JP3180474B2 - Anodizing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anodizing method for anodizing a surface of a metal film formed on an insulating substrate.

[0002]

2. Description of the Related Art For example, in a TFT panel used for a TFT active matrix liquid crystal display device, a gate wiring and a data wiring are formed orthogonally to each other on an insulating substrate made of glass or the like. And the thin film transistor (TF
T) is formed, and pixel electrodes are arrayed and formed so as to correspond to these thin film transistors, respectively. Generally, as this TFT panel, a gate wiring is formed on a substrate, and a data wiring is formed of an insulating film covering the gate wiring. The one formed above is known.

The thin film transistor of this TFT panel is
A gate electrode formed integrally with the gate wiring, a gate insulating film formed on substantially the entire surface of the substrate covering the gate electrode and the gate wiring, and facing the gate electrode on the gate insulating film. It comprises a semiconductor film made of a-Si (amorphous silicon) and source and drain electrodes formed on the semiconductor film. The source electrode is connected to a pixel electrode, and the drain electrode is a data line. Is connected to

The gate wiring and data wiring of the above-mentioned TFT panel are generally formed of a low-resistance metal such as Al, and a gate wiring which is a lower metal film and a gate formed integrally with the gate wiring. The surface of the electrode is anodized except for the terminal portion of the gate wiring.

The anodizing of the surfaces of the gate wiring and the gate electrode, which are the lower metal film, is performed between the gate wiring and the data wiring, and between the gate electrode and the source,
This is to prevent the occurrence of interlayer short circuit by sufficiently increasing the dielectric strength between the drain electrode and the gate electrode. If the surface of the gate wiring and the gate electrode is anodized to form an oxide film on the surface, the gate wiring can be formed. In addition, since the gate electrode and the data wiring and the source and drain electrodes are doubly insulated by the oxide film and the insulating film thereon, a sufficient withstand voltage can be obtained.

The anodic oxidation of the lower metal film is performed by the above-mentioned TF.
The present invention is applied not only to the T-panel but also to a multilayer wiring panel in which wiring is formed in a plurality of layers on an insulating substrate. In this multilayer wiring panel, the surface of the lower wiring, which is a lower metal film, is anodized. Thus, the withstand voltage between the wiring and the upper wiring formed thereon via an insulating film is increased.

The anodic oxidation of the lower metal film such as the TFT panel and the multilayer wiring panel is performed by the anodic oxidation apparatus shown in FIG. The anodic oxidation apparatus includes an electrolytic bath 1 filled with an electrolytic solution (for example, an aqueous solution of ammonium borate) 2.
Inside, a net-like cathode 3 made of a corrosion-resistant metal such as platinum is immersed in an electrolytic solution 2 and vertically arranged. The cathode 3 is connected to the negative side of a DC power supply 4.

In the anodic oxidation of the metal film by the anodizing apparatus, the substrate 10 on which the metal film 11 is formed is vertically immersed in the electrolytic solution 2 of the electrolytic solution tank 1 and the oxidized metal film 11 on the substrate 10 is removed. It is performed by applying a formation voltage from a power supply 4 between the metal film 11 and the cathode 3 with the metal film 11 to be oxidized facing the cathode 3.

Thus, the metal film 11 to be oxidized in the electrolytic solution 2
When a formation voltage is applied between the anode and the cathode 3, the metal film to be oxidized 11, which is an anode, undergoes a chemical reaction in the electrolytic solution and is anodic oxidized from the surface thereof. Generate.

The metal film 11 shown in FIG. 3 is, for example, a gate wiring of the above-described TFT panel, and a gate electrode (not shown) of a thin film transistor is integrally formed on each gate wiring. Each of the gate lines is commonly connected to a power supply line 11a formed at an edge portion of the substrate 10 (a portion separated after the completion of the TFT panel or after the assembling of the liquid crystal display element). The supply of
The power supply path 11a is connected to the + side of the power supply 4 by a clip-shaped connecting member 5 for clamping the edge of the substrate.

By the way, it is said that the thickness of the oxide film formed on the surface of the metal film in the above anodic oxidation is determined by the formation voltage applied between the metal film to be oxidized and the cathode.
Therefore, conventionally, the anodic oxidation of the metal film is performed by controlling the formation voltage applied between the metal film to be oxidized and the cathode as follows.

