JP3253295B2 - Manufacturing method of oxide thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a method for producing an oxide thin film by a chemical vapor deposition method.

(Prior art) In recent years, YBa ₂ Cu ₃ O _7-y , Bi ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ , Tl ₂ Ba ₂ Ca ₂ Cu ₃
Oxide superconductor represented by O _y or the like has attracted discovered attention. Conventional superconductors are intermetallic compounds such as Nb ₃ Ge, and their critical temperature (Tc)
Is only 23K, and exhibits superconductivity only under cooling with expensive liquid helium (4.2K), which severely limits the use of superconductors. On the other hand, the above oxide superconductor has a Tc of more than 100K, and exhibits superconductivity under cooling by liquid nitrogen (77K), which is industrially manufactured at low cost, so that it can be used not only for conventional applications but also for conventional applications. New applications have begun to be proposed, including applications to ultra-high-speed logic devices operating at 77K.

By the way, in order to use an oxide superconductor industrially, it is indispensable to produce an oxide crystal having a controlled composition and few defects with good reproducibility. In addition, a flat thin film of an oxide single crystal is indispensable.

In general, a physical method such as sputtering or electron beam evaporation is used for producing an oxide superconductor thin film. Although these methods can obtain a thin film with a relatively simple apparatus, it is difficult to independently control the supply amounts of the elements constituting the oxide superconductor. There is a problem that it is difficult to deposit an oxide superconductor thin film having a desired composition with good reproducibility, depending on the shape and the like.

In contrast, the chemical vapor deposition method, the so-called CVD method,
Unlike the above-mentioned physical vapor deposition method, since the supply amount of each raw material including the elements constituting the oxide superconductor can be precisely controlled independently, the development of the thin film composition has been actively pursued recently. Is underway.

For example, Y-Ba-Cu-O system, Bi-Sr
In order to form an oxide superconductor thin film such as -Ca-Cu-O-based or Tl-Ba-Ca-Cu-O-based, since the vapor pressure of the organometallic raw material used is low, the raw material is heated. As a result, the vapor pressure is increased, and the concentration of the raw material to be supplied is increased to obtain a practical deposition rate. However, in order to increase the deposition rate,
When the heating temperature of the raw material is increased, there is a problem that the raw material is deteriorated or deteriorated.

Further, in the conventional MOCVD method, the control of the metal composition has been performed by changing the temperature of the organic metal raw material and the flow rate of the raw material gas to change the supply amount of the raw material. here,
When the composition is controlled only by the heating temperature of the raw material,
Since the vapor pressure of the raw material gas changes exponentially with respect to the heating temperature, precise composition control becomes difficult. Therefore, in order to control the composition more precisely, it is essential to control the flow rate of the raw material. However, when the growth is performed by reducing the pressure in the reaction tube, if the composition is controlled by the flow rate of the raw material, the pressure in the raw material container changes with the change in the flow rate of the raw material. There is a problem that it is difficult to control the composition of the film.

(Problems to be Solved by the Invention) As described above, in the conventional CVD method, when depositing an oxide superconductor thin film, in order to increase the vapor pressure of the organometallic material, the heating temperature of the material is increased. When the film is formed under reduced pressure in the reaction tube, even if the composition of the deposited film is controlled by changing the raw material temperature and the raw material flow rate, the pressure in the raw material container changes. In addition, there is a problem that the concentration of the starting material changes and it becomes difficult to control the composition.

The present invention has been made in order to address such problems, and it is possible to prevent deterioration of raw materials such as organometallics, improve the composition controllability of a deposited film, and produce a single-crystal oxide thin film with good reproducibility. It is an object of the present invention to provide a method for producing an oxide thin film that can be performed.

[Constitution of the Invention] (Means for Solving the Problems) That is, according to the present invention, a plurality of raw materials containing respective metal elements constituting an oxide are heated from a plurality of raw material containers in a reaction container containing a substrate. By supplying a plurality of source gases by this, the crystal of the oxide is deposited on the substrate by a chemical vapor deposition method to produce an oxide thin film, the inside of the container for each of the plurality of source containers A pressure reducing mechanism is provided, and the pressure in the plurality of raw material containers is reduced to a pressure lower than the atmospheric pressure by each of these pressure reducing mechanisms,
By heating the plurality of raw materials, the composition of the metal element constituting the oxide is controlled based on the supply concentrations of the plurality of raw material gases supplied into the reaction vessel.

