JP4615797B2 - Magnetoresistive element, manufacturing apparatus thereof, and magnetic memory device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetoresistive effect element that generates a so-called MR (MagnetoResistive) effect in which a resistance value is changed by a magnetic field applied from the outside, a manufacturing apparatus thereof, and a memory device that stores information using the magnetoresistive effect element. The present invention relates to a configured magnetic memory device.
[0002]
[Prior art]
In recent years, along with the rapid spread of personal communication devices such as portable terminal devices, the devices such as memory and logic that make up these devices are becoming more highly integrated, faster, lower power, etc. There is a demand for higher performance. In particular, increasing the density and capacity of non-volatile memories is a complementary technology that replaces hard disk devices and optical disk devices that are inherently difficult to miniaturize due to the presence of movable parts (eg, head seek mechanism and disk rotation mechanism). It is becoming increasingly important.
[0003]
As the nonvolatile memory, a flash memory using a semiconductor, an FeRAM (Ferro electric Random Access Memory) using a ferroelectric, and the like are widely known. However, the flash memory has a disadvantage that the information writing speed is on the order of microseconds, and is slower than a volatile memory such as a DRAM (Dynamic Random Access Memory) or an SRAM (Static Random Access Memory). In addition, a problem has been pointed out that FeRAM has a small number of rewritable times. Therefore, a magnetic memory device called MRAM (Magnetic Random Access Memory) is attracting attention as a non-volatile memory that does not have these drawbacks. The MRAM performs information recording using a giant magnetoresistive (GMR) type or tunnel magnetoresistive (TMR) type storage element, and is particularly noticeable due to the recent improvement in characteristics of TMR materials. (For example, “Naji et al. ISSCC2001”).
[0004]
Here, the operation principle of the MRAM will be briefly described. The MRAM has magnetoresistive effect type memory elements (cells) arranged in a matrix, and leads (word lines) and read lines that traverse these element groups vertically and horizontally for recording information in specific memory elements. It has a (bit line) and is configured to selectively write information only to elements located in the intersection region. That is, writing to the memory element is performed by controlling the magnetization direction of the magnetic material in each memory element using a combined current magnetic field generated by flowing current through both the word line and the bit line. Generally, either “0” or “1” information is stored according to the direction of magnetization. On the other hand, reading of information from a memory element is performed by selecting a memory element using an element such as a transistor and extracting the magnetization direction of the magnetic material in the memory element as a voltage signal through the magnetoresistive effect. As a film configuration of the memory element, a three-layer structure composed of ferromagnetic material / nonmagnetic material / ferromagnetic material, that is, a structure called a ferromagnetic tunnel junction (MTJ) has been proposed. Therefore, by using the magnetization direction of one ferromagnetic material as the fixed reference layer (pinned layer) and the other as the storage layer (free layer), the magnetization direction in the storage layer corresponds to the voltage signal through the tunnel magnetoresistance effect. Therefore, extraction as a voltage signal as described above can be realized.
[0005]
Subsequently, the selection of the memory element at the time of writing will be described in more detail. In general, when a magnetic field opposite to the magnetization direction is applied in the easy axis direction of a ferromagnetic material, the magnetization direction may be reversed to the direction of the applied magnetic field at a certain critical value ± Hsw (hereinafter referred to as “reversal magnetic field”). Are known. The value of this reversal magnetic field can theoretically be obtained from the minimum energy condition. Furthermore, it is known that the absolute value of this reversal magnetic field decreases when a magnetic field is applied not only to the easy axis but also to the hard axis. This can also be obtained from the minimum energy condition. That is, if the magnetic field applied in the direction of the hard axis is Hx, the reversal magnetic field Hy at this time is Hx. ^(2/3) + Hy ^(2/3) = Hc ^(2/3) The relationship is established. Hc is an anisotropic magnetic field of the memory layer. This curve is called an asteroid curve because it forms an asteroid on the Hx-Hy plane as shown in FIG.
[0006]
The selection of the memory element is easy to explain using this asteroid. In general, in an MRAM having a configuration in which a magnetic field generated from a word line substantially coincides with the direction of the easy axis of magnetization, information is recorded by reversing the magnetization by the magnetic field generated from the word line. However, since there are a plurality of storage elements located at the same distance from the word line, if a current that generates a magnetic field greater than the reversal magnetic field is supplied to the word line, recording is similarly performed for all of the storage elements located at the same distance. Will end up. However, at this time, if a current is passed through the bit line that crosses the storage element to be selected to generate a magnetic field in the hard axis direction, the switching magnetic field in the storage element to be selected is lowered. Therefore, if the reversal magnetic field at this time is Hc (h) and the reversal magnetic field is Hc (0) when the bit line magnetic field is “0”, the word line magnetic field H is Hc (h) <H <Hc (0). Thus, information recording can be selectively performed only on the storage element to be selected. This is a method for selecting a storage element at the time of recording information in the MRAM.
