JPH0511278A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the residual images and burns of the MIM active elements of an active matrix liquid crystal panel by forming an insulating film constituting the MIMs of plural layers of insulating films including specific semiconductor thin films. CONSTITUTION:The 2nd insulating thin film 3 is formed extremely thin (<=100Angstrom mass film thickness) together with the 1st insulating film 2 formed by anodizing the surface of a 1st metal 1. The insulators of the MIM elements are constituted of the multilayered film structures including these two-layered films. The materials of the 2nd insulating thin film 3 are exemplified by IV element semiconductors or the oxides, nitrides, carbides, etc., thereof. The representative materials are Si, SiOX, SiNX, etc. The 2nd insulating film 3 is first sputtered and thereafter, the film of the 2nd metal 4 is continuously formed by an Rf sputtering film forming method. The films of transparent picture element electrodes 5 consisting of ITO, et., are thereafter formed by sputtering and are subjected to photopatterning. The shift of electric characteristics of the MIM elements by the voltage impression thereto is drastically decreased and the restoration time of the characteristic shift is greatly shortened in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in the basic structure of an MIM element, and more particularly to a highly reliable MIM liquid crystal display which eliminates the afterimage phenomenon and burn-in phenomenon of the liquid crystal display caused by the characteristic shift of the MIM element. To do.

[0002]

2. Description of the Related Art First, an MIM element will be defined. This is classified as an active element formed for each pixel for driving an active matrix liquid crystal display. Me
With the tal-Insulator-Metal configuration, the non-linearity of the electrical characteristics is similar to that of a bidirectional diode.

The basic process of the conventional MIM consists of Ta film formation pattern formation-anodic oxidation-Cr film formation pattern formation-ITO film formation pattern formation as a pixel transparent electrode. A cross-sectional view of a conventional MIM element formation substrate is shown in FIG.
A first insulating film 2 is formed on the surface of a first metal 1 such as Ta by a method such as anodic oxidation, and a second insulating film 2 such as Cr is formed on the first insulating film 2.
The metal 4 is formed into a film-forming pattern. Finally, the pixel transparent electrode 5 is formed into a film-forming pattern to complete the MIM element formation substrate.

[0004]

The only drawback of the MIM element, which is the active element of the active matrix liquid crystal panel, is that, in addition to the Pool-Frenkel electric conduction that is originally necessary for ensuring the element performance, it is possible to generate electricity by applying a voltage. There is a phenomenon that the conduction characteristics are shifted. Since this shift amount changes depending on the applied voltage value, there are afterimages and burn-in phenomenon on the display that the display pattern of the liquid crystal display remains for a long time without disappearing. The presumed mechanism of the cause system of this phenomenon is summarized below.

(1) Ion Conduction Theory--Excess mobile ions contained in the bulk of the first insulating film 2 are in a state of relatively freedom of movement, and the movement of these ions causes the MIM element. It is a mechanism that the electric characteristics of are shifted. The types of mobile ions are considered to be metal ions and impurity ions in the metal thin film. Due to this shift, an afterimage and burn-in on the display of the liquid crystal display occur.

(2) Deep level theory ----- There are deep levels due to structural defects in the first insulating film 2 or impurities in the first insulating film 2, and the electric conduction characteristics change depending on the applied voltage value.

(3) Dielectric constant change theory --- The dielectric constant changes depending on the electric field strength. This shifts the electrical characteristics of the MIM element.

For example, when the first insulating film is formed by anodic oxidation of a metal such as Ta, it is known that ions can easily move in the bulk of the first insulating film 2.

This ion is named a mobile ion.
The existence of impurity ions and unoxidized metal ions has been confirmed, and it is fully possible that these act as mobile ions. Therefore, the ionic conduction theory seems to be effective.

An object of the present invention is to improve the structure of the MIM element to eliminate the afterimage and burn-in phenomenon of the liquid crystal display caused by the characteristic shift of the MIM element.

[0011]

The liquid crystal display device of the present invention is characterized by the following seven items.

(1) In a MIM element side substrate of an active matrix liquid crystal display in which a switching element formed for each pixel is an MIM element having a bidirectional diode characteristic, a first metal thin film pattern is formed on a wafer substrate, The insulating film of the MIM element, which is formed by forming an insulating film on the surface of the pattern and forming a film pattern of the opposite electrode on the insulating film, is composed of at least the first insulating film and the second insulating thin film having a mass film thickness of 100 Å or less. It is characterized in that it is formed as a plurality of insulating films including two layers.

(2) The first insulating film is formed on the surface of the first metal thin film pattern, and the second insulating thin film formed thereon is used as a group IV element semiconductor or its oxide, or II.
An IV compound semiconductor or an oxide thereof, and an II-VI compound semiconductor or an oxide thereof.