(Operation) In the method for producing an oxide thin film of the present invention, a plurality of raw material containers are heated, and the pressure in each raw material container is maintained at a constant reduced pressure by a pressure reducing mechanism provided for each of the raw material containers. Is improved in the evaporability of each raw material containing a metal element. Thus, it becomes possible to control the supply concentration of the plurality of organometallic raw materials (source gases) without changing the flow rates of the raw materials, and the composition controllability of the deposited film is improved. Therefore, a single-crystal oxide thin film can be obtained with high reproducibility. Further, by using the reduced pressure in the raw material container together, a practical film forming rate can be obtained without deteriorating the raw material.

(Examples) Hereinafter, the method for producing an oxide thin film of the present invention is described as Bi-Sr-Ca-
An example applied to the production of a Cu—O-based oxide superconductor thin film will be described with reference to the drawings.

FIG. 1 is a schematic view showing the configuration of a CVD apparatus used in this embodiment. In the figure, 1, 2, 3,
Reference numerals 4 denote raw material containers, respectively, which are Bi (C ₆ H ₅ ) ₃ , Sr (DPM) ₂ , and Ca (Org) as organic metal raw materials for Bi, Sr, Ca and Cu which are constituent metal elements of the Bi-based oxide superconductor. DPM) ₂ , CU
(DPM) ₂ and (DPM = C ₁₁ H ₁₉ O ₁₂ ) are accommodated respectively. Each of the raw material containers 1, 2, 3, and 4 is made of stainless steel, and is covered with a mantle heater (not shown), so that heating can be controlled to a fixed temperature within ± 0.5 ° C. of a set temperature. ing. Note that Bi, Sr, C
a, Cu raw material containers 1, 2, 3, and 4 are 70 to 100 respectively.
C., 200-230.degree. C., 190-210.degree. C., 100-120.degree.

Carrier gas piping systems 6, 7, 8, and 9 connected to a high-purity argon gas supply source 5 are inserted into the raw material containers 1, 2, 3, and 4, respectively. , 7, 8, and 9 have mass flow controllers 10, 1
1, 12, 13 and pressure gauges 14, 15, 16, 17 are inserted respectively. The high-purity argon gas supply source 5 is also directly connected to a reaction furnace 20 by a replacement gas supply piping system 19 in which a mass flow controller 18 is interposed.

Source gas supply piping system from each source container 1, 2, 3, 4
21, 22, 23, and 24 are connected to the reaction furnace 20, respectively, and needle valves 25, 26, 27, and 28 are interposed therebetween, and the degree of opening and closing of the needle valves 25, 26, 27, and 28 is provided. By adjusting the pressure, it is possible to control the pressure in each of the raw material containers 1, 2, 3, and 4 to within ± 0.1 Torr of a set value. The source gas supply piping systems 21, 22, 2
The heaters 3 and 24 are kept at a constant temperature, for example, 250 ° C. by a heater (not shown) so that the raw material vapor does not condense.

In the CVD apparatus of this embodiment, as a mechanism for depressurizing the inside of the source containers 1, 2, 3, and 4, the source gas supply piping systems 21, 22, connected to the depressurized reaction furnace 20,
Although the needle valves 25, 26, 27, 28 interposed between 23 and 24 are employed, various mechanisms such as adding an exhaust system to each raw material container can be used.

Then, the inside of each of the raw material containers 1, 2, 3, and 4 is heated to a predetermined temperature, and each of the needle valves 25, 26, 27, and 28 is adjusted to a predetermined decompressed state. And each source gas supply piping system 21,
It is configured to supply each organometallic raw material vapor into the reaction furnace 20 from 22, 23, and 24. In addition, each raw material container 1, 2,
The pressure in 3, 4 is the carrier gas piping system 6, 7,
The pressure is monitored by pressure gauges 14, 15, 16, 17 inserted in 8, 9 and controlled to a predetermined reduced pressure state.

On the other hand, the supply source 29 of the oxygen gas serving as the reaction gas is a reaction gas supply piping system 31 in which the mass flow controller 30 is inserted.
Connected to the reaction furnace 20.

