JPH08120489A - Anodic oxidation and production of thin film transistor using the same - Google Patents

Abstract

PURPOSE: To provide an anodic oxidation method and a producing method of thin film transistor, capable of improving the yield of the thin film transistor by suppressing the fusion of a gate and the failure of pressure resistance. CONSTITUTION: A gate electrode 2 is formed by depositing a metal for the gate electrode, which consists essentially of Al, on a glass substrate 1. Next, a gate insulating film 3 is formed by dipping the gate electrode 2 in an electrolytic solution, prepared so as to regulate the ratio of an ammonium tartrate aq. solution to ethylene glycol to (2:8) to (4:6) and control its pH and liquid temp. respectively to 5-8 and <=40 deg.C, to execute anodic oxidation and further an SiNX film 4, an amorphous Si layer 5, an N<+> amorphous layer 6, a picture element electrode 7, a source and drain electrodes 8, 9 are formed to make the thin film transistor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anodic oxidation method and a method of manufacturing a thin film transistor using the same. More specifically, it is lightweight, thin and has excellent visibility, and an anodizing method for manufacturing a thin film transistor used for a liquid crystal display device which is optimal as a terminal display for audiovisual, office automation equipment and the like, and manufacturing of a thin film transistor using the same It is about the method.

[0002]

2. Description of the Related Art Recently, amorphous silicon thin film transistors (amorphous silicon thin film transistors, hereinafter referred to as aS
An active matrix substrate using (iTFT) as a switching element and a liquid crystal display (LCD.Liquid Crystal Display) using the same can be manufactured in a low temperature process in which a-SiTFT has a high switching ratio and a glass substrate can be used. It is considered to be the most advantageous method for large area and high definition, and each company actively conducts research and development and commercializes it.

Conventionally, this thin film transistor has a structure shown in cross section in FIG. That is, a gate electrode 22 made of a metal film containing aluminum as a main component is formed on a substrate 21 having a surface made of an insulating film such as glass or quartz, a gate insulating film 223 formed by anodic oxidation on the gate electrode, and a second electrode. Silicon nitride (SiN _x ) 24 as a gate insulating film, a channel layer (a-Si) 25, n ⁺ a-Si (semiconductor layer) 26 for making an ohmic contact, a pixel electrode 27, and a source electrode.
And the drain electrodes 28 and 29 and the wiring lead-out portion 30.

Here, a mixture of an ammonium tartrate aqueous solution and ethylene glycol at a ratio of 1: 9 was used as the anodizing electrolyte (Japanese Patent Laid-Open No. 23232.
No. 27).

[0005]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Obtained by anodizing the surface of the gate electrode
Al ₂O₃Alumina) is used as the gate insulating film
However, the alumina used as the insulating film here is a neutral solution.
The film thickness and breakdown voltage are determined by the applied voltage during the anodization used.
It was being done. That is, if a voltage of 100 V is applied, a breakdown voltage of 100
V, 1400 Å (theoretical value 14 Å
Rohm / V) anodic oxide film can be obtained, resulting in insulation
It is better to apply higher voltage to increase
I understand. Also, after anodizing, SiN_X, AS
i, SiN_XAnd to obtain the desired pattern after film formation
Hydrofluoric acid (HF) and buffered hydrofluoric acid
Etching is performed using (BHF), but SiN_XPi
In the presence of humol, the above acid corrodes alumina.
May occur (BHF etching rate of alumina
1000 angstrom / min), gate, so
-Because of the short-to-ground short (GS short). Further
In addition, pinholes are generated on the alumina during anodization.
And similarly SiN_XSource of GS short due to defects in
However, the pinhole decreases as the oxide film thickness increases.
Less (Table 1). From these facts, the alumina film thickness
BHF damage by increasing (increasing applied voltage)
It has the advantages of improved margin and reduced pinholes.

