U.S. patent application number 11/769238 was filed with the patent office on 2007-10-18 for cleaning solution and method for selectively removing layer in a silicidation process.
Invention is credited to Sang-Yong Kim, Kun-Tack Lee.
Application Number | 20070243715 11/769238 |
Document ID | / |
Family ID | 32464514 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070243715 |
Kind Code |
A1 |
Kim; Sang-Yong ; et
al. |
October 18, 2007 |
CLEANING SOLUTION AND METHOD FOR SELECTIVELY REMOVING LAYER IN A
SILICIDATION PROCESS
Abstract
A cleaning solution selectively removes a titanium nitride layer
and a non-reacting metal layer. The cleaning solution includes an
acid solution and an oxidation agent with iodine. The cleaning
solution also effectively removes a photoresist layer and organic
materials. Moreover, the cleaning solution can be employed in
tungsten gate electrode technologies that have been spotlighted
because of the capability to improve device operation
characteristics.
Inventors: |
Kim; Sang-Yong; (Yongin-si,
KR) ; Lee; Kun-Tack; (Suwon-Si, KR) |
Correspondence
Address: |
F. CHAU & ASSOCIATES, LLC
130 WOODBURY ROAD
WOODBURY
NY
11797
US
|
Family ID: |
32464514 |
Appl. No.: |
11/769238 |
Filed: |
June 27, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10728517 |
Dec 5, 2003 |
7265040 |
|
|
11769238 |
Jun 27, 2007 |
|
|
|
Current U.S.
Class: |
438/745 ;
252/79.2; 257/E21.251; 257/E21.309 |
Current CPC
Class: |
C11D 3/3956 20130101;
C11D 7/08 20130101; H01L 21/32134 20130101; H01L 21/31111 20130101;
C11D 11/0047 20130101 |
Class at
Publication: |
438/745 ;
252/079.2 |
International
Class: |
H01L 21/302 20060101
H01L021/302 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2002 |
KR |
2002-76961 |
Claims
1. A method of selectively removing a photoresist layer and organic
materials in a fabricating process of semiconductor devices,
comprising: selectively removing the photoresist layer and organic
materials using a cleaning solution, the cleaning solution
including an acid solution and an oxidation agent containing
iodine.
2. The method of claim 1, wherein the cleaning solution further
comprises water.
3. The method of claim 1, wherein the acid solution includes at
least one of sulfuric acid and phosphoric acid, and the oxidation
agent containing iodine includes at least one selected from the
group consisting of KIO.sub.3, NH.sub.4IO.sub.3, LiIO.sub.3,
CaIO.sub.3, BaIO.sub.3, KI, and NH.sub.4I.
4. The method of claim 2, wherein the cleaning solution includes
water in an amount of about 30 wt % and less, and the oxidation
agent containing iodine in an amount of about 0.003 to 10 wt %.
5. A cleaning solution that selectively removes a titanium nitride
layer and a non-reacting metal layer in a silicidation process,
wherein the cleaning solution includes an acid solution, an
oxidation agent containing iodine, and water.
6. The method of claim 5, wherein the acid solution includes at
least one of sulfuric acid and phosphoric acid, and the oxidation
agent containing iodine includes at least one selected from the
group consisting of KIO.sub.3, NH.sub.4IO.sub.3, LiIO.sub.3,
CaIO.sub.3, BaIO.sub.3, KI, and NH.sub.4I.
7. The method of claim 5, wherein the cleaning solution includes
water in an amount of about 30 wt % and less and an oxidation agent
containing iodine in an amount of about 0.003-about 10 wt %.
8. The method of claim 5, wherein the non-reacting metal layer
includes at least one of cobalt, titanium, and nickel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/728,517 filed on Dec. 5, 2003, which claims priority under
35 U.S.C. .sctn. 119 to Korean Patent Application No. 2002-76961
filed on Dec. 5, 2002, the disclosures of which are herein
incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention generally relates to a method of
removing undesirable layers in semiconductor devices, and more
specifically to a solution and method of removing undesirable
layers that are formed in a silicidation process.
