JPH11314999A - Production of oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a thin film with homogeneous film property and good crystallinity by depositing an oxide with low temp. thermal plasma on a substrate maintained at a desired temp. by heating, then growing the oxide thin film in an amorphous state. heat-treating the film at a temp. higher than the objective temp. to crystallize the oxide thin film. SOLUTION: For example, when lead zirconate titanate (PZT) is produced, a silicon substrate in a vacuum chamber is heated to about 500 deg.C and the chamber is evacuated, while argon gas is supplied and a high frequency current is applied to produce low pressure glow plasma. Diethanolamine in which titanium isopropoxide, lead acetate trihydrate and zirconium acetylacetate are dissolved, and butylcellosolve are atomized and injected into the oxygen plasma to form a film while the substrate is kept at about 500 deg.C. Thus, a uniform noncrystalline PZT thin film is formed. Then the silicon substrate is annealed in a vacuum annealing furnace at about 800 deg.C to change the PZT thin film in a noncrystalline state into a good crystal state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thin film on a substrate by using thermal plasma.
In particular, it is suitable for manufacturing a thin film electronic device using an oxide thin film or a microstructure having rigidity and durability.

[0002]

2. Description of the Related Art A film forming method using thermal plasma includes:
Thermal plasma CVD (JP-A-5-320916), plasma SPRAY-ICP (Appl. Phys. Lett. 14 (1990.1)
0) 1452), plasma flash evaporation method (Japanese Patent Laid-Open No. 5-31)
1462), plasma spraying method (Japanese Patent Laid-Open No. 6-67986)
Are known. In each case, a raw material containing a substance to be formed is supplied into thermal plasma, and the raw material is evaporated, decomposed, or reacted in thermal plasma to form an oxide thin film on a substrate.

FIG. 1 shows a film forming apparatus for executing a film forming method using thermal plasma. Here, the substrate holder 107 is provided with a cooling mechanism as shown in FIG. A case in which PZT (lead zirconate titanate) is formed on a substrate using this apparatus will be described. The substrate is placed in the plasma device, and the induction heating coil 125 and the cooling mechanism are operated to heat and hold the substrate at a temperature of 700 ° C. After the temperature reaches 700 ° C., thermal plasma irradiation is started to start plasma film formation. After the plasma irradiation, the output of the induction heating coil is lowered to absorb the rise in the substrate temperature due to the energy of the plasma, and the substrate temperature is maintained at 700 ° C. An oxide thin film is formed on the substrate by performing plasma deposition for a predetermined time.

[0004]

However, in the conventional method, when the irradiation of thermal plasma having strong energy is started in the film formation start stage, the output adjustment of the induction heating coil cannot follow, and the temperature of 30 ° C. Causes a moderate temperature rise and then settles to 700 ° C.

This change in temperature affects the crystallinity and film characteristics of PZT formed first on the substrate surface. The quality, such as crystallinity, of the initially deposited film material affects the quality of the overall film grown thereon. This is not negligible for electronic components that require films with very good crystallinity, such as superconducting materials. Further, in the ordinary film forming method, for example, the sbutter method is in a thermal non-equilibrium state, whereas the thermal plasma is in an equilibrium state, so that the raw material is in a high energy atomic state in the thermal plasma. . For this reason, it has a feature that crystallizes very easily on the substrate.

[0006] As described above, the substrate temperature control is particularly important in the thermal plasma method.

Accordingly, an object of the present invention is to provide a method of manufacturing an oxide thin film by thermal plasma film formation, which can avoid the influence of a change in substrate temperature inevitably caused by plasma irradiation when starting thermal plasma film formation. To provide.

Another object of the present invention is to provide a method for producing an oxide thin film having a uniform film quality, less oxygen deficiency and good crystallinity.

