JPH04311571A - Method for forming metallic oxide film on substrate - Google Patents

Abstract

PURPOSE:To produce a thick metallic oxide film when a raw liq. is vaporized by the ultrasonic wave and the vapor is brought into contact with a heated substrate to form a metallic oxide film by incorporating a soln. of the metal seeds constituting the metallic oxide into the raw liq. CONSTITUTION:A metallic alkoxide soln. 2 consisting of metals (Pb, Ti, Zr, etc.) and alcohols, for example, is vaporized by an ultrasonic vibrator 1. A carrier gas (N2, Ar, etc.) is introduced from an inlet 3 and a gaseous reactant (O2, NO2, etc.) from an inlet 4, as required, the vaporized material is sent to a substrate 9 (glass, ceramic, etc.) heated by a heater 5 to form the metallic oxide film on the substrate 9. At this time, 1 layers of the metal oxide film can be previously formed on the substrate 9 or an intermediate layer (Pt/Cu/Cr, etc.) for accelerating the crystallization and orientation of the metallic oxide film is prefereably formed between the substrate 9 and the metallic oxide film, and a bias voltage is impressed on the substrate 9. A thick metallic oxide film having about 1-500mu thickness is formed on the substrate 9 is this way.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to a method of forming a metal oxide film on a substrate. In particular, the present invention relates to a method of atomizing a metal oxide forming solution and forming a film on a substrate by thermal decomposition.

0002

[Prior Art] Ceramics made of inorganic oxides have a wide range of functionality depending on their composition. Particularly in the fields of electronic ceramics and optoelectronics, they have dielectric, piezoelectric, pyroelectric, translucent, and electrical properties. It has been put into practical use in many fields by utilizing optical effects, etc. For example, those that utilize dielectricity are used as non-volatile memory FET elements with low threshold drive, those that utilize piezoelectricity are used in ultrasonic piezoelectric elements and actuator elements, and those that utilize pyroelectricity are used in infrared sensors, etc. has been done. In addition, there are optical waveguides, optical switches, spatial modulation elements, image memories, etc. that utilize translucency and electro-optic effects, and the range of practical applications is extremely wide. Conventional methods for producing thin films made of these ceramics include vapor deposition, sputtering, MOCVD, and the like. On the other hand, the bulk body is formed by the hot press method, and its raw material powder is recently made of Sol, which has good uniformity.
- May be created using the Gel method. The advantage of thin films is that element/electronic ceramics and optoelectronic ceramics can be formed on the same substrate. However, in order to realize the various functions mentioned above, the film thickness of these ceramics is required to be at least 1 μm, and when applied to actuator elements, it is required to be at least 100 μm thick. This is impossible with thin film manufacturing methods. In addition, if a bulk body is formed using the hot press method after an element is formed on a substrate, the element will be destroyed, so processing methods such as forming elements/electronic ceramics and optoelectronic ceramics on the same substrate cannot be used. Therefore, it is limited by the device. Recently, a spray firing technique using ultrasonic waves has been developed as a new method for producing oxide fine particles. The spray firing method is a method in which a liquid is atomized using ultrasonic waves at a frequency above the cavitation generation range, that is, in the range of 0.8 MHz to about 2 MHz, and then thermally decomposed or fired to obtain oxide fine particles. However, creating films such as thin films and thick films using this spray firing method has the disadvantage that, for example, the carrier gas thermally decomposes as soon as it is introduced into the furnace, producing fine particles, making it difficult to put into practical use. I couldn't do it.

Furthermore, these inorganic oxides having various functions and their thick films may have to be crystallized or even oriented due to their characteristics. For example, piezoelectric materials such as ZnO and PZT (lead zirconate titanate) are not only crystallized, but also contain carbon.
By being oriented along the axis, it exhibits piezoelectric properties. Generally, the desired characteristics are achieved by poling a ceramic sintered body. This polarization process called polling is 20
This is carried out at a high temperature of about 0° C. by applying an electric field close to dielectric breakdown. At this time, it may be destroyed, and as the number of steps increases, a decrease in yield becomes a problem.

[0004] The object of the present invention is to
The purpose of this method is to form a thick metal oxide film on a substrate, which cannot be obtained using the VD method or the like, using a new method using a spray firing method.

