JPS63221324A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent defective connection of a thin film transistor to a transparent picture element electrode by forming a semiconductor layer for forming a thin film transistor at a part below a transparent picture element electrode. CONSTITUTION:A thin film transistor TrT is formed in a liquid crystal display device on an inside surface of a lower transparent glass substrate 1. A transparent picture element electrode 5C formed for each picture element is connected to one 5B of source drain electrodes of the TrT. The electrode 5C is connected integrally with a transparent electrode layer 5b of the source drain electrodes 5A, 5B. An i-type semiconductor layer 4A formed by elongating an i-type semiconductor layer 4 and an n<+> type semiconductor layer 5D formed by elongating an n<+> type semiconductor layer 5a are provided to a part below the electrode 5C. Since the electrode 5C can be held at a higher position due to the presence of the layer 4A and 5D by this constitution, the stage difference between the connecting part of the electrode 5B to the electrode 5C is reduced. Thus, defective connection of the electrode 5B to the electrode 5C is prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a technique that is effective when applied to a liquid crystal display device, and particularly to a liquid crystal display device in which the display of each pixel of a liquid crystal display section is controlled by a thin film transistor. be.

[Prior art]

In a liquid crystal display device, the display of each pixel in a liquid crystal display section is controlled by a thin film transistor (TPT). This liquid crystal display device is constructed by filling a space between a lower transparent glass substrate and an upper transparent glass substrate with liquid crystal. On the inner surface (liquid crystal side) of the lower transparent glass substrate, a transparent pixel electrode provided for each pixel and a thin film transistor provided for each pixel that controls the voltage applied thereto are provided. A common transparent pixel electrode facing the transparent pixel electrode is provided on the inner surface (liquid crystal side) of the upper transparent glass substrate.

In 1986, Japan Display introduced a thin film transistor with an inverted stagger structure.
'86-The 6th International
al Display Re5aarch Co
nfarenCs, Po5t-Deadline Pa
per, 5ession 8. The one shown in Figure 3 of PD 3) is known. This thin film transistor is formed in a first-order manner.

First, a gate electrode is formed on the surface of a lower transparent glass substrate in a thin film transistor formation region. After this,
An insulating film used as a gate insulating film is formed on the gate electrode.

Next, on the insulating film on the gate electrode, an amorphous silicon layer used as a channel formation region and a pair of source/drain electrodes are formed on the amorphous silicon layer. sauce·
The drain electrode is a highly concentrated n-type packed crystal silicon layer C.
It is formed by sequentially laminating r layers. The amorphous silicon layer and the source/drain electrodes are formed by sequentially stacking the respective formation layers and then etching the respective formation layers all at once using an etching mask.

Next, a transparent pixel electrode (ITO) is formed on the insulating film. The transparent pixel electrode is formed by sputtering. The transparent pixel electrode is also formed on and connected to the source and drain electrodes of the thin film transistor.

[Problem that the invention seeks to solve]

As a result of failure analysis of the liquid crystal display section of the liquid crystal display device described above, the inventor discovered that connection failures between the source/drain electrodes of the thin film transistors and the transparent pixel electrodes frequently occur. For example, consider that this connection failure is caused by the step shape formed by the 7-morphous silicon layer (channel formation region) and source/drain electrodes of the thin film transistor. In other words, the connection failure occurs because the step coverage of the transparent pixel electrode in the stepped portion is poor, resulting in disconnection. The amorphous silicon layer is formed to have a thickness of about 400 nm in order to ensure current capacity in the channel forming region. The source/drain electrodes are formed with a film thickness of about 11G[n+a]. On the other hand, the inventor of the present invention similarly discovered that video signal lines (vertical signal lines) formed in the same process as transparent pixel electrodes also break.

Therefore, point defects occur frequently and the yield of liquid crystal display devices decreases.

An object of the present invention is to provide a technique that can improve the yield of liquid crystal display devices.

Another object of the present invention is a liquid crystal display device.

An object of the present invention is to provide a technique that can prevent poor connection between a thin film transistor and a transparent pixel electrode.

Another object of the present invention is to provide a technique that can prevent disconnection of video signal lines in a liquid crystal display device.

