U.S. patent application number 10/623461 was filed with the patent office on 2005-01-20 for multi-layer barrier allowing recovery anneal for ferroelectric capacitors.
Invention is credited to Bruchhaus, Rainer, Gernhardt, Stefan, Hilliger, Andreas, Hornik, Karl, Lian, Jingyu, Moon, Bum-Ki, Nagel, Nicolas, Wellhausen, Uwe.
Application Number | 20050013091 10/623461 |
Document ID | / |
Family ID | 33541433 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050013091 |
Kind Code |
A1 |
Hilliger, Andreas ; et
al. |
January 20, 2005 |
MULTI-LAYER BARRIER ALLOWING RECOVERY ANNEAL FOR FERROELECTRIC
CAPACITORS
Abstract
A multi-layer barrier for a ferroelectric capacitor includes an
outdiffusion barrier layer permeable to both hydrogen and oxygen.
The outdiffusion barrier layer covers the ferroelectric of the
capacitor. Oxygen passes through the outdiffusion barrier layer
into the ferroelectric during an oxygen anneal in order to repair
damage to the ferroelectric caused during etching. The outdiffusion
barrier layer reduces the decomposition of the ferroelectric by
blocking molecules leaving the ferroelectric during the oxygen
anneal. The multi-layer barrier also includes a hydrogen barrier
layer deposited on the outdiffusion barrier layer after repair of
the ferroelectric by the oxygen anneal. The hydrogen barrier layer
allows the multi-layer barrier to block the passage of hydrogen
into the ferroelectric during back-end processes.
Inventors: |
Hilliger, Andreas;
(Kanagawa-ken, JP) ; Lian, Jingyu; (Wallkill,
NY) ; Nagel, Nicolas; (Dresden, DE) ;
Bruchhaus, Rainer; (Munich, DE) ; Gernhardt,
Stefan; (Kanagawa-ken, JP) ; Wellhausen, Uwe;
(Dresden, DE) ; Moon, Bum-Ki; (Hopewell Junction,
NY) ; Hornik, Karl; (Kanagawa-ken, JP) |
Correspondence
Address: |
FISH & RICHARDSON, PC
12390 EL CAMINO REAL
SAN DIEGO
CA
92130-2081
US
|
Family ID: |
33541433 |
Appl. No.: |
10/623461 |
Filed: |
July 18, 2003 |
Current U.S.
Class: |
361/311 |
Current CPC
Class: |
H01G 4/1245 20130101;
H01L 28/57 20130101; H01G 4/33 20130101 |
Class at
Publication: |
361/311 |
International
Class: |
H01G 004/06 |
Claims
We claim:
1. A multi-layer barrier for a ferroelectric capacitor comprising:
an outdiffusion barrier layer permeable to both hydrogen and oxygen
and covering the ferroelectric of the capacitor, the outdiffusion
barrier layer allowing oxygen to pass through it into the
ferroelectric during an oxygen anneal to repair damage to the
ferroelectric, the outdiffusion barrier layer reducing the
decomposition of the ferroelectric by blocking molecules leaving
the ferroelectric during the oxygen anneal; and a hydrogen barrier
layer deposited on the outdiffusion barrier layer after repair of
the ferroelectric by the oxygen anneal, the hydrogen barrier layer
causing the multi-layer barrier to block the passage of hydrogen
into the ferroelectric during back-end processes.
2. The multi-layer barrier of claim 1, wherein the outdiffusion
barrier layer is comprised of Al.sub.2O.sub.3.
3. The multi-layer barrier of claim 1, wherein the hydrogen barrier
layer is comprised of Al.sub.2O.sub.3.
4. The multi-layer barrier of claim 1; wherein the hydrogen barrier
layer is thicker than the outdiffusion barrier layer.
5. The multi-layer barrier of claim 1, wherein the ferroelectric
includes PZT.
6. The multi-layer barrier of claim 1, wherein the oxygen anneal is
performed at a temperature of at least approximately 500 C.
