U.S. patent application number 10/677035 was filed with the patent office on 2005-03-31 for method to control the interfacial layer for deposition of high dielectric constant films.
This patent application is currently assigned to Sharp Laboratories of America, Inc.. Invention is credited to Conley, John F. JR., Ono, Yoshi.
Application Number | 20050070079 10/677035 |
Document ID | / |
Family ID | 34377526 |
Filed Date | 2005-03-31 |
United States Patent
Application |
20050070079 |
Kind Code |
A1 |
Conley, John F. JR. ; et
al. |
March 31, 2005 |
METHOD TO CONTROL THE INTERFACIAL LAYER FOR DEPOSITION OF HIGH
DIELECTRIC CONSTANT FILMS
Abstract
Methods of forming an interfacial layer on a hydrogen-passivated
substrate are provided. These methods utilize atomic layer
deposition techniques incorporating metal nitrate-based precursors,
such as hafnium nitrate or zirconium nitrate, without introducing a
hydrating agent, or oxidizing agent, such as water, during the
formation of the interfacial layer. Also provided are methods of
forming high-k films, by first forming an interfacial layer on the
surface of a hydrogen-passivated substrate, and then depositing
one, or more, high-k dielectric films.
Inventors: |
Conley, John F. JR.; (Camas,
WA) ; Ono, Yoshi; (Camas, WA) |
Correspondence
Address: |
DAVID C RIPMA, PATENT COUNSEL
SHARP LABORATORIES OF AMERICA
5750 NW PACIFIC RIM BLVD
CAMAS
WA
98607
US
|
Assignee: |
Sharp Laboratories of America,
Inc.
|
Family ID: |
34377526 |
Appl. No.: |
10/677035 |
Filed: |
September 30, 2003 |
Current U.S.
Class: |
438/585 |
Current CPC
Class: |
H01L 21/3141 20130101;
H01L 21/0228 20130101; H01L 21/02205 20130101; H01L 21/02304
20130101; H01L 21/02175 20130101; C23C 16/405 20130101; H01L
21/31645 20130101; C23C 16/45553 20130101 |
Class at
Publication: |
438/585 |
International
Class: |
H01L 021/3205 |
Claims
What is claimed is:
1. A method of forming a high-k dielectric film on a substrate
comprising the steps of: a) providing a hydrogen passivated surface
on a semiconductor substrate within an atomic layer deposition
chamber; b) forming an interfacial layer by heating the substrate
to a temperature below 200 degrees Celsius and introducing
anhydrous hafnium nitrate into the chamber without introducing a
hydrating gas, or an additional oxidizing gas, during the formation
of the interfacial layer; and c) forming a high-k film overlying
the interfacial layer.
2. The method of claim 1, wherein the substrate has a silicon
surface.
3. The method of claim 1, wherein the substrate is heated to a
temperature in the range of approximately 30 to 200.degree. C.
during formation of the interfacial layer.
4. The method of claim 1, wherein forming the interfacial layer
cycles anhydrous hafnium nitrate with a nitrogen purge.
5. The method of claim 1, wherein the step of forming a high-k film
further comprises repeating the steps of: introducing a
hafnium-containing precursor into the chamber, purging the chamber,
introducing H.sub.2O into the chamber, and purging the chamber
until a desired film thickness is achieved.
6. The method of claim 5, wherein the hafnium-containing precursor
is anhydrous hafnium nitrate, hafnium chloride, or
hafnium(tmhd).sub.x.
7. The method of claim 1, wherein the step of forming a high-k film
overlying the interfacial layer further comprises repeating the
steps of: introducing a HfCl.sub.4 precursor into the chamber,
purging the chamber, introducing Hf(NO.sub.3).sub.4 into the
chamber, and purging the chamber until a desired film thickness is
achieved.
8. The method of claim 1, wherein the step of forming a high-k film
forms a high-k metal oxide film selected from the group consisting
of ZrO.sub.2, Gd.sub.2O.sub.3, La.sub.2O.sub.3, CeO.sub.2,
TiO.sub.2, Y.sub.2O.sub.3, Ta.sub.2O.sub.5, Al.sub.2O.sub.3,
HfAlO.sub.x, ZrAlO.sub.x, and HfZrO.sub.x.
