U.S. patent application number 12/000156 was filed with the patent office on 2008-05-22 for method of manufacturing magnetic random access memory (mram).
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. Invention is credited to Tae-wan Kim, Jang-eun Lee, Sang-jin Park, Wan-jun Park.
Application Number | 20080118993 12/000156 |
Document ID | / |
Family ID | 34651242 |
Filed Date | 2008-05-22 |
United States Patent
Application |
20080118993 |
Kind Code |
A1 |
Park; Sang-jin ; et
al. |
May 22, 2008 |
Method of manufacturing magnetic random access memory (MRAM)
Abstract
A magnetic random access memory (MRAM), and a method of
manufacturing the same, includes a switching device and a magnetic
tunneling junction (MTJ) cell connected to the switching device,
wherein the MTJ cell includes a pinned film having a metal film and
a magnetic film, the magnetic film enclosing the metal film.
Inventors: |
Park; Sang-jin;
(Pyeongtaek-si, KR) ; Kim; Tae-wan; (Yongin-si,
KR) ; Park; Wan-jun; (Seoul, KR) ; Lee;
Jang-eun; (Suwon-si, KR) |
Correspondence
Address: |
LEE & MORSE, P.C.
3141 FAIRVIEW PARK DRIVE
SUITE 500
FALLS CHURCH
VA
22042
US
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
34651242 |
Appl. No.: |
12/000156 |
Filed: |
December 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10971704 |
Oct 25, 2004 |
7317219 |
|
|
12000156 |
Dec 10, 2007 |
|
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Current U.S.
Class: |
438/3 ;
257/E21.001 |
Current CPC
Class: |
G11C 11/15 20130101;
H01L 43/08 20130101; H01L 43/12 20130101 |
Class at
Publication: |
438/003 ;
257/E21.001 |
International
Class: |
H01L 21/00 20060101
H01L021/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 24, 2003 |
KR |
10-2003-0074663 |
Claims
1-5. (canceled)
6. A method of manufacturing a magnetic random access memory
(MRAM), comprising: forming a switching device in a substrate;
forming an interlayer dielectric on the substrate to cover the
switching device; forming a stack structure on a predetermined
region of the interlayer dielectric, the stack structure including
a lower electrode, a buffering film, a pinning film, a first
magnetic film, a metal film, a second magnetic film, a tunneling
film, a free magnetic film, and a capping film, and the stack
structure being connected to the switching device; and contacting
the first magnetic film to the second magnetic film in the stack
structure.
7. The method as claimed in claim 6, wherein forming the stack
structure comprises sequentially stacking the lower electrode, the
buffering film, the pinning film, the first magnetic film, the
metal film, the second magnetic film, the tunneling film, the free
magnetic film, and the capping film.
8. The method as claimed in claim 7, wherein forming the stack
structure further comprises: forming a contact hole in the
interlayer dielectric to expose the switching device; filling the
contact hole with a conductive plug; sequentially forming the lower
electrode to cover the conductive plug, the buffering film, the
pinning film, the first magnetic film, the metal film, the second
magnetic film, the tunneling film, the free magnetic film, and the
capping film on the interlayer dielectric; forming a photoresist
pattern on the capping film to define the predetermined region of
the interlayer dielectric; etching the films stacked on the
interlayer dielectric using the photoresist pattern as an etch
mask; and removing the photoresist pattern.
9. The method as claimed in claim 7, wherein contacting the first
magnetic film to the second magnetic film is performed before
stacking the tunneling film, the free magnetic film, and the
capping film.
10. The method as claimed in claim 6, wherein contacting the first
magnetic film to the second magnetic film comprises removing an
outer portion of the metal film.
11. The method as claimed in claim 6, wherein the first magnetic
film and the second magnetic film are formed to different
thicknesses.
12. The method as claimed in claim 10, wherein removing the outer
portion of the metal film comprises etching using an etchant having
a high etch selectivity with respect to the metal film.
