JPH08288519A - Thin film transistor, manufacturing method thereof and liquid crystal display system - Google Patents

Abstract

PURPOSE: To avoid the burning or after image due to block parting on display or the dispersion in introduced voltage while enhancing the TFT characteristics. CONSTITUTION: An insulating film 3 covering a patterned shielding film 2 is formed on a transparent substrate 1. Next, a source region 5 and a drain region 5 made of the first low resistant semiconductor layers are formed in mutually separated state to be respectively connected to a source electrode 4 and a drain electrode 4. Next, the second semiconductor layer 6 is formed extending over the source region 5 and the drain region 5 to form a gate electrode 8 on these regions 5 through the intermediary of a gate insulating film 7. In such a constitution, the first semiconductor layer is formed of the films 5 while the source.drain regions 5 and the gate electrode 8 are self-aligningly formed with the patterned shielding film 2.

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 for, for example, a switching element of a liquid crystal display device, a manufacturing method thereof, and a liquid crystal display device.

[0002]

2. Description of the Related Art There are various types of thin film transistors (TFTs). For example, in a staggered TFT, a source and drain electrode portion is provided on one side with a low-resistance semiconductor layer sandwiched, and a gate electrode is provided on the other side with a gate insulating film interposed between the source and drain electrodes. The part is arranged on the side of the insulating substrate.

The low resistance semiconductor layer in such a staggered TFT is formed on the source and drain electrode portions which are transparent electrodes by decomposing PH ₃ gas by plasma discharge in a plasma CVD (P-CVD) apparatus. Then, the first semiconductor layer is selectively formed, and an amorphous silicon (a-Si) layer is formed thereon as a second semiconductor layer.

[0004]

However, the conventional method has an advantage that the exposure step for patterning the first semiconductor layer can be reduced, but the resistance of the obtained first semiconductor layer is reduced. There is a problem that the TFT characteristics are high and the leak current between the source and the drain is large, so that the TFT characteristics are not good as compared with TFTs having other structures.

Further, in order to solve the above-mentioned difficulties, even if the low resistance first semiconductor layer to be the source and drain electrode portions is formed by film formation, the source and drain regions and the gate electrode are self-aligned. There was a problem that it could not be manufactured. Further, when such a TFT is used as a switching element in a liquid crystal display device, there is a problem that a block separation on the display occurs in each exposure area of the stepper, and burn-in and an afterimage occur due to variations in pull-in voltage. It was

The present invention has been made in order to solve the problems of the prior art, and it is possible to form a low resistance source region and drain region to improve the TFT characteristics, and at the same time, to provide a source region and a drain region. An object of the present invention is to provide a TFT capable of forming a good display by forming a gate electrode in a self-aligned manner, a manufacturing method thereof, and a liquid crystal display device.

[0007]

A TFT of the present invention comprises a source region and a drain made of a low resistance first semiconductor layer on an insulating film formed on a transparent substrate so as to cover a patterned light shielding film. A gate electrode is formed on the second semiconductor layer formed over the source region and the drain region with a gate insulating film interposed therebetween, and the source electrode is formed on the source region. Are electrically connected to the drain region, a drain electrode is electrically connected to the drain region, and the source region, the drain region, and the gate electrode are formed in a self-aligned manner with the light-shielding film. The above object is achieved by the above.

The first semiconductor layer may be made of a microcrystalline semiconductor or a polycrystalline semiconductor.

The gate electrode may be a transparent electrode or a combination of a transparent electrode and a metal electrode.

The light-shielding film may be used as an auxiliary capacitance electrode or a black matrix of a liquid crystal display device.

The second semiconductor layer may be made of amorphous silicon, amorphous silicon germanium or amorphous silicon carbon, or may be made of polycrystalline silicon, polycrystalline silicon germanium or polycrystalline silicon carbon, or microcrystalline silicon. ,
It may be made of microcrystalline silicon germanium or microcrystalline silicon carbon.

