U.S. patent application number 14/481925 was filed with the patent office on 2015-10-08 for resistive random access memory and method of fabricating the same.
The applicant listed for this patent is Winbond Electronics Corp.. Invention is credited to Shuo-Che Chang, Chia-Hua Ho, Po-Yen Hsu, Hsiu-Han Liao, Meng-Hung Lin, Ting-Ying Shen, Bo-Lun Wu.
Application Number | 20150287914 14/481925 |
Document ID | / |
Family ID | 51726316 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150287914 |
Kind Code |
A1 |
Ho; Chia-Hua ; et
al. |
October 8, 2015 |
RESISTIVE RANDOM ACCESS MEMORY AND METHOD OF FABRICATING THE
SAME
Abstract
Provided is a resistive random access memory including a first
electrode layer, a second electrode layer, and a variable
resistance layer disposed between the first electrode layer and the
second electrode layer, wherein the second electrode layer includes
a first sublayer, a second sublayer, and a conductive metal
oxynitride layer disposed between the first sublayer and the second
sublayer.
Inventors: |
Ho; Chia-Hua; (Taichung
City, TW) ; Chang; Shuo-Che; (Taichung City, TW)
; Liao; Hsiu-Han; (Hsinchu City, TW) ; Hsu;
Po-Yen; (New Taipei City, TW) ; Lin; Meng-Hung;
(Taichung City, TW) ; Wu; Bo-Lun; (Changhua
County, TW) ; Shen; Ting-Ying; (Chiayi City,
TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Winbond Electronics Corp. |
Taichung City |
|
TW |
|
|
Family ID: |
51726316 |
Appl. No.: |
14/481925 |
Filed: |
September 10, 2014 |
Current U.S.
Class: |
257/4 ;
438/382 |
Current CPC
Class: |
H01L 45/146 20130101;
H01L 45/16 20130101; H01L 45/08 20130101; H01L 45/1233 20130101;
H01L 45/1253 20130101 |
International
Class: |
H01L 45/00 20060101
H01L045/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2014 |
TW |
103112331 |
Claims
1. A resistive random access memory, comprising a first electrode
layer, a second electrode layer, and a variable resistance layer
disposed between the first electrode layer and the second electrode
layer, wherein the second electrode layer comprises a first
sublayer, a second sublayer, and a conductive metal oxynitride
layer disposed between the first sublayer and the second
sublayer.
2. The resistive random access memory of claim 1, wherein a metal
in the metal oxynitride layer is any one selected from the group
consisting of tantalum, titanium, tungsten, hafnium, nickel,
aluminum vanadium, cobalt, zirconium, and silicon.
3. The resistive random access memory of claim 1, wherein an atomic
ratio of each of nitrogen and oxygen in the metal oxynitride layer
is respectively 5% to 30% and 20% to 60%.
4. The resistive random access memory of claim 3, wherein an atomic
ratio of oxygen in the metal oxynitride layer is 45% to 60%.
5. The resistive random access memory of claim 1, wherein the metal
oxynitride layer has a polycrystalline structure.
6. The resistive random access memory of claim 1, wherein a
thickness of the metal oxynitride layer is between 5 nm and 30
nm.
7. The resistive random access memory of claim 1, wherein the first
sublayer is in contact with the variable resistance layer, a
material of the first sublayer comprises titanium, and a number
ratio of oxygen/titanium in the first sublayer is greater than
0.5.
8. The resistive random access memory of claim 7, wherein a
material of the second sublayer is selected from the group
consisting of titanium nitride, thallium nitride, platinum,
iridium, and graphite.
9. A method of fabricating a resistive random access memory,
comprising: forming a first electrode layer and a second electrode
layer on a substrate; and forming a variable resistance layer
between the first electrode layer and the second electrode layer,
wherein the second electrode layer comprises a first sublayer, a
conductive metal oxynitride layer, and a second sublayer disposed
on the variable resistance layer in sequence.
10. The method of claim 9, wherein the first sublayer comprises
titanium, and the method further comprises performing a heating
step so as to diffuse oxygen in the metal oxynitride layer into the
first sublayer such that a number ratio of oxygen/titanium in the
first sublayer is greater than 0.5.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the priority benefit of Taiwan
application serial no. 103112331, filed on Apr. 2, 2014. The
entirety of the above-mentioned patent application is hereby
incorporated by reference herein and made a part of this
specification.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a memory and a method of
fabricating the same, and more particularly, to a resistive random
access memory and a method of fabricating the same.
