Patent Application
20100078310
This application claims the benefit of priorities from Japanese Patent Application No. 2008-252107 filed Sep. 30, 2008 and Japanese Patent Application No. 2009-76317 filed Mar. 26, 2009, the entire contents of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fabricating method of a magnetoresistive element, preferably a tunneling magnetoresistive element (more preferably a spin-valve type tunneling magnetoresistive element), used for the magnetic reproducing head of a magnetic disk drive unit, the memory element of a magnetic random-access memory, and a magnetic sensor, and to a storage medium.
2. Related Background Art
Japanese Patent Application Laid-Open No. 2003-318465, International Publication No. WO2005/088745, Japanese Patent Application Laid-Open No. 2006-080116, US Patent Application No. 2006/0056115, D. D. Djayaprawira, et al., “Applied Physics Letters,” 86, 092502 (2005), C. L. Platt et al., “J. Appl. Phys.” 81(8), 15 Apr. 1997, W. H. Butler et al., “The American Physical Society” (Physical Review Vol. 63, 054416) 8, Jan. 2001, Shinji Yuasa et al., “Japanese Journal of Applied Physics” Vol. 43, No. 48, pp. 588-590, Apr. 2, 2004, and S. P. Parkin et al., “2004 Nature Publishing Group” Letters, pp. 862-887, Oct. 31 2004 describe a TMR (Tunneling Magneto Resistance)-effect element (hereinafter referred to as the TMR element) using a crystalline magnesium oxide film made of monocrystal or polycrystal as a tunnel barrier film.
An object of the present invention is to provide a fabricating method of a magnetoresistive element (preferably a tunneling magnetoresistive element, more preferably a spin-valve type tunneling magnetoresistive element or the like) having a high MR ratio more improved than that of the related art, and a storage medium.
A first aspect of the present invention is a fabricating method of a magnetoresistive element comprising, on a substrate, a magnetization fixed layer, a magnetization free layer, and a tunnel barrier layer located between the magnetization fixed layer and the magnetization free layer, the method including the steps of: depositing the tunnel barrier layer on the magnetization fixed layer; and depositing the magnetization free layer on the tunnel barrier layer; wherein the step of depositing the magnetization free layer has a deposition step of depositing a ferromagnetic layer containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms by a co-sputtering method using a first target containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms, and a second target containing Co (cobalt) atoms and Fe (iron) atoms, the second target having different B (boron) atom content from that of the first target (however, the second target includes a case where B (boron) atom content is zero).
Furthermore, a second aspect of the present invention is a fabricating method of a magnetoresistive element comprising, on a substrate, a magnetization fixed layer, a magnetization free layer, and a tunnel barrier layer located between the magnetization fixed layer and the magnetization free layer, the method including the steps of: depositing the tunnel barrier layer on the magnetization fixed layer; and depositing the magnetization free layer on the tunnel barrier layer; wherein the step of depositing the magnetization free layer has: a deposition step of depositing an amorphous ferromagnetic layer containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms by a co-sputtering method using a first target containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms, and a second target containing Co (cobalt) atoms and Fe (iron) atoms, the second target having different B (boron) atom content from that of the first target (however, the second target includes a case where B (boron) atom content is zero); and a phase-change step of phase-changing the amorphous ferromagnetic layer to a crystalline ferromagnetic layer.
Still furthermore, a third aspect of the present invention is a storage medium for storing a control program configured to let a computer execute a fabricating method of a magnetoresistive element comprising, on a substrate, a magnetization fixed layer, a magnetization free layer, and a tunnel barrier layer located between the magnetization fixed layer and the magnetization free layer, the method including the steps of: depositing the tunnel barrier layer on the magnetization fixed layer; and depositing the magnetization free layer on the tunnel barrier layer; wherein the step of depositing the magnetization free layer has a deposition step of depositing a ferromagnetic layer containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms by a co-sputtering method using a first target containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms, and a second target containing Co (cobalt) atoms and Fe (iron) atoms, the second target having different B (boron) atom content from that of the first target (however, the second target includes a case where B (boron) atom content is zero).
