JP2633340B2 - Method for forming transparent conductive film - Google Patents

Description

The present invention relates to a method for forming a film for a transparent electrode required for an electronic display such as a plasma display, an electroluminescence display, a liquid crystal display, and a touch panel of a touch input system. More specifically, an indium oxide film containing tin oxide having a low resistivity (hereinafter referred to as an ITO film) is formed on a substrate by magnetron sputtering using a pressure sintered body of indium oxide containing tin oxide as a target. About the method.

[Conventional technology]

Conventionally, as a method for forming a transparent ITO film on a substrate by a sputtering method, there are a method using an indium tin alloy as a target and a method using a sintered indium oxide containing tin oxide as a target. As the former method, the sputtering gas comprising a mixed gas of reduced pressure argon and oxygen, a semi-transparent film comprising mainly lower oxides on a substrate unheated coated, then the membrane of the air or N ₂ For example, there is a method in which heating is performed in a neutral gas or a reducing gas containing hydrogen to make the gas transparent. On the other hand, as the latter method, there is a method in which a substrate is heated in advance in a vacuum chamber and a transparent film is directly formed on the heated substrate by sputtering with an argon gas containing a small amount of oxygen.

[Problems to be solved by the invention]

However, the former film obtained by sputtering an indium-tin alloy target has a slow film etching speed due to the dense structure of the film, so that patterning of a fine transparent electrode can be performed in a short time with high dimensional accuracy. It has the disadvantage of being difficult. On the other hand, the film coated on the heated substrate using the latter sintered body of indium oxide containing an appropriate amount of tin oxide as a target has a resistivity of 1.
It is about 8 to 2.0 × 10 ⁻⁴ Ωcm, and has a drawback that the film thickness must be increased similarly to the former method in order to secure the sheet resistance required for a large area and high definition display.

[Means for solving the problem]

The present invention has been made to overcome the above-mentioned drawbacks of the conventional method of forming an ITO film on a substrate, and has a transparent conductive film having a lower resistivity than the ITO film obtained by the conventional method. A method for forming a film on a substrate is provided.

The method for forming an ITO transparent conductive film on a substrate according to the present invention comprises the steps of: using an oxide containing sintered tin oxide in an atmosphere containing an inert gas such as decompressed argon or a mixed gas of an inert gas and oxygen. Targeting indium,
A first layer having a thickness of 3 to 30 nm is coated on a substrate maintained at a temperature of 200 ° C. or less by a magnetron sputtering method. A second layer film is coated on the first layer film of the substrate by magnetron sputtering in a reduced-pressure atmosphere composed of a mixed gas of an inert gas such as argon and oxygen,
After completion of coating the film, the substrate is cooled, and a gas is introduced into the vacuum chamber.
Coating the first layer at a relatively low substrate temperature,
A method that includes coating a second layer at a relatively high substrate temperature of at least C. As an atmosphere gas for coating the film of the first layer, an inert gas such as argan or a mixed gas of argon and a small amount of oxygen can be used. The total pressure usually used in the magnetron sputtering method is 1 × 10 ^-3 to 1x
Adjusted to 10 ^-2 Torr. Also, the substrate temperature when coating
If the temperature exceeds 200 ° C., the growth of particles becomes remarkable, and it becomes impossible to improve the hole mobility of free electrons in the second layer film required for reducing the resistivity. I do. Further, it is preferable to keep the temperature of the substrate at 100 ° C. or lower in order to lower the resistivity of the film of the second layer.
Coating the first layer film beyond 30 nm would rather increase the overall film resistivity, since the first layer film is coated at a relatively low temperature and therefore has a high resistivity.

