JP3182351B2 - Method for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor used in a liquid crystal display device used for an information processing terminal or a video device, and a method of manufacturing the same. And a method of manufacturing the same. .

[0002]

2. Description of the Related Art Conventionally, a thin film transistor having a pixel electrode formed on a source / drain electrode and a method of manufacturing the same are described in, for example, Kondo et al., A-Si TFT-LCD.
Development of a device simulator for the Internet, IEICE technical report, EID
92-80 (1992-12), pages 23 to 27 are known.

FIG. 5 is a sectional view showing the structure of such a conventional thin film transistor. In the figure, 1 is a substrate made of glass, 2 is a gate electrode whose surface is covered with a gate insulator layer 3, 4, 5, and 6 are an insulator layer, a semiconductor layer,
A channel protective film, 7 is an n-type contact layer by adding impurities, 8 is a source / drain electrode, 9 is a pixel electrode connected to the source / drain electrode 8, and 10 is a protective film.

This thin film transistor is manufactured by the following manufacturing steps. First, after a gate pattern made of Ta is formed on a substrate 1 made of glass, the surface of the gate pattern is made to be Ta ₂ O ₃ by anodic oxidation.
A gate electrode 2 and a gate insulator layer 3 are formed. Next, a SiN film serving as the insulating film 4, an a-Si film, and SiN
After the films are formed in this order, the uppermost SiN film is patterned to form the channel protection film 6. Next, after forming an n-type microcrystalline Si film by adding impurities to the entire surface,
The microcrystalline Si film is patterned together with the a-Si film into a shape corresponding to the source / drain regions to form a contact layer 7 and a semiconductor layer 5. Next, after a Ti film is formed on the entire surface, the Ti film is patterned into a source / drain wiring shape to form a source / drain electrode 8. Next, a film of indium tin oxide (hereinafter abbreviated as ITO) is formed on the entire surface and then patterned to form the pixel electrode 9. Finally, a protective film 10 is formed on the entire surface to form a thin film transistor.

[0005]

In the conventional thin film transistor shown in FIG. 5, the pixel electrode 9 is formed so as to extend over the source / drain electrode 8, and a part of the pixel electrode is formed on the source / drain electrode 8. By connecting to the upper surface, the area of the pixel electrode 9 is increased, thereby making it possible to obtain a liquid crystal display device having a large aperture ratio. However, the source / drain electrodes 8 made of Ti
However, there is a problem that electrical connection having good ohmic characteristics and sufficiently low resistance cannot be obtained.

The present invention has been made in view of the above problems, and provides a thin film transistor which exhibits good ohmic characteristics between a source / drain electrode and a pixel electrode and is connected to a sufficiently low resistance, and a method for manufacturing the same. The purpose is to:

[0007]

In order to achieve the above object, a method of manufacturing a thin film transistor according to the present invention comprises the steps of:
Pixel electrode made of indium tin oxide for drain electrode
Method for manufacturing a thin film transistor by connecting
Source / drain electrodes whose top layer is a molybdenum layer
Poles and have openings on the source / drain electrodes.
To form an organic insulating film,
A portion of the upper surface exposed from the opening of the organic insulating film;
After exposure to oxygen plasma and further ultrasonic washing, reduce
And a part thereof is formed on the upper surface of the source / drain electrode.
Inju so that it is placed in the part exposed from the opening
Forming a pixel electrode made of tin oxide on the organic insulating film
It is characterized by doing. In the above manufacturing method, molybdenum
Contact between indium tin oxide and indium tin oxide
Good ohmic contact between the source / drain electrode and the pixel electrode.
Thin-film transistor that exhibits good
A transistor can be manufactured. In addition, the pixel electrode on the substrate
A liquid crystal display device with a large aperture ratio and a large area can be obtained.
It becomes possible. According to the above manufacturing method,
Pixel electrode with uniform film characteristics without any
Simple thin film transistor with stable driving characteristics
Can be manufactured. Further, according to the manufacturing method,
Molybdenum upper surface openings for source and drain electrodes
Organic substances adhering to the part exposed from the part
And remains after oxygen plasma treatment
Organic waste is removed by ultrasonic washing
As a result, the source / drain electrodes and the pixel
The ohmic properties of the pole connections are further improved,
First, a thin film transistor with further reduced resistance is manufactured.
Can be

[0008]

[0009]

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the present invention, the connection surface of the source / drain electrodes of the thin film transistor to the pixel electrode made of ITO is made of molybdenum.