BACKGROUND OF THE INVENTION
[0003] A conventional semiconductor manufacturing process includes
forming an insulation layer and a conductive layer on a substrate,
a photolithographic process, etc. The photolithographic process
comprises forming a photoresist pattern on an underlying layer to
be patterned, etching the layer exposed by the photoresist pattern,
and then removing the photoresist pattern. In addition, organic
materials or polymer may occur from the reaction between the
underlying layer to be etched and an etching gas. Conventionally,
the photoresist pattern and organic materials or the polymer are
removed by an oxygen plasma ashing and a sulfuric strip
process.
[0004] Operation speed of the devices has a close relationship with
the resistances of the source/drain regions. Therefore, to increase
the operation speed of a device, a metal silicidation process is
used for forming semiconductor devices. The silicidation process
comprises forming a cobalt silicide layer having resistivity lower
than that of silicon from a reaction between cobalt and silicon at
a predetermined temperature. In the silicidation process,
non-reacting cobalt should be removed without removing the cobalt
silicide layer.
[0005] Moreover, in a conventional cobalt silicidation process, a
titanium nitride layer is formed so as to prevent oxidation of
cobalt and agglomeration of the silicide layer in the silicidation
process. Therefore, a titanium nitride layer should be removed
after formation of the silicide layer.
[0006] If the layers are not removed, the layers can serve as
contaminant sources and can cause electric short with neighboring
conductors.
[0007] Conventionally, in the silicidation process, the
non-reacting metal layers and the titanium nitride layers are
removed by a mixture solution including peroxide (H.sub.2O.sub.2),
i.e., a strong oxidation agent.
[0008] Meanwhile, as the semiconductor devices are highly
integrated in an economic point of view, a conventional polysilicon
gate electrode cannot satisfy the needs of the proper operation
speed and the characteristic of a sheet resistance of the gate
electrode. Therefore, a metal layer such as a tungsten layer, which
has resistivity lower than a polysilicon layer, is stacked on the
polysilicon gate electrode to form a metal gate electrode.
Therefore, the low resistivity tungsten gate should also not be
etched (or removed). In addition, a metal interconnection with
tungsten (e.g., a word line or a bit line) should not be etched by
the cleaning solution.
[0009] On the contrary, the peroxide, which is conventionally used
in the silicidation process, etches the tungsten. Thus, the
high-speed devices cannot be embodied using the conventional
peroxide.
[0010] Accordingly, as the need of high-speed devices increases,
the need for a new cleaning solution that can selectively remove
metal layers such as a titanium nitride layer and a cobalt layer
without removing metal layers such a cobalt silicide layer or a
tungsten layer also increases.
SUMMARY OF THE INVENTION
[0011] One aspect of the present invention is to provide a cleaning
solution that selectively removes a titanium nitride layer and a
non-reacting metal layer in a silicidation process and a method of
removing the titanium nitride layer and the non-reacting metal
layer using the same.
[0012] It is another aspect of the present invention to provide a
cleaning solution that selectively removes the titanium nitride and
the non-reacting metal layer without removing tungsten and silicide
layers in a silicidation process applying a tungsten gate process,
and a method of removing the layers using the same.
[0013] It is further another aspect of the present invention to
provide a cleaning solution that selectively removes metal layers
and also removes a photoresist layer and organic materials in the
silicidation process and a method of removing the layers using the
same.
[0014] According to at least one embodiment of the present
invention, the cleaning solution includes an acid solution and an
oxidation agent containing iodine. The cleaning solution may
further include water. This is for increasing a degree of
dissociation of the acid solution and an oxidation agent containing
iodine. Thus, the cleaning capacity of the oxidation agent and the
acid solution is improved. In the exemplary embodiment, the
cleaning solution contains water in an amount of about 30 wt % and
less and the oxidation agent containing iodine in an amount of
0.003 to 10 wt %. The acid solution may include sulfuric acid,
phosphoric acid and a mixture thereof. The oxidation agent
containing iodine includes one or more iodates such as KIO.sub.3,
NH.sub.4IO.sub.3, LiIO.sub.3, CaIO.sub.3, and BaIO.sub.3. If the
cleaning solution includes water, the oxidation agent containing
iodine may further include KI, NH.sub.4I or a mixture thereof
besides the iodate. That is, the oxidation agent containing iodine
includes at least one selected from the group consisting of
KIO.sub.3, NH.sub.4IO.sub.3, LiIO.sub.3, CaIO.sub.3, BaIO.sub.3,
KI, and NH.sub.4I. If the sulfuric acid is used as the acid
solution, the concentration of the sulfuric acid may be about 96%
or more.