In addition, pneumatically operated three-way valves 32, 33, 34, 35, and 36 are interposed in the source gas supply piping systems 21, 22, 23, and 24 and the reaction gas supply piping system 31, respectively. It is electrically driven by a solenoid valve. Three-way valve 32, 33, 3
Reference numerals 4, 35, and 36 have a role of switching between a flow path for feeding the raw material vapor or the reaction gas into the reaction furnace 20 and an exhaust path 37 that is a flow path for discharging to the outside. The above solenoid valves are all controlled by a sequence controller, and each three-way valve 32, 33,
The opening / closing timing and holding time of 34, 35, 36 can be programmed in advance.

The reaction furnace 20 is externally heated by a heater 38, and a sample mounting table 39 having a graphite surface coated with silicon carbide is disposed therein, and a single crystal substrate 40 for thin film growth is placed on the sample mounting table 39. Is placed. The pressure inside the reaction furnace 20 is reduced by a rotary pump 41, and the pressure inside the reaction furnace 20 is reduced.
The pressure is monitored by a pressure gauge 42 attached to and is maintained at a constant value.

Next, Bi-Sr-Ca-Cu-O using the above-mentioned vapor phase growth apparatus was used.
An example of a method for growing a system thin film will be described.

First, a (100) oriented MgO single crystal substrate 40 whose surface has been cleaned by organic cleaning is mounted on a sample mounting table 39. High-purity argon gas is supplied to the reaction furnace 20 from the high-purity argon gas supply source 5 through a replacement gas supply piping system 19 to replace the air in the reaction furnace 20. Next, the rotary pump 41
And adjust the pressure in the reactor 20 to 10 while watching the pressure gauge 42.
Adjust to Torr. Thereafter, high-purity oxygen gas is supplied from the oxygen gas supply source 29 through the reaction gas supply piping system 31, and the sample mounting table 39 and the single crystal substrate 40 are heated by the heater 38.
Heat to a predetermined temperature in the range of 500 ° C to 950 ° C,
Clean 40 surfaces.

The supply of the oxygen gas was stopped by quickly switching the three-way valve 36 and discharging the exhaust gas to the exhaust path 37 so as to reduce the temporary flow rate fluctuation due to the cutoff of the flow path.

On the other hand, while the surface of the single crystal substrate 40 was being cleaned, the argon gas whose flow rate was adjusted from the high-purity argon gas supply source 5 through the mass flow controllers 10, 11, 12, and 13 was supplied to each of the above-described components. The organic metal raw materials are fed into the raw material containers 1, 2, 3, and 4 at a rate of 20 to 100 cm ³ / min. At that time, the pressure of each raw material container 1, 2, 3, 4 was adjusted by needle valves 25, 26, 27, 28 to 1-760T.
While maintaining a constant reduced pressure in the range of orr, each of the raw material containers 1, 2, 3, and 4 is heated to a predetermined temperature.

Each raw material vapor thus obtained is sent to the downstream side through each raw material gas supply piping system 21, 22, 23, 24. At this time, the three-way valves 32, 33, 34, 35 are operated to discharge the raw material at the beginning of evaporation to the exhaust path 37 side. The above is the preliminary step before starting the film formation.

After the above preliminary step is completed, the three-way valves 32, 33, 34, and 35 are operated to introduce the respective raw material vapors into the reactor 20 and to introduce oxygen gas from the reaction gas supply piping system 31 so that the reactor Bi-Sr- is formed on a single crystal substrate 40 arranged in 20.
A Ca—Cu—O-based thin film is deposited.

The deposition conditions for the Bi-Sr-Ca-Cu-O-based thin film were as follows. That is, Bi (C ₆ H ₅ ) ₃ , Sr (DPM) ₂ , Ca (DP
M) ₂ , Cu (DPM) ₂
70 ° C, 210 ° C, 190 ° C, and 100 ° C, and the flow rate of the argon gas fed into each of the raw material containers 1, 2, 3, and 4 was 50 cm ³ /
Minutes. The temperature of the single crystal substrate 40 was 800 ° C., the pressure in the reaction furnace 20 was 10 Torr, and the flow rate of oxygen gas supplied to the reaction furnace 20 was 100 cm ³ / min. The deposition time of the thin film was 60
Minutes.

