JPH08248402A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To enhance gate breakdown strength and to improve a yield without adding stages exclusive of a stage for depositing silicon nitride thin films by removing the silicon nitride thin films exclusive of the thin film on the lower side of gate electrodes. CONSTITUTION: An insulating film is formed as a gate insulating film formed of the silicon oxide thin film 203 of the lower layer and the silicon nitride thin film 204 of the upper layer. The silicon nitride thin film 204 of the upper layer is formed only right under the gate electrodes 212 and is removed in the parts exclusive of the parts right under the gate electrodes 212. Namely, the gate insulating film of a thin-film semiconductor device of a coplanar type to be used as a switching element or peripheral driving circuit is formed into the two-layered structure of the thermal silicon oxide thin film 203 of the lower layer on the side near the active layer 202 and the silicon nitride thin film 204 of the upper layer on the side near the gate electrodes 212 and the silicon nitride thin film 204 exclusive of the film under the gate electrodes 212 is removed simultaneously at the time of etching to form the gate electrodes 212. As a result, the liquid crystal display device having the thin-film semiconductor device of the high gate breakdown strength is obtd. without increasing the special stages exclusive of the state for depositing the silicon nitride thin film 204.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Among thin film semiconductor devices used for a switching element of a liquid crystal display device and a peripheral driving circuit (liquid crystal driver circuit) arranged around a substrate, a polycrystalline thin film semiconductor device having a built-in driving circuit is particularly transparent. Since it is formed on a transparent substrate, its active layer is generally formed by depositing a silicon thin film on the substrate and etching it into an island shape.

For this reason, unlike the case of a semiconductor device formed on a single crystal silicon substrate such as a so-called integrated circuit, the unevenness of the base such as the gate line and the signal line tends to become large at the time of forming the wiring. Therefore, there is a problem that flattening is difficult.

Further, the shape of the end of the active layer may be an inverse taper type. Therefore, the covering property of the insulating film is apt to be deteriorated particularly at the end portion of the active layer, which causes a reduction in the gate breakdown voltage of the semiconductor device, and in the worst case, a short circuit defect occurs in this portion. .

In addition, a thin film semiconductor device used in a liquid crystal display device needs to be driven at a higher voltage than a semiconductor device used in a general memory or the like because of the operating characteristics of the liquid crystal layer, and therefore the breakdown voltage is high. An insulating film having higher (voltage resistance) is required.

Therefore, in the case of an amorphous silicon thin film semiconductor device in which the insulating film must be formed at a low temperature, the gate insulating film is composed of two or more layers of different types such as a silicon oxide film and a silicon nitride film. It is often formed using an insulating film.

Further, in a polycrystalline silicon thin film semiconductor device with a built-in driving device which can use a high temperature process, a high temperature oxidation of a part of a surface layer portion of a silicon film forming an active layer is used as a gate insulating film. Often.

[0008]

However, in the case of forming an insulating film by the thermal oxidation method, if an attempt is made to increase the breakdown voltage by increasing the thickness of the insulating film, the oxidation time will be long and the manufacturing throughput will be high. However, there is a problem in that

In the case of a liquid crystal display device with a built-in driving device, the source / drain regions are formed in the semiconductor layer by adding impurities using an ion implantation device, and CM is used.
An OS (complementary MOS structure) is used, but this is often formed in a self-aligned manner using the gate electrode as a mask.

In this case, impurities are injected into the semiconductor layer through the gate insulating film. However, if the oxide film is simply thickened or two or more kinds of insulating films of different types are laminated, the thick insulating film Impurities must be implanted through the film. Therefore, it is necessary to increase the injection voltage (increase the injection energy). In particular, since an insulating substrate is used, when the implantation energy of the impurity ions at the time of implantation cannot be made large, there is a problem that the manufacturing throughput is significantly reduced.

The present invention has been made to solve such a problem, and an object thereof is to add a gate to a conventional manufacturing process without adding a complicated process other than depositing a silicon nitride thin film. An object of the present invention is to provide a liquid crystal display device including a highly reliable semiconductor device having a high breakdown voltage, which can be formed with a high yield and a good throughput.