(3) The first insulating film is formed on the surface of the first metal thin film pattern, and the second insulating thin film formed thereon is a nitride or carbide of a group IV element semiconductor, or III-V. Compound semiconductor nitride or carbide, II-
It is characterized in that it is a nitride or a carbide of a VI compound semiconductor.

(4) The method of oxidizing the second insulating thin film using an oxide is a sputtering film formation using an oxide target.

(5) When the second insulating thin film is made of an oxide, the oxidizing method is as follows.
It is characterized by a reactive sputtering method using Ar gas mixed with 2 gases.

(6) It is characterized in that the oxidation method when the second insulating thin film is an oxide is a thermal oxidation by heating with a heater after film formation.

(7) The oxidation method when the second insulating thin film is made to be an oxide is thermal oxidation by infrared irradiation or far infrared irradiation in the atmosphere after film formation.

(8) Oxidation when the second insulating thin film is made to be an oxide is performed by setting the substrate temperature during sputtering to 200 ° C. or higher during the next step of forming the pixel transparent electrode by sputtering. It is characterized in that it is achieved by at least one method of setting the 02 flow rate ratio in the inside to 1% or more.

[0020]

First, the most influential mechanism of the shift of the electric characteristics of the element due to the afterimage and image sticking will be described below. In the bulk of the first insulating film, mobile ions of non-oxidized metal, other impurity ions, and the like exist, and the first insulating film is in a state where it can move relatively freely in the insulating film. When driving the MIM element, by applying a drive voltage, these ions move in the bulk of the insulating film.
Due to this movement, the distribution of the ion density in the bulk of the insulating film is biased, and the characteristics of the MIM element change. Alternatively, the ions in the insulating film move and are swept up to the interface between the insulating film and the electrode, and the electrical characteristics of the interface (Schottky emission characteristics, etc.) change due to the ions, and the characteristics of the MIM element change. .

The first of the mechanism for estimating the action of the present invention is:
It is considered that the ions that have moved in the first insulating film of the MIM element are blocked by the second insulating thin film so that the ions do not reach the interface with the electrode. The second insulating thin film is
In this way, it plays the role of an ion barrier. As a result, there is no change in the state of the electrode interface due to the voltage application, and therefore the characteristic shift of the MIM element related to the interface such as the Schottky emission characteristic is also eliminated.

The second mechanism of estimating the action of the present invention is:
The deviation of the ion density distribution in the bulk of the first insulating film of the MIM element is eliminated by the following principle. That is, since the second insulating thin film such as Si, SiOx, SiNx, or SiC is a film that does not easily adsorb ions or the like,
The mechanism is that the ions swept up to the vicinity of the insulating film immediately diffuse into the bulk without being adsorbed on this film. As a result, afterimages and image sticking of the liquid crystal display, which are caused by the uneven distribution of the ion density in the MIM element, are quickly recovered and immediately disappear. .

The third mechanism of estimating the action of the present invention is:
In the case of the MIM structure using the first insulating film formed by oxidizing the surface of the first metal by the anodic oxidation method or the like, by further oxidizing the second insulating thin film, further oxidation of the first insulating film can be achieved. It is possible to make the inside of the first insulating film rich in oxygen by advancing. This reduces the concentration of non-oxidized mobile metal ions in the first metal, reduces the shift in the electrical characteristics of the device caused by the movement of mobile ions, and causes the afterimage phenomenon and burn-in phenomenon of the liquid crystal display. Will be less.

[0024]

Embodiments of the present invention will be described below with reference to the cross-sectional view of the MIM element formation substrate of FIG. As the method of forming the first insulating film 2, a method of oxidizing the surface of the first metal 1 by an anodic oxidation method or the like, a method of forming by thermal oxidation, O 2
There are methods such as plasma oxidation. In addition, SiNx, Si
There is also a method of forming an insulating material such as Cx by a PVD method or a CVD method. There is also a method of forming an organic film material such as polyimide as an insulating film. here,
The most important feature of the present invention is that the first insulating film 2 and the second
The insulating thin film is formed extremely thin, and the I portion of the MIM element, that is, the insulator is formed by a multilayer structure including the two-layer film. The second insulating thin film 3 is formed on the surface of the first insulating film 2. The film thickness of this second insulating thin film 3 is set to 100 Å or less as the mass film thickness. The reason for making it ultra-thin in this way is so as not to affect the nonlinear characteristics required as an active element of the MIM element determined by the physical properties of the first insulating film. The material of the second insulating thin film 3 is a group IV element semiconductor or its oxide,
A nitride, a carbide, a III-V compound semiconductor or an oxide thereof, a nitride, a carbide, and an II-VI compound semiconductor or an oxide, a nitride, or a carbide thereof. Typical materials are
Examples include Si, SiOx, SiNx, and SiC. With this material, since the Rf sputtering film forming method, the plasma CVD method and the like can be used, an in-line type mass production apparatus can be constructed and the film forming speed is remarkably improved. Therefore, it will match the rationalization and cost reduction of future active matrix liquid crystal panels. When forming a film by sputtering,
Since the film forming method of the second metal, which is the electrode on the opposite side of the MIM element, is also generally the sputtering method, continuous film formation can be achieved simultaneously with the second metal in the same sputtering without breaking the vacuum. Of. The sputter deposition sequence for this continuous deposition is
First, the second insulating thin film 3 is sputtered, and then the second metal is sputtered.

