JPH03228805A - Production of oxide thin film - Google Patents

Abstract

PURPOSE:To stably obtain an oxide single crystal thin film having a density close to that of a bulk with good reproducibility at the time of producing an oxide thin film by oxygen beam irradiation vapor deposition by using a metal fluoride as the material for forming the thin film. CONSTITUTION:A film forming chamber 14 is evacuated to a high vacuum, and gaseous O2 is introduced from the gas inlet 9 of an ion source 8 to keep the gas in a plasma chamber 11 at a pressure necessary to produce plasma. When the elements other than oxygen are vapor-deposited, vapor deposition is carried out on a substrate 2 from the K-cell vaporization sources 4a and 4b or an electron beam vaporization source 3. In this case, the fluoride such as BaF2 are packed in the sources 4a, 4b or 3 in place of an elemental metal (Ba, etc.) and vaporized to obtain a stable vaporizing rate. The oxygen ion beam or oxygen plasma beam is produced in the chamber 11, drawn out with specified energy and used to irradiate the substrate 2 on which a thin film is being formed. Besides, nitrides can be used instead of the fluorides.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing various oxide thin films used for superconducting elements, optical elements, piezoelectric elements, surface elastic elements, etc.

[Prior Art] Conventionally, the most commonly used method for producing oxide thin films is sputtering.

However, as is well known, the sputtering method has disadvantages in that the amount of oxygen cannot be sufficiently controlled, and the metal composition ratio cannot be sufficiently controlled due to changes in the target composition ratio over time. Because of this drawback, it has been difficult to obtain sufficient film quality by sputtering, especially when precise compositional control is required, such as when producing an oxide single crystal thin film.

In order to overcome these drawbacks of the sputtering method and obtain a dense oxide thin film with precisely controlled composition, an oxygen beam irradiation deposition method (Conventional Example 1; Japanese Patent Application No. 63-42211) was invented. The apparatus used in this method is shown in FIG.

In the figure, numeral 1 indicates a substrate holder, 2 indicates a substrate, 3 indicates an electron beam evaporation source, 4 indicates a cell, 5 indicates an exhaust port, 6 indicates a Faraday cup, and 7 indicates a film thickness. monitor,
8 indicates an ion source, 9 indicates a gas inlet, 10 indicates a microwave source, 11 indicates a plasma chamber, 12 indicates a neutralizing filament, 13 indicates a substrate heater, and 14 indicates a film forming chamber. be.

The conventional oxygen beam irradiation deposition method using this equipment is
This method combines oxygen beam irradiation with a vapor deposition method that precisely controls the evaporation rate, and is characterized by the ability to easily control the thin film composition, including oxygen, and to produce dense films. As a specific method, all of the thin film constituent materials evaporated by the electron beam evaporation source 3 or single-cell evaporation sources 4a and 4b shown in FIG. An oxide thin film is produced in vacuum by irradiating the substrate 2 with an oxygen ion beam having an energy of 10 to 500 eV at the same time as thin film deposition.

In order to take advantage of the features of this method, it is important to precisely control the thin film composition in addition to controlling the oxygen irradiation amount, and to do this, it is necessary to control the evaporation rate using an evaporation source that is as stable as possible. . As mentioned above, the one-cell evaporation source generally has a higher stability of evaporation rate than the electron beam evaporation source.

However, controlling a stable evaporation rate is difficult. The active metal reacts with oxygen and water vapor remaining in the atmosphere or in the film forming chamber to form oxides and hydroxides. As a result, the evaporation rate becomes unstable over time. In addition, in K-cells, it is difficult to evaporate elements with evaporation temperatures exceeding 1,500°C, and even if the temperature is below 1,500°C, as the temperature rises above 1,300°C, there are problems such as impurity contamination and an extreme reduction in the service life of the cell's constituent materials. There is.

On the other hand, in order to overcome the instability of evaporation caused by this active metal, a method for producing oxide thin films using a metal fluoride such as BaF2 as an evaporation source has been developed in a general evaporation method that does not use oxygen beam irradiation. Published (Conventional example 2
; Mankiewich et al.

Appl, Phys, Lett, 51 (1987
)1753. And, conventional example 3; Manki
Ewich et al, Mat, Res.

