JP4388294B2 - Heat treatment method for single crystal substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat treatment method for a single crystal substrate applied to a thin film growth substrate such as a dielectric material, a magnetic material, and a high-temperature superconductor, or a material for elucidating the expression mechanism of a photocatalytic material.
[0002]
[Prior art]
It is known that the flatness at the atomic level on the surface of a single crystal substrate is greatly affected in the production of a high-quality epitaxial film. Until now, for SrTiO ₃ single crystal substrates and sapphire single crystal substrates, a processing technique capable of obtaining extremely high flatness has been developed. For example, Japanese Patent No. 3252552, Japanese Patent No. 3015261, and Patent No. No. 3244966 is proposed, and the current situation is that an ultra-flattening technique has been established.
[0003]
[Problems to be solved by the invention]
On the other hand, with regard to the TiO ₂ single crystal, many studies have been conducted for elucidation of the mechanism of the photocatalyst and for the application of thin film electronic devices.
However, as far as the inventor knows, there has been no systematic study so far on the atomic level control of the surface of the TiO ₂ single crystal substrate.
An object of the present invention is to enable the surface of a TiO ₂ rutile single crystal substrate (hereinafter abbreviated as “rutile single crystal substrate”) to be highly planarized at an atomic level.
[0004]
[Means for Solving the Problems]
In the present invention, the rutile single crystal substrate having a selected plane orientation is baked for a predetermined time using a heating device such as an electric furnace at a heating temperature of about 300 ° C. to about 1,100 ° C. in the atmosphere. A method of obtaining a height atomic step and terrace structure of about 0.22 nm to about 0.46 nm on the surface of the substrate.
The plane orientation of the rutile single crystal substrate to be heat-treated is selected. The selected plane orientation is a plane orientation that can control the atomic step and terrace structure at a desired height, or a plane orientation that has a lattice constant that matches a crystal lattice of a different material grown on a rutile single crystal substrate. The plane orientation is selected from among (110), (100), (001), (111) and (101), and the range of selection is at least one and at most all plane orientations.
The heating temperature is preferably in the range of about 300 ° C to about 1,100 ° C. When the temperature is lower than about 300 ° C, it is difficult to obtain a desired step on the surface of the rutile single crystal substrate, and when the temperature is higher than about 1,100 ° C, the step height becomes uneven and the surface is highly flat. It may be difficult to obtain a substrate having the property.
The heating time may be about 1 hour in the above heating temperature range, but may be less than 1 hour or more than 1 hour. However, the heating time is relatively determined in relation to the heating temperature, and when the temperature is high, the heat treatment can be performed for a short time, and the treatment can be performed at a low temperature by taking time.
In the stage of firing the rutile single crystal substrate, there are both a case where the substrate surface is washed with a cleaning agent as a pretreatment and a case where the substrate is baked without washing. It is desirable to make it easier to obtain a certain terrace structure. In the cleaning step, which is a pretreatment step, the above effect is enhanced by cleaning with a cleaning agent such as an organic solvent and then with an acidic solvent. As the organic solvent, acetone, ethanol or the like is used, and as the acidic solvent, hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid or the like is used.
[0005]
[Action]
By firing the rutile single crystal substrate having the selected plane orientation (110), (100), (001), (111) or (101) at a predetermined temperature for a predetermined time, the surface of the rutile single crystal substrate is A terrace structure is formed that is an ultra-flat surface with atomic level steps of the desired height.
[0006]
【Example】
Example 1
The surface of the rutile single crystal substrate having the plane orientation (110) is first cleaned with an organic solvent, then cleaned with an acidic solvent, and then the polished rutile single crystal substrate is heated to 400 ° C. in the atmosphere in an electric furnace. Baked for 1 hour at temperature.
Similarly, different heating temperatures for the rutile single crystal substrate, i.e., 500 ° C, 600 ° C, 700 ° C, 800 ° C, 900 ° C, and 1,000 ° C, are also used for one hour. Baked.
