U.S. patent application number 09/797454 was filed with the patent office on 2002-01-10 for cleaning solution for removing damaged portion of ferroelectric layer and cleaning method using the same.
Invention is credited to Hah, Sang-rok, Kwon, Young-min, Lee, Kun-tack, Lee, Kwang-wook, Park, Im-soo.
Application Number | 20020003123 09/797454 |
Document ID | / |
Family ID | 19674224 |
Filed Date | 2002-01-10 |
United States Patent
Application |
20020003123 |
Kind Code |
A1 |
Lee, Kwang-wook ; et
al. |
January 10, 2002 |
Cleaning solution for removing damaged portion of ferroelectric
layer and cleaning method using the same
Abstract
A cleaning solution for use in removing a damaged portion of a
ferroelectric layer, and a cleaning method using the solution. The
cleaning solution includes a fluoride, an organic acid with
carboxyl group, an alkaline pH adjusting agent and water.
Inventors: |
Lee, Kwang-wook;
(Kwacheon-city, KR) ; Park, Im-soo; (Seoul,
KR) ; Lee, Kun-tack; (Suwon-city, KR) ; Kwon,
Young-min; (Suwon-city, KR) ; Hah, Sang-rok;
(Seoul, KR) |
Correspondence
Address: |
Frank Chau, Esq.
F. CHAU & ASSOCIATES, LLP
1900 Hempstead Turnpike, Suite 501
East Meadow
NY
11554
US
|
Family ID: |
19674224 |
Appl. No.: |
09/797454 |
Filed: |
March 1, 2001 |
Current U.S.
Class: |
216/6 ; 148/525;
257/E21.251; 427/79 |
Current CPC
Class: |
C04B 2111/00844
20130101; C11D 7/265 20130101; C04B 41/009 20130101; H01L 21/31111
20130101; C04B 41/91 20130101; C11D 7/02 20130101; C04B 41/5315
20130101; C11D 11/0047 20130101; C04B 41/009 20130101; C04B 35/465
20130101; C04B 41/009 20130101; C04B 35/491 20130101 |
Class at
Publication: |
216/6 ; 148/525;
427/79 |
International
Class: |
H01G 004/00; H01G
013/00; C21D 001/26; C21D 009/00; B05D 005/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2000 |
KR |
00-35705 |
Claims
What is claimed is:
1. A cleaning solution capable of selectively removing a damaged
portion of a ferroelectric layer, the cleaning solution comprising:
a fluoride; an organic acid with carboxyl group; an alkaline pH
adjusting agent; and water.
2. The cleaning solution of claim 1, wherein the pH of the cleaning
solution is about 4.5 to about 6.0.
3. The cleaning solution of claim 1, wherein the fluoride is
hydrogen fluoride, hydroboron tetrafluoride or ammonium
fluoride.
4. The cleaning solution of claim 1, wherein the organic acid is
formic acid, acetic acid or citric acid.
5. The cleaning solution of claim 1, wherein the alkaline pH
adjusting agent is ammonium hydroxide, potassium hydroxide,
tetramethylammonium hydroxide or tetraethylammonium hydroxide.
6. The cleaning solution of claim 1, wherein the content of the
fluoride is about 0.01% to about 1% by weight based on the total
weight of the cleaning solution.
7. The cleaning solution of claim 1, wherein the content of the
organic acid with carboxyl group is about 1% to about 50% by weight
based on the total weight of the cleaning solution.
8. The cleaning solution of claim 1, wherein the content of the
alkali pH adjusting agent is about 0.25% to about 15% by weight
based on the total weight of the cleaning solution.
9. The cleaning solution of claim 1, wherein the damaged portion of
the ferroelectric layer to be removed with the cleaning solution
includes the surface of the ferroelectric layer passed through
annealing after deposition, or the surface of the ferroelectric
layer passed through an etching process.
10. A method of selectively removing a damaged portion of a
ferroelectric layer with a cleaning solution, the method
comprising: providing an integrated circuit substrate having an
exposed ferroelectric layer with the damaged portion; and
contacting the exposed ferroelectric layer with the cleaning
solution, said cleaning solution including a fluoride, an organic
acid with carboxyl group, an alkaline pH adjusting agent, and
water.