[0009]

In order to achieve the above object, a method of manufacturing an oxide thin film according to the present invention comprises a method of forming an oxide thin film on a substrate by a thermal plasma method. A substrate heating step of heating a substrate to be formed to a target temperature of the next step; and depositing an oxide on the substrate by a thermal plasma method while maintaining the substrate at the target temperature, and growing an oxide thin film in an amorphous state. A low-temperature thermal plasma process; and a heat-treating process for heat-treating the substrate at a temperature higher than the target temperature to crystallize the oxide thin film.

[0010] This makes it possible to form an oxide thin film under optimum conditions for forming an oxide and to convert the oxide thin film into a highly crystalline film under optimum heat treatment conditions. Further, even if there is some temperature change in the low-temperature thermal plasma process, the influence on the crystallization in the subsequent heat treatment process is small. Therefore, a higher quality oxide thin film can be formed by the thermal plasma method. Note that the low-temperature thermal plasma process does not mean that the temperature of the thermal plasma itself is low, and that the substrate temperature is maintained at a relatively lower temperature than the conventional example (700 ° C.) in the thermal plasma film forming process. Means

Here, the optimum film forming conditions are, for example, that the solvent organic component of the raw material solution is completely removed, and that the amorphous film of the desired raw material component does not adhere to the substrate. The optimum heat treatment condition is, for example, that a crystal that realizes the required functionality can be uniformly formed in the film.

Preferably, the low-temperature thermal plasma process and the heat treatment process are performed continuously in the same vessel of the thermal plasma apparatus.

As a result, the process is continuous, and improvement in the crystallinity of the film can be expected. Further, productivity is improved.

When the oxide film is a PZT (lead zirconate titanate) film, preferably, the target temperature of the substrate in the film formation is 100 to 500 ° C., and the heat treatment temperature is 500 to 900.
° C. More preferably, the target temperature is between 200 and 500
℃, heat treatment temperature is 600-800 ℃.

When the oxide film is an ITO (indium tin oxide) film, the target temperature is preferably 100.
To 400 ° C., and the heat treatment temperature is 400 to 700 ° C. More preferably, the target temperature is 200 to 400C and the heat treatment temperature is 400 to 600C.

When the oxide film is a YSZ (stabilized zirconia) film, the target temperature is preferably 200 to 800.
℃, heat treatment temperature is 1000 ~ 1300 ℃. More preferably, the target temperature is 300-700C and the heat treatment temperature is about 1100-1300C.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Thermal plasma has a high temperature of 10,000 ° C. or more. The raw material supplied into the thermal plasma decomposes or evaporates, and the component metals are in the form of oxide atoms or are further activated and ionized. After being in the state, it is deposited as an oxide on the substrate. Therefore, it is possible to continuously increase the film thickness without generating cracks during film formation. Further, the film formation speed on the substrate is high. The present invention relates to a method of forming a thin film of a thermal plasma method utilizing the feature that a high-speed and thick film can be formed. And to prevent deterioration of the film characteristics.

First, a film forming apparatus for executing a film forming method using thermal plasma will be described with reference to FIG. The film forming apparatus includes a vacuum chamber 104 for performing a film forming process. A plasma torch section 102 is provided below the vacuum chamber 104. In this portion, a heating coil 124 excited by a high-frequency oscillator 123 is provided, and a thermal plasma 103 is generated therein. Argon gas and oxygen for generating plasma are supplied from a gas source 100 to a plasma torch unit 102. The film forming raw material is introduced into the vacuum chamber 104 from the raw material supply port 101 by a powder supply device 121 for supplying a fine powder raw material and a liquid supply device 122 for supplying a liquid raw material. The film-forming raw material that has entered the vacuum chamber 104 is deposited on the substrate 106 through the thermal plasma 103 and the plasma tail frame portion 105 generated thereon, thereby forming an oxide film. The substrate 106 is fixed on a substrate holder 107.