[0012]

A liquid crystal display device according to the present invention comprises an insulating substrate, an island-shaped active region formed on the insulating substrate, and a source region and a drain formed on both sides of the active region. A thin film semiconductor device including a semiconductor layer having a region, an insulating layer formed to cover the semiconductor layer, and a gate electrode facing the active region of the semiconductor layer with the insulating layer interposed therebetween, In a liquid crystal display device used as a switching element of each pixel portion and / or a liquid crystal driving circuit arranged on the insulating substrate, the insulating film is formed of a lower silicon oxide thin film and an upper silicon nitride thin film. The gate insulating film is characterized in that the upper silicon nitride thin film is formed only under the gate electrode and is removed in a portion other than under the gate electrode.

Further, a semiconductor layer formed on the insulating substrate, island-shaped on the insulating substrate, and having an active region and source and drain regions formed on both sides of the active region, and the semiconductor layer. A thin film semiconductor device having an insulating layer formed so as to cover the active layer and a gate electrode facing the active region of the semiconductor layer via the insulating layer, and a switching element in each pixel portion and / or the insulating layer. In a liquid crystal display device used as a liquid crystal drive circuit arranged on a substrate, the insulating film is a gate insulating film formed of a lower silicon oxide thin film and an upper silicon nitride thin film, and the upper silicon nitride film is formed. The thin film is formed directly below the gate electrode and in a portion along the side surface of the end of the island-shaped semiconductor layer along the lower silicon oxide thin film. The portions other than Tsu portion is characterized in that it is removed.

Also, a semiconductor layer having an insulating substrate, an island-shaped active region, and a source region and a drain region formed on both sides of the active region, the semiconductor layer being formed on the insulating substrate. A thin film semiconductor device having an insulating layer formed so as to cover the active layer and a gate electrode facing the active region of the semiconductor layer via the insulating layer, and a switching element in each pixel portion and / or the insulating layer. In a liquid crystal display device used as a liquid crystal drive circuit arranged on a substrate, the insulating film is a gate insulating film formed of a lower silicon oxide thin film and an upper silicon nitride thin film, and the upper silicon nitride film is formed. The planar shape of the thin film is smaller than that directly below the gate electrode.
It is formed in a wide dimension within μm and is also formed in a portion along the lower silicon oxide thin film which covers the side surface of the end portion of the island-shaped semiconductor layer, and is formed under the gate electrode and in the lower silicon oxide. It is characterized in that the portions other than the portion along the thin film are removed.

The upper silicon nitride thin film is 3 μm thick.
Needless to say, it may be protruded from directly under the gate electrode as long as it is within m. Rather, the LDD structure can be formed by self-alignment by patterning the planar shape so as to positively protrude within 3 μm as described above and using the protruding silicon nitride thin film within 3 μm as a mask. This is because the advantage is obtained.

[0016]

In the liquid crystal display device of the present invention, the gate insulating film of the coplanar type thin film semiconductor device used as a switching element or a peripheral drive circuit is provided with a lower thermal oxide film near the active layer and an upper layer near the gate electrode. It has a two-layer structure with a silicon nitride film, and the silicon nitride film except under the gate electrode is removed at the same time as the etching for forming the gate electrode. That is, the insulating film in the portion corresponding to the gate electrode can be formed thick to have an appropriate thickness in order to obtain good insulating properties, and the thickness of the same layer (insulating film) in the other portions can be thin.
As a result, it is possible to provide a liquid crystal display device including a thin film semiconductor device having a high gate breakdown voltage without increasing a special process other than depositing a silicon nitride thin film.

That is, according to this method, since the insulating film on the active layer side is formed by thermally oxidizing the polycrystalline silicon thin film forming the active layer, there are few defects at the interface between the two and good characteristics are obtained. Can be obtained. On the other hand, since the insulating film other than the lower side of the gate is removed, even if the source / drain regions are formed in a self-aligned manner by implanting impurities using the gate as a mask, there is no decrease in throughput due to an increase in the insulating film thickness. Does not happen.