11. The method of claim 10, wherein the exposed ferroelectric layer
includes the surface of the ferroelectric layer passed through
annealing after deposition on the integrated circuit substrate, and
the step of making the exposed ferroelectric layer contact the
cleaning solution includes etching back the ferroelectric layer by
about 100 .ANG. to about 500 .ANG. from the top of the
ferroelectric layer.
12. The method of claim 10, wherein the exposed ferroelectric layer
is interposed between upper and lower electrode layers, and the
method further comprises forming a capacitor by patterning the
upper electrode layer, the ferroelectric layer and the lower
electrode layer, before contacting the exposed ferroelectric layer
with the cleaning solution.
13. The method of claim 10, wherein the pH of the cleaning solution
is about 4.5 to about 6.0.
14. The method of claim 10, wherein the fluoride is hydrogen
fluoride, hydroboron tetrafluoride or ammonium fluoride.
15. The method of claim 10, wherein the organic acid is formic
acid, acetic acid or citric acid.
16. The method of claim 10, wherein the alkaline pH adjusting agent
is ammonium hydroxide, potassium hydroxide, tetramethylammonium
hydroxide or tetraethylammonium hydroxide.
17. The method of claim 10, wherein the content of the fluoride is
about 0.01% to about 1% by weight based on the total weight of the
cleaning solution.
18. The method of claim 10, wherein the content of the organic acid
with carboxyl group is about 1% to about 50% by weight based on the
total weight of the cleaning solution.
19. The method of claim 10, wherein the content of the alkali pH
adjusting agent is about 0.25% to about 15% by weight based on the
total weight of the cleaning solution.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to a cleaning solution for use
in removing a damaged portion of a ferroelectric layer, and a
method for removing a damaged portion of a ferroelectric layer
using the cleaning solution.
[0003] 2. Discussion of Related Art
[0004] A ferroelectric random access memory (FRAM) can retain its
contents without power for years. FRAM capacitors are kept in a
charged state while the supply of power is suspended. During a
patterning process for forming a FRAM capacitor, active components
of etching gases used for the patterning, such as argon (Ar),
fluorine (F) or chlorine (Cl), react with electrode materials or
ferroelectric materials, thereby resulting in byproducts such as
PbO.sub.2, ZrO.sub.2, TiO.sub.2 or TiO.sub.3, on the surface of a
ferroelectric layer. As a result, the ferroelectric layer is
damaged by the byproducts. The damaged ferroelectric layer serves
as a leakage current path between upper and lower electrodes,
thereby degrading the electrical properties of the FRAM
capacitor.
[0005] In the manufacture of the FRAM capacitor, annealing is
carried out so as to provide the FRAM capacitor with a stable
perovskite structure. However, even after the annealing is
completed, a pyrochlore structure, which is a semi-stable phase,
appears from the top of the ferroelectric layer to a predetermined
depth. If an upper electrode layer is deposited over the
ferroelectric layer having the pyrochlore structure, a desirable
FRAM capacitor having superior performance cannot be obtained. In
this aspect, the ferroelectric layer having the pyrochlore
structure is regarded as a kind of damaged layer, relative to the
whole ferroelectric layer with the perovskite structure.
[0006] Thus, there is a need to perform a cleaning step for
removing such a ferroelectric layer having the semi-stable
pyrochlore structure and a portion of the ferroelectric layer that
is damaged during an etching process in the manufacture of the FRAM
capacitor. A conventional cleaning solution used in the cleaning
step includes hydrogen fluoride (HF) diluted with an alcoholic
solvent, such as methanol, ethanol or isopropyl alcohol, in a
predetermined ratio. However, because the alcoholic solvent of the
cleaning solution is highly volatile, the alcoholic solvent
evaporates with time, hence the cleaning (etching) capability of
the cleaning solution cannot be kept constant, thereby shortening
the lifetime of the cleaning solution. Another disadvantage in
using the conventional cleaning solution lies in that after the
cleaning is completed, a further rinsing step with isopropyl
alcohol (IPA) is needed before a rinsing step with deionized water.
This is because the rinsing step with deionized water is
insufficient to completely remove the cleaning solution from the
surface of the substrate, which causes corrosion of the
substrate.
[0007] Therefore, a need exists for providing a cleaning solution
capable of selectively removing a damaged portion of a
ferroelectric layer, and has a consistent cleaning capability for a
longer period of time.
[0008] A method is also needed for selectively removing a damaged
portion of a ferroelectric layer using the cleaning solution.