[0007]
The MRAM having such a configuration has the following characteristics in addition to being non-volatile and capable of nondestructive reading and random access. That is, since the structure is simple, high integration is easy, and the number of rewritable times is large in order to record information by rotating the magnetic moment in the magnetoresistive effect storage element (for example, 10 ¹⁶ More than once). Furthermore, the access time is expected to be very high, and it has already been confirmed that it can operate in the nanosecond range (for example, 5 ns or less). Further, since the MOS (Metal Oxide Semiconductor) is formed only by the wiring process after manufacturing, the process consistency is good. In particular, it is superior to flash memory in terms of the number of rewritable times, random access, and high-speed operation, and is superior to FeRAM in terms of process consistency. Furthermore, since it is expected that a high integration level similar to that of a DRAM and a high speed performance equivalent to that of an SRAM can be achieved at the same time, there is a possibility of becoming a mainstream memory device.
[0008]
On the other hand, some technical problems have been pointed out regarding MRAM. Specifically, low power consumption and an increase in S / N ratio are strongly desired. On the other hand, for example, low power consumption can be solved mainly by improving the magnetic characteristics of the storage layer, and increasing S / N ratio can be solved by increasing the MR effect (tunnel MR effect in the case of MTJ). Is considered possible. From these facts, the characteristics that the material constituting the memory layer of the MRAM should have must be capable of suppressing the switching magnetic field and generating a high MR effect. As such materials, Co (cobalt) -Fe (iron) binary alloys, Ni (nickel) -Fe binary alloys, Co-Ni-Fe ternary alloys, and the like having various compositions have been proposed.
[0009]
[Problems to be solved by the invention]
In reality, however, the technical problem regarding MRAM is to be solved only by the characteristics in the state where the memory layer is a material single film (single layer film having no multilayer film structure as a magnetoresistive effect element). Is not easy. This is because even if the memory layer in the state of a single material film shows good characteristics, when it is laminated together with other layers to constitute a magnetoresistive effect element, the memory layer in the multilayer structure is This is because it does not always show good characteristics.
[0010]
Specifically, considering the MTJ structure, for example, when a nonmagnetic material sandwiched between ferromagnetic materials is made of an oxide barrier layer, oxygen diffusion from the oxide barrier layer may reach the storage layer. This may cause a change in the magnetic characteristics of the storage layer. In addition, even in a magnetoresistive effect element using a metal nonmagnetic layer, the nonmagnetic layer material can be diffused. Furthermore, by diffusion from not only a nonmagnetic layer sandwiched between ferromagnetic materials such as an oxide barrier layer and a metal nonmagnetic layer, but also a layer adjacent to the storage layer (for example, a protective layer) on the opposite side. However, the magnetic properties of the storage layer can change. That is, in the multilayer film structure, there is a possibility that characteristic changes occur in the memory layer due to the diffusion material from the adjacent layer.
[0011]
In addition, the environment at the time of manufacturing the multilayer structure such as the growth temperature does not necessarily optimize the magnetic characteristics of the storage layer. For example, when a fixed reference layer using an antiferromagnetic material is used, even if the antiferromagnetic material requires ordered annealing at a high temperature, the magnetic properties of the memory layer deteriorate due to the heat treatment. should not be done. For this reason, it is desirable that the ferromagnetic material constituting the storage layer is such that its magnetic characteristics can be flexibly adjusted by some means for various manufacturing environments.
[0012]
Accordingly, in view of the conventional situation as described above, the present invention provides a magnetoresistive element, a manufacturing apparatus thereof, and a magnetic memory device that achieve high performance by obtaining good characteristics even in a multilayer film structure. The purpose is to do.
[0013]
[Means for Solving the Problems]
The present invention has been devised in order to achieve the above object. In a magnetoresistive effect element having a multilayer film structure including two ferromagnetic layers and a nonmagnetic layer sandwiched therebetween, the above-mentioned strong At least one of the magnetic layers is composed of an aggregate of crystal grains and crystal grain boundaries, and the crystal grain boundaries are formed of a diffusion material from a layer adjacent to the ferromagnetic layer to which the crystal grain boundaries belong. Had binding Made of ferromagnetic material with deposited elements The diffusing material is preferentially bonded to the crystal grain boundaries rather than the crystal grains.
