JP2002069616A - Production method for thin film of anatase-type titanium oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method for a thin film of anatase-type titanium oxide, capable of film-forming at a low substrate-temperature, and improving a production efficiency because the limitation of kinds of substrates is diminished and an apparatus same as other apparatuses for forming other layers in producing a device of multi-layer structure, due to film-forming by vacuum process. SOLUTION: This thin film of anatase-type titanium oxide is obtained by film-forming metallic titanium or titanium oxide on a substrately, an arc- discharge ion plating by using a pressure-inclined type plasma gun.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a plasma process which can be used for producing an anatase type titanium oxide thin film used as a photocatalyst or a photovoltaic semiconductor.

[0002]

2. Description of the Related Art Generally, a sol-gel method is used to form an anatase type titanium oxide thin film on a substrate such as glass. A step of immersing the substrate in a dipping solution containing titanium tetraisopropoxide and ethanol as main components and heating the pulled substrate at 500 to 1000 ° C. for several minutes is repeated several times to obtain an anatase-type titanium oxide thin film.

[0003]

However, in the above method, since the substrate must be heated to 500 to 1000 ° C., the types of substrates that can be used are considerably limited. In particular, it cannot be applied to inexpensive substrates such as lined glass.
Further, when fabricating a device having a multilayer structure, the characteristics of other layers may be degraded.

Further, the above-mentioned method requires a number of steps since the step of pulling out of the solution and the step of heating need to be repeated several times. In order to increase the production efficiency, a film formation method with as few steps as possible is desired. Generally, when a device having a multilayer structure is manufactured by a vacuum process, it is desirable that the method of forming the anatase-type titanium oxide thin film be a vacuum process in order to increase the manufacturing efficiency.

[0005]

According to the present invention, as a specific means for solving the above-mentioned conventional problems, metal titanium or titanium oxide is formed on a substrate by using an arc discharge plasma by a pressure gradient type plasma gun. An object of the present invention is to provide a method for producing an anatase-type titanium oxide thin film, characterized in that:

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view for explaining a film forming apparatus for manufacturing an anatase-type titanium oxide thin film. In FIG. 1, a cathode 2 and an anode 3 are arranged in a film forming chamber 1. A crucible 13 made of carbon is placed on the anode 3, and the metal crucible 13, which is a raw material for evaporation, is accommodated in the crucible 13.

A susceptor 5 for holding a substrate is disposed above the anode 3 on which the evaporation raw material is placed, and can be heated to a desired temperature by a heater 6. A substrate 7 such as a glass substrate is held by the susceptor 5,
The anode 3 is arranged to face the crucible 13.

A pipe 9 for introducing a gas is provided through the cathode plate 8 in the cathode 2. Further, a gas introduction pipe 10 is also provided in the film forming chamber 1 so that a gas can be introduced without passing through the cathode 2. An exhaust pipe 12 is connected to the film forming chamber 1 via a gate valve 11. The anode 3 and the cathode plate 8 are connected to a DC power supply 14 for plasma generation in a state where the anode 3 and the cathode plate 8 are electrically separated from the film forming chamber 1. The film forming chamber 1 is grounded.

In forming the film, first, the susceptor 5
A desired substrate 7 is placed on the substrate, heated to a predetermined substrate temperature, and kept constant. Next, the inside of the film forming chamber 1 is maintained at a desired pressure by controlling the gas exhaust amount by the gate valve 11 while introducing the atmospheric gas from the pipes 9 and 10 at a predetermined flow rate. After that, a voltage of several tens to several hundreds of volts is applied between the anode 3 and the cathode plate 8 by the DC power supply 14, so that the arc discharge plasma P
Can be generated. A large amount of electrons in the plasma P flow into the crucible 13 on the anode 3 and collide with the metal titanium 4 in the crucible 13 to heat and evaporate the metal titanium 4.

When the evaporated titanium atoms (or clusters) pass through the plasma P of the DC arc discharge, they collide with active species such as electrons, radicals and ions in the plasma P and reach the surface of the substrate 7. Note that radicals and ionic species reach the surface of the substrate 7. Thus, an anatase type titanium oxide thin film is formed on the substrate 7.

