KR100597714B1 - The improvement method of thermal stability in TMR for MRAM applications - Google Patents

Abstract

The present invention relates to a TMR device for MRM with improved thermal characteristics, and more particularly, to an oxide layer formed on a first ferromagnetic layer, which is a pinned layer in a TMR structure, to block Mn diffusion occurring in an antiferromagnetic layer, and another layer. It is possible to form a uniform oxide layer through heat treatment at the same time to improve the thermal characteristics of the TMR element by preventing the movement to.

Therefore, it is suitable for the requirements of plasma enhanced chemical vapor deposition method and sintering process that are applied for the combination with CMOS in MRAM manufacturing.

MRAM, tunneling magnetic element, oxide layer, thermal characteristics, magnetoresistance ratio, exchange magnetic anisotropy

Description

TMR device for MRM with improved thermal characteristics and manufacturing method {The improvement method of thermal stability in TMR for MRAM applications}

1A and 1B are schematic diagrams of conventional bottom and tower TMR structures.

2A and 2B are schematic diagrams of bottom and tower TMR structures according to the present invention.

3 is a comparative change graph of the magnetoresistance ratio according to the heat treatment temperature of the bottom type TMR device according to the present invention.

4 is a comparative change graph of the exchange bias according to the heat treatment temperature of the bottom-type TMR device according to the present invention.

<Description of Symbols for Main Parts of Drawings>

10 substrate 12 buffer layer

14: antiferromagnetic layer 16: first ferromagnetic layer

18: Al-oxide layer 20: second ferromagnetic layer

22: protective layer 30: oxide layer

The present invention relates to improving the thermal characteristics of a TMR device, and more particularly, to form a suitable oxide layer in the first ferromagnetic layer, which is a pinned layer of the TMR structure, to block Mn diffusion occurring in the antiferromagnetic layer and to move to another layer. The present invention relates to a device and a manufacturing method for improving the thermal characteristics of a TMR device by preventing it and at the same time forming a uniform oxide layer through heat treatment.

Some kinds of magnetic materials change their electrical resistance when placed in a magnetic field.

This phenomenon is called the magnetoresistance effect.

This effect is used in magnetoresistive effect elements (hereinafter referred to as MRAM (magnetic random access memory)) in which magnetic materials such as magnetic heads and magnetic sensors are in the form of magnetic layers.

Such MRAMs require high sensitivity to external magnetic fields and have high response speeds.

A magnetic random access memory (MRAM) using a magnetoresistive (MR) film is L. second. By Xue, Proc. INTERMAG conf. IEEE Trans.Magn. Kyoto (1972), proposed on page 405.

M. yen. Bibeach et al. Phys. Rev. Lett. 61 (198) on page 2472 describes that an artistic lattice film formed of exchange-coupled magnetic films through a nonmagnetic film exhibits a large MR effect (GMR).

The nonmagnetic film used for the GMR film is a conductive film formed from Cu or the like.

Tunneling GMR films (hereinafter referred to as TMR devices) using Al ₂ O ₃ , MgO, etc. as nonmagnetic films have been actively studied, and MRAMs using these TMR devices have been proposed.

1 shows a schematic diagram of a conventional exchange bias type TMR structure.

The bottom type TMR structure of FIG. 1A includes a buffer layer 12, an antiferromagnetic layer 14, a first ferromagnetic layer 16, an Al-oxide layer 18, and a top-to-bottom structure on a substrate 10. The ferromagnetic layer 20 and the protective layer 22 have a structure.

The top TMR structure of FIG. 1B has a buffer layer 12, a second ferromagnetic layer 20, an Al-oxide layer 18, a second ferromagnetic layer 16, and an antiferromagnetic layer 14 from bottom to top over the substrate 10. ) And a protective layer 22.

One of the two ferromagnetic layers 16 and 20 separated by an Al-oxide layer 18, which is a nonmagnetic thin film, is free to rotate, while the other ferromagnetic layer 16 is attached to the antiferromagnetic layer 14. Is fixed.

Therefore, the magnetoresistance depends on whether the magnetizations of the two ferromagnetic layers 16 and 20 are anti-equilibrium or equilibrium depending on the external magnetic field.

In general, the magnetoresistive effect of the TMR element has a large resistance when the arrangement of the ferromagnetic layers 16 and 20 due to tunneling is antiparallel, and a low resistance when parallel.

An advantage of the exchange bias type TMR structure is that a large magnetoresistance can be obtained even in a magnetic field having a low magnetization arrangement in the free layer and the bound layer.

In the exchange bias type TMR device, when the antiferromagnetic layer 14 and the ferromagnetic layers 16 and 20 are in contact with each other, exchange bias is generated at the interface due to exchange anisotropy. It is known to have excellent thermal properties.

