U.S. patent application number 14/340284 was filed with the patent office on 2014-12-25 for wiring film and active matrix substrate using the same, and method for manufacturing wiring film.
This patent application is currently assigned to MITSUBISHI ELECTRIC CORPORATION. The applicant listed for this patent is MITSUBISHI ELECTRIC CORPORATION. Invention is credited to Kazuyuki FUJIWARA, Kazunori INOUE, Takahito YAMABE.
Application Number | 20140377952 14/340284 |
Document ID | / |
Family ID | 47752427 |
Filed Date | 2014-12-25 |
United States Patent
Application |
20140377952 |
Kind Code |
A1 |
FUJIWARA; Kazuyuki ; et
al. |
December 25, 2014 |
WIRING FILM AND ACTIVE MATRIX SUBSTRATE USING THE SAME, AND METHOD
FOR MANUFACTURING WIRING FILM
Abstract
An Al wiring film having a tapered shape is obtained easily and
in a stable manner. An Al wiring film has a double-layer structure
including a first Al alloy layer made of Al or an Al alloy, and a
second Al alloy layer laid on the first Al alloy layer and having a
composition different from a composition of the first Al alloy
layer by containing at least one element of Ni, Pd, and Pt. The
second Al alloy layer is etched by an alkaline chemical solution
used in a developing process of a photoresist, and an end portion
of the second Al alloy layer recedes from an end portion of the
photoresist. Thereafter, by performing wet etching using the
photoresist as a mask, a cross section of the Al wiring film
becomes a tapered shape.
Inventors: |
FUJIWARA; Kazuyuki;
(Kumamoto, JP) ; INOUE; Kazunori; (Kumamoto,
JP) ; YAMABE; Takahito; (Kumamoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
MITSUBISHI ELECTRIC CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
MITSUBISHI ELECTRIC
CORPORATION
Tokyo
JP
|
Family ID: |
47752427 |
Appl. No.: |
14/340284 |
Filed: |
July 24, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13604452 |
Sep 5, 2012 |
|
|
|
14340284 |
|
|
|
|
Current U.S.
Class: |
438/688 |
Current CPC
Class: |
H01L 27/1244 20130101;
H01L 21/76838 20130101; H01L 29/4908 20130101; H01L 29/458
20130101; H01L 21/283 20130101 |
Class at
Publication: |
438/688 |
International
Class: |
H01L 21/768 20060101
H01L021/768; H01L 21/283 20060101 H01L021/283 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2011 |
JP |
2011-193849 |
Claims
1. A method for manufacturing a wiring film, comprising the steps
of: forming a first layer made of Al or an Al alloy; forming, on
said first layer, a second layer made of an Al alloy containing at
least one element of Ni, Pd, and Pt and having a composition
different from a composition of said first layer; coating a
photoresist on said second layer and performing exposure using a
photomask; developing said photoresist after performing the
exposure and etching said second layer by using an alkaline
chemical solution, so that an end portion of said second layer
under said photoresist after the developing recedes from an end
portion of the photoresist; and forming the wiring film including
said first and second layers by etching and patterning said first
and second layers simultaneously by wet etching using said
photoresist after developing as a mask.
2. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a structure of a wiring
film containing aluminum and a method for manufacturing the same,
and more particularly to a wiring film applicable to an electrode
of a thin-film transistor provided on an array substrate or the
like of a liquid crystal display apparatus.
DESCRIPTION OF THE BACKGROUND ART
[0002] For example, aluminum (Al) is known as a material of a
wiring film used as an electrode of a thin-film transistor that is
formed on an array substrate (active matrix substrate) of a liquid
crystal display apparatus. Since an electric resistance of Al is
very low, it has been generally used as a wiring material
conventionally. In this specification, a film obtained not only
from pure Al but also a material containing Al as a main components
such as an Al alloy, and a wiring film resulted from patterning
such a film are broadly referred to as an "Al film" and an "Al
wiring film", respectively.
[0003] A wet etching method using a chemical solution containing
phosphoric acid and nitric acid series is common as a method of
pattern process (patterning). However, since the method is
isotropic etching, a sidewall of an Al wiring film resulted from
patterning becomes substantially vertical. This causes an
insulating film formed on the Al wiring film to have a poor step
coverage characteristic, and, as a result, causes broken wiring of
a wiring film formed on the insulating film, a reduction of a
breakdown voltage of the insulating film, or the like.
[0004] A technique for etching the Al film in a tapered shape is
proposed to solve such a problem in, for example, Japanese Patent
Application Laid-Open Nos. 06-122982, 2001-77098, 2003-127397, and
2007-157755. However, when a composition of a chemical solution
(etchant) changes as an etching process progresses or degrades by
time in such a technique, an inclination of the sidewall of the
tapered Al wiring film acutely changes accordingly. This poses a
problem of a difficulty in managing the composition of the
etchant.
[0005] According to the general wet etching technique for the Al
film described above, the sidewall of the Al wiring film subjected
to the patterning becomes substantially vertical. This causes the
insulating film formed on the Al wiring film to have a poor step
coverage characteristic, and, as a result, causes a reduction of a
breakdown voltage of the insulating film, broken wiring of the
wiring film of an upper layer, or the like, which eventually causes
a drop in the yield of the product.
[0006] Japanese Patent Application Laid-Open Nos. 06-122982,
2001-77098, 2003-127397, and 2007-157755 propose an etching
technique for forming the Al wiring film in a tapered shape.
