JP2001209067A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device which can solve problems caused by the leak current by light in a thin film transistor. SOLUTION: In the active matrix liquid crystal display device incorporating a thin film transistor having a LDD region, a semiconductor layer which constitutes the thin film transistor is formed in the region between a lower light-shielding layer and an upper light-shielding layer, where a part of the light entering from a back light and reflected or transmitted between the lower light-shielding layer and the upper light-shielding layer passes to enter the LDD region of the thin film transistor. Thus, the light entering the LDD region is cut.

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, and more particularly to an active matrix type liquid crystal display device incorporating a thin film transistor.

[0002]

2. Description of the Related Art In recent years, various liquid crystal display devices using a liquid crystal panel as a display for a wall-mounted TV, a projection TV or an OA device have been developed. Among active liquid crystal panels, an active matrix type liquid crystal display in which a thin film transistor, which is an active element, is incorporated in a liquid crystal display device is a high-quality display device for OA equipment because of its advantages that the contrast and the response speed do not decrease even if the number of scanning lines increases. And high-definition display devices,
A projection type liquid crystal display such as a liquid crystal projection has an advantage that a large screen display can be easily obtained.

In general, an active matrix type liquid crystal display device for a light valve used for liquid crystal projection uses an ON / OF for each pixel by injecting strong light into a small element and switching the liquid crystal by a TFT.
F, the transmitted light is controlled in accordance with the image information, and the transmitted light is enlarged and projected on a screen through an optical element such as a lens. Not only the influence but also the light reflected from the optical system such as a lens causes a problem of a light leak current generated by light excitation in a channel portion of the TFT portion, particularly in an LDD (Lightly Doped Drain) region.

[0004] This problem is becoming a problem at an accelerated rate as the size of the projector and the increase in the brightness of the projector have progressed, and the brightness of light incident on the light valve has greatly increased.

Conventionally, in such an active matrix type liquid crystal display device for a light valve, as shown in FIG. 6, gate lines 107 and data lines 105 are arranged in a matrix so as to be orthogonal to each other. ITO, which is a pixel electrode,
TFTs are formed at the intersections of the gate lines 107 and the data lines 105, respectively.

The data line 105 is provided with a data line-TFT contact for supplying a signal to the source region 109 of the TFT, and the pixel electrode ITO and the drain electrode are connected by the ITO-TFT contact. I have. An LDD region 108 is formed between the channel 103 of the TFT and the source / drain electrode 109.

A lower light-shielding layer 102 formed on a transparent insulating substrate such as a glass substrate via a base insulating film, and a black matrix layer 106 provided on the TFT are provided. That is, when the light enters from the substrate opposite to the TFT with the liquid crystal layer interposed therebetween, the incident light is blocked by the black matrix layer 106 and the reflected light from the optical system or the like is blocked by the lower light shielding layer 102.

A black matrix layer is formed on the TFT substrate side with an insulating film layer interposed therebetween, and is formed on the counter substrate side.
In the case of forming on the counter substrate side of T, there is a problem that the aperture ratio cannot be increased because the counter substrate side must be increased to allow about 10 μm as the overlay accuracy of the two substrates. Therefore, to increase the aperture ratio, TF
The case where a black matrix is provided on the same substrate side as T is becoming mainstream.

[0009]

In the case where a black matrix is provided on the same substrate side as the TFT, it is not necessary to expect such a large margin as described above in order to obtain high alignment accuracy using the semiconductor device manufacturing process. No consideration has been given to the positional relationship between the two light-shielding layers and the TFT, and measures to shield light reaching the TFT due to multiple reflections between the two light-shielding layers and the like have not been sufficient. In particular, with the miniaturization and high luminance of the device, the amount of light that reaches the TFT by multiple reflection between the upper and lower light-shielding layers becomes large, and the problem that the light-shielding property is not sufficiently ensured has become apparent.

