JPH03790B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active matrix substrate for driving a liquid crystal display formed of thin film elements.

Recently, active matrix substrates for driving liquid crystal displays for the purpose of image display have been developed in various places. In particular, a method in which a thin film transistor (hereinafter abbreviated as TFT) is formed on a transparent substrate (such as quartz glass) and is used as a switching transistor is attracting attention. FIG. 1 shows a basic structural unit corresponding to one pixel of image display using the active matrix method. In the same figure, 10
1 and 102 are X on the i-th line and i+1 line, respectively
103 indicates the side wiring (gate wiring), and 103 indicates the Y-side wiring (data wiring) in the i-th column. Further, 104 indicates a switching TFT in the i-th row and j-th column, 105 indicates a charge retention capacitor built into the active matrix substrate, and 106 indicates a capacitor corresponding to a liquid crystal display. The active matrix substrate shown in FIG. 2 has conventionally been manufactured by the steps shown in FIG. 2 a to e, and the final structure is as shown in FIG. 2 e. First, a transparent substrate (quartz glass, etc.)
A SiO ₂ film 202 is deposited on 201 by CVD and patterned by photo-etching to form islands 203 of polycrystalline silicon. (FIG. 2a) The surface of the polycrystalline silicon is oxidized to form a gate oxide film, and then a second polycrystalline silicon layer 205 is formed.
Formed by CVD method. (FIG. 2b) After patterning the second polycrystalline silicon layer by photo-etching, it is doped with impurities by ion implantation or thermal diffusion. Portions 205 and 206 are doped with impurities. (FIG. 2c) After depositing a layer insulating film (such as a SiO ₂ film) 207 by CVD, a contact hole 208 is formed by photo-etching. Furthermore, the wiring metal layer 209
(aluminum, etc.) by sputtering or vapor deposition,
Perform patterning by photo etching. (FIG. 2d) A liquid crystal drive electrode layer (ITO film or the like) 210 is formed and patterned by photo-etching. With the above steps, the active matrix board is completed. (Fig. 2 e) In Fig. 2 e, a switching TFT (104 in Fig. 1) is formed in the part 211, and a charge holding capacitor (104 in Fig. 1) is formed in the part 212.
105) in the figure is formed.

The charge retention capacitor formed in this conventional structure is mainly used for the following two reasons (i) to prevent leakage between the gate wiring (101, 102 in Figure 1) and the data wiring (103 in Figure 1); In order to prevent this and to confirm the withstand voltage, the interlayer insulating film (207 in FIG. 2) must be as thick as about 10,000 Å.

(ii) Polycrystalline silicon, which is difficult for light to pass through, in order to make the liquid crystal display transmissive (Figure 2 205)
The area it occupies must be kept as small as possible. Therefore, the capacitor area becomes smaller.

Therefore, the capacitance value cannot be increased beyond a certain level. (If one pixel is ^25000μm2 , the maximum
(approximately 0.2PF) Currently, considering that the lower limit of the total sum of TFT off-current and liquid crystal leakage current obtained through a relatively simple and inexpensive process is 100 pA to 500 pA, it is difficult to create an image display with sufficient display performance. In order to obtain this, it is necessary to increase the capacitance value of the charge holding capacitor (105 in FIG. 1) about 10 times the current value (about 2 pF in the case of one pixel of 25000 μm ² ).

An object of the present invention is to propose a structure of an active matrix substrate for a liquid crystal display that satisfies the above requirements and has good display performance by improving the manufacturing process of TFTs and thin film capacitors.

The gist of the present invention will be explained below using the drawings (Fig. 3 a to f). An active matrix substrate having the structure of the present invention is manufactured as follows. First, a SiO ₂ film 302 is deposited (deposition) on a transparent substrate (quartz substrate, etc.) 301 using the CVD method as in the conventional method.
After that, a first polycrystalline silicon layer 30 is applied thereon.
Deposit 3,304. Furthermore, after depositing a film such as SiO ₂ on the entire surface of the first polycrystalline silicon layer by CVD, the SiO ₂ film is deposited by photo-etching.
A film 305 is obtained by patterning the film. Next, 3
05 as a mask, impurities are doped by ion implantation or thermal diffusion. This results in a polycrystalline silicon portion 303 that is not doped with impurities and a portion 304 that is doped with impurities. 303
is the part where the TFT channel will be formed later. (FIG. 3a) The first polycrystalline silicon layer is patterned by photo-etching.

