JPH04356926A - Anode oxidation of thin metal film pattern - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing thin film transistors that can be used in liquid crystal display devices and the like, and more particularly to a method of anodizing a metal thin film pattern to prevent disconnection during the anodizing process of a gate insulating film.

0002

2. Description of the Related Art It is already known that unevenness and pinholes on the gate insulating film of thin film transistors and the like significantly impair withstand voltage and leakage characteristics. Anodic oxide films are increasingly being used as gate insulating films because they produce films with better characteristics and fewer pinholes than sputtered films. It has been well known that two types of Al2O3 can be obtained by anodizing Al.

One is a porous Al2O3 film, and the other is a nonporous Al2O3 film. The former can be obtained with a strong acid solution such as sulfuric acid, phosphoric acid, or oxalic acid, and the latter can be obtained with a weak acid solution such as boric acid or tartaric acid. However, even when a weak acidic solution is used, unevenness can be seen on the film surface, so when forming thin films such as gate insulating films, neutral salt aqueous solutions or solutions consisting of non-aqueous solvents have been used (especially Kaihei 2-858
Publication No. 26). At this time, in order to selectively form a film, it is necessary to cover the electrode pattern portion with an organic thin film such as photoresist. If the adhesion of the photoresist film is not good, the electrode and liquid will come into direct contact during anodic oxidation, making it impossible to form an anodic oxide film with a predetermined thickness. As a method for anodizing thin film patterns, a method has been proposed in which another insulating protective film is formed between the resist Al films in order to prevent disconnection of the Al (Japanese Patent Laid-Open No. 2-234431).
Publication No.).

0004

[Problems to be Solved by the Invention] However, when anodic oxidation is performed using an aqueous solution consisting of a neutral salt, although the surface unevenness is improved compared to a weakly acidic aqueous solution, a high There is a drawback that when a voltage is applied, irregularities are likely to be formed on the film surface. On the other hand, when an electrolyte solution consisting of a non-aqueous solvent is used, anodization under the same conditions will not cause unevenness on the film surface, but the adhesion of the photoresist film will weaken and the resist film will peel off. There are drawbacks. At that time, the electric field was concentrated on the exposed Al, which often caused wire breakage.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for anodizing a metal thin film pattern, which eliminates unevenness on the film surface, solves the problem of disconnection in the Al thin film pattern, and does not require a complicated process.

[0006]

[Means for Solving the Problems] In order to achieve this object, the method for anodizing a thin metal film of the present invention is characterized in that two types of electrolyte solutions are used. In order to prevent unevenness on the film surface, an electrolyte solution consisting of a non-aqueous solvent is used up to a predetermined voltage, and the voltage application is stopped when the predetermined voltage is reached to prevent peeling of the resist film. Subsequently, a predetermined voltage is applied using an aqueous electrolyte solution to perform anodic oxidation.

[0007]

[Function] By the above-mentioned method, the present invention can prevent unevenness on the membrane surface that occurs in an aqueous solution system since a solution consisting of a non-aqueous solvent is used up to a predetermined voltage. This is because when an aqueous electrolyte solution is used, dissolution of Al is likely to occur simultaneously with oxidation at membrane defect areas during membrane formation. However, when an electrolyte solution made of a non-aqueous solvent is used, resist resistance is not good, so it is not preferable to apply a high voltage for a long time after reaching a predetermined voltage because it may cause disconnection of the Al. Then, using an aqueous electrolyte solution, anodic oxidation is extended at a predetermined voltage until the leakage current value becomes small. When a predetermined voltage is reached, no current flows, so that Al is not dissolved and only oxidation occurs.

[0008] Therefore, unevenness on the film surface does not occur. Furthermore, the resist is not peeled off and the Al wire is disconnected.

[0009]

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

Example 1 Al2 is deposited on a glass substrate 1 by sputtering (FIG. 1a). A resist pattern 3 is formed using the Al thin metal film 2 as a photoresist (FIG. 1b).
).

