JPH0815726A - Liquid crystal display substrate and its production - Google Patents

Abstract

PURPOSE:To provide holding capacitance elements capable of lessening so-called interlayer leakage and to decrease the stages thereof. CONSTITUTION:This liquid crystal display substrate is constituted by forming thin-film switching elements which are turned on by signals from scanning signal lines, transparent electrodes to which the signals from video signal lines are supplied via these thin-film switching elements and the holding capacitor elements for accumulating video signals which are connected to these transparent electrodes in the respective pixel regions on the liquid crystal side surface of one transparent substrate of the transparent substrates which are arranged to face each other via liquid crystals. These holding capacitor elements are composed of laminates formed of lower conductive layers 2 and upper conductive layers via insulating layers. The upper conductive layers 4 of the holding capacitor elements constitute a shape having parts to expose the insulating layers of the lower layers thereof and the peripheral length thereof is formed longer than the peripheral length of the lower conductive layers 2.

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 substrate,
In particular, it relates to improvement of the storage capacitor element incorporated in each pixel.

[0002]

2. Description of the Related Art A liquid crystal display substrate called an active matrix type is one of transparent substrates arranged to face each other with a liquid crystal in between, and a scanning signal line is formed in each pixel region on the liquid crystal side surface of one transparent substrate. A thin film switching element that is turned on by a signal from the transparent electrode, a transparent electrode to which a signal from a video signal line is supplied via the thin film switching element, and a storage capacitor element connected to the transparent electrode.

A transparent electrode common to each pixel is formed on the liquid crystal side surface of the other transparent substrate.

Here, the storage capacitor element is provided for the purpose of reducing the influence of the gate potential change on the potential of the transparent electrode when the thin film switching element is switched, but normally, the storage capacitor element is used for storing a video signal. It is called a capacitive element. Therefore, this storage capacitor element is required to have a certain capacitance value.

[0005]

However, in the liquid crystal display substrate having such a structure, the storage capacitor element is composed of a laminate of a lower conductive layer and an upper conductive layer with an insulating layer interposed. However, the planar shape of each conductive layer was, for example, a shape close to a rectangle and had an area for sufficiently securing the capacitance value.

However, it has been pointed out that the storage capacitor having such a structure has a problem that a leak occurs between each of the conductive layers facing each other through the insulating layer.

Therefore, the present invention has been made under such circumstances, and an object thereof is to provide a liquid crystal display substrate provided with a storage capacitor element capable of reducing so-called interlayer leakage. is there.

Another object of the present invention is to provide a method of manufacturing a liquid crystal display substrate, in which the number of manufacturing steps is reduced.

[0009]

In order to achieve such an object, the present invention is basically constructed by the following means.

Means 1. Among the transparent substrates arranged to face each other via the liquid crystal, in each pixel area of the liquid crystal side surface of one transparent substrate, a thin film switching element that is turned on by a signal from the scanning signal line, and through this thin film switching element A transparent electrode to which a signal from a video signal line is supplied and a storage capacitor element for storing the video signal connected to the transparent electrode are formed, and the storage capacitor element includes a lower conductive layer and an upper layer via an insulating layer. In a liquid crystal display substrate composed of a laminate with a conductive layer, the upper conductive layer of the storage capacitor element,
It is characterized in that it has a shape having a portion exposing the underlying insulating layer, and its peripheral length is longer than that of the underlying conductive layer.

Means 2. A thin film switching element that is turned on by a signal from a scanning signal line in each pixel region of the liquid crystal side surface of one transparent substrate among the transparent substrates arranged to face each other through the liquid crystal, and through this thin film switching element A transparent electrode to which a signal from a video signal line is supplied and a storage capacitor element for storing the video signal connected to the transparent electrode are formed, and the storage capacitor element includes a lower conductive layer and an upper layer via an insulating layer. A semiconductor display substrate comprising a laminated body with a conductive layer, wherein a step of simultaneously forming a polycrystalline semiconductor layer of the thin film transistor and a lower conductive layer of the storage capacitor element with the same material, and gate insulation of the thin film transistor. A layer and a dielectric layer of the storage capacitor at the same time, and a gate electrode of the thin film transistor and an upper conductive layer of the storage capacitor at the same time In a manufacturing method including a step, the upper conductive layer of the storage capacitor is formed to have a portion that exposes an insulating layer below the storage capacitor, and a source layer and a drain layer are formed in a semiconductor layer of the thin film transistor. When the conductive impurities are doped with the gate electrode as a mask and the heat treatment is performed, the lower conductive layer of the storage capacitor is made to have conductivity at the same time.