The source / drain electrodes are generally formed by using a known film forming technique such as a sputtering method or a vacuum deposition method to form an electrode metal film having a molybdenum layer at least on the uppermost layer and patterning the electrode metal film into a predetermined shape. Formed by When the source / drain electrode (electrode metal film) is formed of a single layer of a molybdenum layer, the thickness of the molybdenum layer is usually 0.5 to 1.0 μm. this is,
If the thickness is less than 0.5 μm, the image quality tends to deteriorate due to the influence of the source / drain wiring resistance, and if the thickness exceeds 1.0 μm, the film tends to peel off. As described above, when the source / drain electrode (electrode metal film) is formed of a single layer of a molybdenum layer, the thickness of the molybdenum layer is increased to reduce the resistance of the source / drain electrode. Is a problem in the adhesiveness to the surface to be formed.

Therefore, in order to reduce the resistance of the source / drain electrodes, the source / drain electrodes (electrode metal films) are usually multi-layered. In this case, the source / drain electrode (electrode metal film) has a two-layer structure including a molybdenum layer and a titanium layer, a chromium layer, or a tantalum layer, or a molybdenum layer, an aluminum layer, a titanium layer, a chromium layer, or A three-layer structure including a tantalum layer is preferable.

In the case of a two-layer structure, it is preferable that the thickness of the molybdenum layer is 0.05 to 0.1 μm and the thickness of the titanium layer, chromium layer or tantalum layer is 0.3 to 0.5 μm. In the case of a three-layer structure, the thickness of the molybdenum layer is set to 0.0
5 to 0.1 μm, and the thickness of the aluminum layer is 0.2 to
Preferably, the thickness is 0.5 μm, and the thickness of the titanium layer, the chromium layer, or the tantalum layer is 0.05 to 0.1 μm.

The difference between the two-layer structure and the three-layer structure is whether or not an aluminum layer is formed. In the case of the three-layer structure, the resistance (wiring resistance) of the source / drain electrodes is greatly reduced by the aluminum layer. can do. This is advantageous in increasing the area of a liquid crystal display element in recent years, and for stabilizing the operation characteristics of the element at high speed.

As a matter of course, when the source / drain electrodes have a single-layer structure of a molybdenum layer, the manufacturing process can be simplified as compared with the case of a two-layer structure or a three-layer structure. The cost of the transistor can be reduced.

The pixel electrode made of ITO is formed by a known film forming technique such as a sputtering method or a vacuum evaporation method.
It is formed by patterning an electrode metal film made of TO into a predetermined shape. The thickness of the electrode metal film made of ITO is not particularly limited, but is generally 0.05 to 0.15 μm.
m.

The connection between the pixel electrode made of ITO and the source / drain electrode is formed, for example, by extending the pixel electrode made of ITO to above the source / drain electrode and forming a part of the pixel electrode on the upper surface of the source / drain electrode. After forming an organic insulating film having an opening on the source / drain electrodes, forming a pixel electrode made of ITO on the organic insulating film, and forming a part of the pixel electrode on the organic insulating film. Is connected to the upper surface of the source / drain electrode through the opening. The organic insulating film having the opening,
Although the material and processing method are not particularly limited, it is generally formed by photolithography using a photoresist such as an acrylic resin or a polyamide resin.

