Magnetic memory device and method of manufacturing the same

According to one embodiment, a magnetic memory device includes: a first magnetic layer; a nonmagnetic layer on the first magnetic layer; a second magnetic layer on the nonmagnetic layer; and an insulator film on the nonmagnetic layer surrounding a side surface of the second magnetic layer. The second magnetic layer has an area of a surface facing the nonmagnetic layer smaller than that of the nonmagnetic layer. The nonmagnetic layer includes a first region that is provided between the first magnetic layer and the insulator film. The first region includes an amorphous state.

FIELD

Embodiments described herein relate generally to a magnetic memory device and method of manufacturing the same.

BACKGROUND

A resistance change memory is known as a kind of semiconductor memory device. A magnetoresistive random access memory (MRAM) is known as a kind of resistance change memory. The MRAM features a high-speed operation, a large capacity, and nonvolatileness, and has been researched and developed as a next-generation memory device that replaces a volatile memory such as a DRAM or SRAM.

In the MRAM, a magnetic memory device using a tunneling magnetoresistive (TMR) effect is used as a memory cell for storing information. As the magnetic memory device, an magnetic tunnel junction (MTJ) element having a stacked layer of metal magnetic film/insulating film/metal magnetic film is used. A change in the resistance of the MTJ element is determined by the magnetization states of the metal magnetic films that sandwich the insulating film. That is, the MRAM stores data according to the magnetization state of the MTJ element.

The characteristics of the MTJ element are represented using a write current, a magnetoresistive ratio (MR ratio), and the like as indices, and are affected by the processes of forming the MTJ element. The characteristics of the MTJ element lower or vary due to the influence of, for example, the planarity of an underlayer used when stacking layers or the element isolation process of the MTJ element. To reduce a write/erase current and improve the MR ratio while ensuring a high data retention characteristic, it is necessary to improve the structure and manufacturing method of the MTJ element.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetic memory device includes: a first magnetic layer; a nonmagnetic layer on the first magnetic layer; a second magnetic layer on the nonmagnetic layer; and an insulator film on the nonmagnetic layer surrounding a side surface of the second magnetic layer. The second magnetic layer has an area of a surface facing the nonmagnetic layer smaller than that of the nonmagnetic layer. The nonmagnetic layer includes a first region that is provided between the first magnetic layer and the insulator film. The first region includes an amorphous state.

Embodiments will now be described with reference to the accompanying drawing. Note that in the following explanation, the same reference numerals denote constituent elements having almost the same functions and arrangements. The drawings are schematic. The embodiments merely exemplify devices and methods for embodying the technical concepts of the embodiments, and the technical concepts of the embodiments do not limit the materials, shapes, structures, layouts, and the like of the components to those to be described below.

[1] FIRST EMBODIMENT

A magnetic memory device according to the first embodiment is an magnetic tunnel junction (MTJ) element. A tunnel barrier layer provided between a lower magnetic layer and a side wall provided on the side surface of an upper magnetic layer has an amorphous state. The magnetic memory device will be referred to as an MTJ element in the following description.

[1-1] Structure of MTJ Element

The structure of an MTJ element100according to the first embodiment will be described with reference toFIGS. 1 and 2by exemplifying a case in which a perpendicular magnetization film is used as a storage layer.FIG. 1is a plan view showing the MTJ element100according to the first embodiment.FIG. 2is a sectional view of the MTJ element100taken along a line I-I inFIG. 1.

As shown inFIG. 1, the planar shape of the MTJ element100is, for example, circular or elliptic. Note that the planar shape of the MTJ element100is not limited to this, and various forms can be employed.

As shown inFIG. 2, the MTJ element100has a structure in which an underlayer21, a reference layer (fixed layer)22, a tunnel barrier layer (nonmagnetic layer)23, a storage layer (free layer)24, and a cap layer25are sequentially stacked on a lower electrode20. A protective film26is provided on the side surfaces of the storage layer24and the cap layer25so as to cover the periphery.

The MTJ element100stores data according to the magnetization states of the storage layer24and the reference layer22that sandwich the tunnel barrier layer23. More specifically, the MTJ element100uses a characteristic representing that the resistance value of the MTJ element100changes depending on whether the magnetization states of the storage layer24and the reference layer22are parallel or antiparallel. If the magnetization states are parallel, the MTJ element100has a low resistance state. If the magnetization states are antiparallel, the MTJ element100has a high resistance state. The MTJ element100can thus store data by defining, for example, the low resistance state and the high resistance state as “0” and “1”, respectively. The allocation of the resistance state of the MTJ element100to data can arbitrarily be set.

The storage layer24and the reference layer22are ferromagnetic layers and have a magnetic anisotropy perpendicular to the film surfaces. In the storage layer24and the reference layer22, the magnetization direction (direction of easy magnetization) is perpendicular to the film surface. The MTJ element100having a perpendicular magnetization direction will be referred to as a perpendicular magnetization type MTJ element100in the following description.

The magnetization switching current of the storage layer24is smaller than that of the reference layer22. The magnetization switching current is a current capable of switching the magnetization of the magnetic layer.

As the storage layer24and the reference layer22that implement the perpendicular magnetization type MTJ element100, a magnetic material having an L10structure or L12structure based on an face-centered tetragonal (fct) structure with an orientation along the (001) plane with respect to the in-plane direction is used. To implement perpendicular magnetization in the storage layer24and the reference layer22, a material having a magnetocrystalline anisotropy energy density of 5×105erg/cc or more is preferably used.

As the magnetic material of the storage layer24, for example, a perpendicular magnetization film of an artificial lattice formed by stacking an element such as iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), chromium (Cr), platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), ruthenium (Ru), osmium (Os), rhenium (Re), or gold (Au) or an alloy thereof is used. More specifically, as the perpendicular magnetization film of an artificial lattice, a film formed by stacking a combination of a magnetic layer and a nonmagnetic layer, for example, Co/Pt, Co/Pd, or Co/Ru is used. The magnetic characteristic of the storage layer24is adjusted by the composition of the magnetic layer, the ratio of the magnetic layer to the nonmagnetic layer, and the like. In addition, the storage layer24can also be provided using an antiferromagnetic film such as PtMn or IrMn in combination with an Ru film. As the storage layer24, for example, CoFeB that is an alloy is used. The characteristic of CoFeB changes depending on the composition ratio of Co and Fe and the concentration of boron (B). Hence, CoFeB having properties suitable for the structure of the MTJ element100is used.

As the magnetic material of the reference layer22, an ordered alloy having an L10structure, for example, FePd, FePt, or the like is used. The saturation magnetization and the magnetic anisotropy energy density of the ordered alloy layer can be adjusted by adding an element such as copper (Cu). The reference layer22can also use the same structure as the storage layer24. Note that to fix the magnetization direction of the reference layer22to one direction, an antiferromagnetic layer may be provided next to the reference layer22. As the antiferromagnetic layer, for example, an alloy of Mn and Fe, Ni, Pt, Pd, Ru, Os, or Ir, that is, FeMn, NiMn, PtMn, PdMn, RuMn, OsMn, or IrMn, or CrPtMn or the like is used.

The tunnel barrier layer23is formed from an insulating film and functions as the barrier between the storage layer24and the reference layer22. As the tunnel barrier layer23, an oxide whose crystal structure is an NaCl structure is preferably used. For example, magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), titanium oxide (TiO), vanadium oxide (VO), niobium oxide (NbO), or alumina (Al2O3) is used. When the tunnel barrier layer23is crystal-grown on an alloy structure mainly containing Fe, Co, Ni, or the like, the tunnel barrier layer23formed from an insulating film with a (100) preferred orientation can be obtained. As the alloy mainly containing Fe, Co, Ni, or the like, for example, amorphous CoFeB is used. The tunnel barrier layer23has a film thickness of, for example, about 10 Å and a sheet resistance value of, for example, 10 Ωμm2.

