JP2012142418A - Magnetic device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the interval of a plurality of tunnel junction elements.SOLUTION: The magnetic device comprises an underlying layer 24 having a recess 26 formed in the upper surface, a lower electrode 28 formed on the inner surface of the recess and on the underlying layer on both sides of the recess, a magnetic tunnel junction layer 30 formed on the lower electrode on both sides of the recess, and including a tunnel barrier layer and a magnetization fixed layer and a magnetization free layer sandwiching the tunnel barrier layer vertically, and a plurality of upper electrodes 40 formed on the magnetic tunnel junction layer and separated electrically above the recess.

Description

  The present invention relates to a magnetic device and a manufacturing method thereof, and more particularly to a magnetic device including a magnetic tunnel junction and a manufacturing method thereof.

  An MRAM (Magnetic Random Access Memory), which is a type of nonvolatile memory, includes a magnetic tunnel junction (MTJ) element. The magnetic tunnel junction element includes a structure in which a tunnel barrier layer made of a nonmagnetic material is sandwiched between a magnetization fixed layer made of a ferromagnetic material and a magnetization free layer made of a ferromagnetic material. The magnetization fixed layer includes an antiferromagnetic layer and a pinned layer, and the magnetization of the pinned layer is not easily reversed by the antiferromagnetic layer. On the other hand, the magnetization of the magnetization free layer is easily reversed. For this reason, for example, the magnetization of the magnetization free layer can be reversed using a spin injection method or the like. When the magnetization of the magnetization free layer and the magnetization fixed layer are parallel, the resistance of the magnetic tunnel junction element is reduced. When the magnetizations of the magnetization free layer and the magnetization fixed layer are antiparallel, the resistance of the magnetic tunnel junction element increases. Thus, for example, data can be stored in a nonvolatile manner according to the magnetization direction of the magnetization free layer.

  An MRAM that can store multiple values in one memory cell by providing a plurality of magnetic tunnel junction elements in one memory cell is known.

JP 2005-340468 A JP 2007-258460 A

  However, when a plurality of magnetic tunnel junction elements are formed in one memory cell, it is difficult to narrow the interval between the magnetic tunnel junction elements. This increases the chip size. As described above, when a plurality of magnetic tunnel junction elements are formed close to each other, it is difficult to narrow the interval between the magnetic tunnel junction elements. An object of the present magnetic device and its manufacturing method is to shorten the interval between a plurality of tunnel junction elements.

  For example, a magnetic tunnel junction layer including a lower electrode having a recess on the upper surface, and a magnetization fixed layer and a magnetization free layer that are formed on the lower electrode on both sides of the recess and sandwich the tunnel barrier layer vertically. And a plurality of upper electrodes formed on the magnetic tunnel junction layer and electrically separated above the concave portion.

  For example, a magnetic tunnel including a step of forming a lower electrode having a recess on an upper surface, and a magnetization barrier layer and a magnetization free layer sandwiching the tunnel barrier layer vertically on the lower electrode on both sides of the recess A method of manufacturing a magnetic device, comprising: forming a bonding layer; and forming a plurality of upper electrodes electrically isolated above the recesses on the magnetic tunnel bonding layer. Use.

  According to the present magnetic device and the manufacturing method thereof, the interval between the plurality of tunnel junction elements can be shortened.

FIG. 1 is a circuit diagram of an MRAM cell according to the first embodiment. FIG. 2A to FIG. 2C are schematic views of cells to which magnetic tunnel junction elements are connected. FIGS. 3A to 3C correspond to FIGS. 2A to 2B, respectively, and the current Ic flowing from the magnetization fixed layer to the magnetization free layer and the resistance value between the word line and the bit line. It is a schematic diagram which shows. 4A is a cross-sectional view of the vicinity of the magnetic tunnel junction element of Comparative Example 1, and FIG. 4B is a plan view. FIG. 5 is a diagram illustrating a resistance value with respect to the interval L in the comparative example. FIG. 6 is a cross-sectional view of the MRAM cell according to the first embodiment. FIG. 7A is a cross-sectional view of the vicinity of the magnetic tunnel junction of Example 1, and FIG. 7B is a plan view. FIG. 8A is a cross-sectional view in the case where the upper electrode is formed in the recess, and FIG. 8B is a diagram showing the coverage with respect to the length L of the recess. FIG. 9A to FIG. 9C are cross-sectional views (part 1) illustrating the method for manufacturing the magnetic tunnel junction part of the first embodiment. FIG. 10A to FIG. 10C are cross-sectional views (part 2) illustrating the method for manufacturing the magnetic tunnel junction part of the first embodiment. FIG. 11A and FIG. 11B are cross-sectional views (part 3) illustrating the method for manufacturing the magnetic tunnel junction part of the first embodiment. 12A is a plan view of the magnetic tunnel junction part of Example 1, and FIG. 12B is a diagram showing a resistance value Ra with respect to L. FIG. FIG. 13 is a cross-sectional view of the magnetic tunnel junction element according to the second embodiment.

