U.S. patent application number 14/736698 was filed with the patent office on 2015-10-01 for selective etch chemistry for gate electrode materials.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to John A. Fitzsimmons, David L. Rath, Muthumanickam Sankarapandian.
Application Number | 20150275376 14/736698 |
Document ID | / |
Family ID | 48903247 |
Filed Date | 2015-10-01 |
United States Patent
Application |
20150275376 |
Kind Code |
A1 |
Fitzsimmons; John A. ; et
al. |
October 1, 2015 |
SELECTIVE ETCH CHEMISTRY FOR GATE ELECTRODE MATERIALS
Abstract
A chemical solution including an aqueous solution, an oxidizing
agent, and a pH stabilizer selected from quaternary ammonium salts
and quaternary ammonium alkali can be employed to remove metallic
materials in cavities for forming a semiconductor device. For
example, metallic materials in gate cavities for forming a
replacement gate structure can be removed by the chemical solution
of the present disclosure with, or without, selectivity among
multiple metallic materials such as work function materials. The
chemical solution of the present disclosure provides different
selectivity among metallic materials than known etchants in the
art.
Inventors: |
Fitzsimmons; John A.;
(Poughkeepsie, NY) ; Rath; David L.; (Stormville,
NY) ; Sankarapandian; Muthumanickam; (Niskayuna,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
48903247 |
Appl. No.: |
14/736698 |
Filed: |
June 11, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13828650 |
Mar 14, 2013 |
9070625 |
|
|
14736698 |
|
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13343190 |
Jan 4, 2012 |
8835326 |
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13828650 |
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Current U.S.
Class: |
252/79.1 |
Current CPC
Class: |
C23F 1/02 20130101; C23F
1/32 20130101; C09K 13/00 20130101; C23G 1/205 20130101; H01L
21/283 20130101; C23F 1/40 20130101; H01L 21/823842 20130101; H01L
21/32134 20130101 |
International
Class: |
C23F 1/40 20060101
C23F001/40; C23F 1/02 20060101 C23F001/02; C09K 13/00 20060101
C09K013/00 |
Claims
1. A chemical composition for a stock solution for generating an
etch solution for removal of a metallic material, the chemical
composition comprising: at least one sequestering agent at a
concentration in a range from 200 p.p.m. to 20,000 p.p.m. in weight
percentage; a pH stabilizer including at least one quaternary
ammonium salt or at least one quaternary ammonium alkali; and an
aqueous solution.
2. The chemical composition of claim 1, wherein said sequestering
agent is selected from amines and amino acids.
3. The chemical composition of claim 1, wherein said sequestering
agent is at least one of
1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid (CDTA),
ethyenediaminetetraacetic acid (EDTA) and
diethylenetriaaminopentaacetic acid (DTPA).
4. The chemical composition of claim 1, wherein the pH stabilizer
is selected from the group consisting of at least one quaternary
ammonium salt and at least one quaternary ammonium alkali.
5. The chemical composition of claim 4, wherein the pH stabilizer
is selected from the group consisting of tetraethylammonium
hydroxide, trimethyl-phenyl-ammonium hydroxide,
dimethyl-dipropyl-ammonium hydroxide and tetrapropyl ammonium
hydroxide.
6. The chemical composition of claim 5, wherein the pH stabilizer
is tetraethylammonium hydroxide.
7. The chemical composition of claim 1, wherein the aqueous
solution comprises de-ionized water.
8. The chemical composition of claim 1, wherein the composition
comprises hydrogen peroxide (H.sub.2O.sub.2), benzotriazole,
tetraethylammonium hydroxide, and de-ionized water, and wherein the
composition has a pH in the range of about 7 to about 9.
9. A chemical composition for a stock solution for generating an
etch solution for removal of a metallic material, the chemical
composition comprising: at least one metal protectant at a
concentration in a range from 10,000 p.p.m. to 400,000 p.p.m. in
weight percentage; at least one sequestering agent at a
concentration in a range from 200 p.p.m. to 20,000 p.p.m. in weight
percentage; a pH stabilizer including at least one quaternary
ammonium salt or at least one quaternary ammonium alkali; and an
aqueous solution.
10. The chemical composition of claim 9, wherein said sequestering
agent is selected from amines and amino acids.
11. The chemical composition of claim 9, wherein said sequestering
agent is at least one of
1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid (CDTA),
ethyenediaminetetraacetic acid (EDTA) and
diethylenetriaaminopentaacetic acid (DTPA).
12. The chemical composition of claim 9, wherein said metal
protectant comprises at least one of benzotriazole, 1,2,3 triazole,
1,3,4 triazole, 1,2,4 triazole, imidazole, methyl-thiol-triazole,
thiol-triazole, and triazole acid.
13. The chemical composition of claim 9, wherein the pH stabilizer
is selected from the group consisting of at least one quaternary
ammonium salt and at least one quaternary ammonium alkali.
14. The chemical composition of claim 13, wherein the pH stabilizer
is selected from the group consisting of tetraethylammonium
hydroxide, trimethyl-phenyl-ammonium hydroxide,
dimethyl-dipropyl-ammonium hydroxide and tetrapropyl ammonium
hydroxide.
15. The chemical composition of claim 14, wherein the pH stabilizer
is tetraethylammonium hydroxide.
16. The chemical composition of claim 9, wherein the aqueous
solution comprises de-ionized water.
17. The chemical composition of claim 9, wherein the composition
comprises hydrogen peroxide (H.sub.2O.sub.2), benzotriazole,
tetraethylammonium hydroxide, and de-ionized water, and wherein the
composition has a pH in the range of about 7 to about 9.
Description
BACKGROUND
[0001] The present disclosure relates to a method of removing a
metallic material from a cavity of a microelectronic device. More
particularly, the present disclosure relates to a method of
removing a metallic material employing a chemical solution
including an aqueous solution, an oxidizing agent, and a pH
stabilizer selected from at least one quaternary ammonium salt or
at least one quaternary ammonium alkali.
[0002] High gate leakage current of silicon oxide and nitrided
silicon dioxide as well as depletion effect of polysilicon gate
electrodes limits the performance of conventional semiconductor
oxide based gate electrodes. High performance devices for an
equivalent oxide thickness (EOT) less than 2 nm require high
dielectric constant (high-k) gate dielectrics and metal gate
electrodes to limit the gate leakage current and provide high
on-currents. Materials for high-k gate dielectrics include
ZrO.sub.2, HfO.sub.2, other dielectric metal oxides, alloys
thereof, and their silicate alloys.
[0003] In general, dual metal gate complementary metal oxide
semiconductor (CMOS) integration schemes employ two gate materials,
one having a work function near the valence band edge of the
semiconductor material in the channel and the other having a work
function near the conduction band edge of the same semiconductor
material. A challenge in semiconductor technology has been to
provide two types of gate electrodes having a first work function
at or near the valence band edge and a second work function at or
near the conduction band edge of the underlying semiconductor
material such as silicon. This challenge has been particularly
difficult because the two types of gate electrodes are also
required to be a metallic material having a high electrical
conductivity.