However, it is necessary to severely manage the composition of the
etchant to obtain a predetermined tapered shape in a stable manner.
To do so, it is necessary, for example, to introduce a facility to
constantly monitor the concentration of the etchant, or replace the
etchant more frequently, which eventually increases the cost.
[0007] Further, when an ordinary Al film is used as an electrode of
a thin-film transistor (TFT) of an active matrix substrate for a
liquid crystal display apparatus, contact characteristics between
the TFT and a pixel electrode are drastically degraded due to an
interface reaction with an ITO film which is a transparent pixel
electrode. For this reason, it is difficult to apply the Al wiring
film as a wiring film on the active matrix substrate.
SUMMARY OF THE INVENTION
[0008] It is an object of the present invention to provide a
structure of an Al wiring film and a method for manufacturing the
same, from which a tapered Al wiring film can be obtained easily
and in a stable manner, and which can be applied to an active
matrix substrate of a display apparatus.
[0009] A wiring film according to a first aspect of the present
invention includes a first layer and a second layer laid on the
first layer. The first layer is made of Al or an Al alloy. The
second layer is made of an Al alloy containing at least one element
of Ni, Pd, and Pt and having a composition different from a
composition of the first layer. The wiring film has a tapered shape
in cross section with a width smaller in an upper portion thereof
than a width in a bottom portion thereof.
[0010] A wiring film according to a second aspect of the present
invention includes a first layer, a second layer laid on the first
layer, and a third layer laid on the second layer. The first layer
is made of a first Al alloy containing at least one element of Ni,
Pd, and Pt. The second layer is made of a second Al alloy
containing nitrogen. The third layer is made of a third Al alloy
containing at least one element of Ni, Pd, and Pt. The wiring film
has a tapered shape in cross section with a width smaller in an
upper portion thereof than a width in a bottom portion thereof.
[0011] A method for manufacturing a wiring film according to a
third aspect of the present invention includes the following steps.
A step of forming a first layer made of Al or an Al alloy. A step
of forming, on the first layer, a second layer made of an Al alloy
containing at least one element of Ni, Pd, and Pt and having a
composition different from a composition of the first layer. A step
of coating a photoresist on the second layer and performing
exposure using a photomask. A step of developing the photoresist
after performing the exposure and etching the second layer by using
an alkaline chemical solution, so that an end portion of the second
layer under the photoresist after the developing recedes from an
end portion of the photoresist. A step of forming the wiring film
including the first and second layers by etching and patterning the
first and second layers simultaneously by wet etching using the
photoresist after developing as a mask.
[0012] A method for manufacturing a wiring film according to a
fourth aspect of the present invention includes the following
steps. A step of forming a first layer made of a first Al alloy
containing at least one element of Ni, Pd, and Pt. A step of
forming, on the first layer, a second layer made of a second Al
alloy resulted from adding nitrogen to the first Al alloy. A step
of forming, on the second layer, a third layer made of the first Al
alloy. A step of coating a photoresist on the third layer and
performing exposure using a photomask. A step of developing the
photoresist after performing the exposure and etching the third
layer by using an alkaline chemical solution, so that an end
portion of the third layer under the photoresist after the
developing recedes from an end portion of the photoresist. A step
of forming the wiring film including the first, second, and third
layers by etching and patterning the first, second, and third
layers simultaneously by wet etching using the photoresist after
developing as a mask.
[0013] According to the present invention, the tapered shape of the
Al wiring film can be stabilized without a need to manage the
etchant stricter than in the conventional case. Accordingly, the
step coverage characteristic of the gate insulating film formed on
the Al wiring film is improved, it is possible to prevent the
breakdown voltage from reducing and the wiring film in the upper
layer from breaking, and the yield of the product is improved. In
addition, since the second layer made of an Al alloy containing at
least one element of Ni, Pd, and Pt can obtain an excellent contact
characteristic with an oxide material used as a transparent pixel
electrode, it is easy to apply the wiring film to an electrode of a
thin-film transistor provided in an active matrix substrate of a
display apparatus.
[0014] According to the present invention, the tapered shape of the
Al wiring film can be stabilized without a need to manage the
etchant stricter than in the conventional case. Accordingly, the
step coverage characteristic of the insulating film formed on the
Al wiring film is improved, it is possible to prevent the breakdown
voltage from reducing and the wiring film in the upper layer from
breaking, and the yield of the product is improved. In addition,
since the layer made of an Al alloy containing at least one element
of Ni, Pd, and Pt can obtain an excellent contact characteristic
with an oxide material used as a transparent pixel electrode, it is
easy to apply the wiring film to an electrode of a thin-film
transistor provided in an active matrix substrate of a display
apparatus.