The lower electrode20is made of a metal and used to connect a circuit (not shown) that uses the MTJ element100. The size of the lower electrode20can appropriately be set. If the size of the lower electrode20is smaller than that of the underlayer21, the underlayer21is provided on the lower electrode20and on an interlayer dielectric film around the lower electrode20.

The underlayer21connects the lower electrode20and the reference layer22, and controls the orientation of the reference layer22. As the underlayer21, a refractory metal such as Pt, Ir, Ru, or Cu is used. Note that the underlayer21may be divided into a lower metal layer in contact with the lower electrode20and an orientation control film that controls the orientation of the reference layer22. In this case, as the lower metal layer, for example, Ta, W, Ti, or the like is used. As the orientation control film, for example, Pt, Ir, or Ru, or a stacked film thereof is used.

The cap layer25connects the storage layer24and an upper electrode layer (not shown). As the cap layer25, a metal such as Ru or Ta is used. If the storage layer24is made of CoFeB, boron (B) may be removed when crystallizing the layer. Hence, as the cap layer25, Ta, Ti, hafnium (Hf), zirconium (Zr), or the like is used. These materials have the effect of absorbing boron when crystallizing amorphous CoFeB. Note that the material used for the cap layer25preferably has a small current value (switching current) at the time of switching because it is in contact with the storage layer24that makes magnetization switching. This current value is determined by the friction coefficient, attenuation constant, and damping constant between the storage layer24and the cap layer25. To make these constants small and reduce the switching current, not a metal film but an oxide film, a nitride film, a boride film, a carbide film, or the like may be selected.

The protective film26is provided to surround the side surface of the storage layer24, and prevents a short circuit between the storage layer24and the reference layer22caused by a side surface residue generated in the element isolation process of the MTJ element100. That is, the MTJ element100has a side wall structure with the protective film26provided on the side surface of the storage layer24. As the protective film26, an insulating material is preferably used. For example, Al2O3, a silicon oxide film (SiO2), TiOx, a silicon nitride film (SiN), or the like is used. If the protective film26is an SiN film, the protective film26is formed by, for example, CVD (Chemical Vapor Deposition). The SiN film may be formed by nitriding a deposited polysilicon film. Note that the area of the storage layer24is smaller than that of the reference layer22because the protective film26is provided.

In the MTJ element100according to the first embodiment, the reference layer22and the tunnel barrier layer23have almost the same area, and the storage layer24has an area smaller than that of the reference layer22. A region23A of the tunnel barrier layer23between the reference layer22and the storage layer24has a crystalline state, and a region23B of the tunnel barrier layer23between the reference layer22and the protective film26has an amorphous state. Details will be described later.

A shift adjustment layer may be provided between the reference layer22and the underlayer21or between the storage layer24and the cap layer25. When the shift adjustment layer is provided, a nonmagnetic layer is provided between the shift adjustment layer and the reference layer22or between the shift adjustment layer and the storage layer24. The shift adjustment layer has a magnetization direction set to be antiparallel to the reference layer22, and suppresses a leakage magnetic field applied to the storage layer24. The nonmagnetic layer has a heat resistance to prevent thermal diffusion and a function of controlling the crystal orientation. As the shift adjustment layer, for example, the same material as the reference layer22is used. As the nonmagnetic layer, a nonmagnetic metal such as ruthenium (Ru), silver (Ag), or copper (Cu) is used. Note that if the nonmagnetic layer becomes thick, the distance between the shift adjustment layer and the storage layer24increases, and the magnetic field applied from the shift adjustment layer to the storage layer24becomes small. For this reason, the film thickness of the nonmagnetic layer is preferably, for example, 5 nm or less.

Each of the reference layer22, the nonmagnetic layer, and the shift adjustment layer may have an synthetic antiferromagnetic (SAF) structure. At this time, for example, ruthenium is used as the nonmagnetic layer (coupling layer). The magnetization directions of the reference layer22and the shift adjustment layer are set to be antiparallel using antiferromagnetic coupling by ruthenium. The coupling layer has a film thickness of, for example, 4 Å and a coupling magnetic field of, for example, 5 to 8 kOe.

Interface magnetic layers may be provided between the reference layer22and the tunnel barrier layer23and between the storage layer24and the tunnel barrier layer23. The interface magnetic layer is made of a material having a high polarization ratio. The MTJ element100in which the interface magnetic layer is introduced can obtain a large TMR effect. The interface magnetic layer needs to attain interface matching between the storage layer24or reference layer22and the (100) plane of the tunnel barrier layer23made of an oxide with a NaCl structure. Hence, as the interface magnetic layer, a material having a small lattice mismatch to the (100) plane of the tunnel barrier layer23is preferably selected. For example, CoFeB is used.

In addition, diffusion prevention films may be provided between the reference layer22and the interface magnetic layer and between the storage layer24and the interface magnetic layer. The diffusion prevention films prevent the metal elements of the layers from diffusing in heat treatment processes such as crystallization of the tunnel barrier layer23, insulating film formation, reactive ion etching (RIE), and interconnection formation in the manufacturing process of the MRAM. The diffusion prevention films also hold the crystallinity of the interface magnetic layer, the storage layer24, and the reference layer22. The diffusion prevention films can thus suppress degradation of the magnetic characteristics of the storage layer24and the reference layer22and the electrical characteristics (TMR effect and the like) of the MTJ element100. As the diffusion prevention film, a film made of a refractory metal such as Ti, Ta, W, Zr, Hf, molybdenum (Mo), or niobium (Nb), or a nitride or carbide thereof is used.

Note that the MTJ element100has a shape with a side surface extending in a direction perpendicular to the lower electrode20. The taper angle of the side surface of the MTJ element100is preferably 80° or more, and more preferably, 85° or more. This enables high integration of elements.

As each of the storage layer24and the reference layer22, an in-plane magnetization film having a magnetic anisotropy parallel to the film surface may be used. At this time, the direction of easy magnetization of the storage layer24is parallel to the film surface (or stacking surface). As the in-plane magnetization storage layer24and reference layer22, for example, a magnetic metal containing one of iron (Fe), cobalt (Co), nickel (Ni), manganese (Mn), and chromium (Cr) is usable.

The MTJ element100shown inFIGS. 1 and 2has a top free structure in which the storage layer24is provided above the reference layer22. The MTJ element100is not limited to this, and may have a bottom free structure in which the storage layer24is provided under the reference layer22. In a case of the bottom free structure, the MTJ element100has a structure in which the underlayer21, the storage layer24, the tunnel barrier layer23, the reference layer22, and the cap layer25are sequentially stacked on the lower electrode20. The protective film26is provided on the side surface of the reference layer22, and a region of the tunnel barrier layer23between the storage layer24and the protective film26has an amorphous state. The stacked structure of the MTJ element100is not limited to this, and various forms can be employed.

[1-2] Method of Manufacturing MTJ Element

A method of manufacturing the MTJ element100according to the first embodiment will be described with reference toFIGS. 3, 4, 5, 6, and 7.FIGS. 3, 4, 5, 6, and 7are plan and sectional views showing processes in the manufacture of the MTJ element100according to the first embodiment. Characteristic parts of the processes in the manufacture of the MTJ element100will be described below in detail.

