JPS6247621A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the operating characteristics and the reliability of the device by insulating between a transparent electroconductive film (a ITO film) composed of a picture element electrode and a thin film transistor (TFT), thereby preventing a reaction of the ITO film and the metallic film. CONSTITUTION:The TFT comprises a gate electrode 11, a gate insulating film 12, a semiconductor film 13, a source electrode 18 and a drain electrode 19. The drain electrode 19 is connected with the ITO film 15 of the picture element electrode. The reaction of the film 15 and an Al-Si film 17 of the drain electrode is prevented by lying a P-dopped a-Si film at a junction point of the electrode 19, the film 13 and the film 15, thereby giving an ohmic contact. The indium contd. in the film 15 does not diffuse in the semiconductor film by lying a silicon nitride film 14 between the films 13 and 15, thereby preventing the generation of a deterioration of the TFT characteristics. Thus, the thin film type transistor active matrix liquid crystal display device having the good operation characteristics and the high reliability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention uses arphanu silicon (a
-5i) Regarding an active matrix type axillary crystal display device formed by arranging thin film transistors (TPT) as switching elements in a matrix, in particular source/drain electrodes in the TPT and picture element electrodes formed from a transparent conductive film. The structure utilizes unique manufacturing technology.

<Prior Art> In recent years, in large-capacity display devices using liquid crystals, research has been actively conducted on active polymer IJ Fuchs liquid crystal display devices in which TFTs are formed in the shape of an I-IJ sock on an insulating substrate. Half silicon (poly-5i) and amorphous silicon (a-5i) are used as semiconductor materials for TPT.
, tellurium selenium (CdSe) alloy, etc. In particular, since a-Si is generated at a relatively low temperature, it is possible to form a large number of TPTs on an inexpensive galanic substrate, and the on/off ratio of TPTs can be set to a large value of 105 or more. It is seen as promising. a-Si as a semiconductor material
The structure of a conventional TPT using 200 nm is shown in cross-sectional views in FIGS. 3(A) and 3(B). 1 is a gate electrode, 2 is a gate insulating film, 3 is an a-Si semiconductor film, 4 is a picture element electrode, 5 is a source electrode, 6
is the drain electrode. In this way, the picture element electrode 4 and TFT
are connected and arranged in a matrix on a glass substrate to form one liquid crystal cell substrate. A counter electrode facing the picture element electrode 4 is formed on the other liquid crystal cell substrate, and the voltage applied between both electrodes is switched by TPT.

<Problems to be solved by the invention> T constituting the active material I/lithox type liquid crystal display device
In the substrate on which PTs are arranged, the wiring of the source electrode that inputs the data signal applies sufficient voltage to the liquid crystal.
It is necessary to form the source electrode with a low resistance metal or use low resistance Al as the source electrode.

If A6-5i or the like is used, the following problems arise.

When the TPT has a structure as shown in Figure 3 CB), when a transparent conductive film (ITO film) commonly used as the picture element electrode 4 is etched with a hydrochloric acid etchant, the etching rate of AlO is faster than that of the ITO film. Since the distance between the source and drain electrodes is much larger, it is difficult to accurately pattern the distance between the source and drain electrodes, which is the channel length of the TPT, and there is also the risk of disconnection in the A and L wirings due to seepage of the etching solution. exists. On the other hand, the method of forming the source wiring after patterning the ITO film which becomes the picture element electrode 4 as shown in FIG. 3(A) has the following drawbacks. First of all, when depositing the ITO film, indium (In) diffuses into the a-5i semiconductor film, which adversely affects the characteristics and reliability. Second, Aff or Aj? The ITO film may change in quality when depositing the -5i film. Thirdly, the adhesion between the Ae or An-5i film and the I'TO film is poor and they are likely to peel off at this interface.