When an organic insulating film having an opening is formed by photolithography, the opening has a smaller opening area toward the lower side in the thickness direction of the organic insulating film, and the inner surface becomes an inclined opening. . For this reason,
When an organic insulating film having an opening on the source / drain electrode is formed by photolithography, and a part of the pixel electrode is connected to the upper surface of the source / drain electrode through the opening of the organic insulating film, the following advantages are obtained. . That is, when the pixel electrode made of ITO is extended to above the source / drain electrode and a part of the pixel electrode is directly connected to the upper surface of the source / drain electrode, the end portion of the source / drain electrode is located at Since the pixel electrode cannot follow the shape of this end portion when the step is large, a cut portion or an under-thickness portion may be generated in the pixel electrode. The opening of the organic insulating film formed by photolithography has a smaller opening area toward the lower side in the thickness direction of the organic insulating film, and the inner surface becomes an inclined opening. When the pixel electrode is formed, a part of the pixel electrode is formed stably along the inclined inner surface in the opening from the upper surface of the organic insulating film to the upper surface of the source / drain electrode, and as a result, Interrupted (step line portion) and without excessive small portion of the thickness, are reliably connected to the upper surface of the source and drain electrodes. Note that an unnecessary organic film remains on the upper surfaces of the source / drain electrodes exposed from the openings after the openings are formed in the organic insulating film. Therefore, after forming an opening in the organic insulating film, the source
If a part of the pixel electrode is directly connected to the upper surface of the drain electrode, the connection resistance increases due to the influence of the unnecessary organic substances. Therefore, after forming the opening in the organic insulating film, the upper surface of the source / drain electrode exposed from the opening is exposed to oxygen plasma to remove the remaining unnecessary organic film, and then the pixel electrode is formed. Is preferred. Further, even if the upper surface of the source / drain electrode is exposed to oxygen plasma to remove the organic film, some shavings (scrap) remain. For this reason, it is more preferable to form the pixel electrode after removing the shavings (dust) by ultrasonically washing the upper surfaces of the source / drain electrodes after being exposed to the oxygen plasma.

FIG. 3 is a cross-sectional view of a main part of a contact chain used for evaluating electric characteristics of a connection portion between a source / drain electrode and a pixel electrode in the thin film transistor of the present invention. 5 is a source / drain electrode material film, 13 is a pixel electrode material film, and 12 is an interlayer insulating film between the source / drain electrode material film 11 and the pixel electrode material film 13. Is an organic insulating film. The following four types of contact chains having the above structure were manufactured, and the electrical characteristics of the connection portions between the source / drain electrode material films and the pixel electrode material films were evaluated.

A first contact chain was manufactured as follows. A Ti film having a thickness of 150 nm is formed on a substrate 1 made of glass by a sputtering method using Ar gas, and the Ti film is patterned so that one of the Ti films has a thickness of about 20 μm.
A source / drain electrode material film 11 composed of an island-shaped pattern of 60 μm square is formed. Next, the acrylic resin HR
Approximately 3 μm thick using C305 (trade name, manufactured by JSR)
After the organic insulating film 12 is applied, openings having a diameter of 8 μm are formed at two places of the organic insulating film 12 on the source / drain electrode material film 11 by photolithography. Next, an ITO film having a thickness of 150 nm is formed by a sputtering method using a mixed gas of Ar / O ₂ , and this ITO film is passed through the opening to form the source / drain electrode metal 1.
Then, a pixel electrode material film 13 is formed by patterning so as to be connected to each other.

The second contact chain is composed of the source / drain electrode material film 1 in the first contact chain.
1 was not a Ti film but a Mo film having a thickness of 150 nm formed by a sputtering method using an Ar gas, and the other configurations were completely the same.

The third contact chain is formed of the source / drain electrode material film 1 similarly to the second contact chain.
1 is a Mo film, and after forming an opening in the organic insulating film 12 by photolithography and before forming the pixel electrode material film 13 made of ITO, the source / drain electrode material film 11 ( The Mo film was exposed to oxygen plasma (0.9 Torr, 0.03 W / cm ² ) for 5 minutes, and the other configuration was exactly the same as that of the first contact chain.