9. The method of claim 1, wherein the step of forming a high-k film
forms a multilayer film comprising alternating layers of metal
oxide films selected from the group consisting of ZrO.sub.2,
Gd.sub.2O.sub.3, La.sub.2O.sub.3, CeO.sub.2, TiO.sub.2,
Y.sub.2O.sub.3, Ta.sub.2O.sub.5, Al.sub.2O.sub.3, HfAlO.sub.x,
ZrAlO.sub.x, and HfZrO.sub.x.
10. A method of forming a high-k dielectric film on a substrate
comprising the steps of: a) providing a hydrogen passivated surface
on a semiconductor substrate within an atomic layer deposition
chamber; b) exposing the hydrogen passivated surface to a metal
nitrate containing precursor at a temperature below the thermal
decomposition temperature for the precursor without a hydrating
gas, or an oxidizing gas, to produce self-limiting high-k
interfacial layer; and c) repeating the steps of exposing the
surface to a metal-containing precursor, purging the chamber,
exposing the surface to a hydrating gas, oxidizing gas, or
precursor, and purging to deposit additional high-k material.
11. The method of claim 10, wherein the metal nitrate containing
precursor has the formula M(NO.sub.3).sub.x, where M is a metal
selected from the group consisting of Hf, Zr, Gd, La, Ce, Ti, Y,
Ta, and Al; and x is the valence of M.
12. The method of claim 10, wherein the additional high-k material
is the same material as the interfacial layer.
13. The method of claim 10, wherein the additional high-k material
is different than the interfacial layer.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to methods of
forming thin films and, more particularly, to methods of forming
high dielectric constant films on hydrogen-passivated
substrates.
[0002] Current Si VLSI technology uses SiO.sub.2 as the gate
dielectric in MOS devices. As device dimensions continue to scale
down, the thickness of the SiO.sub.2 layer must also decrease.
Thicknesses of less than 1 nanometer (nm) are expected in the
future. However, the occurrence of high tunneling current through
such thin layers of SiO.sub.2 requires that alternate materials be
considered. Materials with high dielectric constants would permit
gate dielectric layers to be made thicker, and so alleviate the
tunneling current problem. These so-called high-k dielectric films
are defined herein as having a high dielectric constant relative to
silicon dioxide. Typically, silicon dioxide has a dielectric
constant of approximately 4, while it would be desirable to use a
gate dielectric material with a dielectric constant of greater than
approximately 10.
[0003] Because of high direct tunneling currents, SiO.sub.2 films
thinner than 1.5 nm generally cannot be used as the gate dielectric
in CMOS devices. There are currently intense efforts in the search
for the replacement of SiO.sub.2. Metal oxides, such as hafnium
oxide (HfO.sub.2) and zirconium oxide (ZrO.sub.2), are leading
candidates for high-k dielectric materials. The dielectric constant
of these materials is about 20 to 25, which is a factor of 5-6
times that of silicon dioxide, meaning that a thickness of about
5-6 nm of these materials could be used to achieve an equivalent
oxide thickness (EOT) of about 1.0 nm, assuming that the entire
film is essentially composed of the high-k material. One problem
with using high-k materials is that an interfacial layer of silicon
dioxide, or a silicate layer, with a lower dielectric constant
forms during standard processing. Achieving EOT of less than 1.5 nm
is very difficult. An EOT of about 1.0 nm, and below, is expected
to be used for the 0.07 micrometer device generation.
[0004] Deposition of ZrO.sub.2, or HfO.sub.2, using atomic layer
deposition (ALD) tetrachloride precursors has been reported.