[0004] In order to provide two types of gate electrodes, portions
of a conductive material are removed from one type of gate
electrodes while other portions of the conductive material remain
in another type of gate electrodes. Removal of such a conductive
material needs be performed in a controllable manner. In some
cases, removal of a conductive material needs to be performed
selective to another conductive material. While the etch chemistry
of SC1 etch, which employs a combination of ammonium hydroxide and
hydrogen peroxide, is known to etch metallic materials, the etch
rate of the SC1 etch is generally high for most metallic materials,
and provides insufficient etch selectivity among various metallic
materials.
[0005] Thus, an etch chemistry that can provide additional
selectivity or non-selectivity among metallic materials to overcome
the limitations of the SC1 etch is desired.
SUMMARY
[0006] A chemical solution including an aqueous solution, an
oxidizing agent, and a pH stabilizer selected from at least one
quaternary ammonium salt or at least one quaternary ammonium alkali
can be employed to remove metallic materials in cavities for
forming a semiconductor device. For example, metallic materials in
gate cavities for forming a replacement gate structure can be
removed by the chemical solution of the present disclosure with, or
without, selectivity among multiple metallic materials such as work
function materials. The chemical solution of the present disclosure
provides different selectivity among metallic materials than known
etchants in the art.
[0007] According to an aspect of the present disclosure, a method
of forming a microelectronic device is provided. At least one
cavity is formed in a dielectric material layer over a
semiconductor substrate. At least one metallic material is
deposited within the at least one cavity. A portion of the at least
one metallic material is removed by an etch process employing a
chemical composition. The chemical composition includes an aqueous
solution, a pH stabilizer selected from at least one quaternary
ammonium salt or at least one quaternary ammonium alkali, and an
oxidizing agent selected from peroxides and oxidants.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0008] FIG. 1 is a graph comparing etch rates of a chemical
composition according to an embodiment of the present disclosure
and an SC1 solution.
[0009] FIG. 2 is a vertical cross-sectional view of a first
exemplary semiconductor structure after formation of a gate cavity
according to a first embodiment of the present disclosure.
[0010] FIG. 3 is a vertical cross-sectional view of the first
exemplary semiconductor structure after formation of an interfacial
dielectric layer and a gate dielectric layer according to the first
embodiment of the present disclosure.
[0011] FIG. 4 is a vertical cross-sectional view of the first
exemplary semiconductor structure after formation of a work
function material layer and a conductive material layer according
to the first embodiment of the present disclosure
[0012] FIG. 5 is a vertical cross-sectional view of the first
exemplary semiconductor structure after planarization of the
conductive material layer, the work function material layer, and
the gate dielectric layer according to the first embodiment of the
present disclosure.
[0013] FIG. 6 is a vertical cross-sectional view of a second
exemplary semiconductor structure after formation of a gate
dielectric layer and a first work function material layer according
to a second embodiment of the present disclosure
[0014] FIG. 7 a vertical cross-sectional view of the second
exemplary semiconductor structure after thinning of the first work
function material layer employing a patterned photoresist layer
according to the second embodiment of the present disclosure.
[0015] FIG. 8 is a vertical cross-sectional view of the second
exemplary semiconductor structure after deposition of a second work
function material layer, a conductive fill material layer, and
planarization of the conductive fill material layer, the second
work function material layer, the first work function material
layer, and the gate dielectric layer according to the second
embodiment of the present disclosure.
[0016] FIG. 9 is a vertical cross-sectional view of the second
exemplary semiconductor structure after recessing of metallic
materials in the gate cavities according to the second embodiment
of the present disclosure.
[0017] FIG. 10 is a vertical cross-sectional view of the second
exemplary semiconductor structure after formation of outer
conductive material portions and inner conductive material portions
according to the second embodiment of the present disclosure.
[0018] FIG. 11 is a vertical cross-sectional view of the second
exemplary semiconductor structure after recessing of the outer
conductive material portions and the inner conductive material
portions according to the second embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0019] As stated above, the present disclosure relates to a method
of removing a metallic material employing a chemical solution
including an aqueous solution, an oxidizing agent, and a pH
stabilizer selected from at least one quaternary ammonium salt or
at least one quaternary ammonium alkali. Aspects of the present
disclosure are now described in detail with accompanying figures.
Like and corresponding elements mentioned herein and illustrated in
the drawings are referred to by like reference numerals. The
drawings are not necessarily drawn to scale. As used herein,
ordinals such as "first," "second," and "third" are employed merely
to distinguish similar elements, and different ordinals may be
employed to designate a same element in the specification and/or
claims.
[0020] As used herein, a field effect transistor refers to any
planar transistor having a gate electrode overlying a horizontal
planar channel, any fin field effect transistor having a gate
electrode located on sidewalls of a semiconductor fin, or any other
types of metal-oxide semiconductor field effect transistor
(MOSFETs) and junction field effect transistors (JFETs).
[0021] The following describes embodiments of the present
disclosure with reference to the drawings. The embodiments are
illustrations of the disclosure, which can be embodied in various
forms. The present disclosure is not limited to the embodiments
described below, rather representative for teaching one skilled in
the art how to make and use it. Some aspects of the drawings repeat
from one drawing to the next. The aspects retain their same
numbering from their first appearance throughout each of the
preceding drawings.
[0022] The present disclosure provides a chemical solution that
removes at least one metallic material selective to, or without
selectivity to, at least another metallic material during
manufacturing of microelectronic devices such as field effect
transistors. The present disclosure provides a method for
patterning at least one metallic material in cavities surrounded by
a dielectric material layer and located on a semiconductor
substrate.
[0023] Compositions of the chemical solution may be embodied in a
wide variety of specific formulations, as hereinafter more fully
described. In all such compositions, wherein specific components of
the composition are discussed in reference to weight percentage
ranges including a zero lower limit, it will be understood that
such components may be present or absent in various specific
embodiments of the composition, and that in instances where such
components are present, they may be present at concentrations as
low as 0.0001 weight percent, based on the total weight of the
composition in which such components are employed.
[0024] The chemical compositions of the disclosure may be
formulated to remove physically exposed portions of at least one
metallic material selective to dielectric materials such as
dielectric metal oxides or interlayer dielectric materials employed
for metal interconnect structures. The chemical composition may be
formulated to remove at least one work function metal such as TiN,
TiC, TaN, TaC, a carbide of a titanium alloy, or a carbide of a
tantalum alloy, or to remove a contact metal such as W or Al
selective or non-selective to at least one work function metal,
without substantially damaging the underlying gate dielectric
materials or interlayer dielectric materials. The methods of the
present disclosure may be employed for devices where there is only
one work function metal. An additional advantage of the methods of
the present disclosure is manifested where more than one work
function metal is present. While the present disclosure is
illustrated employing an embodiment in which two work function
metals are employed, embodiments are expressly contemplated in
which the illustrated methods of the present disclosure are
extended to cases where more than two work function metals are
employed.