Using the apparatus of FIG. 1, a titanium oxide thin film was formed on a glass substrate under the following conditions. Note that argon gas was introduced from a pipe 9 in the cathode 2 and oxygen gas was introduced from a pipe 10. It is preferable to introduce a rare gas such as argon near the cathode in order to stabilize plasma and protect the cathode plate. Substrate: Corning 7059 glass Substrate temperature: 250 ° C. Oxygen flow rate: 200 sccm Argon flow rate: 10 sccm Pressure: 3 × 10 ⁻³ Torr Voltage between cathode and anode: 70 V

Under these conditions, a titanium oxide thin film could be produced at a deposition rate of 1 nm / s. FIG. 2 shows the X-ray diffraction spectrum of this thin film. It can be seen that a single-phase anatase-type titanium oxide thin film is formed on the substrate.

FIG. 3 shows that the substrate temperature during film formation is 50, 150,
The X-ray diffraction spectrum of a film prepared on Corning 7059 glass under the above conditions at 200, 250 and 400 ° C. is shown. From the spectrum, under the condition of 150 ° C., almost no crystalline peak can be confirmed. On the other hand, at a substrate temperature of 200 ° C. or higher,
A clear peak can be confirmed. That is, it can be determined that the anatase type titanium oxide thin film is formed at a substrate temperature higher than 200 ° C. The upper limit of the substrate temperature is
It was confirmed that an anatase-type titanium oxide thin film could be prepared up to about 500 ° C., which is near the melting point of Corning 7059 glass.

FIG. 4 shows X-ray diffraction spectra of films formed on a glass substrate under the above conditions under different oxygen gas partial pressures. The oxygen gas partial pressure was controlled by changing the flow rate of the oxygen gas introduced into the film formation chamber. From the spectrum, it can be confirmed that a single-phase anatase-type titanium oxide thin film was obtained at an oxygen flow rate of 2.5 mTorr or more.

That is, in order to obtain a single-phase anatase-type titanium oxide thin film, it is necessary that the oxygen partial pressure in the film forming chamber is at least a certain rate higher than the partial pressure of titanium vapor, and the oxygen partial pressure is set to 2.5 mTorr or more. Need to be Note that the upper limit of the oxygen gas partial pressure is about 100 mTorr, and in practice, if the pressure exceeds 50 mTorr, the film forming rate is extremely reduced, so that there is no practicality.

When utilizing the photo-induced current of an anatase type titanium oxide thin film for an element, it is necessary to form a titanium oxide film on a transparent conductive film. A titanium oxide film was formed at a substrate temperature of 250 ° C. on a substrate in which a transparent conductive indium tin oxide film was formed on a glass substrate. The manufacturing conditions and steps are the same as in the above embodiment.

FIG. 5 shows an X-ray diffraction spectrum of the prepared film. From the figure, peaks of only anatase type titanium oxide and indium tin oxide are confirmed. That is, it can be determined that the anatase type titanium oxide film is formed without changing the crystal structure of the indium tin oxide film on the substrate during the film formation.

FIG. 6 shows an example of the current-voltage characteristics of the titanium oxide film formed on the transparent conductive film. The current value is clearly different between the case where ultraviolet light is irradiated and the case where ultraviolet light is not irradiated, and it can be seen that a photo-induced current is flowing. Note that the transparent conductive film is not limited to indium tin oxide. It is also possible to form a titanium oxide film on a thin film of indium oxide, zinc oxide or the like.

Further, depending on the flatness of the surface of the transparent conductive film, the value of the photoinduced current changes even in the anatase type titanium oxide thin film formed under the same conditions. FIG. 6 shows current-voltage characteristics when anatase-type titanium oxide thin films were simultaneously formed on two types of indium tin oxide films having different surface flatnesses.

Even if the anatase type titanium oxide thin film is the same,
If the flatness of the surface is different, the value of the photo-induced current is different. The photo-induced currents of the films having a surface roughness of 4.9 nm and 9.7 nm were 100 μA / cm ² when the applied voltage was 1.5 V.
And 140 μA / cm ² . When a titanium oxide thin film is formed on a transparent conductive film having poor flatness, the surface flatness of the titanium oxide thin film deteriorates, so that the surface area increases and the value of the photo-induced current increases. Therefore, the value of the photo-induced current can be controlled by controlling the flatness of the transparent conductive film.

