Magnetic tunneling junction element having thin composite oxide film

A tunneling junction element comprises: a substrate; a lower conductive layer formed on the substrate; a first oxide layer formed on the lower conductive layer and having a non-stoichiometric composition;a second oxide layer formed on the first oxide layer and having a stoichiometric composition; and an upper conductive layer formed on the second oxide layer, wherein the first oxide layer is oxidized during a process of forming the second oxide layer and has an oxygen concentration which is lower than an oxygen concentration of the second oxide layer and lowers with a depth in the first oxide layer, and the first and second oxide layers form a tunneling barrier.

BACKGROUND OF THE INVENTION

A) Field of the Invention

The present invention relates to a magnetic tunneling junction element having an oxide film such as alumina (aluminum oxide) film.

B) Description of the Related Art

Magnetic tunneling junction elements are known as megnetoresistive elements to be used for magnetic heads, magnetic memories, magnetic sensors and the like. As a magnetic tunneling junction element manufacture method, a method as illustrated inFIGS. 10 to 12is known (e.g., JP-A-2000-91668).

In the process illustrated inFIG. 10, on the surface of a ferromagnetic layer1made of Fe or the like, an aluminum film2of 2 nm in thickness is formed by sputtering. Next, pure oxygen is introduced into a sputtering chamber, and the aluminum layer2is oxidized for 10 minutes by setting an oxygen pressure in a range from 20 mTorr to 200 Torr. An alumina film3is therefore formed on the surface of the aluminum film2as shown inFIG. 11. This alumina film3is used as a tunneling barrier film. Thereafter, in the process illustrated inFIG. 12, a ferromagnetic layer4made of Co—Fe alloy or the like is formed on the alumina film3by sputtering.

As a method of forming an alumina film as a tunneling barrier film, other methods are also known, including (a) a method of exposing an aluminum film in the air to make it subject to natural or native oxidation and (b) a method of subjecting an aluminum film to a plasma oxidation process (for the method (a), refer to JP-2000-91668, and for the method (b), refer to JP-2000-36628).

With the conventional method (b), oxidation becomes likely to be too excessive so that an underlying ferromagnetic layer may be oxidized at the interface with the tunneling barrier film and the variation in a magnetic tunneling resistance may become lower.

With the conventional method (a), it takes a long time, several hours, to complete the oxidation process so that the tunneling barrier film may be formed with pin holes or contaminated by the presence of dusts in the air and the film quality may be degraded.

Although the method illustrated inFIGS. 10 to 12is an improved method of the method (a), an aluminum film2not oxidized is likely to be left under the alumina film3as shown inFIG. 11. The left aluminum film2lowers the variation in the magnetic tunneling resistance. If oxidation of the aluminum film is insufficient, an electrostatic breakdown voltage of the magnetic tunneling junction lowers and a time-dependent change in the variation in the magnetic tunneling resistance becomes large when the magnetic tunneling junction element is placed in a high temperature environment. From these reasons, the reliability of a magnetic tunneling junction element lowers.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel magnetic tunneling junction element having a thin oxide film which can be formed in a short time without oxidizing an underlying layer.

It is another object of the invention to provide a novel magnetic tunneling junction element capable of improving the variation in a magnetic tunneling resistance, the electrostatic breakdown voltage, reliability and productivity of the tunneling junction element.

According to one aspect of the present invention, there is provided a tunneling junction element comprising: a substrate; a lower conductive layer formed on said substrate; a first oxide layer formed on said lower conductive layer and having a non-stoichiometric composition; a second oxide layer formed on said first oxide layer and having a stoichiometric composition; and an upper conductive layer formed on said second oxide layer, wherein said first oxide layer is oxidized during a process of forming said second oxide layer and has an oxygen concentration which is lower than an oxygen concentration of said second oxide layer and lowers with a depth in said first oxide layer, and said first and second oxide layers form a tunneling barrier.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 6illustrate a method of manufacturing a magnetic tunneling junction element according to an embodiment of the invention.