In particular, the lower light-shielding layer and the black matrix are sufficiently formed in the gate line formation region, so that the light-shielding is sufficient. However, in the LDD region and the like, both the light-shielding layer and the black matrix layer have a width to increase the aperture ratio. Is limited. For this reason, in the LDD region of the polysilicon layer sandwiched between the source and the drain, the positional relationship is determined so that incident light from the edge portion of the black matrix layer is not reflected by the lower light shielding layer. However, there has been a problem that the reflected light is reflected by the black matrix, is reflected multiple times with the lower light shielding layer, and reaches the TFT. Of course, the directional components of the incident light and the reflected light include not only a component parallel to the gate line direction but also various directional components, and may enter a channel region below the gate line.

As a means for solving such a problem, Japanese Patent Application No. 10-354845 discloses a method in which the lower light-shielding layer is tapered at the end and defines the positional relationship between the lower light-shielding layer and the upper light-shielding layer which also serves as a data line. It has been proposed to. Japanese Patent Application No. 11-109979 discloses a structure in which a dummy contact is formed in an interlayer film formed near the side surface of a TFT in the channel length direction, and the side wall is also shielded from light by a wiring material formed on the side wall of the dummy contact. Proposed.

Although all of these means are effective means, a new step is required for producing a characteristic structure thereof, and there has been a problem that the manufacturing process becomes complicated.

A first object of the present invention is to provide a liquid crystal display device which can solve the problem caused by the light leakage current of the TFT.

A second object of the present invention is to provide a liquid crystal display device capable of effectively preventing incident light from entering a channel region below a gate line.

A third object of the present invention is to provide a liquid crystal display device capable of efficiently manufacturing the same.

[0016]

According to a first aspect of the present invention, there is provided a lower light-shielding layer laminated on a transparent insulating substrate, and formed in a region on the lower light-shielding layer via a first interlayer film. Having LDD region and source / drain region
A thin film transistor including a semiconductor layer, a gate electrode formed on the thin film transistor via a gate insulating film, and a second interlayer film on the gate electrode, and a source / drain region of one of the thin film transistors A data line to be connected, an upper light-shielding layer formed on the data line via a third interlayer insulating film, and an upper light-shielding layer formed on the upper light-shielding layer via a fourth interlayer insulating film; A liquid crystal display device comprising: a pixel electrode connected to a source / drain region; a region between the lower light-shielding layer and the upper light-shielding layer; The thin film transistor is placed in a region through which light that is reflected or passed through the upper light blocking layer and enters the LDD region of the thin film transistor passes. And disposing the semiconductor layer constituting the data, characterized by shielding such incident light.

According to a second aspect of the present invention, a lower light-shielding layer laminated on a transparent insulating substrate, and a first interlayer film formed in a region on the lower light-shielding layer via a first interlayer film, and an LDD region and a source / source region are formed. A thin film transistor formed of a Si semiconductor layer having a drain region, a gate electrode formed on the thin film transistor via a gate insulating film, and a layer stacked on the gate electrode via a second interlayer film; A data line connected to a source / drain region, an upper light-shielding layer formed on the data line via a third interlayer insulating film, and an upper light-shielding layer formed on the upper light-shielding layer via a fourth interlayer insulating film; A pixel electrode connected to another source / drain region of the thin film transistor, wherein the first interlayer film is interposed in a region on the lower light shielding layer. Together are arranged Te, at least the LDD separated in the same layer as the thin film transistor
The semiconductor device includes a predetermined number of second semiconductor layers formed of a Si semiconductor and formed so as to cover the side of the region, and the gate insulating film or the second interlayer film is interposed between the thin film transistor and the second semiconductor layer. It is characterized by.

Further, in the liquid crystal display device, it is preferable that the second semiconductor layer is formed in the same step as the step of forming the thin film transistor.

In the liquid crystal display device, it is preferable that the source / drain electrode region is connected to the second semiconductor layer.

In the liquid crystal display device, it is preferable that the second semiconductor layer is a source / drain electrode region.

