JPH06175154A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To enhance pressure resistance and display quality by forming an oxidized film by thermal oxidation, etching away a part thereof and forming an HTO film as a method for forming capacitor parts. CONSTITUTION:Quartz is used as a transparent insulating substrate and an intrinsic polycrystalline silicon film or amorphous silicon film is deposited thereon and is formed to the shapes of channel regions and sources 5 and drains 6 of thin-film transistors(TFTs) and lower electrodes 7 of additive capacitors of picture elements. The polycrystalline silicon film or amorphous silicon film deposited thus far is grown to the polycrystalline silicon film 2 by forming the oxidized silicon film 1 by the thermal oxidation. Further, the silicon oxide film 1 of the regions where the additive capacitors of the picture elements are formed is removed and thereafter, the HTO (high-temp. CVD silicon oxide) film is formed, by which a gate insulating film 3 and a dielectric substance film 4 are formed. The films are masked with a resist and phosphorus is introduced as an impurity of an n type by ion implantation. The polycrystalline silicon doped with the impurity is deposited. Gates 8 of the TFTs, the upper electrodes 9 of the additive capacitors of the picture elements and the gate wires are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an active matrix type liquid crystal display device using non-single crystal silicon used for a viewfinder for a video camera or a light valve for a video projector.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device using a thin film transistor can obtain a clear screen display because a predetermined signal potential can be applied to a pixel electrode for each pixel. Therefore, each pixel region tends to be miniaturized. Since the capacity of the liquid crystal decreases with the miniaturization, it is necessary to form a pixel additional capacity to improve the holding characteristic of the drive voltage of the liquid crystal. However, as miniaturization progresses, the area occupied by the pixel additional capacitance becomes too large, and the aperture ratio (ratio of displayable pixel regions) is reduced. Since the dielectric film of the pixel additional capacitance is formed at the same time as the gate insulating film of the thin film transistor to simplify the process,
It has the same film thickness as the gate insulating film. In order to increase the capacity, it is necessary to increase the area and take measures. If the area of the pixel additional capacitance is increased in order to obtain sufficient liquid crystal drive voltage holding characteristics, the aperture ratio becomes low and the screen becomes dark. On the other hand, if the pixel additional capacitance is made small in order to obtain a sufficient aperture ratio, the liquid crystal drive voltage holding characteristic deteriorates, causing screen unevenness and flicker.

Therefore, Extended Abstracts of the 1991 International Conference on Solid State Devices, Inc.
And Materials (Extended Abstracts of the 19
91 International Conference on Solid State Devices
and Materials, pp.641-643), by selectively thinning the dielectric film of the pixel additional capacitance, it is possible to improve the liquid crystal drive voltage retention characteristics without decreasing the aperture ratio. Proposed. The manufacturing method will be described below. First, a first HTO film (high temperature CVD silicon oxide film) is deposited on a patterned polycrystalline silicon film, and only the pixel additional capacitance portion is selected by using photolithography. Etching. After that, a second HTO film is deposited. As described above, the gate insulating film of the thin film transistor is formed by the first and second HTO films, and the dielectric film of the pixel additional capacitance is formed by only the second HTO film. Since the thicknesses of the gate insulating film and the dielectric film are controlled separately, the area of the pixel additional capacitance can be reduced.

In the active matrix type liquid crystal display device, when a video signal is written to a pixel through a source line, a similar idea is obtained by adding a capacitor (hereinafter referred to as a source line holding capacitor) to the source line in order to stabilize writing. It may be applicable when forming. In this case, an interlayer insulating film between the lower wiring layer and the source line layer is used as a dielectric film, a silicon film is used as a lower electrode, and a source line is used as an upper electrode to form a source line storage capacitor. The interlayer insulating film plays a role of preventing vertical conduction at the intersection of the lower gate line and the upper source line, and requires a certain breakdown voltage. The film thickness of the interlayer insulating film is almost determined by this withstand voltage and needs to be 3000 Å or more and cannot be made too thin. However, since the interlayer insulating film is used as the dielectric film for the source line storage capacitor, the dielectric film also has a film thickness of 3000 Å or more,
The electrode area must be fairly large to obtain the required capacitance. If the area of the source line of the upper electrode is widened, for example, by widening it, there is a risk of short-circuiting between adjacent source lines, and it is not possible to increase the area too much.
Therefore, the source line holding capacitance can be increased by the following manufacturing method without making the electrode area too large. First, a first HTO film (high temperature CVD silicon oxide film) is deposited on the patterned polycrystalline silicon film, and only the source line storage capacitor portion is selectively etched by using photolithography. After that, a second HTO film is deposited. As described above, the interlayer insulating film is formed of the first and second two-layer HTO films, and the dielectric film of the source line storage capacitor is formed of only the second HTO film. Since the film thicknesses of the interlayer insulating film and the dielectric film are separately controlled, the area of the source line storage capacitor can be reduced.

