JP3346324B2 - Etching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method, and more particularly to an etching method for a metal wiring on which different kinds of metal films are stacked.

[0002]

2. Description of the Related Art In recent years, as liquid crystal display devices have become larger and higher in density, signal delay caused by electric resistance of gate bus lines and drain bus lines has become a serious problem. Therefore, in order to avoid signal delay, Al, Al alloy, Mo, and the like having a low specific resistance have been widely used as wiring materials.

However, when Al or an Al alloy is applied to, for example, a gate electrode and a gate bus wiring of a thin film transistor as shown in FIGS. 1 and 2, it is difficult to obtain good contact with ITO which is a transparent electrode film. It is difficult to use as a single-layer wiring. on the other hand,
When Mo is used as the wiring material, there is a drawback that the corrosion resistance to moisture is poor and the connection reliability cannot be secured at the terminal portion, and it is also difficult to use it as a single-layer wiring.

Therefore, regardless of the material used, it is necessary to laminate Ti or Cr on the upper layer, which has excellent contact with ITO and has high corrosion resistance. In addition, when forming a gate bus line and a drain bus line, a multi-layered metal film can be formed in a single photolithography step in order to form a multi-layered wiring without increasing the number of photolithography steps compared to the case of a single-layered wiring. A technology for continuously etching is essential.

However, when the etching of the laminated metal film is performed by dry etching, in order to control the cross-sectional shape, RIE (reactive ion etching) is required.
In addition to the restrictions on equipment that must be performed in the mode, there is a problem that the throughput is reduced. on the other hand,
In the conventional method of etching the upper metal film according to the resist pattern when performing the etching of the laminated wiring by wet etching, the lower metal film is etched using the upper metal film as a mask after the etching of the upper metal film. , Undercut occurs.

FIG. 7 shows the conventional etching method.
This will be described with reference to FIG. FIG. 7 shows a metal film laminated on a transparent glass substrate 11 (a lower film is a Mo film 32, and an upper film is a Ti film 3).
It is process sectional drawing which showed typically the process of pattern-processing 3) by wet etching.

[0007] First, as shown in FIG.
Then, a resist pattern 51 having a desired shape is formed by using a known lithography technique (see FIG. 7B). Next, as shown in FIG. 7C, the Ti film 33 is etched using an etching solution for selectively etching only the upper Ti film 33, and then the resist pattern 51 is removed. Subsequently, FIG.
As shown in (d), the Ti film 32 is used as a mask and Mo is used.
The Mo film 32 is etched using an etchant that selectively etches only the film 32.

At this time, since the etching proceeds isotropically, if the Mo film 32 is etched until the transparent glass substrate 11 is exposed, the Mo film 32 is etched to a portion under the Ti film 33, and the etched shape is obtained. Has an undercut shape in which the upper metal film protrudes from the lower metal film. When such an undercut occurs, there occurs a problem that the step coverage of the insulating film becomes poor in the subsequent insulating film forming process.

Therefore, a method of improving the step coverage of an insulating film formed thereover by etching so that the sectional shape of the laminated wiring becomes a step-like shape is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-191448. Kaihei 9-17119
No. 7, for example.

[0010] These methods will be described with reference to FIG. Steps (a) to (c) are the same as the method of FIG. 7 described above, except that after etching the upper metal film (Ti film 33), the substrate is reheated (reflowed) so that the resist pattern 51 is It is characterized by being deformed until it adheres to the surface of the metal film (Mo film 32) (see FIG. 8D). When the lower Mo film 32 is etched in this state, the Mo film 32 is covered in a wider area than the Ti film 33 by the resist pattern 51a spread by the reflow, so that the etching may progress to a lower portion of the Ti film 33. As a result, it can be processed into a step shape (see FIG. 8F).

[0011]

However, in the above-described etching method, a step of reflowing the resist pattern must be added, so that the manufacturing cost is increased and the resist pattern once solidified is deformed again. The entire substrate must be heated to such an extent that the patterning may be defective as a result.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a main object of the present invention is to etch a metal wiring on which different types of metal films are stacked in a step-like shape without reflowing a resist pattern. It is to provide an etching method which can be performed.

