U.S. patent application number 13/932974 was filed with the patent office on 2013-10-31 for magnetoresistive effect element, magnetic memory, and method of manufacturing magentoresistive effect element.
The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Koji Ando, Tadaomi Daibou, Akio Fukushima, Yutaka Hashimoto, Tadashi Kai, Eiji Kitagawa, Hitoshi Kubota, Taro Nagahama, Makato Nagamine, Toshihiko Nagase, Katsuya Nishiyama, Masaru Tokou, Koji Ueda, Kay Yakushiji, Hiroaki Yoda, Shinji Yuasa.
Application Number | 20130288397 13/932974 |
Document ID | / |
Family ID | 45816990 |
Filed Date | 2013-10-31 |
United States Patent
Application |
20130288397 |
Kind Code |
A1 |
Kitagawa; Eiji ; et
al. |
October 31, 2013 |
MAGNETORESISTIVE EFFECT ELEMENT, MAGNETIC MEMORY, AND METHOD OF
MANUFACTURING MAGENTORESISTIVE EFFECT ELEMENT
Abstract
According to one embodiment, a magnetoresistive effect element
includes a first magnetic layer including perpendicular anisotropy
to a film surface and an invariable magnetization direction, the
first magnetic layer having a magnetic film including an element
selected from a first group including Tb, Gd, and Dy and an element
selected from a second group including Co and Fe, a second magnetic
layer including perpendicular magnetic anisotropy to the film
surface and a variable magnetization direction, and a nonmagnetic
layer between the first magnetic layer and the second magnetic
layer. The magnetic film includes amorphous phases and crystals
whose particle sizes are 0.5 nm or more.
Inventors: |
Kitagawa; Eiji;
(Yokohama-shi, JP) ; Daibou; Tadaomi;
(Yokohama-shi, JP) ; Hashimoto; Yutaka;
(Kawasaki-shi, JP) ; Tokou; Masaru; (Yokohama-shi,
JP) ; Kai; Tadashi; (Tokyo, JP) ; Nagamine;
Makato; (Tokyo, JP) ; Nagase; Toshihiko;
(Yokohama-shi, JP) ; Nishiyama; Katsuya;
(Yokohama-shi, JP) ; Ueda; Koji; (Kamakura-shi,
JP) ; Yoda; Hiroaki; (Kawasaki-shi, JP) ;
Yakushiji; Kay; (Tsukuba-shi, JP) ; Yuasa;
Shinji; (Tsukuba-shi, JP) ; Kubota; Hitoshi;
(Tsukuba-shi, JP) ; Nagahama; Taro; (Tsukuba-shi,
JP) ; Fukushima; Akio; (Tsukuba-shi, JP) ;
Ando; Koji; (Tsukuba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Tokyo |
|
JP |
|
|
Family ID: |
45816990 |
Appl. No.: |
13/932974 |
Filed: |
July 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13234720 |
Sep 16, 2011 |
8502331 |
|
|
13932974 |
|
|
|
|
Current U.S.
Class: |
438/3 |
Current CPC
Class: |
H01L 27/228 20130101;
G11C 11/161 20130101; H01L 29/82 20130101; H01F 10/133 20130101;
H01L 43/12 20130101; H01F 41/307 20130101; B82Y 40/00 20130101;
H01L 43/08 20130101; H01F 10/3286 20130101; H01L 43/10
20130101 |
Class at
Publication: |
438/3 |
International
Class: |
H01L 43/10 20060101
H01L043/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2010 |
JP |
2010-210180 |
Claims
1. A method for manufacturing a magnetoresistive effect element,
comprising: depositing stacked layers on a substrate, the stacked
layers comprising a first magnetic material having a multi-layer
structure depositing alternately a first film and a second film, a
second magnetic material, and a nonmagnetic material deposited
between the first magnetic layer and the second magnetic layer, the
first film comprising an element selected from a first group
including Tb, Dy, and Gd and an element selected from a second
group including Co and Fe, and the second film comprising an
element selected from the second group; and, processing the stacked
layer to form a magnetoresistive effect element comprising a first
magnetic layer having perpendicular magnetic anisotropy to a film
surface, a second magnetic layer having magnetic anisotropy in the
direction perpendicular to the film surface, and a nonmagnetic
layer provided between the first magnetic layer and the second
magnetic layer.
2. The method for manufacturing the magnetoresistive effect element
of claim 1, wherein the first magnetic layer comprises amorphous
phases and crystals whose particle sizes are 0.5 nm or more.
3. The method for manufacturing the magnetoresistive effect element
of claim 1, wherein the first film has a film thickness of 2 nm or
less.
4. The method for manufacturing the magnetoresistive effect element
of claim 1, wherein the first film includes 25 atomic % or more of
an element selected from the first group.
5. The method for manufacturing the magnetoresistive effect element
of claim 1, further comprising: forming, during formation of the
stacked layer, an interface layer comprising a third film at a side
of the nonmagnetic material, a fourth film at side of the
multi-layer structure, and a fifth film provided between the third
film and the fourth film, between the nonmagnetic material and the
multi-layer film, the third film comprising at least two elements
selected from a third group including Co, Fe, and B, the fourth
film comprising at least two elements selected from the third
group, and the fifth film comprising an element selected from a
fourth group including Ta, W, Nb, and Mo.
6. The method for manufacturing the magnetoresistive effect element
of claim 1, further comprising: forming, during formation of the
stacked layer, an interface layer comprising a third film at a side
of the nonmagnetic material and a fourth film between the third
film and the multi-layer film, between the nonmagnetic material and
the multi-layer film, the third film comprising at least two
elements selected from a third group including Co, Fe, and B, and
the fourth film comprising an element selected from a fourth group
including Ta, W, Nb, and Mo.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/234,720, filed Sep. 16, 2011, which is based upon and
claims the benefit of priority from prior Japanese Patent
Application No. 2010-210180, filed Sep. 17, 2010, the entire
contents of each which are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a
magnetoresistive effect element, a magnetic memory, and a method of
manufacturing magnetoresistive effect element.
BACKGROUND
[0003] In a spin-transfer-torque MRAM, a magnetoresistive effect
element using a perpendicular magnetic film is effective for
reducing a write current and increasing the capacity of the
memory.
[0004] In the magnetoresistive effect element used in the
spin-transfer-torque MRAM, a material of a perpendicular magnetic
film used in a reference layer is preferably a material which can
be designed to reduce saturation magnetization of a reference layer
in view of shift adjustment of the switching field of the storage
layer.
[0005] For example, in an amorphous TbCoFe film, the saturation
magnetization of the magnetic film can be changed by adjusting a
composition ratio between Tb and CoFe. Therefore, the amorphous
TbCoFe film is a promising material as a reference layer of a
perpendicular magnetic film.
[0006] However, the amorphous TbCoFe film has a low level of heat
resistance in perpendicular magnetic anisotropy. For this reason,
heat treatment for crystallizing a member of a magnetoresistive
effect element (such as a tunnel barrier layer) cannot be executed
with a sufficient amount of heat (heating temperature). Therefore,
it used to be difficult to improve element characteristics of the
magnetoresistive effect element using the amorphous TbCoFe
film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view illustrating a basic
structure of a magnetoresistive effect element according to an
embodiment;
[0008] FIG. 2 is a cross-sectional view illustrating a structure of
a magnetoresistive effect element according to the first
embodiment;
[0009] FIG. 3 is a figure of a step for explaining a method for
manufacturing a magnetoresistive effect element according to the
embodiment;
[0010] FIG. 4 is a figure of a step for explaining a method for
manufacturing the magnetoresistive effect element according to the
embodiment;
[0011] FIG. 5 is a graph illustrating magnetic characteristics of
the magnetoresistive effect element according to the
embodiment;
[0012] FIG. 6A is a figure illustrating a cross-sectional structure
of a magnetic layer of the magnetoresistive effect element;
[0013] FIG. 6B is a figure illustrating a cross-sectional structure
of the magnetic layer of the magnetoresistive effect element;
[0014] FIG. 7 is a figure illustrating a planar structure of a
magnetic layer of the magnetoresistive effect element;
[0015] FIG. 8 is a graph illustrating relationship between magnetic
characteristics of the magnetic layer and an element concentration
in the magnetic layer;
[0016] FIG. 9 is a graph illustrating relationship between magnetic
characteristics of the magnetic layer and an element concentration
in the magnetic layer;
[0017] FIG. 10 is a graph illustrating relationship between
magnetic characteristics of the magnetic layer and an element
concentration in the magnetic layer;
[0018] FIG. 11 is a graph illustrating relationship between
magnetic characteristics of the magnetic layer and an element
concentration in the magnetic layer;
[0019] FIG. 12 is a figure illustrating cross-sectional structures
of the magnetic layer of the magnetoresistive effect element;
[0020] FIG. 13 is a figure illustrating an exemplary structure of a
magnetoresistive effect element;
[0021] FIG. 14 is a figure illustrating magnetic characteristics of
the magnetic layer;
[0022] FIG. 15A is a graph illustrating an analysis result of
EELS;
[0023] FIG. 15B is a graph illustrating an analysis result of
EELS;
[0024] FIG. 16A is a graph illustrating an analysis result of
EELS;
[0025] FIG. 16B is a graph illustrating an analysis result of
EELS;
[0026] FIG. 17 is a cross-sectional view illustrating a structure
of a modification example of the magnetoresistive effect element
according to the first embodiment;
[0027] FIG. 18 is a cross-sectional view illustrating a structure
of a magnetoresistive effect element according to the second
embodiment;
[0028] FIG. 19 is a cross-sectional view illustrating a structure
of a magnetoresistive effect element according to the second
embodiment;
[0029] FIG. 20 is a cross-sectional view illustrating a structure
of a magnetoresistive effect element according to the third
embodiment;
[0030] FIG. 21 is a circuit diagram illustrating an MRAM, i.e., an
application example of the embodiment;
[0031] FIG. 22 is a cross-sectional view illustrating a structure
of a memory cell of the MRAM to which the embodiment is
applied;
[0032] FIG. 23 is a cross-sectional view illustrating a step of a
method for manufacturing the memory cell of the MRAM to which the
embodiment is applied; and
[0033] FIG. 24 is a cross-sectional view illustrating a step of the
method for manufacturing the memory cell of the MRAM to which the
embodiment is applied.
DETAILED DESCRIPTION
[0034] Hereinafter, a magnetoresistive effect element according to
each embodiment will be described in detail with reference to the
drawings. In the following description, constituent elements having
the same functions and/or configurations are denoted with the same
reference numbers, and repeated explanation thereabout will be made
as necessary.
[0035] In general, according to one embodiment, a magnetoresistive
effect element includes a first magnetic layer including
perpendicular anisotropy to a film surface and an invariable
magnetization direction, the first magnetic layer having a magnetic
film including an element selected from a first group including Tb,
Gd, and Dy and an element selected from a second group including Co
and Fe; a second magnetic layer including perpendicular magnetic
anisotropy to the film surface and a variable magnetization
direction; and a nonmagnetic layer between the first magnetic layer
and the second magnetic layer. The magnetic film includes amorphous
phases and crystals whose particle sizes are 0.5 nm or more.
Embodiment
(1) Basic Example
[0036] A basic configuration of a magnetoresistive effect element
according to the present embodiment will be explained with
reference to FIG. 1.
[0037] The magnetoresistive effect element according to the present
embodiment includes magnetic layers 91, 92 and a nonmagnetic layer
93 provided between the two magnetic layers 91, 92.
[0038] The two magnetic layers 91, 92 are perpendicular magnetic
films (magnetization film), and the magnetization of the magnetic
layers 91, 92 is in a direction perpendicular to the film
surface.
[0039] The magnetization direction of one of the two magnetic
layers 91, 92, i.e., the magnetic layer 92, is invariable (fixed),
and the magnetization direction of the other of the two magnetic
layers 91, 92, i.e., the magnetic layer 91, is variable.