[0015] These and other objects, features, aspects and advantages of
the present invention will become more apparent from the following
detailed description of the present invention when taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a cross sectional view of a structure of an Al
wiring film according to a first preferred embodiment;
[0017] FIGS. 2 to 4 are manufacturing process diagrams of the Al
wiring film according to the first preferred embodiment;
[0018] FIG. 5 is a graph indicating a relation between a
composition ratio of Ni, Pd, and Pt of an Al alloy and an etching
rate with respect to a TMAH organic alkaline chemical solution;
[0019] FIG. 6 is a plan view of a structure of a principal portion
of a TFT active matrix substrate according to the first preferred
embodiment;
[0020] FIG. 7 is a cross sectional view of a structure of a
principal portion of the TFT active matrix substrate according to
the first preferred embodiment;
[0021] FIGS. 8 to 11 are manufacturing process diagrams of the TFT
active matrix substrate according to the first preferred
embodiment;
[0022] FIG. 12 is a cross sectional view of a structure of an Al
wiring film according to a second preferred embodiment;
[0023] FIGS. 13 to 15 are manufacturing process diagrams of the Al
wiring film according to the second preferred embodiment; and
[0024] FIG. 16 is a cross sectional view of a structure of a
principal portion of the TFT active matrix substrate according to
the second preferred embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Preferred Embodiment
[0025] FIG. 1 is a cross sectional view of a structure of an Al
wiring film according to a first preferred embodiment. As
illustrated in FIG. 1, an Al wiring film 101 formed on a substrate
100 according to this preferred embodiment has a double-layer
structure including a first Al alloy layer 101a and a second Al
alloy layer 101b formed thereon, and has a tapered shape in cross
section with a width smaller in an upper portion thereof than a
width in a bottom portion thereof.
[0026] The first Al alloy layer 101a is a layer including Al as a
main component. This is not restricted to the Al alloy, but pure Al
may also be used. The second Al alloy layer 101b is made of an Al
alloy containing at least one element of nickel (Ni), palladium
(Pd), and platinum (Pt). The composition of the Al alloy of the
first Al alloy layer 101a is different from the composition of the
Al alloy of the second Al alloy layer 101b.
[0027] In addition, the substrate 100 serving as a base for the Al
wiring film 101 may be a semiconductor substrate such as a silicon
substrate, an insulating substrate such as a glass substrate used
as an active matrix substrate for a display apparatus, or an
interlayer dielectric film provided on another wiring layer.
[0028] Hereinafter, a method for manufacturing the Al wiring film
101 illustrated in FIG. 1 will be described. FIGS. 2 to 4 are
manufacturing process diagrams thereof.
[0029] First, the first Al alloy layer 101a made of Al or an Al
alloy is formed on the substrate 100. Formed on top of it is the
second Al alloy layer 101 made of an Al alloy containing at least
one element of Ni, Pd, and Pt and having different composition from
that of the first Al alloy layer 101a (FIG. 2). In this preferred
embodiment, Al is formed into a film having a thickness of 200 nm
as the first Al alloy layer 101a, and the Al alloy resulted from
adding 3 mol % Ni to Al is formed into a film having a thickness of
20 nm as the second Al alloy layer 101b by sputtering using an Ar
gas.
[0030] Thereafter, a photoresist 102 having a predetermined pattern
is formed on the second Al alloy layer 101b using a photoengraving
technique (FIG. 3). In this preferred embodiment, a positive type
photoresist of a novolak resin is coated by a slit coater or a spin
coater to a thickness of 1.6 .mu.m and is exposed using a
photomask. Subsequently, the resultant is developed using an
alkaline chemical solution to form the photoresist 102 having the
predetermined pattern. In this preferred embodiment, an organic
alkaline developing solution (liquid temperature of 23.degree. C.)
containing 2.4 wt % of tetramethylammonium hydroxide (TMAH) is used
as the alkaline chemical solution.
[0031] Here, since the Al alloy containing at least one element of
Ni, Pd, and Pt is etched by the alkaline chemical solution, the
second Al alloy layer 101b exposed from the photoresist 102 is
etched in a developing process of the photoresist 102. The second
Al alloy layer 101b (thickness of 20 nm) containing 3 mol % Ni used
in this preferred embodiment is etched by the TMAH organic alkaline
developing solution at an etching rate of about 60 nm/min.
Therefore, when the developing process is extended by 20 seconds
after the photoresist 102 is developed, a portion of the second Al
alloy layer 101b exposed from the photoresist 102 is removed.
[0032] When the developing process is further extended, the second
Al alloy layer 101b under the photoresist 102 is etched in a
transverse direction (in-plane direction of the film), and, as
illustrated in FIG. 3, a width of the second Al alloy layer 101b
becomes smaller than a width of the photoresist 102. This means
that ends of the second Al alloy layer 101b individually recede
from ends of the photoresist 102.
[0033] In contrast, the first Al alloy layer 101a made of Al is
hardly etched by the organic alkaline developing solution
containing TMAH. As a result, notches 103 having an undercut shape
are formed between the photoresist 102 and the first Al alloy layer
101a caused by receding of the ends of the second Al alloy layer
101b.
[0034] Thereafter, in wet etching using the photoresist 102 as a
mask, the first Al alloy layer 101a and the second Al alloy layer
101b are simultaneously subjected to etching and patterning, so
that the Al wiring film 101 having the predetermine pattern is
formed (FIG. 4). In this preferred embodiment, an etchant of PAN
series (phosphoric acid, acetic acid, and nitric acid series) is
used for the wet etching.
[0035] During this process, since a notch shape is provided under
the photoresist 102, the ends of the second Al alloy layer 101b and
an upper surface of the first Al alloy layer 101a are isotropically
etched. Specifically, the upper surface of the first Al alloy layer
101a is etched while the ends of the second Al alloy layer further
recede. As a result, the sidewall of the Al wiring film 101 is
inclined, and the Al wiring film 101 has a tapered shape with a
width smaller in the upper portion than a width in the bottom
portion.