[0013]

In order to achieve the above object, according to a first aspect of the present invention, there is provided an etching method for wet-etching a laminated film in which a plurality of metal films made of different types of metals are laminated. After the resist pattern having a predetermined shape is formed on the laminated film, when selectively etching the upper metal film, the end of the resist pattern hangs down by its own weight, and the gap between the resist pattern end and the lower metal film is formed. Then, the upper metal film is over-etched to a predetermined position below the resist pattern so that the etchant of the lower metal film does not penetrate , and then the etch having a viscosity of about 20 centipoise or more is performed.
The lower metal film is etched with an etching solution .

Further, the present invention provides, in a second aspect,
(A) forming a lower metal film made of a first metal on a substrate, and then forming an upper metal film made of a second metal to a predetermined thickness; and (b) forming an upper metal film made of the second metal. Forming a resist pattern having a predetermined shape thereon; (c) selectively etching the upper metal film using the resist pattern as a mask; and (d) forming the resist pattern and the upper metal film. Etching the lower metal film with an etchant having a predetermined viscosity using the mask as a mask, wherein the upper metal film is etched when the upper metal film is etched in the step (c). By over-etching to a predetermined position below the resist pattern,
The end of the resist pattern hangs down by its own weight,
Etchant of the metal film of the lower layer between the underlying metal film and the resist pattern end portion so as not to penetrate the front
Etching the lower metal film in the step (d)
At the time of etching, the viscosity is about 20 centipoise or more
The lower metal film is etched with a liquid .

In the present invention, the is substantially 3μm inwardly from over etching amount of the resist pattern end portion, the thickness of the upper metal film is substantially 50nm or less this
Door is preferable.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An etching method according to the present invention comprises:
In a preferred embodiment, a Mo film (32 in FIG. 5) and a Ti film are formed on a transparent glass substrate constituting a liquid crystal display device.
When a metal film is formed by laminating a film (33 in FIG. 5) in this order to form a metal wiring, a Ti film is over-etched using a resist pattern formed thereon as a mask until a predetermined side etch occurs. By
The edge of the resist pattern hangs down by its own weight, so that the Mo film etchant having a predetermined viscosity does not penetrate between the edge of the resist pattern and the Mo film ,
An etchant with a viscosity of about 20 centipoise or more
This is for etching the metal film of the layer .

By etching in this manner, the cross-sectional shape of the metal wiring can be made stepwise, and the step coverage of the insulating film formed on the metal wiring can be improved.

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; FIG. This embodiment describes an example in which the etching method of the present invention is applied to an active matrix substrate. FIG. 1 is a circuit conceptual diagram showing an active matrix substrate of a liquid crystal display device, FIG. 2A is a plan view of one pixel portion including a thin film transistor (hereinafter abbreviated as TFT), and FIG. T
It is sectional drawing in the AA 'line of an FT part. FIG. 3 is a process cross-sectional view schematically showing a manufacturing process for obtaining the structure of FIG. Further, FIG. 4 is a process sectional view for schematically explaining the etching method of the present embodiment, and FIG. 5 is a sectional view showing dimensions of each part in a state where the upper metal film is etched.

First, the configuration of an active matrix substrate of a liquid crystal display device and one pixel portion including a TFT will be described with reference to FIGS. As shown in the figure,
The semiconductor device applied to this embodiment is a transparent glass substrate 11
, An island-shaped non-doped semiconductor layer 14 facing the gate electrode 12 with the gate insulating film 13 interposed therebetween, and a non-doped semiconductor layer 14 with the n-type semiconductor layer 15 interposed therebetween. Inverted staggered TF having a pair of connected source and drain electrodes 16 and 17
T.

Further, the gate bus line 1 is selectively formed on the surface of the transparent glass substrate 11 and connected to the gate electrode 12 via the gate bus line 18 and the gate insulating film 13.
1 and a drain bus line 19 connected to the drain electrode 17 and a pixel electrode 22 made of a transparent conductive film connected to the source electrode 16 via a contact hole 21 provided in the protective film 20 as shown in FIG. The active matrix substrate is made by disposing them in a matrix as shown in FIG. Then, the gate electrode 12 and the gate bus wiring 18 and the source and drain electrodes 16 and 17 and the drain bus wiring 1
No. 9 has a structure in which a Ti film is laminated on an upper layer and a Mo film is laminated on a lower layer.