Still furthermore, a fourth aspect of the present invention is a storage medium for storing a control program configured to let a computer execute a fabricating method of a magnetoresistive element comprising, on a substrate, a magnetization fixed layer, a magnetization free layer, and a tunnel barrier layer located between the magnetization fixed layer and the magnetization free layer, the method including the steps of: depositing the tunnel barrier layer on the magnetization fixed layer; and depositing the magnetization free layer on the tunnel barrier layer; wherein the step of depositing the magnetization free layer has: a deposition step of depositing an amorphous ferromagnetic layer containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms by a co-sputtering method using a first target containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms, and a second target containing Co (cobalt) atoms and Fe (iron) atoms, the second target having different B (boron) atom content from that of the first target (however, the second target includes a case where B (boron) atom content is zero); and a phase-change step of phase-changing the amorphous ferromagnetic layer to a crystalline ferromagnetic layer.
Still furthermore, a fifth aspect of the present invention is a storage medium for storing a control program configured to let a computer execute a fabricating method of a magnetoresistive element comprising, on a substrate, a magnetization fixed layer, a magnetization free layer, and a tunnel barrier layer located between the magnetization fixed layer and the magnetization free layer, the method including the steps of: depositing the magnetization fixed layer; depositing the tunnel barrier layer on the magnetization fixed layer; and depositing the magnetization free layer on the tunnel barrier layer; wherein both the step of depositing the magnetization fixed layer and the step of depositing the magnetization free layer have a deposition step of depositing a ferromagnetic layer containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms by a co-sputtering method using a target containing Co (cobalt) atoms, Fe (iron) atoms, and B (boron) atoms, and another target containing Co (cobalt) atoms and Fe (iron) atoms, the another target having different B (boron) atom content from that of the target (however, the another target includes a case where B (boron) atom content is zero).
According to the present invention, it is possible to greatly improve an MR ratio achieved with a conventional TMR element.
Hereinafter, preferred embodiments (examples) of the present invention will be described according to the accompanying drawings.
As illustrated in
In addition, in the present invention, the first ferromagnetic layer may have a laminated structure having two or more layers, including the CoFeB layer 121 deposited by a deposition method based on the co-sputtering method using two types of targets and another ferromagnetic layer deposited by a deposition method based on a sputtering method using a single target. Also in the present invention, the “CoFe (1.5)” third ferromagnetic layer 1232 may be changed to a “CoFeB (1.5)” layer 1232 containing B (boron) atoms. Also in the present invention, the “NiFe (1.5)” third ferromagnetic layer 1231 may be changed to an NiFeB (1.5)” layer 1231 containing B (boron) atoms.
Reference numeral 11 denotes a substrate such as a wafer substrate, a glass substrate or a sapphire substrate. Reference numeral 12 denotes a TMR element. The TMR element 12 is formed into a six-layer laminated film structure having the first ferromagnetic layer 121 containing a multicrystal CoFeB (cobalt-iron-boron) alloy, the tunnel barrier layer 122 containing an MgO (magnesium oxide) or BMgO (boron magnesium oxide) multicrystal, the second ferromagnetic layer 1233 containing a multicrystal CoFeB (cobalt-iron-boron) alloy, the nonmagnetic Ta layer 162, and the third ferromagnetic layer which is a laminated film including a multicrystal CoFe (cobalt-iron) alloy and a multicrystal NiFe (nickel-iron) alloy (CoFe layer 1232 and NiCo layer 1231). The nonmagnetic layer 162 formed using a nonmagnetic metal, such as Ta (tantalum) or Ru (ruthenium), or a nonmagnetic insulator, such as Al2O3 (aluminum oxide), SiO2 (silicon dioxide) or Si2N3 (silicon nitride), is interposed between the second ferromagnetic layer and the third ferromagnetic layer. According to the present invention, it is possible for the multicrystal CoFe (cobalt-iron) alloy used for the CoFe layer 1232 to contain an extremely small amount (5 atomic % or smaller, preferably 0.01 to 1 atomic %) of another type of atoms, for example, B (boron) or Pt (platinum) atoms. Reference numeral 13 denotes an underlying electrode layer (foundation layer) provided as the first layer (Ta (tantalum) layer) and reference numeral 14 denotes an antiferromagnetic layer provided as the second layer (PtMn layer). Reference numeral 15 denotes a ferromagnetic layer provided as the third layer (CoFe layer), reference numeral 161 denotes a nonmagnetic spacer layer for exchange coupling provided as the fourth layer (Ru layer).