[0025] The chemical composition of the present disclosure includes
an oxidizing agent and a pH controlling agent in an aqueous
solution. De-ionized water is the principle solvent in the aqueous
solution. The solvent must be at least free of any detrimental ions
or other materials that could interfere with the cleaning action of
the chemical composition or degrade the cleanliness or future
performance of the semiconductor circuit. While de-ionized water is
the most preferred solvent for the chemical composition, it is
understood that other solvent systems with similar salvation
properties to de-ionized water may also act as a possible solvent
for the present disclosure. Thus, an aqueous solution is most
preferred. However, it is understood that other solvent systems
similar to water may also act suitably for the present disclosure.
For example, a 25% isopropanol, 75% de-ionized water solvent system
may also produce satisfactory results.
[0026] The oxidizing agent is preferably a peroxide, for example
hydrogen peroxide and organic peroxides such as benzoyl peroxide.
However, oxidizing agents may also include a non-metal with the
ability to oxidize titanium nitride (TiN) to a soluble compound
without leaving a metallic residue and oxidants that do not leave a
residue or adversely attack films intended to remain undamaged. In
other words, the oxidant should be able to be controlled such that
undesired attack of metal films does not occur. More specifically,
the pH may be adjusted such that the etch rate of one work function
or contact metal may be adjusted to be selective or non-selective
to a work function metal or metals, and/or a surface adsorption
action may occur due to agents in the present disclosure such that
these metals are protected from uncontrolled oxidation. The present
chemical composition as it is so designed with the understanding
that the tetraethylammonium (TEA) ion may act as a passivating
adsorbent with respect to a transition metal present in the alloy
or a lanthanide metal (for example Ti, Ta, alloys including Ti and
carbon, or alloys including Ta and carbon), and as such, provide a
modification of the alloy etch behavior (as compared to a etch
without this a passivating adsorbent action) at the pH value of
operation.
[0027] The pH stabilizer adjusts the pH level in the chemical
composition to a range of about 7 to about 14. In one embodiment,
the amount of the pH stabilizer can be selected such that the pH
level of the working solution is adjusted to a range of about 7 to
about 10. In another embodiment, the amount of the pH stabilizer
can be selected such that the pH level of the working solution is
adjusted to a range of about 7 to about 9. In yet another
embodiment, the amount of the pH stabilizer can be selected such
that the pH level of the working solution is adjusted to a range of
about 7 to about 8. In one embodiment, the weight percentage of the
pH stabilizer in the working solution can be from 0.14% to 14%. In
another embodiment, the weight percentage of the pH stabilizer in
the working solution can be not less than 0.28%. In yet another
embodiment, the weight percentage of the pH stabilizer in the
working solution can be not less than 0.7%. In still another
embodiment, the weight percentage of the pH stabilizer in the
working solution can be not less than 1.4%. In one embodiment, the
weight percentage of the pH stabilizer in the working solution can
be not greater than 7%. In one embodiment, the weight percentage of
the pH stabilizer in the working solution can be not greater than
2.8%. In one embodiment, the weight percentage of the pH stabilizer
in the working solution can be not greater than 1.4%. Quaternary
ammonium salts and quaternary ammonium alkalis are preferred for
use as a pH stabilizer in the present disclosure
[0028] Quaternary ammonium salts (and especially quaternary
ammonium basic salts or quaternary ammonium salts including at
least one quaternary ammonium basic salt) and quaternary ammonium
alkalis are preferred for use as a pH stabilizer in the present
disclosure. A quaternary ammonium compound is a positively charged
ion based on 4 R groups associated with a nitrogen atom having a
descriptive structure as illustrated below
##STR00001##
[0029] Each of R1, R2, R3, and R4 groups may independently be alkyl
or aryl in nature. Each of R1, R2, R3, and R4 group may be
identical or different among one another. Thus, a quaternary
ammonium compound may be symmetrical or asymmetrical. That is, if
an even number of R groups (i.e., R1, R2, R3, and R4 groups) are
identical, the quaternary ammonium compound is referred to as
symmetrical; and if the number of R groups is odd, the quaternary
ammonium compound is referred to as asymmetrical. A quaternary
ammonium salt is a compound where a quaternary ammonium ion is
associated with a corresponding negatively charged ion to produce a
net neutral charge for the overall compound. A quaternary ammonium
alkali is a quaternary ammonium salt where the corresponding
negatively charged ion is a basic ion, which is commonly a
hydroxide ion.
[0030] Tetramethylammonium hydroxide (TMAH) is the quaternary
ammonium compound that is primarily used in the industry. TMAH is a
symmetrical quaternary ammonium compound where all the R groups are
identical and consist of methyl groups. However, TMAH is toxic, and
causes severe and typically unexpected health problems from
exposure. Unlike typical strong bases where an unprotected acute
exposure generally results in a caustic burn, TMAH may also
introduce a complication of decreased respiratory function. Thus, a
quaternary ammonium that does not cause unexpected health side
effects is preferable. In the course of the research leading to the
present disclosure, it has been determined that tetraethylammonium
(TEA) ion does not cause the unexpected health side effects of the
tetramethylammonium ion. Thus, tetraethylammonium hydroxide (TEAH)
is the most preferred pH stabilizer in the present disclosure. In
addition to the ability to adjust pH without the introduction of
extraneous undesirable metal ions, such as alkaline earth or alkali
metal ions, the TEA ion may also act as a passivating adsorbent on
a copper surface at the pH value of the present chemical
composition as it is also designed.
[0031] The preferred use of TEAH does not preclude the use of other
suitable quaternary ammonium hydroxides for use in our solutions.
It is believed that any quaternary ammonium hydroxide that may be
used to adjust pH in a desired range to be suitable for the purpose
of the present disclosure. It is believed that any symmetrical or
asymmetrical quaternary ammonium hydroxide that does not introduce
a complication of decreased respiratory function is a preferred
quaternary ammonium hydroxide. Additionally, if a quaternary
ammonium salt can provide some passivation action, such a
quaternary ammonium salt is even more preferred. In an illustrative
example, one or more of trimethyl-phenyl-ammonium hydroxide,
dimethyl-dipropyl-ammonium hydroxide and tetrapropyl ammonium
hydroxide can be employed as a pH adjustment agent for the
formulation of the present disclosure.