  Embodiments will be described below with reference to the drawings.

  FIG. 1 is a circuit diagram of an MRAM cell according to the first embodiment. As shown in FIG. 1, the source of the transistor Tr is connected to the source line SL. The gate of the transistor Tr is connected to the word line WL. The drain of the transistor Tr is connected to the bit line BL via the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b. The magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b are connected in parallel. The area of the magnetic tunnel junction element 50a is set larger than that of the magnetic tunnel junction element 50b.

  Next, the reason why the memory cell shown in FIG. 1 can store multiple values will be described. FIG. 2A to FIG. 2C are schematic views of cells to which magnetic tunnel junction elements are connected. The transistor Tr is not shown. In FIG. 2A, the magnetic tunnel junction element 50b is connected between the word line WL and the bit line BL. In FIG. 2B, the magnetic tunnel junction element 50a is connected between the word line WL and the bit line BL. In FIG. 2C, the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b are connected in parallel between the word line WL and the bit line BL.

  FIGS. 3A to 3C correspond to FIGS. 2A to 2B, respectively, and the current Ic flowing from the magnetization fixed layer to the magnetization free layer and the resistance value between the word line and the bit line. It is a schematic diagram which shows. When the magnetic tunnel junction element 50a has the high resistance RH1, the magnetization of the magnetization free layer is opposite to the magnetization of the magnetization fixed layer. When the magnetic tunnel junction element 50a has the low resistance RL1, the magnetization of the magnetization free layer and the magnetization of the magnetization fixed layer are parallel. As shown in FIG. 3A, when the magnetic tunnel junction element 50a has a high resistance RH1, when the current Ic becomes smaller than −Ic1 (that is, spin-polarized electrons are injected from the magnetization fixed layer to the magnetization free layer). Then, the magnetization of the magnetization free layer is reversed. Thereby, the magnetic tunnel junction element 50a becomes the low resistance RL1. When the magnetic tunnel junction element 50a has the low resistance RL1, the magnetization of the magnetization free layer is reversed when the current Ic exceeds Ic1. Thereby, the magnetic tunnel junction element 50a becomes the high resistance RH1.

  As shown in FIG. 3B, since the magnetic tunnel junction element 50b has a smaller area than the magnetic tunnel junction element 50a, the current Ic2 at which the magnetization of the magnetization free layer is reversed is smaller than Ic1. The resistance RH2 of the magnetic tunnel junction element 50b is smaller than the resistance RH1, and the resistance RL2 is larger than the resistance RL1.

  As shown in FIG. 3C, when both the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b have the low resistances RL1 and RL2, the resistance value R between the word line WL and the bit line BL is equal to that of RL1 and RL2. The parallel resistance value RL1 ′. When both the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b have the high resistances RH1 and RH2, the resistance value R between the word line WL and the bit line BL is the parallel resistance value RH1 ′ of RH1 and RH2. When the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b are the low resistance RL1 and the high resistance RH2, respectively, the resistance value R between the word line WL and the bit line BL is the parallel resistance value RL2 ′ of RL1 and RH2. . When the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b are the high resistance RH1 and the low resistance RL2, respectively, the resistance value R between the word line WL and the bit line BL is the parallel resistance value RH2 ′ of RH1 and RL2. .

  When both the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b have the high resistances RH1 and RH2, the magnetic tunnel junction element 50b has a low resistance when the current Ic is smaller than -Ic2. Therefore, the resistance value R becomes the resistance value RL2 ′. Further, when the current Ic becomes smaller than Ic1, the magnetic tunnel junction element 50a has a low resistance in addition to the magnetic tunnel junction element 50b. Therefore, the resistance value R becomes the resistance value RL1 ′. When both the magnetic tunnel junction element 50a and the magnetic tunnel junction element 50b have the low resistances RL1 and RL2, the magnetic tunnel junction element 50b becomes a high resistance when the current Ic is larger than Ic2. Therefore, the resistance value R becomes the resistance value RH2 ′. Further, when the current Ic becomes larger than Ic1, the magnetic tunnel junction element 50a becomes high resistance in addition to the magnetic tunnel junction element 50b. Therefore, the resistance value R becomes the resistance value RH1 ′.

