JP2000150984A - Magnetic tunnel element using ozone-oxidized insulating film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic tunnel element which can be used for a magneto- resistance memory array by interposing an insulating film between a hard magnetic film and a soft magnetic film and oxidizing the insulating film in a mixed gas of oxygen and ozone. SOLUTION: Lower electrodes 4 each composed of a first Ti conductive film 2 and a second Cu conductive film 3 are formed on an Si substrate 12. Then magnetic tunnel elements 8 each composed of a hard magnetic layer 5, an insulating film 6, and soft magnetic layer 7 are formed by successively forming Co hard magnetic layers 5 having different coercive forces, insulating films 6 which are formed by oxidizing Al films in a mixed gas of oxygen and ozone, and NiFe soft magnetic layers 7 on the electrodes 4. Therefore, a magnetic tunnel element 8 which does not cause resistance fluctuation and can be used for a magneto-resistance memory array can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic tunnel device using an ozone oxide insulating film, and more particularly, to a magnetic tunnel device having reduced variation in magnetic resistance.

[0002]

2. Description of the Related Art Conventionally, a magnetic tunnel element (hereinafter referred to as TMR)
An element. In (2), since the magnetoresistance change is larger than that of the spin valve and the resistance of the element itself is larger, the TMR element also has a larger element voltage change that changes with respect to a magnetic field change.
For this reason, it is a material suitable for future magnetic heads and magnetoresistive memories (hereinafter, referred to as MRAM).

This TMR element has a structure in which an insulating film is sandwiched between two magnetic films, and the magnitude of the magnetic tunnel current flowing between the magnetic films depends on the angle between the spins of the two magnetic films. By utilizing the change, the magnitude of the magnetic field applied to this element is detected.

[0004] Also, the MRAM utilizes a TMR element,
This is a memory that can be determined by the magnitude of the resistance of a cell in which digital information consisting of 0 and 1 is recorded.

[0005] The insulating film used for this element is mainly an aluminum oxide film having a thickness of 1.5 nm.
The degree is optimal.

Conventionally, a method of forming an aluminum oxide film is roughly classified into a method of directly forming an aluminum oxide film using a target and a method of forming a metal aluminum film and then oxidizing the film. There are two types of methods. The use of metallic aluminum has less physical defects such as pinholes in the film, and this method is mainly used at present. Conventionally, there are roughly two types of methods for oxidizing metallic aluminum: a plasma oxidation method and a natural oxidation method.

[0007] In the natural oxidation method, a formed metal aluminum film is formed in the atmosphere in an atmosphere where the temperature and humidity are controlled.
Alternatively, it is a method in which metal aluminum is oxidized to aluminum oxide by leaving it in a pure oxygen atmosphere for a predetermined time.

The method of oxidizing in an oxygen plasma is a method in which after a metal aluminum film is formed, oxygen at a predetermined pressure is successively introduced into a chamber to generate an oxygen plasma to oxidize the metal aluminum film.

[0009]

However, in the case of the natural oxidation method, sufficient oxygen is not supplied to aluminum in the atmosphere or pure oxygen atmosphere in the case of the natural oxidation method. Many defects are included in the film manufactured by the method described above, and the thickness and quality of an oxide film to be formed vary greatly depending on the position in the wafer.

The method of oxidizing in oxygen plasma is as follows.
By applying ionized oxygen to the film, the metal aluminum film can be oxidized in a shorter time than the natural oxidation method.However, the oxide film formed by the plasma is damaged, and as a result, a uniform bonding surface is obtained. There is a disadvantage that it cannot be done.

Therefore, when the TMR element manufactured by using the above-described oxidation method is used particularly for an MRAM array, if the variation of each cell becomes larger than the rate of the resistance change, the state of each cell of the memory array is changed to the resistance. There is a possibility that judgment cannot be made from the magnitude.

The present invention has been made in view of such a problem, and oxidizes metallic aluminum in a gaseous mixture containing oxygen and ozone so as not to damage an obtained oxide film. An object of the present invention is to provide a magnetic tunnel element which can be used for an MRAM array by producing an insulating film with few defects by supplying sufficient oxygen by ozone to a film at the time of forming an oxide film.

[0013]

According to the present invention, there is provided a magnetic tunnel element having a hard magnetic film and a soft magnetic film having different coercive forces and an insulating film interposed therebetween. The film is characterized by being oxidized in a mixture of oxygen and ozone.

