JPH11193462A - Method for vaporizing organic alkaline-earth metal complex in cvd process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To vaporize an organic alkaline-earth metal complex as the raw material substance of alkaline-earth metal in such a manner that a secular change does not occur therein, and also, a high film forming rate can be obtd. at the time of producing alkaline-earth metal-contg. thin film by a CVD process. SOLUTION: An organic alkaline-earth metal complex 1 is once heated to the m.p. or above and is melted. Then, the molten body is cooled to solidify in a raw material vessel 2, and this solidified organic alkaline-earth metal complex is vaporized at the m.p. thereof or below. Furthermore, the molten body is cast into a cylindrical vessel in such a manner that a solidified layer with an almost fixed thickness stretching in the direction of the longitudinal axis of the vessel is formed, and a carrier gas is allowed to flow through the inside of the vessel in the direction of the longitudinal axis thereof to vaporize the organic alkaline-earth metal complex from the solidified layer at the m.p. thereof or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stably vaporizing a raw material of an alkaline earth metal when producing an alkaline earth metal-containing thin film by a CVD method.

[0002]

2. Description of the Related Art Thin films containing an alkaline earth metal as a component are useful for ferroelectric materials, EL device materials, superconductor materials, and the like, and therefore, methods for producing the thin films have been actively studied.

[0003] As thin film production techniques, physical film forming methods such as vacuum deposition and sputtering, and chemical vapor deposition (C
Chemical film forming methods such as the VD) method are well known. C
The VD method is widely used because it is excellent in controllability of film formation rate, controllability of film composition, high-speed film formability, film formability in a large area, and is suitable for mass production. In manufacturing a capacitor film of a gigabit-class DRAM, a CVD method having excellent step coverage has attracted attention as a most promising thin film manufacturing method.

In the CVD method, an organic metal complex is also used as a raw material for supplying a metal component constituting a thin film. A film forming method using the organic metal complex as a raw material for vaporization is particularly called an MOCVD method. I have. The MOCVD method has been widely studied in the fabrication of ferroelectric thin films, electrode thin films, oxide superconducting thin films, etc. used for DRAM capacitors, and organometallic complexes having β-diketone as a ligand have been used. . Dipivaloylmethane (DP)
Complexes having M) as a ligand generally have the advantages of good vaporization, high thermal decomposition temperature, and low contamination of the film with impurities, and are most frequently used.

In the production of ferroelectric thin films and oxide superconducting thin films containing alkaline earth metals as constituents, organic alkaline earth metal complexes are used as raw materials.
This complex is also a β-diketone-based complex, particularly one having dipivaloylmethane (DPM) as a ligand.

[0006]

In forming an alkaline earth metal-containing material by a CVD method, it has been recommended to use an organic alkaline earth metal complex as a raw material for vaporization as described above. Such an organic alkaline earth metal complex is usually synthesized in the form of a powder, and generally has a high melting point (usually 200 ° C. or higher for a DPM complex). Since the decomposition temperature of the alkaline earth metal DPM complex is relatively low,
If the temperature is too high, decomposition will occur, and if the temperature is higher than 200 ° C, the valves of the CVD equipment will be affected. It is common to make
In this case, according to the experience of the present inventors, it has been found that the film formation rate changes (decreases) with the passage of time, and that the alkaline earth metal content during the film formation changes.

That is, when the organic alkaline earth metal complex as a powder raw material is sublimated from its powder state, it is difficult to maintain a constant film forming rate for a long time. This is not due to the fact that the surface area of the raw material particles decreases as the sublimation progresses, and this decrease in the surface area slows down the evaporation rate, and the evaporation rate fluctuates due to partial fusion of the powders. It is thought. For this reason, in the case of vaporization from the powder state, the amount of steam decreases with time and the fluctuation of the amount of steam inevitably occurs. When the vaporization rate changes, the alkaline earth metal-containing thin film (eg, SrTiO ₃
), It is difficult to control the film formation.

[0008] A solution vaporization CVD method in which the raw material complex is dissolved in an organic solvent and the entire amount of the solution fed into the vaporizer by liquid flow rate control is vaporized has been developed.
A similar film formation rate cannot be obtained unless the film is heated to a temperature higher by about 30 to 50 ° C. than vaporization by solid sublimation. For this reason, clogging of piping in the vaporizer due to decomposition of the raw material in the vaporizer,
There are many problems to be solved, such as the incorporation of decomposition products of solvents used in large amounts into the membrane.