[0014]
According to the magnetoresistive element having the above configuration, in addition to the ferromagnetic layer being composed of an aggregate of crystal grains and crystal grain boundaries, the crystal grain boundaries have a binding property to a diffusing substance. , Diffusion of diffusing material from adjacent layers (eg non-magnetic layers or layers on the opposite side) Than crystal grains Advances preferentially at grain boundaries Because it is supposed to In the other crystal grain portions, the original magnetic characteristics are maintained. Further, the magnetic properties exhibited by the ferromagnetic layer composed of aggregates of crystal grains and grain boundaries depend not only on various heat treatment temperatures but also on the composition and grain size. Therefore, even if the environment such as temperature at the time of manufacturing the magnetoresistive effect element is specified in advance, the magnetic properties of the ferromagnetic layer can be controlled by controlling the composition and particle size of the ferromagnetic layer. Can be adjusted.
[0015]
The manufacturing apparatus of the present invention is a manufacturing apparatus for manufacturing a magnetoresistive effect element having a multilayer structure including two ferromagnetic layers and a non-magnetic layer sandwiched between them. A film forming unit configured to form a magnetic layer, wherein the film forming unit includes at least one of the ferromagnetic layers as a magnetic material including at least one of cobalt, iron, and nickel. A film is formed by adding the above different elements, and the at least one ferromagnetic layer is composed of an aggregate of crystal grains and crystal grain boundaries, and The crystal grain boundaries are formed by the ferromagnetic material on which the different elements are deposited. The diffusion material formed from the adjacent layer of the ferromagnetic layer to which the crystal grain boundary belongs is preferentially coupled to the crystal grain boundary rather than the crystal grain.
[0016]
According to the magnetoresistive element manufacturing apparatus having the above configuration, the ferromagnetic layer is composed of crystal grains and an aggregate of crystal grain boundaries, and the crystal grain boundaries are elements different from the magnetic material. Ferromagnetic material with deposited The magnetoresistive effect element manufactured by the method is configured to preferentially couple the diffusion material from the adjacent layer of the ferromagnetic layer to which the crystal grain boundary belongs to the crystal grain boundary rather than the crystal grain. Depending on the type of the different element, diffusion of the diffusing material from the adjacent layer of the ferromagnetic layer preferentially proceeds at the grain boundary portion, and the original magnetic properties are maintained at the other crystal grain portions. Can be left alone. Even if the environment such as temperature at the time of manufacturing the magnetoresistive effect element is defined in advance, the magnetic properties of the ferromagnetic layer can be controlled by controlling the composition, grain size, etc. of the ferromagnetic layer. It is also possible to adjust.
[0017]
The present invention has been devised to achieve the above object, and comprises a magnetoresistive effect element having a multilayer film structure including two ferromagnetic layers and a nonmagnetic layer sandwiched between them. In the magnetic memory device configured to perform information recording using a change in the magnetization direction of the ferromagnetic layer, at least one of the ferromagnetic layers is a set of crystal grains and crystal grain boundaries. And the crystal grain boundary has a binding property with a diffusion material from a layer adjacent to the ferromagnetic layer to which the crystal grain boundary belongs. Made of ferromagnetic material with deposited elements The diffusing material is preferentially bonded to the crystal grain boundaries rather than the crystal grains.
[0018]
According to the magnetic memory device having the above configuration, in addition to the ferromagnetic layer in the magnetoresistive effect element for performing information recording being composed of crystal grains and aggregates of crystal grain boundaries, the crystal grain boundaries are not diffused substances. Have the connectivity of And more than crystal grains Since the diffusion of the diffusing material from the adjacent layer preferentially proceeds at the crystal grain boundary, even if the magnetoresistive element has a multilayer film structure, the characteristic change in the ferromagnetic layer can be suppressed. Even if the environment such as temperature at the time of manufacturing the magnetoresistive effect element is defined in advance, the magnetic properties of the ferromagnetic layer can be controlled by controlling the composition, grain size, etc. of the ferromagnetic layer. Can be adjusted. Accordingly, good characteristics can be obtained for the magnetoresistive effect element, so that it is possible to realize a reduction in power consumption, an increase in S / N ratio, etc. when information is recorded on the magnetoresistive effect element.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a magnetoresistive effect element, a manufacturing apparatus thereof, and a magnetic memory device according to the present invention will be described with reference to the drawings. Here, a TMR type spin valve element (hereinafter simply referred to as “TMR element”) as a magnetoresistive effect element and an MRAM including a TMR element as a magnetic memory device will be described as examples.
