JP3998309B2 - Vaporization method of organic alkaline earth metal complex in CVD method - Google Patents

Description

[0001]
BACKGROUND 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]
[Prior art]
A thin film containing an alkaline earth metal as a component is useful for a ferroelectric material, an EL element material, a superconductor material, and the like. Therefore, a method for producing the thin film has been actively studied.
[0003]
As a thin film manufacturing technique, a physical film forming method such as a vacuum deposition method and a sputtering method and a chemical film forming method such as a chemical vapor deposition (CVD) method are well known. The CVD method is widely used because it is excellent in controllability of film formation rate, controllability of film composition, high-speed film formation property, film formation property over a large area, etc. and is suitable for mass production. In the production of a capacitor film of a gigabit class DRAM, which has been used, the CVD method having excellent step film property has attracted attention as the most promising thin film production method.
[0004]
In the CVD method, an organic metal complex is also used as a source material for supplying a metal component constituting a thin film, and a film forming method using an organometallic complex as a raw material for vaporization is particularly called an MOCVD method. The MOCVD method has been widely studied in the production of ferroelectric thin films, electrode thin films, oxide superconducting thin films, etc. used in DRAM capacitors, and organometallic complexes having β-diketones as ligands are used. . Among these, complexes containing dipivaloylmethane (DPM) as a ligand have the advantages of generally good vaporization, high thermal decomposition temperature, and low impurity contamination into the film, and are most often used. Yes.
[0005]
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, and these complexes are also β-diketone series, What uses pivaloylmethane (DPM) as a ligand is used.
[0006]
[Problems to be solved by the invention]
When forming an alkaline earth metal-containing material by CVD, 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 a powder form and generally has a high melting point (usually 200 ° C. or higher for a DPM complex). The alkaline earth metal DPM complex has a relatively low decomposition temperature, so decomposition occurs when the temperature is too high, and the valves of the CVD apparatus interfere with the function at 200 ° C. or higher. When vaporizing by the CVD method, it is common to vaporize from a powder state at a temperature below the melting point, but in this case, according to the experience of the present inventors, the deposition rate changes with the passage of time ( It was found that the alkaline earth metal content during film formation changed.
[0007]
That is, if the powdered organic alkaline earth metal complex is sublimated from its powder state, it is difficult to ensure a constant film formation rate for a long time. This is because the surface area of the raw material particles decreases as the sublimation progresses, the decrease in the surface area slows the vaporization rate, and the vaporization rate fluctuates due to partial fusion between the powders. It is thought. For this reason, vaporization from a powder state inevitably results in a decrease in the amount of steam over time and fluctuations in the amount of steam. When the vaporization rate changes, when an alkaline earth metal-containing thin film (for example, SrTiO ₃ ) is produced, it becomes difficult to control the film formation.
[0008]
A solution vaporization CVD method has also been developed in which the raw material complex is dissolved in an organic solvent and the entire solution sent to the vaporizer is vaporized by controlling the liquid flow rate. A similar film forming speed cannot be obtained unless heated. For this reason, there are many problems to be solved such as clogging of piping in the vaporizer due to decomposition of the raw material in the vaporizer and mixing of a large amount of solvent decomposition products into the film.
[0009]
Accordingly, an object of the present invention is to enable stable vaporization of an organic alkaline earth metal complex in a CVD method for producing an alkaline earth metal-containing thin film.
[0010]
[Means for Solving the Problems]
In the present invention, when a thin film containing an alkaline earth metal is prepared by vapor deposition using an organic alkaline earth metal complex as a raw material for CVD, the organic alkaline earth metal complex is once heated to a melting point or higher and melted. The melt is cooled and solidified in a raw material container, and the solidified organic alkaline earth metal complex is vaporized at a temperature below its melting point.
[0011]
Furthermore, the present invention provides 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. The melt is cast into a cylindrical container so that a solidified layer having a substantially constant thickness extending in the longitudinal axis direction of the container is formed, and a carrier gas is passed through the container in the longitudinal axis direction. The organic alkaline earth metal complex is vaporized from the solidified layer at a temperature below its melting point.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In order to solve the above problems, the present inventors have conducted various test studies. Before using the organic alkaline earth metal complex as a film-forming raw material, it was once heated to a melting point or higher and melted. It has been found that the use of a material that has been cooled and solidified (solidified) 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 direction of the container, and a carrier gas is passed through the surface of the solidified layer in the axial direction of the container and vaporized. It was found that the film can be formed more stably.
