KR0174032B1 - Tft for lcd - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor for a liquid crystal display device and a method of manufacturing the same, wherein a lower gate electrode and a gate insulating film are formed on a transparent substrate, and a semiconductor layer pattern made of amorphous silicon is formed thereon, Since the photoresist pattern formed by the back exposure is formed with a high concentration impurity layer for ohmic contact on both sides as a mask, a gate insulating film and an upper gate electrode are formed on the upper side to increase the channel width of the TFT. The aperture ratio can be reduced to improve the reliability, and the reliability of device operation can be improved in TFTs having the same area.

Description

Thin film transistor for liquid crystal display device and manufacturing method thereof

1 is a layout for explaining a thin film transistor for a liquid crystal display device according to the prior art.

2 is a cross-sectional view taken along the line A-A in FIG.

3 is a layout for explaining a thin film transistor for a liquid crystal display device according to the present invention.

4 is a cross-sectional view taken along the line C-C in FIG.

5 is a cross-sectional view taken along the line B-B in FIG.

* Explanation of symbols for main parts of the drawings

1 transparent substrate 2 gate electrode

3: gate insulating film 4: semiconductor layer

5: etching stopper 6: high concentration impurity layer

7: field oxide film 8: contact hole

9 source electrode 10 drain electrode

11 gate line 12 data line

13: pixel electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor for a liquid crystal display (hereinafter referred to as LCD) and a method of manufacturing the same, and in particular, a gate connected to a gate line above and below a semiconductor layer pattern. The present invention relates to a TFT for an LCD and a method of manufacturing the same, by forming an electrode in two layers to improve the aperture ratio of the LCD, to improve definition, and to improve the reliability of device operation.

LCD, which is a kind of flat pannel display, is a device that changes the optical anisotropy by applying electric field to liquid crystal that combines liquidity and optical properties of crystal, and consumes more power than conventional cathode ray tube. Its low volume, small size, large size and high definition make it widely used.

In general, LCDs are configured in such a manner that liquid crystal is sealed between a lower liquid crystal substrate having pixel electrodes formed therein and connected to a switching element, and an upper liquid crystal substrate having common electrodes formed thereon.

Looking at the manufacturing method of the conventional LCD is as follows.

First, a pixel electrode made of indium thin oxide (ITO) and a transparent electrode pattern are formed on a transparent substrate made of quartz, and a protective film and a liquid crystal are formed to prevent a short circuit of the transparent electrode pattern. Alignment films for aligning are formed sequentially.

Then, a rubbing is performed to form valleys having a certain directionality in the alignment layer by using a rubbing roll wound around a cylindrical core to give the alignment layer a direction, thereby completing the lower liquid crystal substrate.

Thereafter, after forming an upper liquid crystal substrate having a common electrode, the upper and lower liquid crystal substrates are sealed by forming spacers and a failure turn so as to have a constant cell height, injecting liquid crystal into the cell cell, and sealing to complete the LCD.

Conventional LCDs as described above are classified into T. ne (Twisted Nematic), S. T. (Super Twisted Nematic), Ferroelectric, TEF LCD, etc., depending on the type of liquid crystal used and the driving method.

TFT LCDs using TFTs as switching elements for pixel operation have faster response speed, wider viewing angles, and larger screens, higher definitions, and higher definitions than other types of LCDs.

The structure of such a TFT can be largely distinguished according to the position of an active layer which is a semiconductor layer pattern. In other words, the semiconductor layer is divided into a staggered type in which the gate electrode and the source / drain electrode are separated, and a coplanar type in which the gate electrode and the source / drain electrode are formed on one surface of the semiconductor layer.

However, in the TFT LCD, a TFT element must be formed on one side of the pixel, and a gate bus and a data bus line must be disposed to operate the element, thereby causing a problem that the aperture ratio of the pixel is lowered.

In particular, the TFT using amorphous silicon as a channel has a lower charge mobility than the case of using a polysilicon layer as a channel, so that the channel width must be made larger, and thus the aperture ratio becomes worse.

1 and 2 are diagrams for explaining the TFT for LCD according to the prior art, which is an example of a staggered TFT, and will be described in association with each other.

