U.S. patent application number 11/752966 was filed with the patent office on 2007-12-06 for etching composition and etching process.
Invention is credited to Taketo Maruyama, Masahide Matsubara.
Application Number | 20070278185 11/752966 |
Document ID | / |
Family ID | 38432938 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070278185 |
Kind Code |
A1 |
Matsubara; Masahide ; et
al. |
December 6, 2007 |
ETCHING COMPOSITION AND ETCHING PROCESS
Abstract
An etching composition which comprises at least one organic
carboxylic acid compound selected from acetic acid, propionic acid,
butyric acid, succinic acid, citric acid, lactic acid, malic acid,
tartaric acid, malonic acid, maleic acid, glutaric acid, aconitic
acid, 1,2,3-propanetricarboxylic acid and ammonium salts of these
acids, a polysulfonic acid compound and water, and an etching
process which comprises etching a conductive film comprising zinc
oxide as the main component using the etching composition described
above.
Inventors: |
Matsubara; Masahide; (Chiba,
JP) ; Maruyama; Taketo; (Chiba, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
38432938 |
Appl. No.: |
11/752966 |
Filed: |
May 24, 2007 |
Current U.S.
Class: |
216/96 ; 216/100;
252/79.1; 252/79.3 |
Current CPC
Class: |
C09K 13/00 20130101 |
Class at
Publication: |
216/096 ;
252/079.1; 252/079.3; 216/100 |
International
Class: |
C03C 15/00 20060101
C03C015/00; C09K 13/00 20060101 C09K013/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2006 |
JP |
145440/2006 |
Claims
1. An etching composition which comprises at least one organic
carboxylic acid compound selected from acetic acid, propionic acid,
butyric acid, succinic acid, citric acid, lactic acid, malic acid,
tartaric acid, malonic acid, maleic acid, glutaric acid, aconitic
acid, 1,2,3-propanetricarboxylic acid and ammonium salts of these
acids, a polysulfonic acid compound, and water.
2. An etching composition according to claim 1, wherein the organic
carboxylic acid compound is acetic acid or ammonium acetate.
3. An etching composition according to claim 1, wherein the organic
carboxylic acid compound is acetic acid and ammonium acetate.
4. An etching composition according to claim 1, wherein the
polysulfonic acid compound is a compound selected from condensation
products of naphthalenesulfonic acid with formaline, ligninsulfonic
acid, polystyrenesulfonic acid and salts of these compounds.
5. An etching composition according to claim 4, wherein the
condensation product of naphthalenesulfonic acid with formaline is
a compound obtained by sulfonation using naphthalene and sulfuric
acid, followed by condensation by addition of formaline or by
condensation by addition of formaline and neutralization with an
alkali.
6. An etching composition according to claim 1, wherein a
concentration of the polysulfonic acid compound is 0.0001 to 10% by
weight.
7. An etching process which comprises etching a conductive film
comprising zinc oxide as a main component using an etching
composition described in claim 1.
8. An etching process according to claim 7, wherein the conductive
film comprises at least one of aluminum and gallium.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an etching composition used
for etching conductive films which comprises zinc oxide as the main
component and are used for display devices such as liquid crystal
displays (LCD) and electroluminescence displays and to an etching
process using the etching composition.
[0003] 2. Description of the Related Art
[0004] As the conductive film for display devices such as liquid
crystal displays and electroluminescence displays, films of indium
tin oxide (ITO) and films of indium zinc oxide (IZO) are widely
used. Due to the decrease in the resources for indium, electrically
conductive materials which can be used in place of ITO and IZO have
been developed.
[0005] Conductive films containing zinc oxide as the main component
are widely used as the Piezoelectric thin films, optical waveguide
films and gas sensitive films and are expected as the material
which can be used in place of conventional conductive films for
display devices. The conductive film containing zinc oxide as the
main component can be supplied at a lower price with greater
stability than indium-based conductive films since zinc is used as
the raw material. Aluminum and gallium are often added to the zinc
oxide films for display devices to decrease electric
resistance.