[0012]

According to the liquid crystal display substrate of the means 1, the upper conductive layer of the holding capacitor element has a shape having a portion exposing the underlying insulating layer, which increases the peripheral length.

As a result, even if the overlapping area of the upper conductive layer with respect to the lower conductive layer is reduced, it is possible to secure the capacitance with the increase of the peripheral length.

This is based on the consideration that the storage capacitor element formed in the pixel region of the liquid crystal display substrate contributes to the so-called fringe capacitance.

Since the overlapping area of the upper conductive layer with respect to the lower conductive layer is reduced, it becomes possible to suppress the generation of leak current during that time.

According to the method of manufacturing the liquid crystal display substrate by the means 2, when the lower conductive layer of the storage capacitor is made conductive, the gate is formed to form the source layer and the drain layer in the semiconductor layer of the thin film transistor. When doping conductive impurities using the electrodes as a mask and performing heat treatment,
You can do it at the same time.

That is, the lower conductive layer of the storage capacitor is
After the same material as the semiconductor layer of the thin film switching element is formed at the same time, usually (conventional), a mask is applied to the material on the thin film switching element side to dope the material on the storage capacitor element with a conductive impurity.

However, without performing this step at all,
At the same time when the source layer and the drain layer of the thin film switching element are formed, the lower conductive film can be made conductive by doping conductive impurities through the exposed portion of the lower insulating layer in the upper conductive layer of the storage capacitor. Like

Therefore, the number of manufacturing steps can be reduced.

[0020]

EXAMPLE FIG. 8 is an explanatory view showing an example of an equivalent circuit in a liquid crystal display substrate according to the present invention.

The liquid crystal display substrate is equipped with a vertical scanning circuit, a video signal driving circuit, a power supply circuit and the like for use.

Although the figure is a circuit diagram, it is drawn corresponding to the actual geometrical arrangement. That is, among the glass substrates arranged to face each other with the liquid crystal interposed therebetween, the glass substrate 1 (usually referred to as the lower glass substrate) has a liquid crystal side surface extending in the x direction in the drawing. And the scanning signal lines GL arranged in parallel in the y direction are formed, and the video signal lines DL extending in the y direction and arranged in parallel in the x direction are formed.

The scanning signal lines GL and the video signal lines DL are insulated from each other by an interlayer insulating film at their intersections.

Each area surrounded by the scanning signal line GL and the video signal line DL is a pixel area provided with the transparent electrode ITO.

Then, the transparent electrode IT in each pixel region
A thin film transistor TFT is arranged near O, and the thin film transistor TFT is turned on by supplying a signal to its gate electrode via the scanning signal line GL.

The video signal from the video signal line DL is
Transparent electrode I via the turned-on thin film transistor TFT
It will be supplied to the TO.

Further, the transparent electrode ITO is connected to one electrode of the storage capacitor element C, and the other electrode is a signal line of the adjacent scanning signal line GL to which the scanning signal is not supplied. It is connected to the.

The storage capacitor element C is provided for the purpose of reducing the influence of the change in the gate potential on the transparent electrode ITO when the thin film transistor TFT is switched, for example, and is usually used for storing a video signal. It is called a capacitive element C.

An embodiment of a method of manufacturing a liquid crystal display substrate having such a structure will be described with reference to FIGS. Hereinafter, description will be made in the order of steps.

Step 1. (FIG. 2A) A lower glass substrate 1 is prepared, a polycrystalline semiconductor layer (poly-Si) 2 is formed on the entire main surface of the lower glass substrate 1, and the polycrystalline semiconductor layer 2 is formed by a photolithography technique. Is used to form a predetermined pattern.

As a result, the polycrystalline semiconductor layer 2 remains in the formation region of the thin film transistor TFT, the transparent electrode ITO and the storage capacitor element C.

Step 2. (FIG. 2B) The remaining polycrystalline semiconductor layer 2 is heat-treated in an oxygen atmosphere to form a silicon oxide film 3 on its surface.

The silicon oxide film 3 functions as a gate insulating film in the formation region of the thin film transistor TFT and as a dielectric in the formation region of the storage capacitor element C.

Here, since the lower layer electrode is usually formed by making the polycrystalline semiconductor layer 2 formed in the formation region of the storage capacitor element C electrically conductive, only that portion is exposed by the photoresist. The crystalline semiconductor layer 2 is doped with a conductive impurity, but in this embodiment, the next step is started without doing so.

Step 3. (FIG. 2C) A polycrystalline semiconductor layer 4 is formed on the entire main surface of the lower glass substrate 1 thus processed, and the polycrystalline semiconductor layer 4 is formed into a predetermined pattern by using a photolithography technique. To do.