[0032] Regardless of whether the passivation action by TEA ions
occur, the ability to adjust pH without the introduction of
extraneous undesirable metal ions and the decreased hazard of TEAH
makes TEAH the most preferred pH stabilizer in one embodiment of
the present disclosure. It is understood that other quaternary
ammonium salts may also act as pH stabilizing agents with or
without the additional passivation action towards a metal or
semi-metal surface and as long as the resultant solution does not
have a detrimental activity towards a metal or semi-metal surface
which can not be mitigated; such a resultant solution is within the
purview of the present disclosure
[0033] The approximate bath life of the chemical composition is in
the range of about 18 hrs to about 22 hrs. When the chemical bath
drops below 10-15% fresh bath, the bath is no longer useful. It is
understood that typical methods used to extend solution bath life
such as replenishment of the consumed oxidizer in a recirculated
solution may be used to extend usable bath life. Additionally, it
is known that trace contamination such as minute amounts of some
metal ions may also dramatically decrease bath life. As such, the
chemical composition of the present disclosure may be of single use
(i.e., dispensed on the wafer for cleaning and sent to drain) or
multiple use (i.e., reclaimed after initial processing use and
stored for additional use). It is recognized that reclamation may
decrease the usable life of a reclaimed chemical bath. The use of a
sequestering agent (oxidant stabilizer) in the chemical bath, if
employed, can increase the life of the bath during reclamation
process use. A sequestering agent may be added to an un-reclaimed
chemical composition; this sequestering agent may extend the usable
bath life of such a composition beyond that of a solution without
the sequestering agent. Through the use of a sequestering agent,
the oxidizer concentration may be controlled such that excessive
oxidant concentration addition to the chemical composition of the
present disclosure is not necessary to compensate for oxidant
consumption by undesired decomposition due to contamination, rather
than by the normal consumption that occurs during the desired
cleaning action of the present chemical composition. Thereby, the
sequestering agent optimizes the concentration to further minimize
the chemical composition's attack on a metal layer by enabling a
minimization of required oxidizer concentration in the present
chemical composition.
[0034] Sequestering agents that can be used in the present
disclosure are amines and amino acids. The preferred sequestering
agents are 1,2-cyclohexanediamine-N,N,N',N'-tetraacetic acid
(CDTA), ethyenediaminetetraacetic acid (EDTA) and
diethylenetriaaminopentaacetic acid (DTPA). The preferential use of
complex sequestering agents, such as CDTA, versus a simple
sequestering agent, such as EDTA, is based on the possibility of
degradation of a simple sequestering agent over time and at
extended exposure to certain temperatures. However, it is
understood that for some methods of application a simple
sequestering agent such as EDTA may be suitable. For example, a
single use system where heating occurs just before the solution
dispenses on a wafer for chemical cleaning.
[0035] A metal protectant may be added to the chemical composition.
The preferred metal protectants for the present disclosure are
hetero-organic inhibitors such as azoles or thiols. Preferably, at
least one of benzotriazole (BTA), 1,2,3 triazole, 1,3,4 triazole,
1,2,4 triazole, methyl-thiol-triazole, thiol-triazole, triazole
acid, and imidazole are used in the chemical composition. The use
of hetero-organic inhibitors as opposed to simple organic compounds
is based on the possibility of degradation of organic compounds
over time and at extended exposure to certain temperatures. Azoles
are organic compounds containing nitrogen atoms with free electron
pairs that are potential sites for bonding with metals and that
enable inhibiting action. Thiols are organic compounds containing
sulfurs atoms with free electron pairs that are potential sites for
bonding with copper and that enable inhibiting action. In general,
Azole compounds are preferred over thiol compound, as incomplete
removal of thiol residues may lead to sulfur atom contamination, a
known detriment to many metal structures. Thus, when thiol
compounds are used, avoidance of Sulfur atom residue is very
important. Also, there is a possibility of introduction of other
heteroatoms beyond the aforementioned N and S such as Se, P, As etc
and/or combinations of heteroatoms either in ring incorporation or
as side groups in molecules of these compounds so there is a wide
range of derivatives that exhibit good inhibition characteristics.
Often when additional heteroatoms are used other attributes
introduced with the heteroatom must also be considered. For
example, it is understood that thiols produce active protection on
many metal surfaces; however, thiol use introduces additional
considerations of potential negative interactions with metal
structures (such as the latent formation of metal sulfides during
subsequent processing); and as such, may require additional post
processing to remove possible sulfur contamination and thus avoid
or minimize the potential for latent metal sulfide formation. As an
example: the post processing steps may include one or more of such
processes as extended rinse times, specialized or extended post
application plasmas, and/or extended vacuum degas processing.
[0036] The amount of the metal protectant in the working solution
of the present disclosure can be in a range from 10 p.p.m. to
50,000 p.p.m. In one embodiment, the amount of the metal protectant
in the working solution can be in a range from 10 p.p.m. to 100
p.p.m. In another embodiment, the amount of the metal protectant in
the working solution can be in a range from 100 p.p.m. to 1,000
p.p.m. In yet another embodiment, the amount of the metal
protectant in the working solution can be in a range from 1,000
p.p.m. to 10,000 p.p.m. In still another embodiment, the amount of
the metal protectant in the working solution can be in a range from
10,000 p.p.m. to 50,000 p.p.m.
[0037] According to an embodiment of the present disclosure,
formulations for the chemical composition of the working solution
can include: [0038] 1. 0.1%-20% in weight percentage of an
oxidizing agent; [0039] 2. 0.14%-14% in weight percentage of a pH
stabilizer; [0040] 3. 0 p.p.m.-50,000 p.p.m. in weight percentage
of at least one metal protectant; and [0041] 4. the balance of
deionized water or a water-based polar solvent in which water is a
predominant portion (more than 1/2) of the solvent.
[0042] An exemplary formulation for the chemical composition of the
working solution can be: [0043] 1. 9% in weight percentage of an
oxidizing agent; [0044] 2. 1.4% in weight percentage of a pH
stabilizer; [0045] 3. 10,000 p.p.m. in weight percentage of at
least one metal protectant; and [0046] 4. the balance of deionized
water or a water-based polar solvent in which water is a
predominant portion (more than 1/2) of the solvent.
[0047] According to another embodiment of the present disclosure,
formulations for the chemical composition of the working solution
can include: [0048] 1. 0.1%-20% in weight percentage of an
oxidizing agent; [0049] 2. 0.14%-1.4% in weight percentage of a pH
stabilizer; [0050] 3. 1 p.p.m.-100 p.p.m. of a sequestering agent;
[0051] 4. 0 p.p.m.-50,000 p.p.m. in weight percentage of at least
one metal protectant; and [0052] 5. the balance of deionized water
or a water-based polar solvent in which water is a predominant
portion (more than 1/2) of the solvent.
[0053] An exemplary formulation for the chemical composition of the
working solution can include: [0054] 1. 9% in weight percentage of
an oxidizing agent; [0055] 2. 1.4% in weight percentage of a pH
stabilizer; [0056] 3. 10 p.p.m. of a sequestering agent; and [0057]
4. 100 p.p.m. in weight percentage of at least one metal
protectant; and [0058] 5. the balance of deionized water or a
water-based polar solvent in which water is a predominant portion
(more than 1/2) of the solvent.
