JPH04354875A - Formation of metal oxide thin film - Google Patents

Abstract

PURPOSE:To stably and inexpensively supply a metallic material and to effectively obtain the thin film by simultaneously using an organometallic compd. having an organometallic complex contg. a first metal and a metal consisting of a second metal as the raw materials add growing the thin film in the vapor phase. CONSTITUTION:When a YBa2Cu3OX thin film is formed, yttrium tetramethylheptadionate and copper tetramethylheptadionate as one kind of organometallics are used as the raw materials for Y and Cu, and metallic Ba is used as the Ba material. Stainless steel vessels 1a and 2a respectively contg. the raw materials 1 and 2 for Y and Cu are heated to 110 deg.C and to 120 deg.C, the vapor are passed through heating pipes 1b and 2b and introduced into a growth chamber, and metallic Ba 3 is vaporized from a conventional effusion cell 3a and introduced. A substrate 4 is heated by a resistance heater 5, and oxygen as an oxidizing gas with the flow rate adjusted by a mass flow controller 6 is introduced into a microwave plasma producer 7, activated and used to form a thin film.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing metal oxide thin films, particularly metals suitable for vapor phase growth of thin films of oxide superconductors, oxide ferroelectrics, oxide semiconductors, and oxide optical materials. This invention relates to a method for producing an oxide thin film.

0002

BACKGROUND OF THE INVENTION In recent years, the importance of developing techniques for forming thin films of metal oxides has been increasing. That is, recently discovered oxide superconductors are expected to be used as superconducting wiring in semiconductor devices, and oxide ferroelectrics are attracting attention as capacitor materials for semiconductor memories. In addition, thin films of various metal oxides are used as conductive materials, piezoelectric materials, light-transmitting materials, and display element materials.
It is desired to improve its functionality.

The metal oxide thin film forming techniques that have been developed so far include molecular beam evaporation (so-called MBE);
Many techniques have been developed, including vacuum evaporation, reactive evaporation, sputtering, ion beam evaporation, pulsed laser evaporation, and chemical vapor deposition. For example, thin films of oxide superconductors can be formed by all of these methods (Yamaka, Tachikawa, Ichinose, co-authors: "Introduction to High Temperature Superconductivity", pp. 92-94, Ohm company).

0004

[Problems to be Solved by the Invention] As mentioned above, although the formation of thin films of high temperature superconductors has been realized using various techniques,
However, both techniques have a problem in that it is extremely difficult to supply metal raw materials. That is, in the above method, depending on the type of raw materials used, (1) technology using metal as raw material, (2) technology using oxide as raw material, (3) technology using metal and oxide as raw material, (4) ) Technologies that use organic metals as raw materials. Among these, technologies in the first to third categories have the problem that when raw materials with low vapor pressure are supplied by heating and evaporation, the evaporation temperature is high, so the supply equipment is easily damaged, as will be described in detail in the next section. . It is also possible to supply by electron beam heating, but when comparing this method and resistance heating method, it is found that the equipment cost is several times higher, the growth rate is slower, and metals with good thermal conductivity cannot be used because of partial heating. There are problems in that the heating efficiency is poor and the lifetime of the electron beam source is about several hundred hours in an oxygen atmosphere. Furthermore, it is possible to supply by sputtering, but in this case there is a problem that the growing film is also sputtered and the film quality deteriorates. In the fourth classification technique, some of the raw materials are unstable, so there is a problem that it cannot be used for a long time, or that only a part of the enclosed amount can be used. and,
These problems are not unique to oxide superconductors, but are common to other metal oxide thin film formation techniques.

The present invention solves the technical problems inherent in the above-mentioned conventional techniques and provides a method for producing a metal oxide thin film using a stable and inexpensive raw material supply method.

[0006]

Means for Solving the Problems In order to achieve the above object, a configuration according to the present invention is adopted. Namely:
According to one aspect of the present invention, (1) a first step (2) of preparing a metal consisting of an organometallic complex containing a first metal element and a second metal element as a metal element raw material; A second step of oxidizing the metal element raw material and vapor-phase growing a metal oxide on the substrate by introducing the metal element raw material and a gas containing oxygen into a growth chamber in which the substrate is disposed.
A method for producing a metal oxide thin film is provided, which includes the following steps.

According to one aspect of the invention, which is also limited,
A method for producing a metal oxide thin film is provided in which the second step is performed by varying the distance between the organic metal inlet to the growth chamber and the substrate and the distance between the metal inlet and the substrate.