306 and 307 are portions that will become the source and drain of the TFT, and 308 is a portion that will be the electrode of the thin film capacitor. (FIG. 3b) Next, first polycrystalline silicon layers 303, 30
6, 307, and 308 to form a TFT gate oxide film 309 and a capacitor insulating film 310.
get. A second polycrystalline silicon layer 311 is deposited over the entire surface. (FIG. 3c) The second polycrystalline silicon layer 311 is patterned by photoetching, and the gate electrode 31 is patterned.
2 and a capacitor electrode 313 are obtained. After that,
The entire surface is doped with impurities by ion implantation or thermal diffusion. At this time, 306, 307 and 308
A portion of the wafer is doped with impurities in combination with that of FIG. 3a. Also, 305
By designing the mask so that the pattern region 312 completely covers the pattern region 312, the parasitic capacitance of the TFT due to gate electrode overlap can be reduced. (FIG. 3d) After depositing an interlayer insulating film (such as a SiO ₂ film) over the entire surface by CVD, contact holes 318, 319, and 320 are formed by photoetching. Furthermore,
After forming a metal wiring layer (aluminum, etc.) on the entire surface by sputtering or vapor deposition, patterning is performed by photoetching to form patterns 321, 322, 32.
Get 3. (FIG. 3e) Finally, a liquid crystal drive electrode layer (such as an ITO film) is formed on the entire surface and patterned by photo-etching to obtain a liquid crystal drive electrode 324.

With the above steps, an active matrix substrate having the structure of the present invention is completed. (FIG. 3 f) In FIG. 3 f, the thin film capacitor is located between the two polycrystalline silicon electrodes 308 and 313 and
13 and the drive electrode 324.
Typically, the thickness of the oxide film 310 is approximately one-tenth of the thickness of the interlayer insulating film 316. Therefore,
By applying the present invention, it becomes possible to fabricate a charge retention capacitor having a capacitance value ten times or more compared to the conventional one. Moreover, the number of steps and costs required for manufacturing can be suppressed to an increase of about 20%.

As described above, in the present invention, a first silicon thin film is deposited on a transparent substrate, a first insulating film is formed on the first silicon thin film, and after patterning the first insulating film,
A step of introducing an impurity into the first silicon thin film using the first insulating film as a mask, a step of patterning the first silicon thin film to form a plurality of island-like regions, and then removing the first insulating film, and a step of removing the first insulating film. forming an insulating film on the insulating thin film, forming a second silicon thin film on the insulating thin film and patterning the second silicon thin film to obtain a gate electrode and a capacitor electrode, interlayer insulation on the second silicon thin film After forming the film, forming a contact hole and forming a conductive wiring layer;
Since the process consists of forming a transparent electrode for driving the liquid crystal on the interlayer insulating film, the gate insulating film of the thin film transistor and the insulating film of the capacitor can be formed simultaneously, and the NOS thin film capacitor with excellent capacitance can be manufactured. can be formed.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining the configuration of one pixel of a liquid crystal display using an active matrix substrate. FIGS. 2a to 2e are diagrams for explaining the conventional active matrix substrate manufacturing process. Figure 3a
-f are diagrams for explaining the active matrix substrate manufacturing process of the present invention.

Claims (1)

[Claims] 1 Depositing a first silicon thin film on a transparent substrate, forming a first insulating film on the first silicon thin film, patterning the first insulating film, using the first insulating film as a mask, and depositing the first silicon thin film on the first silicon thin film. a step of introducing impurities into a thin film, a step of patterning the first silicon thin film to form a plurality of island-like regions, a step of removing the first insulating film, a step of forming an insulating film on the island-like regions, and a step of forming the insulating film on the island-like regions. forming a second silicon thin film on the thin film, patterning the second silicon thin film to obtain a gate electrode and a capacitor electrode, forming an interlayer insulating film on the second silicon thin film, and then forming a contact hole;
A method for manufacturing an active matrix substrate, comprising the steps of forming a conductive wiring layer and forming a transparent electrode for driving a liquid crystal on the interlayer insulating film.