[0015] The acid solution and the oxidation agent containing iodine
effectively remove a titanium nitride and cobalt and also remove a
photoresist layer and organic materials. On the contrary, the acid
solution and the oxidation agent containing iodine do not etch a
cobalt silicide layer and tungsten. The oxidation agent containing
iodine reacts with silicon of a metal silicide layer and forms a
silicon oxide (SiOx) layer thereon as a passivation layer. The
silicon oxide layer has very strong acid proof to the sulfuric
acid. Therefore, the metal silicide layer is protected. In
addition, the oxidation agent containing iodine reacts with
tungsten and forms a passivation layer such as a tungsten trioxide
(WO.sub.3) thereon. The tungsten trioxide passivation layer is a
very stable layer in an acid solution. Therefore, tungsten is
prevented from corrosion.
[0016] The cleaning capacity of the cleaning solution is
proportional to temperature. For example, the cleaning may be
carried out at a temperature range of about room temperature to
about 120.degree. C. The cleaning capacity of the cleaning solution
is also proportional to the amount of the water that is added. The
amount of water that is added to the cleaning solution is about 30
wt % and less.
[0017] A method of selectively removing a metal layer according to
an embodiment of the invention comprises the following steps. A
transistor is formed on a silicon substrate. The transistor
comprises source/drain regions and a gate electrode. A metal layer
that forms the silicide layer is formed over the exposed substrate.
A titanium nitride layer is formed over the metal layer. A
silicidation thermal process is carried out so as to react silicon
with the metal layer. That is, the silicon of the exposed
source/drain region and the metal layer that directly contacts
therewith react with each other to form a metal silicide layer.
Using a cleaning solution, a non-reacting metal layer that does not
participate in the silicidation reaction and the titanium nitride
layer are removed. In this case, the cleaning solution includes an
acid solution and an oxidation agent containing iodine. Preferably,
the cleaning solution further includes water. The cleaning solution
may include water in an amount about 30 wt % and less, and the
oxidation agent containing iodine in an amount about 0.003 to 10 wt
%.
[0018] An exemplary embodiment of a method of forming the
transistor comprises the following steps.
[0019] A gate insulation layer, a polysilicon layer, a tungsten
layer and a capping insulation layer are sequentially formed on the
silicon substrate. A photoresist pattern is formed over the capping
nitride layer, and using the photoresist pattern as an etch mask,
the layers formed thereunder are successively etched to form the
gate electrode. Then, the photoresist pattern is removed. The
source/drain regions are formed in the silicon substrate at both
sides of the gate electrode by performing an ion implantation
process, and nitride spacers are formed on sidewalls of the gate
electrode. In this case, the photoresist pattern may be removed
using the cleaning solution. The metal layer includes at least one
of cobalt, titanium, and nickel.
[0020] According to the above method, the cleaning solution does
not etch a metal silicide layer and tungsten that composes a low
resistive gate electrode but selectively etches a titanium nitride
layer and a non-reacting metal layer. Therefore, a silicidation
process and a tungsten metal gate process can be employed all
together.