[0005]

However, in the above-mentioned prior art, since the CVD method is used for forming the dielectric film of the insulating film and the capacitor, there are the following problems due to the characteristics of the film formation. .

Withstand voltage like a gate insulating film and an interlayer insulating film,
When a CVD film such as HTO is used in the part where reliability is important, the polycrystalline silicon film exposed to the atmosphere and the C
There is a problem in that the interface level is increased at the VD film interface, and the breakdown voltage and reliability are deteriorated due to the level and stress in the pinhole or film.

[0007]

Therefore, a method of manufacturing a liquid crystal display device according to the present invention is to solve the above-mentioned problems, in which a silicon oxide film is used as a dielectric and at least its lower electrode is used as a silicon film. In a method of manufacturing an active matrix type liquid crystal display device in which a capacitor is formed, a step of depositing a non-single-crystal silicon film and then etching into a predetermined pattern, a step of forming an oxide film by thermal oxidation, and a step of forming the oxide film The method is characterized by having a step of selectively removing a portion by etching and a step of forming an HTO film.

[0008]

In the present invention, the portion where the breakdown voltage and reliability are important, such as the gate insulating film, is formed by the oxide film by thermal oxidation and the HTO film. Therefore, the thickness of the insulating film is the oxide film or the HTO film. By adjusting the film thickness of the layer, it can be made the same as the conventional one, and since the first layer is formed of an oxide film by thermal oxidation, the breakdown voltage and reliability are high. In addition, since the dielectric film of the portion where the size of the capacitance is important in consideration of the reliability a little, such as the pixel added capacitance, is formed by only the HTO film by etching the oxide film by thermal oxidation, the dielectric film of the capacitance portion is not formed. The body film can be made thinner than the insulating film portion, and the capacitance can be increased without changing the electrode area.

[0009]

Next, two embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 is a plan view of an active matrix substrate according to the first embodiment of the present invention, and FIG. 1D is a sectional view taken along the line AA 'of FIG.

As shown in FIG. 2, each pixel has a source line 2
In the pixel region surrounded by 6 and the gate line 24, a thin film transistor, a pixel additional capacitance, and a pixel electrode 27 are formed. As shown in FIG. 1D, the thin film transistor is composed of a gate insulating film 3, a channel region, a source 5, a drain 6 and a gate 8. The pixel additional capacitance is composed of the dielectric film 4, the lower electrode 7, and the upper electrode 9. The dielectric film 4 is made thinner than the gate insulating film 3. The charge storage capacity is proportional to the area of the electrode and inversely proportional to the thickness of the dielectric film. For example, it is necessary to double the capacity in order to improve the retention characteristic because the retention characteristic of the display voltage is low and screen unevenness and flicker occur. Gate insulating film 3 and dielectric film 4 for simplifying the process
If the thicknesses are the same, the electrode area must be doubled. Therefore, the aperture ratio is significantly reduced and the screen becomes dark. However, when the dielectric film 4 is selectively thinned to halve the film thickness as in the present invention, it is possible to improve the display quality by eliminating the unevenness and flicker of the screen without changing the aperture ratio. You can In addition, when the display voltage holding characteristic is sufficiently large, the film area is halved to halve the electrode area while keeping the holding characteristic constant, thereby improving the aperture ratio and reducing the screen area. Can be brightened.

