JP3820704B2 - Manganese oxide thin film manufacturing method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for producing a manganese oxide thin film used for lithium battery materials and the like.
[0002]
[Prior art]
Conventionally, manganese oxide as a lithium battery material is manufactured by a firing method in which a bulk is sintered and pulverized and applied onto a substrate. And an electrode is comprised from the bulk of the manganese oxide manufactured in this way, and the positive and negative electrodes are piled up in the form of sandwiching the electrolyte and separator, and a lithium battery is assembled.
[0003]
However, the firing method for producing a bulk of manganese oxide has the following problems. (1). It takes time to fire. (2). It is difficult to obtain a uniform composition because the grain size of the microcrystal grains is not uniform. Therefore, examination and evaluation of physical properties are necessary between the surface and the inside. (3). Since it is an aggregate of fine crystal grains, it has a high electric resistance. In order to compensate for this, an additive such as a conductive material or a binder is required.
[0004]
[Problems to be solved by the invention]
The present inventor has come up with the idea that a thin film rather than a bulk of manganese oxide may be used to solve such a problem. By using a thin film, it is possible to easily achieve shortening of manufacturing time, uniforming of composition, reduction of electric resistance, and the like. Therefore, in order to produce a manganese oxide thin film by the conventional technique, a method of directly depositing manganese oxide or a method by sputtering can be considered.
[0005]
However, these methods make it difficult to obtain a desired composition due to oxygen deficiency. For example, in the method of directly depositing MnO ₂ , oxygen cannot escape with a composition of MnO ₂ because oxygen escapes into the vacuum. In the sputtering method using a MnO ₂ target, oxygen is not deposited well, so that the valence of manganese is reduced due to oxygen deficiency.
[0006]
OBJECT OF THE INVENTION
Therefore, a main object of the present invention is to provide a method and an apparatus for producing a manganese oxide thin film that can easily produce a good quality manganese oxide thin film having a desired composition.
[0007]
[Means for Solving the Problems]
As a result of repeated studies on various thin film manufacturing techniques, the present inventor has found that an improved hot wall epitaxial method meets the above object. The present invention has been made based on this finding.
[0008]
That is, a method for producing a manganese oxide thin film according to the present invention includes a substrate for vapor deposition, an evaporation source that generates manganese vapor, and a hot that transports the manganese vapor from the evaporation source to the substrate while maintaining the uniform temperature. Using a hot wall epitaxial apparatus having a wall in a vacuum chamber and supplying oxygen into the vacuum chamber, the manganese vapor reacts with the oxygen to produce manganese oxide. A manganese oxide thin film is produced by depositing an object on the substrate.
[0009]
An apparatus for manufacturing a manganese oxide thin film according to the present invention uses the manufacturing method according to the present invention, and includes a substrate for vapor deposition, an evaporation source for generating manganese vapor, and the substrate from the evaporation source. A hot wall for transporting the manganese vapor while maintaining a uniform temperature, a vacuum chamber for housing the substrate, the evaporation source and the hot wall, and supplying oxygen into the vacuum chamber to supply the oxygen to the manganese vapor. And an oxygen supply source in contact with each other.
[0010]
The substrate is preferably heated to about 300 ° C. Further, the evaporation source vaporizes solid manganese using heat generated by electric power, and controls the electric power supplied to the evaporation source so that the degree of vacuum in the vacuum chamber is within a predetermined range. It is good. The power control in this case may be any voltage, current, time (pulse width), etc.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic cross-sectional view showing an embodiment of an apparatus for producing a manganese oxide thin film according to the present invention. Hereinafter, description will be given based on this drawing.
[0012]
The manganese oxide thin film manufacturing apparatus 10 of the present embodiment transports a substrate 12 for vapor deposition, an evaporation source 14 that generates manganese vapor Mv, and the manganese vapor Mv from the evaporation source 14 to the substrate 12 while maintaining the temperature at a uniform temperature. The hot wall 16 to be heated, the vacuum chamber 18 that houses the substrate 12, the evaporation source 14, and the hot wall 16, and the oxygen supply source that brings oxygen O ₂ into contact with the manganese vapor Mv by supplying oxygen O ₂ into the vacuum chamber 18. 20.
[0013]
The manufacturing apparatus 10 is an improvement of a general hot wall epitaxial apparatus. The hot wall epitaxial apparatus includes an evaporation source 14, a hot wall 16, and a head unit 22 provided in a vacuum chamber 18.
