JP4902686B2 - Method for manufacturing magnetoresistive element - Google Patents

Description

  The present invention relates to a method of manufacturing a magnetoresistive effect element, and more particularly, to a method of manufacturing a magnetoresistive effect element manufactured using a simple sputtering film forming method and having an extremely high magnetoresistance ratio.

  In recent years, a magnetic memory device called MRAM (Magnetoretic Random Access Memory) has attracted attention as a non-volatile memory, and is entering the stage of practical use. The MRAM has a simple structure, is easy to achieve ultra-high-gigabit integration, and has a very large number of rewritable times because it uses the rotation of the magnetic moment to generate a memory action. It has the characteristic that it can be used as a stand.

  FIG. 4 shows the structure of the MRAM. In the MRAM 101, 102 is a memory element, 103 is a word line, and 104 is a bit line. Each of the large number of memory elements 102 is disposed at each intersection position of the plurality of word lines 103 and the plurality of bit lines 104, and is disposed in a lattice-like positional relationship. Each of the large number of memory elements 102 stores 1-bit information.

  As shown in FIG. 5, the memory element 102 of the MRAM 101 includes a magnetoresistive effect element that stores 1-bit information, that is, a TMR element 110, and a transistor 106 having a switching function at the intersection position of the word line 103 and the bit line 104. Composed. The main element in the memory element 102 is that a TMR (tunneling magneto resistance) element 110 is used. As shown in FIG. 6, the basic structure of the TMR element is a three-layer structure including a ferromagnetic metal electrode (ferromagnetic layer) 107 / tunnel barrier (tunnel barrier) layer 108 / ferromagnetic metal electrode (ferromagnetic layer) 109. This is a laminated structure. The TMR element 110 is composed of a pair of ferromagnetic layers 107 and 109 and a tunnel barrier layer 108 located between them.

As shown in FIG. 6, the TMR element 110 applies an external magnetic field in a state where a predetermined current is applied between the ferromagnetic layers 107 and 109 on both sides of the tunnel barrier layer 108, thereby applying a magnetic field. When the magnetization directions of 107 and 109 are parallel and the same (referred to as “parallel state”), the electrical resistance of the TMR element is minimized (state (A): resistance value R _P ), and the magnetization of the ferromagnetic layer When the directions are parallel and opposite (referred to as “anti-parallel state”), the electrical resistance of the TMR element is maximized (state (B): resistance value R _A ). Therefore, the TMR element 110 can store information as a change in resistance value by creating a parallel state and an antiparallel state by an external magnetic field.

With respect to the above TMR elements, in order to realize a practical gigabit class MRAM, it is required that the difference between the resistance value R _P in the “parallel state” and the resistance value R _{A in} the “anti-parallel state” is large. A magnetoresistance ratio (MR ratio) is used as the index. The MR ratio is defined as “(R _A −R _P ) ÷ R _P ”.

In order to improve the MR ratio, conventionally, the electrode material of the ferromagnetic metal electrode (ferromagnetic layer) has been optimized, or the manufacturing method of the tunnel barrier layer has been devised. For example, Patent Document 1 and Patent Document 2 propose several optimum examples using Fe _x Co _y B _z or the like for the material of the ferromagnetic metal electrode (ferromagnetic layer).

  The MR ratio of the TMR element disclosed in Patent Documents 1 and 2 is lower than about 70%, and further improvement of the MR ratio is necessary.

  Recently, a single crystal TMR thin film using an MgO barrier layer has been reported to produce a single crystal TMR thin film of Fe / MgO / Fe using MBE and an ultra-high vacuum deposition apparatus, and an MR ratio of 88% was obtained. (Non-Patent Document 1). This TMR thin film has a complete epitaxial single crystal structure.

  In order to produce a single crystal TMR thin film using the single crystal MgO barrier layer described in Non-Patent Document 1, it is necessary to employ an expensive MgO single crystal substrate. In addition, advanced film formation techniques such as epitaxial growth of Fe film by expensive MBE equipment and MgO film formation by ultra-high vacuum electron beam evaporation are required, and there is a problem that it is not suitable for mass productivity because of a long film formation time. ing.