[0021] An embodiment of a method of forming the transistor may
comprise the following steps. A gate insulation layer and a
polysilicon layer are sequentially formed over the silicon
substrate. A photoresist pattern is formed over the polysilicon
layer, and the gate electrode is formed by a successive etching of
the layers formed thereunder using the photoresist pattern as an
etch mask. Then, the photoresist pattern is removed. The
source/drain regions are formed in the silicon substrate at both
sides of the gate electrode by performing an ion implantation
process. Nitride spacers are formed on the sidewalls of the gate
electrode. When the metal silicide layer is formed in the
source/drain regions by a silicide thermal treatment, a metal
silicide layer is also formed on the polysilicon at an upper part
of the gate electrode. Thus, the present invention is applicable to
CMOS transistors, which use a dual poly silicon gate. The dual poly
silicon gate is formed by implanting p-type impurities into PMOS
and n-type impurities into NMOS. In this case, the photoresist
pattern may be removed using the cleaning solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Other aspects and features of the present invention will
become apparent form the following detailed description taken in
conjunction with the accompanying drawings that disclose
embodiments of the invention. It is to be understood, however, that
the drawings are designed for the purpose of illustration only and
are not intended as a definition of the limits of the
invention.
[0023] FIG. 1 is a schematic cross-sectional view of a substrate
with a tungsten layer and a titanium nitride layer, a cobalt layer,
or a photoresist layer that can be selectively removed according to
an embodiment of the present invention.
[0024] FIG. 2 is a schematic cross-sectional view of a resultant
structure of a substrate without a titanium nitride layer, a cobalt
layer or a photoresist layer that are selectively removed from the
substrate of FIG. 2.
[0025] FIGS. 3 through 6 are cross-sectional views showing steps of
selectively removing metal layers using an embodiment of a cleaning
solution of the present invention.
[0026] FIGS. 7 through 12 are cross-sectional views showing steps
of selectively removing metal layers using a cleaning solution of
the present invention in a silicidation process according to an
exemplary embodiment.
[0027] FIGS. 13 and 14 are cross-sectional views showing steps of
selectively removing metal layers using a cleaning solution of the
present invention in a silicidation process according to another
exemplary embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] The present invention will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention,
however, may be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein. Rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. In the drawings, the
thickness of layers and regions are exaggerated for clarity. It
will also be understood that when a layer is referred to as being
"on" another layer or substrate, it can be directly on the other
layer or substrate, or intervening layers may also be present.
[0029] FIG. 1 schematically illustrates a substrate 11 with a layer
13 that should not be etched (or removed) and a layer 15 that is
formed thereon and should be selectively etched (or removed). The
layer 13 that should not be etched is any of the layers that are
not etched by the cleaning solution of the present invention. For
example, the layer 13 includes tungsten or metal silicide.
Meanwhile, the layer 15 includes for example, titanium nitride,
cobalt, organic material, or photoresist material.
[0030] Intermediate layers may be further interposed between the
substrate 11 and the non-etched layer 13, and between the
non-etched layer 13 and the etched layer 15.
[0031] Referring to FIG. 2, using the cleaning solution according
to an embodiment of the present invention, only the layer 15 that
should be etched is selectively etched at a proper temperature. The
cleaning solution includes an acid solution and an oxidizing agent
containing iodine (I). Sulfuric acid, phosphoric acid, a mixture
thereof, etc. can be used as the acid solution. The oxidizing agent
containing iodine includes at least one selected from the group
consisting of KIO.sub.3, NH4IO.sub.3, LiIO.sub.3, CaIO.sub.3,
BaIO.sub.3, KI, NH.sub.4I, etc.
[0032] The cleaning solution may further include water so as to
improve the cleaning capacity of the acid solution and the
oxidation agent containing iodine. Water increases the degree of
dissociation of the acid solution and the oxidation agent
containing iodine. Therefore, the added water is proportional to
the cleaning capacity of the cleaning solution. The cleaning
solution may include water of about 30 wt % and less. The cleaning
solution may include the oxidation agent containing iodine of about
0.003 to 10 wt %.
[0033] The cleaning time is inversely proportional to temperature.
That is, the cleaning capacity is proportional to the temperature.
The cleaning may be performed at about room temperature to about
120.degree. C. However, depending on the processing, the processing
condition can be changed and this will be apparent to those skilled
in the art.
[0034] FIGS. 3 through 6 are cross-sectional views showing steps of
selectively removing undesired layers in a silicidation process of
the fabricating process of the semiconductors.