On the other hand, if the film thickness is smaller than 3 nm, the mobility of holes of free electrons in the film of the second layer cannot be increased, so the thickness of the film of the first layer must be in the range of 3 to 30 nm. The atmosphere when the substrate coated with the first layer film is heated to at least 300 ° C. is performed under reduced pressure in order to lower the resistivity of the first layer film. The oxygen partial pressure in the reduced atmosphere is 1 × 10
It is preferably at most ^-4 Torr. In coating the second layer film, the substrate temperature is maintained at a high temperature of 300 ° C. or higher.
At a substrate temperature of 300 ° C. or lower, the crystallinity of the film to be coated is not sufficient, and the hole mobility of free electrons in the film becomes small, so that the resistivity becomes large. Further, the oxygen partial pressure in the atmosphere when coating the second layer film is preferably in the range of 5 × 10 ⁻⁶ to 1 × 10 ⁻⁴ Torr. When the oxygen partial pressure is 5 × 10 ⁻⁶ Torr or less, the particle growth becomes remarkable when the film is deposited, the hole mobility of free electrons decreases, and when the oxygen partial pressure is higher than 1 × 10 ⁻⁴ Torr. Oxygen vacancies in the film are reduced and consequently the density of free electrons is reduced. Therefore, to obtain a low resistivity, the oxygen partial pressure is preferably 5 × 10 ⁻⁶ to 1 × 10 ⁻⁴ Torr, and more preferably 1 × 10 ⁻⁴ Torr.
10 ^{-5 to} 5 × 10 ^-5 Torr is most preferred. Further, in order to obtain the above-mentioned oxygen partial pressure, the total gas pressure of the atmospheric gas is set to 1 × 10 ⁻³ to 1 × 10 ⁻² Torr normally used in magnetron sputtering.
Is adjusted to

The thickness of the film of the second layer of the present invention is determined by the required sheet resistance of the transparent electrode, and is preferably in the range of 20 to 400 nm. When the film thickness exceeds 400 nm, the influence of the first underlayer on the deposition of the second layer film is diminished, and the resistivity of the entire film is hardly reduced. If the film thickness is less than 20 nm, a continuous and uniform film is not obtained, so that it is difficult to obtain a low resistivity.

After coating the second layer film, the substrate is cooled in a reduced-pressure atmosphere, and the temperature of the substrate when air is introduced from the outside is set to 250 ° C. or less. Further, the temperature is most preferably 200 ° C. or lower. When air is introduced when the temperature of the substrate is 250 ° C. or higher, the ITO film coated with oxygen in the air is oxidized,
It is not preferable because the resistivity increases.

As the target used in the present invention, a target obtained by sufficiently mixing a fine powder of tin oxide with a fine powder of indium oxide and press-molding it into a predetermined shape, at a high temperature of, for example, 1000 to
What was fired and sintered at 1500 ° C. can be used. Tin oxide is added as an additive for imparting electrical conductivity to the indium oxide film, and is suitably added in an amount of about 5 to 15% by weight.

As a method for carrying out the present invention, in a batch type magnetron sputtering apparatus, the first to third steps can be performed continuously in a vacuum chamber without breaking the vacuum of the sputtering apparatus, and can be opened and closed. In an in-line type magnetron sputtering apparatus including a plurality of vacuum chambers that can be isolated and connected continuously by a gate valve, the first to third steps can be sequentially performed in a continuous vacuum chamber.

(Operation)

The film of the first layer according to the present invention is a film mainly composed of amorphous because it is coated on a relatively low-temperature substrate,
By heating under reduced pressure after coating, a dense film is formed. The first underlayer film acts so that the grain boundaries of the second layer film to be coated at a high temperature become dense, and reduces the energy barrier to the movement of free electrons at the grain boundaries in the film. Therefore, the mobility of free electrons related to the electrical conductivity of the film is increased, and the resistivity of the entire coated film is reduced.

〔Example〕

Hereinafter, the present invention will be described with reference to Examples. FIG. 1 is a cross-sectional view of one embodiment of a substrate coated with a transparent conductive film obtained by the present invention, wherein 1 is a glass plate, 2 is a film coated by a first coating step, and 3 is a second coating. It is a film coated by the process. FIG. 2 is a sectional view of a substrate coated with a transparent conductive film obtained by a conventional method, and 4 is a transparent conductive film.