[0036] Finally, by removing the photoresist 102, the Al wiring film
101 illustrated in FIG. 1 is completed.
[0037] Since the Al wiring film 101 according to this preferred
embodiment has a tapered shape, it is possible to have a good step
coverage characteristic when an insulating film is formed thereon.
Accordingly, this prevents the breakdown voltage of the insulating
film from reducing, prevents the wire of the wiring film in the
upper layer from breaking, and contributes to improvement of the
yield of the product.
[0038] Further, since a process of patterning the Al wiring film
101 into a tapered shape can be performed during the isotropically
etching of the first Al alloy layer 101a and the second Al alloy
layer 101b, the tapered shape (inclination of the sidewall) of the
Al wiring film 101 is hardly affected by the change of the
composition of the etchant. Therefore, the Al wiring film 101
having a predetermined tapered shape can be obtained easily and in
a stable manner without a need to manage the etchant stricter than
in the conventional case. Accordingly, the cost incurred in
managing the etchant does not increase.
[0039] Although the Al alloy containing 3 mol % Ni is used as the
second Al alloy layer 101b in this preferred embodiment, the
application of the present invention is not restricted to this. An
Al alloy film serves as the second Al alloy layer 101b if at least
one element of Ni, Pd, and Pt is added thereto. Ni, Pd, and Pt are
the elements that belong to group 10 of the periodic law. The
inventors of the present invention confirmed by experiment an
effect in which, by adding an appropriate amount of such an element
to Al, the etching rate (etching speed) of an Al alloy with respect
to an alkaline chemical solution became faster.
[0040] FIG. 5 is a graph indicating a relation between a
composition ratio (additive amount) of Ni, Pd, and Pt of an Al
alloy in which any of Ni, Pd, and Pt is added to Al and an etching
rate with respect to a TMAH organic alkaline chemical solution. The
etching rate represents a value when an Al alloy is etched in an
organic alkaline developing solution (liquid temperature of
23.degree. C.) containing 2.4 wt % of TMAH.
[0041] As indicated in FIG. 5, the composition ratio of Ni, Pd, and
Pt of the Al alloy is 0.5 mol %, the etching rate becomes five
times faster or more as compared with pure Al (the composition
ratio is 0 mol %). Additionally, when the composition ratio of Ni,
Pd, and Pt becomes 1 mol % or larger, the etching rate becomes
almost saturated.
[0042] In a region where the composition ratio of Ni, Pd, and Pt is
smaller than 0.5 mol %, the etching rate largely changes, and
therefore control of the etching amount becomes difficult. At the
same time, since the present invention provides a sufficient effect
when the etching rate is five times or more as compared with the
case of pure Al, it is preferable that the additive amount of Ni,
Pd, and Pt be 0.5 mol % or more. Further, in view of stabilizing
the etching rate, it is preferable to set the additive amount to 1
mol % or more.
[0043] In contrast, when the additive amount of Ni, Pd, and Pt
exceeds 10 mol %, a rate of precipitation of compound phase of
AlNi, AlPd, and AlPt increases, and this may be left as an etching
residue in the alkaline developing solution and may sometimes cause
an etching failure. Accordingly, it is preferable to set the total
additive amount of Ni, Pd, and Pt to be added to Al to 10 mol % or
smaller.
[0044] In addition, although the organic alkaline developing
solution having a concentration of TMAH of 2.4 wt % is used as the
etchant in this preferred embodiment, it is preferable that the
concentration of TMAH be 0.2 wt % or more and 25 wt % or less while
the liquid temperature ranges between 10.degree. C. and 50.degree.
C. When the concentration of TMAH is less than 0.2 wt %, the
etching rate of the Al alloy including Ni, Pd, and Pt is
drastically reduced, making the etching difficult to perform. In
contrast, when the concentration of TMAH exceeds 25 wt %, damage
incurred by the photoresist increases, which causes a concern of
pattern defects.
[0045] Further, the film thickness of the first Al alloy layer 101a
is set to 200 nm, and the film thickness of the second Al alloy
layer 101b formed thereon is set to 20 nm in this preferred
embodiment. However, the film thicknesses thereof are not
restricted to these examples. The inventors of the present
invention confirmed by experiment that as long as the thickness of
the second Al alloy layer 101b was 40 nm or smaller, the Al wiring
film 101 was formed into a substantially smooth tapered shape. When
the thickness of the second Al alloy layer 101b exceeded 40 nm, the
portion of the first Al alloy layer 101a and the portion of the
second Al alloy layer 101b became step-like shapes individually
which are shapes independent from each other, and deterioration in
the step coverage characteristic when an insulating film 101 was
formed on the Al wiring film 101 was observed. Accordingly, when
the thickness of the first Al alloy layer 101a is 200 nm, it is
preferable that the thickness of the second Al alloy layer 101b be
set to 40 nm or smaller. To state it differently, it is preferable
that the thickness of the second Al alloy layer 101b be 1/5 or less
of that of the first Al alloy layer 101a.