Therefore, many studies have been made to develop a new antiferromagnetic layer 14 having improved thermal properties, that is, high exchange magnetic anisotropy strength (H _ex ) and high blocking temperature.

For example, FeMn antiferromagnetic layer materials have been pointed out as low blocking temperatures and corrosiveness, and new antiferromagnetic layer materials such as IrMn, PtMn, and NiMn having a large exchange magnetic field have been proposed.

However, when the antiferromagnetic layer 14 material (IrMn, PtMn, NiMn) increases in temperature, Mn diffuses through the grain boundary and moves to the Al-oxide layer 18, which is a pinned layer and a nonmagnetic layer, so that the magnetoresistance and exchange bias value are increased. There is a problem of being lowered.

In addition, NiO, α-Fe ₂ O ₃ and the like have been proposed as the anti-ferromagnetic layer 14 material, but NiO has a problem of low Neil temperature, and α-Fe ₂ O ₃ has oxygen (oxide). Because of the use, there is a problem in heat dissipation, which increases the temperature of the device.

In addition, by depositing a Fe-oxide layer at the interface of the Al-oxide layer 18, the excess oxygen of the Fe-oxide layer is transferred to the Al-oxide layer 18 during the heat treatment, to form a Fe-oxide layer at the interface Although it is said that the moment of the first ferromagnetic layer 16 due to the diffusion of Mn can be prevented, the Al-oxide layer 18 or the Fe-oxide layer is arranged side by side, and the thickness of the oxygen layer affecting the tunneling phenomenon and There was a problem that the characteristics adjustment is very difficult.

The present invention has been made to solve the above problems, by adding an appropriate oxide layer to the ferromagnetic layer, which is a pinned layer in the TMR structure, to block the diffusion of Mn generated in the antiferromagnetic layer and to prevent it from moving to another layer. It is an object of the present invention to provide a TRM device for MRM and an improved method for improving thermal properties that can form a uniform oxide layer through heat treatment at the same time.

In order to achieve the above object, the present invention provides a buffer layer / antiferromagnetic layer / first ferromagnetic layer / Al-oxide layer / second ferromagnetic layer / A MMR element for MAMA in which protective layers are sequentially stacked or buffer layers / second ferromagnetic layers / Al-oxide layers / first ferromagnetic layers / antiferromagnetic layers / protective layers are stacked in sequence; The first ferromagnetic layer close to the anti-ferromagnetic layer is to provide a TMR element for MRM AAM improved thermal characteristics, characterized in that the oxide layer of 5Å-20Å thickness is formed.

In order to achieve the above object, the present invention provides a buffer layer / antiferromagnetic layer / first ferromagnetic layer / Al-oxide layer / second ferromagnetic layer on top of an Si substrate and on top of an oxide or nitride-treated substrate. The first ferromagnetic layer close to the antiferromagnetic layer by depositing the protective layer, the buffer layer, the second ferromagnetic layer, the Al-oxide layer, the first ferromagnetic layer, the antiferromagnetic layer, and the protective layer in the order of DC magnetron sputtering. An object of the present invention is to provide a method of manufacturing a TMR device for MRMs with improved thermal characteristics, characterized in that an oxide layer is formed on a layer by a natural oxidation method.

Hereinafter, the present invention will be described with reference to the accompanying drawings.

In FIG. 2, the Si substrate (naturally treated with oxide (nitride) or artificially treated with oxide (nitride)) or a buffer layer 12 / antiferromagnetic layer 14 / first ferromagnetic layer 16 / Al-oxide layer 18 / second ferromagnetic layer 20 / protective layer 22 or buffer layer 12 / second ferromagnetic layer 20 / Al-oxide layer 18 / first ferromagnetic layer 16 The bottom and top TMR structures of) / antiferromagnetic layer 14 / protective layer 22 are deposited by direct current magnetron sputtering.

The present invention provides a method of manufacturing TMR having excellent thermal characteristics, characterized in that the oxide layer 30 is formed in the first ferromagnetic layer 16 adjacent to the antiferromagnetic layer 14 during deposition.

The material for forming the buffer layer 12 is Ta, Cu, Au, Al, Pd, Pt, and is formed to have a thickness of 5-200Å with a (111) texture structure.

The material forming the antiferromagnetic layer 14 is formed of FeMn, IrMn, PtMn, or PdPtMn with a thickness of 50-400 kPa.

The material for forming the first ferromagnetic layer 16 is made of CoFe, NiFe and the thickness of 20-200-.

In order to improve the thermal characteristics by forming the oxide layer 30 on the first ferromagnetic layer 16, the thickness of the oxide layer 30 should be very thin. More specifically, if the thickness is 20Å or more, the oxide layer 30 may form a magnetic layer. If the magnetic layers do not exhibit the same characteristics by being disconnected, and the thickness is 5 m or less, the oxide layer 30 does not form an insulating layer, thereby exhibiting the characteristics of a single magnetic layer.

