, Ta, Al, Cu, Au and the like and multilayer films thereof can be used (Ta / Al multilayer film in this embodiment). The upper electrode layer prevents oxidation of the soft magnetic layer 33 and is responsible for electrical connection with a power supply circuit, an amplifier circuit, and the like during sensor operation.
The substrate on which the soft magnetic layer 33 and the upper electrode are formed is ultrasonically cleaned using an organic solvent or the like, and the resist 44 is removed, thereby removing the soft magnetic layer 33 and the upper electrode layer other than the resist opening (FIG. 9G1, 9G2). Therefore, the soft magnetic layer 33 and the upper electrode layer can be formed into arbitrary shapes by photolithography. Further, by performing photolithography a plurality of times, it is possible to produce elements having different shapes for the soft magnetic layer 33 and the upper electrode.
Although the tunnel magnetoresistive element is manufactured by the above microfabrication, the soft magnetic layer 33 is in an as-deposited state in which heat treatment is not performed after the element is manufactured. Therefore, it is possible to develop a magnetoresistive curve having softer magnetic characteristics by performing heat treatment in the magnetic field again on the manufactured element and manipulating the magnetic anisotropy of the soft magnetic layer 33. By performing a heat treatment in a rotating magnetic field or a heat treatment in which the magnetic field direction is changed from the hard axis of the soft magnetic layer 33 to the easy axis, the Hk of the soft magnetic layer 33 is reduced, and higher magnetic field sensitivity is obtained.
In this embodiment, the second magnetic field heat treatment step is performed with the magnetic field direction set to a direction of 90 degrees (arrow A2 direction) with respect to the direction during the first magnetic field heat treatment step (arrow A1 direction). A third heat treatment process in a magnetic field was performed in the 0 degree direction (arrow A1 direction). In the second heat treatment step in a magnetic field, the heat treatment temperature was 200 ° C., and in the third heat treatment step in a magnetic field, the heat treatment temperature was 200 ° C., and the magnetoresistance curve shown in FIG. 8B was obtained. FIG. 8A shows a case where the heat treatment temperature in the second magnetic field heat treatment step is 200 ° C. and the heat treatment temperature in the third magnetic field heat treatment step is 180 ° C. Thus, it can be seen that by increasing the heat treatment temperature in the third heat treatment process in a magnetic field, both Hk and Hc can be reduced and the sensitivity can be increased.

As shown in FIG. 5, the tunnel magnetoresistive element of the present invention is different from the conventional element structure in that the soft magnetic layer is sputtered after the MTJ multilayer film is subjected to the first heat treatment process in the magnetic field. The soft magnetic layer does not adversely affect the process of developing a high TMR ratio by intermediate heat treatment. Therefore, a wide range of material choices for the soft magnetic layer can be provided, and the most suitable material for the application and ease of use, such as ferrimagnetic (eg, permalloy or amorphous), ferromagnetic (eg, ferrite), and microcrystalline alloys. Should be selected.
Also, the free magnetic layer of the conventional tunnel magnetoresistive element has a limit of a film thickness of several nm to several hundred nm, but the soft magnetic layer of several μm is bonded to the free magnetic layer of the tunnel magnetoresistive element of the present invention. The volume of the soft magnetic layer can be very large. Therefore, it can be expected to produce a magnetic sensor having a high SN ratio by greatly reducing white noise and 1 / f noise due to thermal fluctuation of the free magnetic layer.
Furthermore, since the free magnetic layer is located on the outermost surface of the element, the shape can be freely provided. Therefore, it is expected to produce a tunnel magnetoresistive element with a built-in flux concentrator (FC) that concentrates the magnetic flux on the free magnetic layer. Conventionally, the tunnel magnetoresistive element and the FC are manufactured with a physically separated structure. However, in the present invention, the free magnetic layer and the FC are joined as a thin film or an integrated structure, so that the magnetic flux concentration effect is obtained. It is available to the maximum.

The present invention can be used for a tunnel magnetoresistive element and a manufacturing method thereof.