Accordingly, an object of the present invention is to stably vaporize an organic alkaline earth metal complex in a CVD method for producing an alkaline earth metal-containing thin film.

[0010]

According to the present invention, an organic alkaline earth metal complex is prepared by vapor deposition using an organic alkaline earth metal complex as a raw material for vaporization. It is characterized in that it is heated to a temperature higher than its melting point to be melted, the melt is solidified by cooling in a raw material container, and this solidified organic alkaline earth metal complex is vaporized at a temperature lower than its melting point.

Further, in the present invention, when a thin film containing an alkaline earth metal is produced by a CVD method using an organic alkaline earth metal complex as a raw material for vaporization, the organic alkaline earth metal complex is heated to a melting point or higher. The molten material is cast into a cylindrical container so as to form a solidified layer having a substantially constant thickness extending in the longitudinal axis direction of the container, and a carrier gas is injected into the container in the longitudinal axis direction. The organic alkaline earth metal complex is vaporized from the solidified layer at a temperature equal to or lower than the melting point of the solidified layer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The inventors of the present invention have conducted various tests and researches to solve the above-mentioned problems. It has been found that the use of a material that is melted and solidified by cooling (solidification) enables stable film formation and solves the above-mentioned problems. In particular, the melt is cast into a cylindrical container to form a solidified layer having a substantially constant thickness extending in the longitudinal axis direction of the container, and the carrier gas is passed through the solidified layer surface in the container axial direction to vaporize the solidified layer. It was found that the film could be formed more stably.

The organic alkaline earth metal complex used in the present invention is an alkaline earth metal such as Be, Mg, Ca, S
β-diketonates such as r and Ba are suitable, and organic alkaline earth metal complexes having dipivaloylmethane (DPM) as a ligand are particularly suitable. It was also found that such alkaline earth metal β-diketonates, especially those synthesized in an anhydrous solvent or without a solvent, did not undergo decomposition even when temporarily heated above the melting point. Therefore, an alkaline earth metal β-diketonate synthesized in an anhydrous solvent or without a solvent can be suitably used in the practice of the present invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows that a raw material container 2 loaded with an organic alkaline earth metal complex 1 is set in a constant temperature bath 3 maintained at a predetermined temperature, and a complex vapor vaporized in the raw material container 2 is subjected to a carrier gas (FIG. 1). In the figure, there is shown a CVD facility in which a gas is introduced into a reactor 5 through a pipe 4 by an argon gas, and is deposited on a surface of a substrate 6 set in the reactor 5. In this facility, a pipe 7 for introducing oxygen gas to the reactor 5 is provided separately from the pipe 4 for guiding the complex vapor.
The oxygen gas line 7 is connected to the line 4 at a position immediately before the reactor 5, and at the junction, the complex vapor and the oxygen gas are mixed at an adjusted volume ratio so that the two react and react with each other. A thin film of the intended component is formed on the surface of No. 6.

In FIG. 1, reference numeral 8 denotes an exhaust device (rotary pump) for reducing the pressure in the system, 9 denotes an exhaust valve, 10 denotes a cooling trap, and a supply line for supplying complex vapor from the constant temperature bath 3 to the reactor 5. 4 is surrounded by a heat insulating layer 11 at its outer periphery. A heater (not shown) is provided in the heat insulating layer 11 so that the temperature of the inner wall of the pipe 4 is maintained at a temperature higher by 5 to 50 ° C. than the temperature of the thermostatic bath 3. The reactor 5 is heated to a predetermined temperature by a heater 12 attached to the outer periphery of the reactor 5, and the reactor 5 with the heater 12 is set in the pyrolysis furnace 13.

In the present invention, an operation is performed in which the organic alkaline earth metal complex 1 is once heated to a temperature higher than its melting point to be melted, and the melt is cooled and solidified in the raw material container 2. In this case, a cylindrical container is used as the raw material container 2, and the cylindrical container is cooled and solidified so as to form a solidified layer having a substantially constant thickness extending in the longitudinal axis direction. Hereinafter, this embodiment will be specifically described.