[0046] Hereinafter, an example of applying the Al wiring film 101
illustrated in FIG. 1 to a TFT active matrix substrate of a liquid
crystal display apparatus will be described as a specific example
of application. In general, a TFT active matrix substrate has a
structure in which a pixel electrode which is a transparent
electrode and a thin-film transistor (TFT) which is a switching
element for supplying an image signal to the pixel electrode are
provided on a transparent insulating substrate for each of a
plurality of pixels that are arranged in a matrix pattern, and a
source line SL for feeding the image signal to each TFT and a gate
line GL for feeding a drive signal to each TFT are further
provided.
[0047] FIG. 6 is a plan view of a structure of a principal portion
(one pixel region) of a TFT active matrix substrate according to
the first preferred embodiment, and FIG. 7 is a cross sectional
view taken along a line A-B. As illustrated in FIG. 7, the TFT
active matrix substrate has a transparent insulating substrate 1
provided thereon with a gate electrode 2, a gate insulating film 4,
a semiconductor film 5, an ohmic contact film 6, a TFT formed of a
source electrode 7 and a drain electrode 8, a pixel electrode 12
which is a transparent conductive film connected to the drain
electrode 8 of the TFT, and an auxiliary capacitance electrode
3.
[0048] The ohmic contact films 6 interposed between the
semiconductor film 5 and the source electrode 7, and between the
semiconductor film 5 and the drain electrode 8, respectively, are a
low-resistance layer of silicon (Si) added with impurities. A
region in the semiconductor film 5 between the source electrode 7
and the drain electrode 8 serves as a channel portion 9 in which a
channel of the TFT is formed. An interlayer dielectric film 10 for
protecting the channel portion 9 of the TFT is provided on an
entire surface on the transparent insulating substrate 1, and the
pixel electrode 12 is connected to the drain electrode 8 through a
contact hole 11 formed in the interlayer dielectric film 10. In
addition, as illustrated in FIG. 6, the source electrode 7 is
integrally formed with a source line SL to which the source
electrode 7 is connected, and the gate electrode 2 is integrally
formed with a gate line GL to which the gate electrode 2 is
connected.
[0049] In the example illustrated in FIGS. 6 and 7, the Al wiring
film 101 illustrated in FIG. 1 is applied to the gate electrode 2,
the auxiliary capacitance electrode 3, the source electrode 7, and
the drain electrode 8 on the TFT active matrix substrate. This
means that the gate electrode 2 has a double-layer structure formed
of a first Al alloy layer 2a and a second Al alloy layer 2b, and
the auxiliary capacitance electrode 3 has a double-layer structure
formed of a first Al alloy layer 3a and a second Al alloy layer 3b.
Similarly, the source electrode 7 has a double layer structure
formed of a first Al alloy layer 7a and a second Al alloy layer 7b,
and the drain electrode 8 has a double layer structure formed of a
first Al alloy layer 8a and a second Al alloy layer 8b.
[0050] The first Al alloy layers 2a, 3a, 7a, and 8a are
individually made of either Al or an Al alloy as in the case of the
first Al alloy layer 101a illustrated in FIG. 1. The second Al
alloy layers 2b, 3b, 7b, and 8b are individually made of an Al
alloy containing at least one element of Ni, Pd, and Pt as in the
case of the second Al alloy layer 101b illustrated in FIG. 1.
[0051] Hereinafter, a description will be given of a method for
manufacturing the TFT active matrix substrate illustrated in FIGS.
6 and 7. FIGS. 8 to 11 are diagrams of a manufacturing process of
the TFT active matrix substrate.
[0052] First, a transparent insulating substrate 1 such as a glass
substrate is cleaned using a cleaning liquid or pure water, and the
gate electrode 2 having a tapered shape and the gate line GL to
which the gate electrode 2 is connected, and the auxiliary
capacitance electrode 3 are formed on the transparent insulating
substrate 1 (FIG. 8) using a method described with reference to
FIGS. 2 to 4.
[0053] Next, the gate insulating film 4, an Si film serving as the
semiconductor film 5, and an n.sup.+ type Si film (Si film heavily
doped with n-type impurities) serving as the ohmic contact film 6
are sequentially formed, the Si film and the n.sup.+ type Si film
are subjected to patterning using a photoengraving technique, so
that a semiconductor pattern of TFT formed of the semiconductor
film 5 and the ohmic contact film 6 is formed on the gate
insulating film 4 (FIG. 9). At this stage, the ohmic contact film 6
is not yet separated into a source side and a drain side.
[0054] In the process illustrated in FIG. 9 according to this
preferred embodiment, first, a silicon nitride (SiN) film with a
thickness of 400 nm is formed as the gate insulating film 4 by the
chemical vapor deposition (CVD) method under a substrate heating
condition of about 300.degree. C. Thereafter, a film of amorphous
silicon (a-Si) with a thickness of 150 nm is formed as an Si film
serving as the semiconductor film 5, and an a-Si film with a
thickness of 50 nm added with phosphor (P) as an impurity is formed
as an n.sup.+ type Si film serving as the ohmic contact film 6.
Then, a positive type photoresist of a novolak resin is coated by a
slit coater or a spin coater to a thickness of 1.6 .mu.m and is
exposed using a photomask. Subsequently, the resultant is developed
using an organic alkaline chemical solution containing TMAH, and a
photoresist pattern of the pattern of the semiconductor film 5 is
formed. The a-Si film and the n.sup.+ type a-Si film are subjected
to patterning using the photoresist pattern as a mask by dry
etching using a fluorine series gas, and thereby the semiconductor
pattern of the TFT formed of the semiconductor film 5 and the ohmic
contact film 6 is formed. Further, the photoresist pattern is
stripped off and removed using an amine series stripping
solution.
