JPH06104436A - Manufacture of film transistor - Google Patents

Abstract

PURPOSE:To provide an anodization method easy to treat waste liquid, for forming an gate insulating film excellent in insulation breakdown strength, concerning the manufacture of a film transistor. CONSTITUTION:This method includes a step of forming a metallic film, which contains aluminum as its main ingredients, on an insulating substrate 1, and then, etching it, using a mask, so as to form a metallic pattern, and a step of anodizing the metallic film pattern in aqueous solution, which contains organic acid ammonium salt or inorganic acid ammonium salt, forming a gate insulating film 2a on the surface, and forming a gate electrode 2 consisting of the metallic film pattern remaining inside. The metallic film consists of aluminum, or an aluminum, alloy which contains titanium by 4 or less at. %, or an aluminum alloy, which contains tantalum by 4 or less at. %. Moreover, electrolyte contains ammonium adipate or ammonium tartrate by 1wt.% or more and 10wt.% or less, or contains ammonium salicylate by 0.1wt.% or more and 1wt.% or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a thin film transistor (TF).
T) manufacturing method. In recent years, TFTs have come to be used as driving elements for liquid crystal display devices. Such a TFT usually has a structure in which a gate electrode, a gate insulating film, an operating semiconductor film, and a source / drain electrode are sequentially stacked on a glass substrate. Al (aluminum) is used as the gate electrode, and an alumina film obtained by anodizing the Al film is used as a part of the gate insulating film.

The gate insulating film is required to suppress the current leakage between the source / drain electrode and the gate electrode below an allowable value, and has a sufficient withstand voltage to prevent dielectric breakdown due to static electricity in the manufacturing process of the TFT. Must be secured.

[0003]

2. Description of the Related Art It is known that the electrical characteristics of an alumina film formed by an anodic oxidation method change significantly depending on the electrolysis conditions, and optimization of electrolysis conditions is an important consideration for improving performance and reliability. It is an item. Further, the selection of the metal forming the gate electrode and the gate bus line also has a critical influence on the electrolysis conditions.

Conventionally, Al containing a few% of Si or Pd added
There is known an example in which an ethylene glycol solution or a propylene glycol solution (pH 7 ± 0.5) containing 3% ammonium tartrate is used (JP-A-2-85826).
).

In this case, after oxidation, 2
It is known that heat treatment at 00 to 400 ° C suppresses leakage current. The problems here are that the solvent is expensive, the waste liquid must be collected and treated for it, Pd is a rare precious metal and expensive, and Si addition causes hillocks (protrusions) by heat treatment. It is easy to occur.

[0006]

In view of the above problems, it is an object of the present invention to solve the above problems by using an aqueous solution as an electrolytic solution, selecting electrolysis conditions and a metal to be anodized.

[0007]

FIG. 1 is a sectional view showing a TFT of an embodiment. The above-mentioned problems include a step of depositing a metal film containing aluminum as a main component on the insulating substrate 1 and then etching the metal film using a mask to form a metal film pattern, and a step of forming the metal film pattern with an organic acid ammonium salt or A method of manufacturing a thin film transistor, which comprises a step of anodizing an aqueous solution of an ammonium salt of an inorganic acid as an electrolytic solution to form a gate insulating film 2a on the surface and a gate electrode 2 having a metal film pattern remaining inside .

The metal film can be solved by a method of manufacturing a thin film transistor made of aluminum, aluminum containing 4 atomic% or less of titanium, or aluminum containing 4 atomic% or less of tantalum.

Further, the electrolytic solution can be solved by a method of manufacturing a thin film transistor containing 1% by weight or more and 10% by weight or less of ammonium adipate. Further, the electrolytic solution is solved by a method of manufacturing a thin film transistor including 1 wt% to 10 wt% of ammonium tartrate.

Further, the electrolytic solution is solved by a method of manufacturing a thin film transistor containing 0.1 wt% or more and 1 wt% or less of ammonium salicylate.

[0011]

In the present invention, anodic oxidation is performed using an aqueous solution of an organic acid ammonium salt or an inorganic acid ammonium salt as an electrolytic solution. An aqueous solution of an organic acid ammonium salt or an inorganic acid ammonium salt becomes a weak acid or a weak base, and an oxide film having a high withstand voltage can be formed.

If the metal film is made of aluminum, aluminum containing titanium of 4 atomic% or less, or aluminum containing tantalum of 4 atomic% or less, the withstand voltage of the anodic oxide film can be increased, and Hillard does not occur in the gate electrode due to the subsequent heat treatment.

Further, as the electrolytic solution, 1% by weight or more and 10
By using an aqueous solution containing ammonium adipate by weight or less, a gate insulating film having a withstand voltage that can be practically used can be obtained.

Further, as the electrolyte, 1% by weight or more and 10
If you use an aqueous solution containing less than 1% by weight of ammonium tartrate,
A gate insulating film having a withstand voltage that can be practically used can be obtained.

