U.S. patent application number 14/976339 was filed with the patent office on 2017-06-22 for low temperature encapsulation for magnetic tunnel junction.
The applicant listed for this patent is International Business Machines Corporation, Tokyo Electron Limited. Invention is credited to Anthony J. Annunziata, Sebastian U. Engelmann, Eric A. Joseph, Gen P. Lauer, Nathan P. Marchack, Deborah A. Neumayer, Masahiro Yamazaki.
Application Number | 20170179194 14/976339 |
Document ID | / |
Family ID | 59067279 |
Filed Date | 2017-06-22 |
United States Patent
Application |
20170179194 |
Kind Code |
A1 |
Annunziata; Anthony J. ; et
al. |
June 22, 2017 |
LOW TEMPERATURE ENCAPSULATION FOR MAGNETIC TUNNEL JUNCTION
Abstract
A method of making a magnetic random access memory device
comprises forming a magnetic tunnel junction on an electrode, the
magnetic tunnel junction comprising a reference layer positioned in
contact with the electrode, a tunnel barrier layer arranged on the
reference layer, and a free layer arranged on the tunnel barrier
layer; and depositing an encapsulating layer on and along sidewalls
of the magnetic tunnel junction at a temperature of 40 to
60.degree. C. using remote microwave plasma deposition wherein the
encapsulation layer comprises silicon and nitrogen. An MRAM device
made by the aforementioned method is also disclosed.
Inventors: |
Annunziata; Anthony J.;
(Stamford, CT) ; Engelmann; Sebastian U.; (White
Plains, NY) ; Joseph; Eric A.; (White Plains, NY)
; Lauer; Gen P.; (Yorktown Heights, NY) ;
Marchack; Nathan P.; (White Plains, NY) ; Neumayer;
Deborah A.; (Danbury, CT) ; Yamazaki; Masahiro;
(Elmsford, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation
Tokyo Electron Limited |
Armonk
Tokyo |
NY |
US
JP |
|
|
Family ID: |
59067279 |
Appl. No.: |
14/976339 |
Filed: |
December 21, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 43/12 20130101;
H01L 27/222 20130101; H01L 43/02 20130101; H01L 43/08 20130101 |
International
Class: |
H01L 27/22 20060101
H01L027/22; H01L 43/08 20060101 H01L043/08; H01L 43/12 20060101
H01L043/12; H01L 43/02 20060101 H01L043/02 |
Claims
1. A method of making a magnetic random access memory (MUM) device,
the method comprising: forming a magnetic tunnel junction on an
electrode, the magnetic tunnel junction comprising a reference
layer positioned in contact with the electrode, a tunnel barrier
layer arranged on the reference layer, and a free layer arranged on
the tunnel barrier layer; and depositing an encapsulating layer on
and along sidewalls of the magnetic tunnel junction at a
temperature of 40 to 60.degree. C. using remote microwave plasma
deposition, wherein the encapsulation layer comprises silicon and
nitrogen.
2. The method of claim 1, wherein the encapsulating layer has a
thickness of 10 to 60 nanometers.
3. The method of claim 1, wherein remote microwave plasma
deposition uses ammonia and silane as reactant gases.
4. The method of claim 3, wherein the ammonia has a flow rate of 10
to 50 sccm.
5. The method of claim 1, wherein remote microwave plasma
deposition uses argon and helium as inert gases.
6. The method of claim 1, wherein the inert gases have a flow rate
of 500 to 2300 sccm.
7. The method of claim 1, wherein remote microwave plasma
deposition uses microwave power of 2,000 to 6,000 Watts.
8. The method of claim 1, wherein remote microwave plasma
deposition is performed at a pressure of 10 mTorr to 1500
mTorr.
9. The method of claim 1, wherein the MRAM device is a spin torque
transfer MRAM (STT-MRAM) device.