As shown in FIG. 2, the substrate holder 107 is provided with an induction heating coil 125 and a cooling mechanism. The induction heating coil 125 is excited by the induction heating power supply 131 to heat the substrate. The cooling mechanism circulates a coolant, for example, cooling water, so that the substrate holder 107
To cool. The temperature adjustment unit 132 includes an induction heating power supply 131.
The temperature of the substrate 106 is controlled by appropriately controlling the cooling mechanism. That is, this includes heating the substrate to the target temperature, maintaining the target temperature of the substrate, controlling the substrate temperature with a preprogrammed temperature profile, and the like. Excess gas is returned from the outlet 108 of the vacuum chamber 104 to a collection container (not shown) via the gas cooler 141 and the filter 142. The gas in the vacuum chamber 104 is exhausted by the vacuum pump 143 and is maintained at a predetermined pressure. With such an apparatus, an oxide film is formed by a thermal plasma method.

(Example 1) Next, a characteristic film forming process according to an embodiment of the present invention will be described with reference to FIG. First, the case where the oxide is PZT (lead zirconate titanate) will be described.

A silicon substrate 106 on which a platinum electrode is formed by a sputtering method is placed in a vacuum chamber 104 at 500 ° C.
Heated. Chamber 104 and plasma torch unit 1
02 was evacuated to 1 torr or less, and argon gas for plasma generation was supplied into the torch. 10kW, 4MHz at the same time
A low-frequency glow plasma was generated by passing a high-frequency current of the order.

Next, the pressure in the chamber 104 and the plasma torch section 102 is gradually reduced to a constant pressure of about 200 torr, the plasma gas source is replaced with oxygen and the high-frequency power is increased to about 50 kW at the same time. Plasma was generated in the torch part 102 and the chamber 104.

After dissolving titanium isopropoxide in diethanolamine and butyl cellosolve, 2 parts by mole of lead acetate trihydrate and an equimolar amount of zirconium acetyl acetate with respect to titanium were added and dissolved. The obtained organosol was fed at a rate of 0.5 ml / min by a constant-rate feeding pump, and was injected into oxygen plasma in a mist state. Oxygen plasma was always stable, and a film was formed for 10 minutes while keeping the substrate at 500 ° C. The preferred temperature range of the substrate during film formation is 100 to 500 ° C, and the more preferred temperature range is 200 to 500 ° C. Here, the preferable temperature range of the film formation is a temperature range in which the organic component of the raw material solution is allowed to adhere to the substrate and an amorphous film of the desired raw material component is formed. The more preferable temperature is a temperature at which the solvent component of the raw material solution is completely removed and does not adhere to the substrate, and an amorphous film of the desired raw material component is formed.
No organic residues remained in the thin film within the suitable temperature range.

The silicon substrate 106 is taken out into the atmosphere,
The uniformly formed thin film of lead zirconate titanate was evaluated. An electron microscope observation confirmed an amorphous state.

Thereafter, the silicon substrate 16 was annealed in a vacuum annealing furnace at 800 ° C. for 1 minute. The temperature gradient of rising (heating) and falling (cooling) in annealing is appropriately determined according to the material and the intended performance. For example, when the substrate temperature is raised from room temperature to 800 ° C. in 2 seconds, the relative permittivity of the obtained oxide film is 1200.
And high. When the substrate temperature is raised from room temperature to 800 ° C. in 10 seconds, the relative dielectric constant of the oxide film is slightly lowered to 1,000.

The thin film of lead zirconate titanate was evaluated.
The film thickness was 1 μm, and a favorable crystal state was confirmed by observation with an electron microscope. X-ray analysis showed that the crystals were sufficiently crystallized. The crystal was found to have a perovskite-type crystal structure. An aluminum electrode thin film was formed by a vacuum evaporation method, and the electrical characteristics were measured between the aluminum electrode thin film and a platinum electrode on the substrate. As a result, a relative dielectric constant of 1200 was obtained. When the DE hysteresis was measured, a high coercive electric field and a high residual polarization were observed. It was found to be a ferroelectric thin film having.

(Embodiment 2) Next, a case where the oxide is ITO (indium tin oxide) used as a transparent electrode of a TFT will be described with reference to FIG.