[0040] When the magnetization direction of a magnetic layer is
changed, a current Iw greater than or equal to a magnetization
reversal threshold value is passed through the magnetoresistive
effect element 1. The magnetization direction of the magnetic layer
91 whose magnetization is variable is changed by spin transfer
torque. In other words, when spin-polarized electrons act on the
magnetization (spin) of the magnetic layer 91, the magnetization
direction of the magnetic layer 91 is changed. The current Iw
including the spin polarized electron flow in both directions in
the magnetoresistive effect element 1 in accordance with the
direction in which the magnetization direction is changed.
[0041] A part of at least one of the two magnetic layers 91, 92 (in
this case, the magnetic layer 92) has a magnetic film 21 including
at least one element selected from a group (first group) including
terbium (Tb), gadolinium (Gd), and dysprosium (Dy) and at least one
element selected from a group (second group) including cobalt (Co)
and iron (Fe). The magnetic film 21 includes amorphous 29 and
crystal 28. The plurality of crystals 28 in the magnetic film 21
are, for example, crystals (which may also be referred to as
microcrystals) having a particle size (diameter, maximum dimension)
of 5 .ANG. (0.5 nm) or more.
[0042] For example, the magnetic film 21 in the magnetic layer 92
is a TbCoFe film 21. The TbCoFe film 21 serving as the magnetic
film 21 includes amorphous phases 29 including at least one of
elements of Tb, Co, and Fe and crystals (crystal particles or
crystal phase) 28 including at least one of elements of Co and Fe.
For example, the crystals 28 in the TbCoFe film 21 has at least one
of crystal structures having a lattice spacing (first lattice
spacing) of 1.2 to 1.6 .ANG. (0.12 to 0.16 nm) and a lattice
spacing (second lattice spacing) of 1.9 to 2.3 .ANG. (0.19 to 0.23
nm) in a film cross-sectional direction.
[0043] It should be noted that both of the magnetic layers 91, 92
in the magnetoresistive effect element 1 may have the magnetic film
21 including the amorphous phases 29 and the crystals 28.
[0044] As described above, the magnetic film 21 in the magnetic
layer 92 includes the crystals 28 and the amorphous phases 29, and
this can prevent deterioration of the magnetic characteristics of
the magnetic film (such as TbCoFe film) 21 due to the heat
treatment performed at a high temperature (such as 300.degree. C.
or more). Therefore, according to the magnetoresistive effect
element according to the present embodiment, the heat resistivity
of the element can be improved, and crystallization of the
constituent member of the element can be accelerated by heat
treatment with a sufficient amount of heat.
[0045] Therefore, in the magnetoresistive effect element according
to the present embodiment, element characteristics can be
improved.
(2) First Embodiment
[0046] A magnetoresistive effect element according to the first
embodiment will be explained with reference to FIGS. 2 to 17.
(a) Structure
[0047] A structure of the magnetoresistive effect element according
to the first embodiment will be explained with reference to FIG.
2.
[0048] The magnetoresistive effect element 1A according to the
present embodiment is a magnetic tunnel junction (MTJ) element
1A.
[0049] The MTJ element 1A according to the present embodiment
includes a lower electrode 51, an underlayer (foundation layer) 40,
a first magnetic layer 10, a nonmagnetic layer 30, a second
magnetic layer 20, and an upper electrode 52.
[0050] In the MTJ element 1A according to the present embodiment,
the first and second magnetic layers 10, 20 have large
perpendicular magnetic anisotropy to the film surface, and the
magnetization directions of the first and second magnetic layers
10, 20 are perpendicular to the film surface. In other words, the
first and second magnetic layers 10, 20 are perpendicular magnetic
films.
[0051] The magnetization direction of the first magnetic layer 10
is variable. The magnetization direction of the second magnetic
layer 20 is invariable. In the present embodiment, the magnetic
layer whose magnetization direction is variable is referred to as a
recording layer (a magnetization free layer, a free layer, storage
layer), and the magnetic layer whose magnetization direction is in
invariable is referred to as a reference layer (which may also be
referred to as a magnetization invariable layer, a fixing
layer).
[0052] The magnetization direction of the recording layer 10 is
changed by spin torque transfer (supply of a current greater than
or equal to a reversal threshold value). In other words, when spin
polarized electrons act on the magnetization (spin) of the
recording layer 10, the magnetization direction of the recording
layer 10 is changed.
[0053] In this case, "the magnetization direction of the reference
layer 20 is invariable" or "the magnetization direction of the
reference layer 20 is fixed" means that the magnetization direction
of the reference layer 20 is not changed when a magnetization
reversal current (reversal threshold value) used to reverse the
magnetization direction of the recording layer 10 is passed through
the reference layer 20. Therefore, in the MTJ element 1, the
magnetic layer having a large reversal threshold value is used as
the reference layer 20, and the magnetic layer having a reversal
threshold value less than the reversal threshold value of the
reference layer 20 is used as the recording layer 10. In this
manner the MTJ element 1 is formed that includes recording layer 10
whose magnetization direction is variable and the reference layer
20 whose magnetization direction is invariable.
[0054] The MTJ element according to the present embodiment uses,
for example, the spin-transfer-torque magnetization reversal method
to reverse the relative magnetization direction between the
recording layer 10 and the reference layer 20.
[0055] When the magnetization direction of the recording layer 10
is caused to be in parallel to the magnetization direction of the
reference layer 20, i.e., when the magnetization direction of the
recording layer 10 is caused to be the same as the magnetization
direction of the reference layer 20, a current flowing from the
recording layer 10 to the reference layer 20 is supplied to the MTJ
element 1A. In this case, electrons move from the reference layer
20 to the recording layer 10 via the tunnel barrier layer 30.
Majority electrons (spin polarized electrons) passing through the
reference layer 20 and the tunnel barrier layer 30 have the same
direction as the direction of the magnetization (spin) of the
reference layer 20. The spin angular momentum (spin torque) of the
spin polarized electrons is applied to the magnetization of the
recording layer 10, whereby the magnetization direction of the
recording layer 10 is reversed. In this parallel arrangement, the
resistance of the MTJ element 1 becomes the smallest.
[0056] When the magnetization direction of the recording layer 10
is caused to be in antiparallel to the magnetization direction of
the reference layer 20, i.e., when the magnetization direction of
the recording layer 10 is caused to be opposite to the
magnetization direction of the reference layer 20, a current
flowing from the reference layer 20 to the recording layer 10 is
supplied to the MTJ element 1A. In this case, electrons move from
the recording layer 10 to the reference layer 20. Electrons having
spin antiparallel to the magnetization direction of the reference
layer 20 are reflected by the reference layer 20. The reflected
electrons are injected into the recording layer 10 as spin
polarized electrons. The spin angular momentum of the spin
polarized electrons (reflected electrons) is applied to the
magnetization of the recording layer 10, and the magnetization
direction of the recording layer 10 becomes opposite to the
magnetization direction of the reference layer 20 (antiparallel
arrangement). In this antiparallel arrangement, the resistance of
the MTJ element 1 becomes the largest.
[0057] The MTJ element 1A as shown in FIG. 2 is a top pin-type MTJ
element in which the reference layer 20 is stacked (layered) above
the recording layer 10 with the nonmagnetic layer 30 interposed
therebetween.
[0058] In the explanation below, the recording layer 10 and the
reference layer 20 have a multi-layer structure in the MTJ element
1A according to the present embodiment. In the explanation below, a
multi-layer structure (or stacked structure) of a member A and a
member B is denoted as "A/B". This means that the left side of "/",
i.e., the member "A", is stacked on the right side of "/", i.e.,
the member "B".
[0059] The lower electrode 51 is provided on a substrate (not
shown).
[0060] The lower electrode 51 has a multi-layer structure including
Ta/Cu/Ta.
[0061] The tantalum (Ta) film in the lowermost layer of the lower
electrode 51 has a film thickness of 150 .ANG. (15 nm). The Ta film
in the uppermost layer of the lower electrode 51 has a film
thickness of 200 .ANG. (20 nm). The copper (Cu) film sandwiched
between the two Ta films has a film thickness of 350 .ANG. (35
nm).
[0062] The underlayer 40 has an atom close-packed plane.
Accordingly, the recording layer 10 having the large perpendicular
magnetic anisotropy is formed. For example, the underlayer 40 has a
multi-layer structure including Pd/Ir/Ru. The film thickness of the
ruthenium (Ru) film in the lowermost layer is 50 .ANG. (5 nm). The
film thickness of the iridium (Ir) film is 50 .ANG. (5 nm). The
film thickness of the palladium (Pd) film is 2 .ANG. (0.2 nm). The
crystals in the Ru film is orianted in, e.g., the hcp (0001) plane
(c-axis direction), in order to control the crystal oriantations of
the Ir film and the Pd film. The Ir film and the Pd film have an
effect on the recording layer 10 to improve the perpendicular
magnetic anisotropy of the recording layer. When the film
thicknesses of the Ir film and the Pd film are adjusted, the
magnitude of the perpendicular magnetic anisotropy energy of the
recording layer 10 can be changed. It should be noted that the Pd
film of the underlayer 40 may be deemed as a part of the recording
layer 10.
[0063] The recording layer 10 is provided on the underlayer 40. The
recording layer 10 has a multi-layer structure including
CoFeB/Ta/CoB/Co. The cobalt (Co) film in the lowermost layer is in
contact with the upper surface of the Pd film of the underlayer 40.
The Co film 11 is a perpendicular magnetic film (perpendicular
magnetization film). The film thickness of the Co film 11 is, for
example, 5 .ANG. (0.5 nm). The cobalt-boron (CoB) film is provided
on the Co film 11. The film thickness of the CoB film is, for
example, 4 .ANG. (0.4 nm). A tantalum (Ta) film is provided on the
CoB film. For example, the Ta film has a film thickness of 3 .ANG.
(0.3 nm). The cobalt-steel-boron (CoFeB) film is provided on the Ta
film. The film thickness of the CoFeB film is, for example, 8 .ANG.
(0.8 nm).
[0064] A portion 12 between the perpendicular magnetic film (in
this case, Co film) 11 in the recording layer 10 and the
nonmagnetic layer 30, as seen in the multi-layer structure
including CoFeB/Ta/CoB, may be referred to as an interface layer.
It should be noted that, instead of the CoB film disposed between
the Ta film and the Co film, a CoFeB film may be used.
Alternatively, instead of CoFeB in the uppermost layer, an FeB film
may be used. Instead of the Ta film in the interface layer 12, a
tungsten (W) film, a niobium (Nb) film, or a molybdenum (Mo) film
may be used.
[0065] The CoFeB film formed on the Ta film is provided to increase
a difference of resistance (or MR ratio) between a case where the
relationship between the magnetization direction of the recording
layer 10 and the magnetization direction of the reference layer 20
is in parallel and a case where the relationship between the
magnetization direction of the recording layer 10 and the
magnetization direction of the reference layer 20 is in
antiparallel. However, when the thickness of the CoFeB film is
increased, the perpendicular magnetic anisotropy of the recording
layer 10 is deteriorated. Therefore, the film thickness is
preferably adjusted to an appropriate size. For example, the film
thickness of the CoFeB film on the Ta film is preferably within a
range of 7 to 12 .ANG. (0.7 to 1.2 nm).
[0066] Further, Ta film prevents Pd atoms from diffusing into the
nonmagnetic layer 30. As a result, the MR ratio of the MTJ element
improves. However, when the thickness of the Ta film increases, the
Ta atoms diffuse into the nonmagnetic layer 30, which reduces the
MR ratio. Therefore, the film thickness of the Ta film is
preferably less than or equal to 5 .ANG. (0.5 nm).
[0067] The CoB film (or the CoFeB film) and the Co film formed
below the Ta film contribute to the magnitude of the perpendicular
magnetic anisotropy of the recording layer 10. However, when the
film thicknesses of the CoB film (or the CoFeB film) and the Co
film are increased, the magnetization reversal current
(magnetization reversal threshold value) due to the spin transfer
torque with respect to the recording layer 10 increases. Therefore,
the film thicknesses of the CoB film (or the CoFeB film) and the Co
film are preferably less than or equal to 10 .ANG. (1.0 nm).
