JP2536230B2 - Active matrix liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an active matrix liquid crystal display device (LC) including a thin film transistor (TFT) or the like.
Regarding D).

[Prior Art] Conventionally, an active matrix LCD of this type is configured as shown in FIG.

That is, the gate electrode 2 of the TFT is formed on the glass substrate 1, and the gate insulating film 3 is formed on the entire surface to cover the gate electrode 2.
Are formed. An Si film 4, an n ⁺ Si film 5, and a source / drain electrode 6 are sequentially formed on the upper surface of the gate insulating film 3 immediately above the gate electrode 2. And from the top surface, Si
The dug portion 8 reaching the film 4 is formed, the pixel electrode 7 connected to the source / drain electrodes is formed, and the upper surface thereof is covered with the surface protective film 9. As a result, the portion where the gate electrode 2 is arranged is the TFT portion 10,
The portion of the picture element electrode 7 is used as the picture element portion 11.

By the way, the surface protection film 9 of such an active matrix LCD is formed so as to cover the entire TFT section 10 and the picture element section 11. Conventionally, as shown in FIG. 4, the surface protection film 9 is a silicon oxide film (SiN ₂ ), a silicon oxynitride film (SiO _x N _y ), or a silicon nitride film (Si).
₃ N ₄ ) etc. are used. In addition to these films having a constant composition, films having a two-layer structure such as SiO ₂ —Si ₃ N ₄ are also used.

[Problems to be Solved by the Invention] However, the conventional active matrix described above is used.
In the LCD, the surface protection film has the following problems.

That is, the silicon oxide film has a problem that the barrier effect against alkali ions is small and the reliability is not so high.

The silicon nitride film has a sufficient barrier effect against alkali ions, but when it is directly formed on Si, the film stress is large, so that a thick film causes cracks and film peeling, and a thin film causes the channel dug portion 8 to be formed. There is a problem that the covering property at the step portion is not good. Further, the silicon nitride film has a problem that the interface state density is large and channel leak occurs.

Further, the silicon oxynitride film has a property intermediate between the two, but the reproduction stability under the optimum growth conditions is poor,
Even under the optimum conditions, the film quality is halfway.

Further, the two-layer structure film of SiO ₂ —Si ₃ N ₄ has a problem that the film strain and the interface state density at the interface between SiO ₂ and Si ₃ N ₄ are large, and cracks and film peeling occur. there were.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an active matrix liquid crystal display device that does not cause problems such as cracks and film peeling, and has a high barrier effect against alkali ions. And

[Means for Solving the Problems] An active matrix liquid crystal display device according to the present invention is an active matrix liquid crystal display device in which a surface protective film is formed on a back channel dug by etching. Is a silicon oxide film formed on the back channel in contact with semiconductor silicon, a silicon oxynitride film formed on the silicon oxide film, and a silicon nitride film formed on the silicon oxynitride film. And a composition of the silicon oxynitride film that changes gently from the silicon oxide film side to the silicon nitride film side.

[Operation] According to the present invention, since the silicon oxide film is formed on the semiconductor silicon on the back channel side, film stress and interface state density can be reduced, and stable and favorable characteristics can be obtained. You can In addition, since the composition of the silicon oxynitride film, which is the intermediate layer, is gently changed, there is no localization of the interface state as seen in the conventional SiO ₂ —Si ₃ N ₄ interface, and The stress is small, the film can be made thicker, and there is no fear of film peeling. Further, since the uppermost part is the silicon nitride film, the barrier effect against the contamination and invasion of alkali ions is sufficient.

[Embodiment] An embodiment of the present invention will be described below with reference to the accompanying drawings.

First, after forming the TFT section 10 and the picture element section 11, a monosilane (SiH ₄ ) -nitric oxide (NO) system is formed as a surface protection film by a plasma CVD method so as to cover a step of 2800 Å in the channel dug section. To form a SiO ₂ film of 1000 Å, then SiH ₄ −
A silicon oxynitride film of 2000 Å is formed by NO-ammonia (NH ₃ ) system. The growth temperature is 270 ° C. Silicon oxynitride forming time is, the flow rate of SiH ₄ is constant, NO and NH ₃ flow rate decreases with each time, and set to increase, the composition of silicon oxynitride, Si ₃ N of SiO ₂ side Make it change to ₄ side continuously.