JP 2003-304010 A JP 2004-63592 A

Shinji Yuasa, 4 others, “High Tunnel Magnetoresistance at Room Temperature in Fully Epitaxy Fe / MgO / Fe Tunnel Junctions in Full Epitaxial Fe / MgO / Fe Tunnel Junctions by Coherent Spin Polarization Tunneling” Coherent Spin-Polarized Tuning) ”, Nanoelectronics Research Institute, Japan Journal of Applied Physics, published April 2, 2004, Vol. 43, No. 4B, p. L588-L590

  An object of the present invention is to provide a method of manufacturing a magnetoresistive effect element having a high MR ratio, high mass productivity, and high practicality.

  In order to achieve the above object, a method of manufacturing a magnetoresistive effect element according to the present invention is configured as follows.

That is, the present invention provides anti-ferromagnetic and layers, in the method for manufacturing a magneto-resistance effect element comprising a multilayer structure composed of a antiferromagnetic ferromagnetic layer provided on layer and the ferromagnetic layer of the barrier layer There,
A ferromagnetic layer having at least a surface in an amorphous state is formed, and a sputtering method is used to form a (001) plane in the thickness direction from the interface with the ferromagnetic layer to the interface opposite to the ferromagnetic layer. Forming a barrier layer having magnesium oxide having a single crystal structure oriented parallel to the interface;
Performing an annealing process for imparting the required magnetization to the antiferromagnetic layer ;
A method for manufacturing a magnetoresistive effect element, comprising:

  Moreover, the said invention contains as a preferable aspect that the said ferromagnetic layer contains CoFeB.

  According to the present invention, since the tunnel barrier layer, which is an intermediate layer of the magnetoresistive effect element such as the TMR element, is an MgO layer having a single crystal structure, the MR ratio can be extremely increased. When used as a GRAM, it is possible to realize a GRAM ultra-high integration MRAM. Furthermore, by forming the single crystal MgO layer by a sputtering method, a magnetoresistive element suitable for mass production and highly practical can be manufactured.

It is a figure which shows the structure of the magnetoresistive effect element (TMR element) which concerns on this invention. It is a top view of the apparatus which manufactures the magnetoresistive effect element (TMR element) based on this invention. It is a graph which shows the pressure dependence of the magnetic characteristic of the magnetoresistive effect element (TMR element) which concerns on this invention. It is a fragmentary perspective view which shows the principal part structure of MRAM. It is a figure which shows the structure of the memory element of MRAM. It is a figure explaining the characteristic of a TMR element.

  DESCRIPTION OF EMBODIMENTS Preferred embodiments (examples) of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows an example of a laminated structure of magnetoresistive elements according to the present invention, and shows a laminated structure of TMR elements. According to the TMR element 10, for example, a multilayer film having nine layers constituting the TMR element 10 is formed on the substrate 11. In this nine-layer multilayer film, “Ta”, “PtMn”, “70 CoFe”, “Ru”, “CoFeB”, “MgO”, “CoFeB” are directed from the first lowermost layer to the ninth uppermost layer. ”,“ Ta ”,“ Ru ”are stacked in the order of magnetic films. The first layer (Ta: tantalum) is an underlayer, and the second layer (PtMn) is an antiferromagnetic layer. The layers composed of the third layer to the fifth layer (70CoFe, Ru, CoFeB) form a magnetization fixed layer. The substantial magnetization fixed layer is a ferromagnetic layer made of the fifth layer “CoFeB”. The sixth layer (MgO: magnesium oxide) is an insulating layer and a tunnel barrier layer. The seventh layer (CoFeB) is a ferromagnetic layer and a magnetization free layer. The sixth layer (MgO) forms an intermediate layer between a pair of ferromagnetic layers (CoFeB) positioned above and below the sixth layer (MgO). The eighth layer (Ta: tantalum) and the ninth layer (Ru: ruthenium) form a hard mask layer. The above-mentioned magnetization fixed layer (the fifth layer “CoFeB”), the tunnel barrier layer (the sixth layer “MgO”), and the magnetization free layer (the seventh layer “CoFeB”) have a narrow meaning as a basic structure. The TMR element portion 12 is formed. The fifth layer “CoFeB” as the magnetization fixed layer and the seventh layer “CoFeB” as the magnetization free layer are known as amorphous ferromagnetic materials. The MgO layer as the tunnel barrier layer is formed so as to have a single crystal structure in the thickness direction.

