JP3341346B2 - Manufacturing method of nonlinear element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device having a nonlinear element and a method of manufacturing the same, and more particularly to a structure capable of manufacturing the nonlinear element at low cost and a method of manufacturing the same.

[0002]

2. Description of the Related Art In general, in an active matrix type liquid crystal display device, a non-linear element is provided for each pixel region to form a matrix array and a substrate on one side on which a color filter is formed. Is filled with liquid crystal, and the orientation of the liquid crystal in each pixel region is controlled to display predetermined information. Here, a three-terminal element such as a thin film transistor (TFT) or a two-terminal element such as a metal-insulator-metal (MIM) nonlinear element is used as the non-linear element. In order to meet the demand, a method using an MIM type nonlinear element is advantageous because the manufacturing process is short. In addition, when the MIM type nonlinear element is used, a scanning line can be provided on one substrate on which a matrix array is formed, and a signal line can be provided on the other substrate. There is also an advantage that a crossover short circuit between the scanning line and the signal line, which is the cause, does not occur.

In an active matrix type liquid crystal display panel using such an MIM type nonlinear element,
As shown in FIG. 4, between each scanning line 4 and each signal line 5 in each pixel region 2, an MIM type nonlinear element 1 (indicated by a varistor in the figure) and a liquid crystal display element 3 (in the figure, The liquid crystal display element 3 is switched to a display state, a non-display state, or an intermediate state based on signals applied to the scanning lines 4 and the signal lines 5. To control the display operation.

A general structure of such an MIM type nonlinear element will be described with reference to a sectional view of FIG. MI
The M-type nonlinear element 1 is formed on the surface side of the transparent substrate 51 and has a metal film 52 containing Ta atoms as a main component and containing impurity atoms other than Ta atoms conductively connected to the scanning circuit side via the scanning lines 4. , A metal oxide film 53 on the surface side, and a Cr film 54 formed on the surface side and conductively connected to the pixel electrode 55. The metal oxide film 53 is formed by anodic oxidation of the metal film 52 so that the Ta film has a uniform thickness and no pinholes.

[0005] An example of a general process for realizing this structure is as follows.

[0006] 1. A Ta film is deposited on a glass substrate by sputtering, and thermally oxidized to form a T
1. forming an a ₂ O ₅ film; Next, as shown in FIG. 5 (a), a first metal film containing Ta atoms as a main component and containing impurity atoms other than Ta atoms is formed by co-sputtering or electron beam evaporation.
2. depositing and patterning; Next, as shown in FIG. 5B, a step of forming an oxide film on the surface side of the first metal film by performing anodization at 30 V using, for example, a dilute aqueous solution of citric acid as a chemical conversion solution; Next, the substrate in the state of FIG.
4. a heat treatment at a temperature of 600 ° C. for 1 to 2 hours; Next, as shown in FIG. 5C, a Cr film to be a second metal film is deposited by sputtering at about 1500 ° C. and patterned. Next, an ITO film serving as a pixel electrode has been conventionally deposited from a process of depositing about 2000 Å by sputtering and patterning.

[0007]

SUMMARY OF THE INVENTION However, MIM
In the manufacturing process of the liquid crystal display device using the non-linear element, it is necessary to apply a resist to each of the first metal electrode layer, the second metal electrode layer, the pixel electrode, and the three films to process them. Active matrix liquid crystal display devices
Although the TFT method and the MIM method are roughly classified, the MIM method requires one processing of the film on the opposite substrate side of the element substrate, so that the resist exposure step which lowers the yield and lowers the throughput is performed three times. If so, it is difficult to provide a substrate that is overwhelmingly cheaper than the TFT method in which the number of exposure steps is about five. Therefore, it is desired that the resist exposure step of the element substrate be performed twice without deteriorating the electrical characteristics of the MIM type nonlinear element.