Substrates heated to between 300.degree. C. and 400.degree. C. have
been exposed to ZrCl.sub.4, or HfCl.sub.4, precursors alternating
with water vapor in an attempt to form ZrO.sub.2 or HfO.sub.2 films
respectively. However, it is difficult to initiate deposition on
hydrogen terminated silicon surfaces. Hydrogen terminated silicon
surfaces result from standard industry cleaning processes. These
standard cleaning processes, which are often referred to as HF last
clean, typically end in a quick dip in dilute HF. This produces
surfaces which are hydrogen terminated, also known as hydrogen
passivated. With sufficient exposure of the silicon surface to the
reactants, the deposition may eventually be initiated. But, this
results in films that are rough with poor uniformity. Another
problem with tetrachloride precursors is the incorporation of
residual chlorine in the film. The chlorine impurities can result
in long term reliability and performance issues.
[0005] Other precursors use Hf or Zr metal combined with organic
ligands such as iso-propoxide, TMHD
(2,2,6,6-tetramethyl-3,5-heptanedionate), or combinations of
organic ligands with chlorine. These precursors also have a problem
initiating the film deposition on hydrogen terminated silicon
surfaces and will incorporate carbon residues in the film. Large
ligands may also take up enough space that steric hindrance will
prevent the deposition of a uniform monolayer. Up until now, the
successful implementation of ALD Zr and Hf oxides have been either
on an initial layer of silicon oxide, silicon oxynitride, or in the
form of a reduced dielectric constant silicate film, such as
ZrSiO.sub.4 or HfSiO.sub.4. These initial layers may contribute
significantly to the overall EOT.
[0006] The use of metal nitrate precursors, such as
Hf(NO.sub.3).sub.4 and Zr(NO.sub.3).sub.4, has been shown to
provide a means for depositing films onto hydrogen passivated
surfaces, even at low temperatures required for ALD. Problems
related to the interfacial layer, such as the formation of silicon
oxides or silicates, may remain even using metal nitrate
precursors. This may be, in part, due to the presence of H.sub.2O,
during the formation of the interfacial layer, for example in a
process employing alternating exposures, such as
M(NO.sub.3).sub.x/H.sub.- 2O (where M is a metal and x is the
valence of M). The presence of H.sub.2O may affect the interfacial
layer due to the presence of hydrogen, or due to the additional
oxygen provided. Another possible cause is that the NO.sub.3 ligand
is highly reactive and may promote the formation of silicate, or
silicon oxide, at the interface even at moderate temperatures in
the range of 300 to 450 degrees Celsius. Another factor may be that
the amount of oxygen in the M(NO.sub.3).sub.x in excess of that
required to form the desired metal-oxide film, for example using
Hf(NO.sub.3).sub.4 (12:1 O:Hf ratio) to deposit HfO.sub.2 (2:1 O:Hf
ratio).
SUMMARY OF THE INVENTION
[0007] Accordingly, a method is provided to deposit a high-k
material by first forming an interfacial layer overlying a hydrogen
passivated surface. The hydrogen passivated surface is exposed to a
metal nitrate containing precursor without a hydrating gas, or an
oxidizing gas, being introduced until the interfacial layer is
formed to a desired thickness, which may be a self-limited
thickness. H.sub.2O may act as either an oxidizing gas, or a
hydrating gas and so will not be introduced during the formation of
the interfacial layer.
[0008] The metal nitrate containing precursor has the formula
M(NO.sub.3).sub.x, where M is a metal selected from the group
consisting of Hf, Zr, Gd, La, Ce, Ti, Y, Ta, and Al; and x is the
valence of M.
[0009] Additional high-k material may then be deposited over the
interfacial layer. The additional high-k material may be the same
material as the interfacial layer, or a different high-k
material.
[0010] For example, a HfO.sub.2 interfacial layer may be formed
followed by a high-k material selected from ZrO.sub.2,
Gd.sub.2O.sub.3, La.sub.2O.sub.3, CeO.sub.2, TiO.sub.2,
Y.sub.2O.sub.3, Ta.sub.2O.sub.5, Al.sub.2O.sub.3, HfAlO.sub.x,
ZrAlO.sub.x, or HfZrO.sub.x.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a plot of interfacial layer thickness as a
function of the number of precursor cycles.
[0012] FIG. 2 is a plot of the self-limited thickness of the
interfacial layer as a function of temperature.