13. The method as claimed in claim 6, wherein forming the stack
structure comprises sequentially stacking the lower electrode, the
buffering film, the free magnetic film, the tunneling film, the
first magnetic film, the metal film, the second magnetic film, the
pinning film, and the capping film.
14. The method as claimed in claim 13, wherein forming the stack
structure further comprises: forming a contact hole in the
interlayer dielectric to expose the switching device; filling the
contact hole with a conductive plug; sequentially forming the lower
electrode to cover the conductive plug, the buffering film, the
free magnetic film, the tunneling film, the first magnetic film,
the metal film, the second magnetic film, the pinning film, and the
capping film on the interlayer dielectric; forming a photoresist
pattern on the capping film to define the predetermined region of
the interlayer dielectric; etching the films stacked on the
interlayer dielectric using the photoresist pattern as an etch
mask; and removing the photoresist pattern.
15. The method as claimed in claim 13, wherein contacting the first
magnetic film to the second magnetic film is performed before
stacking the pinning film and the capping film.
16. The method as claimed in claim 6, wherein the buffering film is
an amorphous film.
17. The method as claimed in claim 6, wherein the pinning film is a
semi-ferromagnetic film.
18. The method as claimed in claim 6, wherein each of the first and
second magnetic films is a semi-ferromagnetic film.
19. The method as claimed in claim 6, wherein each of the first and
second magnetic films is a cobalt iron (CoFe) film.
20. The method as claimed in claim 6, wherein the metal film is
ruthenium (Ru) or another metal.
21. A method of manufacturing magnetic random access memory (MRAM),
comprising: forming a switching device; and forming a magnetic
tunneling junction (MTJ) cell connected to the switching device,
wherein forming the MTJ cell includes: forming a pinned film having
a single metal film and a magnetic film, the magnetic film
enclosing the metal film; forming a tunneling film; and forming a
free magnetic film, wherein: the tunneling film is disposed between
the free magnetic film and the pinned film, and the metal film
extends laterally within the magnetic film and has a width that is
less than that of the magnetic film.
22. The method as claimed in claim 21, further comprising forming
an interlayer dielectric covering the switching device, wherein the
switching device is connected to the MTJ cell by a conductive plug
that passes through the interlayer dielectric.
23. The method as claimed in claim 22, wherein the first and second
magnetic films contact each other only at sides of the pinned
film.
24. A method of manufacturing magnetic random access memory (MRAM),
comprising: forming a switching device; and forming a magnetic
tunneling junction (MTJ) cell connected to the switching device,
forming the MTJ cell including: forming a pinned film having a
single metal film and a magnetic film, the magnetic film enclosing
the metal film such that exactly one closed loop surrounding the
metal film can be formed in the magnetic film by a magnetic field
generated in the magnetic film; forming a tunneling film; and
forming a free magnetic film, wherein the tunneling film is
disposed between the free magnetic film and the pinned film.
25. The method as claimed in claim 24, wherein forming the free
magnetic film includes: forming a first magnetic film; and forming
a second magnetic film, wherein: an outer portion of the first
magnetic film contacts an outer portion of the second magnetic
film, and the closed loop surrounding the metal film extends
between the tunneling film and the metal film, within the first
magnetic film.
26. The MRAM as claimed in claim 24, wherein the free magnetic film
is a single material.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application based on pending
application Ser. No. 10/971,704, filed Oct. 25, 2004, the entire
contents of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a semiconductor memory
device and a method of manufacturing the same. More particularly,
the present invention relates to a magnetic random access memory
(MRAM) including a magnetic tunneling junction (MTJ) cell and a
method of manufacturing the same.
[0004] 2. Description of the Related Art
[0005] A magnetic random access memory (MRAM) is a memory device
that writes and reads data using a phenomenon in which a resistance
of a magnetic tunneling junction (MTJ) cell varies according to a
magnetization direction of upper and lower magnetic films, which
are separated by an insulating film in the MTJ cell.