In the present invention, the ozone concentration in the mixture of oxygen and ozone is 10 ppm or more and / or the pressure of the mixture of oxygen and ozone is 1T.
The pressure is preferably from orr to atmospheric pressure.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an MRAM using a magnetoresistive element according to an embodiment of the present invention will be specifically described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing a magnetoresistive memory according to an embodiment of the present invention. As shown in FIG. 1, a lower electrode 4 composed of a first conductive film 2 made of Ti and a second conductive film 3 made of Cu is formed on a Si substrate 12. A hard magnetic layer 5 made of Co is formed on the lower electrode 4.
An insulating film 6 formed by oxidizing the film is provided, and a soft magnetic layer 7 made of NiFe is formed on the insulating film 6. The hard magnetic layer 5, the insulating film 6, and the soft magnetic layer 7 form a magnetic tunnel element 8.

An interlayer insulating film 9 made of SiO ₂ is formed in a region covering the substrate 12, the lower electrode 4, and the magnetic tunnel element 8. In the interlayer insulating film 9, a contact hole 10 is formed on the magnetic tunnel element 8. Furthermore, an upper electrode 11 made of Cu is formed so as to bury the contact hole 10. Thus, the magnetoresistive memory 1 is configured.

Next, a method of manufacturing the MRAM shown in FIG. 1 will be described. 2A to 2E are cross-sectional views illustrating a method for manufacturing a magnetoresistive memory in the order of steps.

As shown in FIG. 2A, first, a pre-cleaned Si substrate 12 is attached to a sputtering apparatus.
The vacuum chamber of the sputtering apparatus has a degree of vacuum of 1.0 × 10 ^−7.
After evacuating to Torr or less, 4 mTorr
r Ar gas is introduced into the vacuum chamber. The target size provided in the vacuum chamber is, for example, 126 mm.
For example, a DC power of 200 W is applied to the sputtering gun to form, for example, a Ti film with a thickness of 15 nm as the first conductive film 2, and then form a Cu film with a thickness of 30
It is formed to a thickness of 0 nm.

Subsequently, in a 4 mTorr Ar gas atmosphere, for example, a Co film as the hard magnetic layer 5 is formed by applying a DC power of 100 W to a sputtering gun having a target size of 126 mm at a deposition rate of 6 nm / min. , 30 nm.

Further, on the hard magnetic layer 5, for example, a DC power of 20 W is applied to a sputtering gun having a target size of 126 mm, and an Al film is formed, for example, at 1.8 nm at a film forming rate of 2 nm / min. After the Al film is formed, the substrate 12 is moved to the processing chamber without breaking the vacuum, and oxygen with a purity of 99.9999% is introduced into the silent discharge type ozone generator to control the flow rate and the voltage. A mixture of oxygen and ozone of a predetermined concentration obtained by the above is introduced, for example, at 100 Torr and left for 5 minutes, for example, to oxidize the Al film. Thus, an insulating film 6 formed of aluminum oxide is obtained.

On the insulating film 6, for example, a DC power of 100 W is applied to a sputtering gun having a target size of 126 mm to form a NiFe film of 20 nm as the soft magnetic layer 7 at a film forming speed of 65 nm / min. .

The method of oxidizing the Al film may be either a method in which a mixture of oxygen and ozone is sealed or a method in which the mixture is drawn while being pumped. The vacuum chamber and the gas pressure for the film formation for forming the Al film and the soft magnetic layer 7 are the same as those for the hard magnetic layer 5.

Next, a method of manufacturing the MRAM will be described. As shown in FIG. 2B, first, a resist is patterned into a desired shape of the lower electrode 4. Using an ion milling device, for example, input power 500 V, 40
0 mA, gas pressure 0.2 mTorr, etching rate 70
A desired shape is obtained by etching the lower electrode 4 at nm / min. After that, the resist is removed with acetone.

Then, the resist is patterned into a desired shape for the magnetic tunnel element 8. The desired shape is obtained by etching the magnetic tunnel element 8 using, for example, an input power of 500 V, 400 mA, a gas pressure of 0.2 mTorr, and an etching rate of 12 nm / min using an ion milling apparatus. After that, the resist is removed with acetone.

[0025] As shown in FIG.
The substrate 12 is placed in a vacuum chamber of the apparatus, and for example,
2.0 × 10 in empty chamber^-6Evacuation below Torr
After that, an Ar gas of 5 mTorr is introduced. SiO_Two
For example, an electric power of 900 W is applied to the
SiO 2 as the interlayer insulating film 9 at a degree of 13 nm / min. _Two
A film is formed, for example, to 100 nm.