Further, as the electrolytic solution, 0.1% by weight or more 1
If an aqueous solution containing ammonium salicylate in an amount of less than or equal to wt% is used, a gate insulating film having a withstand voltage that can be practically used can be obtained.

[0016]

EXAMPLE FIG. 1 is a sectional view showing a TFT of an example.
The outline of the manufacturing process will be described. An Al film having a thickness of 2500 Å is formed on the glass substrate 1 by a sputtering method. Next, this Al film is etched using a mask to form a metal pattern corresponding to the gate electrode and the gate bus line connected thereto.

Next, anodic oxidation is performed using an aqueous solution containing an organic acid ammonium salt or an inorganic acid ammonium salt as an electrolytic solution. Alumina film with a thickness of about 2000Å on the surface by anodic oxidation
2a is formed, and the gate electrode 2 is formed leaving an Al film having a thickness of about 800Å inside. The alumina film 2a becomes a gate insulating film.

A SiN film to be the gate insulating film 3 having a thickness of, for example, 1000 Å and an amorphous Si film to be the operating semiconductor film 4 are formed on the entire surface.
A film and a SiN film to be the channel protection film 5 are sequentially formed, a resist is applied on the film, and the back surface exposure from the glass substrate 1 side is used to expose the gate electrode 2 as a mask to develop and develop the channel protection film 5 Leave the resist on top. The channel protective film 5 is etched using the resist as a mask to leave the channel protective film 5 only on the gate electrode 2.

After depositing an n ⁺ -type amorphous Si film which will be the contact layer 6 and a Ti film which will be the source electrode 7 and the drain electrode 8 on the entire surface, etching is performed using a mask for element isolation. A drain bus line 9 of Al film connected to the drain electrode 8 is formed, and a pixel electrode 10 of ITO film connected to the source electrode 7 is formed.

Next, the relationship between the conditions of anodic oxidation and the withstand voltage will be described in detail. An aqueous solution of ammonium adipate is used as the electrolytic solution, and the weight ratio of ammonium adipate is 0.25 to 10
%, The Al film was anodized at a pH value of 6.9 to 7.0 to form an alumina film with a thickness of 770Å on the surface.

FIGS. 2 (a) to 2 (d) show the withstand voltage distribution of a capacitor using an anodic oxide film of ammonium adipate, and show the results of measurement at 20 locations at different locations. The horizontal axis is the applied voltage,
The vertical axis represents the frequency of dielectric breakdown. The electrolysis conditions are also entered in the figure. As shown in these figures, when the amount of ammonium adipate is 1% by weight or more and 10% or less, the breakdown voltage of approximately 40 V or more is secured. When this value is converted into a withstand voltage, it becomes 5 × 10 ⁶ V / cm or more, which is a withstand voltage equivalent to that of a gate insulating film which is currently used without problems.

If the amount of ammonium adipate is less than 1% by weight or more than 10% by weight, the dielectric strength is deteriorated, which is not desirable. Next, an aqueous solution of ammonium tartrate was used as the electrolyte, and the weight ratio of ammonium tartrate was adjusted to 0.25.
The Al film was anodized at a pH value of 6.4 to 6.5, and an alumina film having a thickness of 820 to 840 Å was formed on the surface.

FIGS. 3 (a) to 3 (d) show the breakdown voltage distribution of a capacitor using an anodic oxide film of ammonium tartrate, and show the results of measurement at 20 locations. The horizontal axis shows the applied voltage and the vertical axis shows the frequency of dielectric breakdown. The electrolysis conditions are also entered in the figure. As shown in these figures, the amount of ammonium tartrate is 1
When the weight% is 10% or less, the dielectric breakdown voltage is 40V or more. Converting this to a dielectric strength voltage, 5 × 10 ⁶ V /
The value is more than cm, which is equivalent to the withstand voltage of the gate insulating film that is currently used without problems.

If the amount of ammonium tartrate is less than 1% by weight or more than 10% by weight, the dielectric strength is deteriorated, which is not desirable. Next, using an aqueous solution of ammon salicylate as the electrolytic solution, the weight ratio of ammon salicylate
The anodic oxidation of the Al film was carried out at a pH value of 5.9 to 6.0 while changing it to 0.25 to 10% to form an alumina film having a thickness of 720 to 770Å on the surface.

FIGS. 4 (a) to 4 (d) show the withstand voltage distribution of a capacitor using an anodic oxide film made of ammonium salicylate, and show the results of measurement at 20 different places. The horizontal axis is the applied voltage,
The vertical axis represents the frequency of dielectric breakdown. The electrolysis conditions are also entered in the figure. As shown in these figures, when the amount of ammonium salicylate is 1% by weight or less, the breakdown voltage is about 40 V or more. Converting this to a dielectric strength voltage, 5 × 10 ⁶ V /
The value is more than cm, which is equivalent to the withstand voltage of the gate insulating film that is currently used without problems.