Processes (1) to (6) corresponding toFIGS. 1 to 6will be described in this order.

(1) A substrate10is prepared which is a silicon substrate having a thermally oxidized insulating silicon oxide film on the surface of the substrate. As the substrate10, a substrate made of glass or quartz may also be used.

On the surface of the substrate10, an electrode layer12is formed which is made of a Ti layer having a thickness of 15 nm and a Cu layer having a thickness of 300 nm sequentially formed by sputtering. The electrode layer12is not limited to a lamination of the Cu layer stacked upon the Ti layer. For example, it may be a single layer made of Cr or Ti. Next, an antiferromagnetic layer14is formed on the electrode layer12by sputtering, the antiferromagnetic layer14being made of a Pt—Mn alloy layer having a thickness of 50 nm. Instead of Pt—Mn alloy, other materials such as Rh—Mn alloy and Fe—Mn alloy may be used as the material of the antiferromagnetic layer14.

A ferromagnetic layer16is formed on the antiferromagnetic layer14by sputtering, the ferromagnetic layer16being made of a Ni—Fe alloy layer having a thickness of 6 nm. Instead of Ni—Fe alloy, other metal such as Ni, Fe, or Co, other alloy or intermetallic compound of two or more metals among Ni, Fe and Co, or other material may also be used.

Next, an aluminum film18is formed on the ferromagnetic layer16by sputtering. For example, the thickness of the aluminum film18is 0.3 to 2 nm, e.g. about 1.5 nm. In forming the aluminum film18, a pure aluminum target is used. The sputtering conditions are, for example:

Substrate Temperature: room temperature

(2) An alumina film20is formed on the ferromagnetic layer16through deposition of an alumina film and oxidation of the aluminum film. For example, in the same sputtering chamber as that in which the aluminum film18was formed, the supply of Ar gas is stopped and then O2gas is introduced. In this oxidizing atmosphere, an alumina film is formed by reactive sputtering. The thickness of the deposited alumina film is, for example, 0.1 to 0.5 nm, e.g. about 0.5 nm. In this case, the pure aluminum target used for the aluminum film18is also used. The sputtering conditions are, for example:

Substrate Temperature: room temperature

Under these conditions, an alumina film20having a uniform thickness can be formed, and the thickness of the total alumina film20becomes 0.5 to 2.5 nm.

FIGS. 9A to 9Care diagrams illustrating the progress of oxidation in the aluminum film18. After the aluminum film18is formed on the ferromagnetic film16by sputtering as shown inFIG. 9A, an alumina film20bis formed by reactive sputtering as shown inFIG. 9B. In this case, the aluminum film18is oxidized by the presence of O2gas and the function of O2plasma during the reactive sputtering process, and transformed into an alumina film20a. Therefore, the alumina film20obtained after the completion of the reactive sputtering process contains the alumina film20amade by oxidizing the whole thickness of the aluminum film18without leaving the aluminum film and the deposited alumina film20b, as shown inFIG. 9C. By setting the thickness of the second alumina film20bto the thickness required for completely oxidizing just the whole thickness of the aluminum film18, it is possible to oxidize only the aluminum film18and prevent the oxidation of the ferromagnetic layer16. The thickness of the aluminum film18is usually 1 to 2 nm. The thickness of the second alumina film20bis set to the thickness required for completely oxidizing the aluminum film18having such a thickness. However, it is practically difficult to completely oxidize the aluminum layer18and not to oxidize the ferromagnetic layer16at all. If a film structure regarded effectively as such a structure can be obtained, it can be said that the whole thickness of the conductive layer is substantially oxidized and the ferromagnetic layer is not substantially oxidized. The reactive sputtering process may be performed in another sputtering chamber different from the sputtering chamber used for the previous sputtering process.

(3) Next, a ferromagnetic layer22is formed on the alumina film20by sputtering, the ferromagnetic layer22being made of an Ni—Fe alloy layer having a thickness of 80 nm. Instead of Ni—Fe alloy, the ferromagnetic layer22may be made of other ferromagnetic materials similar to those previously described for the ferromagnetic layer16.