After the film formation and patterning of the second metal, the same process as the conventional process is performed, but the pixel transparent electrode 5 such as ITO is used.
Is formed into a film by sputtering using the Rf sputtering method or the like, and photo-patterning is performed.

The following five methods are used as the oxidation method when the second insulating thin film is an oxide.

Method (1) --- This is a method of forming a film by sputtering using an oxide target. In most cases, the target itself is an insulator, so RF with high frequency voltage applied
The sputtering method is used.

Method (2) --- Reactive sputtering method using Ar gas mixed with O2 gas as the plasma gas during sputtering film formation. In this case, it does not have to be an oxide at the target stage and may be a pure semiconductor or a semiconductor compound such as GaAs.

Method (3) ---- In some cases, the combination of method (1) and method (2) alone (1) may not be able to achieve thin film formation as a complete oxide. The cause mechanism is described below. First, when sputtered by Ar particles, it is divided into a case where the oxide semiconductor is sputtered as it is and a case where the Ar particles are decomposed when the Ar particles collide with the target and are deposited on the substrate as an unoxidized semiconductor. The oxidation rate of the formed film depends on sputtering parameters such as Ar gas pressure and power. This method 3 is a method in which both method (1) and method (2) are simultaneously adopted to obtain a perfect oxide. A complete oxide film can be formed by using an oxide target and further performing reactive sputtering containing O2 gas.

Method (4) ---- heating the heater after film formation,
That is, a thermal oxidation method by resistance heating is first performed to form a film as a normal semiconductor. In a subsequent process, the heater is heated in the atmosphere to oxidize it. This method is effective when the sputtering of the oxide target by RF sputtering cannot be adopted, or when the reactive sputtering method cannot be adopted because the O2 gas is not flown. If the temperature distribution is uniform,
The uniformity of in-plane film formation such as the degree of oxidation and film quality is improved.

Method (5) ---- The thermal oxidation method using infrared rays or far infrared rays after the film formation is used. This principle is also the same as the method (4), in which the film is oxidized by heating in the atmosphere after the film formation process.

Further, when forming the pixel transparent electrode, which is the next step after the second insulating film is formed and the pattern is formed, the sputtering temperature is set to 200 ° C. or higher under the condition that the ITO film is used for the sputtering film formation. The second insulating thin film is also oxidized by using at least one method of setting the 02 flow rate ratio in the plasma gas to 1% or more. The advantage of this is that it is naturally oxidized by optimizing the sputtering conditions in the next ITO film forming process. In particular, it is not necessary to add a step for oxidizing. Also, there is no need to use expensive targets such as oxide targets. Furthermore, there is no need for an element such as reactive sputtering that makes the film quality unstable as viewed from the film forming technique. However, the degree of oxidation in this case does not reach the level of complete oxidation.

Here, the above-mentioned six methods are used as the oxidizing method, but which method is selected depends on the advantages, disadvantages, rationalization of the process, cost reduction, and the extent to which oxidation is performed. It is judged comprehensively from that. The above processes are listed below in order of representative materials.

(1) Sputter deposition of Ta film as first metal, photo patterning (2) First insulating film formation ---- Ta which is the first metal
A Ta2O5 film is formed by anodizing the surface of the film.

(3) Second insulating thin film formation--Typically, Rf sputtering film formation using a SiO2 target.

(4) Second Metal Formation--Typically, sputter film formation using a Cr target and photo patterning. It is also possible to continuously sputter a two-layer film with (3).

(5) Pixel transparent electrode formation --- Rf sputtering film formation using an ITO target, photo patterning.