The CoFeB layer 121 which is the fifth layer is deposited by a co-sputtering method using, for example, a CoFe alloy target having an atomic composition ratio of 70/30 and a CoFeB alloy target having an atomic composition ratio of 60/20/20, different from the former atomic composition ratio. The CoFeB layer 121 is then subjected to a subsequent annealing step performed at a temperature of 200 to 350° C. The CoFeB layer 121 immediately after deposition by the co-sputtering method is preferably amorphous, but may be one of a nanocrystal, a microcrystal (fine crystal) and a multicrystal. The amorphous CoFeB layer 121 is crystallized by an annealing step performed at a temperature of 200 to 350° C. Preferably, the amorphous CoFeB layer 121 can be phase-changed to one of a nanocrystal, a microcrystal (fine crystal) and a multicrystal.
In the present invention, targets are not limited to those having the above-described atomic composition ratios, but targets having atomic composition ratios selected as appropriate may be used. In particular, it is possible to use a combination of two types of targets having B (boron) atom contents different from each other. Examples of other combinations are as follows: As a first example, it is possible to use a combination of a CoFeB alloy target having an atomic composition ratio of 70/20/10 and a CoFeB alloy target having an atomic composition ratio of 60/20/20. Alternatively, as a second example, it is possible to use a combination of a CoFeB alloy target having an atomic composition ratio of 70/25/5 and a CoFeB alloy target having an atomic composition ratio of 50/25/25.
The boron content of the crystalline CoFeB layer 121 is set to within a range of 0.1 to 60 atomic %, preferably 10 to 50 atomic %. Furthermore, in the present invention, it is possible for the above-described two types of targets to contain an extremely small amount (5 atomic % or smaller, preferably 0.01 to 1 atomic %) of atoms other than CoFeB atoms, for example, Pt (platinum) atoms, Ni (nickel) atoms, or Mn (manganese) atoms.
In addition, the co-sputtering method of the present invention preferably sputters the two types of targets at the same time. Alternatively, the co-sputtering method may have a sputtering step performed at a point in time before or after this same point in time, using one of the two types of targets alone.
The layer having the third layer, the fourth layer and the fifth layer is a magnetization fixed layer 19. The magnetization fixed layer 19 in a substantial sense refers to a ferromagnetic layer which is the crystalline CoFeB layer 121 provided as the fifth layer. Reference numeral 122 denotes a tunnel barrier layer, which is an insulating layer, provided as the sixth layer (MgO: multicrystal magnesium oxide or BMgO: boron magnesium oxide). The tunnel barrier layer 122 used in the present invention may be a single multicrystal magnesium oxide or multicrystal boron magnesium oxide layer.
In addition, as illustrated in
The CoFeB layer 1233 which is a magnetization free layer provided as the seventh layer is deposited by a co-sputtering method using, for example, a CoFe alloy target having an atomic composition ratio of 70/30 and a CoFeB alloy target having an atomic composition ratio of 60/20/20, different from the former atomic composition ratio. The CoFeB layer 1233 is then subjected to a subsequent annealing step performed at a temperature of 200 to 350° C. The CoFeB layer 1233 immediately after deposition by the co-sputtering method is preferably amorphous, but may be one of a nanocrystal, a microcrystal (fine crystal) and a multicrystal. The amorphous CoFeB layer 1233 is crystallized by an annealing step performed at a temperature of 200 to 350° C. Preferably, the amorphous CoFeB layer 1233 can be phase-changed to one of a nanocrystal a microcrystal (fine crystal) and a multicrystal.
In the present invention, targets are not limited to those having the above-described atomic composition ratios, but targets having atomic composition ratios selected as appropriate may be used. In particular, it is possible to use a combination of two types of targets having B (boron) atom contents different from each other. Examples of other combinations are as follows: As a first example, it is possible to use a combination of a CoFeB alloy target having an atomic composition ratio of 70/20/10 and a CoFeB alloy target having an atomic composition ratio of 60/20/20. Alternatively, as a second example, it is possible to use a combination of a CoFeB alloy target having an atomic composition ratio of 70/25/5 and a CoFeB alloy target having an atomic composition ratio of 50/25/25.
The boron content of the crystalline CoFeB layer 1233 is set to within a range of 0.1 to 60 atomic %, preferably 10 to 50 atomic %. Furthermore, in the present invention, it is possible for the above-described two types of targets to contain an extremely small amount (5 atomic % or smaller, preferably 0.01 to 1 atomic %) of atoms other than CoFeB, for example, Pt (platinum), Ni (nickel), or Mn (manganese).
In addition, the co-sputtering method of the present invention preferably sputters the two types of targets at the same time. Alternatively, the co-sputtering method may have a sputtering step performed at a point in time before or after this same point in time, using one of the two types of targets alone.