[0035] As illustrated in FIGS. 3, a substrate 31 is provided that
includes a conductive pattern 35 comprising silicon. A layer 33 not
comprising silicon is further interposed between the silicon
pattern 35 and the substrate 31. The conductive pattern 35
comprising silicon is formed to have any shape on a surface of the
layer 33 not comprising silicon. The conductive pattern 35 may be
formed inside the layer 33. In case the conductive pattern 35 is
formed inside the layer 33, the silicon conductive pattern 35 may
be exposed only at the top surface thereof. In addition, another
layer, for example, an insulation layer may be further formed on
both sidewalls of the silicon conductive pattern 35. In this case,
the silicon conductive pattern 35 may be exposed only at the top
surface thereof. In any of the cases, the exposed silicon
conductive pattern 35 and a metal layer that directly contacts
thereon react with each other and form a silicide layer. Then, the
formed silicide layer will be electrically connected by
interconnections in a subsequent process.
[0036] Referring to FIG. 4, a metal layer 37 and a titanium nitride
layer 39 are sequentially formed on the layer 33 not comprising
silicon so as to cover the silicon conductive pattern 35. The metal
layer 37 may be formed of cobalt, titanium, nickel or the like.
[0037] Referring to FIG. 5, a metal silicide layer 41 is formed on
the exposed silicon conductive pattern 35 by performing a silicide
thermal treatment. In this case, a metal layer 37a, which is formed
on the layer 33 not comprising silicon, may not respond to the
silicidation reaction.
[0038] The titanium nitride 39 and the non-reacting metal layer 37a
are removed by the cleaning solution. Therefore, as illustrated in
FIG. 6, a conductive pattern 35 with the metal silicide 41 thereon
is completed.
[0039] The cleaning solution is a mixed solution including acid
solution and an oxidation agent containing iodine. In this
exemplary embodiment, the cleaning solution further includes water.
The cleaning solution may include water in an amount of about 30 wt
% and less. In addition, the cleaning solution may include the
oxidation agent containing iodine in an amount of about 0.003 to
about 10 wt %. The cleaning time is inversely proportional to a
temperature, That is, the cleaning capacity is proportional to the
temperature. The cleaning process may be carried out at about room
temperature to about 120.degree. C.
[0040] The layer 33 not comprising silicon may further include a
tungsten pattern. The cleaning solution reacts with the tungsten
pattern to form a thin tungsten trioxide (WO.sub.3) layer on the
surface thereof as a passivation layer, thereby protecting the
tungsten pattern. In addition, the cleaning solution reacts with
the metal silicide layer 41 and forms a thin silicon oxide layer
(SiOx) on the surface thereof as a passivation layer, thereby
protecting the metal silicide.
[0041] After removing the titanium nitride layer 39 and the
non-reacting metal layer 37a, an insulation layer (not shown) is
stacked and then patterned to form an opening that exposes a
predetermined part of the metal silicide layer 41. Then, the
opening is filled with conductive material such as a metal to form
a metal conductive pattern (or a conductive plug) that is
electrically connected to the silicon conductive pattern 35.
[0042] A silicide layer is interposed between the silicon
conductive pattern 35 and the metal conductive pattern (or a
conductive plug), thereby improving a contact resistive
characteristic or a resistive characteristic of the silicon
conductive pattern 35.
[0043] Referring to FIGS. 7 through 12, a method of removing the
undesired layer will be explained in accordance with an exemplary
embodiment.
[0044] FIGS. 7 through 12 are cross-sectional views showing steps
of removing the undesired layer by the cleaning solution of the
present invention in a silicidation process in accordance with an
exemplary embodiment. For clarity and simplicity, only one
transistor is illustrated in the drawings.
[0045] Referring to FIG. 7, a well is formed in a silicon substrate
100 by doping of impurities. A device isolation process is
performed to form device isolation layers 120 and then channel ions
are implanted. The detailed explanation of the device isolation
process will be omitted because the process is conventional and
well known. Continuously, a gate insulation layer 140, a poly
silicon layer 160, a tungsten layer 180, and a capping nitride
layer 200 are sequentially formed. A conductive barrier layer may
be further formed between the tungsten layer 180 and the
polysilicon layer 160. The tungsten layer 180 speeds up the
operation of the device. The conductive barrier layer prevents the
reaction between the tungsten layer and the polysilicon layer.
