JPH0996836A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain stability with excellent characteristics while substantially preventing the influence of the potential by change, etc., existing above thin-film transistors(TFTs) by forming active layers consisting of specific amorphous silicon on gate electrodes via the insulating films held therebtween. SOLUTION: This liquid crystal display device has an insulating substrate, the gate electrodes formed on this insulating substrate and the active layers 5 consisting of the amorphous silicon formed on the gate electrodes via the insulating films 3 interposed therebtween. Group zero elements of >=0.1atm.% are incorporated into the regions of the range within 50nm from the surface on the side opposite to the gate electrodes of the active layer and the group zero elements are not incorporated or are incorporated at just <=0.1atm.% into the regions exclusive therefrom. The increase in the leak current at the time of off cannot be prevented when only the group zero elements are incorporated at <0.1atm.% into the regions within 50nm from the surface on the side opposite to the gate electrodes of the active layers 4. The element characteristics of the TFTs are deteriorated when the group zero elements are incorporated at >=0.1atm.% in the regions exceeding 50nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a thin film transistor having excellent characteristics and having good display characteristics.

[0002]

2. Description of the Related Art As a display device capable of reducing power consumption,
There is a reflective liquid crystal display device. An example of this reflective liquid crystal display device will be described. First, Si on a glass substrate
After forming the Ox film, a gate electrode layer is formed. Then, an insulating layer composed of a single layer or a laminated layer of SiOx or SiNx, an a-Si layer, and an n ⁺ a-Si layer are sequentially deposited, and n
⁺ sequentially patterning the a-Si layer and the a-Si layer,
An a-Si island pattern is formed.

Next, by patterning the gate insulating film,
A hole for taking out the gate electrode is formed. Further, a metal layer is deposited and patterned to form a signal line electrode layer. In this patterning step, first, a resist pattern is formed, the metal layer is etched using the resist pattern as a mask, and thereafter, an n ⁺ a-Si layer and an a-Si layer are formed using a CDE device or the like.
The layers are etched continuously.

After that, a SiNx film or the like is deposited and patterned to form a passivation film. Then A1
A metal layer such as the above is deposited and patterned to form a pixel electrode layer. After that, a polyimide film serving as a liquid crystal alignment film is deposited to complete the array substrate. Furthermore, by combining with a counter substrate having an ITO layer and a color filter layer and injecting liquid crystal between these substrates, a reflection type liquid crystal display device is completed.

However, in the reflective liquid crystal display device as described above, since the pixel electrode is covered on the upper part of the thin film transistor in order to increase the aperture ratio, the characteristic of the thin film transistor is deteriorated due to the influence of the potential of the pixel electrode. was there. In particular, there is a problem that display characteristics are deteriorated because the leak current at the time of turning off increases.

On the other hand, in order to reduce the cost of the transmissive liquid crystal display device, the following structure has been proposed. That is, first, a SiOx film is formed on a glass substrate, and then a gate electrode layer is formed. Next, SiOx and SiNx
Insulation layer, a-Si layer, and n ⁺
The a-Si layer is sequentially deposited, and the n ⁺ a-Si layer and the a-Si layer are sequentially patterned to form an island pattern of the a-Si layer. Next, an ITO layer is formed by a sputtering method or the like and patterned to form a pixel electrode layer.

After that, the gate insulating film is patterned to form a hole for taking out the gate electrode. Further, a metal layer is deposited and patterned to form a signal line electrode layer. In this patterning step, first, a resist pattern is formed, the metal layer is etched using the resist pattern as a mask, and then the n ⁺ a-Si layer, a
-Si layer is continuously etched. After that, a polyimide film serving as a liquid crystal alignment film is deposited to complete the array substrate. Further, by combining with a counter substrate having an ITO layer and a color filter layer and injecting a liquid crystal between these substrates, a liquid crystal display device is completed.

However, in the above structure, since the passivation film made of the SiNx layer or the like formed before the formation of the polyimide film is usually omitted, the cost can be reduced due to the effect of the process reduction. However, since the polyimide film is in contact with the signal line metal layer or the a-Si layer, when it is used for a long time, charge injection from the signal line metal layer or the like into the polyimide layer occurs, which deteriorates the characteristics of the thin film transistor. There was a problem. Specifically, there is a problem in that the leakage current at the time of off increases due to the influence of the potential of the injected charges, and the reliability of the characteristics deteriorates.