Further, in the liquid crystal display device, the gate electrode is made of a silicon material at least on the lower light-shielding layer side, enters the substrate obliquely, and is multiply reflected by the lower light-shielding film and the upper light-shielding film. Preferably, the light incident on the LDD region of the thin film transistor is absorbed.

According to a third aspect of the present invention, a lower light-shielding layer laminated on a transparent insulating substrate, and a first interlayer film formed in a region on the lower light-shielding layer with an LDD region and a source / light source. A thin film transistor including a Si semiconductor layer having a drain region, a gate electrode formed on the thin film transistor via a gate insulating film, and a second interlayer film stacked on the gate electrode, and one of the thin film transistors A data line connected to the source / drain region; an upper light-shielding layer formed on the data line via a third interlayer insulating film;
A pixel electrode formed through an interlayer insulating film and connected to another source / drain region of the thin film transistor, wherein the gate electrode has at least the lower light-shielding layer side made of a silicon material. The thin film transistor is also arranged at least on the side of the LDD region, and is formed so as to cover the side of the LDD region.

In the liquid crystal display device, it is preferable that the data line covers an upper surface of the gate electrode or the second semiconductor layer with the same region as the lower light shielding layer via the second interlayer film.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION In a preferred embodiment of the liquid crystal display device according to the present invention, according to the present structure, light penetrating by multiple reflection between upper and lower light-shielding layers is absorbed and blocked by a semiconductor layer provided on the side surface of the TFT. This reduces the light reaching the TFT and solves the problem caused by the light leakage current of the TFT that switches the pixel. In the embodiment according to the present invention, the semiconductor layers can be separated and formed simultaneously in the manufacturing process,
Since it is used for shading, there is an advantage that a shading effect can be obtained without adding a new process.

[0025]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

First, referring to FIG. 1, a first embodiment of the present invention will be described.
Will be described. FIG. 1 is a diagram schematically showing a structure of a liquid crystal display device using a polycrystalline silicon thin film transistor according to Example 1 of the present invention,
(A) is a plan view, and (b) is a cross-sectional view between AA ′.

The liquid crystal display device 1 shown in FIG. 1 is manufactured by the following steps. First, a base insulating film (not shown) for covering the glass substrate is formed on a glass substrate (not shown). This is to prevent diffusion of impurities from the glass substrate. Subsequently, a lower light-shielding layer 2 is formed on the upper portion. After forming a first interlayer insulating film (not shown) on this, a thin film semiconductor layer 3 to be a channel portion of the thin film transistor is formed. The thin film semiconductor layer 3 is formed by depositing amorphous silicon (a-Si) using a method such as CVD and then using a method such as heat treatment or laser crystallization to form a high-quality polycrystalline silicon film (p-Si). It forms by doing.

In this embodiment, thereafter, island-shaped regions of the thin-film transistor are formed, and light entering from the light-shielding layer edge is shielded in the lower light-shielding layer 2 pattern on both sides near the transistor channel and the LDD region 8. Semiconductor layer 4
Is used to form a shielding pattern. At this time, the shielding pattern is formed so as to be separated from the thin film transistor and to shield light intrusion into the LDD region 8 in particular.

Thereafter, a gate insulating film (not shown), a gate electrode 7, and a second interlayer insulating film (not shown) are sequentially formed, and then a data line 5 made of Al is formed. This data line is connected to one source / drain of the thin film transistor via a contact hole (not shown). Further, Al serving as a black matrix 6 is formed on this via a third interlayer insulating film (not shown). Finally, a transparent electrode (not shown) is formed via a fourth interlayer insulating film (not shown) to complete the device. At this time, the transparent electrode is formed so as to be connected to the other source / drain of the thin film transistor via a contact hole or the like.

When light is applied to the LDD region and the channel region of the thin film transistor, carriers are generated by the light, and this causes a leak current to make it impossible to perform a normal switching operation. This problem occurs especially in the pixel switch transistor. Therefore, it is necessary to minimize the irradiation light to the thin film transistor forming the pixel switch, particularly to the LDD region and the channel region. In particular, in the case of a TFT substrate for a liquid crystal light valve used under strong irradiation light, a method is adopted in which the upper and lower portions of the TFT are shielded from light so that direct light irradiation is shielded. Light entering due to multiple reflection becomes a problem.