First, a gate electrode 2 having a metal pattern is formed on the transparent substrate 1, and a gate insulating film 3 made of an oxide film is formed on the entire surface of the structure. At this time, one side of the gate electrode 2 is connected to the gate line 11 extending in the horizontal direction with respect to the transparent substrate (1).

In addition, a rectangular semiconductor layer 4 pattern in which a center portion overlaps with the gate electrode 2 is formed of amorphous silicon on the gate insulating layer 3 on the gate electrode 2, and the gate electrode 2 is formed. On the upper semiconductor layer 4 pattern, an etching stopper 5 formed of an oxide film or a nitride film pattern is formed.

A high concentration impurity layer 6 is formed on the semiconductor layer 4 pattern exposed by the etching stopper 5, and a field oxide film 7 is formed on the entire surface of the structure.

In addition, contact holes 8 expose portions of both sides of the high concentration impurity layers 6, and source and drain electrodes 10 and 10 contacting the high concentration impurity layers 6 on each side are formed, respectively. The source electrode 8 and the drain electrode 10 are connected to the data line 12 and the pixel electrode 13 made of a transparent electrode, respectively, extending in the vertical direction.

The LCD TFT using the conventional amorphous silicon layer as the channel is difficult to reduce the width of the channel to form a large TFT, there is a problem that the aperture ratio of the LCD falls.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a TFT for LCD which can improve the aperture ratio by reducing the size of the TFT by forming metal gate electrodes on the upper and lower sides of the amorphous silicon layer pattern. have.

Another object of the present invention is to form a lower gate electrode and a gate insulating film on a transparent substrate, form an amorphous silicon layer pattern overlapping the lower gate electrode and a center portion, and form a gate insulating film and an upper gate electrode on the upper side again. By increasing the width of the channel to reduce the size of the TFT to provide an LCD manufacturing method that can improve the aperture ratio.

The LCD TFT according to the present invention for achieving the above object is characterized in that the first gate electrode formed on the transparent substrate, the first gate insulating film formed on the entire surface of the structure, and the first A semiconductor layer pattern formed on the first gate insulating film so as to overlap the gate electrode and extending to both sides, a high concentration impurity layer formed on the semiconductor layer pattern on both sides of the first gate electrode, and the entire surface of the structure A second gate insulating film, a second gate electrode formed on the second gate insulating film so as to overlap the first gate electrode, and having one side connected to the first gate electrode through a contact hole, and the high concentration impurity layers on both sides. Contact holes exposing the high concentration impurity layer by sequentially removing the second and first gate insulating layers on one side and through the contact hole; As is provided with the source / drain electrodes in contact with the high concentration impurity layer.

To achieve another object, a feature of the TFT manufacturing method for an LCD according to the present invention is to form a first gate electrode on a transparent substrate, to form a first gate insulating film on the entire surface of the structure, and Forming a semiconductor layer pattern overlapping a first gate electrode and a central portion on the first gate insulating film, forming a high concentration impurity layer on the semiconductor layer pattern on both sides of the first gate electrode, and Forming a second gate insulating film on an entire surface of the first gate electrode; and removing portions of the first gate electrode not overlapping with the semiconductor layer pattern, and removing the second gate insulating film on one side of the high concentration impurity layer on both sides to expose each of the first gate electrode. Forming a contact and a high concentration through a contact hole different from the second gate electrode overlapping the first gate electrode and contacting through the contact hole; It consists in a fixing to form a source / drain electrode in contact with the impurity layer.

EMBODIMENT OF THE INVENTION Hereinafter, the TFT for LCD which concerns on this invention, and its manufacturing method are demonstrated in detail with reference to an accompanying drawing.

3 to 5 are diagrams for explaining the TFT for LCD according to the present invention, in which the structure and the manufacturing method are simultaneously described in association with each other.

First, the gate line 11 extending on the transparent substrate 1 made of a transparent material, for example, quartz or glass, has a predetermined width in the horizontal direction, and one side protrudes to become the first gate electrode 2A. It is formed of a metal pattern such as Cr, Ti, or Al, and a first gate insulating film 3A made of an oxide film is formed on the entire surface of the structure.

Subsequently, a pattern of the semiconductor layer 4 overlapping with the first gate electrode 2A at the center portion is formed of amorphous silicon having a rectangular shape on the first gate insulating film 3A, and the first gate electrode 2A is formed. A high concentration impurity layer 6 is formed by implanting N or P-type impurities into the semiconductor layer 4 patterns on both sides by ion implantation or ion showering. In this case, a mask of the ion implantation uses a photoresist pattern (not shown) formed by a backside exposure method using the first gate electrode 2A as a mask.