[0006] The above conductive films are formed on a substrate such as
a glass substrate in accordance with a process for film formation
such as the sputtering process and the ion plating process. Then,
etching is conducted using a resist or the like as the mask, and an
electrode pattern is formed. The etching process includes wet
processes and dry processes. An etching composition is used in the
wet processes.
[0007] It is widely known that zinc oxide is soluble in acids and
alkalis. When a transparent electrode of a display device such as a
liquid crystal display is formed, the following properties are
required for the etching composition:
[0008] (1) A great accuracy of working
[0009] (2) A suppressed amount of residues of etching
[0010] (3) A suitable etching rate
[0011] (4) A suppressed change in the etching property with
dissolution of zinc oxide
[0012] (5) No corrosion of materials such as wiring materials
[0013] The related arts will be described more specifically with
reference to Figures. FIG. 1 shows a sectional view of a laminate
which is obtained by forming a zinc oxide film 2 on a glass
substrate 1, followed by forming a resist 3 patterned in accordance
with the photolithography. FIG. 2 shows a sectional view of a
laminate obtained after etching the laminate shown in FIG. 1 using
the resist 3 as the mask. The great accuracy means that the zinc
oxide film is etched accurately to give the dimensions shown by the
resist pattern. It is preferable that the distance from the end
portion of the resist (a) to the end portion of zinc oxide (b) (the
amount of the side etching) is decreased as much as possible.
[0014] Residues 4 left remaining after the etching cause formation
of the leak current between the electrodes when the residues have
the electric conductivity. The residues 4 may cause a decrease in
adhesion with a film formed above the zinc oxide film 2. Therefore,
the presence of the residues is not preferable.
[0015] An excessively great etching rate is not preferable since
the control of the etching becomes difficult. An etching rate of
about 500 to 2,000 angstrom/min is preferable.
[0016] The concentration of zinc in the etching composition
increases with the progress of the etching. Therefore, it is very
important for etching of transparent electrodes in the industrial
production that the etching composition is a stable fluid having
the etching properties such as the etching rate hardly affected by
the concentration of zinc in the etching composition. When the
stable etching composition having the etching properties hardly
affected by the concentration of zinc is used, the amount of
etching of zinc oxide can be further increased.
[0017] In Japanese Patent Application Laid-Open No. 8(1996)-
330692, a process for forming an electrode pattern for display
devices containing zinc oxide as the main component is described.
It is described that etching can be conducted with excellent
accuracy without formation of residues by the etching using
hydrochloric acid or nitric acid as an acidic solution of 0.005 to
0.2 N. However, when the above etching composition is actually
used, the accuracy is insufficient due to a great amount of the
side etching, and residues are formed. Moreover, the etching rate
changes to a great degree due to the change in the concentration of
the acid caused by vaporization of water and dissolution of zinc
during the etching, and the stable etching cannot be expected.
[0018] In Japanese Patent No. 3258780, an electroluminescence
element for displays and a process for producing the element are
described. It is described that a transparent conductive film can
be formed by etching a zinc oxide film with acetic acid. Although
the etching of a zinc oxide film with an aqueous solution of acetic
acid can be conducted, this process is not preferable due to the
formation of residues.
[0019] In Japanese Patent No. 3345408, an etching composition for
transparent electrodes comprising oxalic acid and a polysulfonic
acid compound is disclosed. This composition relates to ITO films,
and no descriptions on the etching of a zinc oxide film can be
found at all. When a zinc oxide film is etched with an aqueous
solution of oxalic acid, hardly soluble crystals of zinc oxalate
are formed on the substrate and, therefore, this process is not
preferable. Even when a polysulfonic acid compound is added to the
aqueous solution of oxalic acid, crystals of zinc oxalate cannot be
removed by etching.
[0020] In Solid-State Sensor Actuator Workshop (New York: IEEE,
1992 pp 41-45), it is reported that the etching can be conducted at
a suitable etching rate when ammonium chloride is used in the
etching. However, etching residues are formed, and this process
cannot be used.
SUMMARY OF THE INVENTION
[0021] The present invention relates to an etching composition
which forms almost no residues, enables to conduct the etching at a
suitable etching rate and exhibits a suppressed change in the
etching properties when a zinc oxide film containing zinc oxide as
the main component is etched and an etching process using the
composition.