  As described above, multiple values can be stored in one memory cell. Thus, a memory cell capable of storing multiple values can be realized by connecting a plurality of magnetic tunnel junction elements having different areas in parallel between a word line and a bit line.

  In order to explain the problem solved by the embodiment, a comparative example will be described. 4A is a cross-sectional view of the vicinity of the magnetic tunnel junction element of Comparative Example 1, and FIG. 4B is a plan view. As shown in FIG. 4A, a plug metal layer 22 penetrating the insulating film 20 vertically is formed. A lower electrode 28 electrically connected to the plug metal layer 22 is formed on the insulating film 20. A magnetic tunnel junction layer 30 is formed on the lower electrode 28. The magnetic tunnel junction layer 30 includes a tunnel barrier layer, a magnetization fixed layer that sandwiches the tunnel barrier layer, and a magnetization fixed layer. An upper electrode 40 is formed on the magnetic tunnel junction layer 30. The lower electrode 28 is common to the magnetic tunnel junction elements 50a and 50b. The magnetic tunnel junction layer 30 and the upper electrode 40 are separated by the magnetic tunnel junction elements 50a and 50b. A cover film 42 is formed so as to cover the lower electrode 28, the magnetic tunnel junction layer 30, and the upper electrode 40. An insulating film 46 is formed so as to cover the cover film 42. Plug metal layers 48 a and 48 b penetrating the insulating film 46 and the cover film 42 and electrically connected to the upper electrode 40 are formed.

The conditions for forming each layer of the magnetic tunnel junction device according to the manufactured comparative example will be described.
The formation conditions of the lower electrode 28 are as follows.
Layer structure: Ta film, Ru film, NiFe film, Ta film from below Film forming device: Sputtering Film thickness: Ta film 5 nm, Ru film 50 nm, NiFe film 5 nm, Ta film 10 nm
DC applied power: 1kW
Sputtering gas: Ar
Gas flow rate: 15sccm
Gas pressure: 0.02 Pa or less Substrate heating: None

  After the lower electrode 28 is formed, the lower electrode 28 is etched.

The formation conditions of the magnetization fixed layer 32 are as follows.
Layer structure: PtMn film (strong diamagnetic layer), CoFe film, Ru film, CoFeB film from below Film forming device: Sputtering film thickness: PtMn film 15 nm, CoFe film 2.5 nm, Ru film 0.68 nm, CoFeB film 2nm
DC applied power: 200 W for PtMn film, 400 W for other films
Sputtering gas: Ar
Gas flow rate: 20sccm
Gas pressure: 0.02 Pa or less Substrate heating: None

The conditions for forming the tunnel barrier layer 34 are as follows.
Layer structure: MgO film Film forming device: Sputtering Film thickness: 1.2 nm
DC applied power: 200W
Sputtering gas: Ar
Gas flow rate: 30sccm
Gas pressure: 0.5 Pa or less Substrate heating: None

The conditions for forming the magnetization free layer 36 are as follows.
Layer structure: CoFeB film Film forming device: Sputtering Film thickness: CoFeB film 1.5 nm
DC applied power: 250W
Sputtering gas: Ar
Gas flow rate: 15sccm
Gas pressure: 0.02 Pa or less Substrate heating: None

The formation conditions of the upper electrode 40 are as follows.
Layer structure: Ru film, Ta film from bottom Film forming device: Sputtering Film thickness: Ru film 10 nm, Ta film 30 nm
DC applied power: 200W
Sputtering gas: Ar
Gas flow rate: 15sccm
Gas pressure: 0.02 Pa or less Substrate heating: None

After the upper electrode 40 is formed, the upper electrode 40 and the magnetic tunnel junction layer 30 are etched.
The etching conditions for the upper electrode 40 and the magnetic tunnel junction layer 30 are as follows.
Mask: Photoresist Etching equipment: RIE (Reactive Ion Etching) method Etching gas: Methanol Overetching amount: 120-150%
Substrate heating: None

As the cover film 42, a silicon nitride film is formed so as to cover the lower electrode 28, the magnetic tunnel junction layer 30, and the upper electrode 40.
The conditions for forming the cover film 42 are as follows.
Film formation method: Thermal CVD (Chemical Vapor Deposition) method Film thickness: 30 nm
Gas: NH ₃ (100 sccm), SiH ₄ (250 sccm)
Gas pressure: 0.5Pa
Substrate temperature: 250 ° C

  Thereafter, an insulating film 46 is formed so as to cover the cover layer 42. Plug metal layers 48a and 48b penetrating the insulating film 46 and the cover film 42 are formed.