10. A method of making a magnetic random access memory device, the
method comprising: forming a magnetic tunnel junction on an
electrode, the magnetic tunnel junction comprising a reference
layer positioned in contact with the electrode, a tunnel barrier
layer arranged on the reference layer, and a free layer arranged on
the tunnel barrier layer; and depositing an encapsulating layer on
and along sidewalls of the magnetic tunnel junction wherein the
encapsulating layer is formed from SiH.sub.4 and NH.sub.3 at a
temperature of 40 to 60.degree. C. using remote microwave plasma
deposition.
11. The method of claim 10, wherein the encapsulating layer has a
thickness of 10 to 60 nanometers.
12. The method of claim 10, wherein the ammonia has a flow rate of
10 to 50 sccm.
13. The method of claim 10, wherein remote microwave plasma
deposition uses argon and helium as inert gases.
14. The method of claim 10, wherein the inert gases have a flow
rate of 500 to 2300 sccm.
15. The method of claim 10, wherein remote microwave plasma
deposition uses microwave power of 2,000 to 6,000 Watts.
16. The method of claim 10, wherein remote microwave plasma
deposition is performed at a pressure of 10 mTorr to 1500
mTorr.
17. The method of claim 10, wherein the MRAM device is a spin
torque transfer MRAM (STT-MRAM) device.
18. A device comprising: a magnetic tunnel junction arranged on an
electrode, the magnetic tunnel junction comprising a reference
layer positioned in contact with the electrode, a tunnel barrier
layer arranged on the reference layer, and a free layer arranged on
the tunnel barrier layer; an encapsulating layer disposed directly
on the free layer, the encapsulating layer being on and along
sidewalls of the magnetic tunnel junction wherein the encapsulating
layer comprises silicon and nitrogen is formed by remote microwave
plasma deposition at a temperature of 40 to 60.degree. C.
19. The device of claim 18, wherein the encapsulating layer has a
thickness of 10 to 60 nanometers.
20. The device of claim 18, wherein the encapsulating layer has a
refractive index greater than or equal to 2.0.
Description
BACKGROUND
[0001] Spin-transfer torque magnetoresistive random access memory
devices have some benefits over semiconductor-based memories, such
as dynamic random-access memory (DRAM) and static random-access
memory (SRAM). However, in order to compete with dynamic
random-access memory and static random-access memory, the
spin-transfer torque magnetoresistive random access memory devices
need to be integrated into the wiring layers of standard silicon
logic and memory chips.
[0002] Spin-transfer torque magnetoresistive random access memory
device is a type of solid state, non-volatile memory that uses
tunneling magnetoresistance (TMR or MR) to store information.
Magnetoresistive random access memory (MRAM) includes an
electrically connected array of magnetoresistive memory elements,
referred to as magnetic tunnel junctions (MTJs). Each magnetic
tunnel junction includes a free layer and fixed/reference layer
that each includes a magnetic material layer. A non-magnetic
insulating tunnel barrier separates the free and fixed/reference
layers. The free layer and the reference layer are magnetically
de-coupled by the tunnel barrier. The free layer has a variable
magnetization direction, and the reference layer has an invariable
magnetization direction.
[0003] A magnetic tunnel junction stores information by switching
the magnetization state of the free layer. When magnetization
direction of the free layer is parallel to the magnetization
direction of the reference layer, the magnetic tunnel junction is
in a low resistance state. Conversely, when the magnetization
direction of the free layer is antiparallel to the magnetization
direction of the reference layer, the magnetic tunnel junction is
in a high resistance state. The difference in resistance of the MTJ
may be used to indicate a logical `1` or `0`, thereby storing a bit
of information. The tunneling magnetoresistance of a magnetic
tunnel junction determines the difference in resistance between the
high and low resistance states. A relatively high difference
between the high and low resistance states facilitates read
operations in the MRAM.