[0022] As the result of intensive studies by the present inventors,
the present invention has been completed as shown in the
following.
[0023] The present invention provides an etching composition which
contains at least one organic carboxylic acid compound selected
from acetic acid, propionic acid, butyric acid, succinic acid,
citric acid, lactic acid, malic acid, tartaric acid, malonic acid,
maleic acid, glutaric acid, aconitic acid,
1,2,3-propanetricarboxylic acid and ammonium salts of these acids,
a polysulfonic acid compound, and water.
[0024] The present invention also provides an etching process which
contains etching a conductive film containing zinc oxide as a main
component using an etching composition described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 shows a schematic sectional view of a laminate in
which a patterned resist is formed.
[0026] FIG. 2 shows a schematic sectional view of a laminate
obtained after etching the laminate shown in FIG. 1.
[0027] FIG. 3 shows an image of the surface by the SEM observation
after being etched in Example 2 (the etching composition before
adding 0.1% by weight of zinc oxide).
[0028] FIG. 4 shows an image of the surface by the SEM observation
after being etched in Comparative Example 5 (the etching
composition before adding 0.1% by weight of zinc oxide).
DETAILED DESCRIPTION OF THE INVENTION
[0029] The etching composition will be described in the
following.
[0030] The etching composition of the present invention comprises
an organic carboxylic acid compound comprising an organic
carboxylic acid and/or an ammonium salt of an organic carboxylic
acid, a polysulfonic acid compound, and water.
[0031] The organic carboxylic acid compound is at least one
compound selected from acetic acid, propionic acid, butyric acid,
succinic acid, citric acid, lactic acid, malic acid, tartaric acid,
malonic acid, maleic acid, glutaric acid, aconitic acid,
1,2,3-propanetricarboxylic acid, and ammonium salts of these acids.
Among the above organic carboxylic acid compounds, acetic acid,
citric acid, succinic acid, lactic acid, malic acid, tartaric acid
and ammonium salts thereof are preferable, and acetic acid and
ammonium acetate are more preferable.
[0032] It is preferable that the concentration of the organic
carboxylic acid compound comprised in the etching composition of
the present invention is 0.1 to 90% by weight, more preferably 0.2
to 80% by weight and most preferably 0.3 to 70% by weight. When the
concentration is 0.1 to 90% by weight, the stable etching operation
can be conducted while a practically sufficient etching rate is
maintained.
[0033] It is preferable that the concentration of the ammonium salt
of an organic carboxylic acid compound is 3.0 to 90% by weight,
more preferably 4.0 to 80% by weight and most preferably 5.0 to 70%
by weight. When the concentration is 3.0 to 90% by weight, the
stable etching operation can be conducted while a practically
sufficient etching rate is maintained.
[0034] The polysulfonic acid compound comprised in the etching
composition of the present invention is a compound selected from
condensation products of naphthalenesulfonic acid with formaline
(which is preferably a compound obtained by sulfonation using
naphthalene and sulfuric acid, followed by condensation by addition
of formaline or by condensation by addition of formaline and
neutralization with an alkali), ligninsulfonic acid,
polystyrenesulfonic acid and alkali salts of these compounds.
[0035] The condensation product of naphthalenesulfonic acid with
formaline is available as a commercial product, examples of which
include DEMOL N (a trade name; manufactured by KAO Co., Ltd.),
LAVELIN FP (a trade name; manufactured by DAIICHI KOGYO SEIYAKU
Co., Ltd.) and POLITY N100K (a trade name; manufactured by LION
Co., Ltd.)
[0036] The ligninsulfonic acid is available as a commercial
product, examples of which include SAN-X (a trade name;
manufactured by NIPPON SEISHI CHEMICAL Co., Ltd.). When the
polysulfonic acid compound contains a metal such as sodium, the
compound is not suitable for the use in the electronic industry.
The compound can be used after sodium is removed by the treatment
with an ion exchange resin.
[0037] It is preferable that the concentration of the polysulfonic
acid compound is in the range of 0.0001 to 10% by weight. When the
concentration is in the range of 0.001 to 10% by weight, the effect
of removing residues after the etching can be sufficiently
exhibited. The above concentration is more preferably 0.001 to 8%
by weight and most preferably 0.01 to 1% by weight.