DESCRIPTION OF SYMBOLS 1 Tunnel magnetoresistive element 1A Tunnel magnetoresistive element 2 Substrate 3 Underlayer 10 Fixed magnetic layer 20 Insulating layer 30 Free magnetic layer 31 Ferromagnetic layer 33 Soft magnetic layer

Claims

A pinned magnetic layer whose magnetization direction is fixed, a free magnetic layer whose magnetization direction changes under the influence of an external magnetic field, and an insulating layer disposed between the pinned magnetic layer and the free magnetic layer A tunnel magnetoresistive element that forms a magnetic tunnel junction and changes the resistance of the insulating layer by a tunnel effect according to an angular difference between the magnetization direction of the pinned magnetic layer and the magnetization direction of the free magnetic layer,
From the side close to the substrate supporting the magnetic layer and the insulating layer, the pinned magnetic layer, the insulating layer, and the free magnetic layer are laminated in this order.
The tunneling magnetoresistive element, wherein the free magnetic layer includes a ferromagnetic layer having a lower surface joined to the insulating layer, and a soft magnetic layer laminated in contact with the upper surface of the ferromagnetic layer.
2. The easy magnetization axes of the ferromagnetic layer and the soft magnetic layer constituting the free magnetic layer are in the same direction, and are in different directions with respect to the easy magnetization axis of the pinned magnetic layer. Item 2. The magnetoresistive element according to Item 1.
The tunnel magnetoresistive element according to claim 1 or 2, wherein the soft magnetic layer constituting the free magnetic layer is made of a ferromagnetic alloy.
3. The soft magnetic layer constituting the free magnetic layer is made of an alloy of permalloy (NiFe, NiFeCuMο, NiFeCοMο) or amorphous (CoFeSiB, CoFeCrSiB, CoFeNiSiB, NiFeSiB). The tunnel magnetoresistive element described in 1.
3. The tunnel magnetoresistive element according to claim 1, wherein the soft magnetic layer constituting the free magnetic layer is made of a ferrimagnetic alloy.
The tunnel magnetoresistive element according to claim 1 or 2, wherein the soft magnetic layer constituting the free magnetic layer is made of a ferrite alloy.
The tunnel magnetoresistive element according to claim 1 or 2, wherein the soft magnetic layer constituting the free magnetic layer is made of an alloy of microcrystals (NiCuNbSiB, NiCuZrB, NiAlSiNiSrB).
The tunnel magnetoresistive element according to any one of claims 1 to 7, wherein the insulating layer is formed of a material having a coherent tunnel effect.
The tunnel magnetoresistive element according to any one of claims 1 to 7, wherein the insulating layer is formed of any one of magnesium oxide, spinel, and aluminum oxide.
A method for manufacturing a tunnel magnetoresistive element according to any one of claims 1 to 9,
The laminated magnetic layer and the insulating layer are laminated on the substrate, and the ferromagnetic layer constituting the free magnetic layer is laminated, and heat treatment is performed while applying an external magnetic field to the free layer. A first heat treatment step in a magnetic field that forms the easy axis of the ferromagnetic layer constituting the magnetic layer and the easy axis of the pinned magnetic layer in the same direction;
After the first magnetic field heat treatment step, forming the soft magnetic layer constituting the free magnetic layer while applying an external magnetic field in a different direction from that in the first magnetic field heat treatment step. A method of manufacturing a tunnel magnetoresistive element, comprising: an in-magnetic field film forming step of forming an easy magnetization axis of the free magnetic layer in a direction different from the easy magnetization axis of the pinned magnetic layer.
A second heat treatment step in the magnetic field in which, after the film formation step in the magnetic field, heat treatment is performed while applying an external magnetic field in the same direction as in the film formation step in the magnetic field;
11. The third magnetic field heat treatment step of performing heat treatment while applying an external magnetic field in the same direction as in the first magnetic field heat treatment step after the second magnetic field heat treatment step. A method of manufacturing a tunnel magnetoresistive element.