[0014]
The evaporation source 14 and the hot wall 16 are integrally realized by a crucible 24 that houses manganese M inside and a heater 26 that heats manganese M from the outside of the crucible 24. The crucible 24 is made of quartz or the like, for example, and has a bottomed cylindrical shape as a whole. The heater 26 includes a quartz cylinder 261 and a heating resistance wire 262 spirally wound around the outer circumference of the cylinder 261. The heating resistance wire 262 is made of, for example, tungsten or tantalum.
[0015]
The head unit 22 includes a mounting table 221 for mounting the substrate 12, a shutter 223 interposed between the through hole 222 of the mounting table 221 and the open end 241 of the crucible 24, and a halogen lamp 224 for heating the substrate 12. And a temperature sensor 225 such as a thermocouple for detecting the temperature of the substrate 12 and a temperature for controlling the power supplied to the halogen lamp 224 based on the temperature detected by the temperature sensor 225 so that the temperature of the substrate 12 becomes a predetermined value. And a controller 226. The mounting table 221 is fixed to the vacuum chamber 18 by support bars 225 and 226.
[0016]
Various kinds of glass (slide glass, quartz glass, etc.), stainless steel, copper or aluminum are used for the substrate 12. When the substrate 12 is heated, the movement of the substance deposited on the substrate 12 is promoted, so that the film quality is improved. The halogen lamp 224 is a heater for the substrate 12.
[0017]
Oxygen supply 20 includes a gas cylinder 201 that oxygen O ₂ is filled, the opening and closing valve 202 of the oxygen O ₂ for supplying, from the mass flow controller 203 supplies while controlling the oxygen O ₂ at a constant flow rate into the vacuum chamber 18 It is configured.
[0018]
Further, the manufacturing apparatus 10 is provided with a vacuum gauge 301 and a vacuum degree controller 302 for controlling the degree of vacuum by a heater current. The vacuum gauge 301 is, for example, an ion gauge. The vacuum degree controller 302 is constituted by, for example, a microcomputer and a constant current source.
[0019]
A feature of a general hot wall epitaxial apparatus is that epitaxial growth can be performed in a state close to thermal equilibrium, so that a high-quality thin film can be formed, and loss of vapor deposition material can be minimized. The hot wall 16 is located between the evaporation source 14 and the substrate 12, maintains the manganese vapor Mv at a uniform temperature, and serves as a transport pipe for the manganese vapor Mv. Since the evaporation source 14 to the substrate 12 are sealed to some extent, the dissipation of the manganese vapor Mv to the outside can be prevented and the vapor pressure can be controlled to be constant. Since the evaporation source 14, the hot wall 16, and the substrate 12 are thermally weakly coupled, the temperature can be independently controlled within a certain range.
[0020]
Next, an embodiment of a method for producing a manganese oxide thin film according to the present invention will be described by the operation of the production apparatus 10.
[0021]
First, after the vacuum chamber 18 is opened to atmospheric pressure, the substrate 12 and the powdered manganese M are set in the vacuum chamber 18. Subsequently, after the inside of the vacuum chamber 18 is set to a predetermined degree of vacuum by a vacuum pump (not shown), oxygen O ₂ having a constant flow rate is introduced from the oxygen supply source 20 into the vacuum chamber 18, thereby vacuum inside the vacuum chamber 18. The degree is about 10 ⁻⁶ Torr. Here, the heating resistance wire 262 is energized and the halogen lamp 224 is turned on. Then, the heating resistance wire 262 heats the evaporation source 14 and the hot wall 16, and the halogen lamp 224 heats the substrate 12. The thus heated manganese M melts and becomes manganese vapor Mv, leaves the evaporation source 14, and repeatedly collides with the inner wall of the hot wall 16, so that the temperature of the hot wall 16 becomes substantially equal. Move towards. When the shutter 223 is opened, the manganese vapor Mv reacts with oxygen O ₂ on the substrate 12 to become manganese oxide, and re-evaporation and redeposition occur between the substrate 12 and in a state close to thermal equilibrium. Crystal grows. As a result, a single crystal (not shown) of the manganese oxide thin film is formed on the substrate 12.
[0022]
Needless to say, the present invention is not limited to the above embodiment. For example, the manufacturing apparatus 10 may be provided with a reservoir as necessary.
