JP2002129319A - Method for forming metal oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a uniform metal-oxide thin film, particularly a transparent electroconductive film with low resistance, in a low temperature without heating, while preventing a base material from damaging or a quality of the film from deteriorating. SOLUTION: The method for forming the metal oxide thin film is characterized by sputtering at a base material temperature of 100 deg.C or less with a magnetron sputtering apparatus in which a target is arranged aslant so that sputtered particles can be launched in an angle of 75 degree or less against the base material.

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 metal oxide thin film, particularly an ITO film having excellent transparency and conductivity, on a substrate using a magnetron sputtering apparatus.

[0002]

2. Description of the Related Art Since metal oxide thin films such as indium oxide, zinc oxide and tin oxide have transparent conductivity, light-sensitive devices such as optical sensors and photographing devices, touch panels, solar cells, and other fields are used. Widely used in the field. As a method for forming such a metal oxide thin film on a substrate, vacuum deposition, sputtering, CVD, and the like are well known, but a dense film having excellent adhesion can be formed.
In general, sputtering was performed without any restrictions on the deposition material. Then, in order to form a metal oxide thin film having excellent transparency and conductivity by a sputtering method, the base material may be damaged by secondary electrons, X-rays, or negative ions that have been hit from the target surface. It has been considered extremely important to prevent the film quality from deteriorating.

In order to solve these problems, a facing target type magnetron sputtering method has been proposed. In this method, two cathode targets are arranged to face each other, and a magnetic field is applied perpendicularly to the target surface from one target toward the other to perform sputtering. It has the advantage that the applied magnetic field confines the generated secondary electrons and prevents high-speed film formation and electron impact on the substrate.

[0004] However, the facing target type magnetron sputtering method has a structure in which sputtered particles are incident on the substrate from all directions. I could not prevent it. Further, the uniformity of the film thickness and the film thickness distribution are still insufficient.

Further, in order to form a metal oxide thin film having excellent conductivity, it is necessary to raise the temperature of the base material, and for example, it is necessary to form the metal oxide thin film with a resistance as low as 10 ⁻⁴ Ω · cm. In order to obtain a thin film, it is necessary to form a film at a high substrate temperature of about 300 ° C. or to perform a heat treatment at a temperature of 250 ° C. or more after the film is formed. Accordingly, a method for obtaining a transparent conductive film having a low resistance even when formed at a low temperature, which can be applied not only to a substrate having a high heat resistance such as a glass plate but also to a plastic film having a low heat resistance, is provided. Was desired from various directions.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and prevents a substrate from being damaged or a film quality from deteriorating, and a uniform metal oxide thin film at a low temperature without heating. In particular, it is an object of the present invention to provide a method for forming a low-resistance transparent conductive film.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that when a magnetron sputtering apparatus is used, the angle between a target and a substrate is set to a specific range, and the sputtered particles are perpendicular to the surface of the substrate. The present inventors have found that the above problem can be solved by performing sputtering while keeping the base material temperature at a low temperature of 100 ° C. or less while preventing the incidence on the substrate. That is, the present invention provides: (1) Sputtering at a substrate temperature of 100 ° C. or less using a magnetron sputtering apparatus in which a target is arranged at an angle so that sputtered particles enter the substrate at an angle of 75 ° or less. A method for forming a metal oxide thin film, comprising: (2) The method for forming a metal oxide thin film according to (1), wherein reactive sputtering is performed at a substrate temperature of 50 ° C. or less. (3) The method for forming a metal oxide thin film according to (1) or (2), wherein a plurality of targets are arranged around the base material and reactive sputtering is performed while rotating the base material. (4) The metal oxidation according to any one of (1) to (3), wherein a metal target is used as a target, and reactive sputtering is performed using a mixed gas of an inert gas and oxygen gas as a sputtering gas. Method of forming a thin film. (5) The method for forming an ITO thin film according to (4), wherein an indium target and a tin target are used.
Is the gist.

[0008]

Embodiments of the present invention will be described below in detail. First, the present invention relates to a method for forming a metal oxide thin film. The metal oxide thin film is not particularly limited, but may be an indium oxide film, an indium oxide film (ITO film) doped with tin, a zinc oxide film, a zinc oxide film containing gallium oxide, a tin oxide film, antimony or fluorine. And a transparent gas barrier film such as a silicon oxide film. Among them, it is preferable to apply the method of the present invention to the formation of a transparent conductive film such as an ITO film or a zinc oxide film, which is greatly affected by damage to the substrate or deterioration of the film quality.