Symp, Proc, 99 (198g) 119. )
. In the conventional example 2, BaF is used instead of metal Ba.
It is stated that by using No. 2, evaporation was performed stably and the controllability of the thin film composition was improved. However, as described in Conventional Example 3, BaF2 does not dissociate during vapor deposition depending on the general vapor deposition method.
In order to dissociate F2 and remove unnecessary F2 from the thin film, it was necessary to perform heat treatment after vapor deposition in an atmosphere containing water vapor.

[Problems to be Solved by the Invention] The present invention provides an oxide thin film containing as a constituent element a chemically active metal whose evaporation is unstable or a metal that requires high temperature (1300°C or higher) for vapor deposition. It is an object of the present invention to provide a manufacturing method that precisely controls the composition and oxygen composition and does not require processes such as heat treatment after film formation.

[Means for Solving the Problems] In order to achieve the above-mentioned problems, the present invention evaporates and deposits an oxide thin film constituent raw material on a substrate in a high vacuum, and at the same time evaporates oxygen ions with a constant energy. In the method for producing an oxide thin film in which the substrate is irradiated with oxide to form an oxide thin film on the substrate, a metal fluoride or a metal nitride is used as a raw material for forming the oxide thin film. , the degree of vacuum is l X I O”
A vacuum higher than Torr is preferable. Further, it is preferable that the -constant energy oxygen ions are beam-shaped oxygen plasma accelerated to 10 to 500 eV, or beam-shaped oxygen ions extracted from oxygen plasma and accelerated to 10 to 500 eV. Furthermore, the beam-shaped oxygen ions may be neutralized.

[Function] According to the present invention, metal elements that can be evaporated in a sufficiently stable manner remain as single metals, and metal elements that are difficult to evaporate stably because they are chemically active or have a high evaporation temperature are By depositing a thin film on a substrate by well-controlled molecular beam evaporation using an evaporation source filled with oxide thin film constituent elements in the form of metal fluorides or metal nitrides, the metal composition can be changed. A precisely controlled oxide thin film can be obtained.

Further, according to the present invention, at the same time as the above thin film deposition,
By irradiating the deposited film on the substrate with an oxygen plasma beam or oxygen ion beam with an energy of 00 eV,
Sufficient oxidation occurs even in vacuum, and the composition of oxygen is precisely controlled, and the vaporized compounds such as metal fluorides or metal nitrides are dissociated on the substrate during thin film deposition due to the effect of the oxygen beam irradiation, and Since unnecessary elements in compounds such as fluorine can be removed by evaporation from the deposited thin film, there is no need for processes such as heat treatment after thin film deposition, and an oxide thin film without crystal defects can be produced.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but before that, the fundamental structure of the present invention will be explained.

As the oxide thin film manufacturing apparatus used in the method of the present invention, the conventional apparatus shown in FIG. 1 can be used.

According to the method of the present invention, the apparatus shown in FIG. 1 is operated as follows. First, the film forming chamber 14 is made to have a vacuum higher than 1X10-5 Torr using a cryopump or the like. After that, oxygen gas is introduced from the gas introduction port 9 of the ion source 8,
Oxygen gas is introduced into the plasma chamber 11 until the gas pressure (degree of vacuum from I x 10'' to I x 10-5 Torr) necessary to generate plasma reaches, for example, I x 10-' Torr. Then, , in molecular beam evaporation in which elements other than oxygen are deposited, the degree of vacuum (e.g.
1 x 10-' Torr), the K-cell evaporation sources 4a, 4
(b) Vapor deposition is performed on the substrate 2 from the electron beam evaporation source 3.

At this time, the molecular beam intensity is monitored by a monitor 7 such as a crystal oscillator or an ion gauge, and by feeding this back to the evaporation sources, the input power to each evaporation source can be controlled.

Here, instead of filling the one-cell evaporation sources 4a, 4b or the electron beam evaporation source 3 with a single metal (e.g., Ha), a compound (e.g., a fluoride such as BaF2 or a nitride such as BaN6) is used. By filling it with metal and evaporating it in the same way as a single metal, it is possible to obtain a more stable evaporation rate than when using a single metal. Therefore, the composition of the metal in the thin film can be controlled more precisely. Similarly, if a compound such as YF3 is used instead of metal Y, the evaporation temperature can be lowered significantly (e.g., by 300°C or more), which can reduce impurities generated from the evaporation source and reduce K- The effect of reducing destabilization of the evaporation rate due to fatigue of the cell constituent materials can be obtained.

Further, it is generated in the plasma chamber 11 and has a voltage of 10 to 500 eV.
The oxygen ion beam or oxygen plasma beam extracted with energy of is irradiated onto the substrate 2 on which the thin film is being deposited. At this time, the oxygen ion beam is monitored by the Faraday cup 6 and fed back to the microwave source to control the ion current value. At this time, the current value of oxygen ions in the irradiated oxygen ion beam or oxygen plasma beam is variable from 10 to 2000 μA/cm 2 .

The energy of the oxygen ion beam or oxygen plasma beam is such that it supplies the energy necessary to generate thin film crystals without sputtering the thin film or creating crystal defects in the thin film, and has enough energy to dissociate compounds such as BaF2. is set to have.

With such a vapor deposition method, the composition including oxygen can be more stably controlled than with conventional sputtering methods. As a result, an oxide thin film whose composition is precisely controlled can be obtained. In addition, compared to conventional vapor deposition methods that use compound evaporation sources to precisely control the composition, there is no need for an annealing process after film formation, which reduces the number of steps and allows the same film to be formed after film formation. Another advantage is that it enables new processes for device applications, such as the continuous deposition of different thin films indoors.

(Example 1) First production of Ba, YCu, O, film
The degree of vacuum in the film forming chamber 14 shown in the figure is evacuated to lXl0°6 Torr, and then oxygen gas is introduced from the gas inlet 9, and the degree of vacuum in the ion source 8 and the film forming chamber 14 is reduced to lXl0"' T.
It was set as orr. At this time, the oxygen ions generated in the plasma chamber 11 are extracted with an energy of 50 eV, and the Faraday cup 6 of the ion current monitor near the substrate is used to extract the oxygen ions at 250 μA/
The microwave incident power to the ion source was set so as to give an ion current of 1 cm''.

The substrate is 5rTiO, (100) plane and (110
) surface was used. Here, one cell 4 prepared in advance is filled with BaF2, YF, Cu, and evaporated, and the composition of the film deposited on the substrate 2 is Ba:Y:Cu.
= 2:1:3 and the deposition rate on the substrate 2 was 0.8 A/s, the temperature of the cell was controlled separately, and at the same time the oxygen ion beam was heated at 50 eV,
5rTiO, (100
) and (110) plane substrates, polycrystalline or single crystal thin films of Ba, YCuO,s in stoichiometric ratios were obtained. In particular, increase the substrate temperature from 400℃ to 800℃.
Ba, YCuO by keeping at a constant temperature between ℃
A single crystal film of , , was obtained. At this time, 5rTiO, (1
The (001) plane of Ha2YCuO, , is epitaxially grown on the 00) plane, and 5rTiO.

The (110) plane of Ba and YCuO6 was epitaxially grown on the (110) plane. The superconducting transition temperature Tc (the point where electrical resistance becomes zero) of the (001) plane or (110) simple crystal film of Ba, YCuO6, is as high as 88 or more, and the critical current density Jc is also 1X 10 at a temperature of 77. '
As shown in Figure 2 (a), the time fluctuation of the BaF deposition rate was sufficiently small within ±2% per hour, making it difficult to precisely control the composition. As a result, a thin film with a high Tc value and a high Jc value was obtained.On the other hand, when Ba metal is used instead of BaF2, the temporal fluctuation of the Ba deposition rate is shown in Figure 2 (b).
), it is as large as ±30% in one hour, which greatly reduces the controllability of the thin film composition.

In addition, the evaporation temperature of YF is 1100℃ and that of metal Y is 1430℃.
It decreased significantly compared to ℃. As a result, the lifetime of the cell constituent materials is more than tripled, and the time fluctuation of the vapor deposition rate is 110% (1 hour) for metal Y, while YF has a ±
It was reduced to 2%, contributing to improved composition controllability.

In addition, it is possible to achieve such a high T without annealing after deposition.
By showing the c value and Jc value, it was found that BaF2 and YF were dissociated during vapor deposition, and unnecessary F atoms were removed from the deposited thin film. FIG. 3 shows experimental results showing that this dissociation effect is caused by oxygen ion beam irradiation. Figure 3 shows that the more the irradiation ion current is reduced from the optimum value, the more BaF2 in the produced thin film increases.
It was found that the amount of crystals increased. Similar results were obtained for YF.

From the above results, it was found that according to the method for manufacturing an oxide thin film according to the present invention, the composition including oxygen can be sufficiently controlled with good reproducibility even in oxide thin films containing Ba and Y.