[0059] The preferred formulation of the chemical composition is
hydrogen peroxide and TEAH in an aqueous solution, wherein the
composition has a pH in the range of about 7 to about 9. The
chemical composition of the working solution is designed to remove
various metallic compounds including, but not limited to,
Ti-containing alloys including at least one or carbon and nitrogen
and optionally including at least one transition metal and/or at
least one lanthanide metal and Ta-containing alloys including at
least one or carbon and nitrogen and optionally including at least
one transition metal and/or at least one lanthanide metal. As used
herein, Ti-containing alloys and Ta-containing alloys refer to
various stoichiometric or non-stoichiometric compounds including
the various elements within the chemical formulae. In one
embodiment, the composition comprises hydrogen peroxide
(H.sub.2O.sub.2), benzotriazole, tetraethylammonium hydroxide, and
de-ionized water, and the composition has a pH in the range of
about 7 to about 9.
[0060] In one embodiment, a working solution can include a high BTA
salt concentration achieved through in-situ reaction of BTA with
TEAH. In one embodiment, the working solution can be derived from a
stock solution by diluting the stock solution with deionized water
and adding an additional oxidizing agent. The stock solution can be
obtained by dissolving BTA into a solution of TEAH in water.
[0061] In another embodiment, a sequestering agent stock solution
may be used to provide the correct concentration of sequestering
agent to produce the working solution. This can enable more control
in metering the desired level of sequestering agent or sequestering
and passivation agents during the formulation of the working
solution. In this case a calculation is made where the final
desired concentration in the working solution is multiplied by a
factor representing an addition amount that can accurately be
controlled as defined by a reduction in measurement error of this
addition amount. For example: the accuracy of delivering a 10 ppm
amount of a sequestering agent in the working solution may be
increased by creating a stock solution that is 500.times. in
concentration of sequestering agent; and adding a measure of the
stock solution during the production for the working solution that
would result in the desired final concentration of sequestering
agent in the working solution. If such a stock solution were
employed during the production of a working solution, a volume
addition of stock solution that supplied sufficient sequestering
agent and/or passivation agent would be added during this
production such that it would result in the desired concentration
in the working solution.
[0062] We have found that the addition of 5 grams of CDTA added
with stirring to a 300 ml solution consisting of 20 mls of 35% TEAH
dissolved in 300 mls of deionized water dissolves rapidly. Once
these 5 grams of CDTA have fully dissolved into the TEAH--Deionized
water solution, the volume is adjusted to 1 liter producing an
approximate 5000 ppm stock solution. Of CDTA in TEAH aqueous
mixture. Likewise, CDTA could be added to a BTA-TEAH Stock solution
during the production of a BTA-TEAH stock solution to produce a
CDTA, BTA-TEAH stock solution.
[0063] According to an embodiment of the present disclosure,
formulations for the chemical composition of the stock solution can
include: [0064] 1. 0 p.p.m.-400,000 p.p.m. in weight percentage of
at least one metal protectant; [0065] 2. 5-35% (preferably 5%-35%
in weight percentage) of a pH stabilizer; and [0066] 3. the balance
of an aqueous solution (i.e., deionized water or a water-based
polar solvent in which water is a predominant portion (more than
1/2) of the solvent).
[0067] An exemplary formulation for the chemical composition of the
stock solution can be: [0068] 1. 250,000 p.p.m. in weight
percentage of at least one metal protectant; [0069] 2. 28% in
weight percentage of a pH stabilizer; and [0070] 3. the balance of
deionized water or a water-based polar solvent in which water is a
predominant portion (more than 1/2) of the solvent.
[0071] According to another embodiment of the present disclosure,
formulations for the chemical composition of the stock solution can
include: [0072] 1. at least one sequestering agent at a
concentration in a range from 200 p.p.m. to 20,000 p.p.m. in weight
percentage [0073] 2. 5%-35% (preferably 5-35% in weight percentage)
of a pH stabilizer; and [0074] 3. the balance of an aqueous
solution (i.e., deionized water or a water-based polar solvent in
which water is a predominant portion (more than 1/2) of the
solvent).
[0075] An exemplary formulation for the chemical composition of the
stock solution can be: [0076] 1. 2,000 p.p.m. in weight percentage
of a sequestering agent; [0077] 2. 28% in weight percentage of a pH
stabilizer; and [0078] 3. the balance of deionized water or a
water-based polar solvent in which water is a predominant portion
(more than 1/2) of the solvent.
[0079] According to yet another embodiment of the present
disclosure, formulations for the chemical composition of the stock
solution can include: [0080] 1. 0 p.p.m.-400,000 p.p.m. in weight
percentage of at least one metal protectant; [0081] 2. 2%-35%
(preferably 5-35%) in weight percentage of a pH stabilizer; [0082]
3. 200 p.p.m.-20,000 p.p.m. of a sequestering agent; and [0083] 4.
an aqueous solution (i.e., the balance of deionized water or a
water-based polar solvent in which water is a predominant portion
(more than 1/2) of the solvent).
[0084] An exemplary formulation for the chemical composition of the
stock solution can include: [0085] 1. 100000 p.p.m. in weight
percentage of at least one metal protectant; [0086] 2. 28% in
weight percentage of a pH stabilizer; [0087] 3. 5000 p.p.m. of a
sequestering agent; and [0088] 4. the balance of deionized water or
a water-based polar solvent in which water is a predominant portion
(more than 1/2) of the solvent.
[0089] In an illustrative example, 100 grams of BTA can be
dissolved into 0.4 liter of a solution including 35% in weight of
TEAH and balance deionized water ("35% TEAH solution" hereafter).
Vigorous stirring may be employed to dissolve 250 grams of BTA into
the 35% TEAH solution to generate an undiluted BTA and TEAH
containing solution ("undiluted solution" hereafter). This results
in a solution volume expansion to about 0.8 liters. After the
addition of 5 grams of CDTA to this BTA and TEAH containing
solution, sufficient deionized water (about 0.2 liters) is added to
bring the total volume of the diluted solution to 1.0 liter, which
is the stock solution. This stock solution includes 10% weight
percentage of BTA and 0.5% by weight CDTA, i.e., 100,000 p.p.m. of
BTA and 5000 p.p.m. CDTA.
[0090] The working solution including any of the chemical
compositions described above can be applied to a microelectronic
device in multiple ways. The chemical compositions of the present
disclosure provide different relative etch rates among metallic
compounds than previously known etchants such as the SC1 solution.
As used herein, the SC1 refers to a solution including NH4OH
(ammonium hydroxide), H2O2 (hydrogen peroxide), and H.sub.2O
(water).
[0091] The etch rate of the solution including the chemical
composition described above for TiN and TiC (referred to as
"T-etch" formulations) is compared with the etch rates of various
SC1 solutions at different temperatures in Table 1. The ratios in
parentheses in the name of the SC1 formulations refer to the ratios
among H.sub.2O:H.sub.2O.sub.2:NH.sub.4OH.