Further, since the etching characteristics of the silicon nitride film are similar to those of the polycrystalline silicon film, it is easy to remove the silicon nitride film at the same time during the gate etching without using any special means, and under this condition, the lower layer oxide film is oxidized. The selectivity with respect to the silicon film is sufficient.

Further, in a thin film semiconductor device used in a liquid crystal display device, an active layer is formed in an island shape on an insulating substrate. At this time, in the conventional technique, the cross section of the active layer has a sharp end face. 1 (a) because it is difficult for etching to proceed on the raised surface and its vicinity.
As shown in FIG. 6, when the polycrystalline silicon thin film for the gate electrode is etched to form the gate electrode 104, a part of the polycrystalline silicon thin film for the gate electrode is not removed by etching and is activated as an etching residue 104 ′. Wiring was left along the longitudinal direction of the end face of the layer 102, and due to this, short circuits occurred in wiring such as gate wiring (not shown) and signal wiring (not shown). Further, verticality of etching is required in order to surely control the dimensions as the thin film semiconductor device is miniaturized, but at this time, the etching residue at the end of the active layer 102 becomes more severe.

However, according to the present invention, the silicon oxide film 10 that covers the end face of the active layer 102 where etching residue is likely to occur.
3 and its vicinity on the surface of the insulating substrate 101 along the longitudinal direction of the end surface of the active layer 102, as shown in FIG.
06 can be left, and the gate electrode 1
The conductive material, which is a forming material of 04, can be selectively removed by etching without remaining. Even if the silicon nitride film 105, which is an insulating material, remains as the etching residue 106 in this way, a short-circuit defect does not occur, but rather it has an effect of preventing step disconnection when forming an interlayer insulating film later. is there.

Therefore, according to the present invention, it is possible to solve the above-mentioned problems of the prior art.

[0022]

Embodiments of the liquid crystal display device according to the present invention will be described in detail below with reference to the drawings. In this embodiment, an embodiment in which the present invention is applied to a liquid crystal display device including a thin film semiconductor device in which an active layer is formed using a polycrystalline silicon thin film as a material, will be described.

FIG. 2 shows the structure of a sectional view of the drive circuit board of this embodiment and the manufacturing flow thereof. First, on an insulating substrate 201 such as a quartz substrate, a polycrystalline silicon thin film that is a forming material film of an active layer 202 is formed with a thickness of 100 nm as a material for forming an active layer (described later) by a low pressure CVD method.

The polycrystalline silicon thin film as the material for forming the active layer 202 is processed into an island shape by the photolithography method, and then the silicon oxide film 20 to be the lower gate insulating film is formed on the surface thereof.
3 is formed to a thickness of 30 nm by the thermal oxidation method.

Next, a silicon nitride thin film 204 to be an upper gate insulating film is formed to a thickness of 30 nm by the low pressure CVD method. Then, a polycrystalline silicon thin film 205 is formed as a material for forming a gate electrode (described later) by a low pressure CVD method to 400 nm.
Then, an activation heat treatment is performed by adding impurities such as phosphorus (P) (FIG. 2A).

Subsequently, the polycrystalline silicon thin film 205 other than the portion to be the gate electrode 212 later and the gate electrode 2 thereof are formed.
A portion of the silicon nitride thin film 204 other than directly under 12 is simultaneously removed by photolithography, and the gate electrode 212 is removed.
To form.

Subsequently, impurity ions are implanted in a self-aligned manner using the gate electrode 212 as a mask to form a source diffusion region 206 and a drain diffusion region 207 (FIG. 2B).

Next, a silicon oxide film 208, which is an interlayer insulating film, is formed by the CVD method, and contact holes are formed by photolithography to expose a part of the surface of each of the source diffusion region 206 and the drain diffusion region 207. Set up. Then, a conductive material such as aluminum or its alloy thin film is formed by sputtering argon gas.
A film having a thickness of 400 nm is formed and patterned by a photolithography method to form a source connection wiring 209a, a drain connection wiring 209b, and the like.

