JPH04264527A - Active matrix substrate - Google Patents

Abstract

PURPOSE:To reduce the step of a pixel electrode at a contact hole forming section and to surely prevent a disconnection caused by the break and damage of the pixel electrode. CONSTITUTION:The step of the pixel electrode 40 at the contact hole forming section 51 is reduced by embedding a metallic layer 60 in the contact hole 51 opened at an interlayer insulating film 54 and electrically connecting the pixel electrode 40 and the drain electrode 32 of a TFT 30 via a metallic layer 60.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix substrate equipped with TFTs (thin film transistors) as switching elements, and more particularly to an active matrix substrate suitable for high-definition liquid crystal display devices.

0002

2. Description of the Related Art Conventionally, in liquid crystal display devices, EL display devices, plasma display devices, etc., a display pattern is formed on a screen by selectively driving picture element electrodes arranged in a matrix. More specifically, a voltage is applied between a selected picture element electrode and a counter electrode facing it, optically modulating a display medium such as a liquid crystal interposed between these electrodes. The optical modulation is visible as a display pattern. As a driving method for picture element electrodes, an active matrix driving method is known in which individual independent picture element electrodes are arranged and a TFT as a switching element is connected to each picture element electrode and driven. These active matrix drive type liquid crystal display devices have the advantage of being capable of high contrast display and having no restrictions on display capacity, and have been put to practical use in liquid crystal televisions, word processors, computer terminal display devices, etc. has been done.

FIG. 4 shows a conventional example of such an active matrix substrate, in which gate bus lines and source bus lines (none of which are shown) are arranged vertically and horizontally on a glass substrate (transparent insulating substrate) 100. A gate electrode 110 branching from the gate bus line is formed on the gate bus line. A source electrode 131 and a drain electrode 1 are disposed above the gate electrode 110 with a gate insulating film 150 in between.
A TFT 130 with 32 is formed.

[0004] An active matrix substrate having such a structure is produced as follows. First, glass substrate 1
A gate electrode 110 made of metal such as Ta, Cr, etc.
A gate insulating film 150 made of SiNx, SiOx, etc. is formed to cover the gate electrode 110.
Semiconductor layers 160 made of amorphous silicon (hereinafter referred to as a-Si), polycrystalline silicon, CdSe, etc. are laminated in this order. Next, a source electrode 131 and a drain electrode 132 made of Ti, Mo, Al, etc. are formed by patterning to obtain a TFT 130. Note that in order to establish ohmic contact, phosphorus (P) is usually provided between the semiconductor layer 150 and the source electrode 131 and drain electrode 132.
) doped n+a-Si layer 170 is formed.

[0005] Then, an interlayer insulating film (protective film) 154 made of polyimide, acrylic resin, etc. is coated on the substrate 100 on which the TFT 130 is formed as described above, and I
A transparent conductive film such as TO (Indium Tin Oxide) is formed and patterned to form the picture element electrode 1.
form 40. A part of the picture element electrode 140 is the interlayer insulating film 1
It is electrically connected to the drain electrode 132 through a contact hole 151 formed in the drain electrode 54 .

[0006]

However, in the conventional example described above, there is a problem in that a parasitic capacitance is generated between the source bus line and the picture element electrode 140. When an active matrix substrate with such parasitic capacitance is used in a liquid crystal display device, there is a drawback that a display defect called crosstalk occurs.

[0007] To reduce parasitic capacitance, an interlayer insulating film 154 is used.
Just make it thicker. However, if the interlayer insulating film 154 is made thicker, the depth of the contact hole 151 increases accordingly, and the step portion of the picture element electrode 140 connected to the drain electrode 132 through the contact hole 151 becomes larger. Therefore, there is a drawback that the corresponding portion of the picture element electrode 140 is easily broken and disconnection occurs frequently. Such a disconnection of the picture element electrode 140 causes a display defect, resulting in a decrease in the yield of the active matrix substrate and an increase in cost.

SUMMARY OF THE INVENTION The present invention solves the drawbacks of the prior art, and aims to provide an active matrix substrate that can reliably prevent disconnection of picture element electrodes in contact holes and improve yield. .

[0009]

[Means for Solving the Problems] The active matrix substrate of the present invention includes a thin film transistor array in which thin film transistors are arranged in a matrix on a transparent insulating substrate, and a contact hole in a portion corresponding to the drain electrode of the thin film transistor. a transparent insulating film formed to cover the thin film transistor array; a metal layer embedded in the contact hole and connected to the drain electrode; A picture element electrode is electrically connected to the drain electrode, thereby achieving the above object.

0010

[Function] As described above, according to the structure in which a metal layer is buried in the contact hole and the pixel electrode and the drain electrode are electrically connected through the metal layer, the contact hole becomes smaller due to the buried contact layer. The depth, that is, the level difference can be reduced. Therefore, disconnection of the picture element electrode due to the step difference in the contact hole does not occur.

[0011]

[Examples] Examples of the present invention will be described below.

FIGS. 1 and 2 show an active matrix substrate according to an embodiment of the present invention, and this active matrix substrate has gate bus lines 10 and source bus lines 20 arranged vertically and horizontally on a transparent glass substrate 1. The picture element electrodes 40 are arranged in a matrix in a rectangular area surrounded by both bus lines 10 and 20.