This problem is solved in the liquid crystal display device of the present embodiment by forming a light shielding layer using a semiconductor layer near the channel of the thin film transistor and the side surface of the LDD region. That is, the semiconductor light-shielding layer 4 of FIG. 1 blocks light by absorbing light that enters from the side surface by multiple reflection. This means is different from a conventional light-shielding layer made of metal or the like in that it absorbs light rather than reflects it so that T
Since the light reaching the FT is reduced, unnecessary light can be more effectively blocked. In particular, the semiconductor light-shielding layer has a high absorptance to the problematic blue light, and has a high reduction effect.

Next, a liquid crystal display device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a diagram schematically showing a structure of a liquid crystal display device using a polycrystalline silicon thin film transistor according to Example 2 of the present invention,
(A) is a plan view, and (b) is a cross-sectional view along BB '.

The difference between the present embodiment and the first embodiment is that the region where the semiconductor layer 4 for shielding extraneous light is formed is changed, and other structures and manufacturing methods are the same as those of the first embodiment. Is the same as

As shown in FIG. 2, in the liquid crystal display device 11 of this embodiment, a base insulating film (not shown) is formed on a glass substrate, and the lower light shielding layer 2 and the first interlayer insulating film (FIG. (Not shown), a thin film semiconductor layer 3 to be a channel portion of the thin film transistor is formed. Here, in this embodiment,
It is characterized in that an island-shaped region of the thin film transistor is formed, and a shielding pattern is formed so that the semiconductor layer 4 remains in the lower light shielding layer 2 pattern on both sides near the LDD region 8 of the transistor.

Thereafter, a gate insulating film (not shown), a gate electrode 7, and a second interlayer insulating film (not shown) are sequentially formed, and then a data line 5 made of Al is formed. Further, Al serving as a black matrix is formed 6 on this via a third interlayer insulating film. And finally, the fourth
A transparent electrode (not shown) is formed via an interlayer insulating film (not shown) to complete the device.

As described above, the light-shielding effect can be maintained at a high level by the method of forming the light-shielding pattern only on the side surfaces of the LDD. This is not only because the LDD region is a region where the electric field is strong and is more susceptible to light, but also because the channel region is on the gate line and the light-shielding pattern is wide and sufficient light-shielding measures are taken. In this case, the gate line is assumed to be a metal film). On the other hand, the LDD region has a limited light-shielding pattern in order to increase the aperture ratio, and is easily affected by multiple reflected light from the light-shielded edge. Therefore, it is possible to sufficiently shield light even with the structure of this embodiment.

Next, a liquid crystal display device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram schematically illustrating a structure of a liquid crystal display device using a polycrystalline silicon thin film transistor according to Embodiment 3 of the present invention.
(A) is a plan view, and (b) is a cross-sectional view between CC '.

The difference between the present embodiment and the first embodiment is that the region where the semiconductor layer 3 for shielding extraneous light is formed is similarly changed. Same as Example 1.

As shown in FIG. 3, the liquid crystal display device 21 of this embodiment has a base insulating film (not shown), a lower light shielding layer 2 and a first interlayer insulating film on a glass substrate (not shown). After forming (not shown), a thin film semiconductor layer 3 to be a channel portion of the thin film transistor is formed. In this embodiment, the island-like region of the thin film transistor is formed, the semiconductor layer 4 remains in the lower light-shielding layer pattern on both sides near the transistor channel and the LDD region, and the light-shielding pattern is connected to the data line side. It is characterized in that a shielding pattern is formed as described above.

Thereafter, a gate insulating film (not shown), a gate electrode 7, and a second interlayer insulating film (not shown) are sequentially formed, and then a data line 5 is formed. Further, a black matrix 6 is formed on this via a third interlayer insulating film (not shown), and a transparent electrode (not shown) is formed via a fourth interlayer insulating film (not shown). The element is completed.