Next, a method for manufacturing an active matrix substrate will be described. First, as shown in FIG.
The gate electrode 12 and the gate bus wiring 18 made of the upper Ti film 33 and the lower Mo film 32 are formed by known sputtering, photolithography, and etching. This manufacturing method will be described later in detail. Next, a gate insulating film 13 made of, for example, silicon nitride is coated to a thickness of about 400 nm by a plasma CVD method. Further, the non-doped semiconductor film is coated with a thickness of about 300 nm, and the n-type semiconductor film is coated thereon with a thickness of about 30 nm. Next, the non-doped semiconductor layer 14
And an n-type semiconductor layer 15 are formed in an island shape by etching (see FIG. 3B).

Thereafter, as shown in FIG. 3C, the upper layer Ti is again formed in the same manner as the gate electrode 12 and the gate bus wiring 18.
The source electrode 16, the drain electrode 17, and the drain bus wiring 19 are formed by a laminated wiring composed of the film 43 and the lower Mo film 42. Next, using the source and drain electrodes 16 and 17 as a mask, the n-type semiconductor layer 15 is removed by etching. Next, for example, about 20
After covering the entire TFT substrate with a protective film 20 made of 0 nm silicon nitride, only the contact hole 21 for connecting the pixel electrode and the source electrode 16 and the openings 31 and 41 for the gate and drain terminals are opened by etching ( FIG. 3D). Finally, a transparent conductive film made of, for example, indium tin oxide (hereinafter abbreviated as ITO) is formed for about 5 minutes.
Then, the pixel electrode 22 and the transparent electrode films for gate and drain terminals 34 and 44 are formed by photolithography and etching (see FIG. 3E).

Next, the upper Ti film 3 which is a feature of this embodiment
3. Gate bus wiring 1 having a laminated structure of lower Mo film 32
8. A method of manufacturing the gate electrode 12 will be described with reference to FIG. The source electrode 16, the drain electrode 17, and the drain bus wiring 19 having a stacked structure of the upper Ti film 43 and the lower Mo film 42 can be manufactured by the same method.

First, as shown in FIG. 4A, a Mo film 32 and a Ti film 33 are sequentially formed on a glass substrate 11 by a sputtering method using a Mo target and a Ti target. Regarding sputtering, either DC magnetron sputtering or RF magnetron sputtering may be used. The thickness of the Mo film 32 is about 200 to 300 nm in consideration of wiring resistance.
As will be described later, the thickness of the Ti film 33 is approximately 5
It is preferably 0 nm or less.

Thereafter, as shown in FIG. 4B, a positive photoresist pattern 51 is formed by photolithography, and the upper Ti film 33 is wet-etched with a hydrofluoric acid-based etchant. At this time, the resist pattern 51 is over-etched until it is substantially etched by 3 μm or more on one side. As shown in FIG. 4 (c), the shape of the resist here is in a state of being slightly hung by the weight of the resist itself.

Further, as shown in FIG.
The o film 32 is wet-etched with a phosphoric acid-based etchant having a viscosity of about 20 centipoise or more.
Then, since the etchant has a desired viscosity, it does not penetrate into the space between the resist pattern 51 and the lower Mo film 32, and the Mo film 32 can be etched according to the resist pattern 51. become.

To prevent the etching solution from penetrating, the viscosity of the phosphoric acid-based etching solution must be 20 centipoise or more, the side etch amount of the Ti film 33 should be approximately 3 μm or more, and the resist pattern 51 and the lower layer Mo
The interval between the films 32 is preferably about 50 nm or less, which is the reason why the thickness of the Ti film 33 is limited to about 50 nm or less.

The above effect can be obtained by reducing the thickness of the upper metal film to a predetermined value or less and overetching the upper metal film so that the upper metal film is side-etched to a predetermined position below the resist pattern. Without doing
This means that the metal wiring can be etched into a stepped cross-sectional shape, and this effect will be described in detail based on experimental results.

First, after the thickness of the Mo film 32 as the lower metal film is fixed at 200 nm, the thickness and the side etch amount of the Ti film 33 as the upper metal film are changed, and the etching of the laminated wiring is performed by the above method. As a result, as shown in Table 1, when the thickness of the Ti film 33 satisfies the two conditions of about 50 nm and the overetch of the Ti film 33 is approximately 3 μm on one side, the reflow of the resist pattern is not performed. Also, etching could be performed to a step-like cross-sectional shape as shown in FIG.