Polycrystalline semiconductor layer 4 formed in this step
Has a conductive impurity mixed in at the stage of its formation, and has conductivity when formed into a layer.

As a result, the polycrystalline semiconductor layer 4 as a gate electrode remains in the formation region of the thin film transistor TFT, and the polycrystalline semiconductor layer 4 as an upper electrode remains in the formation region of the storage capacitor C. It will be.

In this embodiment, the polycrystalline semiconductor layer 4 as the upper electrode in the storage capacitor C is, in particular,
As shown in FIG. 1 which is a plan view thereof, it has a comb-like shape, so that its peripheral length is long and, as will be described later in detail, the polycrystalline semiconductor layer 2 (which is positioned below it) is formed. The other electrode) constitutes a passage portion for doping conductive impurities.

Step 4. (FIG. 2D) Using the polycrystalline semiconductor layer 4 as a mask, the silicon oxide film 3 exposed from the mask is etched. This allows
The polycrystalline semiconductor layer 2 is exposed outside the region where the polycrystalline semiconductor layer 4 is formed.

Then, by heat treatment in an oxygen atmosphere, a thin silicon oxide film 5 is formed on the surface of the polycrystalline semiconductor layer 4 and the surface of the polycrystalline semiconductor layer 2.

Step 5. (FIG. 3A) Conductive impurities are doped from the main surface of the lower glass substrate 1 thus processed.

As a result, in the formation region of the thin film transistor TFT, the polycrystalline semiconductor layer 2 other than the region where the gate electrode is formed has conductivity, and the drain layer 6 and the source layer 7 are formed.

On the other hand, in the region where the storage capacitor C is formed, as shown in detail in FIG. 5, the polycrystalline semiconductor layer 4 serving as the upper electrode is formed into a comb shape so as to pass through the gap to serve as the lower electrode. Conductive impurities will be doped in the crystalline semiconductor layer 2.

Thereafter, heat treatment is performed to activate the drain layer 6 and the source layer 7, and the polycrystalline semiconductor layer 2 serving as the lower electrode is free from conductive impurities as shown in detail in FIG. It is diffused and becomes conductive throughout its area.

Step 6. (FIG. 3B) A protective film 9 is formed on the main surface of the lower glass substrate 1 thus processed by, for example, depositing a silicon nitride film, and the drain film 6 of the thin film transistor TFT is formed on the protective film 9. A through hole 10 exposing a part of the above is formed, and a drain electrode 11 to which the drain layer 6 is connected is formed on the protective film 9 at the through hole 10.

The drain electrode 11 is formed of, for example, aluminum (Al), and at this time, at the same time, a video signal line (not shown) integrally connected to the drain electrode 11 is formed.
To form.

Further, the protective film 12 is formed so as to cover the drain electrode 11 and the video signal line.

Step 7. (FIG. 3 (c)) The protective film 9 in the region which becomes the pixel substantially is selectively removed by using the photolithography technique to expose the polycrystalline semiconductor layer 2 in this region.

Step 8. (FIG. 4A) A transparent electrode (ITO) 13 is selectively formed on the surface of the polycrystalline semiconductor layer 2 exposed in a region which becomes a pixel substantially. Since the transparent electrode 13 is formed on the upper surface of the polycrystalline semiconductor layer 2 having conductivity, the thin film transistor T
It is formed in a state of being connected to the source layer of the FT.

According to the liquid crystal display substrate constructed as shown in such an embodiment, the upper conductive layer of the storage capacitor C has a shape having a portion exposing the underlying silinco oxide film 3. , As a result, the peripheral length is increased.

As a result, even if the overlapping area of the upper conductive layer with respect to the lower conductive layer becomes small, it is possible to secure the capacitance with the increase of the peripheral length.

This is based on the consideration that the storage capacitor element C formed in the pixel region of the liquid crystal display substrate contributes to the so-called fringe capacitance.

Since the overlapping area of the upper conductive layer with respect to the lower conductive layer is reduced, it becomes possible to suppress the generation of leak current during that time.

Further, according to the above-described method of manufacturing a liquid crystal display substrate, in order to form the source layer and the drain layer in the semiconductor layer of the thin film transistor TFT when the lower conductive layer of the storage capacitor C is made to have conductivity. This can be performed at the same time when the conductive impurities are doped using the gate electrode as a mask and the heat treatment is performed.