As described above, even when the light-shielding pattern is connected to the data line, the light-shielding effect can be obtained. That is, in the case of an isolated pattern, since it is the same as the semiconductor active layer, there is a concern that the potential of the gate line may affect the electric field effect.
However, if the connection is made on the data line side as in this embodiment, such an effect can be reduced. A problem occurs when the photo-generated charges leak to the transparent electrode side for driving the liquid crystal, but does not cause a problem when the charges are connected to the data line side. At this time, the effect can be obtained regardless of whether the light-shielding pattern contains impurities or not.

Also, as in the other configuration of the present invention shown in FIG. 4, the effect can be exerted even in a structure in which the width of Al of data line 5 is enlarged (extended) in the vicinity of the LDD and the channel region. As shown in FIG. 5, when the gate electrode 7 is made of a silicon material, a similar effect can be obtained by forming such a light shielding pattern with the gate electrode.

Further, by using a gate electrode layer having a silicon layer on the lower surface as a gate electrode, reflected light from below can be similarly absorbed and the same effect can be obtained. In particular, when a similar light-shielding pattern is formed using a gate electrode, the space between the light-shielding pattern and the semiconductor can be reduced as compared with the case where the same light-shielding pattern is formed in the same layer as in Embodiment 1 of the present invention. Therefore, there is an advantage that the light-shielding effect can be further enhanced.

Incidentally, in the configuration of FIGS. 2, 3 and 5,
It has been confirmed that the same effect can be obtained even in a structure in which the width of Al of the data line is enlarged as shown in FIG.

[0045]

As described above, according to the structure of the present invention, there is an effect that it is possible to avoid the problem that, as the light becomes stronger, the reflected light is multiply reflected and reaches the transistor. . The reason is that light shielding can be performed with the same material as the semiconductor layer used for the transistor, whereby light absorption efficiency can be increased, and excess light can be selectively absorbed to block light.

Further, according to the structure of the present invention, red light or the like having little influence on the transistor is not absorbed so much that an efficient light-shielding effect is realized. Accordingly, a light-shielding structure can be realized, and an effect of not increasing the number of steps can be obtained.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams schematically showing a structure of a liquid crystal display device according to a first embodiment of the present invention, wherein FIG. 1A is a plan view and FIG.
It is sectional drawing between -A '.

FIGS. 2A and 2B are diagrams schematically illustrating a structure of a liquid crystal display device according to a second embodiment of the present invention, wherein FIG. 2A is a plan view and FIG.
It is sectional drawing between -B '.

3A and 3B are diagrams schematically illustrating a structure of a liquid crystal display device according to a third embodiment of the present invention, wherein FIG. 3A is a plan view and FIG.
It is sectional drawing between -C '.

4A and 4B are diagrams schematically illustrating a structure of a liquid crystal display device according to another embodiment of the present invention, wherein FIG. 4A is a plan view and FIG. 4B is a cross-sectional view taken along line DD ′.

5A and 5B are diagrams schematically illustrating a structure of a liquid crystal display device according to another embodiment of the present invention, wherein FIG. 5A is a plan view and FIG. 5B is a cross-sectional view taken along line EE ′.

6A and 6B are diagrams schematically showing a structure of a conventional liquid crystal display device, wherein FIG. 6A is a plan view and FIG. 6B is a cross-sectional view taken along line XX ′.