SUMMARY
[0004] Disclosed herein is a method of making a magnetic random
access memory device. The method comprises forming a magnetic
tunnel junction on an electrode, the magnetic tunnel junction
comprising a reference layer positioned in contact with the
electrode, a tunnel barrier layer arranged on the reference layer,
and a free layer arranged on the tunnel barrier layer; and
depositing an encapsulating layer on and along sidewalls of the
magnetic tunnel junction at a temperature of 40 to 60.degree. C.
using remote microwave plasma deposition wherein the encapsulation
layer comprises silicon and nitrogen.
[0005] Also disclosed herein is a method of making a magnetic
random access memory device, the method comprising: forming a
magnetic tunnel junction on an electrode, the magnetic tunnel
junction comprising a reference layer positioned in contact with
the electrode, a tunnel barrier layer arranged on the reference
layer, and a free layer arranged on the tunnel barrier layer; and
depositing an encapsulating layer on and along sidewalls of the
magnetic tunnel junction, wherein the encapsulation layer is formed
from SiH.sub.4 and NH.sub.3 at a temperature of 40 to 60.degree. C.
using remote microwave plasma deposition.
[0006] According to yet another embodiment of the invention, an
MRAM device includes: a magnetic tunnel junction arranged on an
electrode, the magnetic tunnel junction comprising a reference
layer positioned in contact with the electrode, a tunnel barrier
layer arranged on the reference layer, and a free layer arranged on
the tunnel barrier layer; and an encapsulating layer disposed on
and along sidewalls of the magnetic tunnel junction, wherein the
encapsulating layer comprises silicon and nitrogen and is formed by
remote microwave plasma deposition at a temperature of 40 to
60.degree. C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The subject matter, which is regarded as the invention is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The forgoing and other
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0008] FIG. 1 is a cross-sectional side view of a patterned
magnetic tunnel junction stack positioned on a contact
electrode.
[0009] FIG. 2 is a cross-sectional side view after depositing an
encapsulating layer on the magnetic tunnel junction stack.
[0010] FIG. 3 shows a simplified block diagram of a batch type
processing system for remote microwave plasma deposition of a
material comprising silicon and nitrogen.
[0011] FIG. 4 shows a simplified block diagram of a single sample
type processing system for remote microwave plasma deposition of a
material comprising silicon and nitrogen.
[0012] FIG. 5 is a flow diagram for remote microwave plasma
deposition of a material comprising silicon and nitrogen.
[0013] FIG. 6 is a graph showing etch traces of different SiN.sub.x
materials as discussed in the examples.
[0014] FIG. 7 is a graph showing energy barrier data for different
SiN.sub.x materials as discussed in the examples.
[0015] FIG. 8 is graph showing coercivity data for different
SiN.sub.x materials as discussed in the examples.
DETAILED DESCRIPTION
[0016] One challenge of integrating spin-transfer torque
magnetoresistive random access memory devices into the wiring
layers of silicon logic and memory chips is encapsulating the
spin-transfer torque magnetoresistive random access memory device
after patterning. The spin-transfer torque magnetoresistive random
access memory device including a magnetic tunnel junction is
encapsulated so that the magnetic layers and tunnel barrier layer
experience minimal degradation during subsequent processing.
Encapsulation of the MRAM device can protect the magnetic tunnel
junction during subsequent processing. However, the deposition
process can degrade the device's magnetic properties if carried out
high temperatures. Lower deposition temperatures have been proposed
for methods such as plasma enhanced chemical vapor deposition
(PECVD) and plasma enhanced atomic layer deposition (PE-ALD)
however the lower temperatures can compromise the quality of the
film or introduce potentially damaging precursors such as
halogenated precursors.
[0017] Physical sputter methods can also employ temperatures below
200.degree. C. but the throughput rate is low because the
deposition rate scales with power and higher power can induce
degradation.
[0018] These issues have been addressed by forming an encapsulating
layer using remote microwave plasma deposition. The encapsulating
layer is formed at a temperature substantially below 200.degree.