Another object of the present invention is to provide a technique that can reduce the manufacturing process of a liquid crystal display device.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Means for solving problems]

A brief overview of two typical inventions disclosed in this application is as follows.

A liquid crystal display device in which a transparent pixel electrode is connected to a thin film transistor is characterized in that a semiconductor layer forming the thin film transistor extends below the transparent pixel electrode.

[Effect]

According to the above-described means, it is possible to reduce the step shape caused by the semiconductor layer of the thin film transistor, and therefore it is possible to prevent poor connection between the source/drain electrode of the thin film transistor and the transparent pixel electrode. Also, similarly,
Breakage of the video signal line can be prevented.

As a result, point defects can be reduced and the yield of liquid crystal display devices can be improved.

Hereinafter, the structure of the present invention will be described together with an embodiment in which it is applied to a liquid crystal display device having a thin film transistor with an inverted staggered structure.

In addition, in all the times for explaining the example.

Components having the same functions are given the same reference numerals, and repeated explanations thereof will be omitted.

[Embodiments of the invention]

A main part of a liquid crystal display section of a liquid crystal display device according to an embodiment of the present invention is shown in FIG. 1 (a plan view of the main part), and FIG. 2 shows a cross section taken along the line ■--■ in FIG.

As shown in FIGS. 1 and 2, the liquid crystal display device includes 1
, 1 A thin film transistor (TPT) T having an inverted staggered structure is provided on the inner surface (liquid crystal side) of a lower transparent glass substrate 1 having a thickness of approximately m+ml.

The thin film transistor T mainly includes a gate electrode 2, an insulating film 3 used as a gate insulating film, an i-type semiconductor layer 4 used as a channel formation region. It is composed of a pair of source/drain electrodes 5A and 5B.

The gate electrode 2 is formed on the surface of the lower transparent glass substrate 1.
For example, it is formed of a Cr layer (or a composite film with a Mo layer laminated thereon). The gate electrode 2 is.

It is integrated with and connected to the scanning line (horizontal signal line) 2A.

The i-type semiconductor layer 4 is formed of an amorphous silicon layer or a polycrystalline silicon layer on the insulating film 3. This i-type semiconductor layer 4 is formed of a thin film of about 30 [n■], which is about one order of magnitude thinner. The i-type semiconductor layer 4 formed of a thin film in this manner is characterized by being less likely to cause malfunction of the thin film transistor T due to induced photocurrent and having a high backlight transmittance.

A pair of source/drain electrodes 5A and 5B are provided on the i-type semiconductor layer 4 and spaced apart from each other.

The source/drain electrodes 5A and 5B are configured so that when the bias polarity of one circuit changes, the source and drain are interchanged in operation. In other words, the thin film transistor T is
Like FET, it is bidirectional.

The source/drain electrodes 5A and 6B are formed of high impurity-concentrated n-type semiconductor layers starting from the lower layer side in contact with the i-type semiconductor layer 4.

It is formed by sequentially stacking a type semiconductor layer 5a, an ITO layer 5b, and a Mo layer 5c. The square-shaped semiconductor layer 5a is formed of an amorphous silicon layer or a polycrystalline silicon layer,
It is configured to reduce the contact resistance value with the i-type semiconductor layer 4. The ITO layer 5b is a compound of indium-tin-oxide and has transparency and conductivity.

The Mo layer 5c has a low resistance value in order to increase the signal transmission speed, and is also used as a wiring material.

One source/drain electrode 5B of thin film transistor T
Transparent pixel electrode (ITO) 6G provided for each pixel
is connected. The transparent pixel electrode 5C constitutes one of the pixel electrodes of the liquid crystal display section.

The transparent pixel electrode 5C is the source/drain electrode 5A.

It is formed in the same manufacturing process and from the same material as the ITO layer 5b of 5B, and is integrally configured and connected thereto. Below the transparent pixel electrode 5C, the i-type semiconductor layer 4 is formed.
There are provided an i-type semiconductor layer 4A in which the i-type semiconductor layer 5a is extended, and a diagonal-shaped semiconductor layer 5D in which the diagonal-type semiconductor layer 5a is extended.