In the TPT structure, a method is generally adopted in which a phosphorus (CP) doped a-3i film is interposed between the non-doped a-Si semiconductor film and the source/drain electrodes in order to establish ohmic contact between the a-Si and the source/drain. It is being In addition, a phosphorus-doped a-5i film is added not only between the non-doped me-5i film and the source-drain electrode, but also between the non-doped a-5i film and the source-drain electrode.
- Between Si film and ITO film or between ITO film and AI<
or A6-5i) It is possible to interpose it between either one of the films. However, phosphorus doped a-8i
A film is interposed between a non-doped a-Si film and an ITO film! : A6 (or A#-5i) membrane,! :IT
Problems with poor adhesion of O film and A7 when depositing Al (or A#-5i film)? There remains the problem that the ITO film reacts with the ITO film and the ITO film changes in quality. Also, lindope a-5i is ITO and 1' (or A6-5i
) In the structure in which the ITO film is interposed between the films, when the ITO film is deposited, the a-5i film and the ITO film react, and the ITO film is deposited in the a-5i film.
The problem remains that n is diffused.

Means for Solving the Problems> The present invention eliminates the above-mentioned drawbacks in a liquid crystal display device having a TPT-added type active material in which TPT source/drain electrodes are formed after forming pixel electrodes. It is intended to do so. That is, for example, a P-doped a-5i film is replaced with a non-doped a-5i film.
Interposed between the film and the source/drain electrode, and
TO film and AI (or A6-
3i) An insulating film is also interposed between the non-doped a-Si film and the ITO film to prevent the reaction between the ITO film and the metal film, that is, AN, by interposing it between the ITO film and the metal film such as AN. This is intended to prevent the reaction between the non-doped a-Si film and the ITO film and improve the characteristics and reliability of TPT.

<Example 1> FIGS. 1A, 1B, and 1C are manufacturing process diagrams of a TPT-added liquid crystal cell substrate for explaining one example of the present invention.

The liquid crystal display device of this embodiment is based on a liquid crystal display cell in which a field effect liquid crystal such as a twinned nematic liquid crystal is sealed, and an IJ sock-like pixel electrode is arranged on one cell substrate, and each pixel It is driven by a TPT addition method in which a TPT switching element is connected to one end of an electrode to generate a matrix display pattern in units of picture elements.

First, as shown in FIG. 1(A), a tank /L/(Ta) is deposited on a transparent substrate such as glass or plastic by sputtering.
) was deposited to a thickness of 200 OA and formed into a predetermined pattern using photolithography to form the gate electrode 11. Next, a first silicon nitride 7 (Si3
N4) The film 12 is superimposed by 2000A, and then the non-doped a-5i film 13 is deposited by 150A using a plasma CVD device.
After depositing 0A, e) a-5i at IJ Sogerahui.
The membrane 13 is formed into an island shape. Thereafter, a second silicon nitride (S 1 3N4) film 14 of 50 OA is deposited on the entire surface, and an ITO film 15 of 200 OA as a transparent conductive film is deposited by vapor deposition. Next, as shown in FIG. 1CB), the ITO film 15 and the silicon nitride layer 14 are formed into a predetermined pattern by photolithography, and the ITO film 15 constitutes a picture element electrode. Thereafter, as shown in FIG. 1(C), a phosphorus (P) doped a-5i film 16 is formed on the entire surface using a plasma CVD apparatus.
l? -5i film 17 by Nubatta ring? 3000
A6-5i film 17 and phosphorus-doped A-5illi film 116 are formed into a predetermined pattern by photolithography to form a source electrode 18 and a drain electrode 19.

Through the above steps, a TPT with connected picture element electrodes is formed on the transparent substrate. This TPT is the gate electrode 11,5i3Nn
Gate insulating film consisting of 12, non-do 1a -S i
A semiconductor film consisting of film 13, l? -81 film 17 and similarly Aj? -3i film 17, and the drain electrode 19 is IT'
It is superimposed on one end of a picture element electrode made of an O film 15 and connected in a heavy electrical manner.

A P-doped a-5i film 16 is interposed at the junction between the drain electrode 19, the pixel electrode, and the semiconductor film, and the ITO film 15 and the Ag
-5i film 17 reaction is prevented and ohmic contact is obtained. A second Si3N layer is formed between the semiconductor film of the non-doped a'-Si film 13 and the ITO film 15 of the picture element electrode.
4 films 14 are interposed, therefore, n in 5 in 1 ITO film 1 is interposed.
does not diffuse into the semiconductor film, and the characteristics of TPT do not deteriorate.