[0006]

[Table 1]

However, when the applied voltage is increased,
In some cases, metal fusing occurs at the boundary between the resist pattern for forming the lead-out wiring electrode portion and the metal during anodization. (Figure 3). If this fusing occurs in the product panel, the drive voltage is not supplied to the wiring, resulting in a line defect and a serious defect. With the conventional ammonium tartrate aqueous solution: ethylene glycol (EG) = 1: 9 electrolyte composition, when the oxidation voltage is increased, this fusing becomes remarkable, so conventional alumina is formed only up to 1500 angstroms (that is, about 105 V). I couldn't. As a countermeasure against this, conventionally, the post-baking temperature, which is performed after the resist patterning, is raised to prevent the fusing (see Japanese Patent Laid-Open No. 3-232274). However, raising the post-baking temperature has a problem that peeling is difficult in resist stripping after anodization. To solve this problem, we found a method that can easily solve this problem by processing at the time of resist patterning, and filed a patent application (Japanese Patent Application No. 5-26218). That is, positive resist coating, pre-baking, exposure, development, post-baking
The result that the fusing can be suppressed by not performing post-baking in the photo process of black or by irradiating UV after the post-baking was obtained. However, this method has another problem of reproducibility of effect and increase of cost such as new capital investment due to increase of process.

The present invention solves the problems found in the anodic oxide film, such as the fusing of the aluminum (Al) gate electrode and the poor withstand voltage, which have been found in the above-mentioned prior art, and is stable without introducing new equipment. An object of the present invention is to provide an anodizing method capable of obtaining an anodized film with a high yield and a method of manufacturing a thin film transistor using the anodizing method.

[0009]

In order to solve the above problems, in the anodizing method of the present invention, the composition of the conventionally used electrolytic solution is such that the ratio of ethylene glycol to the ammonium tartrate aqueous solution is 2: Mix at 8-4: 6 and adjust pH to 5
-8, the gist is to carry out anodization at a liquid temperature of 40 ° C. or lower. That is, in the method of forming an electrode with an anodizable metal thin film containing aluminum or aluminum as a main component on an insulating substrate and then anodizing in an electrolytic solution, the composition of the electrolytic solution is an aqueous solution of ammonium tartrate. It is characterized in that ethylene glycol is mixed at a ratio of 2: 8 to 4: 6, the pH is adjusted to 5 to 8, and the anodic oxidation is performed at an electrolyte temperature of 40 ° C. or lower.

Further, in the above structure, it is preferable that the anodizable metal containing aluminum as a main component is a metal containing a refractory metal in aluminum. Further, in the above structure, it is preferable that when anodizing the electrode, the current is controlled to perform the anodizing, and then the voltage is controlled to perform the anodizing.

Further, according to the method of manufacturing a thin film transistor of the present invention, a pixel electrode is provided on an insulating substrate, and a gate electrode is formed of at least aluminum or an anodizable metal thin film containing aluminum as a main component, and a source electrode and a drain electrode. A method for manufacturing a thin film transistor having a wiring lead-out portion, wherein the gate electrode is mixed with an aqueous solution of ammonium tartrate at a ratio of 2: 8 to 4: 6 in the composition of the electrolyte solution to adjust the pH. It is characterized in that the electrolytic solution temperature is set to 5 to 8 and the anodic oxidation is performed at an electrolyte temperature of 40 ° C. or lower.

In the above structure, it is preferable that the anodizable metal thin film containing aluminum as a main component is formed of a metal containing a refractory metal in aluminum.

In the above structure, it is preferable that the anodizable metal thin film containing aluminum or aluminum as a main component is anodized by controlling the current and then the voltage is controlled.

[0014]

According to the present invention, after an electrode is formed on an insulating substrate with aluminum or an anodizable metal thin film containing aluminum as a main component, the ratio of ethylene glycol to the ammonium tartrate aqueous solution is 2: 8-. Mix at 4: 6,
Anodization is performed at a pH of 5 to 8 and a liquid temperature of 40 ° C. or lower. As a result, it is possible to prevent the occurrence of defects in the anodic oxide film such as the fusing of the aluminum gate electrode and the breakdown voltage, and to obtain a stable anodic oxide film yield without increasing the cost such as new equipment investment accompanying the increase in the number of processes. Well formed.

The composition of the electrolytic solution is such that ethylene glycol is 2: 8 to 4: 6 relative to the ammonium tartrate aqueous solution, because the gate electrode is melted if the ratio of the ammonium tartrate aqueous solution is less than 2. This is because peeling more than 4 is likely to occur and the breakdown voltage of the anodic oxide film is significantly reduced. The reason why the pH is 5 to 8 is that if it is less than 5, the anodic oxide film is dissolved, and if it is more than 8, not only the anodic oxide film but also the resist is dissolved. Also, set the electrolyte temperature to 4
The reason why the temperature is set to 0 ° C. or lower is that if the temperature exceeds 40 ° C., the anodic oxide film is melted and a true breakdown voltage cannot be obtained.