(4) Next, the lamination from the electrode layer12to the ferromagnetic layer22is patterned by an ion milling process using as a mask a resist pattern having a pattern same as a predetermined lower electrode pattern. A lower electrode layer12A made of the remaining electrode layer12is therefore formed. Thereafter, the resist pattern is removed.

Next, the lamination from the antiferromagnetic layer14to the ferromagnetic layer22is patterned by an ion milling process using as a mask a predetermined resist pattern. On the electrode layer12A, a lamination which is made of the antiferromagnetic layer14, ferromagnetic layer16, alumina film20A and ferromagnetic layer22is therefore left, as shown inFIG. 4. Thereafter, the resist pattern is removed. The alumina film20A is used as a tunneling barrier film.

(5) Next, the ferromagnetic layer22is patterned by an ion milling process using a resist pattern having a pattern same as a predetermined element pattern. On the tunneling barrier film20A, the ferromagnetic layer22having a plan shape of a rectangle, e.g., a longer side length of 120 μm and a shorter side length of 20 μm is therefore left. Thereafter, the resist pattern is removed.

(6) An interlayer insulating film24is formed over the substrate10by sputtering, the interlayer insulating film being made of a silicon oxide film and having a thickness of 1000 nm. Contact holes exposing a partial area of the ferromagnetic layer22and the electrode layer12A are formed through the insulating film24by ion milling process using a resist mask pattern. This resist mask pattern is thereafter removed. Then, an electrode layer is formed over the insulating film24, the electrode layer being made of a copper layer having a thickness of 300 nm. This copper layer is patterned to have a predetermined upper electrode pattern so that upper electrode layers26connected to the ferromagnetic layer22and the electrode layer12A can be formed.

In the embodiment described above, although the shape of the ferromagnetic layer22is decided at the process shown inFIG. 5, carried out after the process shown inFIG. 4, the process shown inFIG. 6may be performed directly after the process ofFIG. 4, omitting the process shown inFIG. 5. In this case, the final shape of the ferromagnetic layer22is the same as the shape of the ferromagnetic layer22shown inFIG. 4. In the magnetic tunneling junction element shown inFIG. 6, the antiferromagnetic layer14functions to fix the magnetization direction of the ferromagnetic layer16, and the ferromagnetic layer16becomes a fixed layer. The ferromagnetic layer22has a free magnetization direction (not fixed) and becomes a free layer.

In the state that a predetermined current is allowed to flow between the electrode layers12A and26, as an external magnetic field is applied along an in-plane direction of the ferromagnetic layer22, a relative magnetization angle between the ferromagnetic layers16and22changes with the direction and intensity of the applied magnetic field, and the electric resistance between the electrode layers12A and26changes with a change in the relative magnetization angle. The resistance value becomes minimum if the magnetization directions are parallel, and maximum if they are antiparallel. Therefore, a magnetic field can be detected from a change in the resistance value.

FIG. 7is a graph showing electrostatic breakdown voltage characteristics of an embodiment magnetic tunneling element and a conventional magnetic tunneling element. The embodiment magnetic tunneling junction element was manufactured by a method similar to that illustrated inFIGS. 1 to 6(the shape of the ferromagnetic layer22decided by the process shown inFIG. 4was used and the process shown inFIG. 5was omitted). The conventional magnetic tunneling junction element was manufactured by a similar method used for the embodiment magnetic tunneling junction element, excepting that the tunneling barrier film (corresponding to the film20A shown inFIG. 4) was formed by a natural oxidation method (exposing the aluminum film to the air).

InFIG. 7, the abscissa represents a voltage (V) applied across a pair of electrode layers (12A and26inFIG. 6), and the ordinate represents a rate of change in the electric resistance between the pair of electrode layers. Curves S11and S21indicate the electrostatic breakdown voltage characteristics of the embodiment and conventional magnetic tunneling junction elements respectively. At an applied voltage of 60V, characteristic S21shows a reduced resistance, indicating dielectric breakdown. As seen fromFIG. 7, it can be understood that the embodiment magnetic tunneling junction element has a higher electrostatic breakdown voltage than the conventional magnetic tunneling junction element.