In addition, in the present invention, the layer 81 may be excluded from use and the layer 82 can be located adjacent to the crystalline CoFeB layer 1233. Alternatively, the layer 83 may be excluded from use and the layer 82 can be located adjacent to the crystalline CoFeB layer 121.
The columnar crystal 72 is a conception that encompasses the conception of an acicular crystal, a columnar crystal, or the like. Alternatively, the crystal structure may be a structure having a multicrystal-amorphous mixed region, including a partial amorphous region between aggregates 71 of columnar crystals 72 in part of a multicrystal region.
The columnar crystal of a magnesium oxide or a boron magnesium oxide used in the present invention is preferably a single crystal in which a (001) crystal face is preferentially oriented in a film thickness direction in each column.
In addition, the BMgO (boron magnesium oxide) used in the present invention is represented by a general formula BxMgyOz (where 0.7≦Z/[X+Y]≦1.3, preferably 0.8≦Z/[X+Y]<1.0). In the present invention, it is preferable to use stoichiometrical BMgO (boron magnesium oxide). Even if oxygen-deficient BMgO (boron magnesium oxide) is used, however, it is possible to obtain a high MR ratio.
In addition, the MgO (magnesium oxide) used in the present invention is represented by a general formula MgyOz (where 0.7≦Z/Y≦1.3, preferably 0.8≦Z/Y<1.0). In the present invention, it is preferable to use stoichiometrical MgO (magnesium oxide). Even if oxygen-deficient MgO (magnesium oxide) is used, however, it is possible to obtain a high MR ratio.
The seventh layer, the ninth layer, and the tenth layer, respectively, are a ferromagnetic layer including the crystalline CoFeB layer 1233, a ferromagnetic layer including the crystalline CoFe layer 1232, and a ferromagnetic layer including the NiFe layer 1231. The laminated film having the seventh layer, the ninth layer and the tenth layer can function as a magnetization free layer. A Ta (tantalum) layer 162 for the eighth layer, which is a nonmagnetic metal layer, is located between the seventh layer and the ninth layer. For the eighth layer, it is possible to use a nonmagnetic metal, such as Ru (ruthenium) or Ir (iridium), or a nonmagnetic insulator, such as Al2O3 (aluminum oxide), SiO2 (silicon dioxide) or Si3N4 (silicon nitride), in addition to the Ta (tantalum) layer 162. The film thickness of the eighth layer can be set to 50 nm or smaller, preferably within a range of 0.1 nm to 40 nm. The crystalline CoFeB layer 1233 constituting the seventh layer can be deposited by sputtering using a CoFeB alloy target. The crystalline CoFe layer 1232 constituting the ninth layer can be deposited by sputtering using a COFe alloy target. The crystalline NiFe layer 1231 constituting the tenth layer can be deposited by sputtering using an NiFe alloy target.
The crystalline CoFeB layer 121, the CoFeB layer 1233, the CoFe layer 1232 and the NiFe layer 1231 may have the same crystal structure as that of the aggregate 71 having columnar crystal structures 72 illustrated in
In
Next, an apparatus for fabricating a magnetoresistive element 10 having the above-described laminated structure and a method for fabricating the magnetoresistive element 10 will be described with reference to
A magnetic multilayer film manufacturing apparatus 200 illustrated in
In the manufacturing apparatus 200 for manufacturing a magnetoresistive element, three magnetron sputtering chambers for deposition 201A, 201B and 201C and one etching chamber 203 are provided around the conveyance chamber 202. In the etching chamber 203, a desired surface of the magnetoresistive element 10 is etching-treated. A freely openable and closable gate valve 204 is provided between each of the chambers 201A, 201B, 201C and 203 and the conveyance chamber 202. To each of the chambers 201A, 201B, 201C and 202, there are attached an unillustrated evacuation mechanism, a gas introduction mechanism, a power supply mechanism, and the like.
The manufacturing apparatus 200 for manufacturing a magnetoresistive element is provided with the magnetron sputtering chambers for deposition 201A, 201B and 201C. In each of these chambers 201A, 201B and 201C, it is possible to sequentially deposit the first to ninth layers on the substrate 11 using a high-frequency sputtering method, without breaking the vacuum. On the ceilings of the magnetron sputtering chambers for deposition 201A, 201B and 201C, there are respectively disposed four or five cathodes, i.e., cathodes 31, 32, 33, 34 and 35, cathodes 41, 42, 43, 44 and 45, and cathodes 51, 52, 53 and 54 arranged on appropriate circumferences of the ceilings. In addition, substrates 11 are placed on substrate holders positioned coaxially with the circumferences.