[0013]
The organic alkaline earth metal complex used in the present invention is preferably an alkaline earth metal, for example, β-diketonate such as Be, Mg, Ca, Sr, Ba, etc., and particularly dipivaloylmethane (DPM) as a ligand. Organic alkaline earth metal complexes are preferred. It was also found that such alkaline earth metal β-diketonate synthesized in an anhydrous solvent or without a solvent did not decompose even when temporarily heated to the melting point or higher. Therefore, alkaline earth metal β-diketonate synthesized in an anhydrous solvent or in the absence of a solvent can be preferably used in the practice of the present invention.
[0014]
A preferred embodiment of the present invention will be described below with reference to the drawings.
[0015]
FIG. 1 shows that a raw material container 2 loaded with an organic alkaline earth metal complex 1 is set in a thermostat 3 maintained at a predetermined temperature, and a complex vapor vaporized in the raw material container 2 is a carrier gas (in the example, argon gas). ) Shows the CVD equipment which is led to the reactor 5 through the pipe line 4 and is deposited on the surface of the 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 introducing the complex vapor, and this oxygen gas pipe 7 is connected to the pipe 4 at a position immediately before the reactor 5. When the complex vapor and oxygen gas are mixed at the merging position at an adjusted quantity ratio, both react to produce a thin film of the intended component on the surface of the substrate 6.
[0016]
In FIG. 1, 8 is an exhaust device (rotary pump) for reducing the pressure in the system, 9 is an exhaust valve, 10 is a cooling trap, and the complex vapor supply line 4 from the thermostat 3 to the reactor 5 is The outer periphery is surrounded by a heat insulating layer 11. A heater (not shown) is provided in the heat retaining layer 11 so that the inner wall temperature of the pipe line 4 is maintained at a temperature 5 to 50 ° C. higher than the temperature of the thermostatic chamber 3. The reactor 5 is heated to a predetermined temperature by a heater 12 attached to the outer periphery thereof, and the reactor 5 with the heater 12 is set in the pyrolysis furnace 13 in its entirety.
[0017]
In the present invention, the organic alkaline earth metal complex 1 is once heated to a temperature equal to or 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 cooled and solidified so that a solidified layer having a substantially constant thickness extending in the longitudinal axis direction of the cylindrical container is formed. This embodiment will be specifically described below.
[0018]
In the CVD facility shown in FIG. 1, a thermostat 3 is set with two identical cylindrical raw material containers 2 connected in series. A specific example of the cylindrical raw material container 2 is shown in FIG. In this raw material container 2, branch pipes 16 and 17 in the same direction are connected in the vicinity of the end of a pipe 15 whose both ends are closed, and 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, and the cross-sectional shape thereof is circular (15a), square (15b), elliptical (15c), etc. as shown in FIG. it can. In the facility of FIG. 1, two such cylindrical raw material containers 2 are used. The carrier gas pipe 20 is connected to the branch pipe 16 of one of the containers, and the other branch pipe 17 is connected to the connection pipe 21. Is connected to the branch pipe 16 of the other container, and the branch pipe 17 of the other container is connected to the complex vapor line 4. As a result, in the state in which the valves 18 and 19 are all open, the carrier gas first enters one container, then enters the other container via the connecting pipe 21 and flows to the conduit 4.
[0019]
FIG. 4 illustrates an operation mode in which the organic alkaline earth metal complex 1 is charged into the cylindrical raw material container 2. The operation will be described with reference to FIG. 4. A raw material organic alkaline earth metal complex powder 23 is loaded in a container 25 having a nozzle 24 at the bottom in an inert gas atmosphere, and the bottom nozzle 24 of the container 25 is loaded. The branch pipe 17 of the cylindrical raw material container 2 is connected with the valve 19 closed, and the other branch pipe 16 and the upper opening 26 of the container 25 are connected by a connection pipe 27 to form a closed circuit. Then, the atmosphere in the closed circuit is completely replaced with an inert gas, and the cylindrical raw material container 2 is set in an electric furnace 28 (shown by a broken line) so that it is in a horizontal state. Thereby, the powder in the container 25 is heated to a melting point or higher and melted. This is the stage shown in the uppermost stage of FIG.
[0020]
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 of FIG. 4 shows the middle stage of the pouring. The pouring is continued, and the pouring is finished in a state where the melt is loaded at a predetermined depth with a horizontal liquid surface in the cylindrical raw material container 2 in a horizontal state. The solidified layer having a substantially constant thickness extending in the longitudinal axis direction of the cylindrical raw material container 2 is formed by cooling to. The lowermost diagram in FIG. 4 shows this state, and the solidified layer is indicated by 29. The solidified layer 29 is formed to a depth that occupies a part of the cross section of the container, and a space through which the carrier gas flows is opened above. When the casting of the organic alkaline earth metal complex is completed in this way, the valves 18 and 19 are closed, separated from the loading equipment with the branch pipe, and moved to the CVD equipment. For example, as shown in FIG. Set in 3.