[Explanation of symbols]

 1, 11, 21, 31, 41, 101 Liquid crystal display device 2, 102 Light shielding layer (lower light shielding layer) 3, 103 Semiconductor layer (channel portion) 4 Semiconductor layer (for light shielding) 5, 105 Data line 6, 106 Black matrix Layer 7, 107 Gate line (gate electrode) 8, 108 LDD region 9, 109 Source / drain region

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 2H092 JA24 JB23 JB24 JB32 JB33 JB51 JB52 KA04 KA07 MA29 MA30 NA17 NA22 PA09 PA13 RA05 5C094 AA16 AA25 BA02 BA44 ED15 5F110 AA06 BB01 CC02 DD02 DD11 EE09 GG02 NN03 NN03 PP03

Claims (8)

[Claims] A lower light-shielding layer laminated on a transparent insulating substrate; and a Si formed in a region on the lower light-shielding layer via a first interlayer film and having an LDD region and a source / drain region.
A thin film transistor including a semiconductor layer, a gate electrode formed on the thin film transistor via a gate insulating film, and a second interlayer film stacked on the gate electrode and a source / drain region of one of the thin film transistors A data line to be connected, an upper light-shielding layer formed on the data line via a third interlayer insulating film, and an upper light-shielding layer formed on the upper light-shielding layer via a fourth interlayer insulating film, A liquid crystal display device comprising: a pixel electrode connected to a source / drain region; a region between the lower light-shielding layer and the upper light-shielding layer; The thin film transistor is placed in a region through which light incident on the LDD region of the thin film transistor after being reflected or passed through the upper light shielding layer passes. The liquid crystal display device, characterized in that by disposing the semiconductor layer constituting the register, shields such incident light. A lower light-shielding layer laminated on a transparent insulating substrate; and a Si formed in a region on the lower light-shielding layer via a first interlayer film and having an LDD region and a source / drain region.
A thin film transistor formed of a semiconductor layer, a gate electrode formed on the thin film transistor via a gate insulating film, and stacked on the gate electrode via a second interlayer film, and in one source / drain region of the thin film transistor A data line to be connected, an upper light-shielding layer formed on the data line via a third interlayer insulating film, and an upper light-shielding layer formed on the upper light-shielding layer via a fourth interlayer insulating film;
A liquid crystal display device comprising: a pixel electrode connected to another source / drain region of the thin film transistor; and a pixel electrode disposed in a region on the lower light-shielding layer via the first interlayer film. A predetermined number of second semiconductor layers formed of a Si semiconductor and formed so as to cover at least the side of the LDD region separately in the same layer, wherein the gate insulating film is provided between the thin film transistor and the second semiconductor layer; A liquid crystal display device having the second interlayer film interposed therebetween. 3. The liquid crystal display device according to claim 2, wherein said second semiconductor layer is formed in the same step as the step of forming said thin film transistor. 4. The semiconductor device according to claim 2, wherein said source / drain electrode region is connected to said second semiconductor layer.
The liquid crystal display device as described in the above. 5. The liquid crystal display device according to claim 4, wherein said second semiconductor layer is a source / drain electrode region. 6. The LDD of the thin film transistor, wherein at least the lower light-shielding layer side of the gate electrode is made of a silicon material, enters the substrate obliquely, and is multiple-reflected by the lower light-shielding film and the upper light-shielding film. The liquid crystal display device according to claim 1, wherein light incident on the region is absorbed. 7. A lower light-shielding layer laminated on a transparent insulating substrate, and Si formed in a region on the lower light-shielding layer via a first interlayer film and having an LDD region and a source / drain region.
A thin film transistor including a semiconductor layer, a gate electrode formed on the thin film transistor via a gate insulating film, and a second interlayer film stacked on the gate electrode and a source / drain region of one of the thin film transistors A data line to be connected, an upper light-shielding layer formed on the data line via a third interlayer insulating film, and an upper light-shielding layer formed on the upper light-shielding layer via a fourth interlayer insulating film, A pixel electrode connected to a source / drain region, wherein at least the lower light-shielding layer side of the gate electrode is made of a silicon material, and at least a side of the LDD region of the thin film transistor. Said LD
A liquid crystal display device formed so as to cover the side of the D region. 8. The data line according to claim 1, wherein the data line covers the upper surface of the gate electrode or the second semiconductor layer with the same region as the lower light shielding layer via the second interlayer film. The liquid crystal display device according to any one of the above.