Example 1 A soda-lime glass substrate (dimensions: 50 mm × 50 mm × 3 mm) was washed with a neutral detergent and washed with water and dried with Freon steam. This glass substrate was placed in a sputtering tank of a magnetron sputtering apparatus so that the distance to the target was 50 mm.
As the target, a target obtained by subjecting indium oxide to which tin oxide was added by 10% by weight to pressure molding and firing was used. The inside of the tank of the magnetron sputtering device is set to 7
After reducing the pressure to ^10-6 Torr or less, 98.5% by volume of argon
A mixed gas of 1.5% by volume of oxygen was introduced, and the inside of the sputtering tank was
The pressure was maintained at 3.0 × 10 ⁻³ Torr. Glass substrate temperature 20
° C, a sputtering current of 2 A was applied from a DC power supply to the magnetron cathode to which the target was attached, and sputtering was performed for a predetermined time so that the thickness of the first layer was 15 nm. Thereafter, the introduction gas was stopped, the glass substrate was heated to 300 ° C., and the temperature was maintained at 300 to 310 ° C. by the temperature control mechanism of the substrate heater. The mixed gas was introduced again, and the inside of the sputtering tank was 3.0 × 10
^-3 Torr, and discharge at a sputter current of 2 A to make the thickness of the second layer
Sputtering was performed for a predetermined time so that the thickness became 140 nm. The application of the voltage and the gas introduction were stopped, and the glass substrate was cooled to 250 ° C. Thereafter, the vacuum valve was opened and air was introduced into the vacuum chamber, and a sample 1 coated with an ITO film in two coating steps was obtained.

The film thickness and the sheet resistance of Sample 1 were measured, and the resistivity was calculated. The Hall coefficient was measured to determine the concentration and mobility of free electrons in the film, and a relative value to the concentration and mobility of free electrons in the film of Comparative Sample 2 was calculated. The results are shown in Table 1.

Example 2 Samples 2 to 5 coated with an ITO film by two coating steps were obtained in the same manner as in Example 1 except that the temperature of the glass substrate when coating the first layer film was variously changed. For each of Samples 2 to 5, the film thickness and the sheet resistance were measured, and the resistivity was calculated. The Hall coefficient was also measured to determine the concentration and mobility of free electrons in the film, and the relative values to the concentration and mobility of free electrons in the film of Comparative Sample 2 were calculated. The results are shown in Table 1.

Example 3 In the same manner as in Example 1, except that the thickness of the film of the first layer was variously changed by changing the sputtering time, samples 6 to 11 coated with an ITO film by two coating steps were obtained. . For each of Samples 6 to 11, the film thickness and the sheet resistance were measured, and the resistivity was calculated. The Hall coefficient was also measured to determine the concentration and mobility of free electrons in the film, and the relative values to the concentration and mobility of free electrons in the film of Comparative Sample 2 were calculated. The results are shown in Table 2.

Example 4 Except that the composition of the atmosphere gas when coating the first layer was only argon, and the thickness of the film of the second layer and the temperature of the glass substrate when coating the film of the second layer were variously changed, ,
In the same manner as in Example 3, samples 12 to 14 coated with an ITO film by two coating steps were obtained. For each of Samples 12 to 14, the film thickness and the sheet resistance were measured, and the resistivity was calculated. The Hall coefficient was measured to determine the concentration and mobility of free electrons in the film, and the relative value to the concentration and mobility of free electrons in the film of Comparative Sample 3 was calculated. The results are shown in Table 3.

Comparative Example 1 The temperature of the glass substrate when coating the film of the first layer was 250
A comparative sample 1 coated with an ITO film by two coating steps was obtained in the same manner as in Example 1 except that the temperature was changed to ° C. The film thickness and the sheet resistance of this sample were measured, and the resistivity was calculated. The Hall coefficient was also measured to determine the concentration and mobility of free electrons in the film, and the relative values to the concentration and mobility of free electrons in the film of Comparative Sample 2 were calculated. The results are shown in Table 1.