The other source/drain electrode 5A is integrated with and connected to a video signal line (vertical signal line) 5E. The video signal line 5E has substantially the same structure as the source/drain electrode 5A or 5B.

In this way, in a liquid crystal display device in which a transparent pixel electrode 5C is connected to a thin film transistor T, the i-type semiconductor layer 4 and the n-type semiconductor layer 5a forming the thin-film transistor T are
By extending the i-type semiconductor layer 4A and the n◆-type half body layer 5D below the transparent pixel electrode 5C, the i-type semiconductor layer 4A and the n◆-type semiconductor layer SD form the transparent pixel electrode 5C.
Since the position of the transparent pixel electrode 5C can be raised, the stepped shape of the connection portion between the source/drain electrode 5B and the transparent pixel electrode 5C can be relaxed. What is the shape of the step at the connection part?

It is mainly formed only by the gate electrode 2. Therefore, it is possible to improve the step coverage of the transparent pixel electrode 5C forming layer in the stepped portion of the connection portion, and to prevent poor connection between the source/drain electrode 5B and the transparent pixel electrode 5C.

Moreover, the i-type semiconductor layer 4A and the n-type half body layer 5
D. Since it is formed of a thin film, it is possible to prevent the thin film transistor T from malfunctioning due to the induced photocurrent, and also to prevent the transmittance of the backlight from decreasing.

Similarly, by configuring the video signal 5g5E with substantially the same structure as the source/drain electrode 5A or 5B, the step shape in the extending direction can be alleviated, so that the video signal line 5g Disconnection can be prevented.

As a result, point defects can be reduced and the yield of liquid crystal display devices can be improved.

A protective film 6 is provided on the thin film transistor T and the transparent pixel electrode SC. The protective film 6 is mainly formed to protect the thin film transistor T from moisture etc.
It is formed using a silicon oxide film or a silicon nitride film that is highly transparent and has good moisture resistance.

A shielding film 7 is provided above the protective film 6 on the thin film transistor T to prevent external light from entering the i-type semiconductor layer 4 used as a channel formation region. The shielding film 7 is formed of, for example, a Cr layer.

The thin film transistor T is configured such that when a positive bias is applied to the gate electrode 2, the channel resistance between the source and drain becomes small, and when the bias is reduced to zero, the channel resistance becomes large.

That is, the thin film transistor T is configured to control the voltage applied to the transparent pixel electrode 5C.

The liquid crystal 9 is defined and enclosed in a space formed between a lower transparent glass substrate l and an upper transparent glass substrate 10 by a lower alignment film 8 and an upper alignment film 14 that set the orientation of liquid crystal molecules. .

The lower alignment film 8 is the protective film 6 on the lower transparent glass substrate 1 side.
is formed at the top of the

On the inner surface (liquid crystal side) of the upper transparent glass substrate 10,
Color filter 11, protective film 12. Common transparent pixel electrode (
ITO) 13 and the upper alignment film 14 are sequentially stacked.

The common transparent pixel electrode 13 faces the transparent pixel electrode 5C provided for each pixel on the lower transparent glass substrate 1 side, and is configured integrally with another adjacent common transparent electrode 13.

The color filter 11 is formed by dyeing a dyed base material made of a resin material such as acrylic resin with a dye for each pixel. Dyeing is done using photolithography technology.

The protective film 12 is provided to prevent the dyes used to dye the color filters 11 into different colors from leaking into the liquid crystal 9. The protective film 12 is made of, for example, acrylic resin,
It is made of transparent resin material such as epoxy resin.

In this liquid crystal display device, the layers on the lower transparent glass substrate 1 side and the upper transparent glass substrate 10 side are formed separately, and then the upper and lower transparent glass substrates 10 and 1 are stacked and liquid crystal 9 is sealed between them. It is assembled by

Note that the center portion of FIG. 2 shows a cross section of one pixel portion. The left side is a transparent glass substrate! The left side edge portion of 1 and 10 shows a cross section of the portion where the lead wiring is present. The right side is
A cross section of the right edge portion of the transparent glass substrates 1 and 10 where no lead wiring is present is shown.