[0020]
[Outline of magnetic memory device]
First, a schematic configuration of the entire magnetic memory device according to the present invention will be described. FIG. 1 is a schematic diagram showing a basic configuration example of an MRAM. The MRAM includes a plurality of TMR elements 1 arranged in a matrix. Further, word lines 2 and bit lines 3 intersecting each other are provided so as to cross each TMR element 1 group vertically and horizontally so as to correspond to each of the rows and columns in which these TMR elements 1 are arranged. . Each TMR element 1 is arranged so as to be sandwiched between the word line 2 and the bit line 3 from above and below and located in an intersecting region thereof. The word line 2 and the bit line 3 are well-known in such a manner that a conductive substance such as Al (aluminum), Cu (copper), or an alloy thereof is selectively etched after being chemically or physically deposited. It shall be formed using.
[0021]
FIG. 2 is a schematic diagram showing an example of a cross-sectional configuration of a single TMR element portion constituting the MRAM. In each TMR element portion, a field effect transistor including a gate electrode 5, a source region 6 and a drain region 7 is disposed on a semiconductor substrate 4, and further above the word line 2, TMR element 1 and bit line 3. Are arranged in order. As is clear from this, the TMR element 1 is disposed so as to be sandwiched between the word line 2 and the bit line 3 at the intersection of the word line 2 and the bit line 3 from above and below. The TMR element 1 is connected to a field effect transistor through a bypass line 8.
[0022]
With such a configuration, in the MRAM, a combined current magnetic field is generated by flowing a current through both the word line 2 and the bit line 3 with respect to the storage layer of the TMR element 1, and the storage layer is generated using the combined current magnetic field. Information is written by changing the magnetization direction of. Reading of information from the TMR element 1 is performed by selecting the TMR element 1 using a field effect transistor and extracting the magnetization direction of the information storage layer in the TMR element 1 as a voltage signal.
[0023]
[Configuration of magnetoresistance effect element]
Next, the configuration of the TMR element 1 itself used in such an MRAM will be described. The TMR element 1 has an MTJ structure film configuration. FIG. 3 is a schematic diagram showing a basic configuration example of the MTJ structure. The MTJ structure has a three-layer structure composed of a ferromagnet / insulator / ferromagnet, the direction of magnetization of one ferromagnet layer being a fixed reference layer (pinned layer) 11, and the other being a storage layer (free layer). 12 is used. Information is written (recorded) by changing the magnetization direction of the storage layer 12 by the combined current magnetic field generated by the word line 2 and the bit line 3, and the magnetization in the storage layer 12 is achieved through the tunnel MR effect. The direction and the voltage signal are made to correspond. These two ferromagnetic layers, that is, the insulator layer sandwiched between the fixed reference layer 11 and the storage layer 12 are made of, for example, an oxide of Al (aluminum) and function as the tunnel barrier layer 13. The other layers such as the underlayer 14 and the protective layer 15 are generally made of a material having no magnetism.
[0024]
FIG. 4 is a schematic diagram for more specifically explaining the TMR element having the MTJ structure. As the TMR element 1, for example, a Ta (tantalum) film 22 serving as an underlayer 14 and a PtMn (platinum manganese) film 23 serving as an antiferromagnetic layer are formed on a substrate (for example, a bypass line) 21 that is a film formation target. A CoFeB (cobalt iron boron) film 24 serving as a fixed layer, an Al-Ox (aluminum oxide) film 25 serving as a tunnel barrier layer 13, a CoFeB film 26 serving as a memory layer 12, and a Ta film serving as a protective layer 15. 27 are stacked in order. Of these, the PtMn film 23 and the CoFeB film 24 are laminated to form the fixed reference layer 11.
[0025]
By the way, the TMR element 1 described here has a great feature in the structure of the CoFeB film 24 that constitutes the fixed reference layer 11 and the CoFeB film 26 that is the memory layer 12. FIG. 5 is a schematic diagram showing an outline of the film structure.
