JP3355610B2 - Method for increasing resistance of tin-doped indium oxide film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a tin-doped indium oxide film (hereinafter abbreviated as ITO), and more particularly to a method for forming a transparent electrode of a touch panel.
The present invention relates to a method for forming a TO film having high resistance and excellent uniformity.

[Prior art]

An ITO film is a transparent conductive film, and an ITO glass formed on a glass substrate is widely used for, for example, a liquid crystal display, an electroluminescence display, a surface heating element, an electrode of a touch panel, and the like. When used in such a wide field, ITO can be used depending on the purpose of use.
Various resistance values are required for the film. That is, a low-resistance ITO film for a flat panel display is required, while a high-resistance ITO film for a touch panel is required. The most common method of controlling the resistance value was to change the film thickness.

[0003]

When the resistance value is controlled by changing the film thickness as described above, the visible light transmittance naturally changes. Sheet resistance = specific resistance / film thickness In order to obtain high-resistance ITO, it is necessary to reduce the film thickness.
/ □ to obtain a film with a sheet resistance of 20 to 100 °
However, in this case, it is difficult to control the film thickness uniformly, and the uniformity of the in-plane resistance tends to deteriorate. Further, in order to set the visible light transmittance to a predetermined value, the film thickness is determined, and it is necessary to control the specific resistance in order to obtain a film having a predetermined resistance value with the film thickness.

[0004] The mechanism by which the ITO film develops conductivity is that a small amount of oxygen vacancies in the indium oxide crystal and the In-
Electrons generated by substituting Sn for the O crystal lattice serve as carriers, which move in an electric field. Therefore, the specific resistance (ρ) is determined by the carrier density (n) and the mobility (μ), and the following equation holds. ρ = 6.24 × 10 ¹⁸ / (n × μ) (1) where ρ: Ωcm, n: cm ⁻³ , μ: cm ² / V · se
c.

In the case of an ITO film, a film having a thickness of 300 ° or more usually has a sheet resistance of 100 Ω / □ or less, and has a carrier density of 10 ²⁰ to 10 ²¹ and a mobility of ²⁰ to 5 μm.
0, the specific resistance takes a value of 1 × 10 ^{−4 to} 3 × 10 ⁻⁴ . The resistance value of the ITO film for the touch panel described above is 200 to 1
In this case, a specific resistance value of 5 × 10 ⁻⁴ or more is required to obtain a film having excellent uniformity in consideration of the film thickness. It was difficult to control the specific resistance.

The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a method for forming an ITO film having a sheet resistance of 200 to 1000 Ω / □ and excellent uniformity. And

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on a method of increasing the specific resistance of an ITO film, and found that the tin doping amount in the film was 0.05 to 2.0% by weight based on indium.
Alternatively, it has been found that an ITO film having high resistance and excellent uniformity can be obtained by using the method and a heat treatment at a temperature of 200 ° C. or more in an oxygen-containing atmosphere in combination with the above method, and The present invention has been completed. Less than,
The present invention will be described in detail.

There are two methods for controlling the specific resistance. One is a method for controlling the carrier density of the formula (1), and the other is a method for controlling the mobility. Methods for controlling the carrier density include a method of changing the amount of oxygen vacancies and a method of changing the amount of tin doping. The amount of oxygen vacancy changes depending on the atmosphere and temperature, and utilizes a reversible reaction as shown in the following equation. In ₂ O ₃ → In ₂ O _3-X + X / 2 O ₂ → In ₂ O ₃ (2) In this reaction, the amount of oxygen defects (X) decreases in an atmosphere containing oxygen at a high temperature. However, the resistance is increased due to a decrease in the carrier density, and conversely, the amount of oxygen vacancies increases in a high-temperature and reducing atmosphere, and the resistance is decreased due to an increase in the carrier density.

The relationship between the tin doping amount and the carrier density is expressed by S
When n = 0, n ≒ 10 ^19. However, when Sn is slightly doped, it increases dramatically, and Sn = 1% by weight (In = 1
00), n ≒ 2 × 10 ²⁰ , and Sn = 3 to 1
When it is 0% by weight, the maximum value n ≒ 10 ²¹ is shown. As the doping amount further increases, n tends to decrease monotonically, and Sn = 2
When it is 0% by weight, n ≒ 5 × 10 ²⁰ .