Thereafter, a second gate insulating film 3B made of an oxide film is formed on the entire surface of the structure, and an upper side of the gate line 11 in contact with the first gate electrode 2A and both sides of the high concentration impurity layer 6. The upper and second gate insulating layers 3B and 3A are sequentially removed to form contact holes 8 exposing each of them. In this case, the first and second gate insulating films 3A and 3B are formed by chemical vapor deposition (hereinafter referred to as CVD) or physical vapor deposition (hereinafter referred to as PVD).

Next, the second gate electrode 2B overlaps the first gate electrode 2A and contacts the gate line 11 exposed by the contact hole 8, and the contact hole 8 is formed through both contact holes 8. The source electrode 9 and the drain electrode 10 in contact with the exposed high concentration impurity layer 6 are formed in a metal pattern such as Ti, Cr or Al. In this case, the second gate electrode 2B may not be in contact with the gate line 11 but may be in contact with one side of the first gate electrode 2A, and the source electrode 9 may be integrally formed with the data line 12. The drain electrode 10 is in contact with the pixel electrode 13 having a transparent electrode pattern.

As described above, the TFT for LCD according to the present invention forms a lower gate electrode and a gate insulating film on a transparent substrate, forms a semiconductor layer pattern of amorphous silicon on the top thereof, and is formed on both sides of the semiconductor layer pattern. After forming a photoresist pattern formed of a high concentration impurity layer for MIC contact by a backside exposure as a mask, a gate insulating film and an upper gate electrode were formed on the upper side thereof to increase the channel width of the TFT. In this case, the TFT having the same area has the advantage of improving the reliability of device operation.

Claims (11)

A first gate electrode formed on the transparent substrate, a first gate insulating film formed on the entire surface of the structure, and a first gate insulating film formed on the first gate insulating film, wherein the center portion overlaps with the first gate electrode. The semiconductor layer pattern, the highly doped impurity layer formed on the semiconductor layer patterns on both sides of the first gate electrode, the second gate insulating film formed on the entire surface of the structure, and the first gate electrode. The second gate electrode formed on the second gate insulating layer and connected to the first gate electrode on one side thereof through the contact hole, and the second and first gate insulating layers on the high concentration impurity layer are removed to expose the high concentration impurity layer. A thin film for a liquid crystal display device having contact holes and source / drain electrodes contacting the high concentration impurity layer through the contact hole Transistors. The thin film transistor of claim 1, wherein the transparent substrate is made of quartz or glass. The thin film transistor for liquid crystal display device according to claim 1, wherein the semiconductor layer pattern is formed of amorphous silicon. The thin film transistor of claim 1, wherein the first and second gate electrodes are formed of any one of Ti, Cr, and Al. The thin film transistor of claim 1, wherein the source and drain electrodes are formed of any one of Ti, Cr, and Al. The thin film transistor of claim 1, wherein the first and second gate insulating films are formed of an oxide film. The thin film transistor of claim 1, wherein the high concentration impurity layer is N or P type. Forming a first gate electrode on the transparent substrate, forming a first gate insulating film on the entire surface of the structure, and a semiconductor layer overlapping the first gate electrode and a central portion on the first gate insulating film Forming a pattern; forming a high concentration impurity layer on the semiconductor layer patterns on both sides of the first gate electrode; forming a second gate insulating film on the entire surface of the structure; Forming contact holes exposing portions not overlapping with the semiconductor layer pattern and exposing the high concentration impurity layer, a second gate electrode overlapping the first gate electrode and contacting through the contact hole, and another contact hole; A method of manufacturing a thin film transistor for a liquid crystal display device, comprising the step of forming a source / drain electrode in contact with a high concentration impurity layer through a semiconductor device. 10. The method of claim 8, wherein the high concentration impurity layer is formed using a photosensitive film pattern formed by backside exposure as a mask. The method of manufacturing a thin film transistor for a liquid crystal display device according to claim 8, wherein the high concentration impurity layer is formed by an ion implantation or an ion shower method. 10. The method of claim 8, wherein the first and second gate insulating films are formed by a CVD or PVD method.