[0068] Naturally, it is to be understood that the CoFeB/Ta/CoB
layers have the perpendicular magnetic anisotropy.
[0069] For example, the nonmagnetic layer 30 is a magnesium oxide
(MgO) film. The nonmagnetic layer 30 using an insulating film such
as a MgO film is referred to as a tunnel barrier layer. In the
explanation below, the nonmagnetic layer is referred to as a tunnel
barrier layer 30. The MgO film serving as the tunnel barrier layer
30 has a film thickness of 10 .ANG. (1 nm).
[0070] For example, calcium oxide (CaO), strontium oxide (SrO),
titanium oxide (TiO), vanadium oxide (VO), and niobium oxide (NbO)
may be used as the nonmagnetic layer. The above oxides including
MgO have a crystal structure of sodium chloride (NaCl)
structure.
[0071] When these oxides having the NaCl structure are used as the
nonmagnetic layer (tunnel barrier layer), the oxides are preferably
oriented in the (001) plane (or orientation) and planes equivalent
thereto (or orientation).
[0072] The reference layer 20 is provided on the tunnel barrier
layer 30. In the present embodiment, the reference layer 20 has a
multi-layer structure including at least TbCoFe/CoFeB/Ta/CoFeB.
[0073] The CoFeB film 25 in the lowermost layer of the reference
layer 20 is in contact with the tunnel barrier layer (MgO film) 30.
The film thickness of the CoFeB film 25 in the lowermost layer is
about 15 .ANG. (1.5 nm). The Ta film 26 is sandwiched by the two
CoFeB films 25, 27. The film thickness of the Ta film 26 is about 3
.ANG. (0.3 nm). The CoFeB film 27 on the Ta film 26 has a film
thickness of 4 .ANG. (0.4 nm).
[0074] The TbCoFe film 21 of the uppermost layer of the reference
layer 20 has, for example, a film thickness of 120 .ANG. (12 nm).
The TbCoFe film 21 is a perpendicular magnetic film. The
composition ratio of Tb in the TbCoFe film is, for example, 13
atomic %. However, the composition ratio of Tb in the TbCoFe film
is not limited to this value. The composition ratio of Tb in the
TbCoFe film is preferably greater than or equal to 10 atomic %.
When the composition ratio of Tb in the TbCoFe film is set at a
value greater than or equal to 20 atomic %, the magnetization
direction of the perpendicular magnetic film 21 and the
magnetization direction of the interface layer 22 can be arranged
in antiparallel. Accordingly, a magnetostatic stray field applied
from the reference layer 20 to the recording layer 10 can be
reduced. The magnetostatic stray field applied from the reference
layer 20 to the recording layer 10 changes the magnetization
reversal magnetic field of the recording layer 10, which reduces
the thermal stability (heat resistance) of the recording layer 10.
For this reason, the magnetostatic stray field applied to the
recording layer is preferably zero.
[0075] The magnetostatic stray field applied from the reference
layer 20 to the recording layer 10 is reduced to zero by inserting
a perpendicular magnetic film (bias layer) between the upper
electrode 52 and the reference layer 20 or between the underlayer
40 and the lower electrode 51, wherein the magnetization of the
perpendicular magnetic film (bias layer) is in antiparallel with
the magnetization direction of the reference layer 20.
[0076] When the composition ratio of Tb in the TbCoFe film is set
at a value greater than or equal to 20 atomic %, it is not
necessary to insert the bias layer in order to reduce the
magnetostatic stray field applied from the reference layer 20 to
the recording layer 10 to zero. Accordingly, the MTJ element can be
made as a thin film, and the dimension of the MTJ element in the
stacking direction of the film can be reduced.
[0077] Like the recording layer 10, the reference layer 20 includes
an interface layer 22 in proximity to an interface between the
perpendicular magnetic film (first magnetic film or first
magnetization film) 21 and the tunnel barrier layer 30. In the
reference layer 20, the CoFeB/Ta/CoFeB films 25, 26, 27 correspond
to the interface layer 22 of the reference layer 20. The interface
layer (second magnetic film or second magnetization film) 22 also
includes magnetic anisotropy perpendicular to the film surface.
[0078] In the present embodiment, the Ta film (or the W film, the
Nb film, the Mo film) 26 in the interface layer 22 is referred to
as an intermediate film or an insertion film.
[0079] When the interface layers in the reference layer 20 and the
recording layer 10 are alloy films including at least two of Co,
Fe, and B, a film different from the CoFeB film may be used as a
constituent element of the interface layer.
[0080] The upper electrode 52 is provided on the reference layer
20. The upper electrode 52 has a stacked structure including Ru/Ta.
The Ta film in the lower layer of the upper electrode 52 has a film
thickness of about 50 .ANG. (5 nm). The Ta film is in contact with
the TbCoFe film 21 of the reference layer 20. The Ru film is
stacked on the Ta film. The film thickness of the Ru film is 200
.ANG. (20 nm).
[0081] It is to be understood that in each film of the
magnetoresistive effect element according to the present embodiment
(MTJ element), a very small amount of element constituting films
adjacent to each other may be included, or a thin compound layer of
an element constituting two films adjacent to each other may be
formed in the interface between the two films.
[0082] In the magnetoresistive effect element 1A according to the
first embodiment, the reference layer (second magnetic layer) 20
includes the TbCoFe film 21.
[0083] TbCoFe film 21 includes amorphous phases 29 including at
least one of elements of Tb, Co, and Fe and crystals (crystal
particles or crystal phase) 28 including at least one of elements
of Co and Fe. For example, the crystals 28 in the TbCoFe film 21
are crystals having particle sizes of 5 .ANG. (0.5 nm) or more. In
the explanation below, a crystal particle/crystal phase having a
particle size of 30 .ANG. (3 nm) or less or preferably 10 .ANG. (1
nm) or less is referred to as a microcrystal. For example, the
particle size of a microcrystal is defined as an average particle
size of a plurality of microcrystals included in the magnetic
layer.
[0084] For example, the microcrystal in the TbCoFe film 21 has at
least one of a crystal structure having a lattice spacing of 1.2 to
1.6 .ANG. (0.12 to 0.16 nm) and a lattice spacing of 1.9 to 2.3
.ANG. (0.19 to 0.23 nm) in a film cross-sectional direction. The
TbCoFe film 21 includes at least one of a microcrystal
(nanocrystal) having a lattice spacing of 1.2 to 1.6 .ANG. (0.12 to
0.16 nm) and a microcrystal having a lattice spacing of 1.9 to 2.3
.ANG. (0.19 to 0.23 nm).
[0085] Further, gadolinium (Gd) and dysprosium (Dy) may be further
added to the TbCoFe film 21. Instead of Tb of the TbCoFe film 21,
Gd and Dy may be used. Even when Gd and Dy are used in the
perpendicular magnetic film 21 of the reference layer 20, the
perpendicular magnetic film 21 includes the amorphous phases 29 and
the crystals 28. Instead of Co or Fe, nickel (Ni) and manganese
(Mn) may be used in the perpendicular magnetic film 21 including
the amorphous phases 29 and the crystals 28.
[0086] Since the perpendicular magnetic film (in this case, TbCoFe
film) 21 in the reference layer 20 includes the amorphous phases 29
and the crystals 28, the entire TbCoFe film 21 is not crystallized
even when heat of 300.degree. C. or more is applied to the
reference layer 20. In other words, even when high temperature heat
treatment (of 300.degree. C. or more) is applied to the TbCoFe film
21 including the amorphous phases 29 and the crystals 28, the
amorphous phases 29 is prevented from being crystallized by the
crystals 28 oriented randomly. Therefore, this prevents
deterioration of the magnetic characteristics of the TbCoFe film 21
due to heat.
[0087] Therefore, in the magnetoresistive effect element according
to the present embodiment, the heat resistance is improved, and for
example, sufficient amount of heat can be given to the constituent
members of the magnetoresistive effect element during the heat
treatment for crystallization.
[0088] Therefore, according to the magnetoresistive effect element
according to the present embodiment, the element characteristics of
the magnetoresistive effect element can be improved.
(b) Manufacturing Method
[0089] A method for manufacturing the magnetoresistive effect
element according to the present embodiment will be explained with
reference to FIGS. 3 and 4. FIGS. 3 and 4 are cross-sectional views
illustrating steps of the method for manufacturing the
magnetoresistive effect element. Although a structure of the
magnetoresistive effect element (MTJ element) as shown in FIG. 2 is
shown as an example in this case, the structure is not limited
thereto. It is to be understood that the combination of materials
and the composition of materials used in the element can be changed
as necessary.
[0090] As shown in FIG. 3, an electrode layer 51A for forming a
lower electrode is formed on a substrate 100 using the sputtering
method, for example. The electrode layer 51A has a multi-layer
structure including Ta/Cu/Ta.
[0091] For example, an underlayer 40A is deposited on the electrode
layer 51A using the sputtering method, for example.
[0092] The underlayer 40A has an atom close-packed plane. For
example, the underlayer 40A has a multi-layer structure including
Pd/Ir/Ru.
[0093] A magnetic layer 10A serving as a storage layer is deposited
on the underlayer 40A using the sputtering method, for example. The
magnetic layer 10A has a multi-layer structure including
CoFeB/Ta/CoB/Co, for example. When the magnetic layer 10A is
deposited on the underlayer 40A having an atom close-packed plane,
the magnetic layer 10A having the perpendicular magnetic anisotropy
is formed.
[0094] A nonmagnetic layer (tunnel barrier layer) 30A is deposited
on the magnetic layer 10A. The nonmagnetic layer 30A is, for
example an MgO film.
[0095] A magnetic layer 20A for forming a reference layer is
deposited on the nonmagnetic layer 30A. The magnetic layer 20A has
a multi-layer structure. Layers 25A, 26A, 27A serving as interface
layers for the reference layer are deposited on the nonmagnetic
layer 30A. For example, the interface layer is formed by inserting
a Ta film during the deposition of the CoFeB film. In other words,
the CoFeB film 25A is deposited on the nonmagnetic layer 30A. The
Ta film 26A is deposited on the CoFeB film 25A. The CoFeB film 27A
is deposited on the Ta film 26A. As a result, the interface layers
25A, 26A, 27A having the multi-layer structure including
CoFeB/Ta/CoFeB are formed on the nonmagnetic layer 30A.
[0096] The multi-layer film 21A is deposited on the CoFeB film 27A.
The multi-layer film 21A has a structure made by alternately
stacking a first film 23 and a second film 24. The first film 23 is
stacked on the second film 24.
[0097] When the magnetic layer formed on the interface layer (CoFeB
film) 27A is a TbCoFe film, a CoFe film is used as the first film
23, and a TbCo film is used as the second film 24, for example. In
this case, the first film 23 is referred to as a CoFe film 23, and
the second film 24 is referred to as a TbCo film 24. The CoFe film
23 is deposited on the TbCo film 24. The structure made by stacking
the CoFe film 23 on the TbCo film 24 is also referred to as a
CoFe/TbCo film. The CoFe film 23 is deposited to have a film
thickness of about 3 .ANG. (0.3 nm), for example. The TbCo film 24
is deposited to have a film thickness of about 3 .ANG. (0.3 nm),
for example.
[0098] When the pair of CoFe/TbCo films 23, 24 are adopted as one
cycle, for example, 20 cycles of CoFe/TbCo films 23, 24 are stacked
on the interface layer 27A (above the nonmagnetic layer 30A). It is
to be understood that the number of cycles (the number of stacks)
of the CoFe/TbCo film in the multi-layer film 21A varies according
to the film thickness of the formed magnetic layer (in this case,
the TbCoFe film).
