JPS5848908B2 - Image display device and its manufacturing method - Google Patents

Description

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

An example of an image display device constructed using a liquid crystal and a MOS transistor is described in Document L. T, Liptonet
．． al. ,”A Liquid Crystal T
elevision dis-play usin
g a Sif icon -On -Sapphi
re SwitchingArray,” 19
75, SID Symp. Dig. , PP, 78-79
, (1975).

This is quoted and shown in Figure 1.

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

For example, now gate terminal X. When a gate signal is added to MO
The S-type transistor is turned on, and the video signal passes from the terminal y to the transistor 1 and charges the capacitor 2.

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 phase transition or the magnitude of dynamic scattering according to the voltage, so the liquid crystal cell 3 The light passing through 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 and the resistance of the liquid crystal cell 3 until the next gate signal is applied.

As shown in Figure 1, it is possible to set up a television by scanning unit picture elements in a matrix pattern in the X and Y directions. The same effect as that of a CRT can be obtained by turning on a group of transistors all at once to write a video signal into a group of capacitors and scanning sequentially in the y direction, so-called scanning lines.

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 γ is made of polycrystalline silicon whose surface is oxidized as in 6, and forms the capacitor 2 together with the metal electrode 9. It's intimidating.

The metal electrode 9 forms an ohmic contact with the source 5 through an opening 11 provided in an insulating layer covering the surface of the transistor 1, and the metal electrode 8 is connected to the insulating layer by the aforementioned video signal wiring path y. It makes ohmic contact with the drain 4 through the opening 10 of the drain.

The plan view in Figure 2 is the cross-sectional view taken along line I-1.
As shown in the figure, an integrated circuit for image display is formed on a sapphire substrate 13 here, but it is of course possible to use an ordinary silicon substrate in the case of a reflective image display device.

That is, the semiconductor substrate can be used as one electrode of the capacitor, which simplifies the structure.

A diffusion layer having the same conductivity type as the impurity contained in the semiconductor substrate is formed on the semiconductor substrate, and a metal electrode 9 is formed through the insulating layer.
It is recommended to form a

By filling liquid crystal 16 between the integrated circuit board 13 and the transparent glass plate 14 on which a transparent electrode 15 is formed, the liquid crystal cell 3 formed by the transparent electrode 15 and the metal electrode 9 is formed. 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, FIG. 4 is a microscopic photograph of a plane of a conventional reflective type integrated circuit for an image display device, which was manufactured as a prototype.

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.

This is because during the so-called aluminum sintering process, in which a silicon-aluminum alloy is obtained by applying heat treatment at 400 to 500°C to form ohmic contact between aluminum and the source and drain, the aluminum itself recrystallizes and becomes grain-free. It is well known that the higher the sintering temperature and the longer the sink time, the more rough the aluminum surface becomes.

If the aluminum is deposited using resistance heating evaporation rather than electron beam evaporation, there will be less damage to the semiconductor integrated circuit during evaporation, so it is possible to lower the sintering temperature. 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 the reflection type display device, the metal electrode 9 acts as a reflection plate for the liquid crystal cell, so if the surface is rough as shown in FIG. This can be confused with light scattered from inside the liquid crystal cell, causing abnormalities in the modulation level, and in a state where there is no light scattered from within the liquid crystal cell, that is, in a no-signal state, the light scattered from the rough surface reaches the observer's eyes as a dark level. It turns out.

If the dark level is thick, the contrast ratio (black and white ratio) of the image will naturally decrease, so it is desirable that the surface of the metal electrode 9 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 small-area metal electrode that is in ohmic contact with the diffusion layer is formed in advance, and a large-area metal electrode is adhered to the small-area metal electrode to form the desired shape. Embodiments of the present invention will be described with reference to FIG. 5.

After forming the MOS transistor 1, openings 10 and 11 are formed in the insulating layer 12, which is usually made of silicon oxide, and aluminum is deposited over the entire surface of the semiconductor substrate.

The aluminum above opening 10.11 is then selectively left.

For this purpose, the photomask used to provide the openings 10 and 11 may be used, and if the resist used to provide the openings 10 and 11 is a negative type, a positive type resist may be used.

Thereafter, aluminum sintering is performed to recover damage caused during vapor deposition and to form ohmic contact between the aluminum 1B, 19 on the openings 10, 11 and the drain 4, source 5.

After that, aluminum is deposited on the entire surface of the semiconductor substrate again using a method that causes less damage to the semiconductor substrate, such as resistance heating vapor deposition, and a predetermined pattern is formed to form metal electrodes 8,
Get 9.

By implementing the present invention, most of the reflective electrode 9 is not subjected to heat treatment, so that it is possible to maintain the mirror-like state immediately after vapor deposition.

In this embodiment, the reflective electrode 9 has a diameter of 19600 (μm),
Since the opening 11 has an area of 100 (μm)2, it is only 0.
．． Only 5% of the area is rough.

FIG. 6 is a micrograph of the surface of a unit picture element obtained by carrying out the present invention.

When compared with the conventional example shown in FIG. 4, it will be easy to understand that the effect is even greater.

7 and 8 are enlarged views of the vicinity of the MOS transistor 1 of the conventional type and the present invention.
In contrast to the presence of a small area of aluminum without ohmic contact in the region corresponding to 0, 11, in FIG. 7 the opening 10, 11 is only observed through the aluminum due to the step.

The opening that is one size larger than opening 10.11 is )r”
}This occurred during cutting.

FIG. 4 is a sectional view of an image display device obtained by implementing the present invention, and when compared with the sectional view of FIG.
a first metal layer 18.h in ohmic contact with the diffusion layer;
It can be seen that metal electrodes 8 and 9 are formed on the metal layers 18 and 19.

By carrying out the present invention, a metal electrode having an almost specular state immediately after vapor deposition can be used as a reflective electrode, so that the contrast ratio can be increased from the conventional 4:1 to 10:1 in an image display device that combines a liquid crystal and a semiconductor integrated circuit. It was possible to improve up to.

In this example, both the first metal layer and the second metal layer were made of aluminum, but the metal layer is not limited to aluminum, and the first and second metal layers may be different. It is clear that there is no problem.

[Brief explanation of the drawing]

Figure 1 is a special circuit diagram of an image display device consisting of a liquid crystal and a semiconductor integrated circuit, Figure 2 is a plan view of a unit pixel of a conventional semiconductor integrated circuit for image display, Figure 3 is a cross-sectional view of the same, and Figure 4. is a microscopic photograph of the same plane, FIG. 5 is a cross-sectional view showing an embodiment of the image display device of the present invention, FIG. 6 is a microscopic photograph of the same plane, and FIGS. 7 and 8 are conventional ones. FIG. 2 is an enlarged plane photomicrograph of the main parts of the two of the present invention. 1...MOS type transistor, 2...
Charge storage capacitor, 8, 9...metal electrode,
10.11...Opening to the diffusion layer, 15...
...Transparent electrode, 16...Liquid crystal, 18.19...
. . . A first metal layer forming ohmic contact with the diffusion layer through the opening.

Claims (1)

[Scope of Claims] 1. A diffusion layer formed on a semiconductor substrate, a first metal layer formed in a contact portion of an insulating film on the diffusion layer, and in ohmic contact with the diffusion layer. , a second metal layer formed on the insulating layer so as to be connected to the first metal layer, the second metal layer forming a reflective electrode, and the second metal layer forming a reflective electrode; An image display device characterized in that a metal layer forms one electrode of a capacitor with the insulating layer interposed therebetween. 2. A step of depositing a diffusion layer formed on a semiconductor substrate and a first metal layer through an opening in an insulating layer, and a step of obtaining ohmic contact between the diffusion layer and the first metal layer. and,
A method for manufacturing an image display device, comprising the step of depositing a reflective second metal layer connected to the first metal layer.