[0055] Next, the source electrode 7 having a tapered shape, the
drain electrode 8, and the source line SL to which the source
electrode 7 is connected are formed on the gate insulating film 4,
the semiconductor film 5, and the ohmic contact film 6 (FIG. 10) by
the method described with reference to FIGS. 2 to 4.
[0056] Here, before removing the photoresist pattern used for
patterning the source electrode 7 and the drain electrode 8,
further using the pattern as a mask, the ohmic contact film 6 is
etched by dry etching using a gas containing, for example, chlorine
(Cl). Through this process, the ohmic contact film 6 is separated
into a source side and a drain side. At this stage, a portion of
the semiconductor film 5 in a region from which the ohmic contact
film 6 is removed serves as the channel portion 9 of the TFT. The
photoresist pattern is removed thereafter.
[0057] Next, a silicon nitride (SiNx) film is formed as the
interlayer dielectric film 10 at a film forming temperature of
200.degree. C. According to this preferred embodiment, the SiN film
with a thickness of 300 nm is formed by the chemical vapor
deposition (CVD) method under a substrate heating condition of
about 300.degree. C.
[0058] Thereafter, a photoresist pattern with a region for forming
the contact hole 11 is opened is formed using a photoengraving
technique, and, using the photoresist pattern as a mask, the
contact hole 11 is formed in the interlayer dielectric film 10 by
dry etching using a fluorine series gas.
[0059] Finally, a transparent conductive film is formed on the
interlayer dielectric film 10 including the contact hole 11, and
the resultant is subjected to patterning to form the pixel
electrode 12 (FIG. 11). According to this preferred embodiment, IZO
(indium oxide (In.sub.2O.sub.3)-zinc oxide (ZnO)) is formed into a
film with a thickness of 100 nm as the transparent conductive film
by sputtering using an Ar gas. A photoresist pattern is formed
thereon by a photoengraving technique, and, using the photoresist
pattern as a mask, wet etching is performed using a oxalic acid
series solution to form the pixel electrode 12.
[0060] By the foregoing process, the TFT active matrix substrate
having a structure illustrated in FIGS. 6 and 7 is completed.
[0061] Although it is not illustrated, an alignment film made of
polyimide or the like for aligning the liquid crystal, and a spacer
for securing a gap from an opposing substrate provided thereon with
color filters or the like are formed on a surface of the completed
TFT active matrix substrate. Then, the TFT active matrix substrate
is bonded to the opposing substrate, the liquid crystal is injected
between the two substrates, and the two substrates are sealed
together to thereby form a liquid crystal display panel. Then, a
polarizing plate, a phase plate, a backlight unit, and the like are
arranged outside the liquid crystal display panel to complete the
liquid crystal display apparatus.
[0062] As in the case of this preferred embodiment, the Al wiring
film 101 illustrated in FIG. 1 is applied to the gate electrode 2,
the auxiliary capacitance electrode 3, the source electrode 7, and
the drain electrode 8 on the TFT active matrix substrate. As a
result of this, the step coverage characteristic of the gate
insulating film 4 and the interlayer dielectric film 10 is
improved, and the occurrence of a reduction in the breakdown
voltage or a broken wire in the TFT active matrix substrate can be
suppressed.
[0063] In this preferred embodiment, although the Al wiring film
101 illustrated in FIG. 1 is applied both to the wiring layer for
the gate electrode 2 and the auxiliary capacitance electrode 3, and
the wiring layer for the source electrode 7 and the drain electrode
8, it is also possible to apply the Al wiring film 101 to one of
these.
[0064] In particular, when the Al wiring film 101 illustrated in
FIG. 1 is applied to the source electrode 7 and the drain electrode
8, it is preferable to use, as the first Al alloy layer 7a, an Al
alloy film to which a rare earth metal such as neodymium (Nd),
lanthanum (La), or gadolinium (Gd) is added so that an excellent
contact characteristic is obtained in an interface with the ohmic
contact film 6 which makes contact with lower surfaces of the
source electrode 7 and the drain electrode 8.
[0065] Further, the pixel electrode 12 is connected to the second
Al alloy layer 7b of the source electrode 7. The Al alloy film of
the second Al alloy layer 7b contains the additive element of Ni,
Pd, or Pt. When the interlayer dielectric film 10 and the like are
formed at a high temperature, the additive element agglomerates and
is deposited in an surface layer. This also provides an effect of
improving a contact characteristic with a conductive oxide film
such as IZO or ITO used for the pixel electrode 12.
Second Preferred Embodiment
[0066] FIG. 12 is a cross sectional view of a structure of an Al
wiring film according to a second preferred embodiment. As
illustrated in FIG. 12, an Al wiring film 201 formed on a substrate
100 according to this preferred embodiment has a triple-layer
structure including a first Al alloy layer 201a, a second Al alloy
layer 201b, and a third Al alloy layer 201c which are laminated in
this order, and has a tapered shape in cross section with a width
smaller in an upper portion thereof than a width in a bottom
portion thereof.
[0067] The first Al alloy layer 201a is made of an Al alloy
containing at least one element of Ni, Pd, and Pt. The second Al
alloy layer 201b is made of an Al alloy containing nitrogen (N).