[0099] The combination of the first and second films 23, 24 in the
multi-layer film 21A can be changed as necessary according to the
main components and composition in the formed magnetic layer. When
the formed reference layer is the TbCoFe film, not only the stacked
film including the TbCo film and the CoFe film but also, for
example, a stacked film including a TbFe film and a CoFe film, a
stacked film including a TbCo film and an Fe film, a stacked film
including a TbCo film and a Co film, a stacked film including a
TbFe film and a Co film, a stacked film including a TbFe film and
an Fe film, a stacked film including a TbCoFe film and an Fe film,
a stacked film including a TbCoFe film and a Co film, or a stacked
film including a TbCoFe film and a CoFe film may be used in the
multi-layer film 21A. In this case, two kinds of films 23, 24
having different compositions are used in the multi-layer film 21A,
but three kinds of films or more having different compositions may
also be used in the multi-layer film 21A.
[0100] In order to maintain the perpendicular magnetic anisotropy
of the multi-layer film 21A, the composition ratio of Tb in the
multi-layer film 21A is preferably greater than or equal to 10
atomic %. When the composition ratio of Tb in the multi-layer film
21A is greater than or equal to 10 atomic % or more, the
composition ratio of Tb in the TbCo film serving as the second film
24 is greater than or equal to 25 atomic %. Therefore, the
composition ratio of Tb in the TbCo film serving as the second film
24 is preferably greater than or equal to 25 atomic % or more.
[0101] Instead of the film including Tb, a film including Dy or Gd
may be used in the multi-layer film 21A. For example, a stacked
film including a DyCo film and a CoFe film or a stacked film
including a GdCo film and a CoFe film are used in the multi-layer
film 21A. Alternatively, a film in which a portion of Tb in the
film is replaced with Dy or Gd, i.e., a film including both of Tb
and Dy or a film including both of Tb and Gd, may be used in the
multi-layer film 21A. For example, a stacked film including a
TbDyCo film and an Fe film and a stacked film including a TbGdCo
film and an Fe film are used.
[0102] An electrode layer 52A for forming an upper electrode is
formed on the multi-layer film 21A using the sputtering method, for
example. The electrode layer 52A has a stacked structure including
Ru/Ta.
[0103] Accordingly, a stacked layer (stacked material, stacked
body) for forming the magnetoresistive effect element (MTJ element)
is formed on the substrate. Naturally, it is to be understood that
the order of stacks of each layer is different according to the
structure of the formed magnetoresistive effect element.
[0104] Thereafter, heat treatment is executed on the stacked layer
deposited on the substrate 100. For example, the heat treatment is
executed for about 30 minutes at a heating temperature of about 300
to 400.degree. C.
[0105] When thermal energy is given, interdiffusion of Co, Fe, and
Tb occurs in the films (in this case, CoFe/TbCo film) 23, 24 in the
multi-layer film 21A on the interface layer 27A. Accordingly, as
shown in FIG. 4, the TbCoFe film 21B serving as the perpendicular
magnetic film for the reference layer is formed on the interface
layer 27A.
[0106] The formed TbCoFe film 21B includes the amorphous phases 29
and the crystals (crystal particles or crystal phase) 28. The
amorphous phases 29 includes at least one type of elements of Tb,
Co, and Fe. The crystal 28 includes at least one type of elements
of Co and Fe. The types of elements respectively forming the
amorphous phases and the crystals change in accordance with the
types of constituent elements of the films 23, 24 in the magnetic
film 21B.
[0107] It should be noted that, regardless of the heat treatment,
diffusion of atoms (migration of atoms) at the interface of the
films and temperature rise during deposition may cause
precipitation of the crystals 28 into the multi-layer film 21A when
the CoFe/TbCo film is deposited.
[0108] In the TbCoFe film 21B, the plurality of microcrystals 28
are crystals whose particle sizes are greater than or equal to 0.5
nm. Each microcrystal 28 in the TbCoFe film 21 has at least one of
a crystal structure having a lattice spacing of 1.2 to 1.6 .ANG.
(0.12 to 0.16 nm) and a lattice spacing of 1.9 to 2.3 .ANG. (0.19
to 0.23 nm) in a film cross-sectional direction.
[0109] As described above, the crystals 28 whose crystal structures
are different (random) are formed in the magnetic film (in this
case, TbCoFe film) 21B, so that the crystals 28 having different
crystal structures interfere with each other, which prevents
increase of the size of the crystal particles caused by the thermal
treatment, and prevents crystallization of the amorphous phases 29
of the magnetic film 21B. Therefore, the entire magnetic film 21B
is not crystallized. Further, the magnetic film 21 includes the
amorphous phases 29 and the fine crystals 28, and therefore, even
if the heat treatment (for example, deposition of inter-layer
insulating film) is performed in a step after the MTJ element is
formed, crystallization of amorphous phases, decomposition of
microcrystals, and recrystallization of microcrystals hardly occur
in the perpendicular magnetic film 21B.
[0110] Therefore, the TbCoFe film including the amorphous phases 29
and the microcrystals 28 has large perpendicular magnetic
anisotropy while the magnetic characteristics are not deteriorated
by the heat treatment.
[0111] When the film thickness of the CoFe film 23 is increased to
2 nm or more in order to form crystals whose particle sizes are 20
.ANG. (2 nm) or more in the magnetic film 21B, the CoFe film
becomes an in-face magnetic film. This causes deterioration of the
perpendicular magnetic anisotropy of the reference layer 20 formed
using the CoFe film. Therefore, the CoFe film 23 in the multi-layer
film is preferably formed such that the CoFe film 23 has a film
thickness of 20 .ANG. (2 nm) or less, e.g., 3 to 4 .ANG. (0.3 to
0.4 nm) as described above. On the other hand, since the film
thicknesses of the CoFe film 23 and the TbCo film 24 in the
multi-layer film depend on the particle sizes of the formed
crystals 28, the CoFe film 23 and the TbCo film 24 are preferably
formed to have a thickness of 20 .ANG. (2 nm) or less.
[0112] This heat treatment accelerates crystallization of the
tunnel barrier layer 30A and the first magnetic layer 10A. For
example, the orientation of the (001) plane improves in the MgO
film serving as the tunnel barrier layer 30A. Further, the
interface layer 12 in the first magnetic layer 10A is
lattice-matched with the crystallized tunnel barrier layer 30A, and
is crystallized. Therefore, the MTJ element with the high MR ratio
can be formed.
[0113] Thereafter, for example, the films 51A, 40A, 10A, 30A, 20A,
52A on the substrate 100 are patterned by photolithography
technique, and are processed using the reactive ion etching (RIE)
method or ion milling method. As a result, the magnetoresistive
effect element (MTJ element) 1A as shown in FIG. 2 is formed.
[0114] It should be noted that the heat treatment may be executed
after the magnetoresistive effect element is processed into a
predetermined shape.
[0115] As described above, with the method for manufacturing the
magnetoresistive effect element according to the present
embodiment, the magnetoresistive effect element including the
perpendicular magnetic film (for example, a TbCoFe film) 21 having
high heat resistance can be formed.
[0116] Therefore, according to the method for manufacturing the
magnetoresistive effect element according to the present
embodiment, the magnetoresistive element with high element
characteristics can be provided.
(c) Characteristics
[0117] The characteristics of the magnetoresistive effect element
1A according to the present embodiment will be explained with
reference to FIGS. 5 to 15.
[0118] (c-1) Crystal structure and characteristics of perpendicular
magnetic film
[0119] FIG. 5 illustrates a magnetic resistance (MR) ratio of the
MTJ element 1A according to the present embodiment.
[0120] FIG. 5 illustrates change of the MR ratio when the MTJ
element according to the present embodiment is formed by performing
heat treatment at 300, 325, and 350.degree. C. for 30 minutes.
[0121] As shown in FIG. 5, when the heat treatment is performed at
each temperature, the MTJ element according to the present
embodiment has an MR ratio of 100% or more.
[0122] Further, FIG. 5 indicates that even when the thermal
treatment at 350.degree. C. is performed on the MTJ element
according to the present embodiment, the MTJ element according to
the present embodiment has a high MR ratio (for example, 150% or
more) without any deterioration caused by the heating.
[0123] FIGS. 6A, 6B, and 7 illustrate observation results of the
perpendicular magnetic film of the MTJ element using a transmission
electron microscope (TEM). The perpendicular magnetic film is, for
example, the TbCoFe film.
[0124] The TEM image of FIGS. 6A and 6B illustrates a measurement
result of a dark field image.
[0125] FIG. 6A illustrates a cross-sectional TEM image (dark field
image) of the TbCoFe film according to the present embodiment when
an objective aperture of the TEM is set at a diffraction spot
corresponding to lattice spacing d=1.9 to 2.3 .ANG. (0.19 to 0.23
nm).
[0126] FIG. 6B illustrates a cross-sectional TEM image (dark field
image) of the TbCoFe film according to the present embodiment when
an objective aperture of the TEM is set at a diffraction spot
corresponding to lattice spacing d=1.2 to 1.6 .ANG. (0.12 to 0.16
nm).
[0127] FIG. 7 illustrates a diffraction ring in the TEM image in a
planar direction of the TbCoFe film according to the present
embodiment.
[0128] As described above (see FIG. 3), for example, the TbCoFe
film (first magnetic film) 21 serving as the perpendicular magnetic
film is formed by alternately stacking about 20 cycles of the TbCo
film (about 3 .ANG. [0.3 nm]) 24 and the CoFe film (about 3 .ANG.
[0.3 nm]) 23 during deposition of the films.
[0129] In the setting conditions of the objective apertures as
shown in FIGS. 6A and 6B, it is observed that white spots of about
1 nm are distributed at the same degree within the film. Under the
above setting conditions, the white spots observed by the TEM
correspond to the crystal particles (crystal phase).
[0130] This indicates that the TbCoFe film 21 includes the crystals
whose lattice spacing (first lattice spacing) corresponds to d=1.2
to 1.6 .ANG. (0.12 to 0.16 nm) and the crystal whose lattice
spacing (second lattice spacing) corresponds to d=1.9 to 2.3 .ANG.
(0.19 to 0.23 nm).
[0131] In view of the position of the diffraction ring in FIG. 7,
the crystals included in the TbCoFe film are considered to have a
hexagonal close-packed (hcp) lattice structure in which a lattice
constant in a direction parallel to the in-face direction of the
film is about 2.4 to 2.5 .ANG. (0.24 to 0.25 nm).
[0132] In view of the full-width half-maximum (FWHM) of the
diffraction ring, an average crystal particle size of the crystals
included in the TbCoFe film is considered to be 30 .ANG. (3 nm) in
the direction parallel to the in-face direction of the film.
[0133] Further, as shown in FIG. 7, halo-like (blurry) diffraction
ring is observed. Therefore, in the TEM image under the above
setting conditions, portions other than white spots (for example, a
gray portion) are considered to be amorphous phases.
[0134] These observation results using the TEM indicate that the
TbCoFe film 21 used in the magnetoresistive effect element
according to the present embodiment is the film including the
amorphous phases and the crystals having crystal particle sizes of
0.5 nm or more.
[0135] As shown in FIG. 5, even when the heat treatment is
performed on the element at 300.degree. C. or more, the MTJ element
including the TbCoFe film according to the present embodiment has
an MR ratio of 100% or more without any deterioration in
characteristics due to heat. That is, even when the TbCoFe film is
used as the perpendicular magnetic film, the MTJ element according
to the present embodiment has a high degree of resistance to
temperature.
[0136] As described above, in the present embodiment, the randomly
oriented crystals 28 are precipitated into the TbCoFe film that is
formed by alternately stacking the films having different
compositions (in this case, the TbCo film and the CoFe film). A
pinning site is formed by the precipitated crystals 28.
[0137] The plurality of crystals 28 randomly oriented in the film
make the amorphous phases 29 in the film discontinuous or reduce
the size (volume) of one piece of amorphous phases 29. As a result,
the amorphous phases 29 is less likely to be crystallized.
Alternatively, the crystals 28 randomly included in the film
prevent the atoms constituting the amorphous phases 29 from being
regularly re-oriented by heat. Therefore, even when a large amount
of heat is applied to the TbCoFe film 21, the crystals 28 in the
film are considered to prevent change of the crystal structure of
the TbCoFe film 21, i.e., crystallization of the amorphous phases
29. As a result, the perpendicular magnetic anisotropy of the
amorphous phases 29 is maintained even when the heat treatment is
performed at 300.degree. C. or more.