SUMMARY OF THE INVENTION
[0009] According to an aspect of the present invention, a cleaning
solution is provided that is capable of selectively removing a
damaged portion of a ferroelectric layer, the cleaning solution
comprising a fluoride, an organic acid with carboxyl group, an
alkaline pH adjusting agent, and water. It is preferable that the
pH of the cleaning solution is in the range of about 4.5 to about
6.0.
[0010] It is preferable that the fluoride comprises hydrogen
fluoride, hydroboron tetrafluoride or ammonium fluoride, the
organic acid comprises formic acid, acetic acid or citric acid, and
the alkaline pH adjusting agent comprises ammonium hydroxide,
potassium hydroxide, tetramethylammonium hydroxide or
tetraethylammonium hydroxide.
[0011] It is preferable that the fluoride content is from about
0.01% to about 1% by weight, the content of the organic acid with
carboxyl group is from about 1% to about 50% by weight, and the
content of the alkali pH adjusting agent is from about 0.25% to
about 15% by weight based on the total weight of the cleaning
solution.
[0012] According to another aspect of the present invention, there
is provided a method of selectively removing a damaged portion of a
ferroelectric layer with a cleaning solution, the method
comprising: providing an integrated circuit substrate having an
exposed ferroelectric layer with a damaged portion; and making the
exposed ferroelectric layer contact the cleaning solution, the
cleaning solution including a fluoride, an organic acid with
carboxyl group, an alkaline pH adjusting agent and water.
[0013] It is preferable that the exposed ferroelectric layer
includes the surface of the ferroelectric layer which is passed
through annealing after deposition on an integrated circuit
substrate. Preferably, the exposed ferroelectric layer is contacted
with the cleaning solution to etch back the ferroelectric layer by
a thickness of between about 100 .ANG. to about 500 .ANG. from the
top of the ferroelectric layer.
[0014] It is preferable that the exposed ferroelectric layer is
interposed between upper and lower electrode layers, and the method
further comprises forming a capacitor by patterning the upper
electrode layer, the ferroelectric layer and the lower electrode
layer before contacting the exposed ferroelectric layer with the
cleaning solution.
[0015] Therefore, a cleaning solution according to the present
invention is able to effectively remove a damaged portion of the
ferroelectric layer, while maintaining a consistent cleaning
capability for a longer period of time.
[0016] These and other aspects, features and advantages of the
present invention will described or become apparent from the
following detailed description of the preferred embodiments, which
is to be read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an exemplary flowchart illustrating use of a
cleaning solution according to an aspect of the present invention
in the manufacture of a ferroelectric random access memory (FRAM)
capacitor.
[0018] FIG. 2 is an exemplary graph showing etching rate variations
with respect to hydrogen fluoride content in the cleaning solution
according to an aspect of the present invention, which were
measured to determine an appropriate hydrogen fluoride content of
the cleaning solution.
[0019] FIG. 3 is an exemplary graph showing etching rate variations
with respect to a pH of the cleaning solution according to an
aspect of the present invention, which were measured to determine
an appropriate pH level of the cleaning solution.
[0020] FIG. 4 is an exemplary graph showing etching rate variations
with respect to cleaning time for determining an appropriate
cleaning time for a cleaning process using the cleaning solution
according to an aspect of the present invention.
[0021] FIG. 5 is an exemplary graph showing etching rate variations
of the cleaning solution according to the present invention over
time, which were measured to determine a lifetime of the cleaning
solution.
[0022] FIG. 6 is an exemplary graph showing remnant polarization in
a FRAM capacitor after a conventional cleaning solution and the
inventive cleaning solution is applied to sidewalls of the FRAM
capacitor.
[0023] FIG. 7 is an exemplary graph showing a leakage current
characteristic of a FRAM capacitor after the conventional cleaning
solution and the inventive cleaning solution are each applied to
the sidewalls of the FRAM capacitor.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] A cleaning solution and a cleaning method using the cleaning
solution according to the present invention will now be described
more fully. The cleaning solution according to an aspect of the
present invention, which for convenience will be referred to as
Samsung selective Cleaning Solution or "S.C.S", preferably includes
a fluoride, an organic acid with carboxyl group, an alkaline pH
adjusting agent, and water.