Since the anodizable metal containing aluminum as the main component is a metal containing a refractory metal in aluminum, hillocks with low resistance can be suppressed and a highly reliable anodized film can be obtained. it can.

As the anodic oxidation method, the anodic oxidation is carried out by controlling the current, and then the anodic oxidation is carried out by controlling the voltage, so that the gate electrode is not fused and the pressure resistance is fine without introducing new equipment. Excellent anodic oxide film can be formed.

Further, in the method of manufacturing a thin film transistor of the present invention, a pixel electrode is provided on an insulating substrate, and a gate electrode is formed of at least aluminum or an anodizable metal thin film containing aluminum as a main component, and a source electrode and a drain electrode. A method for manufacturing a thin film transistor having a wiring lead-out portion, wherein the gate electrode is mixed with an aqueous solution of ammonium tartrate at a ratio of 2: 8 to 4: 6 in the composition of the electrolyte solution to adjust the pH. 5 to 8, and anodize at an electrolyte temperature of 40 ° C. or lower. As a result, a highly reliable thin film transistor having an anodic oxide film with excellent withstand pressure without fusing the gate electrode can be obtained without incurring a cost increase such as a new capital investment accompanying an increase in the number of processes. it can.

Forming the aluminum or the anodizable metal thin film containing aluminum as a main component from a metal containing a refractory metal in aluminum suppresses hillocks due to heat, does not melt the gate electrode, and improves yield. It is preferable for obtaining a thin film transistor having a high anodic oxide film.

The anodized metal thin film containing aluminum or aluminum as a main component is anodized under current control and then under voltage control. It is possible to manufacture a thin film transistor having a stable insulating film by stable anodic oxidation, which is a thin film without fusing the gate electrode.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. 1A to 1D are cross-sectional views showing a manufacturing process of a thin film transistor according to an embodiment of the present invention.

The manufacturing process will be described below. First, an aluminum thin film is deposited on a transparent insulating substrate 1 made of a glass substrate or the like by sputtering, and then a resist for obtaining a gate pattern is applied and exposed,
A resist pattern 11 was formed, and a gate electrode 2 was formed by photolithography and etching (FIG. 1 (a)). A resist pattern 11a for obtaining wiring electrodes is formed and anodization is performed (FIG. 1 (b)).

Next, the pH is adjusted to 5 to 8 and a direct current stabilizing power source is used as the anodic oxidation method, and a current is first supplied from the start of the anodic oxidation to a predetermined voltage, for example, 140 V at a constant current density, for example, 5 mA / cm ^2. At the same time when the voltage reaches a predetermined voltage, it is switched to a constant DC voltage, for example, 140 V, anodization is performed until the current reaches a predetermined value, for example, 0.05 mA / cm ² , and the relationship between the anodic oxidation current density and the fusing is investigated. The results are shown in Table 3.

Here, in order to solve the problems of the prior art, the composition, pH (range of 5 to 8) of the anodizing electrolyte, the relationship between the anodizing current density and the fusing were examined under different conditions. As a result, the composition and the current density depended on the fusing, and a region where the fusing did not occur was found (Table 2).

[0025]

[Table 2]

Regarding the pH of the electrolytic solution, the above range is set because there is a problem that the positive resist is dissolved at a pH of 8 or more and the oxide film is dissolved at a pH of 5 or less. On the other hand, as a method of measuring the breakdown voltage, which is one of the characteristics of the oxide film, a counter electrode is formed so as to intersect the anodized gate electrode, and a structure of gate electrode-anodized film-counter electrode is formed. The voltage is applied in steps of 0 V to 1 V, and the voltage at which a current of 1 × 10 ⁻⁴ A flows between both electrodes is defined as the withstand voltage.
This current is approximately 1000 of the current value at the end of anodization.
When observing the sample after measurement, the insulating film is broken. Since the voltage that becomes the breakdown voltage is theoretically equal to the anodic oxidation voltage, the influence of the process conditions can be easily evaluated by measuring the breakdown voltage. When the anodized sample was evaluated using this withstand voltage evaluation method, the withstand voltage was found to depend on the electrolyte composition and temperature (Table 3).

[0027]

[Table 3]

From these results, the electrolytic solution composition of the present invention,
The liquid temperature is, for example, 1% ammonium tartrate aqueous solution is mixed with ethylene glycol 7 at a ratio of 3, and the liquid temperature is 30 ° C.
The gate insulating film 3 was formed to a thickness of 2000 angstroms at a current density of 5 mA / cm ² and a voltage of 140 V (see FIG. 1).
(C)).