[0004] 2. Description of Related Art
[0005] Due to high memory density, fast operating speed, low power
consumption, and low costs, the resistive random access memory has
become an extensively studied memory device in recent years. The
principle of operation thereof is that conductive paths are
generated by some dielectric materials therein when a high voltage
is applied. As a result, the dielectric materials are changed from
a high resistance state to a low resistance state, and can return
to the high resistance state through a "reset" step thereafter.
Accordingly, the dielectric materials can provide the two different
states corresponding to "0" and "1", and can therefore be used as a
memory unit for storing digital information.
[0006] In various resistive random access memories, the hafnium
oxide-based resistive random access memory is highly anticipated
due to good durability and high switching speed. However, it is
often difficult to maintain the currently used titanium/hafnium
oxide (Ti/HfO.sub.2)-based resistive random access memory in a low
resistance state at high temperature, thus causing deterioration of
the so-called "high-temperature data retention". In this regard,
research and improvements are necessary.
SUMMARY OF THE INVENTION
Technical Issue to be Solved
[0007] The invention provides a resistive random access memory and
a method of fabricating the same capable of alleviating the issue
of high-temperature data retention fail of the resistive random
access memory.
Technical Solution
[0008] A resistive random access memory of the invention includes a
first electrode layer, a second electrode layer, and a variable
resistance layer disposed between the first electrode layer and the
second electrode layer, wherein the second electrode layer includes
a first sublayer, a second sublayer, and a conductive metal
oxynitride layer disposed between the first sublayer and the second
sublayer.
[0009] In an embodiment, the metal in the metal oxynitride layer is
any one selected from the group consisting of tantalum (Ta),
titanium (Ti), tungsten (W), hafnium (Hf), nickel (Ni), aluminum
(Al), vanadium (V), cobalt (Co), zirconium (Zr), and silicon (Si).
Preferably, the metal at least includes Ta or Ti.
[0010] In an embodiment, the atomic ratio of each of nitrogen and
oxygen in the metal oxynitride layer is respectively 5% to 30% and
20% to 60%.
[0011] In an embodiment, the atomic ratio of oxygen in the metal
oxynitride layer is 45% to 60%.
[0012] In an embodiment, the metal oxynitride layer has a
polycrystalline structure.
[0013] In an embodiment, the thickness of the metal oxynitride
layer is between 5 nm and 30 nm.
[0014] In an embodiment, the first sublayer is in contact with the
variable resistance layer, the material of the first sublayer
includes Ti, and the number ratio of oxygen/titanium in the first
sublayer is greater than 0.5.
[0015] A method of fabricating a resistive random access memory of
the invention includes the following steps. A first electrode layer
and a second electrode layer are formed on a substrate. A variable
resistance layer is formed between the first electrode layer and
the second electrode layer, wherein the second electrode layer
includes a first sublayer, a conductive metal oxynitride layer, and
a second sublayer disposed on the variable resistance layer in
sequence.
[0016] In an embodiment, the first sublayer includes Ti, and the
fabrication method further includes performing a heating step so as
to diffuse oxygen in the metal oxynitride layer into the first
sublayer such that the number ratio of oxygen/titanium in the first
sublayer is greater than 0.5.
Beneficial Effects
[0017] Based on the above, the invention provides a resistive
random access memory and a method of fabricating the same, wherein
a metal oxynitride layer is disposed between the electrode layers.
The metal oxynitride layer is used as an oxygen diffusion barrier
layer limiting the movement of oxygen ions to the variable
resistance layer and the region between the variable resistance
layer and the metal oxynitride layer. At the same time, when the
resistive random access memory is in a low resistance state
thereof, the metal oxynitride layer can also reduce the probability
of the oxygen ions diffusing back to the variable resistance layer,
thereby increasing the high-temperature data retention of the
resistive random access memory.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0019] FIG. 1 to FIG. 3 are cross-sectional flow charts
illustrating a process of fabricating a resistive random access
memory illustrated according to a first embodiment of the
invention.
[0020] FIG. 4 shows a distribution diagram of oxygen content
varying with different positions in a resistive random access
memory of a second embodiment of the invention and a known
resistive random access memory.