[0025] The S.C.S. includes a range of about 0.01% to about 1% by
weight fluoride, about 1% to about 50% by weight organic acid with
carboxyl group, about 0.25% to about 15% by weight alkaline pH
adjusting agent, and a remaining balance of water.
[0026] In terms of efficiency in the manufacture of semiconductor
devices, a cleaning time of 30 minutes or less is desirable. If the
fluoride content is less than 0.01% by weight, it is impossible to
completely remove a damaged portion of a ferroelectric layer within
the maximum desired period of cleaning time. However, if the
fluoride content exceeds 1% by weight, the etching rate over the
damaged ferroelectric layer is so high that accurate controlling of
the cleaning process is difficult.
[0027] If the organic acid content is less than 1% by weight, the
cleaning capability with respect to the damaged portion of the
ferroelectric layer decreases. Also, for a greater cleaning
efficiency and processing margin, it is desirable that the organic
acid content does not exceed about 50% by weight. The pH adjusting
agent content varies depending on the fluoride and organic acid
contents. Preferably, the pH adjusting agent content is in the
range of between about 0.25% to about 15% by weight based on the
total weight of S.C.S.
[0028] It is preferable that the pH level of the S.C.S is about 6.6
or less. If the pH level of the S.C.S is higher than about 6.6, the
damaged portion of the ferroelectric layer cannot be completely
removed within the maximum desired cleaning time. However, if the
S.C.S exhibits strong acidity less than about pH 4.5, electrode
layers formed above and below the ferroelectric layer are damaged.
In a pH range from about 6.0 to about 6.6, the damaged portion of
the ferroelectric layer can be removed with the S.C.S., but the
etching selectivity with respect to the damaged portion of the
ferroelectric layer drops. Therefore, to selectively remove the
damaged portion of the ferroelectric layer at a constant etching
rate without removing an undamaged portion, it is more preferable
that the pH of the S.C.S. ranges from about 4.5 to about 6.0.
[0029] Preferably, the fluoride for use in the cleaning solution is
hydrogen fluoride (HF), hydroboron tetrafluoride (HBF.sub.4) or
ammonium fluoride (NH.sub.4F).
[0030] Preferably, the organic acid with carboxyl group is formic
acid (HCOOH), acetic acid (CH.sub.3COOH) or citric acid
(C.sub.3H.sub.4(OH)(COOH).sub.3).
[0031] Preferably, the alkaline pH adjusting agent is ammonium
hydroxide (NH.sub.4OH), potassium hydroxide (KOH), tetramethyl
ammonium hydroxide ((CH.sub.3).sub.4NH.sub.4OH), or tetraethyl
ammonium hydroxide ((CH.sub.3CH.sub.2).sub.4NH.sub.4OH).
[0032] The type of ferroelectric layer to which the S.C.S. can be
applied, includes a STO (SrTiO.sub.3) layer, a BST
(Ba,Sr)TiO.sub.3) layer, a PZT (Pb(Zr.sub.xTi.sub.1-x)O.sub.3
layer, and a PLZT (La-doped PZT) layer.
[0033] The main cause of damage to the ferroelectric layer are
oxides of the constituent elements of the ferroelectric layers.
These oxides, such as PbO.sub.2, ZrO.sub.2, TiO.sub.2, TiO.sub.3,
BaO, or SrO, can be removed by the following method.
[0034] Fluorine ion (F.sup.-) derived from fluoride, which has a
strong reducing power, reduces the metal of a metallic oxide. In
addition to the fluorine ion, ammonium and hydroxy ions originating
from a pH adjusting agent and hydrogen ions dissociated from an
organic acid also serve as reductants. Reduction of a metallic
oxide (for example, titanium oxide (TiO.sub.3)) by a fluoride (for
example, hydrogen fluoride (HF), is expressed, for example, by the
following reaction scheme:
TiO.sub.3+6HFTiF.sub.6+3H.sub.2O
[0035] The reduced metallic component is dissolved in the organic
acid by chelation with the organic acid having a carboxyl group, or
in water that is a polar solvent contained in the cleaning
solvent.