The magnetron sputtering apparatus is preferably such that targets are attached to the cathodes 31, 32, 33, 34 and 35, cathodes 41, 42, 43, 44 and 45, and cathodes 51, 52, 53 and 54 and magnets are disposed at the back of the attached targets.
In addition, high-frequency power such as radio-frequency (RF) power is applied from power supply means 207A, 207B and 207C to the above-described cathodes. As the high-frequency power, it is possible to use a frequency within a range of 0.3 MHz to 10 GHz, preferably 5 MHz to 5 GHz, and power within a range of 10 W to 500 W, preferably 100 W to 300 W.
In the foregoing discussion, for example, a Ta (tantalum) target is attached to the cathode 31. A PtMn (platinum-manganese alloy) target is attached to the cathode 32. A CoFeB target is attached to the cathode 33. A CoFe (cobalt-iron alloy) target is attached to the cathode 34. An Ru (ruthenium) target is attached to the cathode 35. The CoFeB layer 121 can be deposited by a co-sputtering method using two types of targets, i.e., the CoFeB target attached to the cathode 33 and the CoFe target attached to the cathode 34.
An MgO (magnesium oxide alloy) target is attached to the cathode 51. A BMgO (boron magnesium oxide) target is attached to the cathode 52. In addition, an Mg (metal magnesium) target is attached to the cathode 53, and BMg (boron-magnesium alloy) target is attached to the cathode 54. A TMR element 122 having the structure illustrated in
A CoFe (cobalt-iron alloy) target for the seventh and ninth layers is attached to the cathode 41. A CoFeB (cobalt-iron-boron alloy) target for the seventh layer fabricated by using a co-sputtering method is attached to the cathode 42. A Ta (tantalum) target for the eighth and eleventh layers is attached to the cathode 43. An Ru (ruthenium) target for the twelfth layer is attached to the cathode 44. An NiFe (nickel iron) target for the tenth layer is attached to the cathode 45. The CoFeB layer 1233 can be deposited by a co-sputtering method using two types of targets, i.e., the CoFeB target attached to the cathode 42 and the CoFe target attached to the cathode 41.
The in-plane directions of the respective targets attached to the cathodes 31, 32, 33, 34 and 35, the cathodes 41, 42, 43, 44 and 45, and the cathodes 51, 52, 53 and 54 and the in-plane direction of a substrate are preferably arranged so as to be non-parallel to each other. By using the non-parallel arrangement, it is possible to sputter a target smaller in diameter than the substrate, while rotating the target. Accordingly, it is possible to deposit magnetic and nonmagnetic films having the same compositions as the compositions of targets with high efficiency. As an example of the above-described non-parallel arrangement, it is possible to arrange both in-plane directions non-parallel to each other, so that an intersecting angle formed by the central axis of each target and the central axis of the substrate is 45° or smaller, preferably 5° to 30°. In addition, as the rotational speed of the substrate at this time, it is possible to use 10 rpm to 500 rpm, preferably 50 rpm to 200 rpm.
Now, an explanation will be made of the deposition conditions of a TMR element 12 which is a principal element portion of the present invention. For the CoFeB layer 121, a CoFe target having a CoFe composition ratio (atomic ratio) of 70/30 and a target having a CoFeB composition ratio (atomic ratio) of 60/20/20 were used as simultaneous targets. For the CoFeB layer 121, Ar (argon gas) was used as a sputter gas and the pressure thereof was set to 0.03 Pa. The CoFeB layer 121 was deposited by magnetron DC sputtering (magnetron sputtering chamber for deposition 201A) at a deposition rate of 0.64 nm/sec. The CoFeB layer (CoFeB layer 121) at this time had an amorphous structure.
Subsequently, the apparatus was changed to a sputtering apparatus (magnetron sputtering chamber for deposition 201C), and an MgO target having an MgO composition ratio (atomic ratio) of 50/50 or a BMgO target having a BMgO composition ratio (atomic ratio) of 25/25/50 was used. Using Ar (argon gas) as the sputter gas and a pressure of 0.2 Pa, among pressures within a preferred pressure range of 0.01 to 0.4 Pa, a tunnel barrier layer 122 which was an MgO or BMgO layer for the sixth layer was deposited by magnetron RF sputtering (13.56 MHz). At this time, the MgO or BMgO layer (tunnel barrier layer 122) had a multicrystal structure having an aggregate 71 of columnar crystals 72 illustrated in
In the present invention, a crystalline (preferably, multicrystal) magnesium oxide layer can be obtained by depositing a crystalline (preferably, multicrystal) metal magnesium layer by a sputtering method using a metal magnesium-containing target and oxidizing the metal magnesium within an oxidization chamber (not shown in the figure) in which an oxidizing gas (oxygen gas, ozone gas, steam, or the like) has been introduced.