Next, P-CVD (plasma chemical vapor deposition)
To further form Si for forming the second gate insulating film.
N _X film 4, an amorphous Si film 5, a gate - DOO-source - stop when the source electrode is etched - become SiN _X film 4
Deposition, photo process, stopper after etching
The layers were processed. Thereafter, similarly, an n ⁺ amorphous Si layer was formed by P-CVD, and photolithography and etching were performed to form an n ⁺ a-Si layer 6 for making an ohmic contact. After that, ITO was deposited by a sputtering method, and the pixel electrode 7 was formed by photolithography and etching. Further, as a source and a drain metal, a Ti (titanium) and Al layer was deposited by a sputtering method, and the source, the drain electrodes 8 and 9 and the wiring lead-out portion 10 were formed by photolithography and etching to complete a thin film transistor ( FIG. 1 (d)).

Table 3 shows the results of evaluation of withstand voltage and GS short of the sample manufactured by the above method. The desired voltage (applied voltage) can be obtained with a stable withstand voltage.
No occurrence of rust was observed, and the effect of the present invention was confirmed.

Although aluminum is used as the metal for the gate in the above-mentioned embodiment, an alloy containing a small amount of refractory metal added to aluminum, that is, Al-Ta (1.0% to 2.%).
0%), Al-Zr (0.5% to 3%), Al-W
(1.0% to 2.0%), Al-Sc (0.5 to 2.5)
%), Al-Ti (0.5% to 1.5%), Al-Mo
It is also possible to use (0.5% -1.5%) etc. Similar to Al, these metals can be anodized and at the same time have the effect of suppressing hillocks due to heat. Further, by forming a laminated structure of an alloy in the upper layer and Al in the lower layer, it is effective in further lowering the resistance and suppressing hillocks.

[0032]

As described above, according to the present invention, ammonium tartrate: ethylene glycol
By anodic oxidation at a pH of 2: 8 to 4: 6, a pH of 5 to 8, and a liquid temperature of 40 ° C. or less, fusing of the gate and prevention of breakdown voltage can be prevented, which is caused by defects in the gate insulating film. Gate
It was possible to obtain an anodic oxide film with a reduced inter-source short. Further, according to the method of manufacturing a thin film transistor using this method, the yield is improved, the obtained thin film transistor has a high withstand voltage, gate fusing, and the gate-source shortage is small and the reliability is low. Improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a thin film transistor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a thin film transistor.

FIG. 3 is a diagram for explaining fusing of an aluminum gate electrode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Gate electrode 3 Gate insulating film 4 SiN _X 5 a-Si layer 6 Semiconductor layer 7 Pixel electrode 8 Source electrode 9 Drain electrode 10 Wiring lead-out part 11 Resist pattern

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/336

Claims (6)

[Claims] 1. A method of anodizing in an electrolytic solution after forming an electrode of an anodizable metal thin film containing aluminum or aluminum as a main component on an insulating substrate,
The composition of the electrolytic solution is a mixture of ammonium glycol tartrate and ethylene glycol at a ratio of 2: 8 to 4: 6,
An anodizing method, characterized in that the pH is set to 5 to 8 and the electrolytic solution temperature is 40 ° C. or lower. 2. The anodic oxidation method according to claim 1, wherein the anodizable metal containing aluminum as a main component is a metal containing a refractory metal in aluminum. 3. The anodizing method according to claim 1, wherein when anodizing the electrode, the current is controlled to perform the anodizing, and then the voltage is controlled to perform the anodizing. 4. A thin film transistor comprising a pixel electrode provided on an insulating substrate, a gate electrode formed of at least aluminum or an anodizable metal thin film containing aluminum as a main component, and a source electrode, a drain electrode, and a wiring lead portion. In the manufacturing method, the pH of the gate electrode is adjusted to 5 to 8 by mixing an aqueous solution of ammonium tartrate with ethylene glycol in a ratio of 2: 8 to 4: 6.
And a method of manufacturing a thin film transistor, characterized in that the anodic oxidation is performed at an electrolyte temperature of 40 ° C. or less. 5. The method of manufacturing a thin film transistor according to claim 4, wherein the aluminum or anodizable metal thin film containing aluminum as a main component is formed of a metal containing a refractory metal in aluminum. 6. The method of manufacturing a thin film transistor according to claim 4, wherein the aluminum or the anodizable metal thin film containing aluminum as a main component is anodized by controlling a current and then by controlling a voltage.