C., typically 40 to 60.degree. C. The encapsulating layer is formed
without using potentially damaging precursors. Furthermore, the
encapsulating layer has a strong signal for endpoint detection in
etching--stronger than the signal for comparable materials made at
150.degree. C. Finally, the encapsulating layer made as described
herein has improved coercive field (Hc) and energy barrier (Eb)
characteristics compared to similar materials deposited at
200.degree. C. using plasma enhanced chemical vapor deposition. The
coercive field is important because it is indicative of data
retention in MRAM devices. Data retention in MRAM devices is
proportional to coercive field (Hc). As a device gets small, Hc
should increase in order to maintain data retention, but in fact Hc
tends to decrease as the device becomes smaller. A method of
maintaining Hc or minimizing Hc loss at smaller device size allows
for smaller devices with minimal loss in data retention.
[0019] The embodiments provide methods of encapsulating devices for
perpendicularly magnetized spin-transfer torque magnetoresistive
random access memory. The disclosed processes improve device
characteristics and reduce magnetic degradation at small device
diameters (e.g., <50 nm).
[0020] FIGS. 1-5 illustrate exemplary methods of making MRAM
devices according to various embodiments. FIG. 1 is a
cross-sectional side view of a patterned magnetic tunnel junction
stack 410 positioned on a contact electrode 401. The magnetic
tunnel junction stack 410 includes a reference layer 402, a tunnel
barrier layer 403, and a free layer 404.
[0021] The contact electrode 401 includes a conductive material(s)
and forms the bottom contact electrode of the MRAM device.
Non-limiting examples of conductive materials for the contact
electrode include tantalum, tantalum nitride, titanium, or any
combination thereof.
[0022] The contact electrode 401 may be formed by depositing a
conductive material(s) onto a surface. The conductive material(s)
may be deposited by, for example, physical vapor deposition (PVD),
ion beam deposition (IBD), atomic layer deposition (ALD),
electroplating, or other like processes.
[0023] To form the magnetic tunnel junction stack 410, the
reference layer 402 is formed on the contact electrode 401; the
tunnel barrier layer 403 is formed on the reference layer 402; and
the free layer 404 is formed on the tunnel barrier layer 403.
[0024] The reference layer 402 and the free layer 404 include
conductive, magnetic materials, for example, metals or metal
alloys. The reference layer 402 and the free layer 404 may be
formed by employing a deposition process, for example, PVD, IBD,
ALD, electroplating, or other like processes.
[0025] The reference layer 402 and the free layer 404 may include
one layer or multiple layers. The reference layer 402 and the free
layer 404 may include the same materials and/or layers or different
materials and/or layers.
[0026] Non-limiting examples of materials for the reference layer
402 and/or the free layer 104 include iron, cobalt, boron,
aluminum, nickel, silicon, oxygen, carbon, zinc, beryllium,
vanadium, boron, magnesium, or any combination thereof.
[0027] The reference layer 402 has a thickness that may generally
vary and is not intended to be limited. In some embodiments, the
reference layer 102 has a thickness 10 to 25 nm. In other
embodiments, the reference layer 402 has a thickness of 2 to 10
nm.
[0028] The free layer 404 has a thickness that may generally vary
and is not intended to be limited. In some embodiments, the free
layer 404 has a thickness of 2 to 5 nm. In other embodiments, the
free layer 404 has a thickness of 1 to 2 nm.
[0029] The tunnel barrier layer 403 includes a non-magnetic,
insulating material. A non-limiting example of an insulating
material for the tunnel barrier layer 403 is magnesium oxide (MgO).
The tunnel barrier layer 403 may be formed on the reference layer
402 by, for example, radiofrequency (RF) sputtering in some
embodiments. Alternatively, the tunnel barrier layer 403 is formed
by oxidation (e.g., natural or radical oxidation) of a magnesium
(Mg) layer deposited on the reference layer 402. After oxidation,
the MgO layer may then be capped with a second layer of Mg. The
thickness of the tunnel barrier layer 403 is not intended to be
limited and may generally vary.