[0026]
The CoFeB films 24 and 26 are formed by adding B (boron), which is an element different from these magnetic materials, to a magnetic material such as Co and Fe, which are general ferromagnets. Thus, it has a structure composed of an aggregate of fine crystal grains 31 and crystal grain boundaries 32. Note that the term “fine” as used herein means that the average particle diameter is approximately 2 to 100 nm when the crystal grains 31 are approximated to a spherical shape for the reason described later.
[0027]
More specifically, in the CoFeB films 24 and 26, the composition of the crystal grains 31 and the composition of the crystal grain boundaries 32 are different, and B is precipitated at the crystal grain boundaries 32. That is, by adding B, the B mainly forms a crystal grain boundary 32, thereby forming a structure composed of fine crystal grains 31 and aggregates of crystal grain boundaries 32. B forming this crystal grain boundary 32 generally has a higher bondability with O (oxygen) than Co or Fe. Therefore, it can be said that the crystal grain boundary 32 has a bondability with O.
[0028]
In the CoFeB films 24 and 26, as B mainly forms the crystal grain boundaries 32, the spin polarizability indicated by the materials (mainly Co and Fe) constituting the fine crystal grains 31 is different from the crystal grain boundaries. It is higher than the spin polarizability indicated by the material constituting 32 (mainly B). In general, electrons have a rotational motion (spin) and become a very small magnet unit. The direction of the magnet (spin) of an electron in a solid usually has two directions, upward and downward. Therefore, the conduction band of a metal is divided into an electron band having an upward spin (upward spin band) and an electron band having a downward spin (downward spin band). In ferromagnets, the shape of the upward spin band and the downward spin band are different, so the number of electrons present at the Fermi level differs between an electron having an upward spin and an electron having a downward spin. The difference in the number of these two electrons is called spin polarizability. This spin polarizability has a large influence on the MR effect, and it is known that the tunnel MR effect increases as the spin polarizability of the ferromagnetic material forming the tunnel junction increases.
[0029]
[Manufacture of magnetoresistive effect element]
Next, a manufacturing procedure of the TMR element 1 having the above configuration and a manufacturing apparatus used therefor will be described. As a manufacturing apparatus of the TMR element 1, for example, a magnetron sputtering apparatus in which the back pressure is exhausted to an ultrahigh vacuum region is used. Then, a Ta film 22, a PtMn film 23, a CoFeB film 24, and an Al film are sequentially laminated on a Si (silicon) substrate 21 whose surface is thermally oxidized. Thereafter, the Al film is plasma oxidized in pure oxygen to obtain a uniform Al—Ox film 25. It is conceivable that the thickness of Al at this time is 1 nm. After obtaining the Al—Ox film 25, the CoFeB film 26 and the Ta film 27 are sequentially formed again using, for example, a magnetron sputtering apparatus. Finally, heat treatment for ordering the PtMn film 23 is performed in a magnetic field at, for example, 280 ° C. for 1 hour.
[0030]
In such a manufacturing procedure, when the CoFeB films 24 and 26 are formed, B, which is an element different from these magnetic materials, is added to a magnetic material such as Co and Fe, and the film formation is performed. Do. However, at this time, the target, the sputtering rate, etc. are set so that the addition ratio of B is 15% or more with respect to the magnetic material containing Co and Fe at a ratio of CoxFe1-x (0.45 <x <0.95) Is adjusted. Specifically, the design composition of the CoFeB films 24 and 26 may be (Co90Fe10) 80B20 (atomic%), for example, and the CoFeB films 24 and 26 may be formed in accordance with this. As a result, the CoFeB films 24 and 26 are formed of aggregates of fine crystal grains 31 and crystal grain boundaries 32, and the crystal grain boundaries 32 are mainly formed of B. This has also been confirmed by observing the deposited CoFeB film 26 with a transmission electron microscope (TEM).
[0031]
[Characteristics of magnetoresistance effect element]
Next, characteristics of the TMR element 1 manufactured as described above will be described. FIG. 6 is an explanatory diagram showing the measurement results of the TMR effect. As shown in the example, when the TMR effect was measured for the TMR element 1 having the above-described configuration, a high magnetoresistance change value of 55% was obtained at room temperature and a bias voltage of 5 mV. On the other hand, in the case of a conventional CoFe type material such as Co75Fe25 (atomic%), the magnetoresistance change rate is about 45% at most. Therefore, in the TMR element 1 in this embodiment, a value exceeding this is obtained.
[0032]
As described above, the reason why the TMR element 1 of the present embodiment can obtain a high magnetoresistance change rate is considered as described below. FIG. 7 is a conceptual diagram for explaining the reason why a high magnetoresistance change rate is obtained.