As one method of making the resist exposure step twice, as shown in JP-A-61-250676, when an ITO film is formed on a silicon film and annealed in an inert gas, a silicon film is formed. Since an oxide film is formed at the interface between the MIM type nonlinear element and the ITO film, the MIM type non-linear element is completed with two times of exposure of the silicon film and the ITO film. However, M of silicon-silicon dioxide-ITO
The IM type non-linear element cannot not only obtain electric characteristics suitable for driving a liquid crystal display device, but also is not suitable for displaying the entire screen because the wiring resistance of a silicon film is considerably higher than that of a metal film. .

Another method is disclosed in JP-A-60-164.
As shown at 724, the second metal film is
It is thinned to the extent and processed simultaneously with the pixel electrode film. However, since the metal film and the pixel electrode film overlap with each other, the transmittance of the substrate on which the MIM type nonlinear element is formed deteriorates, so that the display luminance of the liquid crystal display device cannot be obtained. In addition, there is a problem that uniformity in a screen cannot be obtained because electric characteristics are sensitive to the thickness of the second metal film.

[0010]

Therefore, a method of manufacturing a nonlinear element according to the present invention comprises a step of forming a first metal film on a surface of a substrate, and oxidizing the surface of the first metal film. Forming a first metal oxide film, forming a second metal film on the first metal film, the first metal film, the first metal oxide film and the second Forming a second metal oxide film by oxidizing a side surface of the first metal film to form a second metal oxide film; Forming a transparent conductive film and processing it into a predetermined shape. Further, in the method for manufacturing a nonlinear element according to the present invention, in the method for manufacturing a nonlinear element described above, the second metal film is selectively formed so as not to be conductively connected to the first metal film. It is characterized by becoming.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

FIG. 1 shows a top view of the liquid crystal display device of the present invention. The MIM type nonlinear element 1 is formed on a part of the scanning line 4, and 4 is a scanning line formed of the same material as the first metal film of the MIM type nonlinear element. Is shown.

In FIGS. 1A and 1B, sectional views taken along lines AA 'in which an MIM type nonlinear element is formed and BB' lines in which an MIM type nonlinear element is not formed are shown in FIGS. 2A and 2B, respectively.
Shown in Reference numeral 11 denotes a transparent substrate such as glass or quartz.
1a is deposited by sputtering or tantalum (Ta)
A tantalum oxide film (TaO _x ) is formed by thermally oxidizing the film. Reference numeral 12 denotes a Ta film or an alloy film containing Ta atoms as a main component and capable of being anodized. Reference numeral 13 denotes a first metal oxide film formed by anodizing the metal film 12, and reference numeral 14 denotes a metal film whose type is determined by what kind of process is adopted. Reference numeral 15 denotes a second metal oxide film formed on the side surface of the metal film 12, and reference numeral 16 denotes a pixel electrode.

FIG. 3 shows a process for realizing the structure of FIG.

FIG. 3A shows that a first metal film 12 is deposited on the front side of a transparent substrate having a TaO _X film on the surface, and the surface is anodized to form a first oxide film 13. 150 ℃
The heat treatment described above has been performed, and the second metal film 14 has just been deposited.

The first metal film is mainly composed of Ta atoms, and the amount of impurities to be added should be such that anodic oxidation is possible even when using an alloy film to which impurities are added. When performing the anodic oxidation, the scanning line 4 formed of the first metal film 12 is used.
The terminal part that receives the external signal to the terminal should not be oxidized. The finished substrate on which the MIM type nonlinear element is formed
As shown in FIG. 6, the scanning lines 4 are arranged in a line and external signal input terminals 61 are provided on both sides thereof. Therefore, as shown in Japanese Patent Application Laid-Open No. 58-70555, an organic film such as a resist may be applied to the terminal 61 using a device such as a dispenser so that the terminal 61 is not oxidized in the anodizing step. Then, after the oxidation step is completed, the resist and the like are peeled off.

Furthermore, the deposition of the second metal film 14 should be such that no conductive connection is made with the first metal film 12. That is, in the second anodic oxidation step, if there is an electrical connection between the first metal film 12 and the second metal film 14 that are not immersed in the chemical conversion solution in the substrate, the first metal film 12 and the cathode This is because no voltage is applied during this period, and a voltage is applied between the second metal film and the second metal film, so that the second metal oxide film 15 does not grow.