First, as shown inFIG. 3, the underlayer21, the reference layer22, the tunnel barrier layer23, the storage layer24, the cap layer25, a hard mask27, and a resist28are sequentially formed on the lower electrode20using a known method. The reference layer22and the storage layer24are made of, for example, CoFeB. The tunnel barrier layer23is made of, for example, MgO and has a crystalline state. The hard mask27is made of, for example, SiO2or SiN. Note that a metal film may be used as the hard mask27.

Next, as shown inFIGS. 4 and 5, a desired pattern is formed on the resist28using photolithography, and the hard mask27is processed. In this processing, for example, physical processing by ion beam etching (IBE) is used. After the processing of the hard mask27, the resist28is removed.

As shown inFIG. 6, the layers above the tunnel barrier layer23are processed using the processed hard mask27. In this processing, for example, physical processing by IBE using neon gas as an inert gas is used. The IBE using neon gas will be referred to as Ne etching in the following description. In the IBE of this process, the processing condition, process gas species, post-processing, and the like are preferably optimized so as not to leave the residue in the processing on the side wall of the MTJ element100. In the IBE of this process, for example, neon gas is supplied in a state in which a DC/RF bias is applied to the substrate side on which the MTJ element100is to be formed. As the etching condition at this time, for example, an RF bias of 13.56 MHz is applied to the coil of a vacuum chamber to convert the neon gas into a plasma, and a low frequency of 1 MHz or less is applied to the substrate side, thereby causing etching at low energy. In this process, the tunnel barrier layer23is irradiated with Ne ions. The portion irradiated with the Ne ions changes to an amorphous state as the Ne ions are implanted. That is, the region23A in the crystalline state and the region23B in the amorphous state are formed in the tunnel barrier layer23. The region23B in the amorphous state may be formed only in the upper portion of the tunnel barrier layer23or may reach the lower portion of the tunnel barrier layer23. The region23B in the amorphous state contains the element of the inert gas used for IBE.

As shown inFIG. 7, the protective film26is formed so as to cover the upper surface of the MTJ element100. At this time, to prevent damage to the layers, the protective film26is preferably formed using atomic layer deposition (ALD), chemical vapor deposition (CVD), physical vapor deposition (PVD), or the like.

Next, when the reference layer22and the underlayer21under the tunnel barrier layer23are etched by, for example, IBE using Ar as an inert gas, the structure shown inFIGS. 1 and 2is obtained. Due to the directivity of the IBE, the portions on the bottom side of the tunnel barrier layer23are mainly etched, and the protective film26remains on the side surfaces of the storage layer24and the cap layer25. The MTJ element100is thus element-isolated. The residue of the protective film26formed in this process serves as the side wall of the storage layer24. Note that the protective film26may only cover the side surface of the storage layer24.

In the above-described way, the MTJ element100according to the first embodiment is formed. The region23A of the tunnel barrier layer23between the reference layer22and the storage layer24has the crystalline state, and the region23B of the tunnel barrier layer23between the reference layer22and the protective film26changes to the amorphous state.

[1-3] Effects of First Embodiment

In the MRAM, when the size of the storage layer provided on one surface of the tunnel barrier layer in the MTJ element is made smaller than the size of the reference layer provided on the other surface, the influence of the leakage magnetic field from the reference layer can be reduced. It is therefore possible to obtain an MTJ element in which the magnetization switching characteristic by the spin current of the storage layer is improved, the switching current is reduced, and an excellent retention characteristic is ensured.

When element-isolating the MTJ element, the residue generated by ion beam etching (IBE), reactive ion etching (RIE), or the like adheres to the side surface of the MTJ element in some cases. Since the tunnel barrier layer made of MgO or the like is thin, the residue adhered to the side wall of the MTJ element easily causes a short circuit between the storage layer and the reference layer. In some cases, the electrical characteristic of the MTJ element degrades due to the same reason. To prevent this, before element isolation of the MTJ element, the magnetic layer formed on the upper surface of the tunnel barrier layer is etched. After the protective film (side wall) is formed to cover the upper surface of the processed structure, the MTJ element is element-isolated. This can provide an MTJ element having a side wall structure that prevents a short circuit caused by a residue on the side surface.

However, when argon (Ar) is used as the inert gas in IBE performed for side wall formation, Ar is implanted into the tunnel barrier layer, and the implanted Ar may reach the lower magnetic layer. In this case as well, the electrical characteristic of the MTJ element degrades.

To prevent this, in the MTJ element100according to the first embodiment, Ne lighter than Ar is used as the inert gas in IBE performed for side wall formation. By the IBE using the neon gas, processing can be performed up to the tunnel barrier layer23without implanting any element into the lower magnetic layer. Additionally, in this step, the tunnel barrier layer23in which the neon gas is implanted changes to the amorphous state.

Amorphization of the tunnel barrier layer23by Ne etching will be described with reference toFIG. 8. The stacked structure shown inFIG. 8is obtained by sequentially stacking tantalum (Ta) and magnesium oxide (MgO) on a silicon substrate and performing IBE using neon gas for the MgO layer. For examination, the MgO layer is provided thicker (about 40 to 50 nm) than in a case in which the MgO layer is used in the MTJ element100. In the stacked structure shown inFIG. 8, to acquire a sectional image, carbon (C) is deposited on the amorphized MgO layer.

As is apparent fromFIG. 8, the upper portion of the MgO layer processed by IBEusing neon gas has an amorphous state. Note that the tunnel barrier layer23in the amorphous state can suppress diffusion of a metal film element in contact with the tunnel barrier layer in annealing of post-processing and thus suppress degradation of the electrical characteristic of the MTJ element100. In addition, the amorphized tunnel barrier layer23can be used as an etching stopper because its etching rate in IBE is low.

As described above, according to the first embodiment, it is possible to provide the MTJ element100that suppresses degradation of the electrical characteristic.

Note that in electrical characteristic evaluation of the MTJ element100according to the first embodiment, the element sheet resistance value (RA value) was 10 Ωμm2, and the magnetoresistive ratio (MR ratio) was 100% or more.

In the first embodiment, the MTJ element100has a top free structure in which the storage layer24is stacked above the reference layer22. However, the structure is not limited to this, and a bottom free structure in which the positions of the reference layer22and the storage layer24are replaced may be employed.

Note that IBE for amorphizing the tunnel barrier layer23may use helium (He) as the inert gas in place of neon (Ne). When argon (Ar) is used as the inert gas in IBE, the same effects as described above can be obtained by adjusting the DC/RF bias and causing deceleration.

[2] SECOND EMBODIMENT

In the second embodiment, alteration processing such as oxidation, nitriding, or boronizing is performed for a metal hard mask used in element isolation of an MTJ element100, thereby improving the etching selectivity of the metal hard mask.

A method of manufacturing the MTJ element100according to the second embodiment will be described with reference toFIGS. 9, 10, 11, and 12.FIGS. 9, 10, 11, and 12are plan and sectional views showing steps in the manufacture of the MTJ element100according to the second embodiment.

First, as shown inFIG. 9, an underlayer21, a reference layer22, a tunnel barrier layer23, a storage layer24, a cap layer25, a hard mask27, and a resist28are sequentially formed on a lower electrode20. The hard mask27is made of a metal, for example, Mg.

Next, as shown inFIGS. 10 and 11, a desired pattern is formed on the resist28using photolithography, and processing such as oxidation, nitriding, or boronizing is performed for the hard mask27. A portion of the hard mask27corresponding to the opening of the resist28alters to a hard mask27A of a different reaction compound. The hard mask27A is made of, for example, MgO.