[0008] In the second step, it is particularly preferable to control the vapor phase growth using optical excitation, plasma excitation, electron beam excitation, or a combination of these excitations, but the method is not limited to these excitation methods. .

[0009] Furthermore, the "metal oxide thin film" referred to in the present invention includes, in addition to an oxide superconductor, an oxide semiconductor, an oxide ferroelectric, or an oxide optical material.

According to yet another limited aspect of the present invention, the first step comprises forming an organometallic compound having an organometallic complex containing the first metal element having a vapor pressure of about 10-2 Pa or more at 1000°C. and a second one in which the temperature difference between the temperature at which the vapor pressure is 10-2 Pa or more and the decomposition temperature is 30°C or more
A method for producing a metal oxide thin film is provided, which is a step of preparing a metal consisting of a metal element as a metal element raw material. In other words, by adopting a new raw material introduction method that uses both a metal with a relatively low evaporation temperature and an organic metal with relatively high stability as raw materials, we solved the problem of difficulty in stably supplying raw materials. can.

[0011]

[Operation] In the present invention, a metal oxide thin film is grown in a vapor phase using both a metal and an organic metal as raw materials. In other words, not only can the material supply form to the growth chamber be selected from steam or organic gas depending on the characteristics of each of the multiple types of metal elements used, but also these supply forms can produce metal oxide thin films that are prone to film quality deterioration. Able to grow with high quality.

[0012] In the present invention, in particular, at 1000°C, about 10
The effect is particularly remarkable when the raw materials are a metal with a vapor pressure of -2 Pa or more and a highly stable organic metal with a temperature difference of 30° C. or more between the temperature at which the vapor pressure becomes 10-2 Pa and the decomposition temperature. The condition that the vapor pressure is about 10-2 Pa is an important condition for growing a thin film at a practical rate. The condition of 1000° C. or lower is a temperature at which the raw material can be stably evaporated for several thousand hours or more using a normal resistance heating method. In the case of resistance heating, the lifetime decreases exponentially as the temperature increases due to evaporation and oxidation of the heater, as well as increased heat dissipation. For example, when the raw material evaporation temperature is 1200° C., the period of continuous use is about 1000 hours. As a selection condition for the organic metal, the condition that the temperature difference between the temperature at which the vapor pressure is 10@-2 Pa and the decomposition temperature is 30 DEG C. or more is an important condition for preventing deterioration of the raw material during evaporation. Since the evaporation temperature of organic metals is below 500°C,
If the evaporation temperature is 30° C. or more lower than the decomposition temperature in this temperature range, the decomposition rate will decrease by one order of magnitude or more.

Another feature of the present invention is that the metal raw material inlet and the organic metal inlet from the substrate are supplied at different distances from each other. This is based on the fact that when an oxidizing gas is supplied to the growth chamber to proceed with film growth in order to generate an oxide, the mean free path differs between metals and organic metals due to their different sizes. Since metals have a long mean free path, there is no problem such as a decrease in the adhesion coefficient even if the inlet is separated from the substrate; in fact, by separating it,
The uniformity of the film growth rate on the substrate is improved. On the other hand, since organic metals have a short mean free path, even if the inlet is close to the substrate, the uniformity of the film growth rate on the substrate is good, and if the inlet is far away, the efficiency of raw material utilization decreases.

The present invention will be explained in detail below with reference to Examples.

[0015]

[Example 1] The effectiveness of producing a YBa2Cu3Ox thin film, which is a typical oxide superconductor, according to the present invention will be explained using a reactive vapor deposition method and a chemical vapor deposition method as comparative examples.

FIG. 1 shows a conceptual diagram of the thin film forming apparatus used in the present invention. Among the metal elements, the raw materials for Y and Cu are yttrium tetramethylheptadione (hereinafter referred to as Y(THD)3), which is a type of organic metal, and the raw material for copper tetramethylheptadionate (hereinafter referred to as Cu(THD)2), and Ba. Only B
a metal. The supply to these MgO substrates is Y
For raw material 1, a stainless steel container 1a filled with it is heated to 110°C and introduced into the growth chamber through a heating pipe 1b, and for Cu raw material 2, a stainless steel container 2a filled with it is heated to 120°C. It is introduced through a pipe 2b, and Ba metal 3 is evaporated and introduced from a normal effusion cell 3a. In this apparatus, a substrate 4 is heated by a resistance heater 5, and the flow rate of oxygen used as an oxidizing gas is adjusted to a predetermined value by a mass flow controller 6, and the oxygen is introduced into a microwave plasma generator 7 and activated.