A description will be given below in accordance with the steps in FIG. First, quartz is used as a transparent insulating substrate. Using a low pressure CVD apparatus or a plasma CVD apparatus, an intrinsic polycrystalline silicon film or an amorphous silicon film is removed by 500 to 2
000Å Accumulate. The shape of the channel region of the thin film transistor, the source 5 and the drain 6 and the lower electrode 7 of the pixel additional capacitance is formed by using photolithography. The subsequent thermal oxidation step and HTO film formation are the features of the present invention. As a result of thermal oxidation, as shown in Fig. 1 (a), 200-1500Å
The silicon oxide film 1 is formed. Since the processing is performed at a high temperature of 900 to 1200 ° C., the deposited polycrystalline silicon film or amorphous silicon film grows into a polycrystalline silicon film 2 having a grain size of 0.1 to 2 μm. The silicon oxide film 1 in the region where the pixel additional capacitance is formed is removed by photolithography as shown in FIG. After this, HT
By forming the O film, as shown in FIG.
100-2000 with gate insulating film 3 of 00-3000Å
The dielectric film 4 of Å is formed. This is masked with a resist, and phosphorus is introduced by ion implantation as an n-type impurity. Impurity-doped polycrystalline silicon is 1500 to
8000Å are deposited to form the gate 8 of the thin film transistor, the upper electrode 9 of the pixel addition capacitor and the gate line 24 of FIG. In the present invention, the gate line and the upper electrode are the same, but the upper electrode line may be formed of a different material. If a low resistance material such as MoSi _x or WSi _x is used instead of polycrystalline silicon, it is effective in reducing display anomalies due to the delay of the gate signal. In the thin film transistor, phosphorus (boron when forming p-type) is introduced as an n-type impurity except for the channel region which is intrinsic polycrystalline silicon. Here, the introduction of phosphorus uses the ion implantation with the gate 8 as a mask to form the source 5 and the drain 6 in a self-aligned manner. After forming the thin film transistor and the pixel additional capacitance in this way, an interlayer insulating film 3000 to 1500 is formed.
Deposit 0Å HTO film. In order to bake the interlayer insulating film and activate impurities such as phosphorus, 800 to 1100
Anneal in a nitrogen atmosphere in a furnace at ℃. After opening the contact holes, a source line 11 made of a low resistance metal film such as aluminum is formed on the source 5, and a pixel electrode 12 made of a transparent conductive film such as ITO is formed on the drain 6. A moisture resistant protective film (not shown) is formed on this, and the substrate process of the liquid crystal display device of the present invention is completed.

FIG. 5 is a plan view of an active matrix substrate according to a second embodiment of the present invention, FIG. 3 (d) is a sectional view taken along the line BB 'of FIG. 5, and FIG. 4 is a sectional view taken along the line CC' of FIG. FIG.
FIG. 6 is an equivalent circuit diagram of a commonly used active matrix substrate. 61 is a source line holding capacitor, 62 is a video line, 63 is a lower electrode of the source line holding capacitor, 64 is a gate line, 65 is a source line, 66 is a source line drive circuit, 67
Is a gate line drive circuit.

The source line holding capacitance is the lower electrode 31 (5
2), the dielectric film 34, and the upper electrode 36 (51). In the pixel, the gate line 32 (54) and the source line 35
(53) is insulated by the interlayer insulating film 37. The dielectric film 34 is made thinner than the interlayer insulating film 37.
When the area of the upper electrode 36 is widened to increase the capacitance,
There is a possibility of short-circuiting between the adjacent upper electrodes. However, when the dielectric film 34 is selectively thinned as in the present invention, the capacitance can be increased without changing the area of the upper electrode 36.