[0036] The organic acid according to the present invention, which
serves as a reductant and a dissolving agent as described
previously, protects an exposed capacitor electrode layer formed on
the surface of an integrated circuit substrate, for example, an
iridium (Ir), ruthenium (Ru) or platinum (Pt) layer, or an iridium
oxide (IrO.sub.2) or ruthenium oxide (RuO.sub.2) layer, from
corrosion or damage. In particular, a metallic oxide layer is
spontaneously formed on the exposed electrode layer. As the
metallic oxide layer is reduced into metal ions by the reaction
with a reductant contained in the S.C.S, the organic acid forms a
chelate complex with the metal ions. As a result, the exposed
surface of the electrode layer is covered with the stable chelate
complex, so that the exposed electrode layer is protected from
corrosion or damage.
[0037] The pH adjusting agent according to the present invention is
used for appropriately adjusting the pH level of the S.C.S, such
that the etching selectivity with respect to the damaged portion of
the ferroelectric layer increases while keeping the reducing power
of the fluoride constant. In addition, the pH adjusting agent
properly adjusts the pH of the S.C.S. to minimize the damage of the
electrode layer. Considering these aspects, a suitable pH level of
the S.C.S adjusted by the pH adjusting agent preferably ranges from
about 4.5 to about 6.0.
[0038] A method for manufacturing a FRAM capacitor using the S.C.S.
according to the present invention will be described with reference
to FIG. 1. A storage electrode layer, which is electrically
connected to a source region, is formed over a semiconductor
substrate with a sub structure (step 100). The storage electrode
layer may be formed of the platinum group metals including platinum
(Pt), iridium (Ir), ruthenium (Ru) and rhodium (Rh). To improve the
fatigue characteristic, the storage electrode layer may be formed
of a metallic oxide layer, such as an IrO.sub.2, RuO.sub.2,
RhO.sub.2 or LaSrCoO.sub.3 layer.
[0039] Next, a ferroelectric layer is formed over the storage
electrode layer (step 110). The ferroelectric layer may be formed
of a STO, BST, PZT or PLZT layer. The ferroelectric layer having a
desired thickness can be formed by a single deposition and
annealing, or alternatively, deposition to a predetermined
thickness and a baking process can be repeated until a
ferroelectric layer having a desired thickness is formed. In the
latter case, after the ferroelectric layer reaches the desired
thickness, annealing is carried out on the resultant structure. The
deposition and baking processes can be repeated to make the
composition and properties of the ferroelectric layer uniform.
Although the ferroelectric layer is completed through these
processes, a semi-stable pyrochlore phase also forms on the top of
the ferroelectric layer. To remove the damaged portion having the
semi-stable pyrochlore phase from the ferroelectric layer, the
ferroelectric layer is made to contact with the S.C.S. according to
the present invention (step 120). Step 120 is performed for a
predetermined time period in which the ferroelectric layer can be
etched back between about 100 .ANG. to about 500 .ANG.. Preferably,
step 120 is carried out for about 30 to 600 seconds, but more
preferably, for about 30 to about 180 seconds. In step 120, the
substrate with the ferroelectric layer may be dipped in a S.C.S.
bath or the S.C.S may be spread over the ferroelectric layer.
[0040] If the ferroelectric layer has a whole perovskite structure
through the annealing performed after the deposition, the step 120
of removing a damaged portion of the ferroelectric layer using the
S.C.S. can be omitted.
[0041] After the damaged portion of the ferroelectric layer has
been removed, a plate electrode layer is formed over the resultant
structure (step 130). The plate electrode layer may be formed of
the same material used for the storage electrode, i.e., a Pt group
metal or an oxide of the Pt group metal.
[0042] Next, the plate electrode layer, the ferroelectric layer and
the storage electrode layer are consequently patterned to form a
capacitor (step 140). This patterning is carried out by dry etching
using an etching gas containing, for example, Ar, F or Cl. During
the patterning, active components of the etching gas, such as, for
example, Ar, F or Cl, react with the the electrode materials or
ferroelectric material, thereby resulting in byproducts such as,
for example, PbO.sub.2, ZrO.sub.2, TiO.sub.2 or TiO.sub.3, on the
sidewalls of the ferroelectric layer, which cause damage to
sidewalls of the ferroelectric layer.
[0043] Subsequently, the substrate with the FRAM capacitor is
cleaned with the S.C.S. to remove a damaged portion of the
ferroelectric layer (step 150).