[0006] FIG. 1 illustrates a cross-sectional view of a conventional
MTJ cell included in a conventional MRAM.
[0007] Referring to FIG. 1, the conventional MTJ cell M1 of the
conventional MRAM includes an amorphous buffering film 12 and a
pinning film 14, which is a semi-ferromagnetic film, that are
sequentially formed on a lower electrode 10. A pinned film 16 is
formed on the pinning film 14. The pinned film 16 includes a first
ferromagnetic film 16a, a metal film 16b, and a second
ferromagnetic film 16c, which are sequentially formed on the entire
surface of the pinning film 14. Arrows in FIG. 1 indicate
directions of magnetic fields in the first and second ferromagnetic
films 16a and 16c. It can be seen that a direction of a magnetic
field in the first ferromagnetic film 16a is opposite to a
direction of a magnetic field in the second ferromagnetic film
16c.
[0008] Generally, a film including a metal film having magnetic
films disposed on and under the metal film, e.g., the pinned film
16, is called a synthetic anti-ferromagnetic (SAF) film. In an SAF
film, spin directions of upper and lower magnetic films are fixed
in an antiparallel state due to a thickness of the metal film. In
the SAF film, an exchange bias between the upper and lower magnetic
films exceeds 1000 Oe. Thus, the thermal stability of the SAF film
is superior to that of a single magnetic film. Accordingly, the SAF
film has widely been used as a pinned film of an MTJ cell.
[0009] Referring again to FIG. 1, a tunneling film 22 is formed on
the second ferromagnetic film 16c of the pinned film 16. A free
magnetic film 24 and a capping film 26 are then sequentially formed
on the tunneling film 22. The direction of the magnetic field of
the free magnetic film 24 is determined by an external magnetic
field. The capping film 26 protects the free magnetic film 24.
[0010] The MTJ cell generates a stray magnetic field, which is
caused by the first ferromagnetic film 16a and/or the second
ferromagnetic film 16c. This stray magnetic field affects the free
magnetic film 24 by causing a kink when the free magnetic film 24
is switched.
[0011] More specifically, the stray magnetic field affects a
portion, in particular, an outer portion, of the free magnetic film
24 while the free magnetic film 24 is being switched. As a result,
the affected portion of the free magnetic film 24 operates
abnormally in that it is later in switching than other portions
thereof or enters a substantially different magnetization
state.
[0012] The effect of the stray magnetic field depends on the
thicknesses of the elements constituting the MTJ cell M1. As an
example, FIGS. 2 through 5 are graphs showing the influence of a
stray magnetic field on the switching characteristic of the free
magnetic film 24 depending on thicknesses of the elements of the
MTJ cell M1.
[0013] FIG. 2 shows the switching characteristic of the free
magnetic film 24 when the first ferromagnetic film 16a, which is a
lower magnetic film of the pinned film 16, is thicker than the
second ferromagnetic film 16c, which is an upper magnetic film
(hereinafter, the first case).
[0014] In FIG. 2, reference characters C1 and C2 denote a first
magnetization state indicating unit and a second magnetization
state indicating unit (hereinafter, first and second indicating
units), which indicate the magnetization states of the free
magnetic film 24 and the first and second ferromagnetic films 16a
and 16c in the first case. In the first and second indicating units
C1 and C2, two lowermost arrows indicate the magnetization state of
the first ferromagnetic film 16a, an intermediate arrow indicates
the magnetization state of the second ferromagnetic film 16b, and
an uppermost arrow indicates the magnetization state of the free
magnetic film 24.
[0015] Referring to FIG. 2, in the first case, there exists a
region P1 in which the free magnetic film 24 is abnormally switched
in a switching characteristic curve of the free magnetic film 24.
Thus, a switching magnetic field is shifted.