[0033]
In general, the two ferromagnetic layers sandwiching the tunnel barrier layer 13, that is, the fixed reference layer 11 and the storage layer 12, which play an important role in realizing the TMR effect, particularly the interface with the tunnel barrier layer 13. The spin polarizabilities of the ferromagnetic layers 11 and 12 in the vicinity are important. However, in reality, as shown in FIG. 7B, diffusion of O (oxygen) occurs from the Al—Ox film 25 which is the tunnel barrier layer 13 through this interface, and the vicinity of the interface is ferromagnetic. The body oxide layer 33 is formed. In general, since the polarizability decreases due to oxidation, the TMR effect for the conventional one is based on this reduced spin polarizability.
[0034]
On the other hand, in the TMR element 1 of the present embodiment, both the CoFeB film 24 constituting the fixed reference layer 11 and the CoFeB film 26 that is the storage layer 12 are composed of aggregates of fine crystal grains 31 and crystal grain boundaries 32. It has a structure. Moreover, B having a bonding property with O is precipitated at the crystal grain boundary 32. Therefore, as shown in FIG. 7A, the O diffused from the Al—Ox film 25 that is the tunnel barrier layer 13 is preferentially combined with the crystal grain boundary 32 where B is precipitated, and the crystal grain 31 Therefore, it is contained in the material constituting the crystal grain boundary 32 more than the material constituting the material. That is, it is considered that the crystal grain boundaries 32 are preferentially oxidized and the oxidation into the crystal grains 31 is suppressed.
[0035]
As described above, in the TMR element 1 according to the present embodiment, the region in which the oxygen diffusion from the Al—Ox film 25 adjacent to the CoFeB films 24 and 26 preferentially occurs is important for the TMR effect. A region where the spin polarizability of the interface is not lowered (inside the crystal grains 31) remains, and it is considered that a high TMR effect can be realized. Such a high TMR effect corresponds to a large signal output in the MRAM and can realize a high S / N ratio.
[0036]
Further, there are other advantages of having a structure composed of an aggregate of fine crystal grains 31 and crystal grain boundaries 32. In general, when a TMR element is used in an MRAM, reducing the reversal magnetic field of the storage layer in the TMR element is one of the major issues. This is because the reversal magnetic field determines the magnitude of the recording current, and the magnitude of the recording current leads to the magnitude of power consumption. Usually, the reversal magnetic field of the memory layer is determined by the anisotropic magnetic field and the demagnetizing field of the film. However, if the CoFeB film 26 that is the storage layer 12 has a structure composed of aggregates of crystal grains 31 and crystal grain boundaries 32, the orientation of each crystal grain 31 is substantially random, so The properties cancel each other and become almost zero. That is, the component resulting from the anisotropy of the film in the reversal magnetic field is zero. Therefore, according to the TMR element 1 of this embodiment, it can also contribute to the reduction of a reversal magnetic field.
[0037]
Incidentally, the magnetic anisotropy of the film depends on the heat treatment temperature. Therefore, also in the CoFeB film 26, when heated to the above heat treatment temperature (for example, 280 ° C.) or more, crystal grain growth proceeds and desired characteristics may not be obtained. However, crystal grain growth can be controlled by the composition of the film, etc., and by selecting a composition whose characteristics are optimal at the temperature at which the film is exposed in an actual device process, a high TMR effect and a low anisotropic magnetic field can be obtained. It is possible to realize. That is, even when the manufacturing environment such as the heat treatment temperature is defined in advance, the magnetic characteristics of the storage layer 12 can be controlled by controlling the composition, grain size, etc. of the ferromagnetic material constituting the storage layer 12. It is also possible to adjust.
[0038]
In this embodiment, the CoFeB films 24 and 26 sandwiching the Al—Ox film 25, that is, the two ferromagnetic layers sandwiching the tunnel barrier layer 13 are both aggregates of fine crystal grains 31 and crystal grain boundaries 32. The case of having a structure consisting of the above has been described as an example, but such a structure may be included only in one of the ferromagnetic layers. That is, even when only one of the ferromagnetic layers is composed of an aggregate of crystal grains 31 and crystal grain boundaries 32, the influence of oxygen diffusion from the Al—Ox film 25 can be suppressed, which is favorable. Soft magnetic properties can be obtained. Therefore, the structure composed of the aggregate of the crystal grains 31 and the crystal grain boundaries 32 may be applied to at least one of the two ferromagnetic layers.