A gate electrode 11 is provided on the gate bus line 10.
is branched, and the source bus line 20 has a source electrode 31
is branched. A TFT 30 functioning as a switching element is formed at the position of the gate electrode 11. This TF
T30 includes the source electrode 31 and drain electrode 32, and has the structure shown in FIG.

The structure of the active matrix substrate and its manufacturing procedure will be explained below with reference to FIG. Figure 1 (
As shown in a), a Ta film with a thickness of 300 nm is first formed on a glass substrate 1 by sputtering, and then
The Ta film is patterned by photolithography to form the gate electrode 11 (at this time, the gate bus line 10 shown in FIG. 2 is formed at the same time). Next, by a plasma CVD method, a gate insulating film 50 made of a SiNx film with a film thickness of 400 nm is placed on the glass substrate 1 so as to cover the gate electrode 11, a semiconductor layer 52 made of a-Si with a film thickness of 100 nm, and a semiconductor layer 52 made of a-Si and phosphorus (P ) doped film thickness 40n
m n+a-Si layers 53 are successively laminated and patterned into the cross-sectional shape shown.

Next, a Mo film with a thickness of 200 nm is deposited on the glass substrate 1 by sputtering so as to cover these.
A film is formed and patterned to form the source electrode 31 (
At this time, the source bus line 20 shown in FIG. 2 is formed at the same time. ) and a drain electrode 32 are obtained, thereby creating a TFT array in which TFTs 30 are arranged in a matrix.

Next, as shown in FIG. 1(b), SiNx with a thickness of 1 μm is deposited on the glass substrate 1 by plasma CVD.
An interlayer insulating film 54 is formed. Next, Figure 1(c
), a Ta film 55 with a thickness of 1 μm is laminated on the entire surface of the interlayer insulating film 54 by sputtering, and a resist 56 is applied thereon.

Next, as shown in FIG. 3(d), the Ta film 55 and the resist 56 are dry etched under the same etching grade conditions. With this dry etching,
A contact hole 51 is opened in a portion of the interlayer insulating film 54 corresponding to the drain electrode 32 . Then, a metal layer 60 made of a Ta film is buried in the bottom of the contact hole 51. This reduces the depth of contact hole 51.

Next, a film thickness of 10
A 0 nm ITO film is laminated on the interlayer insulating film 54, and then patterned to obtain the picture element electrode 40 shown in FIG. 1(e). A part of the patterned picture element electrode 40 is connected to the metal layer 60 buried in the contact hole 51. As a result, the picture element electrode 40
and the drain electrode 32 are electrically connected to create an active matrix substrate.

According to such a connection structure, the metal layer 60
Because of the presence of the step, it is possible to reduce the level difference in the part of the picture element electrode 40 that goes over the peripheral edge of the contact hole 51 and is electrically connected to the metal layer 60. Will not break. Therefore, disconnection of the picture element electrode 40 does not occur. Moreover, since the level difference can be reduced, when it is incorporated into a liquid crystal display device, there is an advantage that the display characteristics can be improved. In other words, it is possible to reduce the disturbance in the alignment of liquid crystal molecules in the stepped portion.

FIG. 3 shows another embodiment of the invention,
In this embodiment, Al is used as the metal layer 60 buried in the contact hole 51, and acrylic resin is used as the interlayer insulating film 54. When acrylic resin is used as the interlayer insulating film 54, the surface of the interlayer insulating film 54 can be flattened, so that the level difference of the pixel electrode 40 in the contact hole 51 forming area is further reduced. Therefore, this is even more preferable in terms of preventing disconnection of the picture element electrode 40 and improving the display characteristics of the liquid crystal display device.

Note that the active matrix substrate according to this embodiment is also produced through the same manufacturing process as in the above embodiment.

[0022]

According to the present invention described above, since the pixel electrode and the drain electrode are electrically connected through the metal layer buried in the contact hole, the difference in level of the pixel electrode in the contact hole forming area can be reduced. can be reduced. Therefore, the picture element electrode does not break at this portion, and disconnection of the picture element electrode can be reliably prevented.

In addition, since the step difference in the picture element electrodes can be reduced, when the active matrix substrate of the present invention is used in a liquid crystal display device, it is possible to reduce the disorder in the orientation of liquid crystal molecules in the step portion. Therefore, there is an advantage that the display characteristics of the liquid crystal display device can be improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view taken along line A-A in FIG. 2, showing the manufacturing process of an active matrix substrate of the present invention.

FIG. 2 is a plan view of an active matrix substrate produced in the process of FIG. 1;

FIG. 3 is a sectional view showing another embodiment of the present invention.

FIG. 4 is a sectional view showing a conventional example of an active matrix substrate.

[Explanation of symbols]

1 Glass substrate 10 Gate bus line 11 Gate electrode 20 Source bus line 30 TFT 31 Source electrode 32 Drain electrode 40 Picture element electrode 50 Gate insulating film 51 Contact hole 54 Interlayer insulation film 60 Metal layer

Claims (1)

[Claims] 1. A thin film transistor array comprising thin film transistors arranged in a matrix on a transparent insulating substrate;
A contact hole is opened in a portion corresponding to the drain electrode of the thin film transistor, and a transparent insulating film is formed to cover the thin film transistor array; a metal layer embedded in the contact hole and connected to the drain electrode; An active matrix substrate comprising a picture element electrode formed on the transparent insulating film and electrically connected to the drain electrode through the metal layer.