[0138] In view of the above facts, even when the heat treatment is
applied to the MTJ element, the TbCoFe film is not deteriorated by
heat, and the deterioration of the characteristics of the MTJ
element including the TbCoFe film are considered to be
prevented.
[0139] As described above, since the TbCoFe film 21 of the MTJ
element according to the present embodiment includes the amorphous
phases 29 and the crystals 28 of 0.5 nm or more, the heat
resistance of the MTJ element having the TbCoFe film 21 is
ensured.
[0140] Therefore, according to the magnetoresistive effect element
according to the present embodiment, the element characteristics
can be improved.
[0141] (c-2) Relationship Between Magnetic Characteristics and
Composition Ratio of Perpendicular Magnetic Film
[0142] Relationship between the composition of the perpendicular
magnetic film (in this case, the TbCoFe film) 21 included in the
MTJ element 1A according to the present embodiment and the magnetic
characteristics of the magnetic film will be explained with
reference to FIGS. 8 to 11. The numerical values as shown in FIGS.
8 to 11 are examples, and the present embodiment is not limited by
the numerical values as shown in FIGS. 8 to 11.
[0143] FIGS. 8 and 9 illustrate relationship between the magnetic
characteristics and the composition ratio of Fe in the CoFe film 23
for forming the TbCoFe film. As shown in FIGS. 8 and 9, the
magnetic characteristics in the TbCoFe film 21 can be changed by
changing the concentration of Fe included in the CoFe film 23. For
example, when the composition ratio of Fe in the CoFe film 23 is
increased, a saturation magnetization Ms, a magnetic switching
field Hc, and a perpendicular magnetic anisotropy constant Ku of
the TbCoFe film can be increased.
[0144] More specifically, for example, when the TbCo film and the
CoFe film are stacked to form the TbCoFe film, the magnetic
characteristics of the TbCoFe film can be improved by increasing
the concentration of Fe in the CoFe film.
[0145] FIG. 8 illustrates relationship between magnetic switching
field of the magnetic layer and a composition ratio of Fe with
respect to Co in the Co Fe film 23 for forming the TbCoFe film, in
the magnetic layer (the reference layer including the interface
layer) having the structure including TbCoFe/CoFeB/Ta/CoFeB.
[0146] The vertical axis of the graph as shown in FIG. 8 represents
the magnetic switching field Hc (unit: Oe) of the magnetic layer.
The horizontal axis of the graph as shown in FIG. 8 represents the
concentration of Fe (unit: vol. %) in each CoFe film in the
CoFe/TbCo stacked film for forming the TbCoFe film.
[0147] FIG. 9 illustrates relationship between saturation
magnetization of the magnetic layer and a composition ratio of Fe
with respect to Co in the CoFe film 23 for forming the TbCoFe film,
in the magnetic layer (the reference layer including the interface
layer) having the structure including TbCoFe/CoFeB/Ta/CoFeB.
[0148] The vertical axis of the graph as shown in FIG. 9 represents
the saturation magnetization Ms (unit: emu/cc) of the magnetic
layer. The horizontal axis of the graph as shown in FIG. 9
represents the concentration of Fe (unit: vol. %) in each CoFe film
in the CoFe/TbCo stacked film for forming the TbCoFe film.
[0149] FIGS. 8 and 9 also show a case where the CoFe film does not
include Fe (Fe: 0 vol. %) or does not include Co (Fe: 100 vol. %)
in the CoFe/TbCo stacked film.
[0150] When the CoFe film does not include Fe, the structure of the
stacked film for forming the perpendicular magnetic film is
Co/TbCo. When the CoFe film does not include Co, the structure of
the stacked film for forming the perpendicular magnetic film is
Fe/TbCo.
[0151] As shown in FIG. 8, when the concentration of Fe in the
CoFe/TbCo stacked film increases, the magnetic switching field of
the magnetic layer (reference layer) improves. On the other hand,
as shown in FIG. 9, when the concentration of Fe in the CoFe/TbCo
stacked film increases, the saturation magnetization of the
magnetic layer (reference layer) improves.
[0152] As described above, when the concentration of Fe in the
TbCoFe film (stacked film for forming the TbCoFe film) is
increased, the magnetic switching field and the saturation
magnetization of the magnetic layer (perpendicular magnetic film)
can be improved. Accordingly, the perpendicular magnetic anisotropy
constant Ku of the magnetic layer can be increased.
[0153] When the TbCoFe film (or the TbFe film) is used in the
reference layer of the perpendicular magnetization, the increase of
the perpendicular magnetic anisotropy constant Ku contributes to
improvement of the thermal stability of the reference layer.
[0154] Therefore, when the magnetization direction of the recording
layer 10 is changed in (i.e., data are written to) the MTJ element
according to the present embodiment, the spin torque applied to the
reference layer 20 can prevent reversal of the magnetization of the
reference layer 20.
[0155] As shown in FIGS. 10 and 11, the magnetic characteristics of
the TbCoFe film 21 can be changed by changing the composition of Tb
in the film 21.
[0156] For example, when the composition of Tb in the TbCoFe film
21 is changed, the saturation magnetization Ms of the TbCoFe film
can be changed.
[0157] FIG. 10 illustrates relationship between magnetic switching
field of the magnetic layer and a composition ratio of Tb in the
TbCoFe film 21, in the magnetic layer (the reference layer
including the interface layer) having the structure including
TbCoFe/CoFeB/Ta/CoFeB.
[0158] The vertical axis of the graph as shown in FIG. 10
represents the magnetic switching field Hc (unit: Oe) of the
magnetic layer. The horizontal axis of the graph as shown in FIG.
10 represents the concentration of Tb (unit: atomic %) in the
TbCoFe film 21.
[0159] FIG. 11 illustrates relationship between saturation
magnetization of the magnetic layer and a composition ratio of Tb
in the TbCoFe film 21, in the magnetic layer (the reference layer
including the interface layer) having the structure including
TbCoFe/CoFeB/Ta/CoFeB.
[0160] The vertical axis of the graph as shown in FIG. 11
represents the saturation magnetization Ms (unit: emu/cc) of the
magnetic layer. The horizontal axis of the graph as shown in FIG.
11 represents the concentration of Tb (unit: atm. %) in the TbCoFe
film 21.
[0161] As shown in FIGS. 10 and 11, the magnetic switching field Hc
of the magnetic layer having the stacked structure including
TbCoFe/CoFeB/Ta/CoFeB attains the maximum value when the
concentration of Tb in the TbCoFe film 21 increases to a
predetermined value. The concentration of the Tb film at which the
magnetic switching field Hc of the TbCoFe/CoFeB/Ta/CoFeB layer
attains the maximum value is referred to as a compensation point.
In FIG. 10, the compensation point of TbCoFe/CoFeB/Ta/CoFeB layer
is obtained when the concentration of Tb is about 20 atomic % to
about 22 atomic %. When the concentration of the Tb film of the Tb
CoFe/CoFeB/Ta/CoFeB layer attains a value more than the
compensation point, the magnetic switching field Hc of the
TbCoFe/CoFeB/Ta/CoFeB layer decreases.
[0162] As the magnetic switching field Hc increases to the
compensation point of the magnetic layer of the
TbCoFe/CoFeB/Ta/CoFeB structure, the saturation magnetization Ms of
the magnetic layer of the TbCoFe/CoFeB/Ta/CoFeB structure
decreases. Then, when the concentration attains a value more than
the compensation point (Tb concentration: about 20 atomic %), the
saturation magnetization Ms of the TbCoFe/CoFeB/Ta/CoFeB layer
increases.
[0163] In the MTJ element, the magnetostatic stray field applied
from the reference layer 20 to the recording layer 10 is preferably
reduced. Therefore, the magnitude of the saturation magnetization
Ms of the reference layer 20 is preferably reduced. According to
the MTJ element according to the present embodiment, the saturation
magnetization of the reference layer 20 including the TbCoFe film
21 can be reduced by adjusting the concentration of Tb in the
TbCoFe film 21.
[0164] As shown in FIGS. 8 and 9, when the concentration of Fe in
the TbCoFe film 21 increases, both the magnetic switching field Hc
and the saturation magnetization Ms increase.
[0165] As shown in FIGS. 10 and 11, when the concentration of Tb in
the TbCoFe film 21 increases to the compensation point, the
magnetic switching field Hc of the TbCoFe film 21 increases, but
the saturation magnetization Ms of the TbCoFe film 21
decreases.
[0166] Therefore, as shown in FIGS. 8 to 11, the magnetic layer
(the reference layer or the recording layer) having predetermined
magnetic characteristics can be formed by changing the composition
ratios of elements constituting the TbCoFe film.
[0167] The film thickness of the reference layer 20 including the
TbCoFe film 21 according to the present embodiment can be reduced
by reducing the stacked layer cycle of the stacked film (for
example, CoFe/TbCo films) for forming the TbCoFe film.
[0168] In the above example, 20 cycles of CoFe/TbCo films are
stacked. When the film thickness of the TbCo film is 3 .ANG. (0.3
nm) and the film thickness of the CoFe film is 3 .ANG. (0.3 nm),
the TbCoFe film of 120 .ANG. (12 nm) is formed by the 20 cycles of
CoFe/TbCo films. Even when 5 cycles of CoFe/TbCo films are formed,
and the TbCoFe film having a film thickness of 30 .ANG. (3 nm) is
formed, the TbCoFe film 21 has perpendicular magnetic
anisotropy.
[0169] Even when the film thickness of the TbCoFe film 21 is about
30 .ANG. (3 nm), the TbCoFe film 21 includes the amorphous phases
and the crystals. Therefore, even when the number of cycles of the
stacked film for forming the TbCoFe film is reduced, and the TbCoFe
film becomes thinner, the TbCoFe film 21 used in the MTJ element
according to the present embodiment has high heat resistance.
[0170] As described above, the film thickness of the reference
layer (TbCoFe film) can be reduced by reducing the number of cycles
(the number of stacks). Accordingly, it is possible to reduce an
aspect ratio (step between the upper surface of the MTJ element and
the substrate) generated when the MTJ element is formed, and it
becomes easier to process the MTJ element.
[0171] It should be noted that the combination of the stacked films
for forming the TbCoFe film 21 is not limited to the stacked
structure including the TbCo film and the CoFe film. For example, a
stacked film including a TbFe film and a CoFe film, a stacked film
including a TbCo film and an Fe film, a stacked film including a
TbCo film and a Co film, a stacked film including a TbFe film and a
Co film, a stacked film including a TbFe film and an Fe film, a
stacked film including a TbCoFe film and a Fe film, a stacked film
including a TbCoFe film and a Co film, or a stacked film including
a TbCoFe film and a CoFe film may be used in the multi-layer film
21A for forming the TbCoFe film.
[0172] In stead of Tb, Dy may be used in the TbCoFe film 21. In
this case, the DyCoFe film is used as the reference layer 20 of the
MTJ element 1A as shown in FIG. 2. A portion of Tb in the TbCoFe
film 21 may be replaced with Dy. In this case, the TbDyCoFe film is
used as the reference layer 20 of the MTJ element 1A. The MR ratio
of the MTJ element can be improved by replacing a portion or all of
Tb in the TbCoFe film 21 with Dy.
[0173] Further, in the TbCoFe film 21, Gd may be used instead of
Tb. In this case, the GdCoFe film is used as the reference layer 20
of the MTJ element 1A as shown in FIG. 2. A portion of Tb in the
TbCoFe film 21 may be replaced with Gd. In this case, the TbGdCoFe
film is used as the reference layer 20 of the MTJ element 1A. The
Curie temperature Tc of the MTJ element can be improved by
replacing a portion or all of Tb in the TbCoFe film 21 with Gd.