FIG. 8is a graph showing the time-dependent change of an MR ratio of the embodiment and conventional magnetic tunneling junction elements when they are placed in an environment of a high temperature of 280° C. The magnetic tunneling junction elements used for the measurement of the characteristics are similar to those described with reference toFIG. 7. An MR ratio is a ratio of the maximum magnetic tunneling resistance to the minimum magnetic tunneling resistance. Curves S12and S22indicate the time-dependent change characteristics of the embodiment and conventional magnetic tunneling junction elements, respectively. As seen fromFIG. 8, it can be understood that the embodiment magnetic tunneling junction element has a smaller time-dependent change in the MR ratio and a higher reliability than the conventional magnetic tunneling junction element.

The times required for forming the tunneling barrier film of the embodiment and conventional magnetic tunneling junction elements were compared. It took two minutes per one substrate (wafer) for the embodiment element, and it took 180 minutes per one substrate for the conventional element. The magnetic tunneling junction elements used for the comparison were similar to those described with reference toFIG. 7. The time taken to form the tunneling barrier film of the embodiment element includes the time taken to form the aluminum film and alumina film as well at the time taken for loading and unloading the substrate into and from a sputtering chamber. The embodiment manufacture method can shorten greatly the time taken to form the tunneling barrier film and improve the productivity.

According to this embodiment, after a conductive film is formed by depositing conductive material on an underlying layer capable of being oxidized, the conductive film is oxidized while oxide of the conductive material is deposited on the conductive film by reactive sputtering in an oxidizing atmosphere. Accordingly, oxidation of the underlying layer can be prevented because of the presence of the conductive film, and oxidation of the conductive film is suppressed more as the oxide of the conductive material deposited becomes thicker. Namely, the conductive film is not positively subjected to the oxidation process, but the phenomenon is utilized by which phenomenon the conductive film is oxidized while the oxide of the conductive material is deposited on the conductive film by reactive sputtering in an oxidizing atmosphere.

According to this embodiment, during the reactive sputtering in the oxidizing atmosphere, oxygen plasma reacts also with the conductive film so that the conductive film can be oxidized sufficiently even at a low temperature. The composite oxide film of a good quality can be formed which has the first oxide film of the oxidized conductive film and the second oxide film of the deposited oxide. Since the sputtering process is used, a thin oxide film can be formed in a short time.

In forming an oxide film, as the conductive material, metal such as aluminum, titanium and magnesium or semiconductor such as silicon can be used.

Since the tunneling barrier film made of the first and second oxide films can be formed by oxidizing only the conductive film without oxidizing the first ferromagnetic layer, variation in the magnetic tunneling resistance can be improved. Since an oxide film of a good quality to be used as the tunneling barrier layer can be formed in a short time, the electrostatic breakdown voltage, reliability and productivity of magnetic tunneling junction elements can be improved.

As above, an oxide film of a good quality can be formed on the underlying layer in a short time without oxidizing the underlying layer.

The oxide film is used as the tunneling barrier film, to improve the variation in magnetic tunneling resistance, electrostatic breakdown voltage, reliability and productivity.

What phenomena occurred on the surfaces and the like of aluminum layers was checked by using samples with scaled-up thicknesses. Each sample was formed by forming an aluminum layer by sputtering and forming an alumina layer on the aluminum layer by reactive sputtering.

As shown inFIG. 13A, an aluminum layer22having a thickness of 100 nm was formed on an underlying layer21in a sputtering chamber. The sputtering conditions were a pure Al target28, an Ar gas (flow rate of 80 sccm, pressure of 8 mTorr) and a DC power of 100 W. The aluminum layer22was formed sufficiently thick to the extent that the whole thickness of the aluminum layer22is not oxidized during the succeeding reactive sputtering process.