DESCRIPTION OF THE EMBODIMENTS
[0021] Exemplary embodiments of the invention are more
comprehensively described in the following with reference to
figures. However, the invention can be embodied in different forms,
and is not limited to the embodiments described in the present
text.
[0022] Referring to FIG. 1, first, a substrate 100 is provided. The
material of the substrate 100 is not particularly limited, and
common materials include, for instance, a semiconductor substrate
such as a silicon substrate. Although not shown in FIG. 1, other
devices may have been formed in the substrate 100. For instance, a
semiconductor device such as a diode or a transistor or a
conductive plug connected to different devices can be formed in the
substrate 100. The semiconductor device such as a diode or a
transistor can be used as a switching device of the resistive
random access memory, and can be electrically connected to the
structure described in FIG. 2 to FIG. 3 through a conductive
plug.
[0023] Then, a first electrode layer 102 is formed on the substrate
100. The material of the first electrode layer 102 is not
particularly limited, and any known conductive material can be
used. For instance, the material can be titanium nitride (TiN),
thallium nitride (TaN), titanium aluminum nitride (TiAlN), a
titanium tungsten (TiW) alloy, tungsten (W), ruthenium (Ru),
platinum (Pt), iridium (Ir), graphite, or a mixture or a stacked
layer of the materials. In particular, TiN, TaN, Pt, Ir, graphite,
or a mixture thereof is preferred. The method of forming the first
electrode layer 102 is not particularly limited, and common methods
include, for instance, a physical vapor deposition process such as
direct current sputtering or radio frequency magnetron sputtering.
The thickness of the first electrode layer 102 is not limited, but
is generally between 5 nm and 500 nm.
[0024] Referring to FIG. 2, next, a variable resistance layer 104
is formed on the first electrode layer 102. The material of the
variable resistance layer 104 is not particularly limited. Any
material for which the resistance can be changed through the
application of a voltage can be used, and common materials include,
for instance, hafnium oxide (HfO.sub.2), magnesium oxide (MgO),
nickel oxide (NiO), niobium oxide (Nb.sub.2O.sub.5), titanium oxide
(TiO.sub.2), aluminum oxide (Al.sub.2O.sub.3), vanadium oxide
(V.sub.2O.sub.5), tungsten oxide (WO.sub.3), zinc oxide (ZnO), and
cobalt oxide (CoO). The variable resistance layer 104 can be formed
by a PVD or a chemical vapor deposition (CVD) process.
Alternatively, since the thickness of the variable resistance layer
104 is generally limited to a very thin range (such as 2 nm to 10
nm), the variable resistance layer 104 can also be formed by an
atomic layer deposition process.
[0025] Referring to FIG. 3, then, a second electrode layer 106 is
formed on the variable resistance layer 104, wherein the second
electrode layer 106 includes a first sublayer 108, a conductive
metal oxynitride layer 110, and a second sublayer 112 disposed on
the variable resistance layer 104 in sequence.
[0026] The material of the first sublayer 108 can be a material
more readily bonded with oxygen in comparison to the variable
resistance layer 104, and examples thereof include titanium (Ti),
tantalum (Ta), zirconium (Zr), hafnium (Hf), aluminum (Al), nickel
(Ni), or an incompletely oxidized metal oxide of the metals. The
forming method of the first sublayer 108 is not particularly
limited, and can include, for instance, a physical or chemical
vapor deposition process. The thickness of the first sublayer 108
is also not particularly limited, but is generally between 5 nm and
50 nm.
[0027] The metal oxynitride layer 110 can include a material
represented by MN.sub.xO.sub.y, wherein M can be Ta, Ti, W, Hf, Ni,
Al, Va, Co, Zr, or Si, and is preferably Ta or Ti. In the
MN.sub.xO.sub.y material, the atomic ratio of N is preferably
between 5% and 30%, and the atomic ratio of 0 is preferably between
20% and 60%, more preferably between 45% and 60%.
[0028] In the case that the material of the metal oxynitride layer
110 is TiN.sub.xO.sub.y, the forming method thereof can include
directly forming a TiN.sub.xO.sub.y thin film through a PVD method.
Alternatively, a Ti or TiN thin film can also be first formed, and
then the TiN.sub.xO.sub.y thin film is obtained by applying an
annealing treatment to the thin film in a N.sub.2O gas environment
or applying a N.sub.2O plasma treatment to the thin film.