[0017] The growth temperature was 700°C, the microwave power for plasma generation was 200W, and the oxygen partial pressure was 10-4to.
FIG. 2 shows the temperature dependence of the electrical resistance of the YBa2Cu3Ox thin film grown as rr. As shown in the figure, the superconducting transition starting temperature is about 92 K, and the zero resistance temperature is 88 K, and the properties are almost the same as the original properties of the bulk material.

Even when this thin film formation was repeated for a total of 2000 hours, the raw material supply remained stable within ±5%.

On the other hand, in the reactive vapor deposition method taken up as a comparative example, YBa2
A Cu3Ox thin film can be produced. However, in this case, the evaporation temperature of Y metal is as high as 1300°C and the evaporation temperature of Cu metal is 1100°C, so the effusion cell for Y evaporation deteriorates in 800 hours, and the effusion cell for Cu evaporation deteriorates in 1300 hours. have done. Y and Cu can also be evaporated by using electron beam heating, but in reality, due to the high thermal conductivity of metals, it is necessary to increase the current density of the electron beam, and in addition, in an oxygen atmosphere. The electron beam heating device deteriorated after 400 hours.

In addition, in the chemical vapor deposition method, the raw materials for Y and Cu are Y(THD)3, Cu(THD)2,
barium tetramethylheptadionate (hereinafter referred to as Ba(THD)2) is used as the Ba raw material;
HD)2 is unstable, and the time for stable film growth is extremely short, within several tens of hours.

Furthermore, in the apparatus of the present invention shown in FIG.
The distance between the inlet of (THD)3 and Cu(THD)2 and the substrate was 10 cm, and the distance between the Ba metal surface of the effusion cell and the substrate was 40 cm, so that they were uniformly spread over a substrate with a diameter of 50 cm. It has been realized that a film can be formed. If the introduction port for the organic metal is placed further apart than this, the ratio of the organic metal that reaches the substrate due to evaporation in the gas phase will decrease at a rate greater than the square of the distance, resulting in a decrease in raw material utilization efficiency. Furthermore, if the metal inlet is brought closer, the uniformity of film growth will decrease.

[Example 2] A typical transparent piezoelectric material, commonly called PLZT, (Pb, La) (Zr, Ti
) A method for producing O3 according to the present invention will be explained.

In this case as well, the structure of the apparatus was the same as that shown in FIG. 1, and the raw materials used were Pb metal for Pb, an acetylacetone complex for La, and butyl alkoxide for Zr and Ti. Then, Pb metal is introduced by an effusion cell,
Other organometallics were introduced into the growth chamber through a heating pipe from a stainless steel container.

[0024] The growth temperature was 700°C, the microwave power for plasma generation was 200W, and the oxygen partial pressure was 10-4to.
The optical transmittance of the PLZT thin film grown as rr is 100
%, which is a sufficient value for an optical ceramic. Furthermore, when the film thickness was increased, an electro-optic effect was also confirmed. When producing a PLZT thin film using a reactive vapor deposition method, it is extremely difficult to evaporate Ti metal. Furthermore, when producing a PLZT thin film by chemical vapor deposition, it is necessary to use alkyl lead or an acetylacetone complex as the Pb raw material, but both have problems with stability.

[Example 3] A method for producing BaTiO3, which is a typical oxide dielectric, according to the present invention will be explained. In this case as well, the structure of the apparatus was the same as that shown in FIG. 1, and the raw materials used were Ba metal for Ba and butyl alkoxide for Ti. Then, Ba metal was introduced through an effusion cell, and Ti butyl alkoxide was introduced into the growth chamber from a stainless steel container through a heating pipe.

[0026] The growth temperature was 800°C, the microwave power for plasma generation was 100W, and the oxygen partial pressure was 10-3to.
The relative dielectric constant of the BaTiO3 thin film grown as rr was about 1000, which was a value sufficient for use as a dielectric material for a capacitor. Since the pressure in the growth chamber was high, the thin film coverage was also good.

[Example 4] As an example of manufacturing an oxide semiconductor thin film, a method for manufacturing a Nb-doped SrTiO3 thin film will be described.