The glass substrate 1 is placed in the vacuum chamber 104.
06, which was heated to 300 ° C. Chamber 10
4 and the plasma torch 102 are evacuated to 1 torr or less,
Argon gas for plasma generation was supplied into the torch 102. At the same time, a high-frequency current of about 10 kW and 4 MHz was passed to generate low-pressure glow plasma. Next, the pressure in the chamber 104 and the plasma torch 102 is gradually reduced to a constant pressure of about 200 torr, and the plasma gas source is replaced with oxygen. At the same time, the high-frequency power is increased to about 50 kW to convert the thermal plasma into the torch and Generated in the chamber.

5 parts by weight of indium 2-ethylhexanoate was dissolved in benzene, and stannous 2-ethylhexanoate was added in an amount of 2 mol% with respect to indium. The obtained organosol was added at a rate of 0.5 ml
The solution was fed at a rate of, and injected as a mist into the oxygen plasma. The oxygen plasma is always stable, and the substrate is kept at 300 ° C.
The film was formed for 10 minutes while maintaining the temperature.

The glass substrate was taken out into the atmosphere, and the uniformly formed ITO thin film was evaluated. The film thickness is 0.5 μm,
An electron microscope observation confirmed an amorphous film. X-ray analysis showed that crystallization was insufficient, and the electrical characteristics were measured. As a result, the specific resistance showed a high value of 5 * 10 ⁻³ Ωcm.

Next, when the glass substrate was placed in a vacuum annealing furnace and vacuum-annealed at 550 ° C. for 1 minute, the ITO thin film was crystallized, the conductivity was improved, and the specific resistance was 1 * 10 ⁻⁴ Ωcm. Decreased to. Further, the transmittance in the visible region was high, and it was sufficiently applicable as a transparent electrode.

Even if this film formation was repeated, no corrosion occurred in the chamber, and stable production was possible. In addition, no contamination of the thin film with impurities due to corrosion was detected.

Example 3 An example of forming a thin film of YSZ (stabilized zirconia), which is a material of a superconducting device, will be described with reference to FIG.

The nickel substrate 1 is placed in the vacuum chamber 104.
06 and heated to 500 ° C. The chamber 104 and the plasma torch unit 102 were evacuated to 1 torr or less, and argon gas for plasma generation was supplied into the torch unit 102. At the same time, a high-frequency current of about 10 kW and 4 MHz was passed to generate low-pressure glow plasma. Next, the pressure in the chamber 104 and the plasma torch unit 102 is gradually reduced to a constant pressure of 200 torr, the plasma gas source is replaced with oxygen, and at the same time, the high-frequency power is increased to about 50 kW to change the thermal plasma to the torch unit. 102 and in chamber 104.

Zirconium acetylacetonate and yttrium acetylacetonate in an amount of 5 mol% based on zirconium were dissolved in acetic acid and ethyl carbitol, and a small amount of triethylene glycol was added. The obtained organosol was fed at a rate of 5 ml / min by a constant-rate feed pump, and was injected into oxygen plasma in the form of a mist. The oxygen plasma was always stable, and the film was formed for 20 minutes while keeping the substrate at 500 ° C.

The nickel substrate 106 is taken out into the atmosphere,
The uniformly formed zirconia thin film was evaluated. The film had a thickness of 30 μm and could be peeled off from the nickel substrate.
X-ray analysis showed a monoclinic system.

Next, after heating at 1200 ° C. for 1 minute in a vacuum annealing furnace, the system was gradually cooled. When X-ray analysis was performed again, it was found to be cubic stabilized zirconia. It has a very dense structure, showing high Young's modulus and high environmental reliability and chemical resistance.

Even if this film formation was repeated, no corrosion occurred in the chamber, and stable production was possible. In addition, no contamination of the thin film with impurities due to corrosion was detected.