[0030] After depositing the magnetic tunnel junction stack 410
layers on the contact electrode 401, the magnetic tunnel junction
stack 410 is patterned. In some embodiments, a hard mask material
layer may be disposed on the magnetic tunnel junction stack 410.
The hard mask material layer is then patterned by etching, for
example, using a reactive ion etch (ME) process or a halogen-based
chemical etch process (e.g., including chlorine-containing gas
and/or fluorine-containing gas chemistry). The pattern from the
hard mask is transferred into the free layer 404, tunnel barrier
layer 403, and reference layer 401. The free layer 404, tunnel
barrier layer 403, and reference layer 402 are etched by, for
example, performing a MRAM stack etch process. The stack etch
process may be a ME process or an ion beam etch (IBE) process.
[0031] FIG. 2 is a cross-sectional side view after depositing an
encapsulating layer 501 on the magnetic tunnel junction stack 410.
The encapsulating layer 501 comprises SiN.sub.x, wherein x is the
ratio of N to Si and x is 0.2 to 1.3. The encapsulating layer 501
encapsulates the magnetic tunnel junction stack 410. The
encapsulating layer 501 is deposited on the exposed surface and
sidewalls of the magnetic tunnel junction stack 410 and contacts
the contact electrode 401.
[0032] The thickness of the encapsulating layer 501 may generally
vary and is not intended to be limited. In some embodiments, the
thickness of the encapsulating layer 501 is 10 to 60 nm. In other
embodiments, the thickness of the encapsulating layer 501 is 20 to
40 nm. To achieve a desired encapsulating layer thickness of, for
example, silicon nitride, several cycles of deposition may be
performed.
[0033] The encapsulating layer 501 is deposited by remote microwave
plasma deposition. In remote microwave plasma deposition one or
more ammonia gases are subjected to microwave radiation. The
irradiated gas or gases are then reacted at a temperature of 40 to
60.degree. C. and the reaction product is deposited on the magnetic
tunnel junction stack 410.
[0034] FIG. 3 shows a simplified block diagram of an exemplary
batch-type processing system for remote microwave plasma deposition
of a silicon-nitrogen-containing film on a magnetic tunnel junction
stack. The batch-type processing system 1 contains a process
chamber 10 and a process tube 25 therein that has an upper end 23
connected to a exhaust pipe 80, and a lower end 24 hermetically
joined to a lid 27 of cylindrical manifold 2. The exhaust pipe 80
discharges gases from the process tube 25 to a vacuum pumping
system 88 to maintain a pre-determined reduced pressure in the
processing system 1. A substrate holder 35 for holding a plurality
of magnetic tunnel junction stacks is placed in the process tube
25. The substrate holder 35 resides on a turntable 26 that is
mounted on a rotating shaft 21 penetrating the lid 27 and driven by
a motor 28. The turntable 26 can be rotated during processing to
improve overall film uniformity or, alternately, the turntable can
be stationary during processing. The lid 27 is mounted on an
elevator 22 for transferring the substrate holder 35 in and out of
the reaction tube 25. When the lid 27 is positioned at its
uppermost position, the lid 27 is adapted to close the open end of
the manifold 2.
[0035] A cylindrical heat reflector 30 is disposed so as to cover
the reaction tube 25. The heat reflector 30 has a mirror-finished
inner surface to suppress dissipation of radiation heat radiated by
main heater 20, bottom heater 65, top heater 15, and exhaust pipe
heater 70. A helical cooling water passage (not shown) is formed in
the wall of the process chamber 10 as a cooling medium passage.