That is, the lower conductive layer of the storage capacitor C is formed of the same material as the semiconductor layer of the thin film switching element TFT and at the same time, and then (usually) usually, a mask is applied to the material on the thin film switching element TFT side. The material on the side of the storage capacitor C is doped with conductive impurities.

However, without performing this step at all,
At the same time as forming the source layer and the drain layer of the thin film switching element TFT, the lower conductive film is made conductive by doping conductive impurities through the exposed portion of the lower insulating layer in the upper conductive layer of the storage capacitor C. Will be able to.

Therefore, the number of manufacturing steps can be reduced.

In the above-described embodiment, the shape of the upper conductive layer of the storage capacitor element C is comb-shaped as shown in FIG. 1, but the shape is not limited to this shape. Needless to say, as shown in the figure, it may have a shape having through holes scatteredly arranged.

Even in this case, the peripheral length of the upper conductive layer can be increased. Then, it is possible to dope the lower conductive layer positioned in the lower layer with conductive impurities through the holes.

[0060]

As described above, according to the liquid crystal display substrate of the present invention, it is possible to provide a storage capacitor element capable of reducing so-called interlayer leakage.

Further, according to the method for manufacturing a liquid crystal display substrate of the present invention, the number of steps can be reduced.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram showing an embodiment of a liquid crystal display substrate according to the present invention.

2A to 2D are process diagrams showing an embodiment of a method for manufacturing a liquid crystal display substrate according to the present invention.

3A to 3C are process diagrams subsequent to the process shown in FIG.

FIG. 4A is a process drawing that follows the process shown in FIG.

FIG. 5 is an explanatory diagram showing a main part in one step of a method of manufacturing a liquid crystal display substrate according to the present invention.

FIG. 6 is an explanatory diagram showing a main part in one step of a method of manufacturing a liquid crystal display substrate according to the present invention.

FIG. 7 is a main part configuration diagram showing another embodiment of the liquid crystal display substrate according to the present invention.

FIG. 8 is a circuit diagram showing an embodiment of an equivalent circuit in the liquid crystal display substrate according to the present invention.

[Explanation of symbols]

 2 ... Polycrystalline semiconductor layer (lower conductive layer) 3 ... Silicon oxide film (dielectric) 4 ... Polycrystalline semiconductor layer (upper conductive layer)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Sato 3300 Hayano, Mobara-shi, Chiba Electronic device division, Hitachi, Ltd. (72) Hirofumi Koshi 3300 Hayano, Mobara-shi, Chiba Hitachi, Ltd. Electronic device business Inside (72) Inventor Hiroko Hayada 3300 Hayano, Mobara-shi, Chiba Hitachi, Ltd. Electronic Device Division

Claims (2)

[Claims] 1. A thin film switching element which is turned on by a signal from a scanning signal line in each pixel region on the liquid crystal side surface of one transparent substrate among transparent substrates arranged to face each other through a liquid crystal, and the thin film. A transparent electrode to which a signal from a video signal line is supplied via a switching element and a storage capacitor element for storing the video signal connected to the transparent electrode are formed, and the storage capacitor element has an insulating layer interposed therebetween. In a liquid crystal display substrate composed of a laminate of a lower conductive layer and an upper conductive layer, the upper conductive layer of the storage capacitor has a shape having a portion exposing the lower insulating layer and its peripheral length. Is longer than that of the lower conductive layer, a liquid crystal display substrate. 2. A thin film switching element which is turned on by a signal from a scanning signal line in each pixel region on the liquid crystal side surface of one transparent substrate among transparent substrates arranged to face each other through a liquid crystal, and the thin film. A transparent electrode to which a signal from a video signal line is supplied via a switching element and a storage capacitor element for storing the video signal connected to the transparent electrode are formed, and the storage capacitor element has an insulating layer interposed therebetween. A semiconductor display substrate formed of a laminate of a lower conductive layer and an upper conductive layer, the step of simultaneously forming the polycrystalline semiconductor layer of the thin film transistor and the lower conductive layer of the storage capacitor element with the same material, Forming a gate insulating layer of the thin film transistor and a dielectric layer of the storage capacitor at the same time; a gate electrode of the thin film transistor and an upper conductive layer of the storage capacitor; In the manufacturing method including the step of simultaneously forming, the upper conductive layer of the storage capacitor is formed so as to have a portion that exposes the insulating layer of the lower layer thereof, and a source layer and a drain layer are formed in the semiconductor layer of the thin film transistor. A method for manufacturing a liquid crystal display substrate, characterized in that when a conductive impurity is doped with a gate electrode as a mask for heat treatment and heat treatment is performed, the lower conductive layer of the storage capacitor element is made to have conductivity at the same time.