[0016] FIG. 3 shows a switching characteristic of the free magnetic
film 24 when the second ferromagnetic film 16c is thicker than the
first ferromagnetic film 16a (hereinafter, the second case).
[0017] In FIG. 3, reference characters C3 and C4 denote a third
magnetization state indicating unit and a fourth magnetization
state indicating unit (hereinafter, third and fourth indicating
units), which indicate the magnetization states of the free
magnetic film 24 and the first and second magnetization state
indicating units 16a and 16c in the second case. In the third and
fourth indicating units C3 and C4, a lowermost arrow indicates the
magnetization state of the first ferromagnetic film 16a, two
intermediate arrows indicate the magnetization state of the second
ferromagnetic film 16c, and an uppermost arrow indicates the
magnetization state of the free magnetic film 24.
[0018] Referring to FIG. 3, in the second case, there exists a
region P4 in which the free magnetic film 24 is abnormally switched
in a lower right portion of a switching characteristic curve of the
free magnetic film 24. Thus, a switching magnetic field is
shifted.
[0019] FIG. 4 shows a switching characteristic of the free magnetic
film 24 when the first ferromagnetic film 16a is as thick as the
second ferromagnetic film 16c and both are relatively thick
(hereinafter, the third case).
[0020] In FIG. 4, reference characters C5 and C6 denote a fifth
magnetization state indicating unit and a sixth magnetization state
indicating unit (hereinafter, fifth and sixth indicating units),
which indicate the magnetization states of the free magnetic film
24 and the first and second ferromagnetic films 16a and 16c in the
third case. In the fifth and sixth indicating units C5 and C6, two
lowermost arrows indicate the magnetization state of the first
ferromagnetic film 16a, two intermediate arrows indicate the
magnetization state of the second ferromagnetic film 16c, and an
uppermost arrow indicates the magnetization state of the free
magnetic film 24.
[0021] Referring to FIG. 4, in the third case, there exist regions
P2 and P3 in which the free magnetic film 24 is abnormally switched
in left and right portions of a switching characteristic curve of
the free magnetic film 24. Thus, a switching magnetic field is
shifted.
[0022] FIG. 5 shows a switching characteristic of the free magnetic
film 24 when the first ferromagnetic film 16a is as thick as the
second ferromagnetic film 16c and both are relatively thin
(hereinafter, the fourth case).
[0023] In FIG. 5, reference characters C7 and C8 denote a seventh
magnetization state indicating unit and an eighth magnetization
state indicating unit (hereinafter, seventh and eighth indicating
units), which indicate the magnetization states of the free
magnetic film 24 and the first and second ferromagnetic films 16a
and 16c. In the seventh and eighth indicating units C7 and C8, a
lowermost arrow indicates the magnetization state of the first
ferromagnetic film 16a, an intermediate arrow indicates the
magnetization sate of the second ferromagnetic film 16c, and an
uppermost arrow indicates the magnetization state of the free
magnetic film 24.
[0024] Referring to FIG. 5, in the fourth case, although there is
no region in which the free magnetic film 24 is abnormally switched
in a switching characteristic curve of the free magnetic film 24 as
opposed to the first through third cases. However, a switching
magnetic field is still shifted.
SUMMARY OF THE INVENTION
[0025] The present invention is therefore directed to a magnetic
random access memory (MRAM) and a method of manufacturing the same,
which substantially overcome one or more of the problems due to the
limitations and disadvantages of the related art.
[0026] It is a feature of an embodiment of the present invention to
provide an MRAM, and a method of manufacturing the same, that
prevents shifting of a switching magnetic field, thereby improving
the reliability of the MRAM.
[0027] It is another feature of an embodiment of the present
invention to provide an MRAM, and a method of manufacturing the
same, that avoids a kink, i.e., a region in which a free magnetic
film is abnormally switched, which is caused by a stray magnetic
field, in a switching characteristic curve, thereby improving the
reliability of the MRAM.
