JPH01267616A - lcd display - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a liquid crystal driving substrate in which a TPT (thin film transistor) is formed on a transparent glass substrate, and in particular, a light shielding film is provided to eliminate the influence of light on the TPT characteristics. The present invention relates to a structure suitable for reducing the off-state current of TPT.

[Conventional technology]

Conventionally, regarding TPT substrates for liquid crystal drives with light-shielding films, for example, Proceedings of the SID
voQ, 1 25/1 (1984) pp. 11-16 (
Proceedings of the SID, vo
Q, 125/1 (1984) ppH~16).

[Problem to be solved by the invention]

2. Description of the Related Art There is active development of devices in which TPTs (thin film transistors) are formed in a matrix on an insulating substrate such as glass to drive liquid crystals to display images. In such a liquid crystal display device, the TPT for driving the liquid crystal must be used under strong light irradiation due to its device configuration, but when the TPT is driven under such strong light irradiation, the active layer may be damaged. Due to photoexcited electrons and holes, T
The off-state current of the PT increases, causing a serious problem in driving the liquid crystal.

In order to solve this problem, a conventional structure in which a light-shielding film is provided above the active region of the TPT is shown in FIG. After forming an island-shaped polysilicon film on a transparent glass substrate 1, a gate insulating film 5. The gate polysilicon layer 6 is deposited and patterned, and impurity ions are implanted.
Self-aligned source/drain layer 2. Channel layer 3. Gate insulating film 5. A gate polysilicon layer 6 is formed. After forming a passivation film 79, a transparent electrode 10° which is a pixel electrode, and a wiring metal 8, a light shielding film 9 is formed of a metal such as AQ to a size that covers the junctions 4 at both ends of the channel layer 3 in order to prevent the generation of photoexcitation current. be done.

In this process, if the polysilicon layer is deposited by low pressure CVD, it will be deposited on both sides of the substrate, so the polysilicon layer on the back side of the substrate is finally removed.

However, although this conventional method of blocking light is effective against light from the top of the substrate, it cannot block light from the back surface of the bottom of the substrate because the glass substrate 1 is transparent. A photoexcitation current is generated in the channel layer 3 and TP
This will cause an increase in the off-state current of T. In addition, in order to reliably block light, it is desirable that the size of the light shielding film 9 is large, but on the other hand, in order to obtain a clear image, TPT requires a reduction in the area ratio (aperture ratio) of light passing through the pixel area. It is necessary to make it larger. Since the polysilicon layer has a light-shielding property, the size of the light-shielding film 9 that maximizes both the aperture ratio and the light-shielding property is determined by the size of the source/drain layer 2. The best size is the same as that of the island-shaped polysilicon layer forming the channel layer 3.

In order to make the light-shielding film 9 the same size as the island-like polysilicon layer in the conventional example shown in FIG. 2, it is necessary to form the wiring metal 8 and then form an insulating film because it is necessary to insulate it from the wiring metal 8. The light shielding film 9 must be formed, which complicates the manufacturing process.

An object of the present invention is to provide a structure that blocks light more reliably without complicating the process.

[Means to solve the problem]

A structure for achieving the above purpose is shown in FIG.

The polysilicon layer deposited on the back surface of the glass substrate 1 when forming the source/drain layer 2, the channel layer 3, and the gate polysilicon layer 6 is used as the source/drain layer 2. Channel N!
Batter to the same size as the island-shaped polysilicon consisting of I3, -
By stripping and leaving it as the back light shielding film 11, stronger light shielding can be achieved with a minimum of additional steps, and the above object is achieved.

[Effect]

In FIG. 1, a back light shielding film 1 made of polysilicon is shown.
1 exhibits color and can block light, so the channel layer 3
Since the photoexcitation generated current within the TPT can be suppressed, the off-state current of the TPT can be suppressed.

Next, the shape of the 1A-plane light-shielding film 11 will be explained with reference to FIG. In FIG. 3, photolithography techniques are used in the -shell during patterning after gate polysilicon ff1ll deposition. At this time, as shown in FIG. 3-a, a positive photoresist 12, which is a photosensitive material, is applied to both sides of the glass substrate 1, and a photomask 12 for patterning the gate polysilicon layer 6 is placed on the top of the glass substrate 1. Deploy. When exposed using this method, the source/drain layer 2 in FIG.
Since the island-shaped polysilicon layer 14 forming the channel layer 3 does not transmit light, the photoresist 13 on the back surface corresponding to this layer remains as shown in Figure b.