The sealing material 15 shown on the left and right sides of FIG. 2 is configured to seal the liquid crystal 9, and is designed to seal the entire circumference of the transparent glass substrates 1 and 10 except for the liquid crystal sealing opening (not shown). is formed along. The sealing material 15 is made of, for example, epoxy resin.

Common transparent pixel electrode 13 on the upper transparent glass substrate 10 side
is connected to the lead wiring layer formed on the lower transparent glass substrate 1 side at least in one place by a silver paste material 16. This lead wiring layer is the gate electrode 2 described above. It is formed in the same manufacturing process as the source/drain electrodes 5A and 5B.

The alignment film 8.14, the transparent pixel electrode 5C1, the common transparent pixel electrode 13. Each layer of the protective film 6 and the insulating film 3 is formed inside the sealing material 15. The polarizing plate 17 is a lower transparent glass substrate! , are formed on the outer surface of each of the upper transparent glass substrates 10.

Next, regarding the method of forming the liquid crystal display device, FIGS. 3 to 5 (plan views of main parts of the liquid crystal display section shown for each manufacturing process) and FIGS. This will be briefly explained using a cross-sectional view of a main part of a liquid crystal display section. In addition, the 6th
9 to 9 are cross-sectional views taken along the line 1--2 in FIG. 1.

First, a lower transparent glass substrate 1 made of 7059 plate glass is prepared.

Next, as shown in FIGS. 3 and 6, gate electrodes 2 and scanning lines 2A are placed on the inner surface of the lower transparent glass substrate 1.
form. The gate electrode 2 and the scanning line 2A are on the surface of the lower transparent glass substrate 1.

For example, 100[n] Cr layers are formed by sputtering.
It can be formed by forming a film with a certain thickness and then patterning it using photolithography technology.

Next, an insulating film 3 is formed to cover the gate electrode 2 and the scanning line 2A. The insulating film 3 is formed, for example, of a silicon nitride film formed by plasma CVD using a mask deposition method, and is formed to have a film thickness of about 300 nm.

Next, substantially the entire surface of the lower transparent glass substrate 1 is covered.

#! An i-type semiconductor layer and an n-type semiconductor layer are sequentially laminated on the i-edge film 3. Each of the i-type semiconductor layer and the n1-type semiconductor layer is formed by plasma CVD. [A film thickness of about nml, a square-shaped semiconductor layer is 300 [
The a n" type semiconductor layers, each formed with a film thickness of about nml, are formed as thin films in order to increase the transmittance of the backlight, similarly to the i type semiconductor layer. In other words, the thin film transistor T
It is preferable that the total thickness of the i-type semiconductor layer and the n-type semiconductor layer is about 1000 nm or less as the semiconductor layer.

Next, an ITO layer is formed on top of the square shaped semiconductor layer. The ITO layer is formed by sputtering, for example, and
The thickness of the film is approximately 100 m. This ITO layer is formed on the i-type semiconductor layer and the n-type semiconductor layer to reduce the step shape at the connection portion between the thin film transistor T and the transparent pixel electrode 5c.

Good step coverage.

Next, as shown in FIGS. 4 and 7, the ITO layer, the n-type semiconductor layer, and the i-type semiconductor layer are sequentially patterned, except for the channel formation region of the thin film transistor T. As a result of this patterning, in the thin film transistor formation region, the i-type semiconductor layer 4. is used as a channel formation region. A rectangular semiconductor layer 5a and an ITO layer 5b, which are used as a pair of source and drain electrodes, are respectively formed. In addition, in the transparent pixel electrode formation region, the i-type semiconductor layer 4
A transparent pixel electrode 5C made of an ITO layer is formed on the A and n° type half body layers 5D. Also.

In the video signal line formation region, a video signal line (5
E) is formed.

The ITO layer is wet-etched using a photoresist mask shown by a dashed line in FIG. 7 with an etching solution containing, for example, hydrochloric acid, nitric acid, and pure water. The n゛゛ semiconductor layer and the i-type semiconductor layer are formed by the patterned I
Using the TO layer as a mask, dry etching is performed with a mixed gas of SFG and CCl24.