[0038] The etching composition of the present invention may be used
after pH is adjusted at a desired value by adding an acid or an
alkali. It is preferable that pH is 2 to 9. When pH is in this
range, corrosion of aluminum used as the wiring material can be
prevented. pH is more preferably 3 to 8 and most preferably 3 to
7.
[0039] The etching composition of the present invention can be
prepared by mixing the above materials and water in the prescribed
amounts. The content of each material can be adjusted within the
desired range by suitably adjusting the amount of water.
[0040] The etching process will be described in the following.
[0041] The etching process of the present invention comprises
etching a conductive film comprising zinc oxide as the main
component using the etching composition of the present
invention.
[0042] The conductive film used for the etching in accordance with
the process of the present invention is not particularly limited as
long as the film comprises zinc oxide as the main component. The
film may comprise one or a plurality of types of metals other than
zinc. In particular, it is preferable that the film comprises at
least one of aluminum and gallium since the electric resistance is
decreased. Zinc oxide is the main component when the content of
zinc oxide in the conductive film is the greatest among the
components of the conductive film.
[0043] It is preferable that the etching composition of the present
invention is used in the condition of a temperature in the range of
the room temperature to 80.degree. C., more preferably in the range
of the room temperature to 70.degree. C. and most preferably in the
range of the room temperature to 60.degree. C. The time for etching
the zinc oxide film with the etching composition can be suitably
set with consideration on the etching rate (about 500 to 2,000
angstrom/min) suitable for the thickness of the treated film and
the temperature of the treatment.
[0044] The procedures in the etching process of the present
invention are not particularly limited as long as the above etching
composition can be uniformly brought at the position for the
etching by circulation, and any of the dipping process and the
shower process can be used. When the dipping process is used, the
procedures are not particularly limited as long as the etching
composition on the substrate can be replaced, and the process in
which the etching composition is made flow down on the inclined
substrate, the process in which the substrate itself is shaken (the
dipping process with shaking) or the process in which the etching
composition is stirred in a tank can be used. The shower pressure
in the shower process and the method of shaking in the dipping
process with shaking can be suitably decided with consideration on
the properties of the fluid.
EXAMPLES
[0045] The present invention will be described more specifically
with reference to Examples and Comparative Examples in the
following. However, the present invention is not limited to the
examples.
Examples 1 to 16 and Comparative Examples 1 to 8
[0046] A zinc oxide film (the thickness: 1,000 angstrom) containing
3% by atom of gallium was formed on a glass substrate in accordance
with the sputtering process. A resist pattern was formed on the
zinc oxide film in accordance with the photolithography. By using
an etching composition shown below in Table 1 or an etching
composition obtained by adding 0.1% by weight of zinc oxide to an
etching composition shown in Table 1, the etching treatment was
conducted under the following condition. The rest of the etching
composition was water.
[0047] Temperature of the substrate: 30.degree. C.
[0048] Procedure of the treatment: The substrate was dipped into
the etching composition while the substrate was shaken (the dipping
process with shaking).
[0049] Time of dipping: The time twice at the time required for the
etching (the just-etching time)
[0050] The substrate treated by the etching was cleaned with water
and dried by blowing nitrogen gas. The etching rate and the
condition of residues were examined on the substrate treated by the
etching. The results are shown in Table 2.
[0051] The etching rate was obtained by dividing the thickness of
the zinc oxide film (1,000 angstrom) with the just-etching time.
The presence or the absence of residues was examined by observation
using a scanning electron microscope (SEM).
[0052] "Residues after etching" in table 2 shows the result
obtained with the composition before adding 0.1% by weight of zinc
oxide. The result obtained with the composition after adding 0.1%
by weight of zinc oxide was the same as the result obtained with
the composition before adding 0.1% by weight of zinc oxide.