In the CVD equipment shown in FIG. 1, a constant-temperature bath 3 is set with two cylindrical raw material containers 2 of the same shape connected in series. FIG. 2 shows a specific example of the cylindrical raw material container 2. In this raw material container 2, branch pipes 16 and 17 in the same direction are connected near the end of a pipe 15 having both ends closed,
Valves 18 and 19 are attached to the branch pipes 16 and 17, respectively. The pipe 16 is an equal-diameter pipe having the same cross-section in the axial direction. As shown in FIG. 3, the cross-sectional shape may be circular (15a), square (15b), elliptical (15c), or the like. it can. In the equipment shown in FIG. 1, two such cylindrical raw material containers 2 are used. A carrier gas pipe 20 is connected to a branch pipe 16 of one of the containers, and a connection pipe 21 is connected to the other branch pipe 17. Is connected to the branch pipe 16 of the other vessel, and the branch pipe 17 of the other vessel is connected to the complex vapor line 4. This allows valves 18 and 1
When all 9 are open, the carrier gas first enters into one container and then into the other container via the connecting pipe 21,
It flows to line 4.

FIG. 4 illustrates an operation mode of charging the organic alkaline earth metal complex 1 into the cylindrical raw material container 2. The operation will be described with reference to FIG. 4. A powder 23 of the organic alkaline earth metal complex as a raw material is
Is charged in a container 25 having an inert gas atmosphere, and the branch pipe 17 of the cylindrical raw material container 2 is connected to the bottom nozzle 24 of the container 25 with its valve 19 closed, and The branch pipe 16 and the upper opening 26 of the vessel 25 are connected by a connection pipe 27 to form a closed circuit. The atmosphere in the closed circuit is completely replaced with an inert gas, and the cylindrical raw material vessel 2 is in a horizontal state. Thus, it is set in the electric furnace 28 (shown by a broken line). As a result, the powder in the container 25 is heated to the melting point or higher and melted. Up to this point, Figure 4
At the uppermost stage.

When the raw material powder is completely melted in the container 25, the valve 19 is opened and the melt is poured from the container 25 into the cylindrical raw material container 2. The middle diagram in FIG. 4 shows a halfway stage of the pouring. The pouring is continued, and the pouring is completed in a state where the melt is loaded at a predetermined depth with a horizontal liquid level in the cylindrical raw material container 2 in a horizontal state.
Next, by cooling the cylindrical raw material container 2 to normal temperature, a solidified layer having a substantially constant thickness extending in the longitudinal axis direction of the cylindrical raw material container 2 is formed. The lowermost diagram in FIG. 4 shows this state, and the solidified layer is indicated by 29. The solidified layer 29 has a depth occupying a part of the cross section of the container, and a space through which the carrier gas flows is opened above the solidified layer 29. When the casting of the organic alkaline earth metal complex is completed in this way, the valves 18 and 19 are closed, the pipe is disconnected from the loading equipment with the branch pipe attached, and moved to the CVD equipment, for example, as shown in FIG. Set in 3.

In this way, once the powdered organic alkaline earth metal complex raw material is heated and melted and cooled and solidified in the raw material container 2, its surface area is much smaller than that of the powdered raw material, It was found that the change with time in the amount could be almost completely suppressed. This is considered to be due to the fact that the fluctuation of the surface area is extremely small even when the evaporation proceeds. Further, even when the carrier gas flows through the cylindrical raw material container 2, it is possible to suppress the entrainment of the powder in the carrier gas as in the case of evaporating from the powder. Therefore, it is possible to prevent the powder from reaching the reactor 5 and contaminating the film.

In particular, the organic alkaline earth metal complex 1 is cooled and solidified so that a solidified layer having a substantially constant thickness in the axial direction is formed in the cylindrical raw material container 2 extended in the axial direction as described above. When the carrier gas is allowed to flow in one direction in the axial direction of the container, the raw material near the saturated vapor pressure near the branch pipe 17 on the outlet side of the container is obtained despite the vaporization from the solid state. It was found that steam was obtained.

This relationship becomes better as the length of the cylindrical raw material container 2 is longer and as the ratio of length / diameter (inner diameter of the pipe) is larger. In practice, the dimensions of the container, the flow rate of the carrier gas, and the like may be appropriately selected so as to obtain a substantially saturated vapor pressure near the branch pipe 17 on the container outlet side. If the cylindrical raw material containers 2 are connected in series, the raw materials can be used without waste. The example of FIG. 1 shows an embodiment in which two cylindrical raw material containers 2 are connected.