[0028] At least one of the above and other features and advantages
of the present invention may be realized by providing a magnetic
random access memory (MRAM) including a switching device and a
magnetic tunneling junction (MTJ) cell connected to the switching
device, wherein the MTJ cell includes a pinned film having a metal
film and a magnetic film, the magnetic film enclosing the metal
film.
[0029] The metal film may be ruthenium (Ru) or another metal and
the magnetic film may be a cobalt iron (CoFe) film.
[0030] The magnetic film may include a first magnetic film and a
second magnetic film, wherein an outer portion of the first
magnetic film contacts an outer portion of the second magnetic
film. The first magnetic film and the second magnetic film may be
formed of the same magnetic material. A thickness of a first
portion of the magnetic film, which is disposed on the metal film,
may be different from a thickness of a second portion of the
magnetic film, which is disposed under the metal film.
[0031] At least one of the above and other features and advantages
of the present invention may be realized by providing a method of
manufacturing a magnetic random access memory (MRAM) including
forming a switching device in a substrate, forming an interlayer
dielectric on the substrate to cover the switching device, forming
a stack structure on a predetermined region of the interlayer
dielectric, the stack structure including a lower electrode, a
buffering film, a pinning film, a first magnetic film, a metal
film, a second magnetic film, a tunneling film, a free magnetic
film, and a capping film, and the stack structure being connected
to the switching device, and contacting the first magnetic film to
the second magnetic film in the stack structure.
[0032] Forming the stack structure may include sequentially
stacking the lower electrode, the buffering film, the pinning film,
the first magnetic film, the metal film, the second magnetic film,
the tunneling film, the free magnetic film, and the capping film.
In this case, forming the stack structure may further include
forming a contact hole in the interlayer dielectric to expose the
switching device, filling the contact hole with a conductive plug,
sequentially forming the lower electrode to cover the conductive
plug, the buffering film, the pinning film, the first magnetic
film, the metal film, the second magnetic film, the tunneling film,
the free magnetic film, and the capping film on the interlayer
dielectric, forming a photoresist pattern on the capping film to
define the predetermined region of the interlayer dielectric,
etching the films stacked on the interlayer dielectric using the
photoresist pattern as an etch mask, and removing the photoresist
pattern. In this method, contacting the first magnetic film to the
second magnetic film may be performed before stacking the tunneling
film, the free magnetic film, and the capping film.
[0033] Contacting the first magnetic film to the second magnetic
film may include removing an outer portion of the metal film. The
first magnetic film and the second magnetic film may be formed to
different thicknesses. Removing the outer portion of the metal film
may include etching using an etchant having a high etch selectivity
with respect to the metal film.
[0034] Alternatively, forming the stack structure may include
sequentially stacking the lower electrode, the buffering film, the
free magnetic film, the tunneling film, the first magnetic film,
the metal film, the second magnetic film, the pinning film, and the
capping film. Forming the stack structure may further include
forming a contact hole in the interlayer dielectric to expose the
switching device, filling the contact hole with a conductive plug,
sequentially forming the lower electrode to cover the conductive
plug, the buffering film, the free magnetic film, the tunneling
film, the first magnetic film, the metal film, the second magnetic
film, the pinning film, and the capping film on the interlayer
dielectric, forming a photoresist pattern on the capping film to
define the predetermined region of the interlayer dielectric,
etching the films stacked on the interlayer dielectric using the
photoresist pattern as an etch mask, and removing the photoresist
pattern. In this method, contacting the first magnetic film to the
second magnetic film may be performed before stacking the pinning
film and the capping film.