The third Al alloy layer 201c is made of an Al alloy containing at
least one element of Ni, Pd, and Pt. The first Al alloy layer 201a
and the third Al alloy layer 201c may have an identical
composition. Also, the second Al alloy layer 201b may be formed by
adding nitrogen to an Al alloy which is the same as that used for
the first Al alloy layer 201a or the third Al alloy layer 201c.
[0068] The substrate 100 serving as a base for the Al wiring film
201 may be a semiconductor substrate such as a silicon substrate,
an insulating substrate such as a glass substrate used for the
active matrix substrate, or an interlayer dielectric film provided
on another wiring layer.
[0069] Hereinafter, a method for manufacturing the Al wiring film
201 illustrated in FIG. 12 will be described. FIGS. 13 to 15 are
manufacturing process diagrams thereof. First, a triple-layer
structure is formed on the substrate 100 by sequentially forming,
by sputtering using the Ar gas, the first Al alloy layer 201a made
of the Al alloy containing at least one element of Ni, Pd, and Pt,
the second Al alloy layer 201b resulted from azotizing an Al alloy
film, and the third Al ally layer 201c made of the Al alloy
containing at least one element of Ni, Pd, and Pt (FIG. 13).
[0070] In this preferred embodiment, in view of simplifying the
manufacturing process, the first Al alloy layer 201a and the third
Al alloy layer 201c use an Al alloy having an identical
composition, and the second Al alloy layer 201b uses an Al alloy
resulted from azotizing the same Al alloy. In this case, the first
Al alloy layer 201a, the second Al alloy layer 201b, and the third
Al alloy layer 201c can be formed by the sputtering method using a
consistent identical target in the above-mentioned sputtering
process. With this arrangement, when the second Al alloy layer 201b
is formed, merely a process of mixing the Ar gas with a nitrogen
gas and performing the reactive sputtering is performed.
Accordingly, a reduction in the manufacturing cost and an
improvement in the productivity can be expected. It is preferable
that the additive amounts of Ni, Pd, and Pt in the first Al alloy
layer 201a, the second Al alloy layer 201b, and the third Al alloy
layer 201c, individually, be 0.5 mol % or more and 10 mol % or less
(more preferably, 1 mol % or more and 10 mol % or less) as in the
case of the second Al alloy layer 101b in the first preferred
embodiment.
[0071] The second Al alloy layer 201b is a layer having a low
etching rate with respect to the organic alkaline developing
solution. The etching rate of the Al alloy with respect to the
alkaline developing solution is reduced by adding atoms of nitrogen
(N). It is preferable that the additive amount of atoms of nitrogen
(N) to the second Al alloy layer 201b be 10 mol % or more so that
the etching rate of the second Al alloy layer 201b is sufficiently
reduced (1/5 or less of the etching rate of the first Al alloy
layer 201a and the third Al alloy layer 201c).
[0072] However, if the additive amount of the atoms of N is
excessively increased, the conductivity of the second Al layer 201b
is impaired, it is preferable to limit the additive amount to such
an amount by which the conductivity of the second Al alloy layer
201b is maintained. Considering Ti, Cr, Mo, Ta, W, and alloys
thereof which are generally used for the wiring film of a
semiconductor device as a reference, and assuming that an upper
limit of a specific resistance value of the second Al alloy layer
201b is 200 .mu..OMEGA.cm, it is preferably that the additive
amount of the atoms of N be 40 mol % or less.
[0073] After the triple-layer structure formed of the first Al
alloy layer 201a, the second Al alloy layer 201b, and the third Al
alloy layer 201c is formed, a photoresist 102 having a
predetermined pattern is formed on the third Al alloy layer 201c
using a photoengraving technique (FIG. 14). In this preferred
embodiment, the photoresist 102 is formed by coating and exposing a
positive type photoresist of a novolak resin, and by developing
using a TMAH organic alkaline chemical solution.
[0074] Here, since the Al alloy containing at least one element of
Ni, Pd, and Pt can be etched by the TMAH organic alkaline chemical
solution, the third Al alloy layer 201c exposed from the
photoresist 102 is etched by extending the time of the developing
process of the photoresist 102. As a result, the third Al alloy
layer 201c under the photoresist 102 is etched in a transverse
direction (in-plane direction of the film), and a width thereof
becomes smaller than that of the photoresist 102. This means that
ends of the third Al alloy layer 201c individually recede from ends
of the photoresist 102.
[0075] In contrast, the second Al alloy layer 201b which is an
azotized Al alloy is highly resistant to the TMAH organic alkaline
chemical solution, and therefore is hardly etched. Accordingly, as
illustrated in FIG. 14, notches 103 having an undercut shape are
formed between the photoresist 102 and the second Al alloy layer
201b, the under cut shape being caused by receding of the ends of
the third Al alloy layer 201c.
[0076] Thereafter, in wet etching using the photoresist 102 as a
mask, the first Al alloy layer 201a, the second Al alloy layer
201b, and the third Al alloy layer 201c are simultaneously
subjected to etching and patterning, so that the Al wiring film 201
having the predetermine pattern is formed (FIG. 15). In this
preferred embodiment, an etchant of PAN series (phosphoric acid,
acetic acid, and nitric acid series) is used for the wet
etching.