The fourth contact chain is formed of the source / drain electrode material film 1 similarly to the second contact chain.
1 is a Mo film, and after forming an opening in the organic insulating film 12 by photolithography and before forming the pixel electrode material film 13 made of ITO, the source / drain electrode material film 11 ( The Mo film) was exposed to oxygen plasma (0.9 Torr, 0.03 W / cm ² ) for 5 minutes, and further washed with ultrasonic waves (Megasonic: 950 kHz, 1
200 W) for 5 minutes, and the other configuration was exactly the same as that of the first contact chain.

FIG. 4 shows the results of the evaluation. Between AB in FIG. 3 (that is, for one contact chain, the connection portion is 3
There are four. 4) shows the current-voltage characteristics. (− × −) in FIG. 3 indicates the characteristic line of the first contact chain, and (−−−)
○-) is the characteristic line of the second contact chain, (-□
-) Is the characteristic line of the third contact chain, (-△-)
Are the characteristic lines of the fourth contact chain.

FIG. 4 shows that the source / drain electrode material film 11 is formed of a first contact chain (-
In the case of ×-), the current / voltage characteristics are non-linear, good ohmic characteristics are not obtained, and the resistance per connection is as high as about 800Ω (when 5 V is applied in FIG. 4). In the case where the source / drain electrode material film 11 is the second contact chain (− ○ −) made of a Mo film, the current / voltage characteristics are closer to linear compared to the case of the first contact chain, and the ohmic characteristics are improved. It can be seen that the resistance per connection is also reduced to about 500Ω (when 5 V in FIG. 4 is applied). Further, in the case of the third contact chain (-□-) in which the source / drain electrode electrode material film 11 is an Mo film and the Mo film is exposed to oxygen plasma before the pixel electrode material film 13 is formed, the current / voltage It can be seen that the characteristics are almost linear and good ohmic characteristics are obtained, and the resistance per connection is also reduced to about 110Ω (when 5 V is applied in FIG. 4). Further, the fourth contact chain (− △ −) in which the source / drain electrode electrode material film 11 is made of Mo film, the Mo film is exposed to oxygen plasma before the pixel electrode material film 13 is formed, and ultrasonic cleaning is performed. In the case of ()), it can be seen that the current-voltage characteristics are almost linear and good ohmic characteristics are obtained, and the resistance value per connection is also reduced to about 100Ω (when 5 V in FIG. 4 is applied).

[0032]

【Example】

(Embodiment 1) FIG. 1 is a sectional view showing a structure of a thin film transistor according to Embodiment 1 of the present invention, and FIG.
FIGS. 2A to 2B are cross-sectional views showing the steps of manufacturing the thin film transistor shown in FIG. In these figures, FIG.
The same reference numerals denote the same or corresponding portions, and 21 denotes a source / drain lower electrode made of a barrier metal (Ti);
Reference numeral 22 denotes a source / drain middle layer electrode made of a low-resistance metal (Al), and reference numeral 23 denotes Mo that is joined (connected) to the pixel electrode 9 through an opening formed in the organic insulating film 12 using the organic insulating film 12 as interlayer insulation. It is a source / drain upper layer electrode composed of

Hereinafter, the manufacturing process will be described with reference to FIG. First, a 350 nm-thick Al layer was formed on a substrate 1 made of glass (Corning Co., # 1737 glass (trade name)).
After a Zr alloy (Zr: 1 atomic%) film is formed by a sputtering method using Ar gas, it is etched into a gate pattern, and the surface is further AlZed by anodic oxidation.
A gate electrode 2 and a gate insulator layer 3 were formed as an r-alloy oxide film (FIG. 2A).

