U.S. patent application number 14/019961 was filed with the patent office on 2014-09-18 for atomic layer deposition of reduced-leakage post-transition metal oxide films.
This patent application is currently assigned to Intermolecular, Inc.. The applicant listed for this patent is Intermolecular, Inc.. Invention is credited to Sean Barstow, Chi-I Lang, Michael Miller, Sandip Niyogi, Kurt Pang, Prashant B. Phatak.
Application Number | 20140273525 14/019961 |
Document ID | / |
Family ID | 51523560 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140273525 |
Kind Code |
A1 |
Pang; Kurt ; et al. |
September 18, 2014 |
Atomic Layer Deposition of Reduced-Leakage Post-Transition Metal
Oxide Films
Abstract
Metal-oxide films (e.g., aluminum oxide) with low leakage
current suitable for high-k gate dielectrics are deposited by
atomic layer deposition (ALD). The purge time after the
metal-deposition phase is 5-15 seconds, and the purge time after
the oxidation phase is prolonged beyond 60 seconds. Prolonging the
post-oxidation purge produced an order-of-magnitude reduction of
leakage current in 30 .ANG.-thick Al.sub.2O.sub.3 films.
Inventors: |
Pang; Kurt; (Fremont,
CA) ; Barstow; Sean; (San Jose, CA) ; Lang;
Chi-I; (Cupertino, CA) ; Miller; Michael; (San
Jose, CA) ; Niyogi; Sandip; (San Jose, CA) ;
Phatak; Prashant B.; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Intermolecular, Inc. |
San Jose |
CA |
US |
|
|
Assignee: |
Intermolecular, Inc.
San Jose
CA
|
Family ID: |
51523560 |
Appl. No.: |
14/019961 |
Filed: |
September 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61779740 |
Mar 13, 2013 |
|
|
|
Current U.S.
Class: |
438/785 ;
438/778 |
Current CPC
Class: |
H01L 21/02104 20130101;
H01L 27/1462 20130101; H01L 29/1606 20130101; H01L 27/14698
20130101; H01L 29/778 20130101; H01L 21/02205 20130101; H01L
21/0228 20130101; H01L 21/283 20130101; H01L 21/02178 20130101;
H01L 22/14 20130101; H01L 29/786 20130101; H01L 21/02175 20130101;
H01L 21/28575 20130101; H01L 21/3065 20130101; H01L 29/66742
20130101; H01L 21/02172 20130101; H01L 21/02189 20130101; H01L
22/12 20130101; H01L 21/02005 20130101; H01L 21/76864 20130101;
H01L 29/66477 20130101; H01L 21/02181 20130101; H01L 29/41
20130101; H01L 27/14643 20130101 |
Class at
Publication: |
438/785 ;
438/778 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Claims
1. A method of forming a metal oxide film on a substrate in a
process chamber, the method comprising: exposing the substrate to a
metal precursor; performing a first purge of the chamber; exposing
the substrate to an oxygen precursor; and performing a second purge
of the chamber; wherein the second purge has a duration longer than
about 60 seconds.
2. The method of claim 1, wherein the second purge has a duration
between about 60 seconds and about 120 seconds.
3. The method of claim 1, wherein the second purge has a duration
between about 65 seconds and about 80 seconds.
4. The method of claim 1, wherein the first purge has a duration
shorter than about 15 seconds.
5. The method of claim 4, wherein the first purge has a duration
between about 5 seconds and about 15 seconds.
6. The method of claim 1, wherein the metal oxide film formed by
exposing the substrate to the metal precursor, performing the first
purge, exposing the substrate to the oxygen precursor, and
performing the second purge has an effective thickness between
about 0.6 .ANG. and about 1.2 .ANG..
7. The method of claim 1, further comprising repeating the steps of
exposing the substrate to the metal precursor, performing the first
purge, exposing the substrate to the oxygen precursor, and
performing the second purge until the metal oxide film is between
about 2 .ANG. and about 50 .ANG.thick.
8. The method of claim 7, wherein the metal oxide film has a
leakage current density less than about 0.1 microamps per square
centimeter.
9. The method of claim 7, wherein the metal oxide film has a
leakage current density less than about 0.05 microamps per square
centimeter.
10. The method of claim 7, wherein the metal oxide film has a
leakage current density between about 0.01 and about 0.05 microamps
per square centimeter.
11. The method of claim 1, further comprising repeating the steps
of exposing the substrate to the metal precursor, performing the
first purge, exposing the substrate to the oxygen precursor, and
performing the second purge until the metal oxide film is between
about 2 .ANG. and about 10 .ANG.thick.