In the present invention, the above-mentioned metal oxide thin film is formed on a substrate using a magnetron sputtering apparatus. The magnetron sputtering apparatus includes a DC method and an RF method. In the present invention, the discharge stability is good, the interaction between the cathodes when a plurality of targets are used is small, and the controllability of the plasma is improved. It is preferable to use a DC magnetron sputtering apparatus which is excellent in the above.

A method of using a metal oxide target as a target used in sputtering,
Any of the methods of reactive sputtering using a metal target is applicable, but a reactive sputtering method using a metal target is preferred. For example, when forming an indium oxide film (ITO film) doped with tin as a metal oxide thin film, instead of using a target obtained by sintering and molding an expensive mixture of indium oxide and tin oxide, an indium oxide film is used. It is preferable to use two targets, a tin alloy or indium target and a tin target. In particular, reactive sputtering using two targets, an indium target and a tin target, is inexpensive, and the mixing ratio of indium and tin and the bonding ratio of indium and oxygen can be finely adjusted.

When a metal oxide target is used as a sputtering gas, an inert gas such as Ar, Ne, or Xe, or a mixture of these inert gases with a small amount of oxygen is used. In this case, a mixed gas of an inert gas and oxygen is used. Further, the sputtering gas pressure is, for example, A when reacting sputtering is performed.
It is preferable that the r gas introduction flow rate is> 50 sccm and the oxygen gas introduction flow rate is about 3 to 7 sccm.

Next, a method for forming a metal oxide thin film of the present invention using the above-described magnetron sputtering apparatus will be described with reference to the drawings. FIG. 1 is a conceptual diagram showing an example of the positional relationship between a target 11 and a substrate 12 according to the present invention. FIG. 2 shows a target 1 when the substrate 12 is rotated.
The positional relationship between the substrate 1 and the base material 12 is changed by a position change (A,
3B is a schematic plan view showing an example of the sputtering apparatus 1 used in the present invention. In the present invention, as shown by θ in FIGS. 1 and 2, the sputtered particles irradiated from the target 11 disposed in the chamber of the magnetron sputtering apparatus 1
It is necessary to arrange the target 11 at an angle to the substrate so as to be incident on the substrate 12 at an angle of 75 ° or less, preferably 50 ° or less with respect to the substrate.

Further, in the present invention, it is preferable to arrange a plurality of targets 11 around the substrate 12 and perform sputtering while rotating the substrate 12. In this case, as is clear from FIGS. 2A and 2B, the rotation of the base material 12 changes the positional relationship with the target 11. Therefore, when the base material 12 is rotated or becomes nearly parallel to the target 11 as shown in FIG. 2B, the base material 12 and the target 11 are prevented from entering the base material 12 so that the sputtered particles 3 do not enter the base material 12. Must not overlap. As described above, by rotating the substrate 12 in the chamber, it is possible to arrange the target 11 not only in the front but also in the rear as shown in FIG. And tin can be used as targets, respectively, so that it is possible to form an ITO film having a more varied composition range than when using an indium-tin alloy having a predetermined composition. Note that, in this case, it is preferable that the current be controlled for each target 11. That is, for example, in forming the ITO film, since indium and tin have different evaporation rates, it is preferable to set each to an appropriate evaporation rate.

Further, in the present invention, it is preferable to adjust the bias voltage to adjust the ion bombardment applied to the substrate 11. The preferred bias voltage at this time is 0
~ -80V. If the bias voltage exceeds -80 V, the ion bombardment is so strong that the thin film is damaged, which is not preferable.

In the present invention, the above-described magnetron sputtering apparatus 1 is used. Most importantly, the sputtering is performed under the condition that the substrate temperature is 100 ° C. or less, preferably 50 ° C. or less. It is. The above-described sputtering apparatus 1 is effective in alleviating collision of high-energy particles to the base material 12 to prevent a rise in the base material temperature. However, conventionally, in providing high conductivity, a high base material temperature is required. In other words, while it has been widely accepted that sputtering is performed at a temperature at which crystallization is likely to occur, the method of the present invention prevents damage to the substrate 12 and the film by adopting the above method, and as a result, a high conductivity is obtained. The most characteristic feature is that a thin film provided with can be formed.

Therefore, as a substrate used in the present invention, it is possible to use not only a glass plate but also a plastic film or sheet in which it is difficult to raise the substrate temperature. Examples of such a plastic include polyethylene terephthalate, polyethylene naphthalate, polycarbonate, acrylic resin, polypropylene, and polyethylene.