The method of manufacturing a TFT according to the present invention comprises the steps of forming a light-shielding film on a transparent substrate, patterning the light-shielding film, forming an insulating film over the light-shielding film, and a low-resistance first insulating film on the insulating film. A step of forming a semiconductor layer, and a step of applying a negative resist on the first semiconductor layer and exposing from the back surface side of the substrate to pattern the source region and the drain region which are separated from each other in a self-aligned manner with the light shielding film. A step of forming a second semiconductor layer over the source region and the drain region, and forming a gate insulating film on the second semiconductor layer; and forming a transparent conductive film on the gate insulating film. A step of forming, a step of applying a positive resist on the transparent conductive film and exposing from the back side of the substrate to pattern the gate electrode in a self-aligned manner with the light-shielding film, and a step of connecting to the source region to form the source electrode To And forming a drain electrode connected to the drain region, the object is achieved.

In the liquid crystal display device of the present invention, a liquid crystal layer is provided between a pair of substrates, and the TFT is provided on one of the pair of substrates.
Are formed as switching elements, which achieves the above object.

[0014]

In the TFT of the present invention, since the first semiconductor layer is formed by film formation, a low resistance source region and drain region can be obtained, and the leak current between the source and drain can be reduced. it can.

When a negative resist is used in the patterning of the first semiconductor layer and a positive resist is used in the patterning of the transparent electrode to be the gate electrode, the back side of the substrate is exposed to light and the light-shielding film formed by patterning The source region, the drain region, and the gate electrode can be formed in a consistent manner.

By using a combination of a transparent electrode and a metal electrode as the gate electrode, it is possible to cope with a larger liquid crystal display device.

When the light shielding film is used as the auxiliary capacitance electrode or the black matrix, the aperture ratio of the liquid crystal display device can be increased.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1E shows a stagger type TFT of this embodiment. In this TFT, an insulating film 3 is formed so as to cover the patterned light shielding film 2 on the transparent substrate 1. A source electrode 4 and a drain electrode 4 are formed on the insulating film 3, and a source region 5 and a drain region 5 made of a low-resistance first semiconductor layer are connected to the source electrode 4 and the drain electrode 4, respectively. They are formed so as to be separated from each other. A second semiconductor layer 6 is formed over the source region 5 and the drain region 5, and a gate electrode 8 is formed on the second semiconductor layer with a gate insulating film 7 interposed therebetween. Further, a protective film 9 is formed so as to cover it. The source region 5, the drain region 5 and the gate electrode 8 are formed in self-alignment with the light shielding film 2.

This TFT can be manufactured as follows. First, on the transparent substrate 1 made of glass or the like, a film of tantalum, titanium or the like having a thickness of about 250 nm is formed by sputtering and patterned into an island shape as shown in FIG. Since the width of the light-shielding film 2 determines the channel length in a later step, it is necessary to pattern the light-shielding film with high accuracy.
Is desirable. Next, an insulating film 3 made of SiO ₂ or the like having a thickness of about 250 nm is formed by sputtering or P-CVD so as to cover the patterned light shielding film 2.

Next, the thickness is about 300 by sputtering.
A tantalum film having a thickness of nm is formed and patterned as shown in FIG. 1B to form the source electrode 4 and the drain electrode 4. Subsequently, SiH ₄ gas, H ₂ gas, and PH ₃ gas are introduced into the P-CVD apparatus to form a film, so that the conductivity of the first impurity-added low-resistance first semiconductor layer is 0.01 Ωcm ^−1. A film of n-type microcrystalline silicon of about 100 Ωcm ⁻¹ is formed. A negative resist is applied on the first semiconductor layer, and back exposure is performed from the substrate 1 side together with an exposure mask to form a resist film in self-alignment with the light shielding film 2. By etching the first semiconductor layer using this as a mask, the source region 5 and the drain region 5 are formed in self-alignment with the light-shielding film 2.

An i-type amorphous silicon film is formed thereon by a P-CVD method and patterned into an island shape as shown in FIG. 1C to form a second semiconductor layer 6. On top of that, Si _{3 having a} thickness of about 250 nm is formed by P-CVD
A gate insulating film 7 made of N ₄ or SiO _{2 is} formed.