[0029] It should further be mentioned that, the metal oxynitride
layer 110 is conductive, and even if the thickness thereof is
slightly greater, the overall electrical conductivity of the second
conductive layer 106 is unaffected. Therefore, in comparison to the
disposition of other dielectric layers, in terms of the metal
oxynitride layer 110, the thickness thereof does not need to be
strictly limited (for instance, the thickness does not need to be
limited to the level of a few nanometers). The thickness thereof
can be between, for instance, 5 nm and 30 nm.
[0030] Moreover, the metal oxynitride layer 110 can have a
polycrystalline structure.
[0031] The material and the forming method of the second sublayer
112 can be similar to the first electrode layer 102 and are not
repeated herein. The thickness thereof can also be close to the
first electrode layer 102, and is preferably between 20 nm and 50
nm.
[0032] After the second electrode layer 106 is formed, the
fabrication of the resistive random access memory is preliminary
complete. Next, if high potential difference is established between
the first electrode layer 102 and the second electrode layer 106,
then oxygen ions (O.sup.2-) in the variable resistance layer 104
leave the variable resistance layer 104 and enter the first
sublayer 108 due to attraction from a positive potential.
[0033] As a result, conductive filaments formed by oxygen vacancies
are formed inside the variable resistance layer 104, and the
resistive random access memory is thereby converted from a high
resistance state to a low resistance state.
[0034] It should be mentioned that, in a subsequent process (such
as a packaging process), a high-temperature treatment is performed
on the structure shown in FIG. 3 such that oxygen in the metal
oxynitride layer 110 is diffused into the first sublayer 108, and
oxygen in the variable resistance layer 104 may also be diffused
into the first sublayer 108 at the same time, thereby increasing
the number ratio of oxygen/titanium (the material of the first
sublayer 108 is exemplified by titanium) in the first sublayer 108.
For instance, the oxygen/titanium ratio may be greater than 0.35,
greater than 0.5, or even be greater than 0.6. The effect of
increased oxygen content is described below with reference to FIG.
4.
[0035] Moreover, although the first electrode layer 102, the
variable resistance layer 104, and the second electrode layer 106
are formed on the substrate 100 in sequence in the above as an
example, those having ordinary skill in the art should understand
that the invention is not limited to the particular sequence. In
other embodiments, the electrode layer including two sublayers and
the metal oxynitride layer can also be first formed on the
substrate. Next, the variable resistance layer is formed on the
electrode layer, and then the other electrode layer is formed on
the variable resistance layer.
[0036] The second embodiment of the invention relates to a
resistive random access memory that is explained below with
reference to FIG. 3.
[0037] The resistive random access memory of the invention includes
a first electrode layer 102, a second electrode layer 106, and a
variable resistance layer 104 disposed between the first electrode
layer 102 and the second electrode layer 106, wherein the second
electrode layer 106 includes a first sublayer 108, a second
sublayer 112, and a conductive metal oxynitride layer 110 disposed
between the first sublayer 108 and the second sublayer 112. In the
embodiment shown in FIG. 3, the first sublayer 108 is in contact
with the variable resistance layer 104. In the case that the
material of the first sublayer 108 includes Ti, the number ratio of
oxygen/titanium in the first sublayer 108 is preferably greater
than 0.5.
[0038] The resistive random access memory of the present embodiment
has better high-temperature data retention and has better cyclic
bearing capacity. A possible mechanism thereof is described
below.
[0039] FIG. 4 shows a distribution curve of oxygen content in two
different resistive random access memories. In particular, curve I
corresponds to the resistive random access memory of the second
embodiment of the invention, and curve II corresponds to a known
resistive random access memory. The beneficial effects of the
resistive random access memory of the invention are described below
with reference to FIG. 4.
[0040] The known resistive random access memory includes a first
electrode layer 202, a second electrode layer 206, and a variable
resistance layer 204 disposed therebetween, and the second
electrode layer 206 includes a first sublayer 208 and a second
sublayer 212. For comparison, the description for FIG. 4 is based
on the assumption that the first electrode layer 202, the variable
resistance layer 204, the first sublayer 208, and the second
sublayer 212 are respectively the same as the first electrode layer
102, the variable resistance layer 104, the first sublayer 108, and
the second sublayer 112 of FIG. 3.