Next, the first metal film 12, the first metal oxide film 13,
The second metal film 14 is processed at one time as shown in FIG. Since the main component of the first metal film 12 is Ta, that of the first metal oxide film 13 is TaOx, and only hydrofluoric acid is a material capable of etching both films, the second metal film When the metal 14 is made of a metal etched with hydrofluoric acid, such as Mo, Ti, and W, a three-layer film can be processed at a time, which is preferable for increasing the throughput and reducing the cost. If the second metal film 14 is a metal that cannot be etched with hydrofluoric acid, the same resist is processed twice using different etching solutions.

Next, as shown in FIG. 3C, the first metal film 1 is formed.
2 is oxidized to form a second metal oxide film 15.
There are two types of methods for forming the second metal oxide film 15, and each will be described.

First, it may be formed by using an anodic oxidation method. As shown in FIG. 2B, the MIM type nonlinear element 1 for controlling the alignment state of the liquid crystal has a first metal film-first metal oxide film-second metal film. MIM type nonlinear element 21 and first metal film-second metal oxide film-I
Second MIM consisting of a pixel electrode formed of a TO film
The non-linear elements 22 are arranged in parallel. By the way, if the ITO film is used as an electrode, the voltage-current characteristics become unstable, which is not preferable. Therefore, the second metal oxide film is made of a material having a higher insulating property than the first metal oxide film. Most of the flowing current may flow through the first MIM type nonlinear element 21. For example, the anodic oxidation chemical may be phosphoric acid when forming the first metal oxide film, and may be citric acid when forming the second metal oxide film. Here, in order to make the thickness of the second metal oxide film thicker than that of the first metal oxide film, a method of making the formation voltage and current density larger than those at the time of manufacturing the first oxide film is also conceivable. This is not a means to be used because the second metal film may peel off. Another method for forming a second metal oxide film is to use a thermal oxidation method in an oxygen atmosphere.
When heat treatment is performed in an oxygen atmosphere at 450 to 500 ° C., a metal oxide film having a predetermined thickness can be obtained by controlling the time thereafter. In this case, when the second metal film is oxidized in the oxidation step, electrical conduction with the pixel electrode cannot be obtained.
It is preferable to use a metal that is not easily oxidized at a temperature of about 500 ° C., such as gold or platinum, because it is a simple process. If a metal that can be oxidized is used for the second metal film,
The oxide film may be etched and used. Next, as shown in FIG. 3D, a transparent conductive film 16 such as an ITO film, which is to be a pixel electrode and is conductively connected to the second metal film 14, is deposited, and a resist is processed thereon into a predetermined shape. The ITO film is etched using the mask. Here, the etching solution for the ITO film is desirably an aqueous solution of hydrobromic acid that does not easily etch the metal film because there is a portion where the metal film is used as the base film. At this stage, the MIM type nonlinear element is completed, but the second metal film 14 remains on the scanning line 4 in FIG. 1 and the elements on the same scanning line are short-circuited. Therefore, after the etching of the ITO film, the processed IT
Using the O film as a mask, the second metal film in the portion 6 on the scanning line 4 where the MIM nonlinear element 1 is not formed is etched. As described above, the MIM type nonlinear element for driving the liquid crystal is completed in two steps of exposing the resist.

FIG. 1 shows a substrate using the MIM type non-linear element manufactured through this process. However, since the element is formed on the scanning line, the aperture ratio can be increased and a bright liquid crystal display device can be obtained. In addition, the MIM type nonlinear element as shown in FIG. 2 mainly has a portion 21 through which a current flows, and uses only the surface side of the first metal film 12 and does not use the side surface. become. In other words, when the first metal film 12 is etched, it becomes a shape as shown in FIG. 7 and it is difficult to control the length 1 of the side portion 72, and the voltage-current characteristics and the capacitance of the MIM type nonlinear element are different in the substrate, and This is a major cause of display unevenness of the display device. However, in the present invention, only the portion of the front side 71 is MIM.
Since the element becomes a non-linear element and the size of the element can be made uniform within the substrate, this display unevenness has almost disappeared.