Next, as shown inFIG. 12, after removal of the resist28, element isolation processing is performed using the hard masks27and27A. In this processing, for example, physical processing by IBE using gas mainly containing Ar is used. Since the etching rate of the hard mask27A is lower than that of the hard mask27, the MTJ element100can be processed into a desired shape without patterning the hard mask27itself. In the MTJ element100after the processing, the hard mask27A has been removed. If the hard mask27A remains in the MTJ element100after the processing, it is removed by separately performing etching. On the other hand, the hard mask27made of a metal has a function as an electrode, and may therefore remain in the MTJ element100.

As described above, in the manufacturing method of the MTJ element100according to the second embodiment, alteration processing of the hard mask27is performed, thereby forming a region in the hard mask27to which etching selectivity is imparted. This enables processing using the hard mask27A that is hardly etched and improves the variation and the shape of the MTJ element100after the processing. It is therefore possible to provide the MTJ element100that suppresses degradation of the electrical characteristic.

Note that the manufacturing method of the MTJ element100according to the second embodiment is also applicable to the arrangement of the MTJ element100according to the first embodiment.

In the third embodiment, atoms are implanted into a metal hard mask used in element isolation of an MTJ element100, thereby improving the etching selectivity of the metal hard mask.

A method of manufacturing the MTJ element100according to the third embodiment will be described with reference toFIGS. 13, 14, 15, 16, and 17.FIGS. 13, 14, 15, 16, and 17are plan and sectional views showing steps in the manufacture of the MTJ element100according to the third embodiment.

First, as shown inFIGS. 13 and 14, an underlayer21, a reference layer22, a tunnel barrier layer23, a storage layer24, a cap layer25, and a hard mask27are sequentially formed on a lower electrode20. The hard mask27is processed by photolithography and etching. As the hard mask27, a metal such as tantalum (Ta), titanium (Ti), tungsten (W), or molybdenum (Mo) is used.

Next, as shown inFIGS. 15 and 16, an additive atom film29is formed so as to cover the upper surface of the MTJ element100using, for example, chemical vapor deposition (CVD) or physical vapor deposition (PVD). The additive atom film29is made of a material different from that of the hard mask27. As the additive atom film29, nonmetal atoms such as carbon (C), boron (B), or silicon (Si) or metal atoms such as tantalum (Ta) are used.

As shown inFIG. 17, the additive atom film29is etched by Ne etching. Then, the atoms contained in the additive atom film29are implanted into the hard mask27. The region of the hard mask27where the atoms contained in the additive atom film29are implanted will be referred to as a hard mask27B. The hard mask27B has an improved etching selectivity compared to the hard mask27. At this time, a region25A where the atoms contained in the additive atom film29are implanted is formed in the cap layer25as well. However, the etching selectivity of the region25A of the cap layer25is different from that of the hard mask27B.

Next, element isolation processing is performed using the hard masks27and27B. In this processing, for example, physical processing by IBE using Ar as the inert gas is used. The etching rate of the hard mask27B is lower than that of the hard mask27, and the MTJ element100can stably be element-isolated. In the MTJ element100after the processing, the hard mask27B has been removed. If the hard mask27B remains in the MTJ element100after the processing, it is removed by separately performing etching. The MTJ element100thus obtains the same structure as that shown inFIG. 12.

As described above, in the manufacturing method of the MTJ element100according to the third embodiment, metal or nonmetal atoms are implanted into the hard mask27, thereby forming a region in the hard mask27to which etching selectivity is imparted. This enables processing using the hard mask27B that is hardly etched and improves the variation and the shape of the MTJ element100after the processing. It is therefore possible to provide the MTJ element100that suppresses degradation of the electrical characteristic.

Note that the processing of implanting the atoms of the additive atom film29into the hard mask27may use helium (He) as the inert gas in place of neon (Ne). The same effects as described above can be obtained even by IBE in which argon (Ar) is used as the inert gas, and the DC/RF bias is adjusted to cause deceleration.

In addition, the manufacturing method of the MTJ element100according to the third embodiment is also applicable to the arrangement of the MTJ element100according to the first embodiment.

The fourth embodiment is a modification of the third embodiment, in which a metal hard mask is processed after implanting different atoms into it.

A method of manufacturing an MTJ element100according to the fourth embodiment will be described with reference toFIGS. 18, 19, 20, and 21.FIGS. 18, 19, 20, and 21are plan and sectional views showing steps in the manufacture of the MTJ element100according to the fourth embodiment.

First, as shown inFIGS. 18 and 19, an underlayer21, a reference layer22, a tunnel barrier layer23, a storage layer24, a cap layer25, a hard mask27, an additive atom film29, and a resist28are sequentially formed on a lower electrode20. The resist28is processed into a desired pattern by photolithography. As the hard mask27, a metal such as tantalum (Ta), titanium (Ti), tungsten (W), or molybdenum (Mo) is used.

Next, as shown inFIG. 20, the additive atom film29in the opening portion of the resist28is etched by Ne etching. Then, the atoms contained in the additive atom film29are implanted into the hard mask27, and a hard mask27B is formed.

Next, as shown inFIG. 21, the resist28is removed. Subsequently, the hard mask27is processed by wet etching using the hard mask27B as a mask. When element isolation processing is performed using the hard masks27and27B, the MTJ element100obtains the same structure as that shown inFIG. 12. In the MTJ element100after the processing, the hard mask27B has been removed, as in the third embodiment. If the hard mask27B remains in the MTJ element100after the processing, it is removed by separately performing etching.

As described above, in the manufacturing method of the MTJ element100according to the fourth embodiment, the opening portion of the resist28formed by photolithography is used when implanting atoms of the additive atom film29into the hard mask27. The hard masks27and27B are processed into a desired shape by wet etching.

This can form a region in the hard mask27to which etching selectivity is imparted without implanting the atoms of the additive atom film29into the cap layer25. The variation and the shape of the MTJ element100after the processing are more excellent than in the third embodiment. It is therefore possible to provide the MTJ element100that suppresses degradation of the electrical characteristic.

Note that the processing of implanting the atoms of the additive atom film29into the hard mask27may use helium (He) as the inert gas in place of neon (Ne). The same effects as described above can be obtained even by IBE in which argon (Ar) is used as the inert gas, and the DC/RF bias is adjusted to cause deceleration.

In addition, the manufacturing method of the MTJ element100according to the fourth embodiment is also applicable to the arrangement of the MTJ element100according to the first embodiment.

In the fifth embodiment, atoms of a metal hard mask are implanted into a cap layer25, and the cap layer25is used as a hard mask.

A method of manufacturing an MTJ element100according to the fifth embodiment will be described with reference toFIGS. 22, 23, 24, and 25.FIGS. 22, 23, 24, and 25are sectional views showing steps in the manufacture of the MTJ element100according to the fifth embodiment.

First, as shown inFIGS. 22 and 23, an underlayer21, a reference layer22, a tunnel barrier layer23, a storage layer24, the cap layer25, a hard mask27, and a resist28are sequentially formed on a lower electrode20. The resist28is processed into a desired pattern by photolithography. As the hard mask27, a metal such as tantalum (Ta), titanium (Ti), tungsten (W), or molybdenum (Mo) is used.

Next, as shown inFIG. 24, the hard mask27in the opening portion of the resist28is etched by Ne etching. Then, the atoms contained in the hard mask27are implanted into the cap layer25. A region25A of the cap layer25where the atoms contained in the hard mask27are implanted attains improved etching selectivity and can therefore be used as a hard mask when element-isolating the MTJ element100.

Next, as shown inFIG. 25, the resist28is removed. Subsequently, the cap layer25is processed by wet etching using the region25A of the cap layer25as a mask. When element isolation processing is performed using the region25A of the cap layer25, the MTJ element100obtains the same structure as that shown inFIG. 12. Note that the region25A of the cap layer has conductivity, and may therefore be left or removed after the element isolation processing.