[0046] A photoresist pattern 220 is formed that defines a gate
electrode on the capping nitride layer 200. The underlying layers
exposed by the photoresist pattern 220 are etched to form a gate
electrode 240 that corresponds to the photoresist pattern 220 as
illustrated in FIG. 8. After the photoresist pattern 220 is
removed, ions are implanted to form impurity diffusion layers 260
in the substrate 100 at both sides of the gate electrode 240. The
implanted ions have a conductivity type opposite to the silicon
substrate 100. For example, if the silicon substrate 100 is p-type,
the implanted ions are n-type. The impurity diffusion layers 260
correspond to source/drain regions. The photoresist pattern 220 may
be removed in the manner that is well known to those skilled in the
art, for example, by an oxygen plasma ashing and a sulfuric acid
strip process. In addition, the photoresist pattern 22 may be
removed using the cleaning solution of the present invention. The
cleaning solution will be explained.
[0047] Nitride spacers 280 are formed on both sidewalls of the gate
electrode 240. That is, a silicon nitride layer is formed and then
etched back to form the nitride spacers 280.
[0048] Referring to FIG. 9, after a pre-cleaning is performed, a
cobalt layer 300 is formed so as to form a silicide layer. The
pre-cleaning is carried out to remove a native oxide layer of the
silicon substrate 100 and a damaged layer of the silicon substrate
100. For example, the pre-cleaning process may be performed in a
two-step treatment.
[0049] That is, a first treatment is done using a mixture of
NH.sub.4OH and H.sub.2O.sub.2 and a second treatment is
continuously carried out using fluoric acid (HF), such as to cure
the native oxide layer and the substrate. Meanwhile, the cleaning
process may comprise a first treatment using a mixture gas of CF4
and O2 and a second treatment using HF.
[0050] A titanium layer or a nickel layer may replace the cobalt
layer 300. The cobalt layer 300 may be formed by any method that is
well known to those skilled in the art, for example, a sputtering
method.
[0051] Referring to FIG. 10, a titanium nitride 320 is formed on
the cobalt layer 300. The titanium nitride 320 may be formed by any
method that is well known to those skilled in the art, such as a
sputtering method. The titanium nitride layer 320 is formed to
prevent oxidation of the cobalt layer 300 and to prevent
agglomeration of the silicide layer.
[0052] Referring to FIG. 11, a silicidation thermal process is
performed to react the cobalt layer 300 with silicon of the silicon
substrate directly underlying the cobalt layer 300 (i.e.,
source/drain regions 260). Thus, a cobalt silicide layer
(CoSi.sub.2) 340 is formed. As a result, the cobalt layer 300a of
regions other than the source/drain regions 260 remain without
reaction because there is no direct contact with the silicon.
[0053] Referring to FIG. 12, the titanium nitride layer 320 and the
non-reacting cobalt layer 300a are removed through a cleaning
process. The cleaning process utilizes a cleaning solution
comprising an acid solution and oxidation agent containing iodine.
The cleaning solutions may be utilized for removing the photoresist
pattern 220 that is mentioned above.
[0054] The acid solution includes sulfuric acid, phosphoric acid,
or a mixture thereof. The oxidation agent containing iodine
includes at least one of KIO.sub.3, NH.sub.4IO.sub.3, LiIO.sub.3,
CaIO.sub.3, BaIO.sub.3, KI, NH.sub.4I, etc. This is only an example
and any other oxidation agent containing iodine can be utilized.
The oxidation agent containing iodine removes the titanium nitride
layer 320 and the non-reacting cobalt layer 340a but does not
remove (or etch) a cobalt silicide layer 340 and a tungsten layer
180a that composes the gate electrode 240. This is, the oxidation
agent containing iodine reacts with the silicon of the cobalt
silicide layer to form a thin silicon oxide layer (SiOx) such as a
silicon dioxide layer on the surface of the cobalt silicide layer
as a passivation layer. In addition, the oxidation agent containing
iodine reacts with tungsten to form a thin tungsten trioxide layer
(WO.sub.3) that is stable to the acid on the surface thereof, as a
passivation layer.