  As shown in FIG. 4B, the lengths La and Lb of the produced magnetic tunnel junction elements 50a and 50b are 100 nm and 80 nm, respectively. The width W of the magnetic tunnel junction elements 50a and 50b is 140 nm. The distance between the upper electrodes 40 of the magnetic tunnel junction elements 50a and 50b is L.

FIG. 5 is a diagram illustrating a resistance value with respect to the interval L in the comparative example. The resistance value Ra is a resistance value when the magnetic tunnel junction element 50a is in a high resistance state (a state where the magnetization fixed layer and the magnetization free layer are magnetized in opposite directions). The intervals L were set to 5 nm, 10 nm, 15 nm, and 20 nm. When an isolated magnetic tunnel junction element with La = 100 nm and W = 140 nm is manufactured and the resistance value Ra is measured, it is 11Ω / μm ² . Therefore, the resistance value Ra should be 11 Ω / μm ² regardless of the interval L, but the resistance value Ra becomes small when the interval L is 10 nm or less. This is because an etching product at the time of etching the upper electrode 40 and the magnetic tunnel junction layer 30 remains in the region 62 of FIG. As a result, the upper electrode 40 and the lower electrode 28 are short-circuited via the etching product. Note that generation of an etching product resulting from etching is a problem that may occur regardless of the materials and etching conditions exemplified in the comparative example. As described above, when a plurality of magnetic tunnel junction elements are formed, if the interval cannot be reduced, the chip size increases and the cost increases. In the first embodiment, such a problem is solved.

  FIG. 6 is a cross-sectional view of the MRAM cell according to the first embodiment. A transistor Tr is formed on the silicon semiconductor substrate 10. The transistor Tr includes a gate electrode 12, a source region 13, and a drain region 14. The gate electrode 12 is formed on the semiconductor substrate 10 (or a diffusion region in the semiconductor substrate) via a gate insulating film. The gate electrode 12 also functions as the word line WL.

  A source region 13 and a drain region 14 having a conductivity type opposite to that of the semiconductor substrate 10 are formed in the semiconductor substrate 10 on both sides of the gate electrode 12. On the semiconductor substrate 10, a plug metal layer 15 and a wiring layer 16 penetrating the interlayer insulating film are laminated. In FIG. 6, the interlayer insulating film is not shown. The source region 13 is connected to the source line SL formed by the wiring layer 16 via the plug metal layer 15 and the wiring layer 16. The drain region 14 is connected to one of the magnetic tunnel junctions 60 via one or more plug metal layers 15 and wiring layers 16. The other of the magnetic tunnel junctions 60 is connected to a bit line BL formed from the wiring layer 16. A logic circuit may be formed on the chip including the MRAM using the same wiring layer 16 or the like.

  FIG. 7A is a cross-sectional view of the vicinity of the magnetic tunnel junction of Example 1, and FIG. 7B is a plan view. As shown in FIG. 7A, a plug metal layer 22 penetrating the insulating film 20 is formed. A base layer 24 is formed on the insulating film 20. A recess 26 is formed on the plug metal layer 22 of the base layer 24. Lower electrodes 28 are formed on the inner surface of the recess 26 of the base layer 24 and on the base layer 24 on both sides of the recess 26. A recess of the lower electrode 28 is formed in the recess of the base layer 24. The lower electrodes 28 on both sides of the recess 26 are electrically connected via the lower electrode 28 formed in the recess 26. A magnetic tunnel junction layer 30 is formed on the inner surface of the concave portion of the lower electrode 28 and the lower electrode 28. The magnetic tunnel junction layer 30 includes a tunnel barrier layer 34, a magnetization fixed layer 32 and a magnetization free layer 36 that sandwich the tunnel barrier layer 34 in the vertical direction. The magnetic tunnel junction layer 30 may be formed on at least the lower electrodes 28 on both sides of the recess 26, and the magnetic tunnel junction layer 30 may not be formed in the recess 26.