[0023]
【Example】
Next, an embodiment of the manufacturing apparatus shown in FIG. 1 will be described with reference to FIGS.
[0024]
FIG. 2 is an X-ray diffraction diagram showing the substrate temperature dependence of crystallinity in the manganese oxide thin film manufactured by the manufacturing apparatus of FIG.
[0025]
The crystallinity of the manganese oxide thin film was examined by changing the substrate temperature Tsub from 200 ° C. to 600 ° C. The polycrystalline manganese oxide remained as it was up to the substrate temperature of 200 ° C., but a single crystal manganese oxide thin film was obtained at the substrate temperature of 300 ° C. As a result of examining the relative intensity (200) / (220) of X-ray diffraction of the manganese oxide thin film, the maximum of this intensity ratio was 300 ° C. That is, it was found that a single crystal manganese oxide thin film can be obtained at a specific temperature (300 ° C.).
[0026]
FIG. 3 is a graph of an X-ray diffraction peak showing the dependence of crystallinity on oxygen flow rate in the manganese oxide thin film manufactured by the manufacturing apparatus of FIG.
[0027]
In FIG. 3, the horizontal axis represents the oxygen flow rate, and the vertical axis represents the peak intensity of the (200) plane of X-ray diffraction. It can be seen that the crystallinity of the manganese oxide thin film increases as the oxygen flow rate is increased. Thus, it was found that the crystallinity of the manganese oxide thin film depends on the oxygen flow rate.
[0028]
FIG. 4 is an X-ray diffraction diagram showing the dependence of crystallinity on the oxygen flow rate in the manganese oxide thin film produced by the production apparatus of FIG.
[0029]
FIG. 4 shows X-ray diffraction peaks when the oxygen flow rate is low and when it is high. When the oxygen flow rate was low, the manganese oxide thin film showed a polycrystalline peak pattern, and when the oxygen flow rate was high, the manganese oxide thin film showed a single crystal peak pattern. Therefore, it is possible to produce a single crystal manganese oxide thin film with good crystallinity by increasing the oxygen flow rate.
[0030]
FIG. 5 is a graph showing the relationship between the heater current and the degree of vacuum when the manganese oxide thin film is manufactured by the manufacturing apparatus of FIG.
[0031]
The heater current is a current that flows through the heating resistance line 262 of the heater 26. Therefore, by controlling the heater current, the power supplied to the evaporation source 14, that is, the heat generation amount can be controlled. As shown in FIG. 5, when the heater current is small below the point (A), the temperature required for the evaporation of manganese M has not been reached, so the degree of vacuum is balanced between the oxygen flow rate and the suction capacity of the vacuum pump. Is in a state. Eventually, when the heater current exceeds the point (B) and evaporation of manganese M begins, the degree of vacuum does not deteriorate due to the manganese vapor pressure, but the degree of vacuum improves. This is because manganese M and oxygen O ₂ react and adhere to the substrate 12 and the vacuum chamber 18. When the heater current further increases and exceeds the point (C), the evaporation rate of manganese M becomes larger than the generation rate of manganese oxide, and the degree of vacuum decreases due to the manganese partial pressure.
[0032]
FIG. 6 is an X-ray diffraction pattern of the thin film obtained at points (A), (B), and (C) shown in FIG.
[0033]
It was found that the composition at point (A) was γ-Mn ₂ O ₃ , the composition at point (B) was Mn ₃ O ₄ , and the composition at point (C) was α-Mn and MnO. Therefore, a manganese oxide thin film as shown in FIG. 6 can be obtained by controlling the heater current so that the degree of vacuum becomes the position of the point (B) in FIG. Such control is possible by the vacuum gauge 301 and the vacuum controller 302 that stores the relationship of FIG.
[0034]
FIG. 7 is a graph showing the relationship between the oxygen flow rate, the deposition rate of manganese, and the surface state of the thin film when the manganese oxide thin film is produced by the production apparatus of FIG.
[0035]
In FIG. 7, the thin film whose surface indicated by black circles is black-brown is manganese oxide, and the thin film whose surface indicated by white circles is metallic luster (silver) is manganese (metal). As is clear from FIG. 7, it can be seen that there is clearly a region (black circle portion) where manganese oxide can be generated, which is obtained by appropriately selecting the oxygen flow rate and the deposition rate of manganese. The oxygen flow rate can be controlled by the oxygen source 20. The deposition rate (evaporation rate) of manganese can be controlled by the heater current using the relationship shown in FIG.