12. The method of claim 1, further comprising repeating the steps
of exposing the substrate to the metal precursor, performing the
first purge, exposing the substrate to the oxygen precursor, and
performing the second purge until the metal oxide film is between
about 25 .ANG. and about 35 .ANG.thick.
13. The method of claim 1, wherein the metal precursor comprises an
aluminum, zirconium, or hafnium precursor.
14. The method of claim 13, wherein the metal precursor comprises
an aluminum precursor.
15. The method of claim 14, wherein the aluminum precursor
comprises trimethylaluminum.
16. The method of claim 1, wherein the oxygen precursor comprises
water or ozone.
17. The method of claim 1, wherein the second purge comprises
flooding the chamber with an inert gas.
18. The method of claim 16, wherein the inert gas comprises argon,
nitrogen, or helium.
19. The method of claim 1, wherein the first purge comprises
flooding the chamber with an inert gas.
20. The method of claim 19, wherein the inert gas comprises argon,
nitrogen, or helium.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Prov. Pat. App. No.
61/779,740, filed 13 Mar. 2013, the entirety of which is
incorporated herein by reference for all purposes.
BACKGROUND
[0002] Related fields include thin-film semiconductor device
manufacture, particularly atomic layer deposition of oxide
films.
[0003] As integrated circuit feature sizes decrease, other device
dimensions also decrease to maintain the proper device operation.
For example, as gate conductor widths decrease, the thickness of
the gate dielectric needs to decrease to provide proper capacitance
to control the transistor.
[0004] Silicon dioxide (SiO.sub.2), a gate dielectric used in
larger scale devices, would need to be <1.5 nm thick to be used
in a sub-100 nm MOSFET device. Unfortunately, SiO.sub.2 is subject
to high tunneling leakage in thicknesses <2 nm. The tunneling
leakage increases power consumption and reduces device reliability.
Materials with dielectric constants, k, greater than the SiO.sub.2
's value of 3.9 ("high-k materials") have been studied as
replacements for SiO.sub.2. For example, a .about.5 nm-thick layer
of material with k=20 (e.g., a transition metal oxide such as
hafnium oxide), has the same capacitance as a SiO.sub.2 layer that
is only 1 nm thick; thus, its "equivalent oxide thickness" (EOT)
would be 1 nm. Tunneling leakage current decreases rapidly with
physical thickness, and is very low through a 5 nm gate.
[0005] Tunneling, however, is not the only source of unwanted
leakage current that inhibits progress in fabricating reliable
smaller-scale transistors (and other components, such as memory
cells). Material properties, such as mobile charge-carrying defects
and metallic nanoclusters that can form in metal-oxide layers
subjected to sufficiently strong electric fields, facilitate
leakage by other mechanisms that cannot be mitigated by simply
thickening the layer. These material properties are often highly
dependent on process conditions and methods of forming the high-k
layers, but the variables can be challenging to measure and
correct. In particular, films of aluminum oxide (Al.sub.2O.sub.3)
and other metal oxides such as hafnium oxide (HfO.sub.x) and
zirconium oxide (ZrO.sub.x) are prone to high or inconsistent
leakage current at thicknesses of 2-10 .ANG..
[0006] Therefore, a need exists for a method of forming metal-oxide
films with consistently low leakage current from all leakage
mechanisms.
SUMMARY
[0007] The following summary presents some concepts in a simplified
form as an introduction to the detailed description that follows.
It does not necessarily identify key or critical elements and is
not intended to reflect a scope of invention.
[0008] Metal-oxide films made by atomic layer deposition (ALD) are
formed by alternating cycles of metal deposition and oxidation
("A-B cycling"). Each cycle deposits a monolayer of metal oxide.
Each cycle includes exposing the substrate to a metal precursor;
purging the chamber to remove unreacted precursors and by-products;
exposing the substrate to an oxygen precursor; and purging the
chamber a second time. A typical purge duration is 5-15 seconds. If
the purge after the exposure to the oxygen precursor is prolonged
to longer than 60 seconds, the leakage current in the resulting
film is markedly reduced.
[0009] In some embodiments, the second purge has a duration longer
than 60 seconds; for example, 60-120 seconds or 65-80 seconds. The
first purge can be kept short, less than 15 seconds or 5-15
seconds. Each of the monolayers may have an effective thickness
between about 0.6 .ANG. and about 1.2 .ANG., and the A-B cycle may
be repeated until the metal oxide film is between about 2 .ANG. and
about 50 .ANG.thick. The resulting film may have a leakage current
density less than about 0.1 microamps per square centimeter
(.mu.A/cm.sup.2); sometimes it may be less than about 0.05
.mu.A/cm.sup.2 or 0.01-0.05 .mu.A/cm.sup.2.