Therefore, in the present invention, the oxide layer 30 is formed by using a natural oxidation method, but when oxidized in the main chamber, the target in the main chamber is contaminated, and then, when the magnetic layer 30 is formed, the oxide attached to the target must be removed. There is a complicated problem in the process of forming an oxide layer in the main chamber and then moving to a load-lock chamber to change the chamber atmosphere to an oxygen atmosphere, while maintaining a 1mTorr-100Torr partial pressure for 1 minute to 20 hours. The surface of the single ferromagnetic layer 16 is oxidized to form an oxide layer 30.

Preferably the oxygen partial pressure is advantageously within 5-200 mTorr, 5 minutes-5 hours.

The oxygen partial pressure is lowered, the oxidation time is increased, the oxygen partial pressure is increased, and the oxidation time is shortened.

The oxide layer 30 may be formed at a pure oxygen partial pressure and may be oxidized by mixing oxygen and nitrogen at a ratio of 9: 1 to 2: 8 in an appropriate ratio of oxygen and nitrogen.

In addition to the natural oxidation method, the oxide layer 30 may be formed by a plasma oxidation method, a reactive sputtering method, or the like.

After the oxide layer 30 is formed, the first ferromagnetic layer 16 and the Al-oxide layer 18, the second ferromagnetic layer 20, and the protective layer 22 which are not moved to the main chamber and are not stacked again in FIG. 2A are formed. ) And the antiferromagnetic layer 14 and the protective layer 22 are formed in FIG. 2B.

The Al-oxide layer 18 is formed to be 5-25 Å by plasma oxidation or natural oxidation.

The material forming the second ferromagnetic layer 20 is formed of NiFe, Cofe, NiFe / CoFe to a thickness of 10-200Å.

In this case, the composition ratio of NiFe is Ni ₈₁ Fe ₁₉ (wt%), and the composition ratio of CoFe is Co ₉₀ Fe ₁₀ (at%).

The ferromagnetic material having soft magnetic properties is not limited to this composition.

The material for forming the protective layer 22 is made of Ta, Cu, oxide, or nitride and has a thickness of 10 to 200 mW.

As described above, the TMR device manufactured by inserting the oxide layer 30 in the middle of the first ferromagnetic layer 16 in the middle has a slight effect of the oxide layer 30. By performing heat treatment at or above the blocking temperature, a uniform oxide layer 30 can be formed.

Although the oxide layer 30 before the heat treatment has a non-uniform interface, the oxide layer 30 uniformly generated by the heat treatment at a temperature of 50-450 ° C. prevents the diffusion of the antiferromagnetic layer 14 due to heat generated during device manufacturing. To do.

Hereinafter, the present invention is specifically carried out in the Examples.

The first embodiment includes a buffer layer 12, an antiferromagnetic layer 14, and a first ferromagnetic layer (on a Si substrate (a substrate which is naturally oxide (nitride) or artificially oxide (nitride)) or a glass substrate. 16), a bottom TMR structure of the Al-oxide layer 18, the second ferromagnetic layer 20, and the protective layer 22 is deposited by direct current magnetron sputtering.

The base pressure of the main chamber is maintained at 2 × 10 ⁻⁸ or less to make the atmosphere of the main chamber as clean as possible and to suppress the incorporation of impurities into the sample.

The deposition conditions were sputtering partial pressure of 1-2mTorr, sputtering power of 20-100W and deposition rate of 0.5-2Å / sec.

The Al-oxide layer 18 is formed by performing plasma oxidation for 1-20 mTorr of oxygen partial pressure and oxidation time of 1-60 seconds in the load-lock chamber without performing in the main chamber to prevent oxidation of the target in the main chamber. Or 1-500 mTorr, oxidation time 1 min-10 hours, and natural oxidation.

The sample is then moved back to the main chamber and the remaining layers are deposited.

In order to form the oxide layer 30 between the first ferromagnetic layer 16 adjacent to the antiferromagnetic layer 14, the first ferromagnetic layer 16 is first formed as much as half the thickness of the first ferromagnetic layer 16. Thereafter, as in the manufacture of the Al-oxide layer 18, the sample is moved to a load-lock chamber and formed by performing natural oxidation by 1-500 mTorr and an oxidation time of 1 minute to 10 hours.

With this sample, a TMR device having a size of 25x25 mu m 2 is manufactured by using a micro-fabrication process.

Thereafter, in order to give an effect of the oxide layer 30 of the oxidized film, a magnetic field is applied in a vacuum of ² × 10 ⁻⁶ Torr and heat-treated to 150-450 ° C.