[0041] As described above, in general, the operating principles of
the resistive random access memory involve forming conductive
filaments formed by oxygen vacancies in the variable resistance
layer through the movement of oxygen ions and thereby converting
the originally insulated dielectric material into a low resistance
state. Using the known resistive memory illustrated in FIG. 4 as an
example, when a voltage is applied thereto, oxygen ions enter the
first sublayer 208 from the variable resistance layer 204. However,
a long-enduring issue of the prior art is that after a plurality of
writings are performed on the resistive random access memory,
oxygen ions may cross the first sublayer 208 and enter the second
sublayer 212, and not be able to return into the variable
resistance layer 204, thus causing the device to fail.
[0042] It can be known by observing curve I and curve II of FIG. 4
that, the main difference between the invention and prior art is
that, through the disposition of the metal oxynitride layer 110, a
high oxygen content region is formed between the variable
resistance layer 104 and the second sublayer 112. The region can be
used as an oxygen diffusion barrier layer to prevent oxygen ions
from entering the second sublayer 112 during the repeat writing
process. As a result, the issue above can be alleviated.
[0043] Another common issue of the resistive random access memory
is that the first sublayer is generally formed by metal (refer to
paragraph 0025), and the diffusion rate of oxygen ions in those
metal materials recited in paragraph 0025 is relatively high. Even
in room temperature, a certain chance exists for oxygen ions to
return back into the variable resistance layer through diffusion.
As soon as excessive oxygen ions return to the variable resistance
layer and are recombined with oxygen vacancies, the conductive
filaments may become severed such that the device cannot be
maintained in a low resistance state, which is the issue of "HTDR
fail".
[0044] For the solution to the issue, please refer to FIG. 4.
Although the material of each of the first sublayer 108 and the
first sublayer 208 is the same, the oxygen content in the first
sublayer 108 is higher than the oxygen content in the first
sublayer 208. This is because in the fabrication process of the
resistive random access memory, the film layers may be affected by
a high-temperature process after being formed, such that oxygen
ions are diffused between adjacent film layers. In the known
resistive random access memory, oxygen ions are diffused into the
first sublayer 208 from the variable resistance layer 204; and in
the resistive random access memory of the invention, oxygen ions
are diffused into the first sublayer 108 from the variable
resistance layer 104 and the metal oxynitride layer 110. Since
there are more sources of oxygen ions, the oxygen content in the
first sublayer 108 is higher than the oxygen content in the first
sublayer 208. For instance, if the material of the first sublayer
is Ti, then the number ratio of oxygen/titanium in the first
sublayer 108 may be about 0.65, and the number ratio of
oxygen/titanium in the first sublayer 208 may be about 0.35.
Moreover, the number ratio of nitrogen/titanium is substantially
the same for both.
[0045] The inventors discovered that, in a metal layer containing
oxygen, the higher the oxygen concentration, the lower the
diffusion rate of oxygen ions. Therefore, the diffusion rate of
oxygen ions in the first sublayer 108 is lower than the diffusion
rate of oxygen ions in the first sublayer 208. In other words, in
comparison to prior art, in the resistive random access memory of
the invention, the probability of severed conductive filaments
caused by oxygen ions diffusing back to the variable resistance
layer 104 by heat disturbance is reduced. That is, the resistive
random access memory of the invention has better thermal stability.
It should be mentioned here that, provided the metal oxynitride
layer 110 is disposed between the first sublayer 108 and the second
sublayer 112, the above effect can be achieved. However, if the
metal oxynitride layer 110 is composed of O-rich metal oxynitride
(atomic ratio of oxygen is about 45% to 60%), then the effect is
more significant.
[0046] Based on the above, the invention provides a resistive
random access memory and a method of fabricating the same, wherein
a metal oxynitride layer is disposed between electrode layers. The
metal oxynitride layer is used as an oxygen diffusion barrier layer
limiting the movement of oxygen ions to the variable resistance
layer and the region between the variable resistance layer and the
metal oxynitride layer. At the same time, when the resistive random
access memory is in a low resistance state thereof, the metal
oxynitride layer can also reduce the probability of oxygen ions
diffusing back to the variable resistance layer, thereby increasing
the HTDR of the resistive random access memory.
[0047] Although the invention has been described with reference to
the above exemplary embodiments, the invention is not limited
thereto. It will be apparent to one of the ordinary skill in the
art that modifications to the described embodiments may be made
without departing from the spirit of the invention. Accordingly,
the scope of the invention is defined by the attached claims and
not by the above detailed descriptions.
* * * * *