Then, as shown in FIG. 2D, a resist is patterned into a desired shape for the interlayer insulating film 9. Etching is performed using an ion milling device, and then the interlayer insulating film 9 is immersed in acetone and treated in an ultrasonic cleaner for 30 minutes to remove the resist and form a contact hole 10 having a desired shape.

As shown in FIG. 2 (e), the one having the contact hole 10 formed therein is set in a vacuum chamber,
For example, after evacuating the inside of the vacuum chamber to 2.0 × 10 ⁻⁶ Torr or less, an Ar gas at 5 mTorr is introduced. For example, a 300 nm Cu film is formed as the upper electrode 11 on a Cu target at an electric power of 200 W and a film formation rate of 30 nm / min. Then, the resist is patterned into a desired shape for the upper electrode 11. Using an ion milling device, for example, input power 500 V, 400 m
A, gas pressure 0.2 mTorr, etching rate 70 nm
The desired shape is obtained by etching the upper electrode 11 at a rate of / min. After that, the resist is removed with acetone. Through the above steps, the MRAM 1 is obtained.

According to this embodiment, as the insulating film, aluminum oxide with little damage is obtained by oxidizing the Al film in a mixture of oxygen and ozone. That is, since an insulating film with few physical defects is formed, the variation among cells does not become larger than the ratio of the magnetoresistance change,
The state of each cell of AM1 is judged from the magnitude of the resistance, and MR
The information stored in the AM 1 can be statically read.

In the above embodiment, the Al film is formed by the sputter deposition method, but is not limited thereto.
The film may be formed by a high vacuum evaporation method, an ion beam sputtering method, or the like.

In the above embodiment, the hard magnetic layer 5 and the soft magnetic layer 7 are made of Co and NiFe, respectively. However, the present invention is not limited thereto.
Other magnetic materials such as iFeCo can also be used.

Further, in the above embodiment, the pressure of the mixture of oxygen and ozone is preferably 1 Torr or more because ozone has a high decomposition rate under reduced pressure.

[0032]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples that fall outside the scope of the claims.

First Embodiment An MRAM 1 manufactured by the manufacturing method of the embodiment shown in FIG.
0 and a MR array manufactured by the manufacturing method of the comparative example.
The result of comparing the characteristics of the AM10 cell array and the AM10 cell array will be described.

The MRAM 10 of the comparative example has the following (a)
The insulating film was formed by any one of the steps (c) to (c).
In the comparative example, only the method of forming the insulating film is different from that of the example, and the other configuration and the manufacturing method are the same.

(A) Natural Oxide Film Method After forming an Al film on the hard magnetic layer to a thickness of 1.8 nm, it is taken out of the vacuum chamber and placed in a thermo-hygrostat controlled at a temperature of 30 ° C. and a relative humidity of 0% for 24 hours. The aluminum oxide film was obtained from the Al film.

(B) Pure oxygen oxidation method After forming an Al film on the hard magnetic layer to a thickness of 1.8 nm, oxygen gas having a purity of 99.9999% up to 100 mTorr is introduced without breaking vacuum, and then for a predetermined time. The aluminum oxide film was obtained by leaving it to stand.

(C) Plasma Oxidation Method After forming an Al film on the hard magnetic layer to a thickness of 1.8 nm, an oxygen gas having a purity of 99.9999% up to 100 mTorr was introduced without breaking vacuum. Frequency 1
An oxygen plasma was generated by applying a high frequency of 3.56 MHz, and exposed to the plasma for 1 minute to obtain an aluminum oxide film.

The magnetoresistive memories manufactured according to the above-described embodiment and comparative example are placed in a Helmholtz coil, and a predetermined constant current is applied between the upper and lower electrodes to change the voltage applied between the upper and lower electrodes with respect to the magnitude of the magnetic field. Was measured. The results are shown in FIGS. In FIG. 3, the vertical axis shows the resistivity, and the horizontal axis shows the oxidation methods of the examples and comparative examples (a) to (c), and shows the resistivity of the examples and comparative examples. FIG.
The ordinate indicates the magnetic tunnel resistance change rate, and the abscissa indicates the oxidization methods of the examples and comparative examples (a) to (c), and indicates the magnetic tunnel resistance change rates of the examples and comparative examples.

From FIGS. 3 and 4, in this embodiment using the ozone oxidation method, the variation in resistivity is 15%, which is the maximum magnetic tunnel resistance change rate obtained by the conventional method for each cell. This is about 8%, and static reading of information is possible. On the other hand, in Comparative Examples (a) to (c), the variation of each cell is larger than the magnetic tunnel resistance change rate, and the information cannot be determined due to the magnitude of the resistance.