In this way, the thin film transistor T is formed using the ITO layer forming the transparent pixel electrode 5c as an etching mask, but by forming each of the type semiconductor layer 5b and the i-type semiconductor layer 5a, the latter mask forming step can be eliminated. Therefore, the manufacturing process of the liquid crystal display device can be reduced.

Further, using the ITO layer forming the transparent pixel electrode 5C as an etching mask, the thin film transistor T and the transparent pixel electrode 5 are etched.
A curved semiconductor layer 5D that alleviates the step shape at the connection portion with C.
By forming the i-type semiconductor layers 4A and 4A, the latter mask forming step can be omitted, so that the number of manufacturing steps for the liquid crystal display device can be reduced. Video signal line (
The same applies to 5E).

Next, as shown in FIGS. 5 and 8, the ITO layer 5b and the n1 type semiconductor layer 5a on the channel formation region of the thin film transistor T are sequentially patterned.

A pair of source/drain electrodes (5A, 5B) are formed. The source/drain electrodes (5A, 5B) are formed using a photoresist mask indicated by a dashed line in the figure. I
The TO layer 5b is patterned using the above-mentioned etching solution, and the n-type half body layer 5b is patterned using a hydrochloric acid etching solution.

Next, as shown in FIGS. 1 and 9, on the ITO layer 5b forming the source/drain electrodes (5A, 5B) and the video signal line (5E), a 1MO layer 5c forming a Mo layer 5C. is formed by etching a Mo layer with a thickness of about 1100Cn formed by sputtering, for example, with an etching solution containing a mixture of nitric acid, phosphoric acid, acetic acid, and pure water using a photoresist mask. By performing this step, the source/drain electrodes 5A and 5B and the video signal line 5E are completed, and as a result, the thin film transistor T is completed.

Next, by forming the protective film 6, the lower transparent glass substrate 1 on which the thin film transistor T and the transparent pixel electrode 5C are formed is completed. The protective film 6 is formed by, for example, plasma CVD.
It is formed using a silicon nitride film formed in .

As above, the invention made by the present inventor has been specifically explained based on the above embodiments, but the present invention is not limited to the above embodiments, and can be modified in various ways without departing from the gist thereof. Of course.

〔Effect of the invention〕

A brief explanation of the effects obtained by typical inventions disclosed in this application is as follows.

In a liquid crystal display device, poor connection between thin film transistors and transparent pixel electrodes can be prevented, so point defects can be reduced and yields can be improved.

[Brief explanation of drawings]

FIG. 1 is a plan view showing the main parts of the liquid crystal display section of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a plan view of the main parts shown in FIG.
The sectional view taken along the line -■, and FIGS. 3 to 5 are plan views of the main parts of the liquid crystal display section shown in each manufacturing process. 6th to 913iil are main part sectional views of the liquid crystal display section shown for each manufacturing process. In the figure, 1, 10...transparent glass substrate, 9...liquid crystal,
2... Gate electrode, 3... Insulating film, 4,4A...
i-type semiconductor layer, 6A, 5B... source/drain electrode, 5C... transparent pixel electrode, 5D, 5a... is type semiconductor layer, 5E... video signal line, 5b... ITO layer, 5
c...Mo layer. T: Thin film transistor. 5! Figure 7

Claims (1)

[Claims] 1. In a liquid crystal display device in which a transparent pixel electrode is connected to one source electrode or drain electrode of a thin film transistor, a semiconductor layer forming the thin film transistor extends below the transparent pixel electrode. A liquid crystal display device characterized by: 2. The semiconductor layer is an i-type semiconductor layer forming a channel region of the thin film transistor, an n^+ type semiconductor layer forming a source electrode or a drain electrode of the thin film transistor, or both of the above semiconductor layers. A liquid crystal display device according to claim 1. 3. The transparent pixel electrode is formed on the semiconductor layer, and the semiconductor layer is formed using the transparent pixel electrode as an etching mask. The liquid crystal display device described in . 4. The liquid crystal display device according to claim 3, wherein the semiconductor layer is formed of a thin film of about 100 [nm] or less.