Next, a plasma enhanced chemical vapor deposition (hereinafter referred to as p
Abbreviated as a CVD method), a silicon nitride film (SiNx) serving as the insulating film 4, an a-Si film serving as the semiconductor layer 5,
A silicon nitride film (SiN) serving as a channel protection film 6 described later
x) in order of thickness 200 nm, 50 n
After forming a film with a thickness of 150 nm, the upper silicon nitride film (SiNx) was patterned to form a channel protective film 6 (FIG. 2B). Next, p-
After forming an n-type amorphous Si film having a thickness of 50 nm by adding an impurity of P (phosphorus) by a CVD method to form a contact layer 7, Ti, Al and Mo are further mixed with Ar gas. 100n thick each by sputtering method used
After forming a film having a thickness of m, 350 nm, and 100 nm, these are patterned into a source / drain region shape together with the semiconductor layer 5 and the contact layer 7 by etching to form a source / drain lower layer electrode 21 made of Ti;
1 and a source / drain upper electrode 23 made of Mo were formed.
(C)). Here, the channel protective film 6 is formed of the semiconductor layer 5.
Is used to protect the semiconductor layer 5 in a portion to be a channel of the thin film transistor when etching is performed.

Next, an organic insulating film 12 made of an acrylic resin (HRC305 (trade name, manufactured by JSR Corporation)) having a thickness of about 3 μm is applied to the entire surface of the substrate, and then the source / drain upper electrode 23 is formed by photolithography. 8μ in diameter
m openings were formed (FIG. 2D).

Next, a thickness of 150 nm is applied to the entire surface of the substrate.
An ITO film is formed by a sputtering method using an Ar / O ₂ mixed gas, and the ITO film is formed along the inclined inner surface of the opening of the organic insulating film 12 with the source film.
The pixel electrode 9 was formed by etching into a predetermined pixel electrode pattern so that a portion joined (connected) to the upper surface of the drain upper layer electrode 23 was left, thereby completing the thin film transistor (FIG. 2E). ).

In the thin film transistor of the present embodiment thus obtained, the pixel electrode 9 made of an ITO film is connected to the upper surface of the upper electrode 23 made of Mo as the source / drain electrode, and the source / drain electrode and the pixel electrode 9 are connected. Was connected with good ohmic characteristics and low resistance (about 500Ω). Further, the resistance (wiring resistance) of the source / drain itself was sufficiently reduced by the source / drain middle layer electrode 22 made of Al (0.15Ω / □).

(Embodiment 2) Since the manufacturing process of the thin film transistor according to the second embodiment is obtained by adding another process to the manufacturing process of the thin film transistor of the first embodiment, only this point will be described in detail.

First, the same steps as in Example 1 (FIG. 2A)
After that, an opening having a diameter of 8 μm was formed on the organic insulating film 12 (see FIG. 2D). Next, the surface of the source / drain upper layer electrode 23 exposed from the opening is subjected to oxygen plasma (0.9 Torr, 0.03
W / cm2) for 5 minutes. Next, an ITO film having a thickness of 150 nm was formed on the entire surface of the substrate by a sputtering method using an Ar / O ₂ mixed gas in the same manner as in Example 1, and the ITO film was formed on the organic insulating film 12. Etching is performed in a predetermined pixel electrode pattern so that a portion joined (connected) to the upper surface of the source / drain upper layer electrode 23 remains along the inclined inner surface of the opening.
The pixel electrode 9 was formed, and the thin film transistor was completed (see FIG. 2E).

In the thin film transistor of this embodiment thus obtained, the pixel electrode 9 made of an ITO film is connected to the upper surface of the upper electrode 23 made of Mo as the source / drain electrode. Was connected with excellent ohmic characteristics and extremely low resistance (about 100Ω).

(Embodiment 3) Since the manufacturing process of the thin film transistor according to the third embodiment is obtained by adding another process to the manufacturing process of the thin film transistor of the second embodiment, only this point will be described in detail.