As shown in FIG. 2, the growth rate of each component of the Bi—Sr—Ca—Cu—O-based thin film deposited by the above-described method depends on the pressure in the organometallic raw material containers 1, 2, 3, and 4. It turned out to be inversely proportional. That is, since the film formation rate can be increased by reducing the pressure inside the raw material container, the raw material temperature can be set lower than before. As a result, deterioration of the raw material due to thermal decomposition or the like can be prevented, and crystal growth with good reproducibility can be achieved.

Based on the above results, the flow rate of each organometallic raw material vapor was adjusted so as to have a composition of the superconducting phase by adjusting the pressure in each raw material container 1, 2, 3, and 4 to obtain a Bi-based oxide. A superconductor thin film was formed. Bi (C ₆ H ₅ ) ₃ and Sr (DP
The pressure in each of the raw material containers 1, 2, 3, and 4 containing the respective organic metal raw materials of M) ₂ , Ca (DPM) ₂ , and Cu (DPM) ₂ was set to 40 Torr.

As a result of X-ray diffraction, the obtained thin film was found to be a Bi ₂ Sr ₂ CaCu ₂ O ₈ single-phase film in which no different phases were observed. The superconducting transition temperature of the thin film was 80 K, and a similar thin film could be obtained with good reproducibility.

In addition, by controlling the composition, the superconducting transition temperature shows 85K
An i ₂ Sr ₂ Ca ₂ Cu ₃ O ₁₀ single phase film was also obtained. The reason why the superconducting transition temperature of this thin film is lower than the bulk value is the growth temperature,
This is because the growth conditions such as the oxygen flow rate have not been optimized, and the superconducting transition temperature can be improved by optimizing the growth conditions.

In the above embodiment, the production of a Bi-based oxide superconductor thin film has been described as an example, but the present invention is not limited to this, and Y-Ba-Cu-O-based, Tl-Ba-Ca −Cu
Of course, it can be applied to the formation of various oxide superconductor thin films such as -O type. Further, the organic metal raw material and oxygen as an oxidizing agent are not limited to the above-described embodiment, and it is natural that other raw materials can be effectively used.

Further, the present invention is not limited to film formation of an oxide superconductor, but can be applied to film formation of general oxides such as ferroelectric oxides such as LiNbO ₃ , BaTiO ₃ , and PbTiO ₂ . In addition, various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described above, according to the present invention, by evaporating the organometallic raw material at a low heating temperature at which the raw material deterioration does not occur, the pressure in the organic metal raw material container is controlled in a reduced pressure state. Even if you go, you can get a practical growth rate,
In addition, it is possible to form a film excellent in reproducibility and precision composition controllability. Therefore, it is extremely effective, for example, for producing a high-performance superconducting electronic device using an oxide superconductor thin film.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the structure of a MOCVD vapor phase growth apparatus used in one embodiment of the present invention, and FIG. 2 shows the relationship between the pressure in the organometallic raw material container and the film growth rate in one embodiment of the present invention. FIG. 1, 2, 3, 4 ... Organometallic raw material container, 5 ... High purity argon gas supply source, 6, 7, 8, 9 ... Carrier gas piping system, 10, 11, 12, 13, 18, 30 ... ... Mass flow controller, 14, 15, 16, 17, 42 ... Pressure gauge, 19 ... Replacement gas supply piping system, 20 ... Reactor, 21, 22, 23, 24 ... 26, 27, 28 ... Needle valve, 29
…… Oxygen gas supply source, 31 …… Reaction gas supply piping system, 38…
... Heater, 39 ... Sample table, 40 ... Single crystal substrate for thin film growth, 41 ... Rotary pump.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 1/00 C30B 1/00-35/00 C23C 16/00-16/56

Claims (1)

(57) [Claims] A plurality of source gases are supplied from a plurality of source containers by heating a plurality of source materials containing respective metal elements constituting an oxide into a reaction vessel containing a substrate. When depositing the oxide crystals by a chemical vapor deposition method to produce an oxide thin film, a mechanism is provided for decompressing the inside of each of the plurality of source containers, and the plurality of decompression mechanisms are used for the plurality of containers. The pressure in the raw material container is reduced to the atmospheric pressure or lower, and the oxides are heated based on the supply concentrations of the plurality of raw material gases supplied into the reaction container by heating the plurality of raw materials, respectively. A method for producing an oxide thin film, comprising controlling the composition of a constituent metal element.