In such a cylindrical raw material container 2, in the flow direction of the carrier gas, the concentration of the complex vapor is lower on the upstream side and higher on the downstream side. Therefore, semi-permanent continuous operation can be achieved by connecting a plurality of cylindrical raw material containers 2 designed in a length such that a saturated vapor pressure can be obtained near the outlet of the container in a series and feeding them sequentially. It becomes possible. This embodiment will be described with reference to FIG.

FIG. 5 shows that two cylindrical raw material containers 2a and 2b, each of which is charged with a predetermined amount of an organic alkaline earth metal complex once melted and cooled and solidified, are connected in series via a connecting pipe 21, and are connected to an upstream container. A state is shown in which the carrier gas is introduced from the side of the branch pipe 16 of 2a and is supplied to the reactor 5 from the side of the branch pipe 17 of the downstream vessel 2b (the constant temperature bath is omitted). In this way, when vaporization from the solid complex is started so as to obtain a saturated vapor pressure of the complex near the outlet of the upstream vessel 2a, a gas close to the saturated vapor pressure is fed into the downstream vessel 2b, so that only a small amount is evaporated. Instead, most of the complex vapor is vaporized from the upstream vessel 2a, so that the solid raw material 1a in the upstream vessel 2a is reduced preferentially.
The thickness of the solid raw material 1a of the upstream container 2a decreases from the state A in FIG. 5 to the state B, and the upstream container 2a eventually becomes empty as in the state C in FIG. In the container 2b, the solid raw material 1b is sufficiently present.

Then, the empty upstream container 2a is removed and
The downstream-side container 2b is moved up to the upstream side, and a new cylindrical raw material container 2c is connected to the downstream side to newly supply. This state is shown in FIG. This causes the downstream container 2b to evaporate preferentially, returning to the state of FIG. 5A. Thereafter, by repeating this, the complex vapor having substantially the same concentration can be continuously transferred to the reactor. In addition, it is only necessary to newly supply the starting complex when it is almost empty, so that the starting material can be used up without waste.

As described above, according to the present invention, it is possible to stably generate a constant concentration of the vapor of the organic alkaline earth metal complex. Therefore, the film forming rate is stable even after a lapse of time, and a uniform film can be formed. In the above-described embodiment, the description has been made mainly on the evaporation of the organic alkaline earth metal complex. However, when the vapor of another raw material is simultaneously introduced into the reactor, a facility for introducing the vapor of another raw material into the reactor may be provided. I just need. Further, in addition to the embodiment shown in FIG. 4 in which the organic alkaline earth metal complex is melted in another container and injected into the raw material container 2 to be cooled and solidified, the powder raw material is put into the raw material container 2 set in the CVD equipment. Alternatively, the powder raw material can be melted in the raw material container 2 and cooled and solidified in the raw material container 2 as it is.

[0028]

EXAMPLE Hereinafter, strontium oxide was deposited on a silicon substrate using bis [dipivaloylmethanato] strontium [Sr (DPM) ₂ ] as an organic alkaline earth metal complex by the CVD equipment shown in FIG. Examples of the present invention in which a film is formed will be described.

Example 1 [Sr (DPM) ₂ ] used
Is a powder obtained by reacting metal strontium and dipivaloylmethane in dehydrated toluene. As shown in FIG. 4, the powder is once melted and formed into a pipe having a length of 50 cm and an inner diameter of 1 cm. It was poured into a cylindrical raw material container and cooled and solidified in this container.

As shown in FIG. 1, two of these are connected in series, set in a thermostat 3 maintained at 200 ° C., and the Si substrate 6 in the reactor 5 is
Heated and maintained at ° C. And A at a flow rate of 100 mL / min.
The r gas is fed into the upstream cylindrical raw material container 2, and the gaseous oxygen is fed from the pipe 7 at the same flow rate of 100 mL / min, and the pressure inside the reactor 5 is maintained at 10 Torr by driving the rotary pump 8. Film formation was performed in this state. At that time, a heating tank 11 with a heater was provided in the pipe 4 from the cylindrical raw material container 2 to the reactor 5 so that the inner wall temperature of the pipe 4 was maintained at 220 ° C.

When a film was formed under these conditions for 30 minutes, a strontium oxide thin film having a thickness of 330 nm (about 650 nm per hour) was obtained.

An experiment was conducted again under the same conditions in which the film formation time was increased by 5 hours each up to 35 hours, and the film formation rate at each time was measured to determine the film formation rate of strontium oxide. FIG. 6 shows the result.