The mobility (μ) is the carrier (electron or hole)
The amount is mainly dependent on ITO crystallinity. That is, the crystallinity is good,
If the amount of impurities is small, the mobility of the carrier is high. On the other hand, the crystallinity is low, and if the number of crystal defects, dislocations, and crystal grain boundaries is large, the carrier is trapped and the value is low. In addition, impurities are a major factor that hinders the movement of carriers, and a small amount of doping usually has a large effect on mobility.

The relationship between the Sn doping amount and the mobility shows that the mobility shows a high value of 40 or more in the case of a small amount of Sn, but monotonically decreases at a doping amount of 2% by weight or more, and 30 or less at 10% by weight or more. Value.

From the results of these studies, 200 to 1000
As a method for obtaining an ITO film excellent in Ω / □ uniformity,
A method for controlling the n-doping amount has been found. That is, to improve uniformity, a film thickness of 150 ° or more is required, and at this time, the specific resistance must be controlled at a value of 3 × 10 ⁻⁴ or more. As a first method, an IT in which the Sn doping amount is 0.05 to 2.0% by weight based on In.
O film. As a second method, when the Sn doping amount is In
By using an ITO film that is 10 to 40% by weight, a high-resistance film is obtained.

When the Sn doping amount is 0.05 to
The 2.0 wt% film has a low carrier density and a high mobility, and a film having a uniform in-plane sheet resistance can be obtained by controlling the Sn doping amount with an accuracy of 0.05% or less. When the Sn doping amount is in the range of 0.1 to 1.5% by weight, the specific resistance (ρ) can be estimated by the following approximate expression. logρ = −2.83−0.4X (3) where ρ: Ωcm X: wt% of Sn with respect to In

The film having a Sn doping amount of 10 to 40% by weight with respect to In has a carrier density of about 5 × 10 ²⁰ / cm ³ , a mobility of 30 or less, and a specific resistance of 5 to 5. 8x1
The value is 0 ^-4 Ωcm. In this case, the Sn doping amount may be accurate to the order of several percent, which is a condition in which the allowable range of the doping amount is wider and the film is easily formed as compared with the case of the minute doping. However, if it is desired to obtain a specific resistance of 8 × 10 ⁻⁴ Ωcm or more with this Sn doping amount, it is necessary to increase the specific resistance by controlling the amount of oxygen defects. That is, the specific resistance can be further increased by heating the formed ITO film to 200 ° C. or more in an atmosphere containing oxygen. 250 ° C x 30
About 1.5 times in the treatment for about 30 minutes, about 2 times in
Since it increases about 2.5 times at 50 ° C. × 30 minutes, it is possible to control the final specific resistance.

As a method for forming the ITO film, a generally known method can be adopted. That is, in a sputtering method, an electron beam evaporation method, an ion plating method, a chemical vapor deposition method (CVD method), a pyrosol method, or the like,
By forming a film so that the above amount Sn is doped in the TO film, a high-resistance ITO film is formed. The conditions vary depending on the film formation method, such as the transparency of the obtained film and the ease of chemical etching. However, in general, this should be dealt with by changing the Sn doping amount under the conditions for forming a low-resistance ITO film for LCD. Is possible.

That is, in the sputtering method, the Sn composition of the target may be changed, in the electron beam evaporation method and the ion plating method, the Sn composition of the pellet may be changed, and in the CVD method and the pyrosol method, the Sn composition in the raw material may be changed. As a result, regardless of which method is used, an ITO film having a high resistance and controlled to a predetermined value can be obtained.

When it is desired to obtain a specific resistance of 8 × 10 ⁻⁴ Ωcm or more with an ITO film having a Sn doping amount of 10 to 40% by weight, a sputtering method, an electron beam evaporation method, and an ion plating method are used. At the end of the film formation, a gas containing oxygen is introduced into a vacuum film formation chamber, and the treatment is performed at a temperature of 200 ° C. or higher for a predetermined time, whereby a high-resistance ITO film with good uniformity can be obtained. In the case of the CVD method and the pyrosol method, after the film formation is completed, an oxygen-containing gas is introduced into the film formation chamber for a predetermined period of time.
By treating at a temperature of 00 ° C. or higher, an ITO film of 200 to 1000 Ω / □ with good uniformity can be obtained. In addition, when the Sn doping amount is 0.05 to 2.0% by weight, the same treatment can be performed.

The specific resistance of the ITO film obtained by an ordinary method is 3 × 10 ⁻⁴ Ωcm or less, and in order to obtain a film having a resistance of 200 to 1000 Ω / □, the film thickness must be extremely thin. Therefore, only a film having poor uniformity was obtained.
In the present invention, the Sn doping amount is set to 0.05 to 2.0% by weight or 1%.
This is a method in which the content is 0 to 40% by weight, and a high-resistance film with good uniformity can be easily obtained.