As described above, in the manufacturing method of the MTJ element100according to the fifth embodiment, atoms of the hard mask27are implanted into the cap layer25, thereby improving the selectivity of the cap layer25. This enables processing using the cap layer25A that is hardly etched and improves the variation and the shape of the MTJ element100after the processing.

Note that the processing of implanting the atoms of the hard mask27into the cap layer25may use helium (He) as the inert gas in place of neon (Ne). The same effects as described above can be obtained even by IBE in which argon (Ar) is used as the inert gas, and the DC/RF bias is adjusted to cause deceleration.

In addition, the manufacturing method of the MTJ element100according to the fifth embodiment is also applicable to the arrangement of the MTJ element100according to the first embodiment.

In the sixth embodiment, when forming a storage layer24, a magnetic layer having an amorphous state is formed as a thick film, and high-temperature annealing is performed, thereby forming a magnetic layer having an excellent crystalline state. After the annealing, etchback processing is performed by Ne etching, thereby obtaining desired film thickness.

A method of manufacturing an MTJ element100according to the sixth embodiment will be described with reference toFIGS. 26 and 27.FIGS. 26 and 27are sectional views showing steps in the manufacture of the MTJ element100according to the sixth embodiment.

First, as shown inFIG. 26, an underlayer21, a reference layer22, a tunnel barrier layer23, a storage layer24, and a cap layer25are sequentially formed on a lower electrode20. The storage layer24is made of, for example, CoFeB in an amorphous state, and its film thickness is more than normal, for example, 30 Å. The cap layer25is made of, for example, tantalum (Ta), and its film thickness is more than normal, for example, 10 Å.

Next, annealing is performed at a temperature higher than normal to prompt crystallization of the magnetic layer of CoFeB or the like. The temperature used in this annealing is, for example, 450° C. or more. In a stacked structure of MgO/CoFeB, CoFeB grows in a crystal orientation state matching the MgO interface while diffusing boron (B) outward from the MgO (001) film. At this time, since the CoFeB layer is thick, diffusion of a metal such as Ta that forms the cap layer25to the vicinity of the interface of the tunnel barrier layer23is suppressed.

Next, as shown inFIG. 27, the storage layer24and the cap layer25are etched back by Ne etching to make the storage layer24have a desired film thickness. The same manufacturing method as in the first to fifth embodiments is applicable to the subsequent processes.

In sputter etching used for etchback processing, a rare gas such as argon (Ar) is normally used. In the sputter etching using Ar, however, the constituent atoms of the cap layer25may be implanted into the lower magnetic film by Ar particles.

To prevent this, etchback processing is performed by etching using neon gas as an inert gas. This makes it possible to suppress implantation of the atoms of the cap layer25into the magnetic layer at the time of etchback processing of the magnetic layer and form a magnetic film with excellent crystallinity without degradation of the interface. This processing also has the advantage of planarizing the magnetic film of CoFeB or the like by Ne ions.

Implantation of a metal into a magnetic layer by Ne etching will be described with reference toFIGS. 28A and 28B.FIGS. 28A and 28Bshow experimental results obtained by performing Ne etching for a structure in which Ta serving as a cap layer is stacked on a magnetic layer made of CoFeB as profiles obtained by performing energy dispersive X-ray spectroscopy (EDX) for a section of the structure.

The ordinate of each ofFIGS. 28A and 28Bcorresponds to the intensity, and the abscissa corresponds to a position in the thickness direction. The abscissa of each ofFIGS. 28A and 28Bcorresponds to the lower layer to the upper layer from left to right.FIG. 28Ashows the profile of a structure obtained by performing Ne etching for the surface of a CoFeB layer, andFIG. 28Bshows the profile of a structure obtained by performing Ne etching halfway through the CoFeB layer.

As shown inFIGS. 28A and 28B, Ta of the cap layer is implanted into the CoFeB layer by Ne etching. The depth to implant Ta is suppressed to the vicinity of the MgO layer corresponding to the tunnel barrier layer even in a case in which CoFeB is etched halfway. Ne etching is superior in controlling the implantation depth because of the weak implantation effect.

As described above, in the sixth embodiment, etchback processing by Ne etching is performed for the storage layer24and the cap layer25, which are formed thick. This can form a magnetic layer in an excellent crystalline state and manufacture the MTJ element100with an improved MR ratio and interface perpendicular magnetic anisotropy.

Note that the manufacturing method of the MTJ element100according to the sixth embodiment is also applicable to a magnetic layer other than the storage layer24.

Additionally, in the sixth embodiment, the MTJ element100has a top free structure in which the storage layer24is stacked above the reference layer22. However, the structure is not limited to this, and a bottom free structure in which the positions of the reference layer22and the storage layer24are replaced may be employed.

In the seventh embodiment, a magnetic layer is formed in a crystalline state with a little amount of impurity and then amorphized by Ne etching, thereby controlling the orientation of an MTJ element100.

A method of manufacturing an MTJ element100according to the seventh embodiment will be described with reference toFIGS. 29, 30, 31, 32, and 33.FIGS. 29, 30, 31, 32, and 33are sectional views showing steps in the manufacture of the MTJ element100according to the seventh embodiment.

First, as shown inFIG. 29, an underlayer21and a reference layer22are sequentially formed on a lower electrode20. Next, Ne etching is performed for a reference layer22. The reference layer22is made of, for example, CoFe and has a crystalline state. The reference layer22in the crystalline state will be referred to as the reference layer22A.

As shown inFIG. 30, when Ne etching is performed for the reference layer22A, the reference layer22A is doped with Ne and amorphized. The reference layer22in the amorphous state will be referred to as a reference layer22B. In this embodiment, the reference layer22is doped with Ne at 1×1014cm−2by a pull-in voltage of, for example, 1 KV and amorphized.

Next, as shown inFIG. 31, a tunnel barrier layer23and a storage layer24are sequentially formed on the reference layer22. Subsequently, Ne etching is performed for a storage layer24. The storage layer24is made of, for example, CoFe and has a crystalline state. The storage layer24in the crystalline state will be referred to as the storage layer24A.

As shown inFIG. 32, when Ne etching is performed for the storage layer24A, the storage layer24A is doped with Ne and amorphized. The storage layer24in the amorphous state will be referred to as a storage layer24B. In this embodiment, the storage layer24is doped with Ne at 1×1014cm−2by a pull-in voltage of, for example, 1 KV and amorphized.

Next, as shown inFIG. 33, a cap layer25is formed on the storage layer24, and high-temperature annealing is performed, thereby crystallizing the reference layer22and the storage layer24. The annealing for crystallizing the reference layer22and the storage layer24is performed, for example, in vacuum at 360° C. for 1 hr. With this annealing, MgO in the tunnel barrier layer23is crystallized, and CoFe in the reference layer22and the storage layer24is also crystallized. The same manufacturing method as in the first to sixth embodiments is applicable to the subsequent processes.

In the MTJ element formed from a stacked layer of metal magnetic film/insulating film/metal magnetic film, the orientation needs to be controlled to obtain a high MR ratio. In a case in which CoFe is used as the metal magnetic films (storage layer24and reference layer22), and MgO is used as the insulating film (tunnel barrier layer23), it is necessary to form CoFe/MgO/CoFe whose orientation is controlled to (100). The MR ratio increases when CoFe and MgO match in the (100) plane direction, and the crystallinity of CoFe becomes high.