[0009]

As described above, the conventional reflective liquid crystal display device has a problem that the off-current increases due to the influence of the potential of the pixel electrode and the display characteristics are deteriorated. Further, the transmissive liquid crystal display device without the passivation film also has a problem that the off current increases and the reliability of the characteristics is poor.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display device which is not easily affected by the potential due to charges or the like above a thin film transistor and which has excellent stability of characteristics.

[0011]

In order to solve the above problems, the present invention (claim 1) provides an insulating substrate, a gate electrode formed on the insulating substrate, and a gate electrode on the insulating substrate. A thin film transistor having an active layer made of amorphous silicon formed with an insulating film interposed therebetween. 0.1 atom is formed in a region within 50 nm from a surface of the active layer opposite to the gate electrode. % Or more Group 0 element is contained, and a Group 0 element is not contained in the other region, or less than 0.1 atomic% is provided, and a liquid crystal display device is provided. .

The present invention (Claim 2) provides the liquid crystal display device (Claim 1) in a region within 50 nm from a surface of the active layer opposite to the gate electrode,
Provided is a liquid crystal display device containing 0.1 atomic% to 1.0 atomic% of argon.

The structure, operation, and principle of the liquid crystal display device of the present invention will be described in more detail below. In the thin film transistor in the liquid crystal display device according to the present invention, in the region within 50 nm from the surface of the active layer opposite to the gate electrode (hereinafter referred to as the back channel interface), 0.
It contains 1 atom% or more of a Group 0 element.

The content of the Group 0 element in the region within 50 nm from the back channel interface is 0.1 atom%.
The above is preferable. Further, it is preferably 1 atomic% or less. Further, the region within 30 nm of the back channel interface contains 0.1 atom% or more of a Group 0 element, and the region other than that contains no or less than 0.1 atom%. It is preferable.

50 nm from the back channel interface of the active layer
When the region within the range contains less than 0.1 atom% of the Group 0 element, the effect of the present invention that prevents the increase of the leak current at the time of off cannot be obtained. On the other hand, if it exceeds 1 atomic%, the resistance in the vicinity of the back channel decreases, conversely the leak current increases, and the display characteristics may deteriorate.

As the group 0 element, argon, neon,
Although krypton, xenon, etc. can be used, argon is most preferred. The element contained in the region of 50 nm from the back channel interface must be a Group 0 element because these elements do not bond with silicon in the active layer. When an element other than the group 0 element is contained, these elements form a bond with silicon in the active layer and hinder the formation of a dangling bond of silicon, which is not preferable. Further, with a small-sized element such as hydrogen, the element escapes in the heat step, and the effect of the present invention cannot be obtained.

50 nm from the back channel interface of the active layer
The group exceeding 0 must contain no group 0 element or less than 0.1 atom%.
When the group 0 element is contained in the region exceeding 50 nm from the back channel interface of the active layer in an amount of 0.1 atom% or more,
The element characteristics of the thin film transistor are deteriorated, and the display characteristics of the liquid crystal display device are deteriorated.

The off-leakage current increases due to the influence of the potential above the thin film transistor, because the potential causes the potential of the interface between the normal gate side and the opposite side (hereinafter referred to as back channel) in a-Si forming the active layer of the transistor. It has been found that the cause is that the band bends near the interface), electrons are accumulated, a channel is generated, and a current flows. Therefore, in order to reduce this current, it is sufficient to prevent the band from bending at the interface of the back channel (band-belding) and to generate the channel.

The present inventors have considered that increasing the interface state density is effective as a method for preventing such band bending. Therefore, in the present invention, plasma processing is performed using a reactive ion etching (RIE) device or the like to damage the vicinity of the back channel interface. By performing the biased plasma treatment in this manner, physical damage of ions is applied to the back channel portion of the a-Si layer, and thus the interface state can be easily formed.

This is because a-Si is caused by ion damage.
It was found that this is because the Si-H bond and the Si-Si bond in the inside were broken to form a dangling bond of Si. it is conceivable that. Furthermore, the inventors of the present invention perform plasma treatment using an inert element such as Ar,
It was found that the interface states can be formed efficiently. This is because, in general, ions of plasma species may remain in a-Si due to plasma treatment, and when an active element is used, it reacts with Si in a-Si to form a dangling bond of Si. It is considered that there is a possibility of preventing the formation, but when an inert element is used, such a concern is considered to disappear.