[0005]

[Structure] The present invention transports a vaporized substance obtained by vaporizing a raw material liquid using ultrasonic waves to a substrate presence area together with a carrier gas and a reaction gas that can be present as necessary, and the carrier gas flow is directed toward the substrate. In a method of forming a metal oxide film on a substrate by heating the substrate to a temperature at which a vaporized substance reacts and forms a metal oxide upon contact, the raw material liquid is a metal constituting the metal oxide. The present invention relates to a method for forming a metal oxide film on a substrate, characterized in that it contains a solution of seeds.

[0006] As the substrate for forming the metal oxide film, an ordinary substrate can be used as it is, but it is also possible to use one with one or more metal layers provided on its surface in advance. Further, it is preferable to provide an intermediate layer between the substrate and the metal oxide layer to promote crystallization and orientation of the metal oxide film. Furthermore, it is preferable that a bias voltage is applied to the substrate that is brought into contact with the carrier gas. The raw material liquid contains a solution of metal species constituting the metal oxide. Specifically, the raw material liquid contains (1) a monovalent solution of the metal constituting the metal oxide or its salt; and/or an alcoholic solution obtained by dissolving or reacting with a polyhydric alcohol, (2) a solution obtained by further ligand-exchanging the solution of (1) above with a β-dicarbonyl compound, (3) the above (1) or A solution obtained by further adding an alkoxide compound to the solution (2) can be used. Of course, the raw material liquid may be composed of a metal-organic compound and an organic solvent, but an aqueous solution containing corresponding metal ions can also be used without using an expensive metal-organic compound.

[0007] Examples of metal organic compounds include methoxide, ethoxide, propoxide, and
Examples include alkoxides such as butoxide and acetate compounds. The water-soluble metal salts for forming the aqueous solution containing the corresponding metal ions include Zn, Cu, Ti,
Examples include nitrates, sulfates, halides, acetates, and phosphates of metals such as Pb, Li, Nb, Al, Zr, Fe, Co, and Ni. Examples of the alcohol include monohydric alcohols such as methanol, ethanol, propanol, and butanol, dihydric alcohols such as ethylene glycol, trihydric alcohols such as glycerin, cellosolve, and carbitol. Examples of the β-dicarbonyl compound include acetylacetone, ethylacetoacetate, diethylmalonate, and the like, which form metal complexes by changing the ligand. For example, tributoxyaluminum and ethyl acetoacetate are reacted to form a metal complex. Examples of alkoxide compounds include metal alkoxides made of the above metals and alcohols, such as Pb(OR)2, Ti(OR)4, Zr(
OR)4, Al(OR)3, LiOR, Nb(OR)5
and so on. However, R is an alkyl group. Carrier gases include N2, Ar, etc., and reactive gases include O2, NO2, NO, H2O, etc. Examples of the substrate include various glasses, ceramics, semiconductors (Si), stainless steel, single crystal substrates such as MgO and SrTiO, and heat-resistant polymer substrates (>200° C.). Further, the metal forming the metal layer is not particularly limited as long as it functions as an electrode and also improves the adhesion with the inorganic oxide to be formed. Regarding adhesion, for example, the inorganic oxide to be formed is easily compatible with Pt, and when glass or the like is used as the substrate, the intermediate layer may be multilayered such as Pt/Cu/Cr or Pt/Ti. By utilizing this metal and applying a DC substrate bias during film formation, a thick film alignment film can be obtained. The intermediate layer that promotes the crystallization and orientation of the metal oxide used in the present invention is, for example, an intermediate layer that has a lattice constant close to the lattice constant of the oriented plane of the metal oxide to be created, and furthermore, A thick film alignment film can be obtained by depositing a vapor-deposited film of metal or the like on such an amorphous material, and by selecting the metal species and matching the lattice constants. In this case, a metal oriented thin film is used as an intermediate layer by vapor deposition, but it can also be created by sputtering or CVD, and materials other than metals may also be used.