Then, by performing heat treatment at 450 ° C. for 30 minutes in a nitrogen atmosphere, the above-mentioned source connection wiring 2 is formed.
09a and drain connection wiring 209b and the surface of the source diffusion region 206 and the surface of the drain diffusion region 207, respectively, are interdiffused to form wiring (FIG. 2).
(C)).

Next, the silicon oxide film is formed by an atmospheric pressure CVD method 6
It is formed to a thickness of 00 nm to obtain an interlayer insulating film 210.

Then, a contact hole for making contact with a pixel electrode 211 (described later) made of ITO is formed in the interlayer insulating film 210 by a photolithography method.

Subsequently, an ITO film having a thickness of 150 nm is formed by sputtering with an argon gas, and the ITO film is patterned by a photolithography method to form a pixel electrode 2.
11 is obtained (FIG. 2 (d)).

The thin film semiconductor device for a liquid crystal display device, the main part of which is completed in this way, has a gate breakdown voltage of 50V. In addition, the defective rate of the thin film semiconductor device due to defective gate insulation was 0.01%.

It was confirmed that the effect of the present invention is remarkably large as compared with the gate withstand voltage of 30 V and the defect rate of 0.03% when the conventional single layer of thermal oxide film is used as the gate insulating film.

The above-mentioned upper silicon nitride thin film 204 is formed.
Is within 3 μm, directly below the gate electrode 212,
It goes without saying that it is okay to protrude. Rather, the LDD structure can be formed by self-alignment by patterning the planar shape so as to positively protrude within 3 μm as described above and using the silicon nitride thin film 204 in the protruded region within 3 μm as a mask. The advantage is that you can. Therefore, when the LDD structure is required, it is preferable to form the LDD structure because the LDD structure can be easily obtained.

As shown in FIG. 1B, the silicon oxide film 103 covering the end face portion of the island-shaped active layer 102 and the surface of the insulating substrate 101 in the vicinity thereof (that is, the active layer 10).
2 on both sides, in FIG. 2, on the surface of the silicon oxide film 203 at the end face portion of the active layer 202 and in the vicinity thereof on the insulating substrate 201),
Along the longitudinal direction, the silicon nitride thin film 106 (the silicon nitride thin film 20 in FIG. 2) that is a material for forming the upper gate insulating film is formed.
You may leave 4) positively. By positively leaving the silicon nitride thin film 204 in this manner, an effect of eliminating a film formation defect called so-called step disconnection when the silicon oxide film 208 or the like is laminated as an interlayer insulating film so as to cover this portion Can be obtained.

By leaving the silicon nitride thin film 204 in this way, the etching rate of the silicon nitride thin film 204 is different from the etching rate of the lower silicon oxide film 203 and the etching rate of the upper polycrystalline silicon thin film 205. Therefore, since the control is sufficiently accurate and simple, the present invention can be easily realized.

[0038]

As is clear from the detailed description above, according to the present invention, the gate insulating film has a laminated structure of a lower thermal oxide film and an upper silicon nitride film, and silicon nitride other than the lower side of the gate electrode is formed. With the structure in which the thin film is removed, the gate breakdown voltage is high and the yield is good without adding a process other than the deposition of the silicon nitride thin film to the conventional process. In addition, since the thickness of the insulating film other than under the gate electrode does not increase, throughput does not decrease when implanting impurities for forming the source / drain.

Further, since a low pressure CVD method having a good covering property can be used to form the silicon nitride film as the upper layer of the gate insulating film, in the case of a liquid crystal display device using an island-shaped polycrystalline silicon thin film as an active layer. However, the silicon nitride layer alleviates irregularities at the island ends, so that a thin film semiconductor device with less breakage of the gate electrode can be obtained.

