JPS5848907B2 - image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reflective electrode used in an image display device, and an object of the present invention is to improve the contrast ratio of an image by shaping a metal reflective electrode with a flat surface.

An example of an image display device constructed using a liquid crystal and a MOS transistor is described in Document L. T. Lipton et.
al ,, //ALiquid Crystal T
elevision Displaying a
Silicon-On-Sapphire S
witchingarray, ”1975,
SID Symp. Dig. , P.P. 78-79,
(1975).

This is quoted and shown in Figure 1.

A unit picture element is composed of a MOS transistor 1, a charge storage capacitor 2, and a liquid crystal cell 3.

For example, if a gate signal is applied to gate terminal X now, the MOS
type transistor 1 is turned on, and the video signal is transmitted to terminal y. The capacitor 2 is charged through the transistor 1.

Even if the gate signal disappears, while the charge stored in the capacitor 2 applies a voltage to the liquid crystal cell 3, the liquid crystal cell 3 changes the degree of phase transition or dynamic scattering according to the piezoelectricity, so the liquid crystal cell The light passing through 3 can continue to be modulated by the video signal voltage.

The charge stored in the capacitor 2 leaks through the off-resistance of the transistor 1 and the resistance of the liquid crystal cell 3 until the next gate signal is applied.

As shown in Figure 1, the unit picture elements are arranged in a matrix.
It is possible to configure a television by scanning the screen in the x and y directions.As mentioned earlier, the transistors are turned on all at once in the x direction to write the video signal to the capacitors, and the An effect equivalent to that of a CRT can be obtained by sequential scanning, so-called line scanning.

FIG. 2 shows a plan view of one unit picture element when the unit picture element shown in FIG. 1 is integrated into an integrated circuit.

Here, a reflective image display device will be described.

The transistor consists of a drain 4, a source 5, and a gate 6, 6 is a polycrystalline silicon gate and wiring, and 7 is made of polycrystalline silicon whose surface is oxidized as in 6, and forms the capacitor 2 together with the metal electrode 9. ing.

Note that 6 and 7, which are more preferable than polycrystalline silicon, are diffused with appropriate impurities to provide conductivity.

The metal electrode 9 forms an ohmic contact with the source 5 through an opening 11 provided in the silicon oxide layer, which is an insulating layer covering the surface of the transistor, and the metal electrode 8 also connects to the video signal wiring path y, as described above. Ohmic contact is made with the drain 4 through the opening 10 of the insulating layer.

A cross-sectional view of the plan view of FIG. 2 taken along I-1 is shown in FIG. It is also possible to use SOS with a silicon single crystal thin film on a substrate.

By filling a liquid crystal 16 between the integrated circuit board 13 and a transparent glass plate 14 having a transparent electrode 15 adhered on one main surface, a certain liquid crystal cell is formed by the transparent electrode 15 and the metal electrode 9. 3 is constructed.

Note that 12 is the above-mentioned insulating film covering the surface of the transistor 1.

Light 17 incident from above the glass plate 14 undergoes appropriate scattering or phase transition by the liquid crystal cell 3, and is further reflected by the metal electrode 9 to obtain a reflective image display device.

Therefore, it is desirable that the reflective electrode 9 has a flat surface, preferably a mirror surface.

Now, Figure 4 is a microscopic photograph of the planar surface of a prototype conventional integrated circuit for a reflective image display device, and the size is 160 μm.
x210 μm.

The metal electrode 9 is made of aluminum with a thickness of about 1 μm and is formed by vapor deposition.

As is clear from this photo, the aluminum surface has many pit-like fine irregularities.

A silicon-aluminum alloy is obtained by heat treatment, usually at 400 to 500°C, to form ohmic contact between the aluminum and the source and drain.

This is because the aluminum itself recrystallizes to form grains (crystal grain boundaries) during the so-called aluminum sintering process, and it is well known that the higher the sink temperature and the longer the sintering time, the more rough the aluminum surface becomes. .

If aluminum is deposited using resistance heating vapor deposition instead of electron beam vapor deposition, there will be less damage to semiconductor integrated circuits during vapor deposition, so it is possible to lower the sintering temperature, but it is still possible to avoid a certain degree of surface roughness. I can't do it.

In addition, impurity contamination from the boat is unavoidable in resistance heating evaporation, and recently it is common to deposit aluminum by electron beam evaporation. Since the temperature is set high, surface roughness is unavoidable regardless of the method used to deposit aluminum.

In a reflective image display device, the metal electrode 9 acts as a reflector for the liquid crystal cell, so if the surface is rough as shown in FIG. 4, the amount of scattered light on the surface increases and the inside of the liquid crystal cell. When there is no scattered light from inside the liquid crystal cell, that is, no signal, the scattered light from the rough surface reaches the observer's eyes as a dark level. become.

When the dark level is large, contrast 1 as a picture iron
・Since the ratio (black and white ratio) naturally decreases, the metal electrode 9
It is desirable that the surface be as smooth as possible.