Further, the thickness of the thick metal oxide according to the present invention is the thickness necessary to realize its function, and although the required thickness varies depending on the material and device, it is generally 1 μm. 500 μm or less. The apparatus used in the present invention is illustrated in FIG. In the figure, 1 is an ultrasonic transducer, 2
3 is a carrier gas inlet, and 4 is an inlet for a reaction gas as required. 5 is a heater for preheating during gas transfer, 6 is a substrate holder and a heater for heating the substrate, 7 is an external heater for heating the substrate from the outside of the quartz firing furnace, and 8 is a bias for applying a bias to the substrate. 9 is a sample substrate on which a film such as a Si wafer is deposited. Incidentally, this reaction may be carried out under reduced pressure if necessary, and a vacuum evacuation system for this purpose may be installed. The metal oxide formed on the substrate according to the present invention is a commonly-called inorganic oxide, and is not particularly limited, and includes, for example, SiO2, Al2O3, Na2O,
In addition to insulating materials called new glass such as B2O3, dielectric materials such as BaTiO3 and SrTiO3, P
b Piezoelectric materials such as (Zr, Ti)O, (Mn, Ni, F
e,Co)3O4,BaTiO3,(Ba,Sr)Ti
Semiconductive materials such as O3, SnO2, ZnO, MgCr2O4-TiO2, β-alumina, ZrO2, In2O
- Conductive (or ionically conductive) materials such as SnO2, Y
Superconducting materials such as Ba2Cu3Ox (X=τ−δ), (
Pb, La) (Zn, Ti) O3, LiNbO3, Li
Polarizing materials such as TaO3, (Pb, Ba, La)Nb2
O6, (Pb,K)Nb2O6, (Sr,Ba)Nb2
O6, further (Mn, Zn)O, Fe2O3, BaFe
Examples include so-called electronic ceramics and optoelectronic ceramics such as magnetic materials such as 12O19.

[0009]

[Example] Hereinafter, the present invention will be explained in detail with reference to an example. It should be noted that the present invention is not limited to the following examples unless it exceeds the gist thereof. Example 1 (corresponding to claim 1) The production of a piezoelectric ZnO film is shown. To provide zinc ions, various zinc salts, such as zinc nitrate dissolved in water, are prepared. The concentration is 0.
It is 1 mol/1. A mist of this aqueous solution is generated by applying energy from an ultrasonic vibrator to this aqueous solution. Nitrogen was used as a carrier gas, and oxygen was further flowed as a reaction gas. At this time, the flow rate is controlled so that the flow inside the quartz reactor (tube-shaped) becomes laminar. At this time, the heater 5 is used to preheat to 80°C. The substrate used was a Si wafer with good heat absorption (for IR) and good heat conduction. A sample is held in a substrate holder, and the temperature is set slightly lower than the thermal reaction temperature using an in-heater 6 in the holder, thereby suppressing the thermal reaction of zinc ions and promoting substrate adsorption. The generation of ZnO by thermal reaction is provided with energy by an externally provided lamp heater. The lamp heater is a Xe flash lamp or an arc lamp.
Alternatively, a halogen lamp that emits infrared radiation may be used, and in this example, a halogen lamp was used. However, since the radiant energy of the lamp needs to be applied in pulses, the shutter was linked to heat the lamp in pulses to thermally decompose it. In addition,
If necessary, this reaction can be carried out under reduced pressure or
This may be performed by applying a direct current bias to the substrate. Example 2 (corresponding to claims 4 and 6) Ferroelectric Ba[Ti
y(y=1-x)Zrx]Creation of an O3 film is shown. To provide barium ions, various barium salts such as barium nitrate are dissolved and reacted at 80° C. for 4 hours using ethylene glycol as a polyhydric alcohol. The concentration is 0.1 mol/1. Or
Metallic barium may be dissolved in butyl alcohol. To this solution, a Ti alkoxide compound, isopropoxide titanium, and normal propoxide zirconium were added. The following is the same as in Example 1. However, oxygen as a reactive gas was not used in this case. Example 3 (corresponding to claim 5) Superconductor YBa2Cu3Ox
(x=τ−δ) shows the creation of the film. To provide barium ions, various barium salts such as barium nitrate are dissolved and reacted at 80° C. for 4 hours using ethylene glycol as a polyhydric alcohol. Furthermore, 2,4-pentadione is added to perform a ligand exchange reaction. Do the same with yttrium. Additionally, copper nitrate was similarly dissolved in ethylene glycol. A mixture of these solutions was used. Furthermore, as a means for supplying copper, aqueous solutions of various copper salts, such as copper nitrate and copper chloride, may be used. The following is the same as in Example 1. however,
Oxygen, which is a reactive gas, was used when copper was supplied from an aqueous solution, but oxygen gas was not used in other cases. Example 4 (corresponding to claim 2) The production of a piezoelectric PZT (lead zirconate titanate) C-axis alignment film is shown. The solution is 1 lead acetate
titanium tetraisopropoxide per mole.
5 mol, zirconium tetrapropoxide was adjusted to 0.5 mol, and the concentration was 0.5 mol in methoxyethanol.
It was dissolved to a concentration of 5 mol/l. By applying energy from the ultrasonic transducer 1 to this solution, a mist of this solution is generated. Nitrogen is used as a carrier gas, and the flow rate is controlled so that the flow inside the quartz reactor (tube-shaped) becomes laminar. At this time, heating is performed using the heater 5 so that the preheating temperature becomes 80°C. The substrate 9 used was a Si wafer with good heat absorption (for IR) and good heat conduction. Further, as an intermediate layer, Pt was deposited by EB evaporation at a substrate temperature of 300°C. Next, this sample is held in the substrate holder 6, and the temperature is set slightly lower than the thermal decomposition temperature using an in-heater in the holder, and each metal-organic compound, that is, lead acetate, titanium tetraisopropoxide, etc. , suppresses thermal decomposition of zirconium tetrapropoxide and promotes substrate adsorption. The generation of PZT by thermal decomposition is provided with energy by an externally provided lamp heater 7. The lamp heater may be a Xe flash lamp, an arc lamp, or an infrared-emitting halogen lamp, and in this example, a halogen lamp was used. However, since the radiant energy of the lamp needs to be applied in a pulsed manner, the shutter was linked to heat the lamp in a pulsed manner for thermal decomposition. For substrate bias, use a DC power supply and set the output to 20
The voltage was set to 0V. Further, the direction of the bias cannot be determined unconditionally, and in the case of other inorganic oxides, a good alignment film may be obtained even at -200V. Note that, if necessary, this reaction may be performed under reduced pressure. Example 5 (corresponding to claim 3) Pt as the intermediate layer of Example 4
Example 4 was repeated except that a (111) alignment film was used.