Further, since the lower layer of the gate is a silicon nitride film which is an insulator, even if the end portion of the island-shaped active layer has a reverse taper, the short circuit of the wiring due to the etching residue does not occur.

[Brief description of drawings]

FIG. 1 is a sectional view (a) showing a state where an etching residue of a gate electrode material occurs in a thin film semiconductor device according to a conventional technique, and a sectional view (b) of a thin film semiconductor device according to the present invention.

FIG. 2 is a cross-sectional view showing an outline of a structure of a thin film semiconductor device used in a liquid crystal display device according to the present invention and a manufacturing process flow thereof.

[Explanation of symbols]

 101 ... Insulating substrate 102 ... Active layer (polycrystalline silicon thin film) 103 ... Silicon oxide film 104 ... Polycrystalline silicon thin film for gate electrode 105 ... Silicon nitride film 106 ... Etching residue (Polycrystalline silicon) 201 ... Insulating substrate 202 ... Active layer (Polycrystalline silicon thin film) 203 ... Silicon oxide film 204 ... Silicon nitride thin film 205 ... Polycrystalline silicon thin film 206 ... Source diffusion region 207 ... Drain diffusion region 208 ... Silicon oxide film (interlayer insulating film) 209a Source connection wiring 209b ... Drain connection wiring 210 ... Interlayer insulating film 211 ... Pixel electrode 212 ... ... Gate electrode

Claims (3)

[Claims] 1. A semiconductor layer having an insulating substrate, an island-shaped active region, and a source region and a drain region formed on both sides of the active region, the semiconductor layer being formed on the insulating substrate in an island shape. A thin film semiconductor device having an insulating layer formed so as to cover the active layer and a gate electrode facing the active region of the semiconductor layer via the insulating layer, and a switching element in each pixel portion and / or the insulating layer. In a liquid crystal display device used as a liquid crystal drive circuit arranged on a substrate, the insulating film is a gate insulating film formed of a lower silicon oxide thin film and an upper silicon nitride thin film, and the upper silicon nitride thin film is formed. The liquid crystal display device, wherein the thin film is formed only under the gate electrode and is removed in a portion other than under the gate electrode. 2. A semiconductor layer having an insulating substrate, an island-shaped semiconductor region formed on the insulating substrate, and an active region and source and drain regions formed on both sides of the active region, and the semiconductor layer. A thin film semiconductor device having an insulating layer formed so as to cover the active layer and a gate electrode facing the active region of the semiconductor layer via the insulating layer, and a switching element in each pixel portion and / or the insulating layer. In a liquid crystal display device used as a liquid crystal drive circuit arranged on a substrate, the insulating film is a gate insulating film formed of a lower silicon oxide thin film and an upper silicon nitride thin film, and the upper silicon nitride thin film is formed. The thin film is formed immediately below the gate electrode and along the lower silicon oxide thin film covering the side surface of the end portion of the island-shaped semiconductor layer, and directly below the gate electrode and along the lower silicon oxide thin film. A liquid crystal display device characterized in that it is removed in the portion other than the portion. 3. A semiconductor layer having an insulating substrate, an island-shaped active region, and a source region and a drain region formed on both sides of the active region, the semiconductor layer being formed on the insulating substrate. A thin film semiconductor device having an insulating layer formed so as to cover the active layer and a gate electrode facing the active region of the semiconductor layer via the insulating layer, and a switching element in each pixel portion and / or the insulating layer. In a liquid crystal display device used as a liquid crystal drive circuit arranged on a substrate, the insulating film is a gate insulating film formed of a lower silicon oxide thin film and an upper silicon nitride thin film, and the upper silicon nitride thin film is formed. The thin film is formed so that the planar shape dimension is within 3 μm wider than directly below the gate electrode, and is also formed in a portion along the lower silicon oxide thin film that covers the side surface of the end portion of the island-shaped semiconductor layer. Oh The liquid crystal display device is characterized in that it is removed under the gate electrode and in a portion other than the portion along the lower silicon oxide thin film.