However, CoFe has a (110) preferred orientation. If films are deposited in the order of CoFe/MgO/CoFe, CoFe(110)/MgO(100)/CoFe(110) is formed, and the MTJ element100with plane matching cannot be formed.

In a manufacturing method of an MTJ element according to a comparative example, first, CoFeB/MgO/CoFeB is formed using CoFeB in an amorphous state in place of CoFe. Out diffusion of B is caused by annealing, and CoFe is crystallized using MgO as a seed. CoFe/MgO/CoFe with matching in the (100) plane direction can thus be formed. As an out diffusion method of B, Ta layers are provided on and under CoFeB/MgO/CoFeB, and Ta is caused to absorb B. The higher the annealing temperature is, the lower the B concentration in CoFe is.

However, when annealing is performed in out diffusion of B, diffusion of Ta in CoFe also progress at the same time as the absorption of B by Ta. Hence, if CoFeB is used as the metal magnetic film, the concentrations of impurities such as B and Ta in the metal magnetic film cannot be reduced, and the MR ratio cannot be improved.

In the manufacturing method of the MTJ element100according to the seventh embodiment, ion implantation is used as a method of forming CoFe in the amorphous state. More specifically, when stacking CoFe/MgO/CoFe as the MTJ element100, the lower and upper CoFe films are deposited and then exposed to an inert gas (for example, Ne plasma) to amorphize CoFe. The amorphized CoFe is crystallized by annealing using MgO as a seed.

With the manufacturing method of the MTJ element100according to the seventh embodiment, a CoFe/MgO/CoFe structure with a (100) orientation can thus be obtained. Since amorphous CoFe with a low impurity concentration can be obtained without adding B, the MTJ element100having an excellent crystalline state and excellent electrical characteristic can be provided.

Note that in this embodiment, Ne is used as the doping gas for amorphizing CoFe. Even in a case in which an inert gas such as He, Ar, or Kr is used, the same effect as Ne can be obtained by appropriately adjusting the doping amount by the pull-in voltage. The same effect can also be obtained by ion-implanting Co or Fe into the CoFe layer.

In this embodiment, CoFe that does not contain B is used as the storage layer24and the reference layer22. However, the material is not limited to this, and CoFeB with a low B content may be used.

Additionally, in the seventh embodiment, the MTJ element100has a top free structure in which the storage layer24is stacked above the reference layer22. However, the structure is not limited to this, and a bottom free structure in which the positions of the reference layer22and the storage layer24are replaced may be employed.

In the eighth embodiment, a metal is doped into a region on the opposite side of the contact to a tunnel barrier layer23in each of a reference layer22and a storage layer24.

The structure of an MTJ element100according to the eighth embodiment will be described with reference toFIGS. 34 and 35.FIG. 34is a plan view showing the MTJ element100according to the eighth embodiment.FIG. 35is a sectional view of the MTJ element100taken along a line VIII-VIII inFIG. 34.

The MTJ element100has a structure in which an underlayer21, a bulk reference layer22C, the reference layer22, the tunnel barrier layer23, the storage layer24, a bulk storage layer24C, and a cap layer25are sequentially stacked on a lower electrode20.

The bulk reference layer22C and the bulk storage layer24C are formed by doping a metal into the reference layer22and the storage layer24, and have an amorphous state. In the bulk reference layer22C and the bulk storage layer24C, a metal such as Ta or Mo is doped by 1% or more. The rest of the arrangement is the same as in the first to seventh embodiments.

A method of manufacturing the MTJ element100according to the eighth embodiment will be described with reference toFIGS. 36, 37, 38, and 39.FIGS. 36, 37, 38, and39are sectional views showing steps in the manufacture of the MTJ element100according to the eighth embodiment.

First, as shown inFIG. 36, the underlayer21, the reference layer22, and the cap layer25are sequentially formed on the lower electrode20. Next, Ne etching is performed for the cap layer25and part of the reference layer22. The reference layer22is made of, for example, CoFeB. The cap layer25is made of a metal such as Ta or Mo.

As shown inFIG. 37, when Ne etching is performed, the reference layer22is doped with the atoms of the cap layer25and changes to an amorphous state. The reference layer22doped with the atoms of the cap layer25will be referred to as the bulk reference layer22C.

Next, as shown inFIG. 38, the reference layer22, the tunnel barrier layer23, the storage layer24, and the cap layer25are sequentially formed. Next, Ne etching is performed for the cap layer25and part of the storage layer24. The storage layer24is made of, for example, CoFeB.

As shown inFIG. 39, when Ne etching is performed, the storage layer24is doped with the atoms of the cap layer25and partially changes to an amorphous state. The storage layer24doped with the atoms of the cap layer25will be referred to as bulk storage layer24C.

The same manufacturing method as in the first to seventh embodiments is applicable to the processes subsequent to forming the cap layer25on the storage layer24. Note that the bulk reference layer22C and the bulk storage layer24C maintain the amorphous state even if an annealing process of crystallizing the reference layer22and the storage layer24is performed.

In an MRAM, to implement a microcell, a high MR ratio, perpendicular magnetic anisotropy, suppression of a leakage magnetic field of the reference layer, and a low profile to facilitate processing are necessary as the characteristics of the MTJ element. For the high MR ratio and perpendicular magnetic anisotropy, crystal matching of ferromagnetic layers on the interface of the tunnel barrier layer is important. For suppression of a leakage magnetic field of the reference layer and processing facilitation, it is necessary to lower the magnetization (lower the Ms) of the ferromagnetic layers.

To improve both, a metal such as Ta or Mo is doped into CoFeB ferromagnetic layers (storage layer24and reference layer22). More specifically, the ferromagnetic layers are formed with a concentration distribution of a metal such as Ta or Mo. The interface portions of the storage layer24and the reference layer22with respect to the tunnel barrier layer23are ferromagnetic layers with a low Ms mainly containing the ferromagnetic component. On the other hand, the bulk storage layer24C and the bulk reference layer22C doped with the metal are spaced part from the interfaces of the tunnel barrier layer23. Metal doping in each ferromagnetic layer is performed by etching the cap layer25made of Ta, Mo, or the like by ions of Ne or the like.

Each of the reference layer22and the storage layer24can attain a high MR ratio because of the main components of CoFeB in the vicinity of the interface of the tunnel barrier layer23, and can obtain high perpendicular magnetic anisotropy. The bulk reference layer22C can attain a low MS and reduce the leakage magnetic field by doping of Ta or Mo. The bulk storage layer24C can reduce the write current.

In the above-described way, the MTJ element100according to the eighth embodiment can lower the Ms of the ferromagnetic films without lowering the MR ratio.

Note that in the eighth embodiment, the MTJ element100has a top free structure in which the storage layer24is stacked above the reference layer22. However, the structure is not limited to this, and a bottom free structure in which the positions of the reference layer22and the storage layer24are replaced may be employed.

In the ninth embodiment, when manufacturing an MTJ element100using an SAF structure, Ne etching is performed for the surface of a coupling layer, thereby improving planarity.

The structure of the MTJ element100according to the ninth embodiment will be described with reference toFIGS. 40 and 41.FIGS. 40 and 41are plan and sectional views, respectively, showing the MTJ element100according to the ninth embodiment.

The MTJ element100has a structure in which an underlayer21, a reference layer22, a nonmagnetic layer (coupling layer)33, an interface magnetic layer (high-orientation magnetic reference layer)31, a tunnel barrier layer23, an interface magnetic layer (high-orientation magnetic storage layer)32, a storage layer24, and a cap layer25are sequentially stacked on a lower electrode20.