Then, the thickness is about 20 by sputtering.
A transparent conductive film made of 0 nm indium oxide, tin oxide or the like is formed. This transparent conductive film is patterned to be slightly thicker than the light-shielding film 2 using a positive resist, and then the back surface is exposed from the substrate 1 side to form a resist film in self-alignment with the light-shielding film 2. The transparent conductive film is etched by using this as a mask to form the gate electrode 8 in a self-aligned manner with the light shielding film 2. When the transparent conductive film is patterned to be slightly thicker than the light shielding film 2 as described above,
It has the following advantages: That is, when the width of the gate electrode 8 becomes narrower than between the source region 5 and the drain region 5 which are low resistance layers, the low resistance layer (source region or drain region) is added to the channel layer formed under the gate electrode 8. Although a current flows from No. 5, the semiconductor layer 6 having a high resistance flows, causing a voltage drop and deteriorating the characteristics. At this time, if the flow is several μm, the characteristic becomes defective. On the contrary, a little thicker (wider)
Then, since the current flows from the low resistance layer (source region or drain region) 5 through the semiconductor layer 6 by several hundred angstroms to the channel layer having low resistance, it is possible to prevent the deterioration of characteristics from occurring easily.

Thereafter, the thickness is about 250 by P-CVD method.
A protective film 9 made of Si ₃ N ₄ or SiO ₂ having a thickness of 9 nm is formed.

Stagger type TFT thus obtained
In addition, since the source region 5 and the drain region 5 having low resistance can be obtained and the leak current between the source and the drain can be reduced, the characteristics can be improved.

A liquid crystal panel can be formed by bonding the above-mentioned TFT substrate and a counter substrate on which a color filter and a black matrix are formed, and then injecting liquid crystal into a gap between both substrates to divide the liquid crystal. A liquid crystal module is completed by attaching an integrated circuit for a driver or the like to this liquid crystal panel. In the liquid crystal display device thus obtained, since the source region 5 and the drain region 5 of the TFT and the gate electrode 8 are formed in a self-aligning manner, block separation on the display occurs, and burn-in due to variation in pull-in voltage. It is possible to prevent the occurrence of an afterimage.

(Embodiment 2) FIG. 2E shows a TFT having an improved coplanar structure according to this embodiment. In this TFT, the source electrode 4 and the drain electrode 4 are not on the insulating film 3,
The gate insulating film 7 and the interlayer insulating film 10 are formed on the interlayer insulating film 10 formed so as to cover the gate electrode 8.
It is connected to the source region 5 and the drain region 5 through the contact hole formed in. Other than that, the configuration is similar to that of the first embodiment. In the manufacture of this TFT, the source electrode 4 and the drain electrode 4 are formed after the gate electrode 8 is formed, not before the first semiconductor layer is formed.

First, the source electrode 4 and the drain electrode 4
2 is carried out in the same manner as in Example 1 except that the film is not formed.
The steps (a) to (d) are performed.

Next, an interlayer insulating film 10 made of SiO ₂ or the like is formed by P-CVD so as to cover the gate electrode 8. Next, by patterning and etching steps, contact holes are formed in the gate insulating film 7 and the interlayer insulating film 10 so as to reach the source region 5 and the drain region 5. After that, a metal film of aluminum alloy, titanium or the like is formed by sputtering. By patterning the source region 5 and the drain region 5
A source electrode 4 and a drain electrode 4 which are electrically connected to are formed.

The improved coplanar structure TFT thus obtained has good characteristics similar to those of the first embodiment, and prevents block separation on the display, and burn-in and afterimage due to variation in pull-in voltage. You can Also,
In the TFT having this structure, the gate electrode 8, the source electrode 5 and the drain electrode 5 can all be formed in the final step, and therefore, there is little effect of hillocks and the like, and it is easy to use a low-resistance aluminum alloy or the like. . Further, in order to improve the reliability and the yield rate, a protective film may be formed on this.

Although an n-type microcrystalline semiconductor is used as the first semiconductor layer 5 having a low resistance in the above embodiment, an n-type polycrystalline semiconductor formed by a solid phase growth method or a laser annealing method may be used. . In this case, in addition to silicon, polycrystalline silicon germanium or polycrystalline silicon carbon can be used. Further, the above-described microcrystalline semiconductor and polycrystalline semiconductor that can be used in the present invention are not limited to n-type, but p-type can be used.

Although the transparent electrode is used as the gate electrode 8, a transparent electrode and a metal electrode may be combined, and in that case, it is possible to correspond to a larger liquid crystal display device.