  Upper electrodes 40 are respectively formed on the magnetic tunnel junction layers 30 on both sides of the recess 26. Above the recess 26, the upper electrode 40 is electrically separated by the recess 26. The upper electrode 40 is not formed on at least a part (for example, the bottom surface) of the recess 26. An insulating film 44 is embedded in the recess 26. The upper surfaces of the insulating film 44 and the upper electrode 40 are planarized. The upper electrode 40, the magnetic tunnel junction layer 30, and the lower electrode 28 are processed into a predetermined shape. An insulating cover layer 42 is formed so as to cover the upper electrode 40 and the insulating film 44. An insulating film 46 that covers the cover layer 42 is formed. Plug metal layers 48 a and 48 b that penetrate through the insulating film 46 and the cover layer 42 and reach the upper electrode 40 are formed.

  FIG. 7B is a plan view showing the upper electrode 40, the upper surface of the insulating film 44, and the recess 26. As shown in FIG. 7B, the length La of the magnetic tunnel junction element 50a is larger than the length Lb of the magnetic tunnel junction element 50b. Thus, the area of the upper electrode 40 is different on both sides of the recess 26.

  In order to form the magnetic tunnel junction elements 50a and 50b, the upper electrodes 40 on both sides of the recess 26 are formed so as to be electrically separated from each other. For this reason, the upper electrode 40 is prevented from being formed in at least a part of the recess 26. The formation conditions of the upper electrode 40 were examined. FIG. 8A is a cross-sectional view when the upper electrode 40 is formed in the recess 26. The depth H of the recess 26 was changed to 100 nm and the length L was changed. As the upper electrode 40, a Ta film having a film thickness of 40 nm was used. The formation conditions of the upper electrode 40 are the same as those in the comparative example except for the DC applied power. The ratio A / B × 100 between the film thickness A of the upper electrode 40 and the film thickness B of the upper electrode 40 on the base layer 24 when the depth of the side wall of the recess 26 is 50% was defined as the coverage (%). In FIG. 8A, the lower electrode 28 and the magnetic tunnel junction layer 30 are not shown, but the depth H and length L of the recess 26 form the lower electrode 28 and the magnetic tunnel junction layer 30. It is the value after

  FIG. 8B is a diagram showing the coverage with respect to the length L of the recess. The length L of the recess 26 is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 and 40 nm. Conditions A, B, and C are 120 W, 150 W, and 200 W, respectively, of the DC applied power when the upper electrode 40 is formed. As shown in FIG. 8B, in any of the conditions A to C, when the length L of the recess 26 is reduced, the coverage is zero. In particular, the coverage is likely to be zero when the direct-current applied power is small. Thus, by setting the depth H and length L of the recess 26 and the formation conditions of the upper electrode 40, the upper electrodes 40 on both sides of the recess 26 can be electrically separated.

  Next, the manufacturing method of the magnetic tunnel junction part of Example 1 is demonstrated. FIG. 9A to FIG. 11B are cross-sectional views showing a method for manufacturing the magnetic tunnel junction part of the first embodiment. As shown in FIG. 9A, the insulating film 20 is formed from a silicon oxide film. The insulating film 20 may be an insulating film such as a low-k insulating film. A plug metal layer 22 penetrating the insulating film 20 is formed using copper. The plug metal layer 22 may be a metal such as tungsten, for example. A base layer 24 is formed of a silicon oxide film on the insulating film 20 and the plug metal layer 22 using the CVD method. The base film 24 may be an insulating film such as a low-k insulating film. As shown in FIG. 9B, a recess 26 penetrating the base layer 24 is formed. The bottom surface of the recess 26 is in contact with the plug metal layer 22. The depth of the recess 26 can be controlled by, for example, a processing time when polishing the surface of the base layer 24 using a CMP (Chemical Mechanical Polishing) method. In Example 1, the depth of the recess 26 is 100 nm.

  As shown in FIG. 9C, the lower electrode 28 is formed in the recess 26 and on the base layer 24. The formation conditions of the lower electrode 28 are the same as those in FIG.

The following ranges can also be used as the formation conditions of the lower electrode 28.
Layer structure: Ru film, Ta film from below Film thickness: Ru film 5-15 nm, Ta film 10-40 nm
Other conditions or other metals may be used to form the lower electrode 28.