TABLE-US-00001 TABLE 1 Comparison of etch properties of the T- etch
formulations and SC1 formulations T pH (at Etch rate Etch rate Etch
rate (.degree. 20.degree. for TiN for TiC ratio between Formulation
C.) C.) (nm/min) (nm/min) TiN and TiC SC1 (25:1.5:1) 40 10.5 3.4
25.2 0.13 SC1 (50:1.5:1) 50 10.5 4.7 25.8 0.18 SC1 (100:1.5:1) 50
10.5 2.0 16.6 0.18 SC1 (84:20:1) 40 9.6 7.4 16.0 0.46 T-etch pH 9.5
40 9.5 3.4 1.7 1.99 T-etch pH 9.5 50 9.5 7.3 3.5 2.04 T-etch pH 9.0
50 9 7.1 4.1 1.76
[0092] Table 1 illustrates that the T-etch solution provides
different etch characteristics than SC1 solutions that are
typically employed to remove metallic materials in the art.
Specifically, the SC1 solutions etch TiC faster than TiN by a
factor of at least 2, while the T-etch solutions etch TiN faster
than TiC by a factor in a range from 1.76 to 2.04.
[0093] FIG. 1 shows a comparison of etch rates for a T-etch
solution having a pH of 9.0, including 100 p.p.m. of CDTA, and at a
temperature of 40.degree. C. with etch rates for an SC1 solution
including 50:1.5:1 of H.sub.2O:H.sub.2O.sub.2:NH.sub.4OH and at a
temperature of 40.degree. C. for various metallic materials
including TiN, a nitride of a Ti alloy #1, a nitride of a Ti alloy
#2, TiC, Ti alloy #1, Ta alloy #2, and Ti alloy #2. The absolute
etch rate and etch selectivity of the T-etch solution depends on
the composition of the various alloys.
[0094] The distinct etch characteristics of the chemical
composition of the present disclosure can be employed alone, or in
combination with another etchant such as an SC1 solution, to etch
selectively, or non-selectively, at least one material selected
from conductive metallic nitrides, conductive metallic carbides,
elemental metals, and intermetallic alloys of at least two
elemental metals from patterned or unpatterned structures (such as
gate cavities) on a semiconductor substrate. In one embodiment, the
at least one metallic material can include at least one material
selected from Ti-containing alloys including at least one or carbon
and nitrogen and optionally including at least one transition metal
and/or at least one lanthanide metal and Ta-containing alloys
including at least one or carbon and nitrogen and optionally
including at least one transition metal and/or at least one
lanthanide metal. Other transition and lanthanide metals, metal
carbides, and metal nitrides may also be used to control the
desired work function properties. The chemical composition of the
present disclosure is believed to be usable to etch any work
function metal known in the art. It is understood that the
effectiveness and etch rate of the chemical composition of the
present disclosure would vary depending on the species of the work
function metal.
[0095] In one embodiment, the at least one metallic material can be
a plurality of metallic materials that include a first metallic
material and a second metallic material, and an SC 1 etch chemistry
can provide an etch selectivity that is greater than 1 for the
second metallic material relative to the first metallic material
(i.e., etch the second metallic material faster than the first
metallic material), and the chemical composition of the present
disclosure provides an etch selectivity that is less than 1 for the
second metallic material relative to the first metallic material
(i.e., etch the first metallic material faster than the second
metallic material). As used herein, an "etch selectivity" of an
etchant solution for a first material relative to a second material
refers to the ratio of the etch rate of the first material in the
etchant solution to the etch rate of the second material in the
etchant solution. In an illustrative example, the first metallic
material can be TiN, and the second metallic material can be
selected from Ti-containing alloys including at least one or carbon
and nitrogen and optionally including at least one transition metal
and/or at least one lanthanide metal and Ta-containing alloys
including at least one or carbon and nitrogen and optionally
including at least one transition metal and/or at least one
lanthanide metal.
[0096] In one embodiment, the at least one metallic material can be
a plurality of metallic materials that include a first metallic
material and a second metallic material, and the chemical
composition can provide a greater etch rate for the first metallic
material than an SC1 etch chemistry, and the chemical composition
can provide a lesser etch rate for the second metallic material
than the SC1 etch chemistry. In an illustrative example, the first
metallic material can be TiN, and the second metallic material can
be selected from a Ti-containing alloy including at least one or
carbon and nitrogen and optionally including at least one
transition metal and/or at least one lanthanide metal, and a
Ta-containing alloy including at least one or carbon and nitrogen
and optionally including at least one transition metal and/or at
least one lanthanide metal.
[0097] Application of the chemical composition of the present
disclosure in wet etch processes for removing at least one metallic
material is herein illustrated employing various exemplary
semiconductor structures.
[0098] Referring to FIG. 2, a first exemplary semiconductor
structure according to a first embodiment of the present disclosure
includes a semiconductor substrate 8, on which various components
of field effect transistors are formed. The semiconductor substrate
8 can be a bulk substrate including a bulk semiconductor material
throughout, or a semiconductor-on-insulator (SOI) substrate (not
shown) containing a top semiconductor layer, a buried insulator
layer located under the top semiconductor layer, and a bottom
semiconductor layer located under the buried insulator layer.
[0099] Various portions of the semiconductor material in the
semiconductor substrate 8 can be doped with electrical dopants of
n-type or p-type at different dopant concentration levels. For
example, the semiconductor substrate 8 may include a semiconductor
material layer 10. The semiconductor material layer may include a
doped well (not shown) as needed.
[0100] A disposable gate material layer is deposited and
lithographically patterned to form disposable gate structures.
After various processing steps known in the art for replacement
gate processing schemes, a planarization dielectric layer 60 is
deposited over the disposable gate structures. Preferably, the
planarization dielectric layer 60 is a dielectric material that may
be easily planarized. For example, the planarization dielectric
layer 60 can be a doped silicate glass or an undoped silicate glass
(silicon oxide). The planarization dielectric layer 60 is
planarized employing the disposable gate structures as stopping
structures. The top surface 63 of the planarization dielectric
layer 60 can be substantially horizontal after planarization. The
disposable gate structures are removed selective to the
planarization dielectric layer 60 to form gate cavities 25, one of
which is illustrated in FIG. 2.
[0101] Referring to FIG. 3, an interfacial dielectric layer 31 can
be optionally formed on the exposed surface of the semiconductor
material layer 10 by conversion of the exposed semiconductor
material into a dielectric material. The formation of the
interfacial dielectric layer 32 can be effected by thermal
conversion or plasma treatment. A gate dielectric layer 32L is
deposited in the gate cavity 25 and over the planarization
dielectric layer 32L. The gate dielectric layer 32L can be
deposited as a contiguous gate dielectric layer that contiguously
covers all top surfaces of the planarization dielectric layer 60,
all sidewall surfaces of the gate cavity 25, and the top surface of
the interfacial dielectric layer 31.