Japanese Patent Application Laid-Open No. 61-250676 proposes a display panel having a structure as shown in FIG. 1 in which the function of the second metal film 14 and the pixel electrode 16 is limited to the ITO film, and the resist exposure process can be performed in two steps. However, in the MIM type nonlinear element in which the ITO film is the second metal film, the voltage-current characteristics are different between when a positive voltage is applied to the first metal film and when a negative voltage is applied. However, there are problems such as a large change with time and a large change in characteristics at low and high temperatures, and it is not suitable for use as a liquid crystal drive element.

As another structure in which the resist exposure process can be performed in two steps, as shown in Japanese Patent Application Laid-Open No. Sho 60-164724, the thickness of the second metal film is set to about 100 ° and the second metal film is exposed. A method of processing a film and an ITO film simultaneously has been proposed. However, the transmittance of the pixel portion decreases,
Due to problems such as a large change with time when a voltage is applied, the performance as a liquid crystal display element is lower than that of the structure of the present invention.

The voltage-current characteristics of the MIM type nonlinear element are as follows:
When a Ta film is used as the first metal film, the film quality, what kind of impurities are added, the type of anodizing chemical solution used to form the first metal oxide film, and the type of the second metal film It is known that it greatly changes depending on the conditions. However, in the structure of the present invention, although the type of the second metal film is limited by the process to be taken, it is possible to adopt a target condition without being limited by the process for the other elements. is there.

[0025]

As described above, according to the present invention, by forming the MIM type nonlinear element as shown in FIG. 2, the element can be completed only by performing the resist exposure process twice, so that a low-cost active matrix type element can be obtained. Can be provided. In this structure, there is no need to change the material of the portion that forms the MIM type nonlinear element, and there is no need to change the physical properties of each film, so that the electrical characteristics do not change. When the second metal oxide film is formed by the anodic oxidation method, the film can be prepared if the first metal film and the second metal film are electrically insulated,
The manufacturing process of the present invention can be adopted.

[Brief description of the drawings]

FIG. 1 is a top view of a MIM type nonlinear element of the present invention.

FIG. 2 is a cross-sectional view of the MIM type nonlinear element of the present invention.

FIG. 3 is a diagram showing a manufacturing process of the MIM type nonlinear element of the present invention.

FIG. 4 is an equivalent circuit diagram of an active matrix liquid crystal display device.

FIG. 5 is a diagram showing a manufacturing process of a conventional MIM type nonlinear element.

FIG. 6 is a view showing a method of selective anodic oxidation in a manufacturing process of the MIM type nonlinear element of the present invention.

FIG. 7 is a sectional view showing an etched shape of a first metal layer of a conventional MIM type nonlinear element.

[Explanation of symbols]

1 MIM nonlinear device 2 pixel region 3 liquid crystal display device 4 with no scanning line 5 signal lines 6 MIM nonlinear device scanning line region 11, 51 transparent substrate 11a, 51a TaO _X film 12, 52 first metal film 13, 53 First metal oxide film 14, 54 Second metal film 15, 55 Second metal oxide film 16 Pixel electrode 21 First MIM type nonlinear element 22 Second MIM type nonlinear element 61 External signal input terminal 62 Anodizing A region where an organic film is applied during the process 71 A portion which becomes a taper when the first metal layer is etched 72 A portion where the first metal layer is not etched

Claims (2)

(57) [Claims] A step of forming a first metal film on a surface side of the substrate; a step of oxidizing a surface side of the first metal film to form a first metal oxide film; Forming a second metal film on the film, processing the first metal film, the first metal oxide film and the second metal film into a predetermined shape by a single resist exposure, A step of oxidizing a side surface of the first metal film to form a second metal oxide film, and a step of forming a transparent conductive film on the second metal film and processing it into a predetermined shape. A method for manufacturing a non-linear element, comprising: 2. The method for manufacturing a nonlinear element according to claim 1, wherein said second metal film is selectively formed so as not to be conductively connected to said first metal film. Manufacturing method of a nonlinear element.