Further, with a small-sized element such as hydrogen, even if it remains in a-Si, it is easily desorbed in a subsequent heat step, but the inert element has a large size,
It is not desorbed even in the subsequent heat step.

If the ion damage is too large, a
The resistance in the vicinity of the back channel of the -Si layer decreases, and the off leak current increases. Therefore, moderate damage is required.

An experiment was conducted by actually forming an electrode (back gate electrode) above the thin film transistor (on the side opposite to the gate) and applying a voltage (back gate voltage). That is, 0
The off-current was measured by changing the gate voltage in the range of -15V to 25V while applying the back gate voltage of -30V. The results are shown in FIGS. FIG.
FIG. 2 shows the relationship between the gate voltage and the off current in the case of a thin film transistor in which the back channel interface was not plasma-treated, and FIG. 2 is the gate voltage and the off current in the case of a thin film transistor in which the back channel interface was plasma-treated. Shows the relationship.

From FIG. 1 and FIG. 2, when the back channel interface was not plasma-treated, the off-current increased with the application of the positive voltage (FIG. 1), but the plasma treatment was performed with Ar plasma. It can be seen that the increase in the off current is no longer observed when it is performed (FIG. 2).

As described above, the back channel interface is subjected to the plasma treatment using the inert element such as Ar,
An interface state is formed, and band bending due to the potential on the thin film transistor can be prevented, thereby preventing electrons from accumulating near the back channel interface of a-Si and preventing an increase in leak current at the time of off. be able to. As a result, it is possible to obtain a reflective liquid crystal display device and a transmissive liquid crystal display device having good display characteristics.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the drawings to explain the present invention more specifically. Example 1 FIG. 3 is a sectional view showing a manufacturing process of a liquid crystal display device according to an example of the present invention, and FIG. 4 is a plan view thereof.

First, SiO is formed on a glass substrate (not shown).
An x film 1 is formed, and a gate electrode layer 2 is formed on this SiOx film. (FIG. 3 (a)). Next, SiOx and SiN
An x-single-layer or laminated insulating layer, an a-Si film 5, and an n ⁺ a-Si film 6 are sequentially deposited to form an n ⁺ a-Si film 6, a
The -Si film 5 is sequentially patterned to form an a-Si island pattern (FIG. 3B).

Next, by patterning the gate insulating film,
A hole 7 for taking out the gate electrode is formed (see FIG. 3).
(C)). Then deposit a metal layer, pattern,
The signal line electrode layer 8 is formed. In this patterning step, first, a resist pattern is formed, the metal layer is etched using the resist pattern as a mask, and then the n ⁺ a-Si film 6 and the a-Si film 5 are continuously formed by using a CDE device or the like. Selectively etch. Then, plasma processing using Ar gas is performed (FIG. 3D).

The plasma treatment is performed as follows. That is, using a parallel plate type RIE processing device, an area of 6
The sample was placed on a cathode electrode of 00 cm ² and the pressure was adjusted to 10
The plasma treatment was performed under the conditions of Pa, power of 100 W, and treatment time of 10 seconds to 10 minutes.

By this plasma treatment, the region 9 within 30 nm from the back channel interface of the a-Si layer 5 is formed.
0.2 atomic% of Ar was included. Note that A
It is also possible to use other noble gases such as Ne, Kr, Xe instead of r plasma.

Next, a SiNx film is deposited and patterned to form a passivation layer 10 (FIG. 3).
(E)). Next, a metal layer such as A1 is deposited and patterned to form the pixel electrode layer 11 (FIG. 3 (f)).

After that, a polyimide layer serving as a liquid crystal alignment film is deposited to complete the array substrate. This array substrate
A reflection type liquid crystal display device is completed by combining with a counter substrate having an ITO layer and a color filter layer and injecting liquid crystal between these substrates.

When the display characteristics of this liquid crystal display device were examined, good display characteristics were shown. Comparative Example 1 A reflective liquid crystal display device was produced in the same manner as in Example 1 except that the back channel interface was not subjected to plasma treatment, and the display characteristics were examined. As a result, the display characteristics were deteriorated.