[0174] The DyCoFe film, the TbDyCoFe film, the GdCoFe film, or the
GdTbCoFe film also includes amorphous phases and crystals whose
average crystal particle sizes are less than or equal to 3 nm,
preferably less than or equal to 1 nm, and whose particle sizes are
greater than or equal to 0.5 nm.
[0175] As described above, the magnetic characteristics of the
magnetic layer used in the magnetoresistive effect element can be
controlled by adjusting the composition of the perpendicular
magnetic film (for example, a TbCoFe film) including the amorphous
phases and the crystals.
[0176] Therefore, according to the magnetoresistive effect element
according to the present embodiment, the element characteristics
can be improved.
(d) Structure of Interface Layer of Reference Layer
[0177] The structure of the interface layer in the reference layer
will be explained with reference to FIGS. 12 to 16B.
[0178] As shown in FIG. 2, in the magnetoresistive effect element
(MTJ element), the interface layer 22 is provided between the
TbCoFe film 21 and the tunnel barrier layer 30 (for example, an MgO
film). In this manner, the interface layer 22 is provided in the
reference layer 20, so that the MR ratio of the MTJ element is
improved.
[0179] For example, a CoFeB film is used as the interface layer 22.
The CoFeB film having had no heat treatment immediately after the
deposition (as-deposit) has an amorphous structure. When a
single-layer CoFeB film is provided between the TbCoFe film and the
MgO film, and the CoFeB film is subjected to the heat treatment,
the crystals in the CoFeB film are oriented along the bcc (001)
plane and planes equivalent thereto with the MgO film being the
underlayer. This crystallization of the CoFeB film improves the MR
ratio of the MTJ element.
[0180] However, when the temperature of the heat treatment is
greater than or equal to 350.degree. C., the crystallized CoFeB
film functions as the underlayer for the TbCoFe film, and the
crystals in the amorphous TbCoFe film (TbCoFe film without
microcrystal) are also oriented in the bcc (001) plane and planes
equivalent thereto. As a result, the perpendicular magnetic
anisotropy of the amorphous TbCoFe film is deteriorated.
[0181] FIG. 12 illustrates observation results of the MTJ element
with the TEM when the heating temperature and the structure of the
interface layer are changed. FIG. 13 illustrates a structure of the
MTJ element used for the observation with the TEM.
[0182] The structure of the MTJ element used for the observation is
as follows.
[0183] The lower electrode 51 is provided on the substrate (not
shown). The lower electrode 51 has a structure in which a Ta film
51b is stacked on a W film 51a, and the film thickness of the Ta
film 51b is 50 .ANG. (5 nm).
[0184] The underlayer 40 is provided on the lower electrode 51. The
underlayer 40 has a structure in which an Ir film 40b is stacked on
an Ru film 40a. The film thickness of the Ru film 40a is set at
about 50 .ANG. (5 nm), and the film thickness of the Ir film 40b is
set at about 30 .ANG. (3 nm). The underlayer 40 has an atom
close-packed plane. The crystals in the Ru film 40a are oriented in
the hcp (0001) plane (orientation) in order to control the crystal
orientation of the Ir film 40b.
[0185] The recording layer 10 having the multi-layer structure is
provided on the underlayer 40. The recording layer 10 has the
interface layer 12.
[0186] In the recording layer having the multi-layer structure, the
PdCo film 11 is provided between the underlayer 40 and the
interface layer 12 of the recording layer 10. The PdCo film is a
perpendicular magnetic film.
[0187] The PdCo film 11 is formed by depositing the stacked film
including the Pd film and the Co film during deposition of the
films. The stacked film including the Pd film and the Co film is
formed with two cycles of Pd/Co stacked films. In other words,
during deposition of the films, the Pd/Co stacked film is made with
the two Co films and the two Pd films. During deposition of the
films, each Co film is deposited to have a thickness of 3.5 .ANG.
(0.35 nm), and each Pd film is deposited to have a thickness of 3.5
.ANG. (0.35 nm). During deposition of the films, the Co film serves
as the lowermost layer in the stacked structure, and the Co film is
deposited to be in contact with the upper surface of the
underlayer.
[0188] The interface layer 12 of the recording layer 10 is provided
on the PdCo film 11. The interface layer 12 of the recording layer
10 has the structure including CoFeB/Ta/CoFeB. The CoFeB film 15a
in the lower layer (at the side of the PdCo film) has a film
thickness of 5 .ANG. (0.5 nm). The CoFeB film 15c in the upper
layer (at the side of the nonmagnetic layer) has a film thickness
of 9 .ANG. (0.9 nm). The Ta film 15b sandwiched by the two CoFeB
films has a film thickness of 3 .ANG. (0.3 nm).
[0189] The recording layer 10 is formed on the underlayer having an
atom close-packed plane, so that the recording layer 10 becomes the
perpendicular magnetic film.
[0190] The MgO film 30 serving as the tunnel barrier layer
(nonmagnetic layer) is provided on the interface layer 12 of the
recording layer 10. The MgO film 30 has a film thickness of 10
.ANG. (1 nm). The crystals in the MgO film 30 are oriented in the
(001) plane and planes equivalent thereto (for example, the (002)
plane). It is to be understood that the crystal orientation of the
MgO film in the (001) plane is equivalent to the orientation of the
MgO film in [001] orientation (<001> orientation).
[0191] A reference layer 20' is provided on the MgO film 30. The
reference layer 20' includes the interface layer 22 and a TbCoFe
film 21'.
[0192] The interface layer 22 of the reference layer 20' is
provided between the TbCoFe film 21' and the MgO film 30. In the
present embodiment, the interface layer 22 has a multi-layer
structure including CoFeB/Ta/CoFeB. In other words, in the present
embodiment, the interface layer 22 has a structure in which the Ta
film is inserted between the two CoFeB films 25, 27.
[0193] The CoFeB film 25 in the lower layer (at the side of the
nonmagnetic layer) has a film thickness of 12 .ANG. (1.2 nm). The
CoFeB film 27 in the upper layer has a film thickness of 5 .ANG.
(0.5 nm). The Ta film 26 sandwiched between the two CoFeB films has
a film thickness of 3 .ANG. (0.3 nm).
[0194] The CoFeB film 25 in the lowermost layer of the interface
layer 22 is in contact with the MgO film (tunnel barrier layer) 30
oriented in the (001) plane.
[0195] The TbCoFe film 21' is provided on the interface layer 22.
The TbCoFe film has a film thickness of 120 .ANG. (12 nm).
[0196] The upper electrode 52 is provided on the TbCoFe film 21'.
The upper electrode 52 has a stacked structure including an Ru film
52b and a Ta film 52a. The Ta film 52a in the lower layer has a
film thickness of 50 .ANG. (5 nm). The Ru film 52b in the upper
layer has a film thickness of 200 .ANG. (20 nm).
[0197] Not only a sample having the Ta film 26 inserted into the
interface layer 22 of the reference layer 20' but also a sample not
having any Ta film inserted into the interface layer 22 of the
reference layer 20' are made and measured in order to compare the
effect of the heat treatment.
[0198] FIG. 12 shows a sample having been subjected to heat
treatment at 300.degree. C. for 30 minutes and a sample having been
subjected to heat treatment at 350.degree. C. for 30 minutes.
[0199] Images (a) and (b) of FIG. 12 show cross-sectional images,
obtained with the TEM, of the sample not having any Ta film
inserted into the CoFeB film of the interface layer 22 of the
reference layer 20'. Image (a) of FIG. 12 corresponds to the sample
having been subjected to the heat treatment at 300.degree. C. Image
(b) of FIG. 12 corresponds to the sample having been subjected to
the heat treatment at 350.degree. C.
[0200] Images (c) and (d) of FIG. 12 show cross-sectional images,
obtained with the TEM, of the sample using the interface layer of
the reference layer according to the present embodiment, i.e., the
sample having the Ta film 26 inserted into the CoFeB film 25, 27 of
the interface layer 22 of the reference layer 20'. Image (c) of
FIG. 12 corresponds to the sample having been subjected to the heat
treatment at 300.degree. C. Image (d) of FIG. 12 corresponds to the
sample having been subjected to the heat treatment at 350.degree.
C.
[0201] As shown in images (a) and (b) of FIG. 12, when the sample
having been subjected to the heat treatment at 350.degree. C.
(image (b) of FIG. 12) is compared with the sample having been
subjected to the heat treatment at 300.degree. C. (image (a) of
FIG. 12), in a case where the Ta film is not inserted into the
CoFeB film of the interface layer 22 of the reference layer 20',
the interface between the TbCoFe film 21' and the CoFeB film 27 in
the sample having been subjected to the heat treatment at
350.degree. C. (image (b) of FIG. 12) is moved upward (toward the
TbCoFe film 21'). In other words, as shown in image (b) of FIG. 12,
the film thickness of the interface layer 22 is thicker than the
film thickness of the interface layer 22 of the sample in image (a)
of FIG. 12.
[0202] This indicates that when the heat treatment is performed at
350.degree. C., the crystals in the interface layer 22 are oriented
in the (001) plane while the MgO film 30 oriented in (001) serves
as the underlayer for the interface layer 22, and along with the
crystallization of the interface layer 22, the crystals in the Tb
CoFe film 21a' at the side of the interface layer 22 are oriented
in the bcc (001) plane and planes equivalent to the (001) plane by
the heat treatment. In the TbCoFe film 21', the TbCoFe film 21b' at
the side of the upper electrode is less affected by the
crystallization.
[0203] In contrast, as shown in the images (c) and (d) of FIG. 12,
when the Ta film 26 is inserted into the CoFeB films 25, 27 of the
interface layer 22 of the reference layer 20' (in the case of the
present embodiment), the position of the interface between the
TbCoFe film 21' and the CoFeB film 27 and the film thickness of the
TbCoFe film 21' hardly changes even if the heat treatment is
performed at 350.degree. C. Therefore, when the Ta film is inserted
into the CoFeB film of the interface layer, the crystallization
growth of the TbCoFe film 21' using the MgO layer oriented in (001)
as the underlayer is prevented.
[0204] Each of the graphs in FIG. 14 shows the magnetic
characteristics of the MTJ element observed with the TEM as shown
in FIG. 12.
[0205] Graphs (a) and (b) of FIG. 14 show the magnetic
characteristics of the element when the Ta film is not inserted
into the interface layer 22 of the reference layer 20. Graphs (a)
and (b) of FIG. 14 correspond to the samples in images (a) and (b)
of FIG. 12, respectively. Graph (a) of FIG. 14 shows the magnetic
characteristics of the MTJ element (magnetic layer) having been
subjected to the heat treatment at 300.degree. C. Graph (b) of FIG.
14 shows the magnetic characteristics of the MTJ element having
been subjected to the heat treatment at 350.degree. C.
[0206] Graphs (c) and (d) of FIG. 14 show the magnetic
characteristics of the MTJ element in which the Ta film 26 is
inserted into the interface layer 22 of the reference layer 20.
Graphs (c) and (d) of FIG. 14 correspond to the samples in images
(c) and (d) of FIG. 12, respectively. Graph (c) of FIG. 14 shows
the magnetic characteristics of the MTJ element (magnetic layer)
having been subjected to the heat treatment at 300.degree. C. Graph
(d) of FIG. 14 shows the magnetic characteristics of the MTJ
element having been subjected to the heat treatment at 350.degree.
C.
[0207] The magnetic characteristics as shown in FIG. 14 shows an
M-H curve of each MTJ element.
[0208] In each of graphs (a) to (d) in FIG. 14, the horizontal axis
of the graph corresponds to an applied magnetic field H (unit:
kOe), and the vertical axis of the graph corresponds to a
magnetization M (unit: emu) of the MTJ element (magnetic
layer).
[0209] As shown in graph (b) of FIG. 14, when the temperature of
the heat treatment applied to the MTJ element reaches about
350.degree. C., the perpendicular magnetic anisotropy of the
element deteriorates.
[0210] As shown in graph (b) of FIG. 14, when the perpendicular
magnetic characteristics deteriorate, this will cause decrease of
retention energy of the MTJ element, larger distribution in the
element characteristics, increase of the write current, and
decrease of read output, which cause serious problems in the
operational characteristics and reliability of the MTJ element and
the memory using the MTJ element.