Below, a description will be given according to the steps in FIGS. First, quartz is used as a transparent insulating substrate. The thermal oxidation process, which is the core of the present invention, is 900 to 120.
Since it is performed in a furnace at 0 ° C., it is expensive due to heat resistance, but it is preferable to use quartz. Using a low pressure CVD apparatus or a plasma CVD apparatus, an intrinsic polycrystalline silicon film or an amorphous silicon film is deposited by 500 to 2000 liters. The channel region and the source 41 and the drain 43 of the thin film transistor of FIG. 4 are formed by using photolithography. A silicon oxide film 43 of 200 to 1500 Å is formed by thermal oxidation. This is masked with a resist, and phosphorus is introduced by ion implantation as an n-type impurity. Impurity-doped polycrystalline silicon is 1500 to
8000Å deposited, thin film transistor gate 44,
Lower electrode 3 of gate line 32 and source line storage capacitor of FIG.
1 is formed. In the thin film transistor, phosphorus (boron when forming p-type) is introduced as an n-type impurity except for the channel region which is intrinsic polycrystalline silicon. Here, the introduction of phosphorus forms the source 41 and the drain 43 in a self-aligned manner by utilizing ion implantation using the gate 44 of FIG. 4 as a mask. After forming the thin film transistor and the lower electrode of the source line-added capacitor in this manner, thermal oxidation is performed again to obtain 2000 to 3000 as shown in FIG.
A Å silicon oxide film 33 is formed. The silicon oxide film 33 in the region for forming the source line storage capacitor is removed by photolithography as shown in FIG. After this,
By forming the HTO film, as shown in FIG. 3C, the interlayer insulating films 37, 45 and 1 of 3000 to 6000Å are formed.
A dielectric film 34 of 000 to 2000 Å is formed. Annealing is performed in a furnace at 800 to 1100 ° C. in a nitrogen atmosphere in order to harden the interlayer insulating film. After opening the contact hole, the source line 35 (46) made of a low resistance metal film such as aluminum, the upper electrode 36 of the source line holding capacitor and the pixel electrode 47 made of a transparent conductive film such as ITO are formed. A moisture resistant protective film (not shown) is formed on this, and the substrate process of the liquid crystal display device of the present invention is completed.

In the present invention, a portion requiring a withstand voltage such as an interlayer insulating film or a gate insulating film is highly reliable because the first insulating film is an oxide film formed by thermal oxidation.

[0017]

As described above, the liquid crystal display device of the present invention has the following effects.

The reliability is improved in a portion requiring a withstand voltage such as an interlayer insulating film or a gate insulating film.

The capacitance using the insulating film as a dielectric can be increased without changing the electrode area.

Due to these effects, the display quality of the screen such as the reliability of the element and the aperture ratio can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a method of manufacturing the liquid crystal display device of FIG. (AA 'sectional view of FIG. 2)

FIG. 2 is a plan view of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view showing the method of manufacturing the liquid crystal display device of FIG. (BB 'cross section of FIG. 5)

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

FIG. 5 is a plan view of a liquid crystal display device according to a second embodiment of the invention.

FIG. 6 is a circuit diagram of a commonly used liquid crystal display device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Silicon oxide film 2 ... Intrinsic polycrystalline silicon film 3 ... Gate oxide film 4 ... Dielectric film 5 ... Source 6 ... Drain 7 ... Lower electrode 8 .... -Gate 9 ... Upper electrode 10 ... Interlayer insulating film 11 ... Source line 12 ... Pixel electrode 21 ... Source 22 ... Drain 23 ... Lower electrode 24 ... Gate line 25・ ・ ・ Upper electrode 26 ・ ・ ・ Source line 27 ・ ・ ・ Pixel electrode 31 ・ ・ ・ Lower electrode 32 ・ ・ ・ Gate line 33 ・ ・ ・ Silicon oxide film 34 ・ ・ ・ Dielectric film 35 ・ ・ ・ Source line 36 ... upper electrode 37 ... interlayer insulating film 41 ... source 42 ... gate insulating film 43 ... drain 44 ... gate 45 ... interlayer insulating film 46 ... source line 47 ...・ Pixel electrode 51 ・ ・ ・ Upper electrode 52 ・ ・ ・ Lower electrode 53 ・ ・ ・ Source 54 ... Gate line 55 ... Source 56 ... Drain 57 ... Pixel electrode 61 ... Source line storage capacity 62 ... Video line 63 ... Lower electrode 64 ... Gate line 65. ..Source line 66 ... Source line drive circuit 67 ... Gate line drive circuit

Claims (2)

[Claims] 1. In an active matrix type liquid crystal display device having a drive circuit using a TFT formed of a polycrystalline silicon film, as a method of forming a capacitor portion, a non-single crystal silicon film is deposited and then etched into a predetermined pattern. A step, a step of forming an oxide film by thermal oxidation, a step of selectively etching away a part of the oxide film, and a CV
And a step of forming an insulating film by the D method. 2. The method of manufacturing a liquid crystal display device, wherein the capacitance portion is an additional capacitance of a pixel.