7. The multi-layer barrier of claim 1, wherein the outdiffusion
barrier layer reduces the decomposition of the ferroelectric by
blocking lead molecules from leaving the ferroelectric during the
oxygen anneal.
8. The multi-layer barrier of claim 1, wherein the outdiffusion
barrier layer reduces the decomposition of the ferroelectric by
blocking lead molecules from leaving the ferroelectric during the
oxygen anneal.
9. The multi-layer barrier of claim 1, wherein the outdiffusion
barrier layer is deposited by sputtering.
10. The multi-layer barrier of claim 1, wherein the hydrogen
barrier layer is deposited using sputtering or atomic layer
deposition.
11. A method for manufacturing a multi-layer barrier for a
ferroelectric capacitor comprising the steps of: depositing on the
ferroelectric of the capacitor an outdiffusion barrier layer
permeable to both hydrogen and oxygen; performing an oxygen anneal
to repair damage to the ferroelectric; allowing oxygen to pass
through the outdiffusion barrier layer to the ferroelectric while
using the outdiffusion barrier layer to reduce decomposition the
ferroelectric during the oxygen anneal; depositing a hydrogen
barrier layer on the outdiffusion barrier layer after repair of the
ferroelectric by the oxygen anneal; and using the multi-layer
barrier with the deposited hydrogen barrier layer to block the
passage of hydrogen into the ferroelectric during back-end
processes.
12. The method of claim 11, wherein the outdiffusion barrier layer
is comprised of Al.sub.2O.sub.3.
13. The method of claim 11, wherein the hydrogen barrier layer is
comprised of Al.sub.2O.sub.3.
14. The method of claim 11, wherein the hydrogen barrier layer is
thicker than the outdiffusion barrier layer.
15. The method of claim 11, wherein the ferroelectric includes
PZT.
16. The method of claim 11, wherein the oxygen anneal is performed
at a temperature of at least approximately 500 C.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to barrier layers in
ferroelectric devices.
BACKGROUND OF THE INVENTION
[0002] The ferroelectric materials in FeRAM (Ferroelectric Random
Access Memory) and high K materials in DRAM are generally annealed
at high temperatures (500 C or above) in oxygen ambient to recover
from process damage, e.g. damage caused by the Reactive Ion Etching
(RIE) of the materials. During the anneal, the ambient oxygen
diffuses into the ferroelectric material and reacts at the high
temperature to bring about the recovery. Usually a barrier layer
(e.g. Al.sub.2O.sub.3) is deposited prior to the annealing in order
to prevent the ferroelectric from decomposing at the elevated
temperatures. When PZT is used as the ferroelectric, it is
important that the barrier reduce the outdiffusion of the lead from
the PZT.
[0003] The barrier layers of the prior art also need to prevent
hydrogen from diffusing into and damaging the ferroelectric during,
for example, back-end BEOL. Some examples of BEOL processes include
insulator deposition, copper processing and forming gas anneal. The
barrier layer can be optimized to prevent the diffusion of hydrogen
into the ferroelectric, but this optimized layer will also result
in a barrier against the oxygen. With less oxygen diffusing into
the ferroelectric, the result is a less effective recovery
anneal.
[0004] One option is to continue the recovery anneal for a longer
time at a higher temperature, but this causes problems, especially
for capacitors having capacitor on plug structures. Poly silicon
plugs or tungsten plugs (contact plugs) are often used as vertical
interconnects to connect the bottom electrode of the ferroelectric
capacitor to the transistors. In ferroelectric capacitors such
contact plugs form a capacitor on plug (COP) structure. In COP
structures, a barrier at the top of the plug prevents oxygen from
passing from the ferroelectric to the plug. If the recovery anneal
proceeds for too long at a high temperature then the oxygen will
pass through that barrier at the top of the plug and will oxidize
the plug material causing the contact to fail.
[0005] As for the PZT, it would be desirable to have a barrier that
would allow oxygen to pass into the ferroelectric during an anneal
process while also preventing the ferroelectric from decomposing
due to the high temperatures of the anneal. It would additionally
be desirable for the barrier to prevent hydrogen from entering and
causing damage to the ferroelectric during BEOL processing.
