JPS62264686A - Formation of mim nonlinear element - Google Patents

Abstract

PURPOSE:To provide an underlaid M layer of an MIM element in a safe and simple manner, by patterning the underlaid M layer by means of the lift-off technique using photoresist shaped to have overhangs. CONSTITUTION:P-type photoresist 9 is applied on a glass substrate 8. An underlaid M layer and an inversed pattern mask 10 are provided thereon. The structure is exposed and developed to form a mask 9 having overhangs 91. A metal film of Ta 11 is adhered over the surface. During this process, the substrate 8 is cooled with liquid of N2 so as to protect the resist 9 from beat. After that, unrequired portions of the Ta film 11 are removed together with the resist 9 so that a predetermined pattern of the underlaid M layer can be obtained. According to this method, the works can be performed more safely because there is no need of using fluoric acid or a high-temperature furnace. Further, the number of processes can be decreased substantially.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for forming an MIM nonlinear element used in a liquid crystal display device, and more specifically to a method for patterning an M layer as described below.

[Background of the invention]

They are now being used not only for desks but also for various information devices, and there is a desire for an increase in their display capacity.

Therefore, matrix driving is being considered in which a so-called MIM nonlinear element (hereinafter referred to as an MIM element) having a three-layer structure of metal-insulator-metal is combined with a pixel electrode to improve display quality.

[Problems with conventional technology and purpose of the present invention] Conventional MI
As shown in FIG. 2 as a cross-sectional view, the M element is constructed by providing a tantalum oxide film 2 as a protective film on a glass substrate 1 (FIG. 2-(a)), and then forming the lower M layer of the M I M element. A tantalum metal film 6 is formed, necessary portions are covered with a photoresist 4 (FIG. 2-(b)), and patterned by etching. Next, the surface of the metal tantalum film 3 is anodized to form a tantalum oxide film 5 (FIG. 2-(C)) to form a single layer, and a metal chromium film 6 is further formed as the upper M layer of the M I M element. The manufacturing order was as follows: first, the pixel electrode 7 was formed using a transparent conductive film (FIG. 2-(d)).

Hydronic acid etchant (
For example, it is essential for protecting the substrate glass 1 from a mixed solution of hydrofluoric acid dinitric acid and water (1:10:10), and has a completely transparent and smooth surface that is resistant to etching. Therefore, a tantalum oxide film obtained by thermally oxidizing a metal tantalum film is generally used.

As mentioned above, in the production of conventional MIM elements, MIM
Extra steps are required, such as forming a metal tantalum film and thermally oxidizing it, which are not necessary for the element structure, and furthermore, thermal oxidation of the metal mental film requires a high temperature of 500°C or more. There is a problem in that an expensive heat-resistant glass must be used as the substrate glass 1.

In addition, when etching the metal tantalum film 6 of the lower M layer, the etchant used contains hydrofluoric acid, so it was necessary to pay close attention to the impact on the human body and pollution during manufacturing. .

The present invention is aimed at safely and easily patterning the lower M layer of an M I M device, thereby shortening the process and enabling free selection of substrates, thereby making it possible to pattern the lower M layer of an M I M device at low cost.
This provides an M element.

[Structure of the invention]

The present invention uses a lift-off method using a photoresist formed in an overhang shape for patterning the lower M layer.

In the commonly used lift-off method, the film thickness of the lower M layer (
(approximately 0.1 μm or more), a film is formed not only on the top of the photoresist but also on the side surfaces, making it difficult to remove the photoresist with a peeler.

In the present invention, the photoresist (positive type) for patterning the lower M layer is exposed using a mask with an inverted shape to the pattern of the lower M layer, and then immersed in a non-aqueous poor solvent such as chlorobenzene to be diffused. The overhang shape is obtained by developing the film and then developing it. For this reason, if a lower M layer, typically made of tantalum, is formed on the photoresist using, for example, a vacuum evaporation method, no film will be formed on the portions that are in the shadow of the overhang, that is, on the side surfaces of the photoresist. During lift-off, the photoresist can come into direct contact with the peeling solution, so that quick lift-off is possible.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

First, a positive type photoresist 9 is placed on a glass substrate 8.
(Shipley AZ 1350 J) was applied to a thickness of about 1.5 μm (Figure 3-(a)). In this case, the glass substrate 8 may be inexpensive soda lime glass. This was prebaked at 80°C for 30 minutes to volatilize the solvent in the photoresist 9, and then exposed to light through an exposure mask 10 having an inverted shape to the pattern of the lower M layer (Fig. 3- (b)). In normal photolithography, development is performed immediately after this, but in this example, after exposure,
After immersion in chlorobenzene for 5 minutes, development was performed.

Through this process, the side shape of the photoresist 9 is changed to
As shown in Figure-(C)), it has an overhang 91. In this example, the depth of overhang 91 was approximately 0.5 μ.