  A magnetic tunnel junction layer 30 is formed in the recess 26 and on the lower electrode 28. The magnetic tunnel junction layer 30 includes a tunnel barrier layer 34, a magnetization fixed layer 32 and a magnetization free layer 36 that sandwich the tunnel barrier layer 34 in the vertical direction. The formation conditions of the magnetization fixed layer 32, the tunnel barrier layer 34, and the magnetization free layer 36 are the same as those in FIG.

The formation condition of the magnetization fixed layer 32 can also be in the following range.
Film thickness: PtMn film 5-20 nm, CoFe film 1.5-3.5 nm, Ru film 0.5-1.0 nm, CoFeB film 1.0-3.0 nm
DC applied power: 200-800W
Gas flow rate: 15-30sccm

The formation conditions of the tunnel barrier layer 34 can also be in the following ranges.
Film thickness: 0.5-1.5nm
Gas flow rate: 30sccm

The formation conditions of the magnetization free layer 36 can also be in the following ranges.
Film thickness: CoFeB film 1.0-2.0 nm
DC applied power: 200-300W
Gas flow rate: 15-30sccm
The formation of the magnetization fixed layer 32 and the magnetization free layer 36 may use other conditions or other ferromagnetic materials. The tunnel barrier layer 34 may be formed under other conditions or other nonmagnetic materials.

  An upper electrode 40 is formed in the recess 26 and on the magnetic tunnel junction layer 30. The formation conditions of the upper electrode 40 are the same as those in FIG.

The formation conditions of the upper electrode 40 can also be in the following ranges.
Layer structure: Ta film, Ru film, Ta film from bottom Thickness: Ta film 80 nm, Ru film 10 nm, Ta film 1 nm
DC applied power: 200-1000W
Gas flow rate: 10-30sccm
The formation of the upper electrode 40 may use other conditions or other metals.

  If the surface morphology deteriorates in the process from the lower electrode 28 to the upper electrode 40, the characteristics deteriorate. Therefore, the process from the lower electrode 28 to the upper electrode 40 is preferably performed without being exposed to the atmosphere.

As shown in FIG. 10A, an insulating film 44 is formed using a silicon oxide film so that the recess 26 is embedded.
The formation conditions of the insulating film 44 are as follows.
Film formation method: Thermal CVD (Chemical Vapor Deposition) method Film thickness: 50 to 80 nm
Gas: N ₂ O (50-100 sccm), SiH ₄ (250 sccm)
Gas pressure: 0.1-1.0 Pa
Substrate temperature: 350 ° C
The insulating film 44 may be formed using other conditions or other insulators such as a silicon nitride film.

  As shown in FIG. 10B, the insulating film 44 is polished until the upper surface of the upper electrode 40 is exposed using the CMP method. As shown in FIG. 10C, the upper electrode 40, the magnetic tunnel junction layer 30, and the lower electrode 28 are etched using a photoresist or a hard mask.

  As shown in FIG. 11A, a silicon nitride film is used as the cover film 42 so as to cover the lower electrode 28, the magnetic tunnel junction layer 30, and the upper electrode 40. The method for forming the cover film 42 is the same as in FIG.

Note that the conditions for forming the cover film 42 can also be in the following ranges.
Film thickness: 10-30nm
_{Gas: NH 3 (50~100sccm), SiH} 4 (250sccm)
Gas pressure: 0.1-1.0 Pa
The cover film 42 may be formed using other conditions or an insulating film other than the silicon nitride film.

  As shown in FIG. 11B, an insulating film 46 is formed using a silicon oxide film so as to cover the cover film 42. The insulating film 46 may be an insulating film such as a low-k insulating film. Plug metal layers 48 a and 48 b that penetrate through the insulating film 46 and the cover layer 42 and are electrically connected to the upper electrode 40 are formed. Thus, the magnetic tunnel junction 60 according to the first embodiment is completed.

  12A is a plan view of the magnetic tunnel junction part of Example 1, and FIG. 12B is a diagram showing a resistance value Ra with respect to L. FIG. The resistance value Ra is a resistance value when the magnetic tunnel junction element 50a is in a high resistance state (a state where the magnetization fixed layer and the magnetization free layer are magnetized in opposite directions). As shown in FIG. 12A, the lengths of the magnetic tunnel junction elements 50a and 50b (the length of the upper electrode 40) L1 and L2 were set to 100 nm and 80 nm, respectively. The width W of the magnetic tunnel junction elements 50a and 50b was 140 nm. The length L of the recess 26 after forming the lower electrode 28 and the magnetic tunnel junction layer 30 was 5 nm, 10 nm, 15 nm, and 20 nm.