As described above, with respect to 7 cases having the above-mentioned plane orientation, the lower limit set to 400 ° C., the upper limit set to 1,000 ° C., and the heating temperature sequentially increased to 100 ° C., individually fired and then subjected to an atomic force microscope. When the surface of the rutile single crystal substrate was observed, a step and terrace structure having a height of 0.32 nm was formed on the surface at any heating temperature in the seven cases. The terrace width changed relatively depending on the crystal axis accuracy of the surface of the rutile single crystal substrate, that is, the deviation from the plane orientation (110).
In this observation, SPA300 / SPI3800 manufactured by SII was used as an atomic force microscope (AFM). The observation range is 1 × 1 μm ² .
1A and 1B are a perspective view and a cross-sectional view of an AFM image of an orientation plane (110) in the rutile single crystal substrate after baking at a heating temperature of 900 ° C. On the surface of the rutile single crystal substrate, a structure having Step 2 with a height of 0.32 nm and Terrace 1 with a terrace width exceeding 100 nm was formed.
[0007]
(Example 2)
The surface of the rutile single crystal substrate having a plane orientation (100) is first cleaned with an organic solvent, then cleaned with an acidic solvent, and then the polished rutile single crystal substrate is heated to 400 ° C. in the atmosphere in an electric furnace. Baked for 1 hour at temperature.
Similarly, different heating temperatures for the rutile single crystal substrate, namely, 500 ° C, 600 ° C, 700 ° C, 800 ° C, 900 ° C, 1,000 ° C, and 1,100 ° C, respectively. Each was baked for 1 hour.
As described above, 8 cases having the above-mentioned plane orientation, the lower limit set to 400 ° C., the upper limit set to 1,100 ° C., and the heating temperature sequentially increased to 100 ° C. were each fired and then subjected to rutile using the atomic force microscope. When the surface of the single crystal substrate was observed, a step and terrace structure having a height of 0.46 nm was formed on the surface at any heating temperature. The terrace width relatively changed depending on the crystal axis accuracy of the surface of the rutile single crystal substrate, that is, the deviation from the plane orientation (100). The observation range is 1 × 1 μm ² .
2A and 2B are a perspective view and a cross-sectional view of an AFM image of the orientation plane (100) in the rutile single crystal substrate after baking at a heating temperature of 800 ° C. On the surface of the rutile single crystal substrate, a structure having Step 2 with a height of 0.46 nm and Terrace 1 with a terrace width exceeding 100 nm was formed.
[0008]
(Example 3)
The surface of the rutile single crystal substrate was heat-treated under the same conditions as those shown in Example 1 except for the selected plane orientation and heating temperature.
In this example, the plane orientation was (001), and the heating temperature was two cases of 800 ° C and 900 ° C.
When the surface of the fired rutile single crystal substrate was observed with the atomic force microscope, a step and terrace structure having a height of 0.30 nm were formed on the surface at any heating temperature. The terrace width relatively changed depending on the crystal axis accuracy of the surface of the rutile single crystal substrate, that is, the deviation from the plane orientation (001). The observation range is 1 × 1 μm ² .
FIGS. 3A and 3B are a perspective view and a cross-sectional view of an AFM image of the orientation plane (001) in the rutile single crystal substrate after baking at a heating temperature of 900 ° C. FIG.
On the surface of the rutile single crystal substrate, a structure having a step 2 having a height of 0.30 nm and a terrace 1 having a terrace width exceeding 100 nm was formed.
[0009]
(Example 4)
The surface of the rutile single crystal substrate was heat-treated under the same conditions as those shown in Example 1 except for the selected plane orientation and heating temperature.
In this example, the plane orientation was (111), and the heating temperature was 500 ° C, 600 ° C, 700 ° C, 800 ° C and 900 ° C.
When the surface of the rutile single crystal substrate after firing was observed with the atomic force microscope, a step and terrace structure having a height of 0.22 nm was formed on the surface of the rutile single crystal substrate in any case (heating temperature). It was. The terrace width relatively changed depending on the crystal axis accuracy of the surface of the rutile single crystal substrate, that is, the deviation width from the plane orientation (111). The observation range is 1 × 1 μm ² .
4A and 4B are a perspective view and a cross-sectional view of an AFM image of the orientation plane (111) in the rutile single crystal substrate after baking at a heating temperature of 800 ° C. On the surface of the rutile single crystal substrate, a structure having Step 2 with a height of 0.22 nm and Terrace 1 with a terrace width exceeding 80 nm was formed.