0010

[Effects] The present invention makes it possible to form a thick film that was previously impossible to create, and moreover, the amount of expensive alkoxide compounds used can be reduced compared to usual, and as a result, the film can be manufactured at low cost. In the examples, piezoelectric material ZnO, ferroelectric material Ba[Tiy (y=1-x)Zrx]O3, and superconductor YBa2Cu3Ox (x=τ-δ) were exemplified. It is possible to create thin and thick films of inorganic oxides such as electronic ceramics and new glass.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a membrane manufacturing apparatus used in an example of the present invention.

[Explanation of symbols]

1 Ultrasonic vibrator 2 Metal-organic compound and solvent 3 Carrier gas inlet 4 Reaction gas inlet 5 Heater for preheating 6 Heater for substrate holder and substrate heating 7 External heater 8 Electrode 9 for applying bias to the substrate 9 Substrate

Claims (6)

[Claims] Claim 1: A vaporized substance obtained by vaporizing a raw material liquid using ultrasonic waves is transported together with a carrier gas to an area where a substrate exists, and when the carrier gas flow contacts the substrate, the vaporized substance reacts to form a metal oxide. A method of forming a metal oxide film on a substrate by heating the substrate to a forming temperature, wherein the raw material liquid contains a solution of metal species constituting the metal oxide. A method of forming metal oxide films. 2. The method for forming a metal oxide film on a substrate according to claim 1, wherein the substrate on which the metal oxide film is formed has in advance one or more metal layers on its surface. 3. Forming a metal oxide film on the substrate according to claim 1 or 2, wherein an intermediate layer for promoting crystallization and orientation of the metal oxide film is provided on the substrate before forming the metal oxide film. how to. 4. Metal oxide on the substrate according to claim 1, 2 or 3, wherein the raw material liquid is a solution obtained by dissolving or reacting a metal constituting the metal oxide or a salt thereof in an alcohol. Method of forming a film. 5. The raw material liquid is a solution obtained by dissolving or reacting a metal constituting the metal oxide or a salt thereof in an alcohol and exchanging ligands with a β-dicarbonyl compound. A method for forming a metal oxide film on the substrate according to item 1, 2 or 3. 6. The method for forming a metal oxide film on a substrate according to claim 1, 2 or 3, wherein the raw material solution is the solution according to claim 3 or 4 to which an alkoxide compound is added.