[0102] The gate dielectric layer 32L can be a high dielectric
constant (high-k) material layer having a dielectric constant
greater than 3.9. The gate dielectric layer 32L can include a
dielectric metal oxide, which is a high-k material containing a
metal and oxygen, and is known in the art as high-k gate dielectric
materials. Dielectric metal oxides can be deposited by methods well
known in the art including, for example, chemical vapor deposition
(CVD), physical vapor deposition (PVD), molecular beam deposition
(MBD), pulsed laser deposition (PLD), liquid source misted chemical
deposition (LSMCD), atomic layer deposition (ALD), etc.
[0103] Exemplary high-k dielectric material include HfO.sub.2,
ZrO.sub.2, La.sub.2O.sub.3, Al.sub.2O.sub.3, TiO.sub.2,
SrTiO.sub.3, LaAlO.sub.3, Y.sub.2O.sub.3, HfO.sub.xN.sub.y,
ZrO.sub.xN.sub.y, La.sub.2O.sub.xN.sub.y, Al.sub.2O.sub.xN.sub.y,
TiO.sub.xN.sub.y, SrTiO.sub.xN.sub.y, LaAlO.sub.xN.sub.y,
Y.sub.2O.sub.xN.sub.y, a silicate thereof, and an alloy thereof.
Each value of x is independently from 0.5 to 3 and each value of y
is independently from 0 to 2. The thickness of the gate dielectric
layer 32L, as measured at horizontal portions, can be from 0.9 nm
to 6 nm, and from 1.0 nm to 3 nm. The gate dielectric layer 32L may
have an effective oxide thickness on the order of or less than 2
nm. In one embodiment, the gate dielectric layer 32L is a hafnium
oxide (HfO.sub.2) layer.
[0104] Referring to FIG. 4, a work function material layer 134L is
deposited within the gate cavity 25. The work function material
layer 134L includes a metallic material that controls the work
function of a field effect transistor to be subsequently formed.
The first work function material layer 34L can include p-type work
function materials as known in the art, or n-type work function
materials as known in the art. In one embodiment, the work function
material layer 134L includes a metallic material that adheres to
the gate dielectric layer 32L without delamination. In one
embodiment, the work function material layer 134L can be a TiN
layer or a TiN alloy layer. The work function material layer 134L
can be deposited by physical vapor deposition (PVD), atomic layer
deposition (ALD), and/or chemical vapor deposition (CVD). The
thickness of the work function material layer 134L, as measured at
a horizontal portion above the interfacial dielectric layer 31 can
be, for example, from 3 nm to 20 nm, although lesser and greater
thicknesses can also be employed.
[0105] A conducive fill material layer 137L is subsequently
deposited to fill the gate cavity 25. The conductive fill material
layer 137L can include an elemental metal, an alloy of at least two
elemental metals, a metallic nitride material, a metallic carbide
material, or a combination thereof. The conductive fill material
layer 137L can be deposited by physical vapor deposition (PVD),
atomic layer deposition (ALD), and/or chemical vapor deposition
(CVD).
[0106] Referring to FIG. 5, a replacement gate structure is formed
in the gate cavity 25 (See FIG. 2) by removing portions of the
conductive fill material layer 137L, the work function material
layer 134L, and the gate dielectric layer 32L from above the top
surface of the planarization dielectric layer 60, for example, by
chemical mechanical planarization (CMP). The replacement gate
structure includes a gate dielectric (31, 32), which includes the
interfacial dielectric layer 31 and a U-shaped gate dielectric 32,
which is a remaining portion of the gate dielectric layer 32L. The
replacement gate structure further includes a gate electrode (134,
137). The gate electrode (134, 137) includes a work function
material portion 134 and a conductive fill material portion 137.
The work function material portion 134 is a remaining portion of
the work function material layer 134, and the conductive fill
material portion 137 is a remaining portion of the conductive fill
material layer 137L.
[0107] Referring to FIG. 6, a second exemplary semiconductor
structure according to a second embodiment of the present
disclosure can be derived from a variation of the first exemplary
semiconductor structure of FIG. 2 in which multiple gate cavities
are formed. The gate cavities can include, for example, a first
gate cavity 25A and a second gate cavity 25B. A first interfacial
dielectric layer 31A and a second interfacial dielectric layer 31B
can be formed at the bottom surfaces of the first and second gate
cavities (25A, 25B), respectively, in the same manner as in
formation of the interfacial dielectric layer 31 in FIG. 3. A gate
dielectric layer 32L can be formed in the same manner as in the
first embodiment.
[0108] A first work function material layer 34L is deposited within
the first gate cavity 25A and the second gate cavity 25B. The first
work function material layer 34L includes a metallic material that
controls the work function of a first field effect transistor to be
subsequently formed in a region underlying the first gate cavity
25A. The first work function material layer 34L can include p-type
work function materials as known in the art, or n-type work
function materials as known in the art. In one embodiment, the
first work function material layer 34L includes a metallic material
that adheres to the gate dielectric layer 32L without delamination.
In one embodiment, the first work function material layer 34L can
be a TiN layer. The first work function material layer 34L can be
deposited by physical vapor deposition (PVD), atomic layer
deposition (ALD), and/or chemical vapor deposition (CVD). The
thickness of the first work function material layer 34L, as
measured at a horizontal portion above the first or second
interfacial dielectric layer (31A, 31B) can be, for example, from 3
nm to 20 nm, although lesser and greater thicknesses can also be
employed.
[0109] Referring to FIG. 7, a photoresist material layer 57
including a photoresist material is applied in the gate cavities
(25A, 25B) and over the planarization dielectric layer 60, for
example, by spin coating, and is lithographically patterned such
that a portion of the photoresist material fills the first gate
cavity 25A, and the photoresist material is not preset in the
second gate cavity 25B. The portion of the first work function
material layer 34L in the second gate cavity 25B and a vicinity
thereof can be thinned or removed by an isotropic etch. In one
embodiment, the isotropic etch can employ a solution including the
chemical composition of the present disclosure. In another
embodiment, the isotropic etch can employ an etchant known in the
art such as an SC1 solution. In yet another embodiment, the
isotropic etch can be a multistep process in which a solution
including the chemical composition of the present disclosure is
employed in one of the steps and a conventional etch solution such
as an SC1 solution is employed in another of the steps.
[0110] In one embodiment, the portion of the first work function
material layer 34L in the second gate cavity 25B and a vicinity
thereof can be thinned to form a thinned first work function
material 34N. The thickness of the thinned first work function
material layer 34N can be selected such that the work function of a
gate electrode to be subsequently formed in the second gate cavity
25B is affected significantly by another metallic material to be
deposited on the thinned first work function material layer 34N. In
one embodiment, the thickness of the thinned first work function
material layer 34N can be in a range from 0.5 nm to 3.0 nm,
although lesser and greater thicknesses can also be employed. The
portion of the first work function material layer 34L that is
covered by the photoresist material layer 57 is herein referred to
as an unthinned first work function material layer 34K. The
photoresist material layer 57 is subsequently removed, for example,
by ashing.