[0030]

[Table 1]

The reason why the reflow does not need to be performed is that the resist droops by its own weight due to the side etch of about 3 μm, and the gap between the resist of 50 nm originally and the lower metal film is further narrowed. This is probably because the etchant cannot penetrate into the gap.

However, the results in Table 1 are obtained by using a phosphoric acid-based etching solution having a high viscosity of 43 centipoise as an etching solution for the lower metal film. Therefore, depending on the viscosity of the etchant, the etchant penetrates into the gap between the resist pattern 51 and the Mo film 32 as the lower metal film,
The Mo film 32 is also side-etched, and may not be etched according to the resist pattern.

Then, next, the thickness of the Ti film 33 is set to 50 n.
For the sample satisfying the two conditions in which the overetch amount of the m and Ti films 33 is approximately 3 μm or more on one side, the lower layer Mo
As a result of changing the viscosity of the etchant of the film 32 and etching the laminated wiring by the above method, when the etchant of 43 centipoise and 20 centipoise was used,
Although it was possible to etch in steps as intended,
When an etchant of 11 centipoise was used, it was confirmed that the etchant penetrated between the resist pattern 51 and the lower Mo film 32, and the lower Mo film 32 was also side-etched (see Table 2).

[0034]

[Table 2]

However, in the evaluation of Table 2, since the viscosity was changed by changing the mixing ratio of the phosphoric acid-based etching solution, the etching rate was also changed at the same time. It may be simply because the etching rate is slow. Therefore, Table 2
Cannot be concluded that the method is applicable to all phosphoric acid-based etchants having a viscosity of 20 centipoise. Then, in order to further determine the viscosity itself that cannot penetrate into the gap of 50 nm, the following evaluation was performed.

First, a film having a thickness of 50
The Mo film 32 of nm is coated, and a photoresist wiring pattern is formed by photolithography. Next, the Mo film 32 is etched with a phosphoric acid-based etchant so that a side etch of about 3 μm on one side occurs.
FIG. 5 shows the structure of the sample at this time. The sample was etched with a phosphoric acid-based etchant using the amount of side etch as an initial value, and the etching rate in the direction parallel to the substrate was measured from the increase in side etch. FIG. 6 shows the result.

In FIG. 6, the horizontal axis indicates the viscosity of the etching solution, and the vertical axis indicates the side etch index defined this time (≡etching rate in the direction parallel to the substrate / etching rate in the direction normal to the substrate). FIG. 6 shows that at a viscosity of 20 centipoise or more, the etching rate in the direction parallel to the substrate is zero, regardless of the value of the etching rate in the direction normal to the substrate.
From the above results, it was confirmed that the etching solution having a viscosity of about 20 centipoise or more did not penetrate into the 50 nm gap between the resist and the lower metal film regardless of the etching rate in the normal direction of the substrate.

As described above, a wiring having a laminated structure composed of the first layer metal film made of the Mo film 32 and the second layer metal film made of the Ti film 33 provided on the first layer metal film, In the method of forming an electrode by wet etching, the thickness of the upper Ti film 33 is set to approximately 50 nm or less,
When the film 33 is etched, one side is over-etched so as to be approximately 3 μm or more on one side.
By using an etchant having a viscosity of about 20 centipoise or more as the etchant 2, the upper layer T
After the etching of the i-film 33, the lower Mo film 32 is continuously etched without reheating the resist and reflowing, whereby the wiring cross section can be formed in a stepped shape.
Therefore, an increase in the number of steps for reheating and dry etching of the resist can be prevented, the manufacturing cost can be reduced, and the deformation and deterioration of the resist pattern due to reheating can be prevented. Can be improved.

Further, in the above-described embodiment, the wiring and the electrode in which the Ti film 33 is laminated on the upper layer and the Mo film 32 is laminated on the lower layer have been described. However, the present invention is not limited to the above-mentioned constitution, and the gate bus wiring and the Regarding the electrodes, the upper layer is a Cr film,
Even when the lower layer is made of an Al film or an Al alloy film, it can be etched into a stepwise cross-sectional shape by the same etching method as in the above-described embodiment. In this case, Cr
A nitric acid-based etching solution was used as the etching solution for A.
As the etchant for 1 or Al alloy, a phosphoric acid-based etchant having a viscosity of about 20 centipoise or more may be used as in the above-described embodiment.