In this case as well, the structure of the apparatus was the same as that shown in FIG. 1, and as for the raw materials, Sr metal was used for Sr, and butyl alkoxide was used for Nb and Ti. Then, Ba metal was introduced through an effusion cell, and Nb and Ti butyl alkoxide were introduced into the growth chamber from a stainless steel container through a heating pipe.

[0029] The growth temperature was 800°C, the microwave power for plasma generation was 100W, and the oxygen partial pressure was 5X10-5.
A 0.5% Nb-doped SrTiO3 thin film grown as torr has a carrier concentration of 1020/cm.
3. It was a semiconductor with a mobility of 10 cm2/Vs (300K). Since the crystal structure of this thin film is a cubic crystal with an axial length of 0.391 nm, it is suitable for the heteroepitaxial growth of oxide superconductors whose basic structure is a perovskite structure.
On this Nb-doped SrTiO3 thin film, YBa2Cu3Ox with superconducting properties close to that shown in Fig. 2 was formed by the method of Example 1.
A thin film was formed.

[Example 5] A YBa2Cu3Ox thin film was formed on an MgO substrate in the same manner as in Example 1, and a SrTiO3 thin film of about 30 Å was formed thereon in the same manner as in Example 5. Similar to 1, YBa2Cu3Ox
A thin film was formed. When the voltage-current characteristics between the upper and lower YBa2Cu3Ox thin films were measured at 4K, a tunnel current and a Shapiro step due to microwaves were observed. That is, it has become clear that a Josephson junction element can be manufactured according to the present invention.

[0031]

[Effects of the Invention] According to the present invention, metal oxide thin films, particularly thin films of oxide superconductors, oxide ferroelectrics, oxide semiconductors, and oxide optical materials, can be stably produced for a long time by vapor phase growth. This has made it possible to greatly increase the productivity of products such as superconducting devices, electronic devices, and optical devices.

In the example, crystallization is promoted using plasma excitation, and the growth temperature is lowered by about 200°C. Although similar effects can be obtained using excitation such as optical excitation or electron beam excitation, the effects of the present invention can be achieved regardless of whether such excitation techniques are used. In addition, in the examples, only examples using oxygen as the oxidizing gas were shown, but
The effects of the present invention can also be achieved with gases containing oxygen such as ozone and nitrogen oxide.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle configuration of an apparatus for producing an oxide superconductor thin film, which is a typical embodiment of the present invention.

FIG. 2 is a diagram showing the superconducting properties of a thin film produced according to the present invention.

[Explanation of symbols]

1...Y raw material, 1a...stainless steel container enclosing Y raw material, 1b...heating pipe, 2...Cu raw material, 2a...Cu
Stainless steel container filled with raw materials, 2b... heating pipe, 3... Ba metal, 3a... effusion cell, 4...
Substrate, 5... resistance heater, 6... mass flow controller for adjusting oxygen flow rate, 7... microwave plasma generator.

Claims (5)

[Claims] 1. A method for producing a metal oxide thin film, which comprises the following steps. (1) A first step of preparing an organic metal having an organometallic complex containing a first metal element and a metal consisting of a second metal element as metal element raw materials. A second step of oxidizing the metal element raw material and growing a metal oxide on the substrate in a vapor phase by introducing a metal element raw material and a gas containing oxygen.
process 2. The method for producing a metal oxide thin film according to claim 1, wherein the second step includes determining the distance between the organic metal introduction port into the growth chamber and the substrate, and the distance between the metal introduction port and the substrate. A method for producing a metal oxide thin film by varying the distance between the substrates. 3. The method for producing a metal oxide thin film according to claim 1, wherein the second step uses any one of photoexcitation, plasma excitation, electron beam excitation, or a combination of these excitations to stimulate the vapor phase. A method for producing metal oxide thin films with controlled growth. 4. The method for producing a metal oxide thin film according to claim 1, wherein the second step involves vapor phase growth of an oxide superconductor, an oxide semiconductor, an oxide ferroelectric material, or an oxide optical material. A method for producing a metal oxide thin film, which is a process. 5. The method for producing a metal oxide thin film according to claim 1, wherein the first step is performed at 1000° C. for about 10 −
An organic metal having an organometallic complex containing the first metal element having a vapor pressure of 2 Pa or more, and a second metal element having a temperature difference of 30°C or more between the temperature at which the vapor pressure becomes 10-2 Pa or more and the decomposition temperature. A method for producing a metal oxide thin film, which is a process of preparing a metal as a metal element raw material.