As is clear from the above description, it has been impossible to prevent the surface of the metal electrode from becoming rough with the conventional manufacturing method in which heat treatment is performed after patterning the metal electrode.

Therefore, in the present invention, a thin semiconductor layer is deposited on the surface of the metal electrode, and an alloy layer is formed by heat treatment to prevent roughness on the surface of the metal electrode. will be described with drawings.

FIG. 5 is a sectional view of an image display device showing an embodiment of the present invention. After forming a MOS transistor 1, an opening 10.11 is provided in a silicon oxide layer 12, and a drain 4 and a source 5 are partially connected. Aluminum vapor deposition is performed on the exposed entire surface of the semiconductor substrate.

The steps up to this point are the same as those for manufacturing a normal MOS transistor.

Thereafter, a thin layer of polycrystalline silicon is deposited on the aluminum.

For example, if the aluminum film thickness is 1 μm, 1000
Around A is optimal.

Of course, if the metal electrode is aluminum, the deposition of polycrystalline silicon is
It must be performed by sputter deposition rather than the VD method.

Thereafter, heat treatment is performed to recover the damage caused during vapor deposition, and the aluminum on the openings 10 and 11 is
Ohmic contact is formed between the drain 4 and source 5.

The heat treatment also causes the thinly deposited polycrystalline silicon to form an alloy with the aluminum, resulting in ohmic contact.

Finally, a predetermined pattern is formed through a photoresist process to obtain metal electrodes 8 and 9 and alloy layers 18 and 19.

By carrying out the present invention, recrystallization of the aluminum layer (metal electrode) 9 during aluminum sintering is suppressed by alloying the aluminum 9 with the polycrystalline silicon 19, so that roughness on the surface of the metal electrode 9 can be significantly prevented. .

The thicker the polycrystalline silicon, the better its effectiveness; however, if it is thick, the alloy layer will not be uniform and will become heavily wavy and cannot be said to be flat, and the ohmic properties between the alloy layer 19 and the metal electrode 9 will deteriorate. This is not preferable, and furthermore, the metallic color of aluminum is lost and the reflectance is lowered.

On the other hand, if the polycrystalline silicon is too thin, all of the polycrystalline silicon will be dissolved into aluminum during alloying, making it impossible to suppress the generation of grains.

Therefore, there is an optimal range for the thickness of polycrystalline silicon, and when the thickness of aluminum is 1 μm, the sintering temperature is 40
When the temperature was 0 to 500°C, remarkable effects were obtained for 500 to 2,000 people.

FIG. 6 shows a microscopic photograph of the surface of a unit picture element obtained by implementing the present invention, and it can be easily seen that the effect is inferior when compared with the conventional example shown in FIG.

Moreover, when comparing FIG. 5 and FIG. 3, the openings 10, 1
It can be seen that alloy layers 18 and 19 of a semiconductor material are deposited on the metal electrodes 8 and 9 which are in ohmic contact with the diffusion layers 4 and 5 through 1.

By implementing the present invention, it is possible to use a very flat and mirror-like alloy layer as a reflective electrode, thereby increasing the contrast ratio from the conventional 4:1 to 8:1 in an image display device that combines a liquid crystal and a semiconductor integrated circuit. It was possible to improve up to.

Further, depending on the driving method, the metal wiring 8, which is the video signal wiring path, may operate in the same way as the picture element electrode 9, resulting in a loss of image clarity.

In this case, it is sufficient to deposit a silicon oxide layer, which is an insulator, to expose only the pixel electrode 9 and electrically insulate the metal wiring 8. The alloy layer formed by the present invention has the advantage that it is not etched by a hydrofluoric acid-based etching solution used for opening windows, and can continue to maintain a mirror-like state.

It goes without saying that the gist of the present invention is not limited to the use of aluminum as the metal electrode and polycrystalline silicon as the semiconductor layer as described in the embodiments.

[Brief explanation of the drawing]

Fig. 1 is an equivalent circuit diagram of an image display device using a liquid crystal and a semiconductor integrated circuit, Fig. 2 is a plan view of a unit pixel of a conventional image display semiconductor integrated circuit, Fig. 3 is a cross-sectional view of the same, and Fig. 4 is a plan view of a unit picture element of a conventional image display semiconductor integrated circuit. The figure is a microscopic photograph of the same plane, FIG. 5 is a sectional view showing one embodiment of the image display device of the present invention, and FIG. 6 is a microscopic photograph of the same plane. 1...MOS type transistor, 2...
Charge storage capacitor, 8, 9...metal electrode,
15...Transparent electrode, 16...Liquid crystal, 1
8.19...Alloy layer formed on metal electrodes 8 and 9.

Claims (1)

[Claims] 1. A reflective semiconductor layer is formed on a metal electrode that is in ohmic contact with a diffusion layer formed on a semiconductor substrate, and the metal electrode and the reflective semiconductor layer are alloyed. image display device.