[0036]
If the heater current and the halogen lamp current are controlled based on the temperature of the evaporation source 14 and the temperature of the substrate 12, a problem arises as to where the measurement point is set, and the control method becomes complicated. On the other hand, when the degree of vacuum is used as a reference as described above, the degree of vacuum is constant everywhere in the vacuum chamber 18, and thus the control method is simple.
[0037]
【The invention's effect】
According to the method and apparatus for manufacturing a manganese oxide thin film according to the present invention, a manganese oxide thin film is manufactured by reacting manganese vapor and oxygen using a hot wall epitaxial apparatus, and thus has a desired composition. A good quality manganese oxide thin film can be easily manufactured. Therefore, shortening of manufacturing time, uniforming of composition, reduction of electric resistance, etc. can be easily achieved. Further, by using the manganese oxide thin film as a lithium battery positive electrode material, the lithium battery electrode can be made thinner and lighter.
[0038]
Further, the composition of the manganese oxide thin film can be easily controlled in situ by controlling the power supplied to the evaporation source so that the degree of vacuum in the vacuum chamber is within a predetermined range.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an embodiment of an apparatus for producing a manganese oxide thin film according to the present invention.
FIG. 2 is an X-ray diffraction diagram showing the substrate temperature dependence of crystallinity in a manganese oxide thin film manufactured by the manufacturing apparatus of FIG.
3 is a graph of an X-ray diffraction peak showing the dependence of crystallinity on oxygen flow rate in a manganese oxide thin film manufactured by the manufacturing apparatus of FIG.
4 is an X-ray diffraction diagram showing the dependence of crystallinity on oxygen flow rate in a manganese oxide thin film produced by the production apparatus of FIG. 1. FIG.
FIG. 5 is a graph showing a relationship between a heater current and a degree of vacuum when a manganese oxide thin film is manufactured by the manufacturing apparatus of FIG. 1;
6 is an X-ray diffraction pattern of the thin film obtained at points (A), (B), and (C) shown in FIG.
7 is a graph showing the relationship between the oxygen flow rate, manganese deposition rate, and the surface state of the thin film when the manganese oxide thin film is produced by the production apparatus of FIG. 1. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Manganese oxide thin film manufacturing apparatus 12 Substrate 14 Evaporation source 16 Hot wall 18 Vacuum chamber 26 Heater 224 Halogen lamp 225 Temperature sensor 226 Temperature controller 301 Vacuum gauge 302 Vacuum degree controller M Manganese Mv Manganese vapor O ₂ oxygen

Claims (6)

  A hot wall epitaxial apparatus comprising a substrate for vapor deposition, an evaporation source that generates manganese vapor, and a hot wall that transports the manganese vapor from the evaporation source to the substrate while maintaining a uniform temperature in a vacuum chamber. The manganese vapor and the oxygen are reacted by supplying oxygen into the vacuum chamber to produce manganese oxide, and the manganese oxide is deposited on the substrate to produce a manganese oxide thin film. The manufacturing method of a manganese oxide thin film.   A substrate for vapor deposition, an evaporation source that generates manganese vapor, a hot wall that transports the manganese vapor from the evaporation source to the substrate while maintaining a uniform temperature, and the substrate, the evaporation source, and the hot wall are accommodated. An apparatus for producing a manganese oxide thin film, comprising: a vacuum chamber for performing the above operation; and an oxygen supply source for bringing oxygen into contact with the manganese vapor by supplying oxygen into the vacuum chamber. The manufacturing method of the manganese oxide thin film of Claim 1 which heats the said board | substrate to about 300 degreeC . The evaporation source is intended to steam the manganese solid using the heat generated by the power, claim 1, the vacuum degree of the vacuum chamber controls the power supplied to the evaporation source so as to have a predetermined range Or the manufacturing method of the manganese oxide thin film of 3 description . The apparatus for producing a manganese oxide thin film according to claim 2, further comprising: a head unit that mounts and heats the substrate, and a temperature controller that controls the temperature so that the head unit is heated to about 300 ° C. The evaporation source includes a heater that vaporizes solid manganese using heat generated by electric power, and controls a power supplied to the evaporation source so that the vacuum in the vacuum chamber is in a predetermined range. The manufacturing apparatus of the manganese oxide thin film of Claim 2 or 5 provided with these .

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