Next, this was post-baked at 120°C for 30 minutes, and then a metal tantalum film 11, which would become the lower M layer, was formed to a thickness of about 0.3μ by vacuum evaporation (Fig. 3-(d)). ). At this time, in order to protect the photoresist 9 from radiant heat, the glass substrate 8 was sufficiently cooled with liquid nitrogen. Thereafter, using a peeling solution, the metal tantalum film 11 is removed together with the photoresist 9.
By removing unnecessary parts of the metal tantalum film 11
A predetermined pattern of the lower M layer was obtained (Fig. 3-(
e)).

At this time, due to the overhang shape of the photoresist 90, it is not hindered by the formed metal tantalum film 11.
Since the side surface of the photoresist could come into contact with the peeling solution, the photoresist 9 and the metal tantalum film 11 formed thereon could be immediately removed.

Next, the patterned tantalum metal 11 was anodized in an oxalic acid aqueous solution, and a tantalum oxide film 12 was formed on the surface to a thickness of about 0.05 μm to form a single layer.
Furthermore, a metal chromium film 16 is formed as the upper M layer by vacuum evaporation, and finally the pixel electrode 14 is made of ITO (indium metal).
If formed with a tin oxide film, M
The IM nonlinear element was completed.

Note that the metal chromium film 16 and the pixel electrode 14 were patterned by etching using commonly used photolithography.

Instead of the chlorobenzene used in the examples above, toluene, xylene, trichloroethylene, etc. may be used (basically, if it is a non-aqueous poor solvent, the photoresist can be formed in an overhang shape. .

In addition to tantalum, niobium,
Although pulp metals such as aluminum can be used,
When depositing high melting point metals such as tantalum and niobium,
Since the substrate temperature rises to 100° C. or more due to radiant heat, deterioration and deformation of the photoresist occur. Therefore, in the above embodiment, the photoresist was protected by cooling the substrate, but in the same manner as in the above embodiment, MIM
We were able to manufacture the device. In addition, plasma discharge at low pressure,
If the throwing power is reduced, forming the lower M layer by sputtering is also effective in preventing deterioration and deformation of the photoresist, and MIM elements can be manufactured in the same manner.

The upper M layer is not limited to chromium as long as it is basically conductive, and MIM elements could be similarly manufactured using nichrome, gold, ITO, etc.

〔Effect of the invention〕

As described above, according to the present invention, the lower M layer typified by the metal tantalum film, which was conventionally patterned by etching with a hydrofluoric acid etchant, can be patterned by the lift-off method.

This eliminates the need for a protective layer on the glass substrate, which was previously formed through a process called thermal oxidation at high temperatures of 500°C or higher, significantly shortening the process, and at the same time making it possible to use inexpensive soda glass for the substrate. It became possible to use it. Therefore, this led to a significant reduction in manufacturing costs. Furthermore, safety during manufacturing has also been significantly improved by eliminating the use of hydrofluoric acid and the use of a 500°C heating furnace.

Note that the MIM device manufactured according to the present invention has the following characteristics:
No inferiority was found compared to MIM elements manufactured using conventional processes.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part showing the structure of an MIM nonlinear element formed by the method of the present invention, and FIG. 2(a) is a sectional view of a main part of the element. 1.8...Glass substrate, 3.11...Metal tantalum film, 5.12...Tantalum oxide film, 6.16.
...Metallic chromium film, 7.4...Pixel electrode, Figure 2, Figure 3, Figure 3 (e) Procedural amendment (method) 1 Indication of the case 1985 Patent Application No. 4299 2, Title of the invention MIM nonlinear element formation method 3, relationship with the amendment person case Patent applicant address 2-1-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo Name (19
6) Citizen Watch Co., Ltd. May 26, 1988 5. Subject of amendment [column for brief explanation of drawings in specification] 6. Contents of amendment Brief explanation of drawings Figure 1 shows the method of the present invention. FIG. 2 is a cross-sectional view of a main part showing the structure of the MIM nonlinear element to be formed. FIGS.
Figure (al (bl fc) fdl tel) is a cross-sectional view of a main part of an MIM element to explain the present invention in detail. 1.8...Glass substrate, 3.11...Metal tantalum film, 5,12... ...Tantalum oxide film, 6,13...Metal chromium film, 7,4...Pixel electrode.

Claims (1)

[Claims] A thin metal film that will become the lower M layer is patterned into a predetermined shape on the surface of the substrate, the surface is anodized to form the I layer, and a thin metal film or a transparent conductor thin film is further laminated on top of that as the upper M layer. A method for forming an MIM nonlinear element, the method comprising patterning a lower M layer by a lift-off method using a photoresist patterned in a cross-sectional shape having an overhang.