FIG. 4 shows a control pattern of the formation voltage in the conventional anodic oxidation method. In the conventional case, the formation voltage applied between the metal film to be oxidized and the cathode is changed by the formation current (current) flowing through the metal film to be oxidized. The current flowing between the metal film to be oxidized and the cathode through the electrolytic solution is kept constant and is raised to a predetermined voltage value. After the voltage value reaches the predetermined value, the formation of the value is performed. Hold the voltage application for a certain time, and then
The application of the voltage is stopped to end the anodic oxidation.

That is, in this anodic oxidation method, the formation voltage applied between the metal film to be oxidized and the cathode is increased to a predetermined value in a constant current mode, and then the formation voltage of the predetermined value is set in a constant voltage mode. Conventionally, the application of the formation voltage in the constant voltage mode is continued until the value of the current flowing through the metal film to be oxidized becomes equal to or less than a set value (almost a value close to 0) Va, When the current value falls below the set value Va, it is determined that the thickness of the oxide film has reached a desired value, and the anodic oxidation has been completed at this point.

FIG. 5 is a cross-sectional view of a metal film 11 (for example, a gate wiring formed on a substrate 10) anodized by the above-described conventional anodizing method, and an oxide film 12 formed on the surface of the metal film 11 is formed. Has a withstand voltage of substantially the same value as the formation voltage between the non-oxidized portion of the metal film 11 and another conductive film (not shown) formed on the oxide film 12.

[0015]

However, the oxide film formed on the surface of the metal film by the above-mentioned conventional anodic oxidation method has a defect a as shown in FIG. There is a problem that when a voltage is applied between the portion and another conductive film formed on the oxide film, the oxide film is broken down in the vicinity of the defective portion a.

According to the present invention, anodic oxidation of a metal film capable of obtaining a highly reliable oxide film having a sufficient withstand voltage over the entire area by preventing defects of an oxide film formed on the surface of the metal film from occurring. It is intended to provide a method.

[0017]

According to the anodic oxidation method of the present invention, the voltage applied between the metal film to be oxidized and the cathode is increased while the current value is kept constant, and the voltage value is increased. The voltage application is stopped when a predetermined value corresponding to the film thickness is reached.

[0018]

According to the anodic oxidation method of the present invention, the formation voltage applied between the metal film to be oxidized and the cathode is increased to a predetermined value in a constant current mode, and thereafter, in a constant voltage mode in a conventional anodic oxidation method. The anodic oxidation is terminated by immediately stopping the voltage application without applying the voltage, and the oxide film formed on the surface of the metal film to be oxidized by this anodic oxidation method has a substantially uniform oxide without defects. It is a film, and its withstand voltage is sufficient throughout the oxide film.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing a control pattern of a formation voltage applied between a metal film to be oxidized and a cathode, and FIG. 2 is a cross-sectional view of the anodized metal film.

In the anodizing method of this embodiment, the surface of the metal film formed on the substrate is anodized using the anodizing apparatus shown in FIG.
As shown in the control pattern of the formation voltage shown in FIG. 1, the formation voltage applied between the metal film to be oxidized on the substrate and the cathode is changed by the formation current flowing through the metal film to be oxidized. While maintaining the value of the current flowing between the membrane and the cathode constant, the voltage is raised to a predetermined voltage value, and when the voltage value reaches the predetermined value, the voltage application is stopped.

That is, in this anodizing method, the formation voltage applied between the metal film to be oxidized and the cathode is increased to a predetermined value in a constant current mode, and thereafter, the voltage in the constant voltage mode in the conventional anodizing method is increased. Without applying the voltage, the voltage application is immediately stopped to end the anodic oxidation.

The metal film to be oxidized whose surface is anodized by the anodic oxidation method will be described. The metal film 11 shown in FIG. 2 is, for example, a gate wiring formed on a substrate 10 of a TFT panel. Numeral 11 denotes Ti (titanium) or T on aluminum (Al) which is a low resistance metal.
a It is formed of an Al-based alloy containing a high melting point metal such as tantalum (about several weight%).