[0017]

According to the present invention, since the target 11 is disposed and the sputtered particles are made to enter the substrate 12 at an angle of 75 ° or less, the high energy at an incident angle perpendicular to the substrate 12 or exceeding 75 ° is obtained. Not only prevents the substrate from being damaged by secondary electrons, X-rays, or negative ions that have been hit from the target surface, and also prevents the film quality from deteriorating. Can also be prevented. Therefore, even if the substrate temperature is 100 ° C. or less, for example, when forming a transparent conductive film,
It has become possible to form a high quality metal oxide thin film on the order of 0 ^-4 Ω · cm. Further, by rotating the substrate 12, a uniform thin film can be formed.

[0018]

The present invention will be described below with reference to examples. Example 1 Using a DC magnetron sputtering apparatus 1 shown in FIG. 3, a pure metal of indium (purity 99.9%) was placed at the position B of the target 11 and a pure metal (purity 99.9%) of tin was placed at the position D. %). A metal oxide thin film was formed. In addition, reactive sputtering was performed using a glass plate as the substrate 12 for the substrate holder 2. Sputtering was performed according to the following procedure. First, target 1
1. After the substrate 12 is mounted, when the inside of the chamber reaches a predetermined degree of vacuum (4.3 × 10 ⁻¹ Pa), the substrate 12 is sputtered and cleaned by sealing Ar gas. Thereafter, oxygen gas is introduced to rotate the substrate holder 2 at a rotational speed of 12 ° C.
While rotating at rpm, substrate temperature is room temperature (25 ° C),
Ar gas introduction flow rate 55sccm, oxygen gas introduction flow rate 5s
Sputtering was performed for 30 minutes under the conditions of ccm, a coil current of 30 A, an anode voltage of 20 V, and a bias voltage of −30 V, with the current of the indium target being 0.1 A and the current of the tin target being 0.01 A. The angle of incidence of the sputtered particles on the substrate 12 at this time is 7
5 ° or less.

The obtained ITO thin film has a thickness of 1000 angstroms, and has a specific resistivity of 2.0 as shown in FIG.
Even if the position from the center of the substrate was changed to 0 × 10 ^{−4 to} 5.0 × 10 ⁻⁴ Ω · cm, the dispersion of the specific resistance was small, and an extremely excellent transparent conductive film having a transmittance of 92% was obtained. . Further, when the surface was observed with a tunnel microscope to confirm the smoothness of the surface, the surface was smooth as shown in FIG.

[0020]

According to the method of the present invention, the substrate and the film are prevented from being damaged during sputtering. It has become possible to form an excellent thin film. Therefore, it is possible to easily provide a transparent conductive film using a plastic as a base material, which has been considered difficult, and thus it is possible to use a metal oxide thin film in a wider field than before.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a positional relationship between a target 11 and a base material 12 according to the present invention.

FIG. 2 is a conceptual diagram showing a positional relationship between a target 11 and a substrate 12 when the substrate 12 is rotated in the method of the present invention, according to a position change (A, B) accompanying the rotation.

FIG. 3 is a schematic plan view showing one example of a sputtering apparatus 1 used in the present invention.

FIG. 4 is a graph showing the relationship between the position of a substrate and the specific resistivity of the ITO film obtained in Example 1.

FIG. 5 is a tunnel microscope photograph showing a surface state of the ITO film obtained in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sputtering apparatus used in this invention 11 Target 12 Substrate 2 Substrate holder 3 Sputtered particle θ Incident angle of sputtered particle

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masanao Orihara 1515 Nakatsu-cho, Marugame-shi, Kagawa Prefecture F-term in Okura Industrial Co., Ltd. (reference) 4K029 AA09 AA11 BA43 BA50 BC09 CA06 CA15 DC03 DC39 EA08 5E032 AB10 BA15 BB20 CB01 CC18 5G323 BA01 BB05

Claims (5)

[Claims] The present invention is characterized in that sputtering is performed at a substrate temperature of 100 ° C. or less by using a magnetron sputtering apparatus in which a target is arranged at an angle such that sputtered particles enter the substrate at an angle of 75 ° or less with respect to the substrate. Of forming a metal oxide thin film. 2. The method for forming a metal oxide thin film according to claim 1, wherein the sputtering is performed at a substrate temperature of 50 ° C. or less. 3. A method comprising: disposing a plurality of targets around a substrate;
3. The method for forming a metal oxide thin film according to claim 1, wherein sputtering is performed while rotating the substrate. 4. The metal oxide according to claim 1, wherein a metal target is used as a target, and reactive sputtering is performed using a mixed gas of an inert gas and an oxygen gas as a sputtering gas. Method of forming a thin film. 5. The method of forming an ITO thin film according to claim 4, wherein an indium target and a tin target are used.