[0010] The metal precursor may include a precursor for aluminum,
zirconium, or hafnium. An aluminum precursor may include
trimethylaluminum (TMA). The oxygen precursor may include water or
ozone. Either the first (post-metal) or the second (post-oxygen)
purge may include flooding the chamber with an inert gas such as
argon, nitrogen, or helium.
BRIEF DESCRIPTION OF DRAWINGS
[0011] FIG. 1 illustrates an example of a metal-oxide semiconductor
field effect transistor (MOSFET) device.
[0012] FIG. 2 is an example flowchart for forming a high-k metal
oxide layer by atomic layer deposition (ALD).
[0013] FIG. 3 is an example flowchart of a process for testing
leakage current in candidate high-k metal oxide ALD films by
forming a test stack.
[0014] FIG. 4 is an example graph of leakage current results for
candidate Al2O3 gate-dielectric films in a Si/SiOx/Al2O3/TiN test
stack.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0015] FIG. 1 illustrates an example of a metal-oxide semiconductor
field effect transistor (MOSFET) device. The MOSFET can be
incorporated into integrated circuits, interconnected with other
devices. The MOSFET may include a substrate 101, which may include
one or more underlying layers on a silicon, silicon-on-insulator,
silicon-germanium, or germanium wafer or other base. Source region
102 and drain region 103 in substrate 101 may be doped with
arsenic, phosphorous, boron or other suitable materials using a
self-aligning ion implantation process or other suitable process.
Other components, such as n-well or p-well regions, may be included
in some devices.
[0016] A gate stack fabricated on substrate 101 includes high-k
gate dielectric layer 104, gate electrode layer 105, and gate
conductor layer 106. Spacers 107 are formed between the gate stack
{104, 105, 106} and the surrounding interlayer dielectric (ILD)
108. High-k dielectric layer 104 may include a metal oxide such as
Al.sub.2O.sub.3, HfO.sub.x, or ZrO.sub.x. High-k dielectric layer
104 provides a sufficient equivalent oxide thickness (EOT) to
prevent leakage current through the gate due to tunneling.
[0017] Gate electrode layer 105 is formed on high-k dielectric
layer 104 and may include aluminum, polysilicon, or other suitable
conductive materials (e.g., TiN, TaN, HfN, RuN, WN, W, MoN, TaSiN,
RuSiN, WSiN, HfSiN, TiSiN, etc.). Spacers 107 (made of SiO.sub.2,
Si.sub.3N.sub.4, tetraethyl Orthosilicate (TEOS) or other suitable
dielectric materials) isolate gate electrode 105 and high-k
dielectric layer 104 from source region 102 and drain region
103.
[0018] Various processes exist for creating the MOSFET structure.
For example, in a "gate-first" process, high-k dielectric layer
104, gate electrode layer 105, and gate conductor layer 106 may be
initially formed as blanket layers on substrate 101. Then the
layers may be patterned (e.g., by dry or wet etching or
lithography) to remove everything except the gate stack. Afterward,
the surrounding structures are fabricated; source 102 and drain 103
dopants are implanted, spacers 107 are formed, and the ILD 108 is
added.
[0019] In an alternative "gate-last," "dummy gate," or "replacement
gate" process, high-k dielectric layer 104 is also initially formed
as a blanket layer on substrate 101. However, a sacrificial
material (e.g., polysilicon) temporarily takes the place of gate
electrode layer 105 and gate conductor layer 106; it is deposited
on top of high-k dielectric layer 104 and patterned along with it
to form a dummy gate stack. The surrounding structures are
fabricated around the dummy gate stack. Afterward, the sacrificial
material is removed by etching or another suitable process, to be
replaced by gate electrode layer 105 and gate conductor layer 106.
The dummy gate approach can be advantageous if the materials of
gate electrode layer 105 and gate conductor layer 106 can be
damaged by some of the processes for making the surrounding
structure (e.g., high temperature).
[0020] FIG. 2 is an example flowchart for forming a high-k metal
oxide layer by atomic layer deposition (ALD). A substrate is
positioned 201 in a process chamber. In part "A" of the cycle, a
metal precursor (e.g., TMA, some other aluminum precursor, or a
hafnium or zirconium precursor) is then introduced into the chamber
so that the substrate is exposed to it 202. The exposure may
include a "pulse" of precursor flowing into the chamber, followed
by a time delay when no additional precursor flows but the
precursor already present reacts with, or adheres to the substrate.