[0039]
In the present embodiment, the case where O diffused from the Al—Ox film 25 is preferentially combined with B that has precipitated in the crystal grain boundaries 32 has been described as an example. The diffusion material is not particularly limited as long as 32 has bonding properties with the diffusion material from the adjacent layer. Therefore, the diffusing material may be from a layer other than the Al—Ox film 25 (for example, the Ta layer 27). However, it is desirable that the crystal grains 31 and the crystal grain boundaries 32 have different compositions and have a difference in affinity for diffusion of various elements. If there is a difference, the material constituting the crystal grain boundary 32 contains more diffusive material than the material constituting the crystal grain 31, and the spin polarizability indicated by the material constituting the crystal grain 31 is high. This is because it becomes higher than the spin polarizability exhibited by the material constituting the crystal grain boundary 32. That is, the realization of good soft magnetic characteristics is ensured.
[0040]
In order to obtain such good soft magnetic properties, it is a guide that the size of the crystal grains 31 is equal to or less than the width of the domain wall. The width of the domain wall is generally about 100 nm although it depends on the constituent material. Accordingly, the upper limit of the size of the crystal grain 31 is preferably about 100 nm (average grain diameter when approximated to a spherical shape). On the other hand, the lower limit of the size of the crystal grains 31 is not limited as long as it does not become an amorphous state, and it is preferable that the lower limit is about 2 nm, which is a superparamagnetic limit.
[0041]
In the present embodiment, the case where the design composition of the CoFeB films 24 and 26 is (Co90Fe10) 80B20 has been described as an example. However, in view of the essence of the invention, the composition is not limited to this. For example, it is effective to use a binary alloy or a ternary alloy such as Ni—Fe, Co—Ni, or Co—Ni—Fe based on various compositions as the base Co—Fe system. .45 <x <0.95), a high TMR effect can be expected. On the other hand, for such a magnetic material as a base, it is desirable to add B considering that the diffusion material from the Al-Ox film 25 is O, but in addition to this, Si, C ( Addition of carbon), Hf (hafnium), Ta, N (nitrogen), Cu, Nb (niobium), etc. is also effective. That is, it is sufficient if one or more different elements including B are added. Therefore, the addition ratio of the different elements is not limited to the ratio of 20% only for B as described in the present embodiment. However, in order to reliably form a structure composed of an aggregate of the crystal grains 31 and the crystal grain boundaries 32, and to make the crystal grain boundaries 32 have bonding properties with a diffusing substance, one or more different elements as a whole The addition ratio of is desirably 15% or more.
[0042]
Furthermore, the film configuration of the TMR element 1 is not limited to that illustrated. For example, instead of the so-called bottom-type TMR element 1 in which the fixed reference layer 11 is stacked first (downward) than the storage layer 12, the storage layer is stacked (downward) before the fixed reference layer. The same applies to so-called top-type TMR elements. Of course, not only the TMR element but also the nonmagnetic material layer between the storage layer and the fixed reference layer may be a GMR type composed of Cu or the like.
[0043]
【The invention's effect】
As described above, according to the present invention, the ferromagnetic layer in the magnetoresistive effect element is composed of fine crystal grains and crystal grain boundaries, and the crystal grain boundaries have a bonding property to a diffusing substance. Therefore, even in the multilayer film structure, the influence of diffusion from the adjacent layer on the ferromagnetic layer can be suppressed and good characteristics can be obtained, and as a result, a high MR effect can be realized. Furthermore, it can contribute to the reduction of the reversal magnetic field by suppressing the magnetic anisotropy. Therefore, when a magnetic memory device is configured using the magnetoresistive effect element, the performance of the magnetic memory device can be improved through low power consumption, a high S / N ratio, and the like.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a basic configuration example of an MRAM.
FIG. 2 is a schematic diagram showing a configuration example of a single TMR element portion constituting the MRAM.
FIG. 3 is a schematic diagram showing a basic configuration example of an MTJ structure.
FIG. 4 is a schematic view for more specifically explaining a TMR element having an MTJ structure.
FIG. 5 is a schematic diagram showing an outline of a film structure of a ferromagnetic layer in a TMR element to which the present invention is applied.
FIG. 6 is an explanatory diagram showing a measurement result of a TMR effect.
FIGS. 7A and 7B are conceptual diagrams for explaining the reason why a high magnetoresistance change rate can be obtained, in which FIG. 7A shows an example of a film structure in the present invention, and FIG. 7B shows an example of a conventional film structure; FIG.