The reason why the metal film to be oxidized is made of an Al-based alloy containing a high melting point metal is to form a good oxide film 12 on the surface of the metal film. A good oxide film cannot be obtained by anodizing this,
If the metal film to be oxidized is an Al-based alloy film containing a high melting point metal such as Ti or Ta, an oxide film (Al ₂ O ₃ film) 12 of good film quality can be formed on the surface.
The anodic oxidation of the Al-based alloy film can be performed using, for example, a low-concentration aqueous solution of ammonium borate as an electrolytic solution.

In the anodic oxidation method, the voltage application is stopped immediately after the formation voltage applied between the metal film to be oxidized and the cathode is increased to a predetermined value in the constant current mode. As shown in FIG. 2, the oxide film 12 formed on the surface is an oxide film having a substantially uniform thickness without any defective portions, and has a sufficient withstand voltage throughout the oxide film.

In contrast to this anodic oxidation method, in the conventional anodic oxidation method, a defect occurs in the oxide film formed on the surface of the metal film. It is considered that this defective portion occurs as follows.

That is, in the conventional anodic oxidation method, after the formation voltage is increased to a predetermined value in the constant current mode, the voltage of that value is increased for a certain period of time in the constant voltage mode (there is a current value flowing through the metal film to be oxidized. (Until the voltage drops below the set value), but if the voltage is continuously applied after the formation voltage is increased to the predetermined value, the voltage is generated on the surface of the metal film during the voltage application in the constant current mode. The dielectric breakdown occurs in the portion of the oxide film that has a low withstand voltage, a formation current flows from the metal film to the electrolyte through the portion where the breakdown has occurred, and the portion that has become the current path of the metal film is further reduced. To be anodized
A defect a as shown in FIG. 5 occurs in the oxide film formed on the surface of the metal film. The formation current decreases as shown in FIG. 4 as the portion of the metal film that has become the current path is further anodized.

The oxide film formed on the surface of the metal film by the conventional anodic oxidation method has a sufficient withstand voltage at every part when viewed partially. However, since this oxide film is not homogeneous, the oxide film is not uniform. When a voltage is applied between the non-oxidized portion and another conductive film formed on the oxide film, the oxide film is broken down near the defect portion a.

On the other hand, in the anodic oxidation method of the above embodiment, the voltage application is stopped immediately after the formation voltage is increased to a predetermined value corresponding to a desired thickness of the oxide film in the constant current mode. Since a suitable oxide film is formed, its dielectric strength is sufficiently high.

Therefore, the metal film 1 is formed by this anodic oxidation method.
The oxide film 12 formed on the surface of the metal film 11 does not break down when a voltage is applied between the non-oxidized portion of the metal film 11 and another conductive film formed on the oxide film 12.

[0030]

According to the anodic oxidation method of the present invention, the voltage applied between the metal film to be oxidized and the cathode is increased while the current value is kept constant, and when the voltage value reaches a predetermined value. Since the voltage application is stopped, it is possible to prevent a defect from occurring in the oxide film formed on the surface of the metal film, and to obtain a highly reliable oxide film having a sufficient withstand voltage over the entire region. .

[Brief description of the drawings]

FIG. 1 is a control pattern diagram of a formation voltage applied between a metal oxide film and a cathode according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a metal film anodized by the anodizing method of the present invention.

FIG. 3 is a perspective view of an anodizing apparatus.

FIG. 4 is a control pattern diagram of a formation voltage applied between a metal film to be oxidized and a cathode, showing a conventional anodic oxidation method.

FIG. 5 is a cross-sectional view of a metal film anodized by a conventional anodizing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Substrate 11 ... Metal film to be oxidized 12 ... Oxide film

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25D 11/00-11/24

Claims (2)

(57) [Claims] 1. A metal film formed on an insulating substrate is opposed to a cathode in an electrolytic solution, and a voltage is applied between the metal film and the cathode to anodize the surface of the metal film. In the method, the voltage applied between the metal film to be oxidized and the cathode is increased while keeping the current value constant, and when the voltage value reaches a predetermined value corresponding to the thickness of the anodized film. An anodic oxidation method comprising stopping voltage application. 2. A method according to claim 1, wherein the metal film to be oxidized comprises a metal containing a high melting point metal.
The anodic oxidation method according to claim 1, wherein the anodic oxidation method is an l-based alloy film.