[0040]

As described above, according to the etching method of the present invention, when etching a metal film having a laminated structure, after etching the upper metal film, the wiring section is formed in a step-like shape without reheating the resist. Therefore, there is no need to newly add a step for resist reheating or dry etching, and the effect that the step coverage of the insulating film formed on the metal wiring can be improved. Further, since the resist reheating step is not performed, the deformation and deterioration of the resist pattern due to the reheating can be prevented, so that the production yield can be improved.

The reason is that in the present invention, when wet-etching a wiring and an electrode having a laminated structure composed of a lower metal film and an upper metal film provided thereon, the film thickness of the upper film is approximately 50 nm. The following, when etching the upper layer film, side-etch approximately 3 μm or more on one side,
By using an etchant having a viscosity of about 20 centipoise or more as an etchant for the underlayer film, the etchant can be prevented from seeping between the resist pattern and the underlayer film, and the underlayer film is excessively etched. It is because it can prevent.

[Brief description of the drawings]

FIG. 1 is a circuit conceptual diagram showing an active matrix substrate of a liquid crystal display device to which the present invention is applied.

FIGS. 2A and 2B are views showing one pixel portion including a thin film transistor of a liquid crystal display device to which the present invention is applied, where FIG. 2A is a plan view and FIG. 2B is a cross-sectional view taken along line AA ′ of FIG. is there.

FIG. 3 is a process sectional view schematically showing a manufacturing process of a thin film transistor of a liquid crystal display device to which the present invention is applied.

FIG. 4 is a process sectional view for explaining an etching method according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view showing an etching state of the etching method according to one embodiment of the present invention.

FIG. 6 is a diagram for explaining an effect of the present invention.

FIG. 7 is a process sectional view showing a conventional etching method.

FIG. 8 is a process sectional view showing a conventional etching method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Transparent glass substrate 12 Gate electrode 13 Gate insulating film 14 Non-doped semiconductor layer 15 N-type semiconductor layer 16 Source electrode 17 Drain electrode 18 Gate path wiring 19 Drain path wiring 20 Protective film 21 Contact hole 22 Pixel electrode 23 Gate terminal 24 Drain terminal 31 41 Opening 32, 42 Mo film 33, 43 Ti film 34, 44 Transparent electrode film 51 Resist pattern 51a Reflowed resist pattern

Claims (7)

(57) [Claims] 1. An etching method by wet etching of a laminated film in which a plurality of metal films made of different kinds of metals are laminated, wherein after forming a resist pattern of a predetermined shape on the laminated film, an upper metal film is selectively formed. When etching to
The end of the resist pattern hangs down by its own weight,
The upper metal film is over-etched to a predetermined position below the resist pattern so that the etchant of the lower metal film does not penetrate between the end portion of the resist pattern and the lower metal film, and then the Is about 20 centipoise or more etchant
And etching the lower metal film . (A) forming a lower metal film of a first metal on a substrate, and then forming an upper metal film of a second metal to a predetermined thickness; and (b) Forming a resist pattern of a predetermined shape on the upper metal film; (c) selectively etching the upper metal film using the resist pattern as a mask; (d) forming the resist pattern and Etching the lower metal film with an etchant having a predetermined viscosity using the upper metal film as a mask. In the method of etching the upper metal film in the step (c), By over-etching the upper metal film to a predetermined position under the resist pattern, the edge of the resist pattern hangs down by its own weight, and So that the etching solution of the lower metal film does not penetrate between the end of the strike pattern and the lower metal film.
And etching the lower metal film in the step (d).
Etching with a viscosity of about 20 centipoise or more
And etching the lower metal film with an etching solution . 3. The etching method according to claim 1, wherein the amount of over-etching is approximately 3 μm inside the edge of the resist pattern. 4. The etching method according to claim 1, wherein the thickness of the upper metal film is about 50 nm or less. Wherein said upper metal layer is a Ti film, an etching method according to any one of claims 1乃<br/> optimum 4, wherein the lower metal film is a Mo film . Wherein said upper metal layer is a Cr film, an etching method according to any one of claims 1 to 4, wherein the lower metal film is an Al film or Al alloy film. 7. The etching method according to any one of claims 1 to 6 is applied to the metal film laminated on the active matrix substrate of a liquid crystal display device.