Comparative Example 2 A reflective liquid crystal display device was prepared in the same manner as in Example 1 except that the plasma treatment was performed in an atmosphere containing hydrogen on the back channel interface, and the display characteristics were examined. The display characteristics are shown.

It is considered that the display characteristics are deteriorated because the effect of the present invention is lost as a result of hydrogen being released by the heat treatment in the manufacturing process after the plasma treatment. Embodiment 2 FIG. 5 is a sectional view showing a manufacturing process of a liquid crystal display device according to an embodiment of the present invention, and FIG. 6 is a plan view thereof.

First, SiO is formed on a glass substrate (not shown).
An x film 1 is formed, and a gate electrode layer 2 is formed on this SiOx film. (FIG. 5 (a)). Next, SiOx and SiN
An x-single-layer or laminated insulating layer, an a-Si film 5, and an n ⁺ a-Si film 6 are sequentially deposited to form an n ⁺ a-Si film 6, a
The -Si film 5 is sequentially patterned to form an a-Si island pattern (FIG. 5B).

Next, an ITO film is formed by a sputtering method or the like,
The pixel electrode layer 11 is formed by patterning (see FIG. 5).
(C)). After that, the gate insulating film is patterned,
A hole for taking out the gate electrode is formed (FIG. 5D).
Further, a metal layer is deposited and patterned to form the signal line electrode layer 8. In this patterning step, first, a resist pattern is formed, the metal layer is etched using the resist pattern as a mask, and then n ^{+ a} − is formed by using a CDE device or the like.
The Si film 6 and the a-Si film 5 are continuously etched. Then, in the same manner as in Example 1, plasma processing using Ar gas is performed. By this treatment, 0.2 atomic% of Ar was introduced into the region 9 of 30 nm from the back channel interface of the a-Si layer 5.
Is included.

After that, a polyimide layer to be an alignment film of liquid crystal is deposited to complete the array substrate. This array substrate
A liquid crystal display device is completed by combining with an opposite substrate having an ITO layer and a color filter layer, and injecting liquid crystal between them. When the display characteristics of this liquid crystal display device were examined, good display characteristics were shown.

[0039]

As described above, according to the present invention,
By performing a plasma treatment of an inert element such as Ar on the back channel portion of the active layer made of a-Si, it is possible to suppress an increase in off-leakage current due to the influence of the potential on the electrodes and charges on the thin film transistor. It is possible to obtain a liquid crystal display device having excellent display characteristics.

[0040]

[Brief description of drawings]

[0041]

FIG. 1 is a characteristic diagram showing an increase in off-current due to an influence of a potential above a thin film transistor of a conventional liquid crystal display device.

[0042]

FIG. 2 is a characteristic diagram showing a decrease in off-current due to an influence of a potential above a thin film transistor of a liquid crystal display device of the present invention.

[0043]

FIG. 3 is a sectional view showing a manufacturing process of the liquid crystal display device according to the first embodiment of the present invention.

[0044]

FIG. 4 is a plan view of the liquid crystal display device according to the first embodiment of the present invention.

[0045]

FIG. 5 is a cross-sectional view showing the manufacturing process of the liquid crystal display device according to the second embodiment of the present invention.

[0046]

FIG. 6 is a plan view of a liquid crystal display device according to a second embodiment of the present invention.

[0047]

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Undercoat SiOx layer 2 ... Gate electrode layer 3 ... Gate insulating film 5 ... a-Si layer 6 ... n ⁺ a-Si layer 7 ... Signal line electrode layer 8 ... Passivation SiNx layer 9 ... Pixel electrode layer

Claims (2)

[Claims] 1. A thin film transistor having an insulating substrate, a gate electrode formed on the insulating substrate, and an active layer made of amorphous silicon formed on the gate electrode with an insulating film interposed therebetween. 0.1 atomic% or more of a Group 0 element is contained in a region within 50 nm of the surface of the active layer opposite to the gate electrode, and the other region contains a Group 0 element. Group element is not contained or 0.
A liquid crystal display device characterized by containing less than 1 atomic%. 2. The region of the active layer, which is within 50 nm from the surface opposite to the gate electrode, is 0.1 atomic% to
The liquid crystal display device according to claim 1, wherein the liquid crystal display device contains 1.0 atomic% of argon.