If the amount of ammonium salicylate exceeds 1% by weight, the dielectric strength will deteriorate, which is not desirable. Also,
When the amount of ammon salicylate was less than 0.1% by weight, the resistance of the electrolyte solution increased and anodic oxidation by constant current was impossible.

Further, with respect to the case of using an aqueous solution of triammonium citrate, ammonium phthalate, and ammonium oxalate as the electrolytic solution, anodic oxidation was performed according to the above, and the dielectric strength was examined. As a result, in order to obtain a practically desirable dielectric breakdown voltage of 5 × 10 ⁶ V / cm or more, an ammonium citrate and ammonium phthalate solution of 0.1 wt% or more and 1 wt% or less is desirable, and ammonium oxalate of 0.1 wt% or less is desirable. % To 4% by weight was desired.

The chemical solution described above was an aqueous solution of an organic acid ammonium salt. Next, an aqueous solution containing an inorganic acid ammonium salt was examined. As a result of investigating an aqueous solution containing both ammonium tetraborate and boric acid, 0.1% by weight or more and 1% by weight or less of ammonium tetraborate and 0.1% by weight or more and 2% by weight or less
The following aqueous solutions containing boric acid were desired. As a result of investigating an aqueous solution containing diammonium hydrogen phosphate, an aqueous solution of 0.1% by weight or more and 1% by weight or less was desired.

The above is the result of examining the anodic oxidation of the Al film. Instead of the Al film, an Al-Ti film containing 4 atomic% or less of Ti, or an Al-T containing 4 atomic% or less of Ta.
Regarding the a film, the result of anodization using an aqueous solution containing an organic acid ammonium salt or an inorganic acid ammonium salt as an electrolytic solution and examining the dielectric strength was that the dielectric strength was higher than that of the Al film.

When anodizing using an aqueous solution containing an organic acid ammonium salt or an inorganic acid ammonium salt as an electrolyte,
In particular, it is not necessary to recover the chemical solution, and the usual acid-alkali treatment may be applied and discarded.

If it is desired to further reduce the leak current, heat treatment may be performed. At this time, Al film, Al-T
No hillock (protrusion) is generated from the i film or the Al-Ta film.

[0032]

As described above, according to the present invention,
By anodic oxidation, a gate insulating film having a withstand voltage of 5 × 10 ⁶ V / cm or more can be obtained. Since the electrolytic solution is an aqueous solution containing an organic acid ammonium salt or an inorganic acid ammonium salt, no special waste liquid treatment facility is required. No hillocks are generated from the gate electrode even if heat-treated after anodization.

The present invention is particularly suitable for driving a liquid crystal display device.
This contributes to the high reliability of the FT matrix.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a TFT of an example.

FIG. 2 is a withstand voltage distribution of a capacitor using an anodic oxide film of ammonium adipate.

FIG. 3 is a withstand voltage distribution of a capacitor using an anodized film of ammonium tartrate.

FIG. 4 is a withstand voltage distribution of a capacitor using an anodic oxide film of ammonium salicylate.

[Explanation of symbols]

 1 is an insulating substrate, 2 is a glass substrate, 2 is a gate electrode, 2a is a gate insulating film, and 3 is an anodized film, 3 is a gate insulating film, 4 is an operating semiconductor film, 5 is a channel protective film, 6 is a contact layer, and 7 is a source electrode. The drain electrode 9 is the drain bus line 10 is the pixel electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G02F 1/136 500 9018-2K H01L 21/28 J 9055-4M 29/40 A 9055-4M

Claims (5)

[Claims] 1. A step of depositing a metal film containing aluminum as a main component on an insulating substrate (1) and thereafter etching the metal film using a mask to form a metal film pattern, and the step of forming the metal film pattern with an organic acid. Anodizing an aqueous solution of ammonium salt or inorganic acid ammonium salt as an electrolytic solution to form a gate insulating film (2a) on the surface and forming a gate electrode (2) consisting of a metal film pattern remaining inside A method of manufacturing a thin film transistor, comprising: 2. The method of manufacturing a thin film transistor according to claim 1, wherein the metal film is made of aluminum, aluminum containing 4 atomic% or less of titanium, or aluminum containing 4 atomic% or less of tantalum. 3. The method of manufacturing a thin film transistor according to claim 2, wherein the electrolytic solution contains 1 wt% or more and 10 wt% or less of ammonium adipate. 4. The method of manufacturing a thin film transistor according to claim 2, wherein the electrolytic solution contains 1 wt% or more and 10 wt% or less of ammonium tartrate. 5. The method of manufacturing a thin film transistor according to claim 2, wherein the electrolytic solution contains 0.1 wt% or more and 1 wt% or less of ammonium salicylate.