Further, the value of the photo-induced current can be increased by exposing the anatase type titanium oxide thin film produced by the above-mentioned production method to hydrogen plasma generated by a pressure gradient type plasma gun. The device is the same as the configuration of FIG.
Hydrogen gas or a mixed gas of argon and hydrogen flows from the gas introduction pipe 9 or 10 into the film formation chamber. A substrate having an anatase type titanium oxide thin film formed on its surface is arranged on the susceptor 5 and maintained at an appropriate temperature. An arc discharge hydrogen plasma is generated in the chamber 1, and the anatase type titanium oxide thin film is exposed to the hydrogen plasma. Note that since this method is the same as the step of forming the titanium oxide film, there is an advantage that the hydrogen plasma treatment can be continuously performed in the same chamber immediately after forming the titanium oxide film. As an example of the hydrogen plasma treatment, FIG. 7 shows a change in the photo-induced current when the hydrogen plasma treatment is performed under the conditions of a pressure of 5 mTorr, a discharge current of 100 A, and a substrate temperature of 250 ° C.

By applying a hydrogen plasma treatment to a 140 μA / cm ² anatase-type titanium oxide thin film when the photo-induced current value is 1.5 V, the current value becomes 170 μA / cm ^2.
A / cm ² , indicating that the current value was improved by this treatment.

[0023]

According to the present invention, there is provided a vacuum process capable of forming an anatase type titanium oxide film at a low substrate temperature. Further, since the film is formed by the vacuum process, when manufacturing a device having a multilayer structure, the same device as that for forming the other layers can be used, so that the manufacturing efficiency can be increased. Furthermore, changing the flatness of the transparent conductive film surface,
The treatment with hydrogen plasma can improve the photo-induced current value of the anatase-type titanium oxide thin film.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining an embodiment of the present invention.

FIG. 2 is a view showing an X-ray diffraction spectrum of the produced anatase type titanium oxide thin film.

FIG. 3 is a diagram showing X-ray diffraction spectra of anatase-type titanium oxide thin films prepared at several substrate temperatures.

FIG. 4 is a diagram showing an X-ray diffraction spectrum of an anatase type titanium oxide thin film prepared at several partial pressures of oxygen gas.

FIG. 5 is a diagram showing an X-ray diffraction spectrum of an anatase type titanium oxide thin film formed on an indium tin oxide film.

FIG. 6 is a diagram showing a difference in current-voltage characteristics of an anatase-type titanium oxide thin film formed on indium tin oxide films having different surface flatness.

FIG. 7 is a diagram showing changes in current-voltage characteristics due to hydrogen plasma processing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Film-forming chamber 2 ... Cathode 3 ... Anode 4 ... Titanium metal 5 ... Susceptor 6 ... Heater 7 ... Substrate 8 ... Cathode plate 9 ... Gas introduction pipe 10 ... Gas introduction pipe 11 ... Gate valve 12 ... Exhaust pipe 13 ... Crucible 14 ... DC power supply P ... Plasma

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Masanori Tani 2-9-13-1 Nakameguro, Meguro-ku, Tokyo Inside Stanley Electric Co., Ltd. (72) Masami Kumei 2-9-1-13 Nakameguro, Meguro-ku, Tokyo No. F term in Stanley Electric Co., Ltd. (reference) 4G047 CA02 CB04 CC03 CD02 CD07 4K029 AA09 BA48 BB02 BD00 CA03 CA04 DD06 EA03 EA05 EA08 GA02

Claims (6)

[Claims] 1. A method for producing an anatase-type titanium oxide thin film, comprising forming metal titanium or titanium oxide on a substrate using arc discharge ion plating with a pressure gradient plasma gun. 2. The method for producing an anatase type titanium oxide thin film according to claim 1, wherein the substrate temperature during the film formation is 200 to 500 ° C. 3. An oxygen gas partial pressure in a film forming chamber is 2.5 mTo.
The method for producing an anatase-type titanium oxide thin film according to claim 1, wherein the thickness is at least rr. 4. The method for producing an anatase-type titanium oxide thin film according to claim 1, wherein an anatase-type titanium oxide thin film is formed on the transparent conductive film. 5. The method according to claim 4, wherein the photoinduced current value of the anatase-type titanium oxide thin film is controlled by changing the flatness of the surface of the transparent conductive film. 6. The method for producing an anatase-type titanium oxide thin film according to claim 1, wherein the anatase-type titanium oxide thin film is further treated with hydrogen plasma generated by a pressure gradient plasma gun. .