[0036] The batch-type processing system 1 contains a gas delivery
system that includes a gas supply line 45. The gas supply line 45
is connected to silane gas source 95 and remote plasma source 94. A
remote plasma source refers to a plasma source that is positioned
remote from the process chamber, i.e., outside of the chamber in
which the substrate will be processed, such that the excited gas
must thereafter be delivered to the process chamber. The silane gas
source 95 can be further mixed with an inert carrier gas such as
argon (Ar). Alternatively, if the vapor pressure of the silane gas
is high enough, a bubbling system that utilizes and an inert
carrier gas can be used instead. The remote plasma source 94 is
configured for exciting ammonia gas from the ammonia gas source 96.
The remote plasma source 94 is a microwave plasma source where the
microwave power can be 1000 Watts (W) to 6,000 W. The microwave
frequency can, for example, be 2.45 GHz.
[0037] The excited ammonia gas is mixed with silane gas from the
gas source 95 in the gas supply line 45 downstream from the remote
plasma source 94. The resulting excited gas mixture is then flowed
into the reaction tube 25 of the process chamber 10. Though not
specifically shown, it is also contemplated that the excited
ammonia gas from remote plasma source 94 may be mixed with the
silane gas from gas source 95 downstream of the remote plasma
source 94 but inside the process chamber 10 prior to introducing
the excited gas mixture to the reaction tube 25. In the embodiment
illustrated in FIG. 3, the gas delivery system further contains a
gas injection system 46. The excited gas mixture exits the gas
injection system 46 through a plurality of holes 47 and flows over
the substrates 40, thereby depositing a silicon-nitrogen-containing
film on the magnetic tunnel junction stacks.
[0038] The vacuum pumping system 88 comprises a vacuum pump 86, a
trap 84, and automatic pressure controller (APC) 82. The vacuum
pump 86 can, for example, include a dry vacuum pump capable of a
pumping speed up to 20,000 liters per second (and greater). During
processing, the process pressure can be adjusted by the APC 82. The
trap 84 can collect unreacted precursor material and reaction
by-products from the process chamber 10.
[0039] The process monitoring system 92 comprises a sensor 75
capable of real-time process monitoring and can, for example,
comprise a mass spectrometer (MS) or a Fourier transform infrared
(FTIR) spectrometer. A controller 90 includes a microprocessor, a
memory, and a digital I/O port capable of generating control
voltages sufficient to communicate and activate inputs to the
processing system 1 as well as monitor outputs from the processing
system 1. Moreover, the controller 90 is coupled to and can
exchange information with gas sources 95 and 96, remote plasma
source 94, motor 28, process monitoring system 92, heaters 20, 15,
65, and 70, and vacuum pumping system 88.
[0040] FIG. 4 shows a simplified block diagram of a processing
system for remote microwave plasma deposition of a
silicon-nitrogen-containing film on a magnetic tunnel junction
stack according to another embodiment of the invention. The
processing system 100 includes a process chamber 110 having a
pedestal 105 for mounting a holder 120 that supports a magnetic
tunnel junction stack 125 and exposes the magnetic tunnel junction
stack 125 to the processing region 160. The substrate holder 120
can be further configured for heating or cooling the substrate
125.
[0041] Ammonia gas from ammonia supply 145 is flowed into the
remote plasma source 205 configured for plasma exciting the ammonia
gas. The remote plasma source 205 is a microwave plasma source
where the microwave power can be 1000 Watts (W) to 6,000 W. The
microwave frequency can, for example, be 2.45 GHz. Downstream from
the remote plasma source 205, a gas source 140 supplies a silane
gas that is mixed with the excited ammonia gas in a gas delivery
system containing a gas supply line 175. Analogously, as described
above for FIG. 1, the gas source 140 can include a liquid delivery
system or a bubbling system. The resulting excited gas mixture 215
is then flowed into the process chamber 110. The excited gas
mixture 215 can be introduced to the processing region 160 in the
process chamber 110 using the gas delivery system that further
contains a gas injection plenum (not shown), a series of baffle
plates (not shown) and a multi-orifice showerhead gas injection
plate 165. Though not specifically shown, it is also contemplated
that the excited ammonia gas from the remote plasma source 205 may
be mixed with the silane gas from gas source 140 downstream of the
remote plasma source 205 but inside the process chamber 110 prior
to introducing the excited gas mixture 215 to the processing region
160. The process chamber 110 is connected to vacuum pump system 150
that can include a turbo-molecular vacuum pump (TMP) capable of a
pumping speed up to about 5,000 liters per second (and greater),
and a gate valve for controlling the gas pressure.