Also in the present invention, a crystalline (preferably, multicrystal) boron magnesium oxide layer can be obtained by depositing a crystalline (preferably, multicrystal) boron magnesium layer by a sputtering method using a boron-magnesium alloy-containing target and oxidizing the boron-magnesium alloy within an oxidization chamber (not shown in the figure) in which an oxidizing gas (oxygen gas, ozone gas, steam, or the like) has been introduced.
In the present embodiment, following on from the above-described step, the substrate was introduced into a sputtering apparatus (magnetron sputtering chamber for deposition 201B), and ferromagnetic layers which were magnetization free layers (CoFeB layer 1233 for the seventh layer, Ta layer 162 for the eighth layer, CoFe layer 1232 for the ninth layer and NiFe layer 1231 for the tenth layer) were deposited. For the CoFeB layer 1233, the CoFe layer 1232 and the NiFe layer 1231, Ar (argon gas) was used as a sputter gas and the pressure thereof was set to 0.03 Pa. The CoFeB layer 1233, the CoFe layer 1232 layer and the NiFe layer 1231 were deposited by magnetron DC sputtering (magnetron sputtering chamber for deposition 201B) at a sputter rate of 0.64 nm/sec. At this time, Ar (argon gas) was used as the sputter gas and the pressure thereof was set to 0.03 Pa for each of the CoFeB layer 1233, the CoFe layer 1232 layer and the NiFe layer 1231. In addition, targets having a CoFeB composition ratio (atomic) of 25/25/50, a CoFe composition ratio (atomic) of 50/50, and an NiFe composition ratio (atomic) of 40/60 were used. Immediately after this deposition, the CoFeB layer 1233, the CoFe layer 1232 and the NiFe layer 1231 had an amorphous structure.
While in this embodiment, the deposition rate of MgO and BMgO films was 0.14 nm/sec, there is no problem even if the films are deposited at a rate ranging from 0.01 nm to 1.0 nm/sec.
Sputtering deposition was performed in the magnetron sputtering chambers for deposition 201A, 201B and 201C, respectively, to complete lamination. An annealing treatment was performed on the magnetoresistive element 10 in a heat treatment furnace. The annealing temperature and time of the element at this time were approximately 300° C. and four hours, and annealing was performed in a magnetic field of 8 kOe. As a result, it was confirmed that the CoFeB layer 121, the CoFeB layer 1233, the CoFe layer 1232 and the NiFe layer 1231 having an amorphous structure had a multicrystal structure having the aggregate 71 of columnar crystals 72 illustrated in
In the first embodiment of the present invention, a substrate (not shown in the figure) within the load lock and unload lock chamber 305 is carried out to the conveyance chamber 301. In this step of carrying out the substrate, the CPU 306 performs a calculation on the basis of a control program stored in the storage medium 312 as a computer-executable program. The CPU 306 transmits a control signal based on the results of this calculation to various apparatus (for example, an unillustrated gate valve, robot mechanism, conveyance mechanism and driving system) mounted on the load lock and unload lock chamber 305 and the conveyance chamber 301 through the bus lines 307 and 311. That is, the above-described step of carrying out the substrate is performed as the result that the CPU 306 controls the execution of the above-described various apparatus using the control signal.
The substrate carried to the conveyance chamber 301 is carried out to the deposition chamber 302. Here, the first layer (Ta layer 13), the second layer (PtMn layer 14), the third layer (CoFe layer 15), the fourth layer (Ru layer 161) and the fifth layer (CoFeB layer 121) illustrated in
In the process of laminating the above-described first to fifth layers, a control signal calculated within the CPU 306 on the basis of the control program stored in the storage medium 312 is transmitted through the bus lines 307 and 308 to various apparatus (for example, an unillustrated mechanism of power supply to cathodes, substrate-rotating mechanism, gas introduction mechanism, exhaust mechanism, gate valve, robot mechanism, conveyance mechanism, and driving system) mounted on the conveyance chamber 301 and the deposition chamber 302. The various apparatus perform predetermined operations on the basis of the received control signal. That is, the process of laminating the first to fifth layers is performed as the result that the CPU 306 controls the execution of the various apparatus using the control signal.