First, the same steps as in the first and second embodiments (FIG. 2)
After passing through (a) to FIG. 2 (c)), an opening having a diameter of 8 μm was formed on the organic insulating film 12 (see FIG. 2 (d)).
Next, as in the second embodiment, the surface of the source / drain upper layer electrode 23 exposed from the opening is exposed to oxygen plasma (0.
9 Torr, 0.03 W / cm 2) for 5 minutes, the surface of the source / drain upper layer electrode 23 was subjected to ultrasonic water washing (megasonic: 950 kHz, 1200 W) for 5 minutes, and then spin-dried. Next, a 150 nm-thick ITO film was formed on the entire surface of the substrate in the same manner as in Example 1.
The ITO film is bonded to the upper surface of the source / drain upper electrode 23 along the inclined inner surface of the opening of the organic insulating film 12 by sputtering using an r / O ₂ mixed gas. )
The pixel electrode 9 was formed by etching into a predetermined pixel electrode pattern, and a thin film transistor was completed (FIG. 2).
(E)).

In the thin film transistor of the present embodiment thus obtained, the pixel electrode 9 made of an ITO film is connected to the upper surface of the upper electrode 23 made of Mo as the source / drain electrode. Was connected with excellent ohmic characteristics and extremely low resistance (about 100Ω).

[0044]

As described above, according to the thin film transistor of the present invention, in a thin film transistor in which a pixel electrode made of indium tin oxide is connected to a source / drain electrode, the source / drain electrode is connected to the pixel electrode. By making the connection surface a surface made of molybdenum, the connection between the source / drain electrode and the pixel electrode is connected with good ohmic characteristics and low resistance. As a result, the drive characteristics are stabilized and the image quality is improved. There is an effect that a liquid crystal display device can be obtained.

According to the method of manufacturing a thin film transistor of the present invention, a method of manufacturing a thin film transistor in which a pixel electrode made of indium tin oxide is connected to a source / drain electrode, wherein the uppermost layer is made of a molybdenum layer After forming the source / drain electrodes, the pixel electrode made of indium tin oxide is formed so that at least a part thereof is disposed on the upper surface of the source / drain electrodes. In addition, there is an effect that the thin film transistor of the present invention can be easily manufactured with good ohmic characteristics and low resistance connected between the pixel electrodes.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a thin film transistor according to Embodiment 1 of the present invention.

2A to 2E are cross-sectional views (FIGS. 2A to 2E) showing process steps of manufacturing the thin film transistor shown in FIG.

FIG. 3 shows a source and a transistor in the thin film transistor of the present invention.
FIG. 4 is a cross-sectional view of a main part of a contact chain used for evaluating electric characteristics of a connection portion between a drain electrode and a pixel electrode.

4 is a diagram showing a result (current / voltage characteristic) of an evaluation test of electrical characteristics of the contact chain shown in FIG.

FIG. 5 is a cross-sectional view illustrating a configuration of a conventional thin film transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Gate insulator layer 4 Insulating film 5 Semiconductor layer 6 Channel protective film 7 Contact layer 8 Source / drain electrode 9 Pixel electrode 10 Protective film 11 Source / drain electrode 12 Organic insulating film 13 Pixel electrode material film 21 Source・ Drain lower layer electrode 22 Source / drain middle layer electrode 23 Source / drain upper layer electrode

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01L 21/768 H01L 21/302 NG02F 1/136 500 (56) References JP-A-4-253342 (JP, A) JP Sho 64-68728 (JP, A) JP-A-6-230427 (JP, A) JP-A 8-15731 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 29 / 786 H01L 21/28 H01L 21/304 642 H01L 21/304 645 H01L 21/3065 H01L 21/336 H01L 21/768 G02F 1/1368

Claims (1)

(57) [Claims] 1. Indium tin for a source / drain electrode
Thin film transistor connecting pixel electrodes made of oxide
A source / drain electrode comprising a molybdenum layer as an uppermost layer.
Formed, an organic insulating having an opening in the source and drain electrodes on the
A film is formed on the upper surface of the source / drain electrodes before the organic insulating film;
The part exposed from the opening is exposed to oxygen plasma and
After washing with ultrasonic water, at least a part of the upper surface of the source / drain electrode
So that it is located at the portion exposed from the opening
A pixel electrode made of judium tin oxide is placed on the organic insulating film.
Method of manufacturing thin film transistor characterized by forming on a thin film
Law.