[0044] Unlike a conventional cleaning solution, the inventive
S.C.S. does not contain a highly volatile alcoholic solvent. Thus,
even though cleaning is performed several times with the inventive
S.C.S., there are no problems associated with a changing volume or
composition ratio of the S.C.S. due to evaporation of an alcoholic
solvent. As a result, the cleaning efficiency of S.C.S. is
consistent. Furthermore, when the inventive cleaning solution is
utilized, the cleaning process can be performed at low temperatures
of 60.degree. C. or less, and particularly, at room
temperature.
[0045] In addition, an S.C.S. solution according to the present
invention does not cause corrosion or damage of electrode layers,
so that contact with the substrate for a longer time period is
allowed. To maximize the process efficiency and the complete
removal of the damaged portion of the ferroelectric layer, the
substrate is preferably contacted with the S.C.S. solution for
about 30 to about 600 seconds, but more preferably, for about 30 to
about 180 seconds.
[0046] After the cleaning process is completed, the substrate is
rinsed with deionized water so as to remove the S.C.S. in which the
damaged portion separated from the ferroelectric layer is dissolved
(step 160). The rinsing process may be performed through two stages
as needed. Lastly, the substrate is dried by spin drying or by
using isopropyl alcohol to evaporate deionized water from the
surface of the substrate, thereby resulting in a complete FRAM
capacitor (step 170). After the drying is completed, the resultant
substrate is transferred for a next step that is required to
integrate a circuit on the substrate.
[0047] Because the inventive S.C.S. is an aqueous solution, a
single rinse with deionized water is sufficient to completely
remove the S.C.S. from the surface of the substrate. Thus, a
further rinsing process with isopropyl alcohol (IPA), which was
required when using a conventional cleaning solution, is
unnecessary when using the inventive S.C.S. In addition, the
inventive S.C.S. exhibits a high etching rate and a high etching
selectivity with respect to a damaged portion of the ferroelectric
layer, so that the damaged portion of the ferroelectric layer can
be effectively removed, thereby improving the electrical properties
of the FRAM capacitor.
[0048] The present invention will be described in greater detail by
means of the following examples. The following examples are for
illustrative purposes and are not intended to limit the scope of
the invention.
Experimental Example 1
Determination of Appropriate Hydrogen Fluoride (HF) content
[0049] To determine an appropriate HF content in the S.C.S.,
samples of the S.C.S. each containing 0.1%, 0.2%, 0.3% and 0.4% HF
by weight based on the total weight of the S.C.S were prepared. Two
S.C.S. samples were prepared for each HF concentration. A
(Pb(Zr.sub.xTi.sub.1-x)O.sub.3 (PZT) layer was deposited to a
thickness of 500 .ANG. on 8 substrates, and baked. This deposition
and baking was repeated once more, and an annealing process was
carried out at 350.degree. C. or more on the resultant structure,
thereby forming a PZT layer having a thickness of 1000 .ANG. on the
substrates. Plasma etching was performed on four substrates with a
gas mixture containing halogen gas, CF.sub.x gas and O.sub.2 gas,
which caused damage to the PZT layers. Next, the four substrates
with the damaged PZT layers were immersed for 30 seconds in the
respective S.C.S samples containing HF at the four different
concentrations. Also, the other four substrates with the whole PZT
layers were immersed for 30 seconds in the respective S.C.S samples
containing HF at the four different concentrations. After the
cleaning in the S.C.S. samples, the etching rate of the PZT layer
was measured for the eight substrates. The results are shown in
FIG. 2.
[0050] As shown in FIG. 2, the damaged PZT layer can be selectively
removed at 0.3% or less by weight HF.
Experimental Example 2
Determination of Appropriate pH Level
[0051] To determine an appropriate pH level of the S.C.S. at which
it exhibits the full cleaning capability, various S.C.S. samples at
pH levels of 4.5, 5.5, 6.0, and 9.0 were prepared. Two S.C.S.
samples were prepared for each pH level. Four substrates with a
damaged PZT layer and four substrates with a whole PZT layer were
prepared in the same way as in Experimental Example 1 above. A
substrate with the damaged PZT layer and a substrate with the
undamaged PZT layer were immersed for 30 seconds in the two S.C.S.
samples at the same pH level, respectively. After the cleaning in
the S.C.S. samples, the etching rate with respect to the PZT layer
was measured. The results are shown in FIG. 3.