[0011] Using a mixture of 0.3 mol/1 ammonium borate and ethylene glycol at a ratio of 1:9, 50
C. and a current density of 1 mA/cm2 (FIG. 1c), and after forming the Al2O3 film 4 up to a predetermined voltage (140V), the voltage application is stopped. Subsequently, using a 0.3 mol/1 ammonium borate aqueous solution, 1
The formation is extended until the leakage current value is 10% or less at a voltage of 40 V (Figure 1d). During this extended time, film defects are repaired and a dense Al2O3 film 5 of 200 nm is formed. Finally, the photoresist 3 is removed (FIG. 1e). Note that the pH of the electrolytic solution was adjusted to 7±0.5.

[0012] When Al is anodic oxidized using the above process, disconnection of Al due to resist peeling does not occur. Glycol may be used instead of ethylene glycol, and neutral salts of solutes such as ammonium phosphate and ammonium tartrate can also provide the same effect.

Embodiment 2 A second embodiment of the present invention will be described with reference to FIG.

An Al film 2 of 350 nm is deposited on the glass substrate 1 by sputtering (FIG. 2a). Form a resist pattern 3 using photoresist 2 (
Figure 2b). Using a 1:9 mixture of 0.1 mol/1 ammonium citrate and propylene glycol, 5
Anodic oxidation was performed at 0°C and a current density of 5 mA/cm2 (Fig. 2c), and after the voltage of 100 V was reached and the voltage was reached,
Stop applying voltage for 3 minutes. After that, a predetermined voltage (14
After forming the Al2O3 film 4 to 0V), the voltage application is stopped (FIG. 2d). Subsequently, a voltage of 140 V is applied using a 0.1 mol/1 ammonium citrate aqueous solution to extend the chemical formation until the leakage current value becomes 10% or less (FIG. 2e). During this extended time, film defects are repaired and a dense Al2O3 film 5 of 200 nm is formed. Finally, the photoresist 3 is removed (FIG. 2f).

When anodic oxidation of Al is performed using the above process, the glycol-based anodization process is divided into two stages, so that peeling of the resist is less likely to occur than in the case of one stage. Since chemical conversion extension was carried out using an aqueous solution, resist peeling does not occur. Therefore, since the Al under the resist is not exposed, disconnection of the Al does not occur. Here, the same type of neutral salt was used as the solute in the nonaqueous solvent solution and the aqueous solution, but the same effect can be obtained when other neutral salts are used.

[0016]

[Effects of the Invention] As described above, the present invention is a method for anodizing a metal thin film pattern. After anodizing to a predetermined voltage with a solution made of a non-aqueous solvent, the leakage current value is reduced by using a solution made of an aqueous solution. By continuing the anodic oxidation up to the point where the metal thin film pattern is removed, the metal thin film pattern can be anodized without breaking the metal thin film pattern or creating irregularities on the film surface. Moreover, it is a method that does not complicate the process.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing a method of anodizing a metal thin film pattern in an embodiment of the present invention.

FIG. 2 is a process diagram of anodic oxidation of a metal thin film pattern by applying voltage in two stages and using two types of electrolyte solutions in the second embodiment of the present invention.

[Explanation of symbols]

1 Glass substrate 2 Al metal thin film 3 Photoresist 4 Al anodized using a solution consisting of a non-aqueous solvent
2O3 film 5 Al2 chemically extended using a solution consisting of water solvent
O3 membrane

Claims (3)

[Claims] Claim 1: Anodizing using a first neutral electrolyte solution made of a non-aqueous solvent until a predetermined voltage is reached, and then using a second neutral electrolyte solution made of an aqueous solvent at the above voltage. 1. A method for anodizing a metal thin film pattern, the method comprising the step of anodizing a metal thin film pattern. 2. The method of anodizing a metal thin film pattern according to claim 1, wherein the solute of the neutral electrolyte solution consists of an oxyacid. 3. The method of anodizing a metal thin film pattern according to claim 2, wherein the solute of the neutral electrolyte solution comprises an ammonium salt of an oxyacid.