[0211] On the other hand, as shown in graph (d) of FIG. 14, when
the Ta film 26 is inserted between the CoFeB films 25, 27 serving
as the interface layer 22, the perpendicular magnetic anisotropy of
the element hardly deteriorates even when the heat treatment is
executed at about 350.degree. C.
[0212] Therefore, when the Ta film 26 is inserted between the CoFeB
films 25, 27 serving as the interface layer 22 for the reference
layer 20' as shown in the present embodiment, the crystallization
of the TbCoFe film 21' (perpendicular magnetic film) in the (001)
plane is prevented in the reference layer 20' even if high
temperature (for example, 350.degree. C. or more) heat treatment is
executed. Therefore, deterioration of the perpendicular magnetic
anisotropy of the reference layer can be prevented.
[0213] FIGS. 15A, 15B, 16A, and 16B illustrate measurement results
of electron energy-loss spectroscopy (EELS). FIGS. 15A and 15B
illustrate EELS measurement results of the MTJ element when the
heat treatment is executed at 300.degree. C. for 30 minutes.
[0214] FIGS. 16A and 16B illustrate EELS measurement results of the
MTJ element when the heat treatment is executed at 350.degree. C.
for 30 minutes
[0215] In FIGS. 15A to 16B, the horizontal axis of each graph
corresponds to a depth from the upper surface of the element in a
direction in which the films are stacked (unit: nm), and the
vertical axis of each graph corresponds to a detected signal
strength (arbitrary unit).
[0216] FIGS. 15A and 16A illustrate EELS analysis results of the
MTJ element in which the Ta film 26 is not provided in the
interface layer 22. FIGS. 15B and 16B illustrate EELS analysis
results of the MTJ element according to the present embodiment in
which the Ta film 26 is provided in the interface layer 22.
[0217] In FIGS. 15A to 16B, a position (depth) where the detection
intensity of Mg is high corresponds to the position of the MgO film
in the element.
[0218] As shown in FIGS. 15A and 16A, when the Ta film is not
provided in the interface layer, Tb (solid line in the graph) is
detected in a portion where the detection peak of Mg appears
(region indicated as A1 or B1 in the graph). This indicates that Tb
diffuses into the MgO film or a portion in proximity to the
interface between the MgO film and the CoFeB film.
[0219] On the other hand, as shown in FIGS. 15B and 16B, when the
Ta film 26 is provided in the interface layer 22, Tb (solid line in
the graph) is hardly detected in the portion where the detection
peak of Mg appears (regions A2, B2) even if the heat treatment is
performed at 350.degree. C. In other words, when the Ta film 26 is
provided (inserted) in the interface layer 22, Tb in the TbCoFe
film 21' can be prevented from diffusing into the MgO film 30 or a
portion in proximity to the MgO film 30.
[0220] As described above, the Ta film 26 inserted between the
CoFeB films 25, 27 serving as the interface layer 22 prevents Tb
included in the TbCoFe film 21' from diffusing into the interface
between the interface layer (CoFeB film) and the tunnel barrier
layer (MgO film) 30. The Ta film 26 in the interface layer 22
functions as diffusion prevention film for Tb.
[0221] As described above, when the Ta film 26 is inserted between
the CoFeB films 25, 27 serving as the interface layer 22 for the
reference layer 20, the crystallinity of the CoFeB film in the
interface layer 22 can be improved while preventing the
crystallization of the TbCoFe film 21'. In addition, the interface
layer 22 has the multi-layer structure including the Ta film 26, so
that Tb in the TbCoFe film can be prevented from diffusing into the
tunnel barrier layer (MgO film) or a portion in proximity to the
tunnel barrier layer.
[0222] Therefore, the MTJ element according to the present
embodiment can attain a high MR ratio.
[0223] In this case, the Ta film 26 is provided between the two
CoFeB films 25, 27. Alternatively, instead of the Ta film 26, a
tungsten (W), niobium (Nb), or molybdenum (Mo) film may be used as
long as it is high melting point metal. For example, the Ta film
(or W film, Nb film, Mo film) is inserted in-situ during deposition
of the CoFeB film.
[0224] It should be noted that the CoFeB film 27 may not be
provided. In this case, as shown in FIG. 17, the structure is such
that a metal film 26 is provided between the perpendicular magnetic
film 21 and the interface layer 25, and the TbCoFe film is in
contact with the Ta film (or W film, Nb film, Mo film). As
described above, even if the CoFeB film 27 is not provided, the MTJ
element according to the present embodiment can attain a high MR
ratio.
[0225] In the two CoFeB films 25, 27 sandwiching the Ta film 26,
the CoFeB film 25 at the side of the tunnel barrier layer 30 and
the CoFeB film 27 at the side of the perpendicular magnetic film 21
may have different composition ratios of Co, Fe, and B. For
example, a CoB film or a CoFe film may be used instead of the CoFeB
film. In the above case, the CoFeB film is used as the interface
layer 22. However, other materials may be used as the interface
layer 22.
[0226] In this case, for example, the Tb CoFe film is formed in the
reference layer. However, it is to be understood that even when Gd
and Dy are used instead of Tb, the same effects can be
obtained.
(e) Conclusion
[0227] In a process of manufacturing the MTJ element or a magnetic
memory using the MTJ element (for example, an MRAM), the magnetic
layer and the MTJ element may be exposed to a process condition of
a high temperature (for example, 350.degree. C. or more) in order
to improve the crystallinity of the nonmagnetic layer (for example,
an MgO film) and the storage layer and form constituent members. In
such high-temperature heat treatment, the amorphous perpendicular
magnetic film serving as the magnetic layer of the MTJ element is
deteriorated, and accordingly, the characteristics of the MTJ
element are deteriorated.
[0228] The perpendicular magnetic film (for example, a TbCoFe film)
including the amorphous phases and the crystals is used in the
magnetic layer (for example, a reference layer) of the MTJ element
according to the present embodiment. As a result, the heat
resistance of the element improves, and the element characteristics
can be improved without being adversely affected by the
heating.
[0229] An interface layer may be provided between the TbCoFe film
and the tunnel barrier layer. In the MTJ element according to the
present embodiment, the Ta film (or W film) is inserted into the
interface layer (for example, a CoFeB film), and the interface
layer having the multi-layer structure including the Ta film or the
W film is formed, such as CoFeB/Ta/CoFeB film.
[0230] When the Ta film (or W film, Nb film, or Mo film) is
inserted into the interface layer 22, the crystallization of the
amorphous perpendicular magnetic film (for example, a TbCoFe film)
caused by the crystallization of the interface layer can be
prevented. Further, this prevents Tb in the TbCoFe film from
diffusing into the tunnel barrier layer (for example, an MgO film)
and a portion in proximity to the interface between the interface
layer and the tunnel barrier layer.
[0231] Therefore, the element characteristics of the perpendicular
magnetization-type magnetoresistive effect element according to the
present embodiment hardly deteriorate even when the heat treatment
is executed.
[0232] As described above, the element characteristics of the
magnetoresistive effect element according to the first embodiment
can be improved.
(3) Second Embodiment
[0233] A magnetoresistive effect element according to the second
embodiment will be explained with reference to FIGS. 18 and 19. In
the magnetoresistive effect element according to the second
embodiment, detailed description about substantially the same
members as those in the magnetoresistive effect element according
to the first embodiment is omitted.
[0234] The magnetoresistive effect element according to the first
embodiment is the top pin-type MTJ element, in which the recording
layer of the perpendicular magnetization is provided below the
tunnel barrier film.
[0235] As shown in FIG. 18, the magnetoresistive effect element
according to the second embodiment (MTJ element) is a bottom
pin-type MTJ element. In other words, on the contrary to the first
embodiment, an MTJ element 1B according to the present embodiment
has a recording layer 10 on a tunnel barrier film 30. A reference
layer 20 is provided below the recording layer 10 with the tunnel
barrier layer 30 interposed therebetween. The reference layer 20
includes a perpendicular magnetic film 21 and an interface layer
22. Like the first embodiment, the perpendicular magnetic film (for
example, a TbCoFe film) 21 also includes amorphous phases 29 and
crystals 28 in the present embodiment.
[0236] As shown in FIG. 19, the perpendicular magnetic film
including the amorphous phases 29 and the crystals 28 may also be
used for a magnetic layer (recording layer) in which magnetization
direction is variable.
[0237] Further, in the magnetoresistive effect elements 1B, 1C
according to the present embodiment, a Ta film (or W film, Nb film,
or Mo film) 26 is provided in the interface layer 22.
[0238] Therefore, like the first embodiment, the magnetoresistive
effect elements 1B, 1C according to the second embodiment can
improve the characteristics of the perpendicular magnetization-type
magnetoresistive effect element.
(4) Third Embodiment
[0239] A magnetoresistive effect element according to the third
embodiment will be explained with reference to FIG. 20. In the
magnetoresistive effect element according to the third embodiment,
detailed description about substantially the same members as those
in the magnetoresistive effect element according to the first
embodiment is omitted.
[0240] A magnetoresistive effect element 1D according to the
present embodiment is different from the magnetoresistive effect
element according to the first and second embodiments in that a
bias layer 59 is provided adjacent to a reference layer 20. A
nonmagnetic layer 58 is provided between the bias layer 59 and the
reference layer 21. A bottom surface (first surface) of a reference
layer 20 is in contact with a tunnel barrier layer 30, and an upper
surface (second surface) of the reference layer 20 is in contact
with a nonmagnetic layer 58.
[0241] The bias layer 58 is a magnetic layer of perpendicular
magnetization. For example, the magnetization direction of the bias
layer 58 is opposite to the magnetization direction of the
reference layer. The bias layer 58 prevents change of thermal
stability between the parallel state and antiparallel state of the
relationship of the magnetization directions of the reference layer
and the recording layer caused by shift of the magnetic switching
field Hc of the recording layer 10 affected by magnetostatic stray
field from the reference layer 20.
[0242] An example of material that can be used as the bias layer 58
includes the perpendicular magnetic film cited as an example of
material that can be used as the reference layer. That is, like the
perpendicular magnetic film 21 in the reference layer 20, the bias
layer 58 is formed using a magnetic film including amorphous phases
29 and crystals 28.
[0243] The material of the nonmagnetic layer 58 between the
reference layer 20 and the bias layer 59 is preferably selected
from such materials that make stable exchange bias when the
magnetization direction of the reference layer 20 and the
magnetization direction of the bias layer 59 are antiparallel. The
material of the nonmagnetic layer 58 is preferably nonmagnetic
metal. For example, the material of the nonmagnetic layer 58 is
selected from Ru, silver (Ag), and Cu.
[0244] An interface layer such as CoFe, Co, Fe, CoFeB, CoB, and FeB
between the nonmagnetic layer 58 (for example, Ru) and the
perpendicular magnetic film serving as the reference layer 20 and
the bias layer 59 may be provided in order to increase antiparallel
coupling between the reference layer 20 and the bias layer 59 via
the nonmagnetic layer 58. This enhances the antiparallel coupling
between the reference layer 20 and the bias layer 59.
[0245] Therefore, in the magnetoresistive effect element according
to the third embodiment, the element characteristics of the
perpendicular magnetization-type magnetoresistive effect element
can be improved, like the magnetoresistive effect element according
to the first and second embodiment.
Application Example
[0246] An application example of the magnetoresistive effect
element (MTJ element) according to the first to third embodiments
will be explained with reference to FIGS. 21 to 24.
[0247] The above MTJ element according to the embodiments is used
as a memory element in a magnetic memory such as a magnetoresistive
random access memory (MRAM). For example, a spin-transfer-torque
MRAM will be explained as the MRAM according to the application
example.
[0248] (a) Configuration
[0249] FIG. 21 is a figure illustrating a circuit configuration in
a memory cell array of the MRAM and a circuit configuration in
proximity thereto.
[0250] As shown in FIG. 21, a memory cell array 9 includes a
plurality of memory cells MC.