The underlying layer is formed of an oxidizable material. Oxide materials such as CrOxwill not be used. There is a possibility that an unintentional native oxide film exists at the film surface, and it is impossible to avoid formation of a very thin native oxide film. Such a native oxide film may be excluded from the consideration.

As shown inFIG. 13B, a first sample S31was formed in the following manner. On the aluminum layer22of 100 nm in thickness, an aluminum oxide layer23having a thickness of about 5 nm was formed in the same sputtering chamber by reactive sputtering (DC power of 100 W) by changing the work gas to O2(100%, flow rate of 80 sccm, pressure of 8 mTorr). The reactive sputtering conditions were the same as those of the above-described embodiment.

The work gas O2can be considered having the functions of: sputtering aluminum; oxidizing flying aluminum particles (depositing the aluminum oxide layer23); forming aluminum oxide by bonding to aluminum on the surface of the underlying aluminum layer22; oxidizing the aluminum layer22because O2attached to the surface of the aluminum layer22is knocked on by flying particles and moved into the aluminum layer22; and the like.

As shown inFIG. 13C, a second sample S32was formed in the following manner. On the aluminum layer22of 100 nm in thickness, an aluminum oxide layer25having a thickness of about 5 nm was formed in the same sputtering chamber by reactive sputtering (DC power of 100 W) by changing the work gas to O2(50%)+Ar(50%) (O2flow rate of 40 sccm, Ar flow rate of 40 sccm, total pressure of 8 mTorr), instead of using O2gas (100%). By using the work gas O2(50%)+Ar(50%) instead of O2gas (100%), oxidation of the work gas was made weak. Although reactive sputtering similar toFIG. 13Bcan be performed by using the work gas which contains O2, the ability of oxidation is weak in correspondence with the reduced amount of O2. Since Ar has a higher sputtering rate than O2, a film forming speed increases.

The samples S31and S32formed with the aluminum oxide layers23and25were analyzed with a spectral ellipsometer. The refractive index shows the value at a wavelength of 400 nm.

FIG. 13Dshows a refractive index distribution in the first sample S31shown inFIG. 13B. A layer24having an effective refractive index n=1.36 was observed between a layer22A and a layer23A. The layer22A had a constant refractive index n=0.48 and can be considered the aluminum layer22. The layer23A had a constant refractive index n=1.78 and can be considered the aluminum oxide layer23.

FIG. 13Eshows a refractive index distribution in the second sample S32shown inFIG. 13C. A layer26having an effective refractive index n=0.95 was observed between a layer22A and a layer25A. The layer22A had a constant refractive index n=0.48 and can be considered the aluminum layer22. The layer25A had a constant refractive index n=1.78 and can be considered the aluminum oxide layer25.

Even if the oxygen pressure in the work gas is changed between 8 mTorr and 4 mTorr, the refractive index of the deposited aluminum oxide layers23A and25A will not change maintaining at n=1.78. It can be considered that alumina (Al2O3) having a stoichiometric composition is formed.

The layers24and26formed adjacent to the deposited aluminum oxide layers (formed by oxidation of the aluminum layers) have the refractive indices n=1.36 and 0.95 which are apparently lower than the refractive index n=1.78 of stoiciometric aluminum oxide. These layers24and26can be considered the aluminum oxide layers having a non-stoichiometric composition rich in aluminum. As the oxygen pressure is reduced by a half from 8 mTorr to 4 mTorr, the refractive index of the aluminum oxide layer26having a non-stoichiometric composition is reduced from 1.36 to 0.95 to be considered richer in aluminum. Since aluminum oxide has a barrier characteristic relative to oxygen, depositing an aluminum oxide layer thick to some degree may suppress oxidation of the aluminum layer. It can be considered that the oxygen pressure at the initial stage of reactive sputtering influences greatly the composition of aluminum oxide having a non-stoichiometric composition.