The MTJ element100includes the coupling layer33and is formed into an SAF (Synthetic AntiFerromagnetic) structure. As the coupling layer33, for example, ruthenium (Ru) is used. The magnetization directions of the interface magnetic layer31and the reference layer22are set to be antiparallel using antiferromagnetic coupling by ruthenium. The coupling layer has a film thickness of, for example, about 4 Å and a coupling magnetic field of, for example, 5 to 8 kOe. The interface magnetic layers31and32are made of a material having a high polarization ratio. For example, CoFeB is used.

A method of manufacturing the MTJ element100according to the ninth embodiment will be described with reference toFIGS. 42 and 43.FIGS. 42 and 43are sectional views showing steps in the manufacture of the MTJ element100according to the ninth embodiment.

First, as shown inFIG. 42, the underlayer21, the reference layer22, and the coupling layer33are sequentially formed on the lower electrode20. The coupling layer33is formed using, for example, sputtering. The film thickness of the coupling layer33is, for example, 15 nm. Next, etching (Ne etching) using neon gas as an inert gas is performed for the surface of the coupling layer33. The film thickness of the etched coupling layer33is, for example, 6 nm. The surface of the coupling layer33is thus planarized, and the crystallinity of the interface magnetic layer32to be formed on it improves. Note that the film thickness of the coupling layer33can be adjusted on the order of 1 nm or less by the magnetic characteristic.

Next, as shown inFIG. 43, the tunnel barrier layer23, the interface magnetic layer32, the storage layer24, and the cap layer25are sequentially formed. The same manufacturing method as in the first to eighth embodiments is applicable to the subsequent processes.

As described above, in the manufacturing method of the MTJ element100according to the ninth embodiment, etching using Ne as the inert gas is performed after deposition of the coupling layer33.

An MTJ element formed from a stacked layer of metal magnetic film/insulating film/metal magnetic film uses a shift adjustment layer to cancel the influence of a leakage magnetic field and the magnetization difference between a reference layer and a storage layer. However, since the shift adjustment layer is distant from the metal magnetic film/insulating film/metal magnetic film and therefore needs a large magnetization, the MTJ element becomes thick, resulting difficulty in microfabrication. When an SAF structure using Ru or the like as a coupling layer is formed, the film thickness of the MTJ element can be decreased.

However, if the planarity of Ru of the coupling layer is poor, the magnetization directions of the magnetic films that sandwich the coupling layer are not parallel, and magnetic anisotropy may become small. When the magnetic anisotropy becomes small, retention degrades.

To prevent this, in the manufacturing method of the MTJ element100according to the ninth embodiment, Ne etching is performed for the metal film of Ru or the like that constitutes the coupling layer33. In the Ne etching, processing progresses while performing etching and readhesion near the surface of the coupling layer33. This improves the planarity of the surface of the coupling layer33.

The effect of the manufacturing method of the MTJ element100according to the ninth embodiment will be described with reference toFIGS. 44A and 44B.FIGS. 44A and 44Bare sectional views showing an experimental result of the steps in the manufacture of the MTJ element100according to the ninth embodiment.FIG. 44Ashows a structure in which ruthenium used for the coupling layer33is deposited to 40 nm on the underlayer, andFIG. 44Bshows a structure after Ne etching is performed for the substrate shown inFIG. 44A.

As shown inFIG. 44A, the Ru layer after deposition has a film thickness of 40 nm and a surface roughness Ra of 0.469 nm. On the other hand, as shown inFIG. 44B, the Ru layer after Ne etching has a film thickness of 37 nm and the surface roughness Ra of 0.190 nm. The Ru layer after Ne etching has an improved surface roughness as compared to the Ru layer before Ne etching.

As described above, the manufacturing method of the MTJ element100according to the ninth embodiment can improve the planarity of the coupling layer33. When the planarity of the coupling layer33improves, it is possible to maintain the parallelism of the magnetization directions of the magnetic films that sandwich the coupling layer33and form an SAF structure having high magnetic anisotropy. It is also possible to reduce the variation in the magnetic films that are in contact via the coupling layer33.

Note that in this embodiment, Ne is used as the doping gas for amorphizing CoFe. Even in a case in which an inert gas such as He, Ar, or Kr is used, the same effect as Ne can be obtained by appropriately adjusting the pull-in voltage.

Additionally, in the ninth embodiment, the MTJ element100has a top free structure in which the storage layer24is stacked above the reference layer22. However, the structure is not limited to this, and a bottom free structure in which the positions of the reference layer22and the storage layer24are replaced may be employed.

[10] ARRANGEMENT EXAMPLES

Arrangement examples of MRAMs in a case in which MTJ elements100according to the first to ninth embodiments are used will be described below. Arrangement Example 1 is an MRAM using the MTJ element100without a side wall on the side surface of a storage layer24. Arrangement Example 2 is an MRAM using the MTJ element100with a side wall provided on the side surface of the storage layer24.

An MRAM according to Arrangement Example 1 will be described with reference toFIGS. 45, 46, 47, and 48.FIGS. 45, 46, 47, and 48are sectional views showing steps in the manufacture of the MRAM according to Arrangement Example 1.

First, as shown inFIG. 45, a trench for element isolation is formed in a region other than a transistor active region on the surface of a semiconductor substrate1, and for example, a SiO2film is buried in the trench. An element isolation region2having a shallow trench isolation (STI) structure is thus formed.

Next, a transistor Tr used to perform a switch operation is formed in the following way. An oxide film3having a thickness of about 60 Å is formed on the semiconductor substrate1by thermal oxidation. An n+-type polysilicon film4doped with, for example, arsenic is formed on the surface of the semiconductor substrate1. A WSix film5and a nitride film6are sequentially formed on the polysilicon film4. After that, the polysilicon film4, the WSix film5, and the nitride film6are processed by normal photolithography and reactive ion etching), thereby forming a gate electrode. A nitride film7is deposited on the gate electrode. After that, a spacer portion formed from the nitride film7is provided on the side walls of the gate electrode using a side wall leaving method by RIE. Next, source/drain regions8aand8bare formed in the surface of the semiconductor substrate1by ion implantation and annealing, although details of the process will be omitted. The select transistor Tr functioning as the switching element of a memory cell is thus formed.

As shown inFIG. 46, after a CVD oxide film9is deposited on the transistor Tr, planarization is performed by chemical mechanical polishing (CMP). A contact hole10communicating with the source/drain region8ais formed in the CVD oxide film9. After that, a thin titanium film is deposited in the contact hole10by sputtering or CVD and annealed in a forming gas, thereby forming a TiN film11. Next, CVD tungsten is deposited on the TiN film11. The tungsten and the TiN film11which exist outside the contact hole10are removed by CMP. The tungsten is thus buried in the contact hole10, thereby forming a contact12. After that, a CVD nitride film13is deposited on the CVD oxide film9and the contact12. A contact hole14communicating with the other source/drain region8bis formed. A TiN film15and tungsten are buried in the contact hole14, thereby forming a contact16, like formation of the contact12. The contact16corresponds to the lower electrode20described in the embodiments.

Next, as shown inFIG. 47, a lower electrode21A of the MTJ element100is formed on the contact16and the CVD nitride film13. The lower electrode21A is made of, for example, Ta having a film thickness of 5 nm.

An orientation control film21B is formed on the lower electrode21A. The orientation control film21B is made of, for example, Pt having a film thickness of 5 nm, and has a (001) plane orientation.

A reference layer22is formed on the orientation control film21B. The reference layer22is made of, for example, Fe50Pt50having a film thickness of 10 nm.

A diffusion prevention layer34is formed on the reference layer22. The diffusion prevention layer34is made of, for example, Ta having a film thickness of 0.5 nm.