[0035] The buffering film may be an amorphous film. The pinning
film may be a semi-ferromagnetic film. Each of the first and second
magnetic films may be a semi-ferromagnetic film. Each of the first
and second magnetic films may be a cobalt iron (CoFe) film. The
metal film is ruthenium (Ru) or another metal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The above and other features and advantages of the present
invention will become more apparent to those of ordinary skill in
the art by describing in detail exemplary embodiments thereof with
reference to the attached drawings in which:
[0037] FIG. 1 illustrates a cross-sectional view of a conventional
MTJ cell included in a conventional MRAM;
[0038] FIGS. 2 through 5 are graphs each showing a switching
characteristic of a free magnetic film depending on thicknesses of
an SAF film in the conventional MTJ cell shown in FIG. 1;
[0039] FIG. 6 illustrates a cross-sectional view of an MTJ cell
included in an MRAM according to a first embodiment of the present
invention;
[0040] FIG. 7 is a graph showing a switching characteristic of a
free magnetic film of the MTJ cell shown in FIG. 6;
[0041] FIG. 8 illustrates a cross-sectional view of an MTJ cell
included in an MRAM according to a second embodiment of the present
invention; and
[0042] FIGS. 9 through 11 illustrate cross-sectional views of
stages in a method of manufacturing the MTJ cell shown in FIG.
6.
DETAILED DESCRIPTION OF THE INVENTION
[0043] Korean Patent Application No. 2003-74663, filed on Oct. 24,
2003, in the Korean Intellectual Property Office, and entitled:
"Magnetic Random Access Memory and Method of Manufacturing the
Same," is incorporated by reference herein in its entirety.
[0044] The present invention will now be described more fully
hereinafter with reference to the accompanying drawings, in which
exemplary embodiments of the invention are shown. The invention
may, however, be embodied in different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. In the figures, the
dimensions of films, layers and regions are exaggerated for clarity
of illustration. It will also be understood that when a layer is
referred to as being "on" another layer or substrate, it can be
directly on the other layer or substrate, or intervening layers may
also be present. Further, it will be understood that when a layer
is referred to as being "under" another layer, it can be directly
under, and one or more intervening layers may also be present. In
addition, it will also be understood that when a layer is referred
to as being "between" two layers, it can be the only layer between
the two layers, or one or more intervening layers may also be
present. Like reference numerals refer to like elements
throughout.
[0045] The structure of an MTJ cell of an MRAM according to
embodiments of the present invention will now be described.
FIRST EMBODIMENT
[0046] FIG. 6 illustrates an MTJ cell included in an MRAM according
to a first embodiment of the present invention. In FIG. 6, an MTJ
cell M2 includes a buffering film 42 and a pinning film 44, which
are sequentially formed on a lower electrode 40. The buffering film
42 may be an amorphous film, and the pinning film 44 may be a
semi-ferromagnetic film. A pinned film 46 is disposed on the
pinning film 44. The pinned film 46 includes first and second
material films 46a and 46b. The first material film 46a is a
semi-ferromagnetic film, for example, a cobalt iron (CoFe) film,
with a predetermined thickness. The second material film 46b of the
pinned film 46 is disposed within the first material film 46a and
extends near an outer portion of the first material film 46a. The
second material film 46b is enclosed by the first material film
46a. A portion of the first material film 46a disposed on the
second material film 46b (hereinafter, an upper portion of the
first material film 46a) may preferably be as thick as a portion of
the first material film 46a disposed under the second material film
46b (hereinafter, a lower portion of the first material film 46a).
However, such a configuration is not necessary, i.e., the upper and
lower portions of the first material film 46a may have different
thicknesses. The second material film 46b may be formed of
ruthenium (Ru) or another metal.
[0047] Since the first material film 46a encloses the second
material film 46b in the pinned film 46, a magnetic field generated
in the first material film 46a forms a closed loop that surrounds
the second material film 46b as illustrated by arrows A in FIG. 6.
Thus, since a stray magnetic field generated in the pinned film 46
is minimized, the influence of the stray magnetic field to the
outside is negligible. A tunneling film 48, which may be thin, is
formed on the pinned film 46. A free magnetic film 50 and a capping
film 52 are then sequentially stacked on the tunneling film 48. The
magnetization direction of the free magnetic film 50 varies
according to the direction of an external magnetic field, and the
capping film 52 protects the free magnetic film 50.