[0251] The plurality of memory cells MC are arranged in an array
form in the memory cell array 9. A plurality of bit lines BL, bBL
and a plurality of word lines WL are arranged in the memory cell
array 9. The bit lines BL, bBL extend in a column direction, and
the word lines WL extend in a row direction. The two bit lines BL,
bBL form a pair of bit lines.
[0252] The memory cell MC is connected to the bit lines BL, bBL and
the word lines WL.
[0253] Each of the plurality of memory cells MC arranged in the
column direction is connected to the common bit line pair BL, bBL.
Each of the plurality of memory cells MC arranged in the row
direction is connected to the common word line WL.
[0254] For example, the memory cell MC includes magnetoresistive
effect element (MTJ element) 1 and a selection switch 2. The MTJ
element explained in the first to third embodiments is used as the
MTJ element 1 in the memory cell MC. In the explanation below, the
MTJ element according to the first embodiment is used as the MRAM.
However, it is to be understood that the MTJ elements according to
the second and third embodiments may also be used as the MRAM.
[0255] For example, the selection switch 2 is a field effect
transistor. Hereinafter, the field effect transistor serving as the
selection switch 2 will be referred to as a select transistor
2.
[0256] One end of the MTJ element 1 is connected to the bit line
BL, and the other end of the MTJ element 1 is connected to one end
of a current path of the select transistor 2 (source/drain). The
other end of the current path of the select transistor 2
(drain/source) is connected to the bit line bBL. A control terminal
(gate) of the select transistor 2 is connected to the word line
WL.
[0257] One end of the word line WL is connected to a row control
circuit 4. The row control circuit 4 controls
activation/deactivation of a word line on the basis of an address
signal provided from the outside.
[0258] One end and the other end of each of the bit lines BL, bBL
is connected to column control circuits 3A, 3B. The column control
circuits 3A, 3B controls activation/deactivation of a bit line on
the basis of an address signal provided from the outside
[0259] Write circuits 5A, 5B are respectively connected to one end
and the other end of each bit line via the column control circuits
3A, 3B. The write circuits 5A, 5B respectively have a source
circuit such as a voltage source and a current source for
generating a write current and a sink circuit for absorbing the
write current.
[0260] In the spin-transfer-torque MRAM, the write circuits 5A, 5B
supplies a write current Iw to memory cell (hereinafter, selected
cell) selected from the outside during data write operation. The
write circuits 5A, 5B pass the write current Iw through the MTJ
element 1 in the memory cell MC in both directions in accordance
with data to be written to the selected cell. In other words, the
write circuits 5A, 5B output the write current Iw passing from the
bit line BL to the bit line bBL or the write current Iw passing
from the bit line bBL to the bit line BL in accordance with the
data to be written.
[0261] Read circuits 6A, 6B respectively are connected to one end
and the other end of each of the bit lines BL, bBL via the column
control circuits 3A, 3B. The read circuits 6A, 6B include a voltage
source or a current source for generating a read current, a sense
amplifier for detecting and amplifying a read signal, a latch
circuit for temporarily holding data, and the like. The read
circuits 6A, 6B supply a read current to a selected cell during
data read operation. The read current is less than the write
current Iw (reversal threshold value), so that the magnetization of
the recording layer is not reversed by the read current.
[0262] The current or the potential at the read node differs
according to the resistance of the MTJ element 1 to which the read
current is supplied. On the basis of the amount of change according
to the resistance, data stored in the MTJ element 1 are
determined.
[0263] In the example as shown in FIG. 21, the read circuits 6A, 6B
are provided at both ends in the column direction. Alternatively,
only one read circuit may be provided at one end in the column
direction.
[0264] FIG. 22 is a cross-sectional view illustrating an example of
a structure of a memory cell MC arranged in the memory cell array
9.
[0265] The memory cell MC is formed in an active region AA of a
semiconductor substrate 70. The active region AA is divided by
insulating films 71 embedded in element isolation regions of the
semiconductor substrate 70.
[0266] The upper end of the MTJ element 1 is connected to a bit
line 76 (BL) via an upper electrode 52. The lower end of the MTJ
element 1 is connected to a source/drain diffusion layer 64 of the
select transistor 2 via the lower electrode 51 and a contact plug
72B. A source/drain diffusion layer 63 of the select transistor 2
is connected to a bit line 75 (bBL) via a contact plug 72A.
[0267] A gate electrode 62 is formed on the surface of the active
region AA between the two source/drain diffusion layers 63, 64 with
a gate insulating film 61 interposed therebetween. The gate
electrode 62 extends in the row direction, and is used as the word
line WL.
[0268] In this case, the MTJ element 1 is arranged immediately
above the plug 72B. Alternatively, an intermediate interconnect
layer may be used, and the MTJ element 1 may be arranged at a
position displaced from the position immediately above the contact
plug (for example, above the gate electrode of the select
transistor).
[0269] FIG. 22 shows an example where one memory cell is provided
in one active region AA. Alternatively, two memory cells may be
arranged adjacent to each other in the column direction in one
active region AA, so that two memory cells share one bit line bBL
and the source/drain diffusion layer 23. This configuration reduces
the cell size of the memory cell MC.
[0270] In FIG. 22, the selection transistor 2 is the field effect
transistor having planar structure. However, the structure of the
field effect transistor is not limited thereto. Alternatively, a
three-dimensional structure field effect transistor such as a
recess channel array transistor (RCAT) and a FinFET may be used as
the select transistor. The RCAT has such a structure in which a
gate electrode is embedded in a recess in a semiconductor region
with a gate insulating film interposed therebetween. The FinFET has
such a structure in which a gate electrode cross a strip-like
semiconductor region (fin) in a grade separation manner with a gate
insulating film interposed therebetween.
[0271] As explained in the first to third embodiments, the
magnetoresistive effect element (MTJ element) according to each
embodiment has heat resistance against high-temperature (about
350.degree. C.), and the element characteristics of the MTJ element
can be improved. In other words, difference between the resistance
of the MTJ element in the low-resistance (parallel) state and the
resistance of the MTJ element in the high-resistance (antiparallel)
state is large. Therefore, there is a large difference in the
amount of change of the potential or the current between the two
static states, and accordingly, data stored in the MTJ element
serving as the memory element can be read with a high degree of
reliability. Therefore, the MRAM using the MTJ element according to
the present embodiment can improve the reliability of data read
operation in the MRAM.
[0272] (b) Manufacturing Method
[0273] A method for manufacturing the memory cell in the MRAM
according the application example will be explained with reference
to FIGS. 23 and 24.
[0274] FIGS. 23 and 24 illustrate a cross section taken in the
column direction of the memory cell MC in each manufacturing step
of the MRAM.
[0275] As shown in FIG. 23, for example, the isolation insulating
films 71 having a shallow trench isolation (STI) structure are
embedded into the semiconductor substrate 70, so that an element
isolation regions are formed. The active regions AA are divided in
the semiconductor substrate 70 by forming the element isolation
regions.
[0276] Then, the select transistor 2 of the memory cell MC is
formed on each active region AA on the semiconductor substrate 70.
The steps for forming the select transistors are as follows.
[0277] The gate insulating film 61 is formed on the surface of the
active region AA. The gate insulating film 61 is a silicon oxide
film formed by the thermal oxidation method, for example.
Subsequently, a conductive layer (for example, a polysilicon layer)
is formed on the gate insulating film 21 by the chemical vapor
deposition (CVD) method, for example.
[0278] The conductive layer is processed into a predetermined
pattern using the photolithography technique and reactive ion
etching (RIE) method, for example. As a result, the gate electrode
62 is formed on the gate insulating film 61. Since the gate
electrode 62 is used as the word line, the gate electrode 62 is
formed to extend in the row direction. Therefore, the gate
electrode 62 is shared by a plurality of select transistors
arranged along the row direction.
[0279] The source/drain diffusion layers 63, 64 are formed in the
semiconductor substrate 70. The diffusion layers 63, 64 are formed
by injecting impurities such as arsenic (As), phosphorus (P) into
the semiconductor substrate 70 by the ion implantation method using
the gate electrode 62 as a mask.
[0280] With the above steps, the select transistor 2 is formed on
the semiconductor substrate 70. In addition, a step for forming a
silicide layer on the upper surfaces of the gate electrode 62 and
the diffusion layers 63, 64 may be further added.
[0281] Then, a first inter-layer insulating film 79A is deposited
on the semiconductor substrate 70 to cover the select transistor 2
using the CVD method, for example. The upper surface of the
inter-layer insulating film 33 is planarized using the chemical
mechanical polishing (CMP) method.
[0282] In the inter-layer insulating film 79A, a contact hole is
formed so that the upper surface of the source/drain diffusion
layer 63 is exposed. For example, tungsten (W) or molybdenum (Mo)
is filled in the formed contact hole, whereby the contact plug 72A
is formed.
[0283] The metal film is deposited on the inter-layer insulating
film 79A and the contact plug 72. The deposited metal film is
processed into a predetermined shape using photolithography
technique the RIE method. As a result, the bit line 75 (bBL)
connected to the current path of the select transistor 2 is
formed.
[0284] Thereafter, a second inter-layer insulating film 79B is
deposited on the inter-layer insulating film 79A and the bit line
75B by the CVD method, for example. Then, a contact hole is formed
in the inter-layer insulating films 79A, 79B so that the surface of
the source/drain diffusion layer 64 is exposed. The contact plug
72B is embedded in the contact hole by the sputtering method or CVD
method.
[0285] The constituent members of the magnetoresistive effect
element 1A according to the present embodiment (MTJ element) are
deposited in order on the inter-layer insulating film 79B and the
contact plug 72B substantially in the same manner as the above
explanation made with reference to FIGS. 3 and 4. The inter-layer
insulating film 79B and the contact plug 72B are used as the
substrate for forming the MTJ element 1A.
[0286] Then, as shown in FIG. 24, after the MTJ element is
processed, an inter-layer insulating film (for example, SiO.sub.2)
79C is formed using the CVD method, for example.
[0287] During the deposition of the inter-layer insulating film
79C, the processed MTJ element 1A is exposed to the temperature
condition of 300.degree. C. or more, for example.
[0288] As described above, the perpendicular magnetic film (for
example, a TbCoFe film) in the magnetic layer (for example, a
reference layer) of the MTJ element 1A according to the present
embodiment includes the amorphous phases and the microcrystals
(crystals of 1 nm or less). The TbCoFe film 21 including the
amorphous phases and the microcrystals in the MTJ element 1A
according to the present embodiment has heat resistance against
high-temperature (350.degree. C. or more). Therefore, even when
high-temperature heat is applied, the entire Tb Co Fe film is not
crystallized, and the amorphous phases do not disappear. Therefore,
this prevents deterioration of the characteristics of the MTJ
element caused by the crystallization of the TbCoFe film 21.
[0289] The interface layer (for example, a CoFeB/Ta/CoFeB film) is
provided, in which the Ta film is inserted between the TbCoFe film
21 and the tunnel barrier layer 30. This prevents Tb in the TbCo Fe
film 21 from diffusing into the tunnel barrier layer 30 and a
portion in proximity to the interface between the tunnel barrier
layer 30 and the reference layer 20 due to the heat applied during
deposition of the inter-layer insulating film.
[0290] Thereafter, the bit line BL is formed on the inter-layer
insulating film 79C using a well-known technique.
[0291] With the above manufacturing steps, the memory cell of the
MRAM according to the application example is formed.
[0292] As explained with reference to FIGS. 21 to 24, the
magnetoresistive effect element according to the present embodiment
(MTJ element) can be applied to the MRAM. As described above,
according to the magnetoresistive effect element according to the
present embodiment (MTJ element), the MTJ element having improved
element characteristics can be provided.
[0293] Therefore, the operational characteristics and reliability
of the memory can be improved in the MRAM according to the
application example by using the magnetoresistive effect element
according to the present embodiment.
[0294] [Others]
[0295] The magnetoresistive effect element according to the first
to third embodiments can improve the element characteristics.
[0296] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *