JP2012025996A - Forming method of transparent conductive thin film, and forming device of transparent conductive thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method and a manufacturing device of an epitaxially-grown transparent conductive thin film, and a novel photoelectronics device having a multilayered structure formed of a crystal thin film.SOLUTION: A base board 5 in a vacuum chamber is heated to 300°C to 500°C, and controlled into a range of 0.05 Pa to 0.3 Pa of inert gas pressure and 5×10Pa to 1.5×10Pa of oxygen partial pressure. By applying high-density plasma irradiation to the base board, the transparent conductive thin film is formed by epitaxially growing a thin film forming material on the crystal base board.

Description

  The present invention relates to a transparent conductive thin film forming method and a transparent conductive thin film forming apparatus used for a light emitting device and a display device.

  As the transparent conductive thin film (hereinafter, also simply referred to as a thin film or a conductive thin film), IZO, ZnO, AZO, GZO and the like are known in addition to ITO widely used in various display devices. As a method for forming these thin films, various methods such as a PLD (Pulsed Laser Deposition) and a sol-gel method have been tried in addition to a vacuum deposition method and a sputtering method. These thin films are generally binary or ternary compounds such as oxides, and the electrical conductivity, optical transparency, and surface flatness, as well as the film composition and crystallinity, vary greatly depending on the formation method. For this reason, even for the same ITO, for example, the formation method and conditions are changed according to the device to be applied, and necessary characteristics are extracted and used for each device.

  Conventionally, the most commonly used methods for forming an ITO film are sputtering and vacuum deposition. Sputtering is widely used in display devices such as liquid crystal panels and touch panels because it can be uniformly formed on a large area substrate and has excellent film quality. On the other hand, when the deposition substrate is a semiconductor such as an LED, sputtering is avoided because of concerns such as damage to the semiconductor and difficulty in ohmic contact with the semiconductor, and vacuum deposition has been used for many years. Has been. However, ITO films formed by evaporation generally tend to be unstable films such as needle crystals, have insufficient chemical resistance in device processes, and require characteristics for thin film characteristics such as transmittance and flatness. Attempts to replace it with other film forming methods have been widely conducted.

Japanese Patent No. 1553959 Japanese Patent No. 1462543

In these sputtering, vacuum deposition, and most other film forming means, heating the substrate during film formation is indispensable for sufficiently reducing the resistivity of the transparent conductive thin film. Taking ITO as an example, in the case of no substrate heating, it is generally very difficult to set the resistivity to 5 × 10 ⁻⁴ Ωcm or less, but by heating the substrate at 200 to 300 ° C., about 2 × 10 ⁻⁴ Ωcm. It becomes possible to reduce by this. For this reason, the film is generally formed by heating the substrate at several hundreds of degrees Celsius except for use in a device such as an organic EL that is damaged at about 100 degrees Celsius.

  However, when the substrate is heated, each crystal grain of the polycrystalline thin film grows large and the surface irregularities become severe, which may cause a serious obstacle in device characteristics due to light scattering. In addition, there has been a problem that the resistivity cannot be sufficiently reduced due to the effects of surface irregularities and crystal grain boundaries. As described above, there has been no high-quality ITO film forming means that satisfies both low resistivity and surface flatness at the same time. A main object of the present invention is to provide a technique for obtaining a high-quality transparent conductive thin film excellent in surface flatness and optical characteristics while ensuring a sufficiently low resistivity.

  On the other hand, conventionally, there are limited means for epitaxially growing a transparent conductive thin film at a low temperature of 500 ° C. or lower. For example, it is difficult to epitaxially grow a semiconductor such as GaN and a transparent conductive thin film such as ITO alternately in multiple layers Met. Another object of the present invention is to provide a new photoelectronic device by realizing such a multilayer structure of crystalline thin films.

In order to solve the above-mentioned problems, the invention of claim 1 is a method of forming a transparent conductive thin film by epitaxially growing a thin film forming material on a crystalline substrate placed in a vacuum chamber. In addition, the substrate placed in the vacuum chamber is heated to 300 ° C. to 500 ° C., the inert gas pressure is 0.05 Pa to 0.3 Pa, and the oxygen partial pressure is 5 × 10 ⁻⁴ Pa to 1.5 × 10 ⁻³ Pa. The transparent conductive thin film forming method is characterized in that the substrate is subjected to high density plasma irradiation in a controlled range.

  According to a second aspect of the present invention, in the method for forming a transparent conductive thin film according to the first aspect, an ECR plasma flow is used as a high-density plasma irradiation method.

The invention described in claim 3 is an apparatus for forming a transparent conductive thin film by epitaxially growing a thin film forming material on a crystalline substrate placed in a vacuum chamber, and forming the thin film by placing the substrate. A vacuum chamber for carrying out the process, means for heating the substrate placed in the vacuum chamber to 300 ° C. to 500 ° C. during the formation of the thin film, and introducing an inert gas and an oxygen gas into the vacuum chamber. Means for controlling the pressure to 0.05 Pa to 0.3 Pa and the oxygen partial pressure in the range of 5 × 10 ⁻⁴ Pa to 1.5 × 10 ⁻³ Pa; and means for performing high-density plasma irradiation on the heated substrate; A device for forming a transparent conductive thin film, comprising:

  According to a fourth aspect of the present invention, in the transparent conductive thin film forming apparatus according to the third aspect, an ECR plasma flow is used as the high-density plasma irradiation method.

It is a figure which shows the cross-section of a typical solid source ECR plasma film-forming apparatus. It is a figure which shows the X-ray-diffraction pattern of the ITO film | membrane formed into a film with the substrate temperature of 350 degreeC. It is a figure which shows the surface morphology change of the ITO film | membrane by film-forming temperature. It is a figure which shows the film thickness dependence of the resistivity of an epitaxial growth ITO film | membrane. It is a figure which shows the transmittance | permeability of an ITO film | membrane.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The present invention relates to a method of epitaxially growing a thin film forming material on a crystalline substrate placed in a vacuum chamber to form a transparent conductive thin film. During the formation of the thin film, the substrate placed in the vacuum chamber is heated to a predetermined temperature. The substrate is epitaxially grown by heating with a high-density plasma and the substrate is irradiated with high-density plasma while the inert gas pressure and oxygen partial pressure are controlled within a predetermined range, and it has low resistance and excellent surface flatness and optical properties. A conductive thin film is formed.

  In this embodiment, as an example of this thin film forming method, an ITO film is formed by sputtering using a solid source ECR (Electron Cyclotron Resonance) plasma film forming apparatus. The solid source type ECR plasma film forming apparatus can generate a plasma flow by utilizing this ECR phenomenon. By applying a voltage to the target placed around the generated plasma flow, ions in the plasma are accelerated and incident on the target to cause a sputtering phenomenon, and the released target particles are deposited on a sample substrate placed nearby. A technique for forming a thin film has already been patented (see Patent Documents 1 and 2).

  First, a solid source ECR plasma apparatus that can be used as a thin film forming apparatus capable of performing the thin film forming method according to the present embodiment will be described. FIG. 1 shows the structure of a solid source ECR plasma apparatus. In the figure, the plasma generation chamber 1 is attached to the sample chamber 2 at an angle, and is connected to the sample chamber via the plasma extraction window 3. Both are sealed spaces isolated from the atmosphere.

  In order to form a thin film on the sample substrate 5 placed on the rotating sample stage 4, first, the plasma generation chamber 1 and the sample chamber 2 are evacuated by a vacuum pump (not shown) through the exhaust passage 6, The substrate heating is started by operating the infrared lamp type heater 7 while rotating the substrate. When the substrate reaches a predetermined temperature, a gas is introduced from the gas inlet 8 or the gas inlet 9 and held at a predetermined pressure.

  Next, after a current is passed through two magnetic coils 10 placed around the plasma generation chamber 1 to generate a magnetic field, the microwave 12 guided to the rectangular waveguide 11 is converted into a microwave below the plasma generation chamber 1. It introduces to the vacuum side through the introduction window 13. As a result, electron cyclotron resonance occurs in the plasma generation chamber 1, and ECR plasma is generated.

  The plasma generated in the plasma generation chamber 1 flows as a plasma flow 14 from the plasma extraction window 3 to the sample substrate 5 along the diverging magnetic field. In this state, when the sputtering power source 15 is turned on and a voltage is applied to the target 16, ions in the ECR plasma are accelerated toward the target 16, and target constituent atoms are released into the vacuum by the ion bombardment. At this time, direct current (DC), alternating current (RF), DC pulse, or the like is used as a sputtering power source applied to the target.

  The particles that have jumped out of the target 16 reach the sample substrate 5 and form a thin film on the substrate. Any solid material can be used as the target material. Typical examples include silicon, aluminum, titanium, zirconium, zinc, carbon, tantalum, molybdenum, tungsten, and compounds such as ITO, IZO, and STO. . In addition, when using oxygen or nitrogen in addition to an inert gas such as argon or xenon when forming a film, a compound thin film such as silicon oxide, silicon nitride, or alumina can be formed even when the target is a single metal. it can.

  The shutter 17 is normally closed and is controlled to be opened and closed when plasma irradiation or sputter film formation processing is performed on the sample substrate 5 for a predetermined time.

In the ITO film formation in the present embodiment, in the apparatus shown in FIG. 1 described above, an ITO target having a Sn composition of 10% is used as the target 16, and argon which is an inert gas is introduced as the gas introduced from the gas inlets 8 and 9. A small amount of oxygen is used. The thin film forming apparatus of this embodiment includes a means for heating a substrate in a temperature range of 300 ° C. to 500 ° C., an inert gas pressure of 0.05 Pa to 0.3 Pa, and an oxygen partial pressure of 5 × 10 ⁻⁴ Pa to 1 during plasma film formation. And a means for controlling in the range of 5 × 10 ⁻³ Pa, and by irradiating a high-density plasma flow by ECR, the ITO film is epitaxially grown, and in addition to low resistivity, excellent surface flatness and transmission characteristics are also satisfied I am letting.

High density plasma irradiation refers to irradiating a substrate with a high density plasma source having an electron density of about 10 ¹¹ cm ⁻³ or more. In addition to the sputtering method using the ECR plasma film forming apparatus shown in FIG. 1, for example, surface wave plasma, helicon wave excitation plasma (HWP: Helicon Wave Plasma), or the like can be used for the high-density plasma.

As conditions for epitaxially growing the ITO film on the sapphire substrate, at least plasma flow irradiation and substrate heating are essential, but there is also an optimum range for oxygen gas partial pressure. The oxygen partial pressure capable of epitaxial growth is approximately in the range of 5 × 10 ⁻⁴ Pa to 1.5 × 10 ⁻³ Pa, and the oxygen flow rate range at this time is 0.2 sccm to 0.6 sccm in the apparatus used this time. When the argon flow rate, power conditions, etc. are changed, the optimum oxygen flow rate also changes on the order of 0.1 sccm. Therefore, it is necessary to accurately determine the oxygen flow rate for each condition.

  There was a tendency for the substrate heating to grow epitaxially on the high temperature side of about 300 ° C. to 400 ° C., but there were conditions for epitaxial growth by increasing the microwave power even at a low temperature of about 200 ° C. However, epitaxial growth could not be performed when the substrate was not heated.

  For high density ion irradiation, it is also preferable to set the film forming pressure to a predetermined value. The film forming pressure is mainly determined by the Ar flow rate. For example, when the Ar flow rate was set to be about 0.05 to 0.3 Pa, epitaxial growth was possible in this entire range. In addition, there was no great dependence on conditions such as target power and coil current.

  On the other hand, not only the ITO film is directly epitaxially grown on the sapphire substrate, but also the substrate on which the GaN film is epitaxially grown in advance using the MOCVD method on the sapphire substrate and the ITO is formed thereon, the epitaxial growth is still possible. confirmed. That is, it was experimentally confirmed that ITO also grows on the GaN substrate. However, the plane orientation of ITO showed {111} instead of {100}, and the orientation was different. Although it is considered that the plane orientation changes depending on the number of lattices of the base crystal at the start of film growth, the film forming conditions for epitaxial growth are almost the same. In addition, the epitaxial growth of ITO has been confirmed on a YSZ single crystal substrate or the like, and many other substrates can be used as long as the crystal has a close lattice constant.

As Example 1 of the present invention, an ITO film was formed by the method of the present invention using the apparatus of FIG. Substrate heating temperature is varied from no heating to 350 ° C., microwave 12 power 800 W, sputtering power 500 W applied to target 16, argon gas flow rate 40 sccm, oxygen gas flow rate 0.5 sccm, current 26 A of two magnetic coils, substrate The rotation was 15 rpm. Both argon gas and oxygen gas were introduced from the gas inlet 8. The film formation pressure at this time was 0.15 Pa, and the oxygen partial pressure was 1.3 × 10 ⁻³ Pa. As the sample substrate 5, a SUS disk having a diameter of 6 inches and a Si wafer and a sapphire wafer set were used. The thickness of the ITO film to be formed was adjusted by changing the film formation time.

  With respect to the deposited sample, the ITO film formed on the Si wafer was irradiated with a helium-neon laser, and the film thickness and refractive index were measured by ellipsometry. In addition to X-ray diffraction, the sapphire substrate was measured for resistivity ρ by a four-probe method, surface morphology observation using AFM, and average roughness Ra.

  FIG. 2 is an X-ray diffraction pattern of an ITO film formed at 350 ° C. As shown in FIG. 2, the strong peak of ITO is only the cubic {100} series, and no other plane orientation was observed. Further, the φ scan of the (222) plane showed 12-fold symmetry, and it was confirmed that the epitaxial growth was performed in three domains on the sapphire substrate. On the other hand, although not shown, peaks other than the {100} series were observed in the ITO film having a substrate temperature of 250 ° C. or lower, and it was found that all were polycrystalline.