[0013] FIG. 3 is flow chart of an embodiment of the present
process.
[0014] FIG. 4 is a cross-sectional view of a substrate.
[0015] FIG. 5 is a cross-sectional view of an interfacial layer on
the substrate.
[0016] FIG. 6 is a cross-sectional view of an additional high-k
layer on the interfacial layer.
[0017] FIG. 7 is a plot of thickness versus precursor cycles for an
example of an interfacial layer followed by an additional high-k
layer.
DETAILED DESCRIPTION OF THE INVENTION
[0018] FIG. 1 is a chart showing the film thickness in angstroms of
an interfacial layer formed using a M(NO.sub.3).sub.x precursor
(where M is metal and x is the valence of M), in this example
Hf(NO.sub.3).sub.4. Generally, M may be Hf, Zr, Gd, La, Ce, Ti, Y,
Ta, or Al. The interfacial layer was formed by providing a hydrogen
passivated semiconductor surface, in this case hydrogen terminated
silicon, in an ALD chamber, and exposing the surface to cycles
comprising two seconds of Hf(NO.sub.3).sub.4 and ten seconds of
N.sub.2 at a temperature of approximately 170 degrees Celsius. This
interfacial layer initially increases with the number of cycles,
but then saturates or self-limits. As shown, using
Hf(NO.sub.3).sub.4 at 170 degrees Celsius this saturation occurs
after about 50 cycles, or 100 seconds total pulse time, of
Hf(NO.sub.3).sub.4. The interfacial layer shown in FIG. 1
saturates, or self-limits, at between approximately 20 and 22
angstroms. The interfacial layer is preferably a high-k material. A
high-k material refers to a material with a dielectric constant
higher than that of silicon dioxide.
[0019] The deposition rate using an equivalent amount of exposure
to Hf(NO.sub.3).sub.4 without the nitrogen purges has substantially
the same growth rate. So that 100 seconds of Hf(NO.sub.3).sub.4
would produce essentially the same thickness as the 50 cycles
shown. Accordingly, the use of nitrogen pulses is not required, but
may be used to improve uniformity.
[0020] FIG. 2 shows the self-limiting thickness of films, which
were produced using Hf(NO.sub.3).sub.4 in connection with the
method described above, as a function of temperature. FIG. 2
suggests that for Hf(NO.sub.3).sub.4 at approximately 200 degrees
Celsius the process changes, and may no longer be self-limiting.
For Hf(NO.sub.3).sub.4 the deposition temperature is preferably
between approximately 30 and 200 degrees Celsius. Although the
exact temperature may vary depending on the equipment used, chamber
pressure, precursor purity, and the M(NO.sub.3).sub.x precursor
used, one of ordinary skill in the art will be able to determine
this temperature without undue experimentation. To achieve the full
benefit of the present method, it would be preferable to stay below
the temperature at which the process is not longer self-limiting,
which will be below the decomposition temperature of the
M(NO.sub.3).sub.x precursor used. For Hf(NO.sub.3).sub.4 the
decomposition temperature is approximately 250 degrees Celsius.
[0021] Referring now to FIGS. 3-6, FIG. 3 is a flowchart
illustrating process steps, while FIGS. 4-6 are cross-sectional
views of the substrate during processing. Step 110 provides with a
hydrogen-passivated surface within an ALD chamber. FIG. 4 shows a
substrate 10 with a hydrogen-passivated surface 12. For purpose of
this illustration, a field oxide 16 is shown, which might
correspond to a replacement gate process. For the sake of
illustration, additional details are not shown. For example, source
and drain regions may have been previously formed although not
shown here.
[0022] Step 112 introduces a metal nitrate comprising precursor of
the form M(NO.sub.3).sub.x, where M is a metal and x is the valence
of M, into the ALD chamber to form the interfacial layer. The metal
M may be Hf, Zr, Gd, La, Ce, Ti, Y, Ta, or Al. During the formation
of the interfacial layer, the presence of H.sub.2O, any additional
hydrating gas, oxidizing gas, or any other reactive gas should be
avoided. The phrases "without hydrating gas," "without oxidizing
gas," or similar phrases should be understood to mean that
additional hydrating, oxidizing, or reactive gas is not being
purposely introduced. It is preferable for these gases to be
eliminated to within the limits of the ALD chamber being used.