  In addition, in FIG. 1, the numerical value described in parentheses in each layer indicates the thickness of each layer, and the unit is “nm (nanometer)”. The said thickness is an example and is not limited to this.

  Next, with reference to FIG. 2, an apparatus and a manufacturing method for manufacturing the TMR element 10 having the above laminated structure will be described. FIG. 2 is a schematic plan view of an apparatus for manufacturing the TMR element 10, which is an apparatus capable of producing a multilayer film including a plurality of magnetic films, and is a sputtering film forming apparatus for mass production.

  The magnetic multilayer film manufacturing apparatus 20 shown in FIG. 2 is a cluster type apparatus, and includes a plurality of film forming chambers based on a sputtering method. In the present apparatus 20, a transfer chamber 22 including a robot transfer apparatus (not shown) is installed at the center position. In the transfer chamber 22 of the magnetic multilayer film manufacturing apparatus 20, two load / unload chambers 25 and 26 are provided, and the substrate (silicon substrate) 11 is loaded / unloaded by each. By alternately using these load / unload chambers 25 and 26, a multilayer film can be produced with high productivity.

  In the magnetic multilayer film manufacturing apparatus 20, for example, three film forming chambers 27 </ b> A, 27 </ b> B, and 27 </ b> C and one etching chamber 28 are provided around the transfer chamber 22. In the etching chamber 28, the required surface of the TMR element 10 is etched. Between each chamber, there is provided a gate valve 30 that isolates both chambers and can be opened and closed as necessary. Each chamber is provided with a vacuum exhaust mechanism, a gas introduction mechanism, a power supply mechanism and the like (not shown).

  In each of the film forming chambers 27A, 27B, and 27C of the magnetic multilayer film manufacturing apparatus 20, the above-described magnetic films are sequentially deposited on the substrate 11 from below by sputtering. For example, four or five targets (31, 32, 33, 34, 35), (41, 42) arranged on an appropriate circumference are respectively provided on the ceiling portions of the film forming chambers 27A, 27B, 27C. , 43, 44, 45), (51, 52, 53, 54). Furthermore, a substrate is disposed on a substrate holder located coaxially with the circumference.

  In the above, for example, the material of the target 31 is “Ta”, and the material of the target 33 is “CoFeB”. The material of the target 41 is “PtMn”, the material of the target 42 is “CoFe”, and the material of the target 43 is “Ru”. Furthermore, the material of the target 51 is “MgO”.

  In order to deposit a magnetic film having an appropriate composition with good efficiency, the plurality of targets are preferably provided so as to be inclined toward each substrate, but may be provided in a state parallel to the substrate surface. . Further, the plurality of targets and the substrate are arranged based on a configuration that rotates relatively. In the apparatus 20 having the above configuration, the magnetic multilayer film shown in FIG. 1 is sequentially formed on the substrate 11 by the sputtering method using the film forming chambers 27A, 27B, and 27C.

  Deposition conditions of the TMR element portion 12 which is a main element portion of the present invention will be described. The magnetization fixed layer (“CoFeB” of the fifth layer) was formed using a target having a CoFeB composition ratio of 60/20/20 at% at an Ar pressure of 0.03 Pa and a sputtering rate of 0.64 Å / sec by magnetron DC sputtering. . Subsequently, the tunnel barrier layer (“MgO” in the sixth layer) uses a target with an MgO composition ratio of 50/50 at%, uses Ar as a sputtering gas, and changes the pressure within a range of 0.01 to 0.4 Pa. A film was formed. Film formation was performed at a sputtering rate of 0.14 レ ー ト / sec by magnetron RF sputtering. Subsequently, a magnetization free layer (seventh layer “CoFeB”) was formed under the same film formation conditions as the magnetization fixed layer (fifth layer “CoFeB”).

  In this example, the deposition rate of the MgO film was 0.14 Å / sec, but there is no problem even if it is formed in the range of 0.01 to 1.0 Å / sec.