[0077] During this process, since a notch shape is provided under
the photoresist 102, the ends of the third Al alloy layer 201c and
upper surfaces of the second Al alloy layer 201b and the first Al
alloy layer 201a are isotropically etched. Specifically, the upper
surfaces of the second Al alloy layer 20 lb and the first Al alloy
layer 201a are etched while the ends of the third Al alloy layer
201c further recede. As a result, the sidewall of the Al wiring
film 201 is inclined, and the Al wiring film 201 has a tapered
shape with a width smaller in the upper portion than a width in the
bottom portion.
[0078] Finally, by removing the photoresist 102, the Al wiring film
201 illustrated in FIG. 12 is completed.
[0079] Since the Al wiring film 201 according to this preferred
embodiment has a tapered shape, it is possible to have a good step
coverage characteristic when an insulating film is formed thereon.
Accordingly, this prevents the breakdown voltage of the insulating
film from reducing, prevents the wire of the wiring film in the
upper layer from breaking, and contributes to improvement of the
yield of the product.
[0080] Further, since a process of patterning the Al wiring film
201 into a tapered shape can be performed during the isotropically
etching of the first Al alloy layer 201a, the second Al alloy layer
201b, and the third Al alloy layer 201c, the tapered shape
(inclination of the sidewall) of the Al wiring film 201 is hardly
affected by the change of the composition of the etchant.
Therefore, the Al wiring film 201 having a predetermined tapered
shape can be obtained easily and in a stable manner without a need
to manage the etchant stricter than in the conventional case.
Accordingly, an increase in the cost incurred in managing the
etchant can be suppressed.
[0081] In this preferred embodiment, in order to smooth the Al
wiring film 201, it is preferable to set a film thickness of the
third Al alloy layer 201c to 1/5 or less of a sum of film
thicknesses of the first Al alloy layer 201a and the third Al alloy
layer 201c. With this arrangement, it is possible to optimize the
notch shape of the photoresist 102 after the developing process and
the tapered shape of the Al wiring film 201 after patterning.
[0082] As in the case of the Al wiring film 101 in the first
preferred embodiment, the Al wiring film 201 having the
triple-layer structure according to the second preferred embodiment
can be applied to the gate electrode 2, the auxiliary capacitance
electrode 3, the source electrode 7, and the drain electrode 8 of
the TFT active matrix substrate illustrated in FIGS. 6 and 7.
[0083] It is also possible to use a combination of the Al wiring
film 101 of the first preferred embodiment and the Al wiring film
201 of the second preferred embodiment. For example, FIG. 16
illustrates a structure of a TFT active matrix substrate in which
the Al wiring film 101 of the first preferred embodiment is applied
to the wiring layer of the gate electrode 2 and the auxiliary
capacitance electrode 3, and the Al wiring film 201 of the second
preferred embodiment is applied to the wiring layer of the source
electrode 7 and the drain electrode 8.
[0084] Referring to FIG. 16, the gate electrode 2 and the auxiliary
capacitance electrode 3 have a double-layer structure including a
first layer (first Al alloy layers 2a and 3a) made of Al or an Al
alloy, and a second layer (second Al alloy layers 2b and 3b) made
of an Al alloy containing at least one element of Ni, Pd, and Pt.
In contrast, the source electrode 7 and the drain electrode 8 have
a triple-layer structure including a first layer (first Al alloy
layers 71a and 81a) made of an Al alloy containing at least one
element of Ni, Pd, and Pt, and a second layer (second Al alloy
layers 71b and 81b) made of an Al alloy containing nitrogen, and a
third layer (third Al alloy layers 71c and 81c) made of an Al alloy
containing at least one element of Ni, Pd, and Pt.
[0085] In particular, when the Al wiring film 201 of the second
preferred embodiment is applied to the source electrode 7 and the
drain electrode 8, the first Al alloy layers 71a and 81a which are
the bottom layer and the third Al alloy layers 71c and 81c which
are the upper layer are made of an Al alloy added with transition
elements of group 10 of Ni, Pd, or Pt. Therefore, it is possible to
obtain an excellent contact characteristic in an interface with the
ohmic contact film 6 which makes contact with lower surfaces of the
source electrode 7 and the drain electrode 8, and further in an
interface with the pixel electrode 12 (conductive oxide film such
as IZO or ITO) which is connected to an upper surface of the drain
electrode 8.
[0086] The a-Si film is used as an example of the semiconductor
film 5 of the TFT active matrix substrate described above. It is
also possible to use a semiconductor of a zinc oxide (ZnO) base, or
a semiconductor of an oxide base including zinc oxide (ZnO) to
which gallium oxide (Ga.sub.2O.sub.3), indium oxide
(In.sub.2O.sub.3), tin oxide (SnO.sub.2), or the like is added.
When such a semiconductor film of the oxide base is used as the
semiconductor film 5, it is possible to obtain a TFT having higher
performance where the carrier mobility is high than in the case of
using the a-Si film.
[0087] In particular, when the Al wiring film 201 of the second
preferred embodiment is applied to the source electrode 7 and the
drain electrode 8, an excellent contact characteristic is achieved
in an interface between the first Al alloy layer 201a which is an
Al alloy added with Ni, Pd, or Pt and the semiconductor film 5 of
the oxide base. This makes it possible to obtain a TFT having
higher performance.
[0088] While the invention has been shown and described in detail,
the foregoing description is in all aspects illustrative and not
restrictive. It is therefore understood that numerous modifications
and variations can be devised without departing from the scope of
the invention.
* * * * *