JPH0542832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device whose constituent members are polycrystalline silicon or amorphous silicon and a conductive transparent electrode, and more particularly to a method for establishing ohmic contact between the two members.

As a large-capacity display device using liquid crystal, an active matrix system using a transistor as a switching device for each pixel is ideal, and the display capacity is theoretically infinite. In this method, a transistor array was conventionally constructed on a silicon substrate or an SOS substrate, and a liquid crystal was sealed between this substrate and a glass plate to form a liquid crystal panel. but,
The method of configuring a transistor array on a silicon substrate or SOS substrate can be easily manufactured using conventional semiconductor manufacturing technology, but due to the high cost of silicon wafers or SOS substrates and the high cost of semiconductor manufacturing, active matrix method The disadvantage of this liquid crystal panel is that it is very expensive. As a method of manufacturing an active matrix liquid crystal panel at a lower cost, it is possible to construct an array of thin film transistors (TFT) using polycrystalline silicon or amorphous silicon on a glass plate to create an active matrix. Proposed. An example of the configuration of a pixel used in a conventional active matrix type liquid crystal display device is shown in FIG.

In FIG. 1, the gate electrode of the switching transistor 1 is connected to the gate line 4, the source electrode is connected to the source line 5, and the drain electrode is connected to the drive electrode of the liquid crystal 3 and one electrode of the capacitor 2. .

FIG. 2 shows an example of a plan view of the structure of one pixel when an active matrix is formed on a glass plate using TFT. 6 is TF
Polycrystalline silicon forms the drain, channel, and source of T., the gate electrode is connected to gate line 4, and the source electrode is connected to source line 5
It is connected to the. On the other hand, if the liquid crystal drive electrode 11 is provided by extending the polycrystalline silicon constituting the drain of the TFT, as can be seen from the figure, there is no need to provide the liquid crystal drive electrode 11 in the manufacturing process. However, in the case of a light transmission type liquid crystal display device, the liquid crystal display electrode 11 must be a transparent electrode with conductivity. Polycrystalline silicon used as a material for TFT6 does not transmit much light even if its thickness is reduced to about 1000 angstroms, and coloring due to interference color occurs, and when used as a drive electrode, the display quality of the liquid crystal display decreases. Significantly decreased.

For this reason, a conductive transparent material must be used as the liquid crystal driving electrode. A common method for display devices using liquid crystals is to use tin oxide or isodium oxide as the conductive transparent material, and it has excellent stability, conductivity, and light transmission, making it ideal as a transparent electrode. It is true.

However, as shown in FIG.
Although it is necessary to make electrical contact with the polycrystalline silicon 6 and the polycrystalline silicon 6, even if the contact hole 9 is opened in the insulating layer above the drain electrode and the polycrystalline silicon 6 and the transparent electrode 11 are directly connected, no electrical contact can be made. Even if it cannot be reached or there is contact, it is not completely ohmic.

The present invention has been made in view of the above points, and is achieved by sandwiching a metal such as aluminum between the polycrystalline silicon containing the source and drain regions of the transistor and the conductive transparent electrode. This enables reliable ohmic contact.

The present invention will be explained in detail below with reference to the drawings.

FIG. 3 explains the manufacturing process of an active matrix liquid crystal display device using TFT according to the present invention, in particular, the drain of the TFT,
FIG. 3 is a cross-sectional view showing an example of the manufacturing process of a contact region with a transparent electrode for driving a liquid crystal in the order of the steps. FIG. 3a shows a cross section of a polycrystalline silicon thin film 13 formed on the surface of the glass plate 12 and etched away in areas other than those to be the drain, channel, and source regions of the TFT. Highly concentrated impurities are diffused into the drain and source regions of the TFT.

Next, as shown in FIG. 3b, a silicon oxide film 14 is formed extending over the surface of the polycrystalline silicon thin film 13. This silicon oxide film is polycrystalline silicon 1
It may be obtained by thermally oxidizing the surface of No. 3, or it may be obtained by a vapor phase reaction growth method. Furthermore, other insulating films such as silicon nitride film, alumina film, etc. may be used instead of the silicon oxide film. Next, a contact hole is opened in the silicon oxide film 14 above the drain region to form a drain electrode extraction window. Then the third
As shown in FIG. 3C, an aluminum thin film 15 is formed extending over at least the entire contact hole formed in FIG. 3B. For this purpose, after forming an aluminum thin film on the entire surface of the glass plate,
The structure shown in FIG. 3c can be achieved by using photolithography to leave aluminum in desired areas and etching away the rest.

Next, a conductive transparent material such as tin oxide or indium oxide is formed on the entire surface as a liquid crystal driving electrode, and a desired pattern of the liquid crystal driving electrode is obtained by photolithography. The cross-sectional structure of the substrate at this time is as shown in FIG. With this structure, by heating the polycrystalline silicon 13 to 300 to 400 DEG C., the polycrystalline silicon 13 and the transparent electrode 16 are brought into complete ohmic conduction with low contact resistance through the aluminum. Aluminum thin film is 1000
Although it is opaque even if it is made as thin as angstroms, the aluminum used in the present invention is formed only on the top of the polycrystalline silicon, so there is no drawback that aluminum is opaque.

Finally, the entire surface of the glass plate is subjected to alignment treatment for liquid crystal to complete one panel plate of the liquid crystal display device.

As described above, according to the present invention, by substantially extending aluminum only in the contact hole connecting polycrystalline silicon and a transparent electrode made of tin oxide or isodium oxide, an ohmic contact between the two can be easily made with low resistance. Moreover, the presence of aluminum does not affect the characteristics of the display device at all.

Note that the material for the TFT in the present invention is not limited to polycrystalline silicon, but may be any non-monocrystalline silicon such as amorphous silicon, and the metal interposed between the drain and the transparent electrode is not limited to aluminum. Even with other metals, the effects of the present invention remain the same.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the configuration of one pixel of an active matrix liquid crystal display device. FIG. 2 is a plan view showing an example of the configuration of one pixel on a panel of a conventional active matrix liquid crystal display device using TFT. Figure 3 a~
d is a sectional view showing an example of a method for manufacturing an active matrix according to the present invention in the order of steps. 1, 6...TFT, 2...Capacitor, 3
...Liquid crystal, 4,7...Gate line, 5,8...
Source line, 9, 10...contact hole,
11... Transparent electrode for driving liquid crystal, 12... Glass plate, 13... Polycrystalline silicon, 14... Silicon oxide, 15... Aluminum, 16... Conductive transparent electrode.

Claims (1)

[Claims] 1. A liquid crystal is sandwiched between two opposing transparent substrates, one of the transparent substrates has transparent electrodes arranged in a matrix, and a thin film transistor is connected to the transparent electrode. In the active matrix liquid crystal display device, the thin film transistor is formed of a non-monocrystalline silicon thin film, the thin film transistor has source and drain regions doped with impurities, and the source and drain regions of the non-monocrystalline silicon and An active matrix liquid crystal display device characterized in that the transparent electrode is formed by vertically sandwiching conductive metal disposed on the source and drain regions without extending beyond the source and drain regions.