  In FIG. 12B, the result of the comparative example shown in FIG. 5 is indicated by a broken line and the result of Example 1 is indicated by a solid line. As shown in FIG. 12B, in the comparative example, the magnetic tunnel junction element was short-circuited when the distance L was 10 nm or less. On the other hand, in Example 1, the resistance value Ra is constant up to the length L of 5 nm.

  In the first embodiment, the recesses 26 electrically separate both sides of the recesses 26 of the plurality of upper electrodes. Thus, unlike the comparative example, the magnetic tunnel junction elements 50a and 50b are not separated by etching. Therefore, as shown in FIG. 12B, the interval between the magnetic tunnel junction elements 50a and 50b can be narrowed. Therefore, the chip size can be reduced, and the cost can be reduced.

  In the first embodiment, the MRAM that can store multiple values in one memory cell has been described as an example. However, when a plurality of magnetic tunnel junction elements having a common lower electrode are formed close to each other, the structure and method of the first embodiment are used. Can be used.

  When applied to an MRAM that can store multiple values in one memory cell as in the first embodiment, it is preferable that the area of the magnetic tunnel junction layer be different on both sides of the recess 26 as shown in FIG.

  6 and 7A, an example in which the plurality of upper electrodes 40 are connected to the bit line BL and the lower electrode 28 is connected to the word line WL has been described. The plurality of upper electrodes 40 may be electrically connected to one of the bit line BL and the word line WL, and the lower electrode 28 may be connected to the other of the bit line BL and the word line WL. Thereby, a plurality of magnetic tunnel junction elements can be connected in parallel between the bit line and the word line.

  Furthermore, it is preferable to include a transistor in which the lower electrode 28 or the plurality of upper electrodes 40 are connected to the drain, the source line SL is connected to the source, and the word line WL is connected to the gate. Thus, a memory cell can be formed using the transistor Tr and a plurality of magnetic tunnel junction elements.

  Furthermore, the bottom surface of the recess 26 of the base layer 24 is the upper surface of the plug metal layer 22 that penetrates the insulating film 20, so that the chip area can be reduced.

  In the first embodiment, the base layer 24 is an insulating film, but the base layer 24 may be a metal, for example. For example, the plug metal layer 22 may be used as a base film, and a recess may be formed on the upper surface of the plug metal layer 22.

  In addition, an insulating film 44 is formed in the recess 26 to electrically isolate the plurality of upper electrodes 40. Thereby, the electrical separation between the upper electrodes 40 becomes more reliable.

  Example 2 is an example in which the underlying electrode is not provided and the lower electrode 28 is provided with the recess 26. FIG. 13 is a cross-sectional view of the magnetic tunnel junction element according to the second embodiment. As shown in FIG. 13, the lower electrode 28 includes a recess 26 on the upper surface. The magnetic tunnel junction layer 30 is formed on the inner surface of the recess of the lower electrode 28 and on the lower electrode 28. The upper electrode 40 is formed on the magnetic tunnel junction layer 30 on both sides of the concave portion of the magnetic tunnel junction layer 30. The upper electrode 40 is electrically separated by a recess.

  Even in the structure of Example 2, the magnetic tunnel junction elements 50a and 50b are not separated by etching as in the comparative example. Therefore, as shown in FIG. 12B, the interval between the magnetic tunnel junction elements 50a and 50b can be narrowed. Therefore, the chip size can be reduced, and the cost can be reduced.

  Note that the recess 26 formed in the lower electrode 28 may have a reverse taper structure in which the upper part is smaller than the lower part. Thereby, it becomes difficult to form the upper electrode 40 on the inner surface of the recess, and the upper electrode 40 can be easily electrically separated by the recess.

  In Example 1 and Example 2, as shown in FIGS. 3A to 3C, the magnetization direction of the magnetization free layer 36 is changed by the spin injection method. Thereby, current consumption can be reduced as compared with the method of changing the magnetization direction of the magnetization free layer 36 using a magnetic field. In addition, the chip size can be reduced.