The above experiment results indicate the following facts, when an aluminum layer is formed by sputtering using a pure Al target and an aluminum oxide layer is deposited on the aluminum layer by reactive sputtering using a pure Al target and a work gas which contains oxygen: 1) aluminum oxide having a stoichiometric composition can be deposited in a wide oxygen pressure range; 2) the aluminum layer in contact with the aluminum oxide layer is oxidized and aluminum oxide having a non-stoichiometric composition is formed; and 3) the composition of aluminum oxide having a non-stoichiometric composition changes with the oxygen pressure (or flow rate) of the atmosphere.

If the alumina film20bof the above-described embodiment is formed by using a mixture gas of O2+Ar and lowering the oxygen flow rate, it is expected to reduce the oxygen composition of the aluminum oxide layer20aformed by oxidation of an aluminum layer. Instead of Ar, other inert gas may be used. By lowering the oxygen flow rate at the initial stage of reactive sputtering, it is expected to regulate the thickness and oxygen concentration of the aluminum oxide layer20a.

The aluminum oxide layer having a non-stoichiometric composition is formed theoretically by oxygen invading from the surface side. It can be considered that the oxygen concentration lowers starting from the surface of the aluminum layer down to a deeper position than the distance that oxygen invades by one phenomenon. Namely, if a secondary oxide layer thick to some degree is formed, the composition thereof has a gradient along the thickness direction.

The phenomenon that the aluminum oxide layer rich in aluminum is formed by lowering the oxygen pressure in the atmosphere during reactive sputtering, suggests that the composition distribution of the secondary oxide layer can be controlled by the oxygen pressure in the atmosphere.

FIG. 14Ashows an embodiment in which an aluminum oxide layer has a non-stoichiometric composition with a controlled oxygen concentration. Deposited on a lower ferromagnetic layer16of Ni—Fe alloy or the like are an aluminum oxide layer31having a non-stoichiometric composition and an aluminum oxide layer32having a stoichiometric composition. On the aluminum oxide layer32, an upper ferromagnetic layer22of Ni—Fe alloy or the like is deposited. A natural oxide film16xexists on the surface of the lower ferromagnetic layer16. The natural oxide film16xmay be removed. If the natural oxide film is removed and a new tunneling insulating layer is formed, the composition and thickness of the tunneling insulating layer can be controlled at a high precision and a high performance tunneling element can be realized. If milling or the like is used for removing the natural oxide film, the surface is likely to become rough and irregular. It is not easy to form a uniform and high quality insulating layer on a rough surface. Whether the natural oxide film is to be removed or not may be determined depending upon the desired performance, conditions and the like. The other structures are similar to the previously described embodiment.

FIG. 14Bis a graph showing an oxygen concentration profile in a depth direction when the natural oxide film16xis not removed. The aluminum oxide layer32having a stoichiometric composition has a constant first oxygen concentration c1. The aluminum oxide layer31having a non-stoichiometric composition has a second oxygen concentration c2which is lower than the first oxygen concentration c1and lowers starting from the upper surface down to a deeper position. The oxygen concentration c2of the aluminum oxide layer31having a non-stoichiometric composition decreases with the depth, and becomes lower than the oxygen concentration of the natural oxide film16xat the interface with the lower ferromagnetic layer16. The aluminum oxide layer31in the neighborhood of the surface is approximately stoichiometrically oxidized. Setting these oxygen concentrations suppresses an increase in the effective thickness of the insulating layer and realizes an efficient tunneling insulating layer.

FIG. 14Cis a graph showing the oxygen concentration distribution when the natural oxide film16xis removed. Similar toFIG. 14B, the aluminum oxide layer32having a stoichiometric composition has the oxygen concentration c1, and the aluminum oxide layer31having a non-stoichiometric composition has the oxygen concentration c2. The natural oxide film16xon the surface of the lower ferromagnetic layer16was removed before sputtering by Ar milling, hydrogen reduction or the like. The oxygen concentration c2of the aluminum oxide layer31having a non-stoichiometric composition is set to become lower than that of the natural oxide film at the interface with the lower ferromagnetic layer16. The aluminum oxide layer31in the neighborhood of the surface is approximately stoichiometrically oxidized. The oxygen concentration is set preferably to have a negligible value at the interface, i.e., one tenth or smaller than the oxygen concentration of the stoichiometric composition, or more preferably one hundredth or smaller. With this arrangement, an efficient tunneling insulating layer can be formed.