[0048] The above-described structure of the pinned film 46
eliminates or minimizes an intensity of a stray magnetic field.
Thus, when the free magnetic film 50 is switched, an influence of
the stray magnetic field on the free magnetic film 50 is
negligible.
[0049] In the MTJ cell M2 according to the first embodiment of the
present invention, the influence of an external magnetic field, in
particular, a magnetic field generated in the pinned film 46, on
the free magnetic field 50 can be eliminated so that a shifting of
the switching field or a kink can be prevented while the free
magnetic film 50 is being switched.
[0050] FIG. 7 is a graph showing a switching characteristic of a
free magnetic film of the MTJ cell shown in FIG. 6.
[0051] In FIG. 7, reference characters C9 and C10 denote a ninth
magnetization state indicating unit and a tenth magnetization state
indicating unit (hereinafter, ninth and tenth indicating units),
which show the magnetic fields of the free magnetic film 50 and the
pinned film 46 of the MTJ cell M2 shown in FIG. 6.
[0052] In the ninth and tenth indicating units C9 and C10, although
the upper portion of the first material film 46a is illustrated as
being as thick as the lower portion thereof in FIG. 6, as noted
above, it is possible to form the upper and lower portions of the
first material film 46a to different thicknesses. Further, the
result shown in FIG. 7 can be applied irrespective of the
thicknesses of the upper and lower portions of the first material
film 46a.
[0053] In FIG. 7, reference character G1 indicates a switching
characteristic curve of the free magnetic film 50. Referring to
FIG. 7, the switching characteristic curve G1 is symmetrical except
in saturation regions of a magnetic polarization. The result shown
in FIG. 7 indicates that a switching field is not shifted during
the switching of the free magnetic field 50.
[0054] As compared with the conventional switching characteristic
curves, as shown in FIGS. 2 through 5, the switching characteristic
curve G1 is substantially closer to an ideal form. That is, no
magnetic field other than a switching magnetic field, e.g., a stray
magnetic field, affects the switching of the free magnetic field
50.
SECOND EMBODIMENT
[0055] FIG. 8 illustrates a cross-sectional view of an MTJ cell
included in an MRAM according to a second embodiment of the present
invention.
[0056] The MTJ cell of the second embodiment is similar to the MTJ
cell of the first embodiment except in that the magnetic film
including the pinned film and the pinning film are disposed on the
tunneling film, and the free magnetic film is disposed under the
tunneling film.
[0057] Referring to FIG. 8, the buffering film 42 is disposed on
the lower electrode 40, and the free magnetic film 50 and the
tunneling film 48 are sequentially stacked on the buffering film
42. The pinned film 46, the pinning film 44, and the capping film
52 are sequentially stacked on the tunneling film 48. The pinned
film 46 includes the first material film 46a and the second
material film 46b included within, i.e., is enclosed by, the first
material film 46a. In addition, an upper electrode (not shown) is
disposed on the capping film 52.
[0058] A method of manufacturing the MRAM including the MTJ cell M2
shown in FIG. 6 will now be described. Since all other processes in
the formation of the MRAM, except for a process of forming the MTJ
cell M2, can be performed by an ordinary method, descriptions
thereof will be omitted.
[0059] Referring to FIG. 9, an interlayer dielectric (ILD) 100 is
formed on a substrate (not shown) to cover a transistor 101, and a
contact hole 102 is formed in the ILD 100 to expose a portion of
the transistor 101. The contact hole 102 is then filled with a
conductive plug 104, and the lower electrode 40 is formed on the
ILD 100 to cover the entire surface of the conductive plug 104.
Although not shown in the drawings, a pad conductive film may be
further formed between the conductive plug 104 and the lower
electrode 40 to connect them. The buffering film 42 and the pinning
film 44 are sequentially formed on the lower electrode 40. The
buffering film 42 is formed of an amorphous material, and the
pinning film 44 is formed of a semi-ferromagnetic material.