In this Example 1, when BaN6 (nitride) was used instead of BaF2 (fluoride), good results similar to those described above were obtained.

(Example 2) LiNb0. Production of thin film LiNb0. grew. After obtaining an oxygen ion beam under the conditions of 50 eV and 100 pA/cm'' in the same manner as in Example 1, the neutralizing filament was heated with electricity, and a thermionic shower was applied to the oxygen ion beam to generate neutral oxygen. Also, Li beam was obtained from K-cell 4.
F was evaporated and Nb was evaporated from the electron beam evaporation source 3, and the sapphire six-sided substrate was irradiated with an oxygen beam at the same time to obtain a LiNbO3 single crystal. Li of the insulator by neutralizing the oxygen ion beam
Even with NbO, precise composition control was possible without charge-up. The refractive index n of the obtained film for light with a wavelength of 633 nm. (normal light) is 2.31, n
l (extraordinary light) is 2.17, and L has a density close to that of the bulk.
iNb0. This shows that a film has been obtained.

Furthermore, even if oxygen plasma containing oxygen ions and electrons is irradiated instead of the neutral oxygen beam irradiation, precise composition control without charge-up is possible, and the same Li
Nb0. A membrane was obtained.

Here, when metallic Li is used instead of LiF, the fluctuation in the evaporation rate is as large as ±40% (1 hour).

The reproducibility of the produced thin film characteristics decreased due to instability of the Li evaporation temperature due to the reaction between Li and moisture in the K-cell, and increased vacuum degree fluctuations due to Li contamination of the inner wall of the film forming chamber 14. Such a problem did not occur when LiF was used.

[Effects of the Invention] As explained above, according to the method for producing an oxide thin film according to the present invention, even if it contains an active metal or a metal that requires high temperature for evaporation, it has a density close to that of the bulk. An oxide single crystal thin film can be formed stably with good reproducibility, with the composition including oxygen being sufficiently controlled. Therefore, oxide superconducting thin films with a high superconducting transition temperature can be stably produced without heat treatment after thin film formation. This has the advantage of widening the range of various applications.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional configuration diagram showing an example of an oxide thin film production apparatus suitable for use in the method of the present invention, and FIG. 2(a) shows the evaporation rate of BaF measured using the apparatus of FIG. 1. FIG. 2(b) is a graph showing the change over time, and FIG. 3 is a graph showing the change over time in the vapor deposition rate of metal Ba. FIG. 3 is a graph showing how the diffraction peak intensity of a BaF2 crystal changes depending on the oxygen ion current density irradiated during film production. 1. Substrate holder, 2. Substrate, 3.
, , , Electron beam evaporation source, 4 , , -cell, 5 , , exhaust port, 6 , , Faraday cup 1, -7. , , , Film thickness monitor, 8. , , , ion source 9 , , gas inlet 10 . ,,,Microwave source, 11, ,Plasma chamber, 12, ,Neutralization filament, 13, ,Substrate heater, 14. ,,,, film formation chamber.

Claims (1)

[Claims] 1) In a high vacuum, the raw materials forming the oxide thin film are evaporated and deposited on the substrate, and at the same time, the substrate is irradiated with oxygen ions of constant energy to form the oxide thin film on the substrate. A method for producing an oxide thin film, characterized in that a metal fluoride is used as the raw material for forming the oxide thin film. 2) Manufacture of an oxide thin film by evaporating the oxide thin film constituent raw material and depositing it on the substrate in a high vacuum, and at the same time irradiating the substrate with oxygen ions of constant energy to form an oxide thin film on the substrate. A method for manufacturing an oxide thin film, characterized in that a metal nitride is used as the raw material for forming the oxide thin film. 3) The method for producing an oxide thin film according to claim 1 or 2, wherein the degree of vacuum is higher than 1 x 10^-^3 Torr. 4) Production of an oxide thin film according to any one of claims 1 to 3, wherein the oxygen ions with constant energy are beam-shaped oxygen plasma accelerated to 10 to 500 eV. Method. 5) The method according to any one of claims 1 to 3, wherein the oxygen ions having a certain energy are beam-shaped oxygen ions extracted from an oxygen plasma and accelerated to 10 to 500 eV. Method for producing oxide thin film. 6) The method for producing an oxide thin film according to claim 5, wherein the beam-shaped oxygen ions are neutralized.