According to this method, the back light shielding film can be self-aligned with the front island polysilicon layer 14.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. (a
) In the figure, 1500 polysilicon layers are deposited on both sides of the substrate by low pressure CVD, and the front surface is patterned to form an island-like polysilicon layer 14 and a back light shielding film a15. After heat treatment is performed to electrically activate the island-like polysilicon layer 14, 1000 5 iOz film is deposited as the gate insulating film 5 by atmospheric pressure CVD. 5. Next, I) deposit a polysilicon layer on both sides of the substrate by low pressure CVD method. Forming Gate Polysilicon Layer 6 and Back Light-shielding Film b16 Next, as shown in ())), photoresist 13 is formed on both sides of the substrate by the method described in FIG. after that,
The surface is etched using this photoresist 13 as a masking material.

A gate polysilicon layer 6 and a gate insulating film layer 5 are formed, and -i-plane light shielding films a and b are patterned on the back surface.

According to this embodiment, the back light shielding film a15. b16 can be patterned in self-alignment with respect to the island-shaped polysilicon layer. Furthermore, since the back light shielding film is deposited simultaneously with the deposition of polysilicon on the five front surfaces, the process of depositing the film as the light shielding film is simplified.

FIG. 5 is an example showing the distribution of the back light shielding film in the glass substrate. When configuring within the glass substrate 1 in order to reduce the number of drive devices externally attached to the glass substrate 1, the light shielding film 11 is left on the entire back surface of the peripheral circuit section 18, and the polysilicon film of each pixel is left on the display section inside the substrate. This is an example in which the back light shielding film 11 is provided in self-alignment with respect to the layer.

Further, the back light shielding film 1 is not limited to polysilicon, and may be made of any material that has light shielding properties and can be patterned; for example, it may be made of a metal such as amorphous silicon or AQ.

Further, a liquid crystal drive display can be manufactured using the thin film semiconductor substrate of the present invention as a component.

〔Effect of the invention〕

According to the present invention, by first providing a back light shielding film, T
The off-state current of the PT can be reduced. Also.

If you use the self-alignment method shown in Figure 3, then Ho! - Since there is no need to form a back light shielding film with dimensions that include mask alignment accuracy, it is possible to form a back light shielding film with a size that maximizes both aperture ratio and light shielding performance.

Furthermore, if a polysilicon layer is used for the back light shielding film, it can be deposited simultaneously with the formation of the front surface polysilicon, thereby simplifying the process.

[Brief explanation of the drawing]

FIGS. 1(a) and (b) are a diagram and an X-Y sectional view showing an embodiment of the present invention, and FIGS. 2(a) and (b) are a structural diagram and an X-Y sectional view of a conventional example. FIG. 3 is a diagram showing one embodiment of the present invention, FIG. 4 is a process diagram of one embodiment of the present invention, and FIGS. 5(a) and (b) are diagrams showing one embodiment of the present invention. . 1...Glass substrate, 2...Source train layer, 3...
...Channel layer, 4.Junction, 5.Gate insulating film,
6... Gate polysilicon layer, 7 - Passivation film, 8... Wiring metal, 9... Light shielding film, 10... Transparent electrode, 11... Back light shielding film, 12... F first -Mask, ]-3... Photoresist, 14... Island polysilicon layer, 15... Back light shielding film a, ]6... Back light shielding film b, Core... Display section, 18...・Peripheral circuit section.

Claims (1)

[Claims] 1. A liquid crystal display having a structure in which a thin film semiconductor element is formed on a transparent insulating substrate, characterized in that a light-shielding film is provided at least in an area on the back surface of the substrate corresponding to an active area of the semiconductor element. . 2. The liquid crystal display according to item 1, wherein the light shielding film is a semiconductor layer. 3. The liquid crystal display according to item 1, wherein the light shielding film is a film deposited during formation of a semiconductor thin film of a thin film semiconductor element. 4. The liquid crystal display according to item 1, wherein the light-shielding film is manufactured by photolithography and processed in self-alignment with the semiconductor layer of the thin-film semiconductor element. 5. The liquid crystal display according to item 1, characterized in that the light shielding film is disposed on both sides of the transparent insulating substrate.