A plan view of one embodiment of the MIM element formation substrate of the present invention is shown in FIG. After forming the pattern of the first metal 1, the surface of the first metal is oxidized by a method such as anodic oxidation to form a first insulating film. This insulating film is formed in the same plane shape as the pattern of the first metal. Next, Si, S
A semiconductor such as iO2, SiNx, or SiC or a semiconductor oxide film or nitride or carbide is formed on the entire surface of the wafer substrate by a film forming method such as sputtering to a film thickness of 100 Å or less.
It is not necessary to form a photo pattern for this film. This is because this film is an insulating film and there is no risk of short circuit with the adjacent pixel or pattern via this film.
As a result, it becomes possible to continuously form a film with the sputtered film of the second metal, which is the next film forming step. A single sputter film forming apparatus can achieve continuous film formation of a two-layer film without breaking the vacuum.

As described above, the first feature of the present invention resides in that the ultrathin film such as a semiconductor or a semiconductor oxide is added to the insulating film of the conventional MIM element. Since the added ultra-thin film has a good insulating property, it is not necessary to add a photo process for pattern formation. In addition, continuous sputtering film formation with the second metal is possible, and the film formation process does not particularly increase.

Therefore, the process is not particularly complicated.

[0041]

[Effect of the Invention] The electrical characteristics of the conventional MIM element are shifted by voltage application. A change in the absolute value of the applied voltage also changes the amount of characteristic shift, and since the recovery time of the characteristic shift is long, this appears as an afterimage phenomenon and a burn-in phenomenon on the display of the liquid crystal display, which deteriorates the display quality. With regard to future applications of liquid crystal panels, it is expected that there will be many uses for displaying still images such as personal computers, workstations, measuring instruments, and in-vehicle navigation systems, and the specifications for afterimages and burn-in phenomena will definitely become strict.

According to the present invention, this characteristic shift is greatly reduced. Also, the recovery time of the characteristic shift is significantly shortened. As a result, it is possible to provide a MIM active matrix liquid crystal display which has a good image quality without an afterimage and a burn-in phenomenon that occur in the entire surface of the liquid crystal display, particularly in the image area. The above effect can be expected without making the MIM manufacturing process particularly complicated.

The first insulating film is a film whose relative dielectric constant and other physical properties are optimized in order to secure the nonlinear performance of the electrical characteristics required for the MIM element. Here, the second insulating film is used. Since the insulating thin film is very thin, the optimized function of the first insulating film can be secured at the same level even if it is a two-layer film. That is, the afterimage and image sticking can be suppressed while maintaining the performance of the first insulating film.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a MIM element formation substrate of the present invention.

FIG. 2 is a sectional view of a conventional MIM element formation substrate.

FIG. 3 is a plan view of one embodiment of the MIM element formation substrate of the present invention.

[Explanation of symbols]

1st metal 2 First insulating film 3 Second insulating thin film 4 second metal 5 pixel transparent electrode 6 First metal

Claims (8)

[Claims] 1. In a MIM element side substrate of an active matrix liquid crystal display in which a switching element formed for each pixel is formed of an MIM element having a bidirectional diode characteristic, a first metal thin film pattern is formed on a wafer substrate. The insulating film of the MIM element in which the insulating film is formed on the surface of the pattern and the opposite electrode is formed on the surface of the pattern is at least the first insulating film and the second insulating thin film having a mass film thickness of 100 Å or less. A liquid crystal display device, which is formed as a plurality of insulating films including layers. 2. The first insulating film is formed on the surface of the first metal thin film pattern, and the second insulating thin film thereon is formed of a group IV element semiconductor or an oxide thereof, or III-
A V compound semiconductor or an oxide thereof, and a II-VI compound semiconductor or an oxide thereof.
The described liquid crystal display device. 3. The first insulating film is formed on the surface of the first metal thin film pattern, and the second insulating thin film formed thereon is a nitride or carbide of group IV element semiconductor, or II.
I-V compound semiconductor nitride or carbide, II-VI
The liquid crystal display device according to claim 1, wherein the compound semiconductor is a nitride or a carbide. 4. The liquid crystal display device according to claim 1, wherein the oxidation method when the second insulating thin film is an oxide is a sputtering film formation using an oxide target. 5. The oxidation method when the second insulating thin film is an oxide is a reactive sputtering method in which a plasma gas used for film formation by sputtering is Ar gas mixed with O 2 gas. The liquid crystal display device according to claim 1. 6. The liquid crystal display device according to claim 1, wherein the oxidation method when the second insulating thin film is made to be an oxide is thermal oxidation by heating with a heater after film formation. 7. The oxidation method when the second insulating thin film is an oxide is thermal oxidation by infrared irradiation or far infrared irradiation in the atmosphere after film formation. Liquid crystal display device. 8. Oxidation when the second insulating thin film is made to be an oxide is carried out at a substrate temperature of 200 ° C. or higher during sputtering during the next step of forming a pixel transparent electrode by sputtering. 2. The liquid crystal display device according to claim 1, which is achieved by at least one of the methods for increasing the 02 flow rate ratio to 1% or more.