[0060] A first magnetic film 106, a metal film 108, and a second
magnetic film 110 are sequentially stacked on the pinning film 44.
The first and second magnetic films 106 and 110 may be formed of
the same magnetic material, i.e., the same ferromagnetic film. For
example, the first and second magnetic films 106 and 110 may be
formed of cobalt iron (CoFe). The metal film 108 may be formed of
ruthenium (Ru). The first and second magnetic film 106 and 110 and
the metal film 108 constitute the pinned film 46 as shown in FIG.
6. After the second magnetic film 110 is formed, the tunneling film
48, the free magnetic film 50, and the capping film 52 are
sequentially formed on the second magnetic film 110.
[0061] A photoresist pattern P is then formed on the capping film
52 to define a predetermined region, i.e., the MTJ cell. The
material films 40, 42, 44, 106, 108, 110, 48, 50, and 52 stacked on
the ILD 100 are etched using the photoresist pattern P as an etch
mask until the ILD 100 is exposed. Thereafter, the photoresist
pattern P is removed, and appropriate cleaning and drying processes
are performed.
[0062] Thus, as shown in FIG. 10, a stack structure S, which is
connected to the transistor 101 via the conductive plug 104 and
includes the now etched films 40', 42', 44', 106', 108', 110', 48',
50', and 52', is formed on the ILD 100.
[0063] After forming the stack structure S, the stack structure S
is wet etched using an etchant having a high etch selectivity with
respect to the metal film 108 for a predetermined time. The wet
etching is performed to remove an outer portion of the metal film
108' and is continued until the outer portion of the metal film 108
is removed and an outer portion of the first magnetic film 106
contacts an outer portion of the second magnetic film 110.
[0064] As a result, as shown in FIG. 11, the first and second
magnetic films 106' and 110' become a single magnetic film 120
enclosing the metal film 108'. Thus, the MTJ cell including a
pinned film 130, which is comprised of the magnetic film 120 and
the metal film 108', is completed on the ILD 100.
[0065] Alternatively, in the foregoing method of manufacturing an
MRAM as described with reference to FIG. 11, the free magnetic film
50 may be stacked before the magnetic film including the pinning
film 44 and the pinned film 130.
[0066] For example, the buffering film 42, the free magnetic film
50, and the tunneling film 48 may be sequentially stacked on the
lower electrode 40. Then, the pinned film 130, the pinning film 44,
and the capping film 52 may be sequentially stacked on the
tunneling film 48. Detailed descriptions of a stacking process of
each material film are the same as in the above descriptions and
will not be repeated.
[0067] As described above, in the MRAM according to the present
invention, the SAF film, which is used as the pinned film of the
MTJ cell, includes the metal film and the magnetic film enclosing
the metal film, so that the magnetic film forms a closed loop
around the metal film. Thus, since a magnetic field generated in
the magnetic film also forms a closed loop, a stray magnetic film
caused by the pinned film is minimized to avoid adversely affecting
the function of the free magnetic film. Therefore, the MRAM
according to the present invention can prevent shifting of a
switching field or a kink caused by the stray field, thereby
improving the reliability of the MRAM.
[0068] Exemplary embodiments of the present invention have been
disclosed herein and, although specific terms are employed, they
are used and are to be interpreted in a generic and descriptive
sense only and not for purpose of limitation. For example, those of
ordinary skill in the art can form the foregoing MTJ cell using an
etching process other than the exemplary wet etching and pattern
the metal film 108 so that the metal film 108 is surrounded by the
first and second magnetic films 106 and 110 when the first magnetic
film 106, the metal film 108, and the second magnetic film 110 are
stacked. Accordingly, it will be understood by those of ordinary
skill in the art that various changes in form and details may be
made without departing from the spirit and scope of the present
invention as set forth in the following claims.
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