SUMMARY OF THE INVENTION
[0006] The present invention provides a barrier that allows oxygen
to pass into a ferroelectric during an anneal process while also
preventing the ferroelectric from decomposing due to the high
temperatures of the anneal. The barrier also prevents hydrogen from
entering and causing damage to the ferroelectric during post-anneal
processing.
[0007] In general terms the present invention includes a
multi-layer barrier for a ferroelectric capacitor having an
outdiffusion barrier layer permeable to both hydrogen and oxygen.
The outdiffusion barrier layer covers the ferroelectric of the
capacitor. Oxygen passes through the outdiffusion barrier layer
into the ferroelectric during an oxygen anneal in order to repair
damage to the ferroelectric caused during etching. The outdiffusion
barrier layer reduces the decomposition of the ferroelectric by
blocking molecules leaving the ferroelectric during the oxygen
anneal. The multi-layer barrier also includes a hydrogen barrier
layer deposited on the outdiffusion barrier layer after repair of
the ferroelectric by the oxygen anneal. The hydrogen barrier layer
allows the multi-layer barrier to block the passage of hydrogen
into the ferroelectric during back-end processes.
[0008] The method for manufacturing the multi-layer barrier
includes the steps of: depositing on the ferroelectric of the
capacitor an outdiffusion barrier layer permeable to both hydrogen
and oxygen; performing an oxygen anneal to repair damage to the
ferroelectric; allowing oxygen to pass through the outdiffusion
barrier layer to the ferroelectric while using the outdiffusion
barrier layer to reduce decomposition the ferroelectric during the
oxygen anneal; depositing a hydrogen barrier layer on the
outdiffusion barrier layer after repair of the ferroelectric by the
oxygen anneal; and using the multi-layer barrier with the deposited
hydrogen barrier layer to block the passage of hydrogen into the
ferroelectric during back-end processes.
BRIEF DESCRIPTION OF THE FIGURES
[0009] Further preferred features of the invention will now be
described for the sake of example only with reference to the
following figures, in which:
[0010] FIG. 1 shows a cut-away view of a ferroelectric capacitor
with a multi-layer barrier of the present invention.
[0011] FIG. 2 shows a magnified diagrammatic view of the
multi-layer barrier of the capacitor of FIG. 1 after deposition of
an outdiffusion barrier layer.
[0012] FIG. 3 shows a magnified diagrammatic view of a portion of
the inventive barrier layer of the capacitor of FIG. 1 after
deposition of a hydrogen barrier layer.
[0013] FIG. 4 is a flowchart illustrating the method for
manufacturing the multi-layer barrier of FIGS. 1-3.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0014] FIG. 1 shows a ferroelectric capacitor (ferrocapacitor) 101.
A PZT layer 103, which in other embodiments can be other
ferroelectric materials, is between a top electrode 105 and a
bottom electrode 107. A metal contact 106 is electrically connected
to the top electrode 105.
[0015] Supporting the bottom electrode 107 is a substructure 109,
composed of TEOS, for example. Passing through the substructure 109
and electrically connecting the bottom electrode to an underlying
silicon active region 113 is a contact plug 111 composed of poly
silicon or Tungsten, for example.
[0016] The bottom electrode 107 can also include a barrier layer
for preventing the diffusion of oxygen from the contact plug 111
into the ferroelectric layer 103.
[0017] Covering the top electrode 105 is a first TEOS hardmask 119
used for etching the top electrode 105 and ferroelectric 103. A
multi-layer barrier 115 covers the hardmask 119, the top electrode
105 and the ferroelectric layer 103. The multi-layer barrier 115 is
comprised of at least two layers, although additional layers can
also be added. A second TEOS hardmask 121 covers the multi-layer
barrier 115 and the bottom electrode 107 and is used to etch the
bottom electrode 107. An outer barrier layer 117 covers the second
TEOS hardmask 121. Rather than TEOS, other hardmask materials can
be used to form the hardmaks 119, 121. In some embodiments the
ferrocapaitor is etched using only a single hardmask, but the
multi-layer barrier 115 can still be used.