FIGS. 14D and 14Eshow cases where oxidation proceeds deeper than the cases ofFIGS. 14B and 14C, respectively. InFIG. 14D, the surface of the ferromagnetic layer16has a native oxide layer. InFIG. 14E, the native oxide layer on the surface of the ferromagnetic layer16is removed. InFIGS. 14B and 14Conly the neighborhood of the aluminum film surface is approximately stoichimetrically oxidized, whereas inFIGS. 14D and 14Ea certain thickness at the surface of the aluminum film is stoichiometrically oxidized. First, a metal aluminum film M is deposited by sputtering on the ferromagnetic layer16. Then, an aluminum oxide film Ox is reactively sputtered on the metal aluminum film M. The sputtered aluminum oxide film Ox with the oxidizing atmosphere oxidizes the underlying aluminum film M, to form a fully oxidized stoichiometric oxide layer32a, and a partly oxidized non-stoichiometric graded oxide film31. The deeper end of the non-stoichiometric oxide film31reaches the underlying ferromagnetic layer16. The deposited stoichiometric oxide layer Ox and oxidized stoichiometric oxide layer32acollectively constitute a stoichiometric oxide layer32. The thicknesses of the stoichiometric oxide film32and the non-stoichiometric graded oxide film31can be controlled by controlling the conditions of the reactive sputtering.

The present invention has been described in connection with the preferred embodiments. The invention is not limited only to the above embodiments. It will be apparent to those skilled in the art that various modifications, improvements, combinations, and the like can be made. For example, the following modifications are possible:

(1) After the ferromagnetic layer22is formed in the process shown inFIG. 3, a conductive film having an anti-etching performance such as Mo may be formed on the ferromagnetic layer22. In this case, it is possible to prevent the ferromagnetic layer22from being etched when the contact hole is formed through the insulating film24by selective etching in the process shown inFIG. 6.

(2) The ferromagnetic layer22is not limited only to a single layer structure, but it may be a multi-layer structure, e.g., a Co layer of 2 nm in thickness may be formed under a Ni—Fe alloy layer.

(3) The antiferromagnetic layer14may be formed on the upper ferromagnetic layer22, to make the ferromagnetic layer22a fixed layer and make the ferromagnetic layer16a free layer.

(4) The material of the tunneling barrier layer20A may be metal oxide or semiconductor oxide (e.g., TiOx, SiO2, MgO, Al2O3+SiO2(sialon), CrOx), metal nitride or semiconductor nitride (AlN, Si3N4), metal oxynitride or semiconductor oxynitride (AlN—Al2O3) or the like.

CrOxand TiOxfilm can be formed by using an apparatus or target which is used in manufacturing a magnetic film for TMR. Threrefore, the manufacturing cost can be made low.

TiOxfilm can also be formed by utilizing a target or apparatus used in the manufacturing process of LSIs. Therefore, the manufacturing cost can be made low.

Nitrides such as AlN and Si3N4, or oxynitrides thereof can be formed by using the same target and apparatus, using N2gas, or NH3gas as the work gas, or the mixture of N2or NH3gas and O2gas. Further, it becomes possible to form a dense film having an improved film quality, capable of enhancing reliability.

Any species of film or any composition can be formed by similar methods, to provide a tunnel barrier film having a similar oxygen concentration profile or nitrogen concentration profile to that in the above-described aluminum oxide film.

(5) Although Cu, Ti, Cr or the like is used as the material of the electrode layer12A, conductive and non-magnetic metal material such as W, Ta, Au and Mo may also be used. These metal materials may also be used as the material of the electrode layer26.