When the patterned light-shielding film 2 is used as an auxiliary capacitance electrode or a black matrix,
The aperture ratio of the liquid crystal display device can be increased.

Although amorphous silicon is used as the second semiconductor layer 6, an amorphous semiconductor (amorphous silicon, amorphous silicon germanium or amorphous silicon carbon, etc.), a polycrystalline semiconductor (polycrystalline silicon, polycrystalline silicon germanium or polycrystalline silicon). Various materials such as carbon) and microcrystalline semiconductors (microcrystalline silicon, microcrystalline silicon germanium, microcrystalline silicon carbon, and the like) can be used.

[0035]

As is apparent from the above description, according to the present invention, a source region and a drain region having a low resistance can be obtained by film formation, and a leak current between the source and the drain can be reduced. A TFT having good characteristics can be obtained.

Further, since the source region, the drain region and the gate electrode can be formed in a self-aligned manner with the patterned light-shielding film, block separation on the display, image sticking and afterimage due to variation in pull-in voltage can be prevented. Can be prevented. Therefore, it can be suitably used for a liquid crystal display device.

Furthermore, by using a combination of a transparent electrode and a metal electrode as the gate electrode, it is possible to cope with a larger liquid crystal display device. When the patterned light-shielding film is used as the auxiliary capacitance electrode or the black matrix, the aperture ratio of the liquid crystal display device can be increased.

[Brief description of drawings]

1A to 1E are cross-sectional views showing a manufacturing process of a TFT according to a first embodiment.

2A to 2E are cross-sectional views showing a manufacturing process of a TFT of Example 2.

[Explanation of symbols]

1 transparent substrate 2 light-shielding film 3 insulating film 4 source electrode and drain electrode 5 low-resistance first semiconductor layer (source region and drain region) 6 second semiconductor layer 7 gate insulating film 8 gate electrode 9 protective film 10 interlayer insulation film

Claims (9)

[Claims] 1. A source region and a drain region formed of a low-resistance first semiconductor layer are formed in a state of being separated from each other on an insulating film formed on a transparent substrate to cover a patterned light shielding film, A gate electrode is formed between the second semiconductor layer formed over the source region and the drain region via a gate insulating film, the source electrode is electrically connected to the source region, and the drain is formed. A thin film transistor in which a drain electrode is electrically connected to the region, and the source region, the drain region, and the gate electrode are formed in self-alignment with the light shielding film. 2. The thin film transistor according to claim 1, wherein the first semiconductor layer is made of a microcrystalline semiconductor or a polycrystalline semiconductor. 3. The gate electrode comprises a transparent electrode or a combination of a transparent electrode and a metal electrode.
The thin film transistor according to. 4. The thin film transistor according to claim 1, wherein the light shielding film is used as an electrode for a storage capacitor or a black matrix of a liquid crystal display device. 5. The thin film transistor according to claim 1, wherein the second semiconductor layer is made of amorphous silicon, amorphous silicon germanium, or amorphous silicon carbon. 6. The second semiconductor layer is polycrystalline silicon,
The thin film transistor according to claim 1, which is made of polycrystalline silicon germanium or polycrystalline silicon carbon. 7. The second semiconductor layer is microcrystalline silicon,
The thin film transistor according to claim 1, which is made of microcrystalline silicon germanium or microcrystalline silicon carbon. 8. A step of forming a light-shielding film on a transparent substrate, patterning the light-shielding film to form an insulating film, and forming a low-resistance first semiconductor layer on the insulating film. And a step of applying a negative resist on the first semiconductor layer and exposing from the back surface side of the substrate to pattern the source region and the drain region which are separated from each other in a self-aligned manner with the light-shielding film; Forming a second semiconductor layer over the drain region and forming a gate insulating film on the second semiconductor layer; forming a transparent conductive film on the gate insulating film; Patterning the gate electrode in a self-aligned manner with the light-shielding film by applying a positive resist on the transparent conductive film and exposing from the back surface side of the substrate; and connecting the source electrode to the source region and the drain region to the drain region. connection Forming a drain electrode, and a method of manufacturing a thin film transistor. 9. A liquid crystal display device in which a liquid crystal layer is provided between a pair of substrates, and the thin film transistor according to claim 1 is formed as a switching element on one of the pair of substrates.