Next, the process chamber is purged 203 to remove any unreacted
metal precursor or by-products from the reaction zone and other
surfaces. The purge may include an evacuation of the chamber, a
pulse of a purge gas, or a combination. Alternatively, the purge
gas may flow continuously through the reaction zone throughout
deposition. The purge gas may be an inert gas such as argon,
nitrogen, or helium. Post-metal purge 203 may have a duration of
less than 15 seconds, such as between 5 and 15 seconds.
[0021] In part "B" of the cycle, an oxygen precursor such as water
(H.sub.2O) or ozone (O.sub.3) is introduced 204 into the chamber,
as a pulse or as a continuous flow, then the chamber is purged 205
a second time. The purge may include an evacuation of the chamber,
a pulse of a purge gas, or a combination. Alternatively, the purge
gas may flow continuously through the reaction zone throughout
deposition. The purge gas may be an inert gas such as argon,
nitrogen, or helium. Post-oxygen purge 205 has a duration longer
than 60 seconds, which may be between 60 and 120 seconds or between
65 and 80 seconds. This completes one ALD cycle, depositing a layer
of metal oxide about 0.6 .ANG.-1.2 .ANG.thick. ALD layer thickness
is typically expressed as an average thickness. A contiguous
monolayer is one molecule thick. However, a non-contiguous
monolayer, where there are empty spaces left between the deposited
atoms, can be less than 1 molecule thick on average.
[0022] If the film is determined 206 to have reached a desired
thickness after the most recent cycle, the process is complete; if
not, another A-B cycle is performed. Thickness determination 206
can be made by monitoring the film thickness or, when the thickness
per cycle is known, simply by counting cycles. For example, the
desired thickness may be in a range of 2-50 .ANG., or 2-10 .ANG.,
or 25-35 .ANG..
[0023] FIG. 3 is an example flowchart of a process for testing
leakage current in candidate high-k metal oxide ALD films by
forming a test stack. A silicon substrate with a silicon oxide
layer is prepared 301 for ALD. A set of trial process parameters
for the metal-oxide ALD is selected 302. The metal oxide is
deposited 303 on the silicon oxide according to the selected
process parameters; for example, by a procedure like that of FIG.
2. Process parameters may include precursor composition, purge gas
composition, pulse and purge times, pulse and purge flow rates,
chamber pressure, substrate or ambient temperature, and variations
of any of those during the deposition. In some test cases, process
parameters may also extend to temperature, duration, ambient gas
composition, or pressure of a post-ALD anneal 304 or optionally to
a post-anneal treatment 305 such as an ozone treatment.
[0024] A conductive layer is then added 306 above the metal oxide.
The conductive layer may operate as an electrode and may also cap
the metal-oxide layer to protect it from the environment outside
the process chamber. The conductive layer may have its process
parameters kept constant for each variation of the metal oxide, or
its process parameters may also be selected for variation.
Optionally, the conductive layer may also be annealed or otherwise
treated after deposition.
[0025] One or more capacitors are formed 307 from the resulting
test stack of Si/SiOx/metal oxide/conductor. A test voltage is
applied 308 and the leakage current is measured 309. Other tests
may also be performed. The results from different sets of process
parameters are compared to select the best metal-oxide process.
Each set of selected process parameters may be implemented and
tested on a separate substrate, or, with equipment and methods such
as the High Productivity Combinatorial system described in U.S.
Pat. No. 7,947,531 (incorporated herein by reference for all
purposes), multiple sets of process parameters may be implemented
and tested on a single substrate.
[0026] FIG. 4 is an example graph of leakage current results for
candidate Al.sub.2O.sub.3 gate-dielectric films in a
Si/SiO.sub.x/Al.sub.2O.sub.3/TiN test stack. The Al precursor was
TMA, the oxygen precursor was H.sub.2O, and the film thickness was
30 .ANG.. The x-axis is the device number, an arbitrary way to
separate the points within a data set. Data set 401 shows the
leakage current distribution for a post-oxygen purge of the
standard 5-15 sec duration. Data set 402 s shows the leakage
current distribution for a post-oxygen purge of a prolonged 70 sec
duration. The prolonged post-oxygen purge caused roughly an
order-of-magnitude decrease in leakage current, to less than 0.1
.mu.A/cm.sup.2; most samples had leakage J.sub.g less than 0.05
.mu.A/cm.sup.2, or between about 0.01 and about 0.05
.mu.A/cm.sup.2.
[0027] Although the foregoing examples have been described in some
detail to aid understanding, the invention is not limited to the
details in the description and drawings. The examples are
illustrative, not restrictive. There are many alternative ways of
implementing the invention. Various aspects or components of the
described embodiments may be used singly or in any combination. The
scope is limited only by the claims, which encompass numerous
alternatives, modifications, and equivalents.
* * * * *