The TMR element 10 that has been formed by sputtering film formation in each of the film formation chambers 27A, 27B, and 27C is subjected to an annealing process in a heat treatment furnace. At this time, the annealing temperature is, for example, about 300 ° C., and the annealing process is performed, for example, in a magnetic field of 8 kOe ( 636.6 kA / m), for example, for 4 hours. Thereby, the required magnetization is given to the PtMn of the second layer of the TMR element 10.

  FIG. 3 shows the result of measuring the magnetic properties of MgO. A high MR ratio was obtained over the entire measured range. In particular, a high MR ratio was obtained in the region where the pressure was 0.05 Pa or more and 0.2 Pa or less. In the region where the pressure is 0.05 Pa or more, it is presumed that the film defects are reduced as a result of the pressure on the substrate increasing and the ion bombardment decreasing. When the pressure was 0.05 Pa or more, the MR ratio increased and the tunnel resistance value (RA) increased. This is presumably because the leakage current of the film was reduced as a result of the formation of a good single crystal film. On the other hand, in the region of 0.05 Pa or less, the tunnel resistance value (RA) decreased and the MR ratio also decreased. This is presumably because defects in the MgO single crystal film increased as a result of increased ion bombardment. As a result of observing the sample with a cross-sectional TEM, the MgO film has a single crystal structure over the entire layer from the lower interface to the upper interface in the entire range of the measured pressure, and the MgO single crystal ( The orientation of the (001) plane was observed. Further, it was observed that the CoFeB layer was formed in an amorphous state.

  In this sample, the ferromagnetic layers on both sides of the MgO layer were formed of amorphous CoFeB, but the same result was observed when only one of the ferromagnetic layers was formed of amorphous CoFeB. This ferromagnetic layer is sufficient if at least the portion in contact with the barrier layer has an amorphous material state.

  On the other hand, when CoFe having a polycrystalline structure was formed as the ferromagnetic layer on both sides of the MgO layer, many transitions were observed in the MgO layer, and a good single crystal film could not be obtained and the characteristics were low. .

At this time, as described above, the MgO target 51 is used as a target, and preferably, an RF (high frequency) magnetron sputtering method is applied. It is also possible to form an MgO film by sputtering an Mg target with a mixed gas of Ar and O ₂ using a recurring active sputtering method.

  In the above, the MgO layer is a single crystal over the entire layer, and has a single crystal structure in which the (001) plane is oriented parallel to the interface. Further, the pair of ferromagnetic layers forming the TMR element portion 12 uses a ferromagnetic layer having an amorphous state such as CoFeTaZr, CoTaZr, CoFeNbZr, CoFeZr, FeTaC, FeTaN, or FeC instead of CoFeB having an amorphous state. Can do.

  The configurations, shapes, sizes, and arrangement relationships described in the above embodiments are merely shown to the extent that the present invention can be understood and implemented, and the numerical values and the compositions (materials) of the respective configurations are as follows. It is only an example. Therefore, the present invention is not limited to the described embodiments, and can be variously modified without departing from the scope of the technical idea shown in the claims.

  The present invention is used as a memory element of an MRAM that can be mass-produced, has high practicality, and can be highly integrated.

10 TMR element 11 Substrate (silicon substrate)
20 Magnetic multilayer film production apparatus 27A, 27B, 27C Deposition chamber

Claims (2)

Antiferromagnetic and layers, a method for manufacturing a magneto-resistance effect element comprising a multilayer structure composed of a antiferromagnetic ferromagnetic layer provided on layer and the ferromagnetic layer of the barrier layer,
A ferromagnetic layer having at least a surface in an amorphous state is formed, and a sputtering method is used to form a (001) plane in the thickness direction from the interface with the ferromagnetic layer to the interface opposite to the ferromagnetic layer. Forming a barrier layer having magnesium oxide having a single crystal structure oriented parallel to the interface;
Performing an annealing process for imparting the required magnetization to the antiferromagnetic layer ;
A method for manufacturing a magnetoresistive effect element, comprising:   The method of manufacturing a magnetoresistive element according to claim 1, wherein the ferromagnetic layer contains CoFeB.

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