Second Embodiment For various magnetic memories with different ozone concentrations in the insulating films manufactured by the above-described embodiment, a magnetoresistive memory is placed in a Helmholtz coil, and a predetermined constant current is applied between the upper and lower electrodes. And the change in voltage applied between the upper and lower electrodes with respect to the magnitude of the magnetic field was measured. The result is shown in FIG. FIG.
Indicates the relationship between the ozone mixture ratio and the resistance and the magnetic tunnel resistance change rate, with the ordinate representing the resistance and the magnetic tunnel resistance change rate and the abscissa representing the ozone mixture ratio. Table 1 shows the standing time, the resistance and the magnetoresistance ratio when the ozone mixture ratio is 30 ppm. FIG. 6 shows Table 1, in which the vertical axis represents the resistance and the magnetic tunnel resistance change rate, and the horizontal axis represents the standing time. The standing time and the resistance and the magnetic tunnel resistance change rate at an ozone mixture ratio of 30 ppm are shown. The relationship is shown. In the drawing, ◆ indicates resistance, and ■ indicates the rate of change in magnetic tunnel resistance.

In FIG. 5, when the ozone concentration increases,
Both the resistance and the magnetic tunnel resistance change rate increase.
Under these conditions, when the ozone mixture ratio is 100 ppm or more, a magnetic tunnel resistance change rate exceeding the 8% resistance variation between cells is obtained. Even when the mixture ratio of ozone is less than 100 ppm, the same value as the case where the mixture ratio of ozone exceeds 100 ppm can be obtained by exposing the insulating film to the mixture of ozone for a long time even if the mixture ratio of ozone is less than 100 ppm. be able to. As shown in FIG. 6 and Table 1, for example, when an ozone mixture having an ozone mixture ratio of 30 ppm is used, the ozone mixture ratio is changed to a resistance and a magnetoresistance equivalent to 100 ppm by leaving the mixture for about 10 minutes. Rate can be obtained.

[0042]

[Table 1]

However, a short treatment is preferable from an industrial viewpoint. Considering this point, the ozone mixture ratio is 100p
pm or more is preferred. As for the high ozone concentration,
From an ozone concentration of 2.5% or more, there is almost no improvement in cell characteristics.

[0044]

As described in detail above, according to the present invention,
By using the ozone oxide insulating film, a magnetic tunnel element having no variation in resistance can be obtained. Therefore, a magnetoresistive memory array capable of statically reading information can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a magnetoresistive memory according to an embodiment of the present invention.

2A to 2E are cross-sectional views illustrating a method of manufacturing a magnetoresistive memory according to the present invention in the order of steps.

FIG. 3 is a graph showing resistance variations of a magnetoresistive memory array on which an insulating film is formed by each method.

FIG. 4 is a graph showing a variation in a magnetoresistance change rate of a magnetoresistive memory array in which an insulating film is formed by each method.

FIG. 5 is a graph showing the relationship between the ozone mixture ratio and the resistance and magnetic tunnel resistance change rate characteristics.

FIG. 6 is a graph showing the relationship between the standing time, the resistance and the magnetoresistance ratio when the ozone mixture ratio is 30 ppm.

[Explanation of symbols]

1; magnetoresistive memory; 2; first conductive film; 3; second conductive film; 4; lower electrode; 5; hard magnetic layer;
7; soft magnetic layer; 8; magnetic tunnel element; 9; interlayer insulating film; 10; contact hole;
12; substrate

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Takashi Hayashi ▲ Hiro ▼ F-term (reference) in Yamaha Co., Ltd. 10-1 Nakazawacho, Hamamatsu-shi, Shizuoka 5D034 BA03 BA15 DA07

Claims (3)

[Claims] 1. A magnetic tunnel device having a hard magnetic film and a soft magnetic film having different coercive forces and an insulating film interposed therebetween, wherein the insulating film is oxidized in a mixture of oxygen and ozone. A magnetic tunnel element using an ozone oxide insulating film, wherein 2. An ozone concentration in a mixture of oxygen and ozone is 10 ppm or more.
A magnetic tunnel element using the ozone oxide insulating film according to the above. 3. The pressure of the mixture of oxygen and ozone is 1
The magnetic tunnel element using the ozone oxide insulating film according to claim 1, wherein the pressure is from Torr to atmospheric pressure.