[0042] FIG. 5 is a flow diagram for remote microwave plasma
deposition of a silicon-nitrogen-containing film on a magnetic
tunnel junction stack. The process 300 includes providing a
substrate in a process chamber at 310. The process chamber can, for
example, be one of the process chambers 1 or 100 shown in FIGS. 3
and 4, respectively.
[0043] At 312, ammonia gas is flowed into and excited in a remote
plasma source. At 314, the plasma-excited ammonia gas is mixed with
silane gas downstream from the remote plasma source. At 316, a
silicon-nitrogen-containing film is deposited on the magnetic
tunnel junction stack in the process chamber from the excited gas
mixture in a chemical vapor deposition process.
[0044] The formation of the excited ammonia gas in the remote
plasma source is separated from the actual mixing of the excited
ammonia gas with the silane gas. This separation can provide
greater control over the deposition process, the composition of the
silicon-nitrogen-containing film, and the film properties. The
excited ammonia gas contains radicals (e.g., N*, NH.sub.x*) which,
when mixed with the silane gas, allow for lowering of the
deposition temperature.
[0045] In one embodiment of the invention, the ammonia gas can
contain a nitrogen-containing gas and the deposited
silicon-nitrogen-containing film can further contain hydrogen. The
nitrogen-containing gas can include N.sub.2, NH.sub.3,
N.sub.2H.sub.2, NO, or N.sub.2O, or a combination of two or more
thereof. The nitrogen-containing gas can, for example, have a gas
flow rate to the plasma source 10 sccm to 50 sccm.
[0046] In one embodiment of the invention, the excited gas mixture
can further contain an inert gas, for example He, Ne, Ar, Kr, or
Xe, or a combination of two or more thereof. The inert gas flow
rate to the plasma source can, for example, be 50 sccm to 2500
sccm. Processing conditions used for depositing a
silicon-nitrogen-containing film can include a process chamber
pressure of 10 mTorr to 150 Torr. The process conditions can
further include a substrate temperature of 40.degree. C. to
60.degree. C.
[0047] Remote microwave plasma deposition at temperatures of 40 to
60.degree. C. using silane and ammonia as reactant cases results in
the formation of an encapsulation layer on a magnetic tunnel
junction without increasing the temperature to a point at which
degradation of the magnetic tunnel junction would occur.
Additionally the resulting encapsulating layer has superior etch
resistance, coercivity and energy barrier properties compared to
encapsulating layers made by other methods. Furthermore,
encapsulating layers having an increasing refractive index appear
to have better etch resistance. The resulting MRAM device has
better data retention that other MRAM devices having an
encapsulating layer made by a high temperature method.
[0048] In some embodiments the MRAM device can undergo further
processing. The further processing can include embedding the
encapsulated device into the back-end-of-line (BEOL) of a CMOS
process route. The encapsulated device may undergo additional
processing after the BEOL of the CMOS route.
EXAMPLES
Examples 1-3
[0049] Table 1 shows the conditions for remote microwave plasma
deposition three different examples. The three examples are
referred to by their respective refractive indices. The deposition
substrate was silicon. The deposition temperature was 60.degree. C.
The deposition time was 60 seconds. The pressure was 90 milliTorr
(mTorr). The microwave power was 4000 Watts (W). The gas flows are
in standard cubic centimeter per unit time (sccm). Results are
shown in Table 2. The deposition rate is in Angstroms per second
(A/s). The refractive index of the deposited material is
abbreviated as RI. The etch rate when exposed to hydrogen fluoride
is expressed in Angstroms per second (A/s) and Angstroms per minute
(A/m).