After introducing the metal nitrate comprising precursor, the
chamber is purged with nitrogen, or an inert gas as shown in step
114. In one embodiment the precursor will be pulsed alternately
with the purge, as indicated by process arrow 116. The alternating
process can continue as desired, for example until the interfacial
layer has reached saturation, and the process becomes self-limited.
In another embodiment, the precursor is introduced for a period of
time, without intermediate purge cycles. After which, the ALD
chamber is purged prior to introducing the precursor used to
deposit the remainder of the dielectric material. FIG. 5 shows the
substrate 10 following formation of the interfacial layer 20.
[0023] For example, Hf(NO.sub.3).sub.4 is used to form an
interfacial layer of HfO.sub.2. In one embodiment,
Hf(NO.sub.3).sub.4 is exposed on the hydrogen passivated substrate
to form the interfacial layer. In another embodiment,
Hf(NO.sub.3).sub.4 is pulsed with alternating purges, using for
example nitrogen, to form the interfacial layer. Either of these
processes can be run until the interfacial layer has reached its
self-limiting thickness. Although the interfacial layer 20 is
self-limiting, in some embodiments the interfacial layer is not
fully formed before proceeding to successive deposition steps. In
this case, it is used only to initiate ALD on hydrogen terminated
Si surface. The interfacial layer 20 will preferably be allowed to
proceed up to 75% or more of the self-limiting thickness.
[0024] Step 120 forms a high-k dielectric film 30, shown in FIG. 6,
overlying the interfacial layer 20. The remainder of the dielectric
film may comprise the same material as the interfacial layer. For
example, cycling a hafnium-containing precursor; a purging gas; a
hydrating gas, an oxidizing gas, or another precursor; and a
purging gas to produce the remainder of the high-k film. Cycles for
producing HfO.sub.2, include the following examples:
Hf(NO.sub.3).sub.4/purge/H.sub.2O/purge;
HfCl.sub.4/purge/H.sub.2O/purge;
Hf(tmhd).sub.4/purge/H.sub.2O/purge; or
Hf(NO.sub.3).sub.4/purge/HfCl.sub.4/purge. The H.sub.2O may be used
as a hydrating gas, an oxidizing gas, or both.
[0025] Step 160 shows an anneal step. In an embodiment, the
interfacial layer and the additional high-k material is annealed
after the additional high-k material is deposited. In another
embodiment of the present method, the interfacial layer is annealed
prior to depositing additional high-k material.
[0026] FIG. 7 shows film thickness versus cycles for a HfO.sub.2
interfacial layer and high-k dielectric layer. Hf(NO.sub.3).sub.4
is used without H.sub.2O to produce the interfacial layer over the
hydrogen passivated surface. As shown by region 62, the interfacial
layer is approaching its self-limited thickness. The process then
alternates between pulses of Hf(NO.sub.3).sub.4 and H.sub.2O, with
intervening nitrogen purges to produce the remainder of the high-k
dielectric layer, shown by region 64, until a suitable thickness is
achieved.
[0027] The high-k dielectric layer 30 does not need to be the same
material as the interfacial layer 20. Even if an HfO.sub.2
interfacial layer 20 is used, the high-k dielectric layer could be
for example: ZrO.sub.2, Gd.sub.2O.sub.3, La.sub.2O.sub.3,
CeO.sub.2, TiO.sub.2, Y.sub.2O.sub.3, Ta.sub.2O.sub.5,
Al.sub.2O.sub.3, HfAlO.sub.x, ZrAlO.sub.x, or HfZrO.sub.x. For
depositing the high-k dielectric layer 30, any suitable precursor
can be used, including nitrate precursors, chlorides, or organic
precursors. Alternatively, the interfacial layer may be formed
using a different material deposited using an M(NO.sub.3).sub.x
precursor.
* * * * *