In the first to third embodiments described above, the annealing of the substrate is taken out of the thermal plasma apparatus and performed in a separate annealing furnace. This can be performed using a substrate heating device provided in the substrate holder 107.
6 to 8 show PZT, ITO, and YS, respectively.
The case of Z is shown. This makes it possible to continuously perform the film forming step by thermal plasma and the heat treatment step of this film in the same container. In this case, the purity of the film and the production cost are preferably reduced.

In the above-described embodiment, the film forming conditions by the thermal plasma method can be set according to the material, and thereafter, the deposited film can be crystallized by the heat treatment under the optimum crystallization conditions. Therefore, the oxide deposition step can be performed under such a condition that the solvent organic component of the raw material solution is completely removed and does not adhere to the substrate. Then, the amorphous film or the crystal film with insufficient performance generated in this case becomes a homogeneous crystal exhibiting the functionality required by the heat treatment in the next step.

In the above embodiment, PZT (piezo element), ITO (transparent electrode), YS
Although the example of Z (superconducting material) is given, the present invention is not limited to this. The present invention is applicable to the formation of various oxide thin films using a thermal plasma method.

The expression "thin film" does not limit the film thickness to a specific thickness. The thermal plasma method is suitable for high-speed and thick film formation.

Although the case of an organosol liquid has been described as a raw material system, other materials such as a powder-based raw material can be used.

Furthermore, the present invention is applicable to the deposition of thin films using a thermal plasma method, and the resulting materials equivalent to oxide thin films are within the scope of the present invention.

[0045]

As described above, according to the present invention,
Since the high-crystalline film formation by the thermal plasma method is not performed in one thermal plasma process as in the prior art, the deposition is performed by thermal plasma and the subsequent crystallization is performed separately. It becomes possible to satisfy the deposition conditions and the crystallization conditions of the film material, respectively. As a result, at the start of the process by the thermal plasma method, the influence of the change in the substrate temperature inevitably caused by the plasma irradiation on the substrate and the influence of the temperature change during the deposition process can be eliminated as much as possible. It is possible to form a thin film.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an apparatus that performs an oxide film formation process using thermal plasma.

FIG. 2 is an explanatory diagram illustrating a substrate holder.

FIG. 3 is an explanatory diagram illustrating an example of a temperature profile in a step of forming a PZT oxide thin film on a substrate.

FIG. 4 is an explanatory diagram illustrating an example of a temperature profile in a step of forming an ITO oxide thin film on a substrate.

FIG. 5 is an explanatory diagram illustrating an example of a temperature profile in a step of forming a YSZ oxide thin film on a substrate.

FIG. 6 is an explanatory diagram illustrating another example of a temperature profile in a step of forming a PZT oxide thin film on a substrate. In this example, film formation and annealing are performed in the same container.

FIG. 7 is an explanatory diagram illustrating another example of a temperature profile in a step of forming an ITO oxide thin film on a substrate. In this example, film formation and annealing are performed in the same container.

FIG. 8 is an explanatory diagram illustrating another example of a temperature profile in a step of forming a YSZ oxide thin film on a substrate. In this example, film formation and annealing are performed in the same container.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 gas source 101 raw material supply port 102 plasma torch section 103 thermal plasma section 104 vacuum chamber 105 plasma tail frame 106 substrate 107 substrate holder 108 exhaust port

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C30B 29/32 C30B 29/32 A H01L 21/31 H01L 21/31 C

Claims (2)

[Claims] 1. A method for producing an oxide thin film on a substrate by a thermal plasma method, comprising: a substrate heating step of heating a substrate on which a thin film is to be formed to a target temperature in a next step; Depositing an oxide on the substrate by a thermal plasma method while maintaining the substrate at the target temperature, a low-temperature thermal plasma process of amorphously growing an oxide thin film, and heat-treating the substrate at a temperature higher than the target temperature A method for producing an oxide thin film, comprising: a heat treatment step of crystallizing the oxide thin film. 2. The method for producing an oxide thin film according to claim 1, wherein the low-temperature thermal plasma step and the heat treatment step are continuously performed in the same container.