TABLE-US-00001 TABLE 1 SiH.sub.4 NH.sub.3 Ar He SiN 2.4 20 19 850
1000 SiN 2.2 20 22 850 1000 SiN 1.9 20 35 850 1000
TABLE-US-00002 TABLE 2 Deposition Refractive 100:1 HF etch 100:1 HF
etch rate A/s index rate A/s rate A/min SiN.sub.x 2.4 13.9 2.39 0.5
31 SiN.sub.x 2.2 15.1 2.22 0.5 31 SiN.sub.x 1.9 17.3 1.91 1.8
110
[0050] As can be seen from the examples, the SiN.sub.x materials
with a higher refractive index showed an increased resistance to
etching when exposed to hydrogen fluoride.
[0051] FIG. 6 shows etch traces for SiN.sub.x materials of the
examples compared to SiN.sub.x materials deposited by plasma
enhanced chemical vapor deposition (PECVD) at 150.degree. C. The
figure shows that the materials produced by remote microwave plasma
deposition demonstrate a strong signal for endpoint etch detection
compared to the material deposited by PECVD. Etch traces are the CN
(386 nm) optical emission spectra collected by etching in a RIE
plasma reactor (using a capacitively coupled plasma source). The
parameters used were: 600 Ws (source power)|600 Wb (bias power)|60
mTorr (pressure)|20 sccm CHF.sub.3|60 sccm CF.sub.4|400 sccm Ar|10
sccm O.sub.2.
[0052] FIG. 8 shows coercivity (H.sub.c) (O.sub.e) for the
SiN.sub.x material having a refractive index of 2.2 as a function
of CD (nm) (critical dimension (CD) measured by transmission
electron microscopy (TEM)). FIG. 8 also shows coercivity (H.sub.c)
(O.sub.e) for an SiN.sub.x material having a similar refractive
index but deposited by plasma enhanced chemical vapor deposition at
200.degree. C. FIG. 7 shows energy barrier data (Eb) for the same
materials. Eb data was obtained through fitting the Hc data using
Sharrock's formula. Both FIGS. 7 and 8 show that SiN.sub.x
materials produced by remote microwave plasma deposition have
superior properties to SiN.sub.x materials produced by plasma
enhanced chemical vapor deposition at 200.degree. C.
[0053] The corresponding structures, materials, acts, and
equivalents of all means or step plus function elements in the
claims below are intended to include any structure, material, or
act for performing the function in combination with other claimed
elements as specifically claimed. The description of the present
invention has been presented for purposes of illustration and
description, but is not intended to be exhaustive or limited to the
invention in the form disclosed. Many modifications and variations
will be apparent to those of ordinary skill in the art without
departing from the scope and spirit of the invention. The
embodiment was chosen and described in order to best explain the
principles of the invention and the practical application, and to
enable others of ordinary skill in the art to understand the
invention for various embodiments with various modifications as are
suited to the particular use contemplated.
[0054] The diagrams depicted herein are just one example. There may
be many variations to this diagram or the steps (or operations)
described therein without departing from the spirit of the
invention. For instance, the steps may be performed in a differing
order or steps may be added, deleted or modified. All of these
variations are considered a part of the claimed invention.
[0055] The descriptions of the various embodiments of the present
invention have been presented for purposes of illustration, but are
not intended to be exhaustive or limited to the embodiments
disclosed. Many modifications and variations will be apparent to
those of ordinary skill in the art without departing from the scope
and spirit of the described embodiments. The terminology used
herein was chosen to best explain the principles of the
embodiments, the practical application or technical improvement
over technologies found in the marketplace, or to enable others of
ordinary skill in the art to understand the embodiments disclosed
herein.
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