Comparative Example 2 A soda-lime glass substrate (dimensions 50 mm × 50 mm × 3 mm) was washed with a neutral detergent, washed with water, and dried with Freon steam. This glass substrate was placed in the same magnetron sputtering apparatus as in Example 1 so that the target distance was 50 mm. The same target as in Example 1 was used as the target. The glass substrate was heated while evacuation of the inside of the tank of the magnetron sputtering apparatus to 7 × 10 ⁻⁶ Torr by a vacuum exhaust pump, and the temperature of the glass substrate was maintained at 300 to 310 ° C. by adjusting the temperature of the substrate heating heater. A mixed gas of 98.5% by volume of argon and 1.5% by volume of oxygen was introduced into the tank, and the inside of the sputtering tank was maintained at a pressure of 3.0 × 10 ⁻³ Torr. Sputter current 2A
Was applied to a magnetron cathode and sputtered for a predetermined time so that the film thickness became 140 nm. The application of voltage and gas introduction were stopped, and the glass substrate was cooled down to 200 ° C., and then air was introduced into the vacuum chamber.
Comparative sample 2 coated with the film was obtained. The film thickness and sheet resistance of this sample were measured, and the resistivity was measured. Further, the Hall coefficient was measured, and the concentration and mobility of free electrons in the film were calculated, and were used as reference values for the concentration and mobility of free electrons in Example 1, Example 2, and Comparative Example 1. The results are shown in Table 2.

Comparative Example 3 A comparative sample 3 coated with an ITO film by one coating step was obtained in the same manner as in Comparative Example 2 except that the temperature of the glass substrate when coating the film was 400 ° C. The film thickness and sheet resistance of this sample were measured, and the resistivity was calculated. The Hall coefficient was measured to determine the concentration and mobility of free electrons in the film, which were used as reference values for the concentration and mobility of free electrons in the sample of Example 3. The results are shown in Table 3.

〔The invention's effect〕

Since the ITO transparent conductive film obtained by the present invention has a lower resistivity than that obtained by the conventional method, the film thickness may be thinner to ensure a predetermined sheet resistance as a transparent electrode of an electronic display. The ability to make the film thinner facilitates pattern processing of the transparent electrode, so the IT according to the present invention
O transparent conductive film enables fine pattern processing of a transparent electrode required for a large area and high definition display to be quickly performed with good yield.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a glass with a transparent conductive film according to the present invention, and FIG. 2 is a cross-sectional view of a glass with a transparent conductive film according to a conventional method. 1 ... glass, 2 ... layer coated in the first coating step, 3 ... layer coated in the second coating step, 4 ...
A transparent conductive film consisting of one layer.

Claims (3)

(57) [Claims] 1. A magnetron sputtering method using a target obtained by sintering indium oxide containing tin oxide in an atmosphere containing a reduced pressure of an inert gas or an inert gas and oxygen. Film thickness of 3 to 3 on substrate surface
A first step of coating a film of indium oxide containing a small amount of tin oxide of 0 nm, and magnetron sputtering in an atmosphere containing a reduced pressure of inert gas and oxygen using the target to at least 300 ° C. A second step of coating a film of indium oxide containing a small amount of tin oxide on the film of the heated substrate, and cooling the substrate to a temperature of 250 ° C. or less in a reduced pressure atmosphere, and then setting the atmosphere to atmospheric pressure. A method for forming a transparent indium oxide film containing tin oxide comprising a third step 2. The method according to claim 1, wherein in the second step, 5 × 10 ^-6 to 1 × 10 ^-4 To
2. A method according to claim 1, wherein the membrane is coated at an oxygen partial pressure of rr. 3. The film coated in the second step has a thickness of 20 to 40.
3. The method according to claim 1, wherein the thickness is 0 nm.