JP2582741B2 - Method of forming epitaxial thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal which is an important component for fully producing the functions of these elements when manufacturing functional elements such as integrated electronic elements and waveguide type optical elements. The present invention relates to a method for forming a thin film.

[0002]

2. Description of the Related Art As is well known, a semiconductor device and a waveguide type optical device are manufactured by using thin film formation and lithography techniques. At this time, as a thin film forming technique, an epitaxial growth technique for growing a thin film in a single crystal state on a single crystal substrate while maintaining a certain relationship such that the axis is common to the crystal lattice of the substrate is important. In order to epitaxially grow a target substance, a substrate having a target orientation is manufactured using a single crystal having a crystal structure and a lattice constant close to the substance, and atoms and molecules serving as components are vapor-phased on the substrate. Alternatively, a method of depositing via a liquid phase is used. For growth via the gas phase, methods such as vacuum evaporation, sputtering, and CVD are used.

FIG. 3 is a conceptual view of a magnetron sputtering apparatus used in a conventional epitaxial growth method. A target 3 for emitting atoms and molecules of a raw material is placed in a vacuum chamber 1 on a substrate heater 11 mounted on a substrate heater 11. 2, and a magnet 12 is arranged around the periphery between the target 3 and the substrate 2. 13 is
A matching box 14 is a high-frequency power supply.
In the above-described apparatus, the atoms and molecules of the raw material are released from the target 3 by the plasma sputtering method, and the single crystal substrate 2 heated to a high temperature by the substrate heater 11 is placed on the single crystal substrate 2.
A single crystal thin film is epitaxially grown.

[0004]

By the way, in any of the above-described formation methods via the gas phase, it is not enough for the atoms and molecules arriving at the substrate to move and rearrange to the correct positions in the crystal lattice. Therefore, it is necessary to keep the substrate at a sufficiently high temperature. Then, in order to increase the growth rate of the epitaxial film, atoms deposited on the substrate per unit area and unit time,
The number of molecules must be increased, but the temperature of the substrate must be further increased to increase the energy required for rearrangement.

On the other hand, when the substrate is heated to a high temperature, atoms and molecules are deposited on the substrate, and a phenomenon of re-evaporation and flying off occurs at the same time, so that the crystal growth is remarkably reduced as the temperature rises. As described above, the rate of epitaxial growth is limited by the conflicting demands of increasing the temperature of the substrate required to activate the rearrangement and suppressing the temperature of the substrate required to suppress re-evaporation. For example, a YBa ₂ Cu ₃ O ₇ film formed by sputtering is 3,600 Å / H, and a LiNbO ₃ film is 1,000 Å / H.
Is known as the limit of the growth rate, and is inefficient from the viewpoint of device production. Further, the substrate needs to be heated to a high temperature in order to activate the rearrangement as described above, and the type of the substrate to be used is also limited to those having a high melting point.

Further, in the epitaxial growth method via a liquid phase, a substrate is immersed in a melt of a target substance to grow a thin film by a solidification reaction. The substrate used at this time must be a single crystal of a substance that has a higher melting point than the target substance and does not react. An example of this is LiTaO.
₃ (Melting point 1,470 ° C.) LiNbO ₃ on the substrate (Melting point 1,2
(30 ° C.) is known. Growth from the liquid phase is faster than growth from the gas phase,
Combinations of thin film materials and substrates that satisfy favorable conditions such as crystal structure, melting point, and non-reactivity are extremely limited. For that purpose, another compound is mixed with the target substance as a flux, a solution having a temperature lower than the original melting point is prepared, and a single crystal having the same composition as the target substance is immersed as a substrate as a substrate to deposit a thin film. A method is conceivable. However, this method has a disadvantage that the flux cannot be completely prevented from being taken into the film as an impurity. The object of the present invention has been made in view of the above circumstances, and is to provide a method for efficiently forming a single crystal thin film by a vapor phase method without using a single crystal of a substance having a high melting point as a substrate. is there.

[0007]

According to the present invention, instead of forming a film on a substrate and performing epitaxial growth simultaneously with the conventional method, the temperature of the substrate is reduced when a thin film is formed on the substrate via a gas phase. An amorphous film made of the constituent elements is formed on the substrate at a temperature below the temperature at which the film does not crystallize, and then a heat treatment is performed to heat the amorphous film to a temperature higher than the crystallization temperature. Let it. Further, a crystallization heat treatment is performed in advance.
Data from the evaporation of each constituent element
At the time of amorphous film formation, based on the data,
The composition of the film after heat treatment matches the composition of the target film.
Thus, the composition of the amorphous film is controlled .

[0008] upper Symbol data in advance, by performing crystallization heat treatment and the amorphous film formation can be obtained by previously measuring the consumption loss of the constituent elements. Also, once this data is obtained, it can be used as it is in the subsequent thin film formation, so that the working efficiency is not hindered. Further, it is desirable that the crystallization heat treatment be performed in an atmosphere having a pressure higher than the atmosphere pressure during the amorphous film formation.

[0009]

At low temperatures, where the rearrangement of atoms and molecules on the substrate surface is inactive, it is difficult to form nuclei for crystallization, but there are fewer atoms and molecules that fly away by re-evaporation. Therefore, according to the method of the present invention, a thin film having an amorphous structure can be formed at a high speed by a gas phase method. The amorphous thin film is then
It is crystallized by heating above the crystallization temperature. At this time, if nucleation is suppressed by using a substrate having the same crystal structure or lattice constant as the substrate, the amorphous film can be made into a single crystal having a constant epitaxy relationship with the substrate. Since the temperature for crystallization is lower than the melting point of the target material, the composition does not change significantly due to the evaporation of the component elements during the heat treatment. Therefore, by forming an amorphous film in which elements that easily evaporate are enriched in advance, a single crystal having a desired composition can be efficiently obtained. The amorphous state is unstable in terms of free energy, and when high pressure is applied,
Transform to a crystalline state at lower temperatures. Further, by performing the crystallization heat treatment at a higher pressure and at a lower temperature, nucleation and evaporation of component elements can be suppressed, and a high-quality single crystal film can be obtained. Further, since the substrate heating temperature can be lowered, it is not necessary to select a substrate having a high melting point, and the degree of freedom in material selection is increased.

[0010]

FIG. 1 and FIG. 2 show an embodiment of the present invention.
Description will be made based on the drawings. FIG. 1 schematically shows an ion beam sputtering apparatus used for forming a single crystal thin film of ferroelectric LiNbO ₃ . A substrate 2 made of a Z-cut LiTaO ₃ single crystal is arranged in a vacuum chamber 1, and two targets 3 a and 3 b are arranged to face this substrate 2. The targets 3a and 3b are compound targets having different contents of Li and Nb.
The target 3b has a composition with a large Li content, and the target 3b has a composition with a small Li content. This target 3
The ion sources 4a and 4b are installed toward the points a and 3b. The vacuum chamber 1 has an exhaust port 5 for evacuating the chamber 1 and a gas inlet 6 for introducing argon gas into the chamber 1. In addition to the vacuum chamber 1, a high-pressure vessel 7 for heat treatment is prepared. The high-pressure vessel 7 is connected to a high-pressure oxygen cylinder 8 via a valve, and a heater 9 for heating the substrate. Are located.

Next, a method of an embodiment using the above apparatus will be described. The inside of the vacuum chamber 1 is evacuated by a vacuum pump (not shown) connected to the exhaust port 5, and then an argon gas is introduced into the vacuum chamber 1 from the gas inlet 6, and the inside of the vacuum chamber 1
Adjusted to × 10 ^-5 Torr. Next, the ion source 4a,
4b and argon in the target were ionized, accelerated at 1200 V and extracted as an ion beam, and targets 3a and 3b were sputtered. The atoms and molecules that have been knocked out of the targets 3a and 3b by sputtering are deposited on the substrate 2 in an amorphous state. This film formation is carried out at room temperature for 30 minutes.
An amorphous film 10 having a thickness of 5,000 angstroms was formed. When this is subjected to crystallization heat treatment, there is a problem that Li evaporates and the chemical composition changes. Therefore,
In order to enrich Li in advance, the current value of the Ar ⁺ ions incident on the target 3a having a large Li content and the target 3b having a small Li content is set to a ratio of 0.7: 1.
1.0 for the Li / Nb ratio of the amorphous film 10
Was controlled to 1.8. Further, the substrate 2 is housed in the high-pressure vessel 7, the valve of the high-pressure oxygen cylinder 8 is opened, oxygen is introduced into the high-pressure vessel 7, and the heater 9 is energized to heat the amorphous film 10. Heat treatment was performed for 60 minutes.

The structure of the film 10a after the heat treatment was examined by X-ray and RHEED (reflection high energy electron diffraction).
Film 10a heat-treated at 400 ° C. in 1 atm of oxygen gas
Remained amorphous, but at 550 ° C., a polycrystalline LiNbO ₃ film was obtained, and further, a monocrystalline LiNbO ₃ film was obtained at 600 ° C. On the other hand, when the oxygen gas pressure was increased to 10 atm, a single-crystal LiNbO ₃ film was obtained even when heat-treated at 550 ° C.
As is clear from this example, the nucleation is effectively suppressed by the heat treatment under pressure and low temperature, and the crystallization is promoted by the heat treatment under pressure. Furthermore, according to the present invention, a target to which a trace amount of an active element is added is used,
Alternatively, by using the third target, it is possible to easily form a single crystal thin film in which physical properties such as electric and optical properties are controlled by doping with an active element.

[0013]

As described above, according to the method for forming an epitaxial thin film of the present invention, first, an amorphous film is formed on a substrate at a low temperature.
Since the amorphous film is heated at a temperature higher than the temperature at which crystallization occurs for a short time, it is possible to form the amorphous film at a speed of 10 times or more as compared with the conventional epitaxial film formation without using a special apparatus. Also, a large number of amorphous films can be formed at once. Further, since the subsequent heat treatment can be performed in a short time, an epitaxial thin film can be efficiently formed, and the process time can be remarkably reduced as compared with the conventional method. In addition, a material having a low melting point can be used for the substrate to be used, and the degree of freedom in material selection is greatly expanded. Furthermore, in the case of forming a single crystal film doped with active trace elements in one deposition process is re-evaporation of the doping element is a particular problem, based on the previously obtained erasing loss data, amorphous deposition
Controls the time component, so that the target component epitaxy
There is an effect that a high quality film can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus used in an embodiment.

FIG. 2 is a schematic enlarged view showing a substrate and a thin film obtained in an example.

FIG. 3 is a schematic diagram of an apparatus used in a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum tank 2 Single crystal substrate 3a target 3b target 7 High pressure vessel 9 Heater for substrate heating

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Toshifumi Yoneuchi 1-3 Takanodai, Yokkaido, Chiba Japan Steel Works, Ltd. (72) Inventor Masafumi Miyashita 1-2-1, Yurakucho, Chiyoda-ku, Tokyo Hibiya Mitsui Building Co., Ltd. Japan Steel Works (56) References JP-A-3-184347 (JP, A) JP-A-64-48411 (JP, A) JP-A-56-131934 (JP, A) JP-A-51-115770 (JP, A) A)

Claims (2)

(57) [Claims] The temperature of a substrate is set to a temperature at which crystallization of a film does not occur.
Amorphous to the substrate via the gas phase while maintaining
Temperature, and then the temperature at which the amorphous film crystallizes.
Heat treatment to heat the amorphous film
Method of forming epitaxial thin film grown by epitaxial growth
In the crystallization heat treatment
Loss data obtained during
Based on the above data, the purpose of the composition of the film after heat treatment is
Composition of the amorphous film to match the composition of the film
Method for forming epitaxial thin film, characterized by controlling temperature 2. The crystallization heat treatment is performed during the amorphous film formation.
It is characterized in that it is performed in an atmosphere with a pressure higher than the atmospheric pressure
The method for forming an epitaxial thin film according to claim 1,