[0010]
(Example 5)
The surface of the rutile single crystal substrate was heat-treated under the same conditions as those shown in Example 1 except for the selected plane orientation and heating temperature.
In this example, the plane orientation was (101), and the heating temperatures were 600 ° C, 700 ° C, and 800 ° C in three cases.
When the surface of the fired rutile single crystal substrate was observed with the atomic force microscope, a step and terrace structure with a height of 0.25 nm was formed on the surface of the rutile single crystal substrate in any case (heating temperature). It had been. The terrace width changed relatively depending on the crystal axis accuracy of the surface of the rutile single crystal substrate, that is, the deviation width from the plane orientation (101). The observation range is 1 × 1 μm ² .
5A and 5B are a perspective view and a cross-sectional view of an AFM image of the orientation plane (101) in the rutile single crystal substrate after baking at a heating temperature of 800 ° C. On the surface of the rutile single crystal substrate, a structure having Step 2 with a height of 0.25 nm and Terrace 1 with a terrace width exceeding 50 nm was formed.
[0011]
【The invention's effect】
According to the present invention, since the surface of a rutile single crystal substrate can be flattened at the atomic level, it can be applied to a material for elucidating the mechanism of expression of a photocatalyst and can be applied to a thin film electronic device having good performance. .
[Brief description of the drawings]
FIGS. 1A and 1B are a perspective view and a cross-sectional view of an AFM image of an orientation plane (110) in a rutile single crystal substrate, respectively.
FIGS. 2A and 2B are a perspective view and a cross-sectional view of an AFM image of an orientation plane (100) in a rutile single crystal substrate, respectively.
3A and 3B are a perspective view and a cross-sectional view of an AFM image of an orientation plane (001) in a rutile single crystal substrate, respectively.
4A and 4B are a perspective view and a cross-sectional view of an AFM image of an orientation plane (111) in a rutile single crystal substrate, respectively.
FIGS. 5A and 5B are a perspective view and a cross-sectional view of an AFM image of an orientation plane (101) in a rutile single crystal substrate, respectively.
[Explanation of symbols]
1 terrace 2 steps

Claims (6)

The TiO ₂ rutile single crystal substrate was baked for 1 hour at a heating temperature of 400 ° C. to 1,000 ° C. in the atmosphere, and 0.32 nm on the surface of the TiO ₂ rutile single crystal substrate having the selected plane orientation (110). A method for heat-treating a single crystal substrate, characterized in that an atomic step and a terrace structure having a height of 5 are obtained. The TiO ₂ rutile single crystal substrate was baked for 1 hour at a heating temperature of 400 ° C. to 1,100 ° C. in the atmosphere, and 0.46 nm was formed on the surface of the TiO ₂ rutile single crystal substrate having the selected plane orientation (100) . A method for heat-treating a single crystal substrate, characterized in that a height atomic step and a terrace structure are obtained . TiO ₂ The rutile single crystal substrate was baked at a heating temperature of 800 ° C. to 900 ° C. in the atmosphere for 1 hour, and the above TiO having the selected plane orientation (001) ₂ A heat treatment method for a single crystal substrate, characterized in that an atomic step and terrace structure having a height of 0.30 nm are obtained on the surface of the rutile single crystal substrate. TiO ₂ The rutile single crystal substrate is baked at a heating temperature of 500 ° C. to 900 ° C. in the atmosphere for 1 hour, and the above TiO having the selected plane orientation (111) ₂ A heat treatment method for a single crystal substrate, characterized in that an atomic step and a terrace structure having a height of 0.22 nm are obtained on the surface of the rutile single crystal substrate. TiO ₂ The rutile single crystal substrate is baked in the atmosphere at a heating temperature of 600 ° C. to 800 ° C. for 1 hour, and the above TiO having the selected plane orientation (101) ₂ A heat treatment method for a single crystal substrate, characterized in that an atomic step and a terrace structure with a height of 0.25 nm are obtained on the surface of the rutile single crystal substrate. TiO as pretreatment ₂ 6. The heat treatment method for a single crystal substrate according to claim 1, wherein the surface of the rutile single crystal substrate is washed with an organic solvent and then washed with an acidic solvent.

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