As can be seen from the results of FIG. 6, the film formation rate shows a constant value of about 650 nm / hour up to 30 hours, indicating that the film formation rate does not change with time.

According to the results shown in FIG. 6, the film formation rate was reduced for 35 hours, but in this case, the upstream cylindrical raw material container was empty and the downstream cylindrical material container was empty. It remained in the raw material container. Therefore, 30 hours to 35
It is considered that the raw material in the upstream cylindrical raw material container was completely evaporated during the time. Therefore, remove the empty container,
The downstream cylindrical raw material container was moved to the upstream side as shown in FIG. 5D, a new raw material container was connected to the downstream side, and film formation was performed again under the same conditions. It returned to the film forming speed.

[Comparative Example] A height of 11 cm and a diameter of 4 cm
20 g of the powder of [Sr (DPM) ₂ ] was charged in an inert atmosphere into a cylindrical container with a lid. An air supply pipe for feeding Ar gas into the container and a pipe for guiding vapor from the container to the reactor were attached to the lid, and the lower end opening of the former air supply pipe was located near the bottom of the powder layer. A thin film of strontium oxide having a thickness of 240 nm was obtained by forming a film for 30 minutes under the same conditions as in Example 1 except that the powder was vaporized from the powder state.

When the film forming speed in the method of the comparative example was measured in the same manner as in Example 1, the result shown in FIG. 7 was obtained. As is clear from the comparison with that of Example 1 in FIG. 6, it is clear that the film formation rate is slow even from evaporation from the powder having a large surface area, and that the film formation rate gradually decreases with time. Recognize.

[0037]

As described above, according to the present invention,
When the organic alkaline earth metal complex is deposited on the substrate by the CVD method, the organic alkaline earth metal complex can be vaporized efficiently and stably with time. Therefore, a high-quality alkaline earth metal-containing thin film can be stably manufactured at a high film forming rate.

[Brief description of the drawings]

FIG. 1 is an equipment layout showing an example of equipment for forming a film by a CVD method.

FIG. 2 is a side view showing an example of a raw material container used in a CVD method.

3 is an enlarged cross-sectional view of the raw material container of FIG. 2 taken along the line XX.

FIG. 4 is a schematic sectional view of equipment for melting and loading an organic alkaline earth metal complex into a cylindrical raw material container.

FIG. 5 is a schematic cross-sectional view of a raw material container showing an example of connecting a cylindrical raw material container to a series and evaporating an organic alkaline earth metal complex.

FIG. 6 is a diagram showing a measurement result of a film forming rate when the method of the present invention was performed.

FIG. 7 is a diagram showing a measurement result of a film forming speed when a comparative method is performed.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 organic alkaline earth metal complex 2 raw material container for organic alkaline earth metal complex 3 constant temperature bath 4 conduit for guiding organic alkaline earth metal complex vapor to reactor 5 reactor 6 substrate 7 conduit for guiding gaseous oxygen to reactor 8 exhaust device 11 Insulation layer

Claims (4)

[Claims] When a thin film containing an alkaline earth metal is produced by a CVD method using an organic alkaline earth metal complex as a raw material for vaporization, the organic alkaline earth metal complex is once heated to a melting point or higher and melted. A method for vaporizing an organic alkaline earth metal complex in a CVD method, wherein the melt is cooled and solidified in a raw material container, and the solidified organic alkaline earth metal complex is vaporized at a temperature lower than its melting point. 2. A method for producing a thin film containing an alkaline earth metal using an organic alkaline earth metal complex as a raw material for vaporization by a CVD method, wherein the organic alkaline earth metal complex is heated to a melting point or higher and melted. The melt is placed in a cylindrical container,
The container is cast so as to form a solidified layer having a substantially constant thickness extending in a longitudinal axis direction of the container, and a carrier gas is passed through the container in the longitudinal axis direction to remove the organic alkaline earth metal complex from the solidified layer. A method for vaporizing an organic alkaline earth metal complex in a CVD method, comprising vaporizing at a temperature not higher than its melting point. 3. The vaporization method according to claim 1, wherein the organic alkaline earth metal complex is an alkaline earth metal β-diketonate. 4. An alkaline earth metal β-diketonate,
4. The vaporization method according to claim 1, wherein the alkaline earth metal and the [beta] -diketone are synthesized in an anhydrous solvent or in the absence of a solvent.