TABLE-US-00001 TABLE 1 Composition Example 1 1% by wt. acetic acid
0.1% by wt. LAVELIN FP Example 2 5% by wt. acetic acid 0.0001% by
wt. LAVELIN FP Example 3 5% by wt. acetic acid 0.1% by wt. LAVELIN
FP Example 4 5% by wt. acetic acid 1% by wt. LAVELIN FP Example 5
5% by wt. acetic acid 0.1% by wt. sodium ligninsulfonate Example 6
5% by wt. acetic acid 0.1% by wt. sodium polystyrenesulfonate
Example 7 5% by wt. citric acid 0.1% by wt. LAVELIN FP Example 8 5%
by wt. succinic acid 0.1% by wt. LAVELIN FP Example 9 5% by wt.
lactic acid 10.0% by wt. LAVELIN FP Example 10 5% by wt. malic acid
0.1% by wt. LAVELIN FP Example 11 5% by wt. tartaric acid 0.1% by
wt. LAVELIN FP Example 12 15% by wt. ammonium acetate 0.1% by wt.
DEMOL N Example 13 15% by wt. ammonium acetate 0.1% by wt. POLITY
N100K Example 14 15% by wt. ammonium succinate 0.1% by wt. LAVELIN
FP Example 15 15% ammonium acetate 0.1% by wt. LAVELIN FP 5% by wt.
acetic acid Comparative 15% by wt. acetic acid Example 1
Comparative 15% by wt. ammonium acetate Example 2 Comparative 5% by
wt. succinic acid Example 3 Comparative 0.1% by wt. hydrochloric
acid Example 4 Comparative 5% by wt. acetic acid Example 5
Comparative 1% by wt. LAVELIN FP Example 6 Comparative 1% by wt.
LAVELIN FP Example 7 (sodium removed) Comparative 0.5% by wt.
LAVELIN FP Example 8 (sodium removed) LAVELIN FP: A condensation
product of naphthalenesulfonic acid with formaline (a compound
obtained by sulfonation using naphthalene and sulfuric acid,
followed by condensation by addition of formaline and
neutralization; the molecular weight: 2,000.about.5,000;
manufactured by DAIICHI KOGYO SEIYAKU Co., Ltd.) DEMOL N: A
condensation product of naphthalenesulfonic acid with formaline
(manufactured by KAO Co., Ltd.) POLITY N100K A condensation product
of naphthalenesulfonic acid with formaline (manufactured by LION
Co., Ltd.)
[0053] TABLE-US-00002 TABLE 2 Etching rate (.ANG./min) content of
zinc oxide (by wt.) Residues 0 0.1 of etching Example 1 1091 857
excellent Example 2 857 857 excellent Example 3 1333 1200 excellent
Example 4 2000 1714 excellent Example 5 1333 1200 excellent Example
6 1333 1200 excellent Example 7 750 706 excellent Example 8 1200
1200 excellent Example 9 1333 1200 excellent Example 10 632 600
excellent Example 11 667 632 excellent Example 12 1091 1000
excellent Example 13 1091 1000 excellent Example 14 750 706
excellent Example 15 2000 2000 excellent Comparative 2000 2000 poor
Example 1 Comparative 857 <200 poor Example 2 Comparative 1500
1500 poor Example 3 Comparative 6000 2400 poor Example 4
Comparative 2000 2000 poor Example 5 Comparative <300 etching
not examination Example 6 possible not possible Comparative 6000
545 excellent Example 7 Comparative 2000 etching not excellent
Example 8 possible Evaluation of residues poor: many residues on
the entire surface excellent: no residues at all
[0054] Images of the surface by the SEM observation after being
etched in Example 2 and Comparative Example 5 (both are the etching
composition before adding 0.1% by weight of zinc oxide) are shown
in FIG. 3 and FIG. 4, respectively. As shown in FIG. 3, the etching
composition used in Example 2 formed no residues of etching. In
contrast, the etching composition used in Comparative Example 5
formed many white dots of residues of etching as shown in FIG.
4.
[0055] It is shown by the results in Tables 1 and 2 that, when the
etching composition of the present invention is used, the
conductive film comprising zinc oxide as the main component can be
etched at a suitable etching rate which is easy for the control,
and the formation of residues of etching is suppressed.
[0056] The decrease in the etching rate is small and the change in
the etching properties is suppressed even when zinc oxide is
dissolved. Therefore, it is shown that the etching composition of
the present invention exhibits the excellent properties as the
etching composition used in the industrial production.
* * * * *