[0019]

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these. Example 1 In ₂ O ₃ powder having an average particle size of 0.2 μm and an average particle size of 0.6
μm of SnO ₂ powder was mixed at 0.4% by weight with respect to In, and the mixture was pulverized for 5 hours in a ball mill. Then, the mixed powder was sintered by hot pressing at 800 ° C. and 400 kg / cm ^2. I got a body. Using this as a target, sputter deposition was performed.

The sputtering conditions were such that a film was formed on a glass substrate using an RF sputtering apparatus. Glass substrate is 1m thick
800cm S on 10cm square soda lime glass
One coated with an iO ₂ film was used. RF output 200
W, gas composition: Ar: O ₂ = 98: 2, substrate temperature = 30
The film formation was performed at 0 ° C. for 4 minutes.

In the obtained ITO film, Sn contained in the film was replaced by ICP.
When analyzed by emission spectroscopy, it was 0.3% by weight, the film thickness was 250 °, the sheet resistance was 450Ω / □, and the specific resistance was 1.1 × 1.
0 ^-3 Ωcm. The sheet resistance uniformity is ± 25.
It was within Ω / □ and was a good film.

Example 2 A sintered body was prepared in the same manner as in Example 1, except that the amount of SnO ₂ powder was 30% by weight. Example 1 targeting this
Sputter deposition was performed under the same conditions as described above. The obtained ITO
When the Sn in the film was analyzed by ICP emission spectroscopy, it was found to be 24.6% by weight.
Ω / □, specific resistance 7.7 × 10 ⁻⁴ Ωcm. Further, the uniformity of the sheet resistance was within ± 20 Ω / □, and the film was excellent.

Example 3 In forming an ITO film by atmospheric pressure CVD (pyrosol film forming method) by ultrasonic atomization, a methyl alcohol solution of InCl ₃ was used as an indium raw material. The concentration is 0.15 mol / l, and SnC
methyl alcohol solution of l ₄ (concentration 0.2 mol /
Using 1), a solution in which 0.65% by weight of Sn was added to In was prepared. The substrate used was a soda lime glass plate having a thickness of 1 mm and 10 cm square coated with a 1000 ° SiO ₂ film. The substrate was set in a pyrosol film forming apparatus, heated to 500 ° C., atomized by ultrasonic at 2 ml / min, introduced into the substrate, and formed into a film for 2 minutes.

In the obtained ITO film, Sn in the film was converted to ICP.
When analyzed by emission spectroscopy, it was 0.5% by weight, the film thickness was 200 °, the sheet resistance was 400Ω / □, and the specific resistance was 8.0 × 1.
0 ^-4 Ωcm. The sheet resistance uniformity is ± 20.
It was within Ω / □ and was a good film.

Example 4 A solution prepared by adding Sn at 25% by weight in Example 3 was prepared, and a film was formed under the same conditions as in Example 3. I obtained
The TO film had a Sn content of 19.6% by weight and a film thickness of 24.
0 °, sheet resistance 270Ω / □, specific resistance 6.5 × 10 ^-4
Ωcm. This film is placed in an electric furnace in an air atmosphere for 30 minutes.
When heat treatment was performed at 0 ° C. for 30 minutes, the sheet resistance was 490.
Ω / □, and the specific resistance increased to 1.2 × 10 ⁻³ Ωcm. Also,
The sheet resistance uniformity was within ± 30Ω / □.

[0026]

According to the present invention, by controlling the amount of Sn doping in the film, it is possible to relatively easily achieve uniformity.
An ITO film having a sheet resistance of 00Ω to 1000Ω / □ can be obtained. In addition, the method and an oxygen-containing atmosphere may be used.
By performing a heat treatment at a temperature of 0 ° C. or higher, a film having a higher resistance can be obtained, and therefore, its practical value is extremely large.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-48-51913 (JP, A) JP-A-61-256944 (JP, A) JP-A-1-115010 (JP, A) JP-A-63-1988 310970 (JP, A) JP-A-57-96402 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03C 17/00-17/42

Claims (2)

(57) [Claims] 1. A method of forming a tin-doped indium oxide film, wherein the film is formed with a tin content of 0.05 to 2.0% by weight based on indium. 2. A method for forming a tin-doped indium oxide film according to claim 1, wherein the heat treatment is performed at a temperature of 200 ° C. or more in an atmosphere containing oxygen after forming the tin-doped indium oxide film.