The substrate comprising a laminated film having layers up to the fifth layer is temporarily returned to the conveyance chamber 301, and is then carried in to the deposition chamber 303. The deposition of a multicrystal magnesium oxide or multicrystal boron magnesium oxide layer 122 as the sixth layer on the amorphous CoFeB layer 121, which is the fifth layer, is executed within the deposition chamber 303.
In the deposition of the magnesium oxide or multicrystal boron magnesium oxide layer 122 for the sixth layer, the control signal calculated within the CPU 306 on the basis of the control program stored in the storage medium 312 is transmitted through the bus lines 307 and 309 to various apparatus (for example, an unillustrated mechanism of power supply to cathodes, substrate-rotating mechanism, gas introduction mechanism, exhaust mechanism, gate valve, robot mechanism, conveyance mechanism, and driving system) mounted on the conveyance chamber 301 and the deposition chamber 303. The various apparatus perform predetermined operations on the basis of the received control signal. That is, the deposition of the sixth layer is performed as the result that the CPU 306 controls the execution of the various apparatus using the control signal.
The substrate comprising a laminated film having layers up to the magnesium oxide or multicrystal boron magnesium oxide layer 122 for the sixth layer is once again temporarily returned to the conveyance chamber 301, and is then carried in to the deposition chamber 304.
Within the deposition chamber 304, the seventh layer (CoFeB layer 1233), the eighth layer (Ta layer 162), the ninth layer (CoFe layer 1232), the tenth layer (NiFe layer 1231), the eleventh layer (Ta layer 17) and the twelfth layer (Ru layer 18) are sequentially laminated on the multicrystal magnesium oxide or multicrystal boron magnesium oxide layer 122 which is the sixth layer. At this stage, the CoFeB layer 1233 for the seventh layer, the CoFe layer 1232 for the ninth layer and the NiFe layer 1231 for the tenth layer preferably have an amorphous structure. In another embodiment, the CoFeB layer 1233 for the seventh layer, the CoFe layer 1232 for the ninth layer and the NiFe layer 1231 for the tenth layer at this stage may have a multicrystal structure.
In the process of laminating and depositing the above-described seventh (CoFeB layer 1232) to twelfth (Ru layer 18) layers, a control signal calculated within the CPU 306 on the basis of the control program stored in the storage medium 312 is transmitted through the bus lines 307 and 310 to various apparatus (for example, an unillustrated mechanism of power supply to cathodes, substrate-rotating mechanism, gas introduction mechanism, exhaust mechanism, gate valve, robot mechanism, conveyance mechanism, and driving system) mounted on the conveyance chamber 301 and the deposition chamber 304. The various apparatus perform predetermined operations on the basis of the received control signal. That is, the process of laminating and depositing the seventh (CoFeB layer 1232) to twelfth (Ru layer 18) layers is performed as the result that the CPU 306 controls the execution of the various apparatus using the control signal.
At this time, in the present embodiment, it is possible to deposit the Ta layer 162 which is the eighth layer and the Ta layer 17 which is the eleventh layer, using the same target attached to the cathode 43.
Examples of the storage medium 312 used in the present invention include computer-readable media, such a hard-disk medium, a magnetooptical-disk medium, a flexible-disk medium, and a general family of nonvolatile memories, including a flash memory and an MRAM, as well as media capable of storing programs.
In addition, in the present invention, the amorphous states of the fifth layer (CoFeB layer 121), the seventh layer (CoFeB layer 1233), the ninth layer (CoFe layer 1232) and the tenth layer (NiFe layer 1231) immediately after deposition can be changed to the multicrystal structure illustrated in
As a comparative example of the present invention, a magnetoresistive element was fabricated using the same method as used in the first embodiment, except that the Ta layer 162 for the eighth layer, the CoFe layer 1232 for the ninth layer and the NiFe layer 1231 for the tenth layer were excluded from use.
Measurement of and comparison between the MR ratios of the magnetoresistive element fabricated in the first embodiment of the present invention and the above-described magnetoresistive element for comparison showed that the MR ratio of the magnetoresistive element of the first embodiment improved by a factor of 1.2 to 1.5 or greater, compared with the MR ratio of the magnetoresistive element for comparison.