[0021]
Thus, 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 becomes much smaller than that of the powder raw material, It was found that the change can be suppressed almost completely. This is thought to be due to the fact that the fluctuation of the surface area is extremely small even when evaporation proceeds. Further, even if the carrier gas is passed 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. For this reason, it is possible to prevent the powder from reaching the reactor 5 and contaminating the membrane.
[0022]
In particular, when 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 extending in the axial direction as described above. In this case, when the carrier gas is allowed to flow in one direction along the axis of the container, a raw material vapor close to the saturation vapor pressure is obtained in the vicinity of the branch pipe 17 on the container outlet side in spite of vaporization from the solid state. I found out that
[0023]
This relationship becomes better as the cylindrical material container 2 is longer and as the ratio of length / bore (inner diameter of the pipe) is larger. In practice, the container dimensions, carrier gas flow rate, and the like may be appropriately selected according to the apparatus conditions so that a saturated vapor pressure is obtained in the vicinity of the branch pipe 17 on the container outlet side. Moreover, if the cylindrical raw material container 2 is connected to the series, the raw material can be used without waste. In the example of FIG. 1, the aspect which connected the two cylindrical raw material containers 2 is shown.
[0024]
In such a cylindrical raw material container 2, the concentration of the complex vapor is lower at the upstream side and higher at the downstream side in the flow direction of the carrier gas. Therefore, if a plurality of cylindrical raw material containers 2 designed so as to obtain a saturated vapor pressure in the vicinity of the outlet of the container are connected in series and fed forward, a semi-permanent continuous operation can be achieved. It becomes possible. This aspect will be described with reference to FIG.
[0025]
FIG. 5 shows a case where two cylindrical raw material containers 2a and 2b loaded with a predetermined amount of an organic alkaline earth metal complex that has been once melted and cooled and solidified are connected in series via a connecting pipe 21 to branch the upstream container 2a. A state is shown in which the carrier gas is introduced from the pipe 16 side and is supplied to the reactor 5 from the branch pipe 17 side of the downstream side container 2b (the thermostat is omitted). In this way, when vaporization from the solid complex is started so that the saturated vapor pressure of the complex is obtained in the vicinity of the outlet of the upstream side container 2a, a gas close to the saturated vapor pressure is sent into the downstream side container 2b, so that it is slightly evaporated. However, since most of the complex vapor is vaporized from the upstream container 2a, the solid raw material 1a in the upstream container 2a is preferentially reduced, and the state from A to B in FIG. The thickness of the solid raw material 1a in the upstream container 2a decreases and eventually the upstream container 2a becomes empty as in the state of FIG. 5C, but even in this state, the solid raw material 1b is sufficiently present in the downstream container 2b.
[0026]
Therefore, the empty upstream side container 2a is removed, the downstream side container 2b is moved upstream, and a new cylindrical raw material container 2c is connected to the downstream side and newly replenished. This state is shown in FIG. This preferentially evaporates from the downstream container 2b and returns to the state of FIG. Thereafter, by repeating this, the complex vapor having substantially the same concentration can be continuously transferred to the reactor. Moreover, since the raw material complex is almost empty, it can be replenished, so that the raw material can be used without waste.
[0027]
As described above, according to the present invention, it is possible to stably generate a vapor having a certain concentration of the organic alkaline earth metal complex. For this reason, the deposition rate is stable over time, and a homogeneous film can be formed. In the above embodiment, the explanation has been made mainly on the evaporation of the organic alkaline earth metal complex. However, when the vapors of other raw materials are also led to the reactor at the same time, a facility for introducing the vapors of the other raw materials is attached to the reactor. That's fine. In addition to the embodiment shown in FIG. 4 in which the organic alkaline earth metal complex is melted in another container and poured into the raw material container 2 and cooled and solidified, the powder raw material is put in the raw material container 2 set in the CVD facility. 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】
In the following, a strontium oxide film is formed 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 invention are given.
[0029]
[Example 1]
The [Sr (DPM) ₂ ] used was a powder obtained by reacting metal strontium with dipivaloylmethane in dehydrated toluene. This powder was once melted and long as explained in FIG. It was poured into a pipe-shaped cylindrical raw material container having a length of 50 cm and an inner diameter of 1 cm, and cooled and solidified in this container.
[0030]
Two of these were connected in series as shown in FIG. 1 and set in a thermostat 3 maintained at 200 ° C., and the Si substrate 6 in the reactor 5 was heated and held at 600 ° C. by a heater 12. Then, Ar gas is sent to the upstream cylindrical raw material container 2 at a flow rate of 100 mL / min, and gaseous oxygen is similarly sent from the pipe 7 at a flow rate of 100 mL / min, and the rotary pump 8 is driven to drive the reactor 5 into the reactor 5. The film was formed while maintaining the pressure at 10 torr. At that time, a heat insulating tank 11 with a heater is provided in the pipe line 4 from the cylindrical raw material container 2 to the reactor 5 so that the inner wall temperature of the pipe line 4 is maintained at 220 ° C.
[0031]
When film formation was performed for 30 minutes under these conditions, a thin film of strontium oxide having a thickness of 330 nm (about 650 nm per hour) was obtained.
[0032]
Again, an experiment was performed in which the film formation time was increased by 5 hours under the same conditions up to 35 hours, and the film formation rate at each time was measured to measure the film formation rate of strontium oxide. The results are shown in FIG.
[0033]
As can be seen from the results of FIG. 6, the deposition rate shows a constant value of about 650 nm / hour up to 30 hours, and it can be seen that the deposition rate does not change with time.
[0034]
Further, according to the result of FIG. 6, the film forming speed is reduced at 35 hours, but in this case, the upstream cylindrical raw material container is empty, and the downstream cylindrical raw material container is empty. Remained. Therefore, it is considered that the raw material in the upstream cylindrical raw material container was completely evaporated during 30 to 35 hours. For this reason, the empty container is removed, the downstream cylindrical raw material container is moved to the upstream side as shown in FIG. 5D, and a new raw material container is connected to the downstream side again under the same conditions. When the film was formed, it returned to the same film formation rate as described above.
[0035]
[Comparative Example]
A cylindrical container with a lid having a height of 11 cm and a diameter of 4 cm was charged with 20 g of [Sr (DPM) ₂ ] powder in an inert atmosphere. An air supply pipe for introducing Ar gas into the container and a pipe for introducing steam from the container to the reactor were attached to the lid, and the lower end opening of the former air supply pipe was positioned near the bottom of the powder layer. Thus, when it formed into a film for 30 minutes on the same conditions as Example 1 except vaporizing from a powder state, the thin film of strontium oxide of thickness 240nm was obtained.
[0036]
Further, when the film formation rate in the method of this 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 Example 1 in FIG. 6, the film formation rate is slow even after evaporation from the powder having a large surface area, and the film formation rate gradually decreases with time. Recognize.
[0037]
【The invention's effect】
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 over time. it can. For this reason, a high-quality alkaline earth metal-containing thin film can be stably produced at a high film formation rate.
[Brief description of the drawings]
FIG. 1 is an equipment layout diagram 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 line XX.
FIG. 4 is a schematic cross-sectional view of a facility for melting and charging 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 in which a cylindrical raw material container is connected in series to evaporate an organic alkaline earth metal complex.
FIG. 6 is a diagram showing the measurement results of the film formation rate when the method of the present invention is carried out.
FIG. 7 is a diagram showing a measurement result of a film formation rate when a comparative method is performed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Organic alkaline-earth metal complex 2 Raw material container of organic alkaline-earth metal complex 3 Constant temperature bath 4 Pipe line which leads organic alkaline-earth metal complex vapor | steam to a reactor 5 Reactor 6 Substrate 7 Pipe line which leads gaseous oxygen to a reactor 8 Exhaust device 11 Thermal insulation layer

Claims (4)

When a thin film containing an alkaline earth metal is prepared by vapor deposition 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. casting into the source container, the cast is vaporized method of the organic alkaline earth metal complex in the CVD method using organic alkaline earth metal complexes, wherein the vaporizing in that a temperature below the melting point formed by.   When producing a thin film containing an alkaline earth metal using the organic alkaline earth metal complex as a raw material for vaporization by the CVD method, the organic alkaline earth metal complex is heated to a melting point or higher and melted. Cast into a cylindrical container so that a solidified layer having a substantially constant thickness extending in the longitudinal axis direction of the container is formed, and a carrier gas is passed through the container in the longitudinal axis direction from the solidified layer. A method for vaporizing an organic alkaline earth metal complex in a CVD method, wherein the organic alkaline earth metal complex is vaporized at a temperature below its melting point.   The vaporization method according to claim 1, wherein the organic alkaline earth metal complex is an alkaline earth metal β-diketonate. The vaporization method according to claim 3, wherein the alkaline earth metal β-diketonate is obtained by synthesizing an alkaline earth metal and a β-diketone in an anhydrous solvent or without a solvent.

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