[0018] The method for manufacturing the multi-layer barrier 115 of
FIG. 1 is described with reference to FIG. 4. Also, FIGS. 2 and 3
show diagrammatic views of a portion 123 of the multi-layer barrier
115 during the method steps.
[0019] The method includes a step 401 wherein an outdiffusion
barrier layer 115a is applied to the PZT 103. FIG. 2 shows the
portion 123 of the multi-layer barrier 115 after performing the
step 401. The outdiffusion barrier layer 115 should be very thin
(2-10 nm, for example) and can be comprised of Al.sub.2O.sub.3, for
example. The outdiffusion barrier layer can be sputtered onto the
PZT 103 at room temperature or at an elevated temperature.
[0020] Next an anneal step 403 is performed. The capacitor 101 is
annealed at a high temperature (500C or above) in oxygen ambient so
that the PZT 103 can recover from process damage, e.g. damage
caused by the Reactive Ion Etching (RIE) of the materials.
Referring again to FIG. 2, the outdiffusion barrier layer 115a is
shown on the surface of the PZT 103. The "X" symbols 201
diagrammatically illustrate the process damage caused to the PZT
103. During the anneal step 403, ambient oxygen 203 diffuses across
the outdiffusion barrier layer 115a and into the ferroelectric to
react at the high temperature and bring about the recovery.
Although the outdiffusion barrier layer 115a is thin enough to
allow the passage of the oxygen 203, due to the different diffusion
coefficients, it is still able to serve as an outdiffusion barrier
layer to reduce the outdiffusion of lead 205 from the PZT 103.
[0021] As explained above with respect to the prior art, it is
important to prevent the PZT 103 from decomposing at the elevated
temperatures of the anneal, step 403. In the present invention, the
barrier layer 115a reduces the decomposition of the PZT 103 by
providing a barrier to reduce the outdiffusion of molecules from
the PZT 103 while at the same time allowing oxygen 203, to pass
through the barrier and into the PZT 103 to bring about the
recovery of the PZT 103 through oxygen annealing. In particular, in
the present invention the barrier layer 115a blocks lead (Pb)
molecules 205 from leaving the PZT ferroelectric 103. The oxygen
anneal step 103 is continued until the damaged PZT 103 is
recrystallized.
[0022] In embodiments where ferroelectrics other than PZT are used,
the barrier layer 115a can be optimized to prevent molecules other
than Pb from leaving the ferroelectric and can allow molecules
other than oxygen to enter the ferroelectric.
[0023] After completion of the anneal step 403 (see FIG. 4), a
hydrogen barrier layer 115b is applied (using sputtering or ALD at
room or elevated temperature, for example) over the outdiffusion
barrier layer 115a to form the multi-layer barrier 115 (see FIG.
3). The hydrogen barrier layer 115b can be thicker than the
outdiffusion barrier layer 115a (approximately 1040 nm thick) and
can also be comprised of Al.sub.2O.sub.3. The thickness and
relatively perfect structure of the hydrogen barrier layer 115b
make it a good hydrogen barrier.
[0024] As explained above with respect to the prior art, it is
important to prevent hydrogen from diffusing into and damaging the
PZT 103 or other ferroelectrics during, for example, back-end BEOL
processes. A path 125 for undesirable hydrogen from the metal
contact 106 through the second TEOS hardmask 121 and Into the
ferroelectric 103 is shown in FIG. 1. The outdiffusion barrier
layer 115a is both hydrogen and oxygen permeable, allowing
undesirable hydrogen, as well as the desired oxygen, to diffuse
into the PZT 103. However, the hydrogen barrier layer 115b, once
applied, substantially prevents hydrogen molecules from passing
through the multi-layer barrier 115 and into the PZT layer 103.
[0025] Still other materials and method steps can be added or
substituted for those above. Thus, although the invention has been
described above using particular embodiments, many variations are
possible within the scope of the claims, as will be clear to a
skilled reader.
* * * * *