Note that the MR ratio refers to a parameter related to a phenomenon (“Magneto-Resistive effect”) in which the electrical resistance of a magnetic film or a magnetic multilayer film also changes as the magnetization direction of the films changes in response to an external magnetic field. The rate of change in the electrical resistance is defined as the rate of change in magnetic resistance (MR ratio).
In the second embodiment of the present invention, a magnetoresistive element was fabricated in completely the same way as in the first embodiment, except that a multicrystal boron magnesium oxide layer was used as the sixth layer in place of the multicrystal magnesium oxide layer for the sixth layer used in the first embodiment. Measurement of the MR ratio of the fabricated magnetoresistive element showed that there was obtained an even more remarkably improved MR ratio (1.5 times or more higher than the MR ratio obtained in the embodiment in which the multicrystal magnesium oxide layer was used), compared with the embodiment in which the multicrystal magnesium oxide layer was used.
Furthermore, in the third embodiment of the present invention, a magnetoresistive element was fabricated using completely the same method as used in the first embodiment, except that the target of the CoFeB layer 121 for the fifth layer was changed to a single CoFeB (atomic composition ratio: 50/30/20) target. In the third embodiment, an advantageous effect similar to that of the first embodiment was obtained (the CoFeB 1233 layer which was a magnetization free layer for the seventh layer was deposited using the same co-sputtering method as used in the first embodiment).
Still furthermore, in the fourth embodiment of the present invention, a magnetoresistive element was fabricated using completely the same method as used in the first embodiment, except that CoFe layer 1232 for the ninth layer was changed to a CoFeB (atomic composition ratio: 50/30/20) layer. In the fourth embodiment, an advantageous effect similar to that of the first embodiment was obtained.
Still furthermore, in the fifth embodiment of the present invention, a magnetoresistive element was fabricated using completely the same method as used in the first embodiment, except that the NiFe layer 1231 for the tenth layer was changed to an NiFeB (atomic composition ratio: 50/30/20) layer. In the fifth embodiment, an advantageous effect similar to that of the first embodiment was obtained.
Still furthermore, in the sixth embodiment of the present invention, a magnetoresistive element was fabricated using completely the same method as used in the first embodiment, except that the MgO layer 122 for the sixth layer was changed to a BMgO layer 122. In the sixth embodiment, there was achieved an improvement greater by a factor 1.5 or more than the result of the first embodiment.
Still furthermore, as a second comparative example, a magnetoresistive element was fabricated using completely the same method as used in the first embodiment, except that the CoFeB layer 1233 which was a magnetization free layer and the CoFeB layer 121 which was a magnetization fixed layer were deposited by a sputtering method using a single CoFeB (atomic composition ratio: 60/20/20) target. Measurement of the MR ratio of the magnetoresistive element fabricated in this comparative example showed a result extremely as low as less than half the MR ratio obtained with the magnetoresistive element of the first embodiment.
As described above, in the present invention, the ferromagnetic layer (reference numeral 1233 in
Also, in the present invention, it is possible to use a crystalline ferromagnetic layer, such as a CoFeTaZr (cobalt-iron-tantalum-zirconium) alloy layer, a CoTaZr (cobalt-tantalum-zirconium) alloy layer, a CoFeNbZr (cobalt-iron-niobium-zirconium) alloy layer, a CoFeZr (cobalt-iron-zirconium) alloy layer, an FeTaC (iron-tantalum-carbon) alloy layer, an FeTaN (iron-tantalum-nitrogen) alloy layer, or an FeC (iron-carbon) alloy layer, in place of the CoFeB layer 121 for the fifth layer.
Also, in the present invention, it is possible to use an Rh (rhodium) layer or an Ir (iridium) layer in place of the Ru (ruthenium) layer for the fourth layer 161.
Also, in the present invention, an IrMn (iridium-manganese alloy) layer, an IrMnCr (iridium-manganese-chromium alloy) layer, an NiMn (nickel-manganese alloy) layer, a PdPtMn (lead-platinum-manganese alloy) layer, an RuRhMn (ruthenium-rhodium-manganese alloy) layer, an OsMn (osmium-manganese) layer, or the like is preferably used in place of the PtMn 14 (platinum-manganese alloy) layer for the second layer. In addition, the film thickness of the layer is preferably 10 to 30 nm.
The present invention can be applied as a memory element of an MRAM which is mass-producible, highly practical, and capable of ultrahigh integration.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-252107 | Sep 2008 | JP | national |
| 2009-076317 | Mar 2009 | JP | national |