[0111] Referring to FIG. 8, a second work function material layer
and a conductive fill material layer are deposited within the first
gate cavity 25A and the second gate cavity 25B. The second work
function material layer includes a metallic material that controls
the work function of a second field effect transistor to be
subsequently formed underneath the second interfacial dielectric
layer 31B. The second work function material layer can include
p-type work function materials as known in the art, or n-type work
function materials as known in the art. In one embodiment, if the
thinned first work function material layer 34N includes a metallic
material that adheres to the gate dielectric layer 32L without
delamination, the metallic material of the second work function
material may be selected without consideration for adhesion to the
dielectric material layer 32L. In one embodiment, the second
conductive fill material layer may completely fill the first gate
cavity 25A and does not completely fill the second gate cavity 25B,
and the conductive fill material layer may completely fill the
second gate cavity 25B.
[0112] The conductive fill material layer, the second work function
material layer, the unthinned first work function material layer
34K, and the thinned first work function material layer 34N are
removed from above the top surface of the planarization dielectric
layer 60 by planarization, which can be, for example, chemical
mechanical planarization (CMP). A remaining portion of the
unthinned first work function material layer 34K filling the first
gate cavity 25A constitutes a first-device first work function
material portion 34A, a remaining portion of the thinned first work
function material layer 34N filling the second gate cavity 25B
constitutes a second-device first work function material portion
34B, a remaining portion of the second work function material layer
filling the first gate cavity 25A constitutes a first-device second
work function material portion 36A, a remaining portion of the
second work function material layer filling the second gate cavity
25B constitutes a second-device second work function material
portion 36B, and a remaining portion of the conductive fill
material layer filling the second gate cavity 25B constitutes a
conductive fill material portion 37. A remaining portion of the
gate dielectric layer 32L in the first gate cavity 25A is the first
gate dielectric 32A, and a remaining portion of the gate dielectric
layer 32L in the second gate cavity 25B is the second gate
dielectric 32B. The first and second gate dielectrics (32A, 32B)
are U-shaped gate dielectrics, each including a horizontal portion
and vertical portions.
[0113] In one embodiment, the second work function material layer
can be a TiC layer or a TiC alloy layer. In this case, the
first-device second work function material portion 36A and the
second-device second work function material portion 36B can be TiC
portions or TiC alloy portions. The conducive fill material layer
can be a metallic nitride layer or a metallic carbide layer. In one
embodiment, conductive fill material layer and the conductive fill
material portion 37 can include TiN or TiN alloys. Each of the
second work function material layer and the conductive fill
material layer can be deposited by physical vapor deposition (PVD),
atomic layer deposition (ALD), and/or chemical vapor deposition
(CVD). The thickness of the second work function material layer, as
measured on sidewall surfaces of the second gate dielectric 32B can
be, for example, from 3 nm to 20 nm, although lesser and greater
thicknesses can also be employed.
[0114] Referring to FIG. 9, a recess etch is performed to remove
upper portions of the first-device first work function material
portion 34A and the first-device second work function material
portion 36A to form a cavity, and to remove upper portions of the
second-device first work function material portion 34B, the
second-device second work function material portion 36B, and the
conductive fill material portion 37 to form another cavity. In one
embodiment, an isotropic etch process can be employed for the
recess etch. In one embodiment, the isotropic etch process can
employ a solution including the chemical composition of the present
disclosure. In another embodiment, the isotropic etch process can
employ an etchant known in the art such as an SC1 solution. In yet
another embodiment, the isotropic etch process can be a multistep
process in which a solution including the chemical composition of
the present disclosure is employed in one of the steps and a
conventional etch solution such as an SC1 solution is employed in
another of the steps.
[0115] In one embodiment, the chemical formulation of the present
disclosure can be employed to simultaneously recess the various
materials of the first-device first work function material portion
34A, the first-device second work function material portion 36A,
the second-device first work function material portion 34B, the
second-device second work function material portion 36B, and the
conductive fill material portion 37 to similar heights in a single
wet etch process. In this case, a single etch process can be
sufficient to recess various metallic portions to similar heights.
In another embodiment, the chemical formulation of the present
disclosure can be employed to simultaneously recess the various
materials of the first-device first work function material portion
34A, the first-device second work function material portion 36A,
the second-device first work function material portion 34B, the
second-device second work function material portion 36B, and the
conductive fill material portion 37 to similar heights in
combination with another chemical formation such as a SC 1
solution.
[0116] Referring to FIG. 10, an outer conductive material layer and
an inner conductive material layer can be sequentially deposited in
the first and second gate cavities (25A, 25B). The first and second
gate cavities (25A, 25B) are filled with the outer conductive
material layer and the inner conductive material layer. In one
embodiment, the outer conductive material layer can include a
metallic nitride material that can function as a diffusion barrier
for gaseous impurities such as oxygen and moisture. For example,
the outer conductive material layer can include TiN, TaN, WN, or a
combination thereof. In one embodiment, the inner conductive
material layer can include an elemental metal or an intermetallic
alloy of at least two elemental metals having high conductivity.
For example, the inner conductive material layer can include W, Al,
or an alloy of W and Al.
[0117] The outer conductive material layer and the inner conductive
material layer are removed from above the top surface of the
planarization dielectric layer, for example, by chemical mechanical
planarization (CMP). The remaining portion of the outer conductive
material layer filling the first gate cavity 25A is herein referred
to as a first-device outer conductive material portion 38A. The
remaining portion of the inner conductive material layer filling
the first gate cavity 25A is herein referred to as a first-device
inner conductive material portion 40A. The remaining portion of the
outer conductive material layer filling the second gate cavity 25B
is herein referred to as a second-device outer conductive material
portion 38B. The remaining portion of the inner conductive material
layer filling the second gate cavity 25A is herein referred to as a
second-device inner conductive material portion 40B.
[0118] Referring to FIG. 11, the materials of the inner conductive
material portions (40A, 40B) and the outer conductive material
portions (38A, 38B) can be etched isotropically or anisotropically.
In one embodiment, an isotropic etch can be performed to recess the
inner conductive material portions (40A, 40B) and the outer
conductive material portions (38A, 38B). The isotropic etch can
employ a solution including the chemical composition of the present
disclosure. The solution of the chemical composition of the present
disclosure can etch elemental metallic materials or intermetallic
alloys of at least two elemental metals at a higher etch rate than
a metallic nitride.
[0119] The description of the present disclosure has been presented
for purposes of illustration and description, but is not intended
to be exhaustive or limited to the disclosure 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 disclosure. The embodiment was chosen and
described in order to best explain the principles of the disclosure
and the practical application, and to enable others of ordinary
skill in the art to understand the disclosure for various
embodiments with various modifications as are suited to the
particular use contemplated.
* * * * *