TPTs and picture element electrodes as described above are arranged in a matrix on a transparent substrate, and the gate electrodes of the TPTs are commonly connected vertically to form a gate wiring, and the source electrodes are commonly connected horizontally to form a source wiring. Form. Each TPT is individually switched by supplying a signal through the source wiring and applying a switching voltage through the gate wiring.

A liquid crystal display device is manufactured by disposing a counter substrate on which a common counter electrode common to each picture element electrode is formed opposite to this transparent substrate, and filling a field-effect liquid crystal in the gap between the counter substrates.

In response to the switching operation of the TPT, a driving voltage is applied from the drain electrode to the liquid crystal between the picture element electrode and the common electrode, and a) liquid crystal display of the IJ socks is performed.

<Example 2> FIGS. 2A, 2B, and 2C are manufacturing process diagrams of a TPT-added liquid crystal cell substrate for explaining another example of the present invention.

20 pieces of tantalum are placed on a black transparent substrate as shown in Figure 2 (A).
0OA is deposited and formed into a predetermined pattern by photolithography to form the gate electrode 21. Next, apply the first silicon nitride i22 2000k to the entire surface.

A non-doped a-Si film 23 was deposited at a thickness of 150 A, and a second silicon nitride film 24 was deposited at a thickness of 500 A, and the second silicon nitride film 24 and a non-doped a-Si film 24 were deposited by photolithography.
, 7 The Si film 23 is formed in a predetermined pattern. After that, as shown in Fig. 2 CB), an ITO film 25 is applied for 30 minutes over the entire surface.
A resist 26 is patterned on the surface of the 00A deposited ITO film 25 that will become a picture element electrode. Next, the resist film 26
ITO film 25. is used as a mask. Second silicon nitride film 2
4 is etched and shaped as shown in FIG. 2(C). At this time, the first silicon nitride film 22 may also be slightly etched, but this does not cause any problem in terms of the characteristics of TPT. Thereafter, the resist film 26 was removed and a phosphorus-doped a-3i film 27 was formed on the entire surface as shown in FIG.
The i film 27 is formed into a predetermined pattern to form a source electrode 29 and a drain electrode 30. Based on the above I) ITO film 25
A TPT to which picture element electrodes consisting of are connected is formed on a transparent substrate. The TPTs are arranged in a matrix on a transparent substrate to produce a liquid crystal display device similar to that of Example 1 described above.

<Effects of the Invention> As explained in detail above, an insulating film is interposed between the a-Si film of the TFT and the ITO film of the picture element electrode, and the insulation film is interposed between the a-5i film and the source/drain electrode and between the ITO film and the source/drain electrode. By interposing a phosphorus-doped a-Si film between the drain electrodes, a thin film transisc active matrix liquid crystal display device with good operating characteristics and reliability can be manufactured. Note that in the present invention, the metal of the source electrode is A1. Ti
, Mo, and other metal materials can be similarly applied.

[Brief explanation of drawings]

FIGS. 1 and 2 are manufacturing process diagrams of essential parts of a TPT-added substrate of a liquid crystal display device, respectively, for explaining one embodiment of the present invention. FIG. 3 is a sectional view of a conventional TPT-added substrate. 11.21... Gate electrode 12.22... First
Silicon nitride film 13.23...a - Si film (non-doped) 14.24... Second silicon nitride film 15.25-ITO film 16.27-
a-S i film (phosphorous doped) 17.28・-・A
l -3i film 18, 29...source electrode 19
．． 30... Drain electrode agent Patent attorney Aihiko Fukushi (and 2 others) 37
Figure 3Figure 2

Claims (1)

[Claims] 1. Arrange pixel electrodes made of transparent conductive film on one side of the cell substrate,
In a liquid crystal display device comprising a thin film transistor connected to each picture element electrode, a semiconductor film of the thin film transistor is made of amorphous silicon, an insulating film is interposed between the semiconductor film and the picture element electrode, and the thin film transistor A liquid crystal display device characterized in that a phosphorus-doped amorphous silicon film is interposed between the source/drain electrodes and the semiconductor film.