[0055] The cleaning solution may include water. If the water is
added to the cleaning solution, activated ions that participate in
the removing reaction increase. In the exemplary embodiment, the
cleaning solution contains water in an amount of about 30 wt % and
less and the oxidation agent containing iodine in an amount of
about 0.003 to about 10 wt %.
[0056] The cleaning time is inversely proportional to temperature.
That is, the cleaning capacity is proportional to the temperature.
The cleaning process may be carried out at about room temperature
to about 120.degree. C.
[0057] More specifically, the silicide thermal treatment will be
explained hereinafter. First, a first thermal treatment is
performed at a proper temperature. The first thermal treatment
forms an intermediate state silicide layer that comprises
stoichiometrically almost cobalt monosilicide (CoSi) and a little
cobalt disilicide (CoSi.sub.2). After the first thermal treatment,
a first cleaning process is carried out using the cleaning solution
so as to remove the non-reacting cobalt layer and the titanium
nitride layer. A titanium nitride layer is formed again and then a
second thermal treatment is performed at a proper temperature. The
second thermal treatment forms a low resistive cobalt silicide
layer 340 that contains stoichiometrically almost cobalt disilicide
(CoSi.sub.2). Finally, a second cleaning process is performed with
the cleaning solution to remove the titanium nitride layer and the
non-reacting cobalt layer.
[0058] FIGS. 13 and 14 are cross-sectional views showing steps of
removing undesired layers using the cleaning solution of the
present invention in a silicidation process according to another
exemplary embodiment. In contrast to the above methods, conductive
material composing a gate electrode comprises only polysilicon. The
gate electrode is employed in a dual gate technology that dopes
impurities of which conductivity type is identical with that of a
channel into the polysilicon composing a gate electrode. The dual
gate has advantages that strengthen the surface function of the
channel and makes a symmetric low-power operation.
[0059] Referring to FIG. 13, briefly explained, a well is formed in
a silicon substrate 100 by an impurity doping. Then, a device
isolation layer 120 is formed by a device isolation process and
channel ions are implanted. A polysilicon gate electrode 160a is
formed that is electrically insulated from the silicon substrate
100 by a gate insulation layer 140a. Continuously, using the
polysilicon gate electrode 160a as an ion implantation mask, ions
are implanted to form impurity diffusion layers 260. Sidewall
spacers 280 are formed on sidewalls of the polysilicon gate
electrode 160a.
[0060] Next, a silicidation process will be performed. A metal
layer and a titanium nitride layer are formed so as to form
silicide. The metal layer directly contacts with not only the
impurity diffusion layers 260 but also the silicon of the upper
part of the polysilicon gate 160a. A silicide thermal treatment is
carried out to form metal silicide layers 340 and 360 on the
impurity diffusion regions 260 and on the gate electrode 160a,
respectively.
[0061] Referring to FIG. 14, the non-reacting metal layer 300a and
a titanium nitride layer 320 are removed by the cleaning solution
including the acid solution and the oxidation agent with iodine in
the same manner as the method fully mentioned above.
[0062] According to embodiments of the present invention, using the
cleaning solution, a non-reacting metal such as cobalt and titanium
and the titanium nitride layer can be effectively removed in the
silicidation process.
[0063] Moreover, the cleaning solution does not etch the tungsten
layer, such that the tungsten gate process can be employed. Thus,
device operation characteristics can be improved. Also, a
photoresist layer and organic materials can be effectively
removed.
[0064] While the present invention has been described in connection
with specific and exemplary embodiments thereof, it is capable of
various changes and modifications without departing from the spirit
and scope of the invention. It should be appreciated that the scope
of the invention is not limited to the detailed description of the
invention hereinabove, which is intended merely to be illustrative,
but rather comprehends the subject matter defined by the following
claims. In addition, it should be construed to include all methods
and devices that are in accordance with the claims.
* * * * *