  In the first and second embodiments, two magnetic tunnel junction elements have been described as an example. However, by using a recess and dividing the upper electrode 40 into three or more, a plurality of three or more magnetic tunnel junction elements are manufactured. can do.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Regarding the embodiment including Examples 1 and 2, the following additional notes are disclosed.
APPENDIX 1: A magnetic tunnel junction including a lower electrode having a recess on the upper surface, and a magnetization barrier layer and a magnetization free layer formed on the lower electrode on both sides of the recess and sandwiching the tunnel barrier layer vertically. A magnetic device comprising: a layer; and a plurality of upper electrodes formed on the magnetic tunnel junction layer and electrically separated above the recess.
Appendix 2: The magnetic device according to Appendix 1, wherein areas of the plurality of upper electrodes are different from each other.
Appendix 3: The plurality of upper electrodes are electrically connected to one of a bit line and a word line, and the lower electrode is connected to the other of the bit line and the word line. The magnetic device described.
(Supplementary Note 4) A lower layer is formed on the inner surface of the recess of the base layer and on the base layer, and the recess of the lower electrode is formed in the recess of the base layer. The magnetic device according to any one of appendices 1 to 3, wherein the magnetic device is formed.
Appendix 5: An insulating film and a plug metal layer vertically penetrating the insulating film, the underlayer being formed on the insulating film, and a lower surface of the recess of the underlayer being an upper surface of the plug metal layer The magnetic device as set forth in appendix 4, wherein:
(Supplementary note 6) The magnetic device according to Supplementary note 3, comprising a transistor in which the lower electrode or the plurality of upper electrodes are connected to a drain, a source line is connected to a source, and a word line is connected to a gate.
Appendix 7: The magnetic device according to Appendix 3 or 6, wherein the base layer is formed on an insulating film, and the bottom surface of the recess of the base layer is an upper surface of a plug metal layer that penetrates the insulating film. .
Supplementary Note 8: The magnetic device according to any one of Supplementary notes 1 to 7, further comprising an insulating film that is formed in the recess and electrically separates the plurality of upper electrodes.
(Supplementary note 9) The magnetic device according to any one of Supplementary notes 1 to 8, wherein a magnetization direction of the magnetization free layer is changed by a spin injection method.
(Supplementary Note 10) Magnetism including a step of forming a lower electrode having a recess on an upper surface, and a tunnel barrier layer and a magnetization fixed layer and a magnetization free layer sandwiching the tunnel barrier layer vertically on the lower electrode on both sides of the recess Forming a tunnel junction layer; and forming a plurality of upper electrodes electrically isolated above the recesses on the magnetic tunnel junction layer. .

20 Underlayer 22 Plug Metal Layer 24 Underlayer 26 Recess 28 Lower Electrode 30 Magnetic Tunnel Junction Layer 32 Magnetization Fixed Layer 34 Tunnel Barrier Layer 36 Magnetization Free Layer 40 Upper Electrode

Claims (6)

A lower electrode having a recess on the upper surface;
A magnetic tunnel junction layer formed on the lower electrode on both sides of the recess, and including a tunnel barrier layer and a magnetization fixed layer and a magnetization free layer sandwiching the tunnel barrier layer vertically;
A plurality of upper electrodes formed on the magnetic tunnel junction layer and electrically separated above the recess;
A magnetic device comprising:   The magnetic device according to claim 1, wherein areas of the plurality of upper electrodes are different from each other. The plurality of upper electrodes are electrically connected to one of a bit line and a word line,
The magnetic device according to claim 2, wherein the lower electrode is connected to the other of the bit line and the word line. Comprising a base layer with a recess,
The said lower electrode is formed in the inner surface of the recessed part of the said base layer, and the said base layer, The recessed part of the said lower electrode is formed in the recessed part of the said base layer, The Claim 1 to 3 characterized by the above-mentioned. The magnetic device according to any one of claims. Comprising an insulating film and a plug metal layer vertically penetrating the insulating film;
5. The magnetic device according to claim 4, wherein the underlayer is formed on the insulating film, and a lower surface of the concave portion of the underlayer is an upper surface of the plug metal layer. Forming a lower electrode having a recess on the upper surface;
Forming a magnetic tunnel junction layer including a tunnel barrier layer and a magnetization fixed layer and a magnetization free layer sandwiching the tunnel barrier layer vertically on the lower electrode on both sides of the recess;
Forming a plurality of upper electrodes electrically isolated above the recesses on the magnetic tunnel junction layer;
A method for manufacturing a magnetic device, comprising:

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