Through the above heat treatment, not only the interface of the Al-oxide layer 18 providing the tunneling effect but also the interface of the oxide layer 30 controlling the diffusion of Mn are simultaneously increased to increase the magnetoresistance ratio and improve the thermal characteristics. Can also contribute.

The figure shows the magnetoresistance ratio according to the annealing temperature after obtaining the MR ratio by measuring the RH curve of the TMR element that has been heat-treated and manufactured the heat-treated TMR element at room temperature using a four-terminal probe method. 3

It can be seen that the magnetoresistance ratio increases as the heat treatment temperature increases in FIG. 3.

In the second embodiment, after the TMR device manufactured in the same manner as in the first embodiment is heat-treated to 150-450 ° C., the exchange bias size is obtained by measuring the MH curve, which is the size of the exchange bias according to the heat treatment temperature of FIG. 4. .

The first comparative example is a buffer layer 12, the antiferromagnetic layer 14, a first ferromagnetic layer (16), Al-oxide layer 18 by using the substrate 10 is deposited by a 1500Å of SiO ₂ on Si, the 2 ferromagnetic layer 20, protective layer 22 TMR elements are fabricated by direct current magnetron deposition; each layer is buffer layer Ta (50Å), antiferromagnetic layer IrMn (80Å), first ferromagnetic layer CoFe (30Å), Al -Oxide layer Al-oxide (15,), second ferromagnetic layer Cofe (45Å), buffer layer Ta (50 하고), except that the oxide layer 30 is not formed on the first ferromagnetic layer 16. Same as the example.

3 shows the change of the magnetoresistance ratio according to the heat treatment temperature in the same manner as in the first embodiment.

Comparative Example 2 has the buffer layer 12, the antiferromagnetic layer 14, a first ferromagnetic layer (16), Al-oxide layer 18 by using the substrate 10 by an SiO ₂ deposited by 1500Å on Si, the 2 ferromagnetic layer 20, protective layer 22 TMR elements are fabricated by direct current magnetron deposition; each layer is buffer layer Ta (50Å), antiferromagnetic layer IrMn (80Å), first ferromagnetic layer CoFe (30Å), Al The oxide layer Al-oxide (15 25), the second ferromagnetic layer CoFe (45Å), the buffer layer Ta (50Å), and after a fine processing process, a TMR element having a size of 25x25μm is manufactured.

4 is the same as in the first embodiment except that the sample is not formed with the oxide layer 30, and the change in the magnetic bias according to the heat treatment temperature is shown in FIG.

Although the present invention has been described in detail in the above embodiments, it should be understood that the present invention is not limited to these embodiments and various changes and modifications may be made without departing from the technical spirit described in the claims.

As described above, according to the present invention, since the oxide layer is formed in the first ferromagnetic layer close to the antiferromagnetic layer, the thermal characteristics can be greatly improved, and thus it can be applied to the next generation spin valve head and the magnetic memory device.

In addition, the thermal characteristics are improved and a uniform oxide layer is formed by heat treatment, which is suitable for the requirements of plasma enhanced chemical vapor deposition and sintering process, which are applied for bonding with CMOS in MRAM fabrication.

Claims (7)

Bottom structure in which a buffer layer / antiferromagnetic layer / first ferromagnetic layer / Al-oxide layer / second ferromagnetic layer / protective layer are sequentially stacked on the Si substrate, Or in a TMR element for an MRAM having a top structure in which a buffer layer, a second ferromagnetic layer, an Al-oxide layer, a first ferromagnetic layer, an antiferromagnetic layer, and a protective layer are sequentially stacked on a Si substrate. The thermal properties are improved by oxidizing the inside of the first ferromagnetic layer adjacent to the bottom-structured Al-oxide layer or the antiferromagnetic layer having the top structure, and having a single ferromagnetic characteristic having a thickness of 5 GPa to 20 GPa. TMR element which is used. A bottom structure is formed in which a buffer layer / antiferromagnetic layer / first ferromagnetic layer / Al-oxide layer / second ferromagnetic layer / protective layer is sequentially stacked on the Si substrate, Alternatively, a top structure is formed in which a buffer layer, a second ferromagnetic layer, an Al-oxide layer, a first ferromagnetic layer, an antiferromagnetic layer, and a protective layer are sequentially stacked on the Si substrate, MRAM for depositing and laminating by direct current magnetron sputtering, and oxidizing an oxide layer in a mixed atmosphere of nitrogen and oxygen in the first ferromagnetic layer to prevent diffusion of the antiferromagnetic layer to have a single ferromagnetic property. Method of manufacturing a TMR device. delete delete delete The method of claim 2, wherein the TMR element is heat-treated at a blocking temperature or higher in vacuum and a magnetic field. The method of manufacturing a TMR element for an MRAM according to claim 6, wherein the heat treatment temperature is 50 to 450 ° C.

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