[0052] As shown in FIG. 3, as the pH of the S.C.S. changes from
weak acidity to weak alkalinity, the etching rate of the S.C.S
solution with respect to the PZT layer decreases. It can be noticed
that the pH level of the S.C.S is preferably about 4.5 to about 6.0
to allow an adjustment of the etching rate and to selectively
remove the damaged PZT layer in the cleaning step.
Experimental Example 3
Determination of Appropriate Cleaning Time
[0053] An appropriate cleaning time was determined using an S.C.S
sample whose composition was optimized based on the results from
Experimental Examples 1 and 2 above. Four substrates with a damaged
PZT layer were prepared in the same way as in Experimental Example
1. Next, the four substrates were immersed in the optimized S.C.S
samples for 60, 90, 120 and 180 seconds, respectively. The amount
of etching was measured for each substrate. The results are shown
in FIG. 4.
[0054] Considering that the thickness of the PZT layer damaged
after the formation of a capacitor is usually about 100 .ANG., it
can be noticed that the appropriate cleaning time is between about
80 to about 100 seconds, and more preferably, about 90 seconds.
Experimental Example 4
Measurement of the Lifetime of the S.C.S
[0055] To measure the storage stability (i.e., the "lifetime") of
the S.C.S. according to the present invention, four S.C.S. samples
were prepared and left for 0, 4, 8 and 16 hours, respectively. Four
substrates with a damaged PZT layer were prepared in the same way
as in Experimental Example 1, and immersed in the respective S.C.S.
samples for 60 seconds. After the cleaning in the S.C.S. samples,
the etching rate was measured for each sample. The results are
shown in FIG. 5.
[0056] As shown in FIG. 5, even after 16 hours have passed from the
preparation of the S.C.S, the cleaning capability of the inventive
S.C.S. remains consistent. In other words, the S.C.S. according to
the present invention has a longer lifetime.
Experimental Example 5
Measurement of Cleaning Capability with a Device
[0057] After depositing an oxide layer over a substrate, an indium
(In) oxide layer and a platinum (Pt) layer were formed in sequence
as lower electrode conductive layers and deposited in sequence over
the oxide layer. Next, an In oxide layer and an iridium (Ir) layer,
which serve as upper electrode conductive layers, were deposited
over the resultant structure, and dry etched using a gas mixture
including a halogen gas, thereby resulting in 7 FRAM capacitors.
One FRAM capacitor was cleaned using a conventional cleaning
solution containing methanol and HF as a control sample, and the
other six FRAM capacitors were separately cleaned using an S.C.S.
according to the present invention. The cleaning time with the
S.C.S. was varied at 60, 90 and 120 seconds. Two FRAM capacitors (A
and B) were cleaned at each cleaning time. Remnant polarization and
leakage current properties of the capacitors were measured after
the cleaning was completed. The results are shown in FIGS. 6 and
7.
[0058] As shown in FIG. 6, capacitance of the FRAM capacitors can
be improved with the inventive S.C.S. by about 20%, compared to the
case of using the conventional cleaning solution. FIG. 7 shows that
the leakage current properties of the FRAM capacitors treated with
the S.C.S., exclusive of the FRAM capacitors cleaned for 60
seconds, are similar to those of the FRAM capacitor treated in the
conventional cleaning solution.
[0059] As previously described, an S.C.S. according to the present
invention is able to effectively remove a damaged portion of a
ferroelectric layer, and does not corrode or damage electrode
layers. Thus, by utilizing the inventive S.C.S. in the manufacture
of a FRAM capacitor, electrical properties, such as leakage current
and capacitance, of the FRAM capacitor can be improved. In
addition, the inventive S.C.S. does not contain a highly volatile
alcoholic solvent, and thus its lifetime is prolonged. Furthermore,
because the inventive S.C.S. is aqueous, a single rinsing process
with deionized water is sufficient to completely remove the
inventive S.C.S. when it is used to remove a damaged ferroelectric
layer. Thus, a rinsing process with isopropyl alcohol, which is
required when using a conventional cleaning solution, is
unnecessary in the case of using the inventive S.C.S.
[0060] Although illustrative embodiments of the present invention
have been described herein with reference to the accompanying
drawings, it is to be understood that the present invention is not
limited to those precise embodiments, and that various other
changes and modifications may be affected therein by persons
ordinarily skilled in the art without departing from the scope or
spirit of the invention. All such changes and modifications are
intended to be included within the scope of the invention as
defined by the appended claims.
* * * * *