FIG. 8 is an asteroid diagram showing an example of a magnetic field response of a memory element constituting an MRAM.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... TMR element, 11 ... Fixed reference layer, 12 ... Memory layer, 13 ... Tunnel barrier layer, 14 ... Underlayer, 15 ... Protective layer, 21 ... Substrate, 22 ... Ta film, 23 ... PtMn film, 24 ... CoFeB film 25 ... Al-Ox film, 26 ... CoFeB film, 27 ... Ta film, 31 ... crystal grain, 32 ... crystal grain boundary

Claims (11)

In a magnetoresistive element having a multilayer structure including two ferromagnetic layers and a nonmagnetic layer sandwiched between them,
Wherein at least one of the ferromagnetic layers is made by adding at least boron magnetic material, and consists of a collection of crystal grains and grain boundaries,
The crystal grain boundary has magnetism, and the spin polarizability indicated by the material constituting the crystal grain is higher than the spin polarizability indicated by the material constituting the crystal grain boundary, and the ferromagnetic material to which the crystal grain boundary belongs has boron deposited to have a binding between the diffusion material from the adjacent layers of the layer,
The magnetoresistive effect element, wherein the diffusing substance is preferentially bonded to the crystal grain boundary rather than the crystal grain.   2. The magnetoresistive element according to claim 1, wherein the composition of the crystal grains and the composition of the crystal grain boundaries are different.   3. The magnetoresistive effect element according to claim 2, wherein a larger amount of the diffusing substance is contained in a material constituting the crystal grain boundary than a material constituting the crystal grain.   The magnetoresistive element according to claim 1, wherein the crystal grains have an average grain size of 100 nm or less when the crystal grains are approximated to a spherical shape. 5. The magnetoresistive element according to claim 4 , wherein the crystal grains have an average grain size of 2 nm or more when the crystal grains are approximated to a spherical shape. The ferromagnetic layer comprising an aggregate of the crystal grains and the crystal grain boundaries is formed by adding at least boron to a magnetic material containing at least one of cobalt, iron, and nickel. The magnetoresistive effect element according to 1. The ferromagnetic layer composed of an aggregate of the crystal grains and the crystal grain boundaries is obtained by adding at least boron to a magnetic material containing cobalt and iron at a ratio of CoxFe1-x (0.45 <x <0.95). the magnetoresistive element according to claim 7, characterized in that Te. 8. The magnetoresistive element according to claim 7 , wherein the addition ratio of boron is 15% or more.   The non-magnetic layer is a tunnel barrier layer made of an insulator, and a ferromagnetic tunnel junction is formed by the non-magnetic layer and two ferromagnetic layers sandwiching the non-magnetic layer. Magnetoresistive effect element. A manufacturing apparatus for manufacturing a magnetoresistive element having a multilayer structure including two ferromagnetic layers and a nonmagnetic layer sandwiched between them,
A film forming means for forming the ferromagnetic layer;
The film forming means forms at least one of the ferromagnetic layers by adding at least boron to a magnetic material containing at least one of cobalt, iron and nickel, and forms the at least one ferromagnetic layer. The body layer is composed of an aggregate of crystal grains and crystal grain boundaries, and the crystal grain boundaries have magnetism, and the spin polarizability indicated by the material constituting the crystal grains is that of the material constituting the crystal grain boundaries. A magnetic material having a higher spin polarizability than the diffusive material from the adjacent layer of the ferromagnetic layer to which the crystal grain boundary belongs, and is preferentially coupled to the crystal grain boundary rather than the crystal grain. Resistance effect element manufacturing equipment. A magnetoresistive effect element having a multilayer structure including two ferromagnetic layers and a nonmagnetic layer sandwiched between them is provided, and information recording is performed by utilizing a change in the magnetization direction of the ferromagnetic layer. In the magnetic memory device configured as described above,
Wherein at least one of the ferromagnetic layers is made by adding at least boron magnetic material, and consists of a collection of crystal grains and grain boundaries,
The crystal grain boundary has magnetism, and the spin polarizability indicated by the material constituting the crystal grain is higher than the spin polarizability indicated by the material constituting the crystal grain boundary, and the ferromagnetic material to which the crystal grain boundary belongs has boron deposited to have a binding between the diffusion material from the adjacent layers of the layer,
The magnetic memory device, wherein the diffusion material is preferentially coupled to the crystal grain boundary rather than the crystal grain.

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