A high-orientation magnetic reference layer31is formed on the diffusion prevention layer34. The high-orientation magnetic reference layer31is made of, for example, Co40Fe40B20having a film thickness of 1 nm.

A tunnel barrier layer23is formed on the high-orientation magnetic reference layer31. The tunnel barrier layer23is made of MgO having a film thickness of, for example, 1 nm.

A high-orientation magnetic storage layer32is formed on the tunnel barrier layer23. The high-orientation magnetic storage layer32is made of, for example, Co40Fe40B20having a film thickness of 1 nm.

Annealing for crystallizing the tunnel barrier layer23, the high-orientation magnetic reference layer31, and the high-orientation magnetic storage layer32is performed, for example, in vacuum at 360° C. for 1 hr. With this annealing, MgO is crystallized. CoFeB films in the high-orientation magnetic reference layer31and the high-orientation magnetic storage layer32are also crystallized. In addition, B is removed from the films, and they change to Co50Fe50films.

Next, a diffusion prevention layer35is formed on the high-orientation magnetic storage layer32. The diffusion prevention layer35is made of, for example, Ta having a film thickness of 0.5 nm.

A shift adjustment layer36is formed on the diffusion prevention layer35. The shift adjustment layer36is made of, for example, a stacked film [Co/Pd]20obtained by stacking Co having a film thickness of 0.4 nm and Pd having a film thickness of 0.8 nm for 20 cycles.

A cap layer25is formed on the shift adjustment layer36. The cap layer25is made of, for example, Ta having a film thickness of 10 nm.

In the above steps, the lower electrode21A, the orientation control film21B, the reference layer22, the diffusion prevention layer34, the high-orientation magnetic reference layer31, the tunnel barrier layer23, the high-orientation magnetic storage layer32, the diffusion prevention layer35, the shift adjustment layer36, and the cap layer25are formed using, for example, sputtering.

Next, a CVD oxide film37serving as a process mask material is deposited on the cap layer25. After that, the CVD oxide film37is patterned by photolithography and RIE, and a photoresist (not shown) used for this is removed.

The cap layer25, the shift adjustment layer36, the diffusion prevention layer35, the high-orientation magnetic storage layer32, the tunnel barrier layer23, the high-orientation magnetic reference layer31, the diffusion prevention layer34, the reference layer22, the orientation control film21B, and the lower electrode21A are etched using RIE. Processing of the MTJ element100is thus completed.

Next, as shown inFIG. 48, an antioxidation protective film40is formed by CVD so as to cover the MTJ element100. The antioxidation protective film40is made of, for example, an SiN film having a film thickness of 5 nm. An interlayer dielectric film41made of an SiO2film is formed on the antioxidation protective film40and the CVD nitride film13by CVD. As the formation conditions of the SiO2film, TEOS and O2are used as row materials, an RF plasma is applied at a substrate temperature of 350° C. This protective film is used for the purpose of suppressing damage degradation such as oxidation of the MTJ element exposed to an atmosphere containing hydrogen and oxygen generated when forming an interlayer dielectric film to be formed on it.

A contact42connected to the cap layer25and a contact43connected to the contact12are formed simultaneously. As for formation of the contacts42and43, contact holes are formed and then filled with W using a TiN barrier layer. The TiN barrier layer is formed by CVD at a deposition temperature of 350° C. using TiCl4and NH3as source gases. W is deposited by CVD using WF6as a source gas. After planarization by CMP, an oxide film44is deposited on the contacts42and43and the interlayer dielectric film41. Trenches are formed in the oxide film44using photolithography and RIE. Al is buried in the trenches and planarized by CMP, thereby forming first interconnections45and46connected to the contacts42and43, respectively. Subsequently, an interlayer film47is deposited on the first interconnections45and46and the oxide film44, and a via hole is formed in the interlayer film47by photolithography and RIE. Al is buried in the via hole and planarized by CMP, thereby forming a via48connected to the first interconnection46. Furthermore, an interlayer film49is deposited on the via48and the interlayer film47, and a trench for a second interconnection is formed by photolithography and RIE. Al is buried in the trench and planarized by CMP, thereby forming a second interconnection50connected to the via48. After that, although not illustrated, an upper interconnection layer is sequentially formed, and a magnetic random access memory is thus completed.

Note that the stacking order of the layers included in the MTJ element100may be reversed. In this case, the MTJ element100has, for example, the following stacked structure. The lower electrode21A made of Ta having a film thickness of 5 nm is formed. Next, the orientation control film21B made of Pt having a film thickness of 5 nm is formed. The orientation control film21B has a (001) plane orientation. The storage layer24made of a stacked film [Co/Pt]5obtained by stacking Co having a film thickness of 0.4 nm and Pt having a film thickness of 0.8 nm for five cycles is formed. Ta having a film thickness of 0.5 nm is formed as the diffusion prevention layer35. The high-orientation magnetic storage layer32made of Co40Fe40B20having a film thickness of 1 nm is formed. The tunnel barrier layer23made of MgO having a film thickness of 1 nm is formed. The high-orientation magnetic reference layer31made of Co40Fe40B20having a film thickness of 1 nm is formed. Ta having a film thickness of 0.5 nm is formed as the diffusion prevention layer34. The reference layer22made of Fe50Pt50having a film thickness of 10 nm is formed. The cap layer25made of Ta having a film thickness of 10 nm is formed.

As the reference layer22, a perpendicular magnetization film made of not Fe50Pt50described above but Co50Pt50, Co30Fe20Pt50, or the like may be used. As the reference layer22, (Fe50Pt50)88—(SiO2)12or the like, which is a structure obtained by dividing the film by SiO2, MgO, or the like, may be used. As the storage layer24, not a Co/Pt artificial lattice but a Co/Pd artificial lattice may be used. The number of stacking cycles can be changed within the range of 1 to 10 in accordance with the characteristic. An alloy of Co and Pt is also usable. Pt is used as the orientation control film21B. However, Ir or Ru or a stacked film thereof may be used.

To fix the reference layer22to one direction, an antiferromagnetic layer may adjacently be provided. As the antiferromagnetic layer, for example, an alloy of Mn and Fe, Ni, Pt, Pd, Ru, Os, or Ir, that is, FeMn, NiMn, PtMn, PtPdMn, RuMn, OsMn, IrMn, CrPtMn, or the like is used.

An MRAM according to Arrangement Example 2 will be described with reference toFIGS. 49 and 50.FIGS. 49 and 50are sectional views showing steps in the manufacture of the MRAM according to Arrangement Example 2. Arrangement Example 2 is different from Arrangement Example 1 only in the portion of the MTJ element100, and a description of common portions will be omitted.

As shown inFIG. 49, the processes up to formation of the cap layer25are the same as in Arrangement Example 1.

Next, a hard mask27(not shown) is formed on the upper electrode, and a protective film26of the MTJ element100is formed by the method of the first embodiment. At this time, the tunnel barrier layer23has partially been amorphized.

The CVD oxide film37serving as a process mask material is deposited on the cap layer25. After that, the CVD oxide film37is patterned by photolithography and RIE, and a photoresist (not shown) used for this is removed.

The cap layer25, the shift adjustment layer36, the diffusion prevention layer35, the high-orientation magnetic storage layer32, the tunnel barrier layer23, the high-orientation magnetic reference layer31, the diffusion prevention layer34, the reference layer22, the orientation control film21B, and the lower electrode21A are etched using RIE. Processing of the MTJ element100is thus completed. The rest of the steps and arrangement is the same as in Arrangement Example 1. Arrangement Example 2 has a structure as shown inFIG. 50.

While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions.