JPH07326761A - Manufacture of thin film transistor with testing electrode - Google Patents

Abstract

PURPOSE:To eliminate a reduction in the yield of a thin film transistor due to a miniaturization of the contact area of a testing electrode with each electrode of the thin film transistor, which is caused by the reason that the dimension of the thin film transistor is reduced with an increase in the accuracy of an active-matrix liquid crystal display, and the connection of a thin film transistor, which is not operated already, with the thin film transistor by a wiring. CONSTITUTION:A testing electrode 8 of a wide area is once formed simultaneously on the region of a display electrode of each thin film transistor along with a source electrode 12, a gate electrode and a drain electrode 10 and after the characteristics of the individual thin film transistors are measured, the smooth connection of the display electrode with the source electrode 12 are made leaving the testing electrode 8 in the form of the connection of one part of the electrode 8 with the electrode 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to reduction of contact resistance of a thin film transistor, and particularly to reducing resistance between a test electrode and a source electrode, between a source electrode and a source electrode, and between a source electrode and a display electrode of an active matrix type liquid crystal display device. Regarding configuration.

[0002]

2. Description of the Related Art In recent years, active matrix type liquid crystal display devices using thin film transistors have been applied to office equipment in order to maintain high sharpness even if the number of pixels increases.

However, when a large number of thin film transistors are arranged in a matrix on a substrate, a short circuit easily occurs between a drain line and a gate line connecting between the thin film transistors.

Since a short circuit between lines causes a cross-shaped line defect on the liquid crystal display device, the display quality of the liquid crystal display device is remarkably deteriorated.

Conventionally, in order to test the switching characteristics and the insulation characteristics between lines of a thin film transistor, an ON signal of the thin film transistor is input to the gate line, and the lines of the same kind are electrically connected and the drain line and the gate line are connected. There is a method of manufacturing an active matrix liquid crystal display device in which an active matrix substrate whose leak current is less than a predetermined value is a good product (Japanese Patent Publication No. 5-58662).

FIG. 7 shows a wiring diagram of a liquid crystal display device for checking a short circuit between lines crossing three-dimensionally.

As shown in FIG. 7, the gate line 2 and the drain line 3 on the liquid crystal panel 1 intersect in a plane.

A thin film transistor 4 is arranged near the intersection of the intersecting gate line and drain line, and the source of the thin film transistor is connected to the display electrode.

The power source 5 is connected between the gate line and the drain line, the ends of which are commonly connected, and the degree of the short circuit between the gate line and the drain line can be known from the magnitude of the value of the ammeter 6.

This manufacturing method takes advantage of the fact that the average value of a thin film transistor having a constant distribution of characteristic values in a substrate can be more accurately obtained by commonly connecting a large number of drain lines or gate lines. Is.

In addition, by connecting adjacent drain lines of the liquid crystal display device in a meandering manner and checking the continuity between the drain lines at both ends of the liquid crystal display device, the liquid crystal display device is checked for the presence or absence of disconnection of the drain line. There was a test method (JP-A-3-184080).

FIG. 8 shows a wiring diagram of the liquid crystal display device for checking the disconnection of the gate line.

In FIG. 8, the left and right ends of the gate line 2 are alternately connected between adjacent gate lines, and the degree of disconnection of the gate line can be known from the resistance values at both ends of the meandering gate line.

This test method is a reasonable method to check the presence / absence of a disconnection between the drain line and the gate line and then the presence / absence of a short circuit between the drain line and the gate line.

Alternatively, there is a matrix display device in which a test electrode extending outside the seal of the liquid crystal display device is provided on the display electrode at the outermost periphery of the active matrix substrate (Japanese Patent Laid-Open No. 62-62160)
-2230).

FIG. 9 shows a plan view of a liquid crystal display device provided with a test electrode extending outside the seal.

As shown in FIG. 9, the liquid crystal panel 1 is divided into an internal display portion and an external non-display portion by a seal 7 made of an epoxy resin which encloses liquid crystal inside.

Normally, the display electrode to which the thin film transistor is connected remains inside the seal, but in the configuration of FIG. 9, the test electrode 8 extends to the non-display portion outside the seal.

This matrix display device has an advantage that a test can be performed even after sealing and a highly reliable test can be performed.

However, in the above-mentioned manufacturing method, since the drain line and the gate line generally intersect in a plane, an insulating film is interposed between them, and a single thin film transistor without the insulating film and the drain line is formed. It was difficult to confirm malfunctions, and the rate of non-defective products fell by that amount.

FIG. 10 is a perspective view of an active matrix substrate in which a general coplanar thin film transistor is used.
Shown in.

As shown in FIG. 10, the drain line 2 made of Al and having a thickness of 2 μm three-dimensionally intersects the gate line 2 made of Mo and having a thickness of 800 Å provided on the substrate.

Although not shown, the gate line and the drain line are usually insulated from each other by 2000 Å to 6000 Å of silicon oxide or silicon nitride.

In FIG. 10, the drain electrode 10 and the source electrode 1
The central portion of 2 is depressed because the thermal insulating film below the central portion is removed and is in contact with the drain and the source of the thin film transistor, respectively.

The size of the contact hole where the heat insulating film is removed, that is, the size of the contact hole is about 5 μm × 5 μm, and it is difficult to contact the tip of the probe, which is inconvenient for measuring the characteristics of each thin film transistor.

In FIG. 10, the drain electrode 10 extending from the drain line 3 is easily broken at the boundary of the semiconductor layer 9 having a net thickness of 1000 Å covered with a thermal oxide film having a thickness of 1000 Å.

On the other hand, contact resistance 200 Ω / □, thickness 800
A part of the display electrode 11 made of ITO of Å extends on the semiconductor layer 9 to form the source electrode 12.

Similarly, since the light transmittance is increased, the thinly formed source electrode 12 is easily broken at the boundary of the semiconductor layer 9.

FIG. 11 is a cross-sectional view of a thin film transistor for showing the structure of the disconnection of the source electrode at the boundary of the semiconductor layer.

In FIG. 11, a thin film transistor made of polycrystalline Si is formed on an insulating substrate 13 such as quartz glass.

A drain 14 and a source 15 of a high concentration impurity layer are formed in a part of the semiconductor layer 9 on the insulating substrate 13 by ion implantation.

The source 15 made of polycrystalline Si is connected to the display electrode 11 made of ITO via the source electrode 12 made of Ti.

Since the drain electrode is connected to the drain line 3, it is possible to arrange the thin film transistors in a matrix on the insulating substrate.
The display electrode 11 formed to a thickness of 0 Å or less is disconnected at the step portion of 2000 Å or more of the semiconductor layer covered with the thermal oxide film.
May occur.

There is a method of manufacturing a thin film transistor in which a gate electrode, a drain electrode, and a source electrode are laminated films of materials for the gate line and the drain line in order to prevent disconnection at a step portion of a semiconductor layer (Japanese Patent Laid-Open No. 61-61). 234076).

According to this structure, the disconnection of the drain electrode and the source electrode can be eliminated, but since the gate electrode is made of the same metal material of two layers, the intersecting gate line and drain line are formed of low resistance Al. It was impossible.

Further, there is a thin film transistor in which a display electrode is formed on a gate insulating film covering a substrate, and at the same time a gate electrode is formed of a transparent electrode to reduce a step at a boundary between semiconductor layers (Japanese Patent Laid-Open No. 61-97864). Issue).

According to the above structure, when the thermal oxide film obtained by thermally oxidizing the semiconductor layer is used as the insulating film, the film thickness becomes two to three times thicker before and after the oxidation. When the thin low-temperature grown insulating film is used, the insulating property between the gate electrode and the polycrystalline semiconductor layer may be impaired.

There is a thin film transistor structure in which the drain electrode, the source electrode and the gate are all formed of Al (M.
K. Hatalis, et. al. , SID 1993
DIGEST, p724-727, (1993)).

Here, the solid solution of silicon in aluminum
The degree is as high as 0.48% by weight at 450 ° C and
Diffusion coefficient of silicon to Ni is 1 × 10 at 450 ℃^-8
cm ²It is as large as / s.

The thin film transistor of this structure has a low resistance A
Since the wiring is formed by l, it is useful, but there is a disadvantage that Al in contact with the semiconductor diffuses to increase the resistance value of the source and drain.

There is a thin film transistor in which the drain electrode, the source electrode, and the gate electrode are all made of a refractory metal to prevent thermal diffusion (Japanese Patent Laid-Open No. 62-219669).

In the above structure, since the gate insulating film can be annealed at a high temperature, the threshold voltage of the thin film transistor can be improved. However, when the wiring and the electrode are commonly made of a refractory metal, the resistance of the drain line and the gate line is increased. There was a drawback that it became high.

As described above, the individual contact holes of the matrix-shaped thin film transistor are small, and it is inconvenient for the probe to come into contact with the thin film transistor. On the other hand, it is necessary to check the disconnection of the wiring composed of the gate line and the drain line or the short circuit between the wirings. Could only be investigated after the interlayer insulating film was formed.

In other words, the yield of the active matrix type liquid crystal display device remains around 50% because it is not known until the defective product of the liquid crystal display device is near the final process.

[0045]

DISCLOSURE OF THE INVENTION The present invention relates to a probe and a source and a drain of a thin film transistor, a source electrode and a display electrode after a test, a source electrode and a source, a drain line and a gate line. To reduce the resistance of
The purpose is to enable testing of individual thin film transistors.

[0046]

According to the present invention, a first step of forming a semiconductor layer on a transparent insulating substrate, a second step of forming a source and a drain containing impurities in a part of the semiconductor layer,
A third step of forming a first insulating film to be laminated on the semiconductor layer, a fourth step of forming a gate formed of a semiconductor layer containing impurities on the first insulating film, and a first metal film on the drain. A drain electrode is formed to cover a part of the insulating film, a source electrode is formed from above the source to the entire area of a display electrode to be formed later, and a gate electrode is connected to the gate electrode with a metal film. A fifth step of forming respective gate lines, a sixth step of etching the source electrode from a source to a partial region of a display electrode to be formed later, and a seventh step of connecting a transparent display electrode to the source electrode. A method of manufacturing a coplanar type thin film transistor comprising: a step of forming a drain line connected between the drain electrodes, wherein the source electrode of the fifth step is used as a test electrode of the thin film transistor. Than it is.

[0047]

According to the present invention, individual thin film transistor characteristics on a substrate can be measured before a short circuit inspection, and at this stage, a substrate having a display defect is found and a defective product is removed.

In practice, in order to measure individual thin film transistors, adjacent source and drain of the thin film transistors scattered in an island shape on the substrate are coupled with a metal film to form respective test electrodes.

Further, the display characteristics of the liquid crystal display device can be known in advance by obtaining the signal response by calculation from the thin film transistor characteristics measured by the metal film and estimating the display quality from this.

Further, when the thin film transistor is used in a projection type liquid crystal display device, the light resistance is important, but the light resistance of the thin film transistor can be easily determined at the substrate stage by direct irradiation of light.

[0051]

1 is a perspective view of a thin film transistor according to the present invention.

In FIG. 1, Mo test electrodes 8 are formed at the same time as Mo gate lines 2 each having a line width of 3 μm in the matrix and having terminal portions of 30 μm for connection to an external circuit at both ends. ing.

The test electrode 8 having a contact resistance of 0.1 Ω / □ and a thickness of 500 Å is a drain on the semiconductor layer 9 having a thickness of 2000 Å,
The drain electrode 10 and the source electrode 12 come into contact with the sources, respectively, and are arranged as electrodes having a high conductivity that cover a region where a transparent display electrode will be formed later and do not transmit light.

The size of the test electrode in contact with the insulating substrate is 50 μm × 50 μm.

Unlike the contact hole having a side of 5 μm on the semiconductor layer, the test electrode 8 has a side of 50 μm, so that the probe is easily contacted.

According to this structure, it is not necessary to finely adjust the pressure between the test electrode and the probe for the disconnection or short-circuit state of each thin film transistor, which can be easily investigated, and the leak current value due to the light irradiation can also be obtained. Can be measured.

Further, even if the display electrode is scratched by the test as in the prior art, it does not cause a pixel defect, and even if the test electrode on the insulating substrate is damaged by the probe, it will be removed later, so there is no worry.

Further, since the contact resistance between the test electrode and the probe is low, it is possible to accurately know the accurate off characteristic of the thin film transistor having a small measured value.

The test electrode connects between the source and drain of the adjacent thin film transistor.

FIG. 2 shows a test circuit diagram of a matrix thin film transistor connected by a test electrode in parallel with the gate line.

In FIG. 2, the opaque test electrodes 8 connected to the left and right of the thin film transistor 4 are connected by a probe 22 to a test circuit composed of a power supply 5 and an ammeter 6.

When an excessive current flows, it means that the thin film transistor is short-circuited, and the leakage current when the thin film transistor is off can be examined by the magnitude of the current value.

FIG. 3 shows a perspective view of a thin film transistor having a resist.

The resist 23 shown in FIG. 3 prevents damage to the gate line and the semiconductor layer during the testing of the thin film transistor with the probe.

After the test, the test electrode 8 in the part without the resist
When the material is Mo, the material is
If Ti is Ti, deionized water and 58% NH_FourOH and 30%
H₂O ₂And remove by dipping in a 5: 1: 1 solution of.

Similarly, the resist is removed from the insulating substrate with a stripping solution.

The shape of the resist is not limited to being left on the semiconductor layer as shown in FIG. 3, but may be formed so as to partially cover the test electrode on the insulating substrate.

Next, a thin film transistor of an embodiment in which the test electrode left by the resist and the transparent display electrode overlap will be described.

FIG. 4 is a perspective view of the thin film transistor of the present invention in which the test electrode of the present invention is partially left.

In FIG. 4, gate line 2 and drain line 3
Is insulated by an interlayer insulating film made of silicon oxide by CVD.

The drain electrode 10 is formed integrally with Mo18 and the drain wire which are in contact with the drain on the semiconductor layer.
It has a two-layer structure with 19.

Since the drain line to be formed later has no other wiring that overlaps with it, it can be formed thick, and as a result, disconnection of the drain electrode at the boundary of the semiconductor layer can be eliminated.

Similarly, the source electrode 12 is formed simultaneously with the Mo 18 and the drain line which are in contact with the source on the semiconductor layer.
It has a two-layer structure with I19.

Al having a thickness of 1 μm, which constitutes the upper layer of the source electrode, exists at the boundary of the semiconductor layer 9, but has a structure in which it does not come into direct contact with the transparent display electrode 11.

On the other hand, the thickness of the lower layer of the source electrode is 5
Mo of 00Å is in contact with the display electrode, and is punched at the contact portion with the display electrode.

The metal forming the lower layer of the source electrode is Ti,
Since it is a metal such as Cr, Mo, or W, and 200 Å or more is necessary to prevent diffusion of Al, even if the display electrode is thinned to 300 Å, there is no disconnection from the source electrode. .

The display electrode of FIG. 4 may be on the insulating substrate or the interlayer insulating film.

FIG. 5 is a sectional view of a thin film transistor of the present invention in which a display electrode is arranged on an interlayer insulating film.

As shown in FIG. 5, SiNx is provided between the drain electrode 3 and the gate electrode 17 which also serves as a gate line.
An inter-layer insulating film 24 made of is formed.

One end of the display electrode 11 is connected to the source electrode which is formed simultaneously with the gate electrode and the drain electrode.

The lower portion of the display electrode, through which light is actually transmitted, is supported by an interlayer insulating film 24 having a thickness of 3000 Å on a transparent insulating substrate.

On the thermal oxide film 20, a gate 25 of a thin film transistor having a high impurity concentration of the thin film transistor is provided.

FIG. 6 is a sectional view of a thin film transistor of the present invention in which display electrodes are arranged on an insulating substrate.

In FIG. 6, the display electrode 11 is overlaid on the Ti 21 having a contact resistance of 0.2 Ω / □ under the source electrode 12.

Therefore, if the lower layer of the source electrode is made thinner than the display electrode, both can be smoothly electrically connected on the insulating substrate 13.

Even if the lower layer of the source electrode is broken at the boundary of the thermal oxide film 20, the thickness of the upper layer of the source electrode is larger than 1.1 times the sum of the thicknesses of the semiconductor layer 9 and the thermal oxide film 20. If so, the source electrode is not broken.

[0087]

According to the method of manufacturing a thin film transistor of the present invention, since the contact resistance is low, it is possible to easily know the detailed characteristics of each thin film transistor, and to repair the short circuit and disconnection of the thin film transistor at an early stage, The yield of the active matrix type liquid crystal display device can be improved by removing the substrate that cannot be repaired.

Further, since the characteristics of each thin film transistor are known, a low resolution liquid crystal display in which the same signal is supplied to a plurality of pixels which does not cause any trouble in using a high resolution liquid crystal display panel having several point defects. It becomes possible to use it for a device.

Alternatively, since the thin film transistor can be irradiated with light without being covered with the interlayer insulating film, there is no attenuation of light intensity in the interlayer insulating film, and an accelerated photodegradation test of the thin film transistor can be performed in a shorter period than usual. You can also do it.

[Brief description of drawings]

FIG. 1 is a perspective view of a test electrode of a thin film transistor of the present invention.

FIG. 2 is a test circuit diagram of the thin film transistor of the present invention.

FIG. 3 is a perspective view of a resist of the thin film transistor of the present invention.

FIG. 4 is a perspective view of a thin film transistor of the present invention.

FIG. 5 is a cross-sectional view of an interlayer insulating film and a display electrode of the thin film transistor of the present invention.

FIG. 6 is a cross-sectional view of a source electrode and a display electrode of the thin film transistor of the invention.

FIG. 7 is a short circuit test circuit diagram of a conventional thin film transistor.

FIG. 8 is a disconnection test circuit diagram of a conventional thin film transistor.

FIG. 9 is a plan view of a test electrode of a conventional thin film transistor.

FIG. 10 is a perspective view of a conventional thin film transistor.

FIG. 11 is a cross-sectional view of a thin film transistor whose gate electrode and source electrode are made of the same material.

[Explanation of symbols]

 1 Liquid Crystal Panel 2 Gate Line 3 Drain Line 4 Thin Film Transistor 5 Power Supply 6 Ammeter 7 Seal 8 Test Electrode 9 Semiconductor Layer 10 Drain Electrode 11 Display Electrode 12 Source Electrode 13 Insulating Substrate 14 Drain 15 Source 16 Disconnection 17 Gate Electrode 18 Mo 19 Al 20 Thermal oxide film 21 Ti 22 Probe 23 Resist 24 Interlayer insulating film 25 Gate

Claims (3)

[Claims] 1. A step of forming a semiconductor layer on a transparent insulating substrate, a step of forming a source and a drain containing impurities in a part of the semiconductor layer, and forming a first insulating film on the semiconductor layer. A step of forming a gate made of a semiconductor layer containing impurities on the first insulating film, a metal gate line is formed between the gates, and a display formed later on the drain and the source. A step of forming a test electrode having a resistance lower than that of the display electrode to the entire area of the electrode, and a step of etching the test electrode to form a source electrode covering a part of the display electrode to be formed later from the source. And a step of connecting the transparent display electrode to the source electrode, the method of manufacturing a thin film transistor with a test electrode. 2. A semiconductor layer on a transparent insulating substrate, a source and a drain containing impurities formed in a part of the semiconductor layer, a first insulating film formed on the semiconductor layer, and the first insulating film. A gate formed of a semiconductor layer containing impurities formed on an insulating film; a source electrode formed on the source and the drain to cover a part of the first insulating film with a metal film; a drain electrode formed on the drain; A gate electrode formed of a metal film on the gate, a gate line connecting between the plurality of gates, and a drain line connecting between the plurality of drains,
A coplanar thin film transistor comprising a second insulating film for insulating between the gate line and the drain line, and a transparent display electrode connected to the source electrode, wherein the source electrode is in contact with the source and the drain, respectively. ,
The drain electrode is made of the same material as the gate electrode having a resistance lower than that of the display electrode and a resistance change smaller than that of Al, and the drain line is made of a material having a resistance lower than that of the gate electrode. A thin film transistor in which the display electrodes are laminated via the second insulating film. 3. A semiconductor layer on a transparent insulating substrate, a source and a drain containing impurities formed in a part of the semiconductor layer, a first insulating film formed on the semiconductor layer, and the first insulating film. A gate formed of an impurity-containing semiconductor layer formed on an insulating film; a source electrode formed on the source and the drain to cover a part of the first insulating film with a metal film; In a coplanar thin film transistor including a gate electrode formed of a metal film on a gate and a transparent display electrode connected to the source electrode, a portion of the source electrode and the drain electrode in contact with the source and the drain, respectively. Is the same material as the gate electrode having a lower resistance than the display electrode and a smaller resistance change than Al, and the drain line is a material having a lower resistance than the gate electrode. The thin film transistor, wherein the source electrode extends from the source through the first insulating film to the insulating substrate.