FIG. 3 is a diagram for explaining a change in the surface morphology of the ITO film depending on the film formation temperature. 3, (a) is an ITO film formed without substrate heating, (b) is an ITO film formed at a substrate heating temperature of 150 ° C., (c) is an ITO film formed at a substrate heating temperature of 250 ° C. (D) shows each surface state of the ITO film formed at a substrate heating temperature of 350 ° C. As shown in (a), (b), and (c), the film is a polycrystalline film with severe irregularities at low temperatures. On the other hand, as shown in (d), the ITO film formed at 350 ° C. was an extremely flat epitaxial film, and no clear crystal grain boundary was observed. As for the measurement results of the resistivity ρ and average roughness Ra of the ITO film, the ITO film of (a) is ρ = 4.2 × 10 ⁻⁴ Ωcm, Ra = 0.92 nm, and the ITO film of (b) is ρ = 2.6 × 10 ⁻⁴ Ωcm, Ra = 3.0 nm, the ITO film in (c) is ρ = 1.9 × 10 ⁻⁴ Ωcm, Ra = 4.5 nm, and the ITO film in (d) is ρ = It was 1.4 × 10 ⁻⁴ Ωcm and Ra = 0.48 nm. That is, Ra was as large as several nanometers in the polycrystalline film (a, b, c), whereas it was as low as 0.48 nm in the epitaxial film (d). The resistivity decreased as the substrate temperature increased, and was 1.4 × 10 ⁻⁴ Ωcm for the epitaxial film.

  FIG. 4 shows the results of measuring the resistivity after forming ITO films having different film thicknesses by changing the film formation time using the epitaxial growth conditions. In general, the resistivity of the normal ITO film increases as the film thickness decreases. On the other hand, as shown in FIG. 4, the resistivity of the epitaxial ITO film is approximately 10 nm until the film thickness becomes extremely thin. The rise of was not seen. This is presumably because there is no scattering of electrons at the grain boundaries.

  The ITO film prepared in this example was confirmed to have excellent characteristics that were not found in the past in terms of optical characteristics as well as electrical characteristics. FIG. 5 is a result of comparing the conventional polycrystalline film and the epitaxial film with respect to the transmittance of the ITO film. a represents the transmittance of the epitaxial film, and b represents the transmittance of the polycrystalline ITO film. In the epitaxial film, the transmission wavelength is extended to the short wavelength side, and it has been clarified that it exhibits excellent transparency even with ultraviolet light.

  As described above, the epitaxial ITO film according to the present invention exhibits characteristics superior to those of the conventional ITO film, and is considered to be an extremely useful technique for realizing a device such as an LED.

  In the above embodiment, ITO was described as an example of the conductive thin film. However, the transparent conductive thin film is not only ITO, but also ternary compounds such as IZO, AZO, and GZO, and oxide thin films such as ZnO. However, the same effect can be obtained when the lattice constant with the substrate is close. In this embodiment, ECR plasma film formation is used. However, the high-density plasma is the same for helicon and surface wave, and can be performed by unbalanced magnetron sputtering or ion beam deposition.

DESCRIPTION OF SYMBOLS 1 Plasma production chamber 2 Sample chamber 3 Plasma extraction window 4 Sample stand 5 Sample substrate 6 Exhaust path 7 Substrate heater 8, 9 Gas inlet 10 Magnetic coil 11 Rectangular waveguide 12 Microwave 13 Microwave introduction window 14 Plasma flow 15 Sputtering power supply 16 Target 17 Shutter

Claims (4)

A method of forming a transparent conductive thin film by epitaxially growing a thin film forming material on a crystalline substrate placed in a vacuum chamber, wherein the substrate placed in the vacuum chamber is formed at 300 ° C. to 500 ° C. during the thin film formation. The substrate is heated to 0 ° C., the inert gas pressure is controlled to 0.05 Pa to 0.3 Pa, the oxygen partial pressure is controlled to a range of 5 × 10 ⁻⁴ Pa to 1.5 × 10 ⁻³ Pa, and high-density plasma irradiation is performed on the substrate. A method for forming a transparent conductive thin film characterized by comprising:   The method for forming a transparent conductive thin film according to claim 1, wherein an ECR plasma flow is used as the high-density plasma irradiation method. An apparatus for epitaxially growing a thin film forming material on a crystalline substrate placed in a vacuum chamber to form a transparent conductive thin film,
A vacuum chamber for placing the substrate to form a thin film;
Means for heating the substrate placed in the vacuum chamber to 300 ° C. to 500 ° C. during thin film formation;
Means for introducing an inert gas and an oxygen gas into the vacuum chamber, setting the inert gas pressure to 0.05 Pa to 0.3 Pa, and controlling the oxygen partial pressure to a range of 5 × 10 ⁻⁴ Pa to 1.5 × 10 ⁻³ Pa; ,
An apparatus for forming a transparent conductive thin film, comprising: means for performing high-density plasma irradiation on the heated substrate.   4. The transparent conductive thin film forming apparatus according to claim 3, wherein an ECR plasma flow is used as the high density plasma irradiation method.