The composition of the film thus formed is shown in FIG. As shown in this figure, the surface protection film 20 is made of Si that contacts the Si film 4.
It has a three-layer structure of an O ₂ layer 21, a silicon oxynitride (Si _x N _y ) layer 22 in contact with the SiO ₂ layer 21, and a Si ₃ N ₄ layer 23 in contact with the layer.

Further, FIG. 2 is a graph showing the composition change of the surface protective film 20 in the film thickness direction.

The silicon oxynitride (Si _x N _y ) layer 22 located in the film thickness d ₁ to d ₂ has a film thickness x ₁ near the film thickness d _{1 in} contact with the SiO ₂ layer 21.
2, y = 0, x = 0, y = 4/3 near the film thickness d _{2 in} contact with the Si ₃ N ₄ layer 23
And its composition is gradually changing.

By forming such a surface protection film 20, film stress and interface state density on the back channel side can be reduced, and stable and favorable TFT characteristics can be obtained. Further, since the composition of the oxynitride layer 22 of the intermediate layer is gradually changed, localization of the interface state density can be prevented, the film stress is small, the film can be made thick, and the problem of film peeling Can be solved. Furthermore, the top is Si ₃ N
_Since it is the _four layers 23, the barrier effect against alkali ions is also sufficient.

It should be noted that the same channel digging as in the above-mentioned embodiment was covered with 2800 Å steps of SiH ₄ -carbon dioxide (CO ₂ ) system with SiO ₂ of 1000.
Å 、 SiH ₄ --CO ₂ --NH ₃ system
2000Å, Si ₃ N ₄ may be formed in 1000Å by SiH ₄ -NH ₃ system. The growth temperature is 270 ° C.

In this embodiment, since CO ₂ is used as the oxygen supply source gas, there is an advantage that the problems such as the corrosiveness, the toxicity, and the combustion supporting property, which are found in the NO gas of the previous embodiment, do not occur.

The thickness of each film of SiO ₂ , SiO _X N _Y and Si ₃ N ₄ may be determined in consideration of the depth of the channel dug portion, TFT characteristics, reliability and the like.

Also, a good TFT without affecting the back channel Si
In order to obtain the characteristics, it is desirable that the SiO ₂ film thickness is 300 Å or more. Furthermore, in order to obtain a sufficient barrier effect against alkali ions, the film thickness of the Si ₃ N ₄ film is preferably 300 Å or more. Si _x O _y is set to a film thickness that provides good step coverage at the channel dug portion.

Needless to say, the present invention can be applied not only to the TFT active matrix type LCD but also to other types of active matrix type LCD such as MIM type.

[Effects of the Invention] As described above, according to the present invention, the surface protection film formed on the back channel by etching has a three-layer structure including a silicon oxide film, a silicon oxynitride film, and a silicon nitride film. In addition, since the composition of the silicon oxynitride film is gradually changed from the silicon oxide film side to the silicon nitride film side, problems such as cracks and film peeling do not occur, and alkali High barrier effect against ions. Therefore, the manufacturing yield is high and the initial characteristics are superior to those of the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the composition of a surface protective film of an active matrix type liquid crystal display device according to an embodiment of the present invention, FIG. 2 is a graph diagram qualitatively showing the composition of the protective film, and FIG. FIG. 4 is a cross-sectional view showing the configuration of a conventional active matrix type liquid crystal display device, and FIG. 4 is a schematic diagram showing the composition of a conventional surface protective film in the device. 1; glass substrate, 2; gate electrode, 3; gate insulating film, 4; Si
Film, 5; n ⁴ Si film, 6; source / drain electrode, 7; pixel electrode,
8: Channel dug portion, 9, 20; Surface protective film, 10; TFT portion, 1
1; picture element part, 21; SiO ² layer, 22; silicon oxynitride layer, 23; Si ₃ N ₄ layer

Claims (2)

(57) [Claims] 1. An active matrix liquid crystal display device having a surface protective film formed on a back channel formed by etching, wherein the surface protective film comprises:
A silicon oxide film formed on the back channel in contact with semiconductor silicon, a silicon oxynitride film formed on the silicon oxide film, and a silicon nitride film formed on the silicon oxynitride film. And the silicon oxynitride film comprises
An active matrix type liquid crystal display device characterized in that its composition is gently changed from the silicon oxide film side to the silicon nitride film side. 2. The active matrix type liquid crystal display device according to claim 1, wherein the silicon oxide film and the silicon nitride film each have a film thickness of 300 Å.