JP3212700B2 - Method for producing composite oxide thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a composite oxide thin film, and more particularly to an improvement in film quality.

[0002]

2. Description of the Related Art First, a composite oxide thin film will be described. The composite oxide is an oxide containing two or more types of metal ions, and may exhibit ferroelectricity and piezoelectricity. Therefore, in recent years, ferroelectric memories, pyroelectric sensors, piezoelectric sensors,
Composite oxide thin films have come to be used in semiconductor devices such as multilayer capacitors.

[0003] In the production of such a composite oxide thin film, not only a vacuum deposition method and a sputtering method, which are general film forming techniques, but also MOCVD (Metal Organic Chemical Vapor).
Deposition), ICB (Ion Curuster Beam), MBE
(Molecular Beam Epitaxy) and the like. These methods are called dry methods. On the other hand, a film forming technique called a wet method is also applied. This wet method is a method of baking using a chemical solution, for example, a sol-gel method.
As a method of manufacturing a composite oxide thin film, a case where a PZT thin film is formed on the upper surface of a silicon thermal oxide film provided on a silicon substrate by MOCVD which is a dry method will be described below.

[0004] A CVD apparatus 3 schematically shown in FIG. 3 is used. A substrate 6 having a silicon oxide film 4 provided on the upper surface of the substrate 6 (see FIG. 2) is prepared and set in the CVD apparatus 3.
Alkoxides of lead, titanium and zirconium are used as source materials, and each solution is supplied to an evaporator 3 with a valve.
0, 32, 34 and kept at a constant temperature. Each source material is fed into the reaction chamber 36 using argon which is an inert carrier gas. At this time, each source material is mixed with oxygen (O ₂ ) on the way and guided into the reaction chamber 36. In addition, re-precipitation of the source material can be prevented by heating the piping system.

Thereafter, the respective source materials flowing into the reaction chamber 36 cause thermal decomposition and oxidation on the substrate 6 heated to 500 to 750.degree. Thereafter, crystallization proceeds in the deposition layer, and the crystalline P of the perovskite structure
It becomes a ZT thin film 38.

On the other hand, as a method for producing a composite oxide thin film,
The case where the PZT thin film 40 is formed on the upper surface of the silicon thermal oxide film 4 provided on the silicon substrate 6 by a wet sol-gel method will be described below with reference to FIGS. 4A and 4B.

First, a sol solution is prepared as follows. P
b (CH ₃ CO ₂ ) .3H ₂ O (lead acetate trihydrate) was dissolved in methoxyethanol at a molar ratio of 1: 5 at 70 ° C.
Heat to 20 ° C. to dehydrate. Add this solution to 90
After cooling to ℃, PbTiO ₃ : PbTiO ₃ = 47: 53
A predetermined amount of titanium isopropoxide and zirconium propoxide are added with stirring so that the molar ratio is as follows. The solution is continuously heated to 125 ° C. to remove reaction by-products. Further, methoxyethanol is added to this solution so that the PZT concentration becomes 0.5 mol / l, and then distilled water having a mole twice as much as that of the PZT sol solution is added. .

Next, a sol solution which has been adjusted at 5000 rpm for 20 seconds is applied to the upper surface of the silicon oxide film 4 shown in FIG.
After drying at 0 to 300 ° C, firing at 650 ° C. By repeating this series of firing steps a plurality of times (six times), a PZT thin film 40 having a desired film thickness as shown in FIG. 3B is obtained.

Thus, a PZT thin film of a perovskite crystal can be formed.

[0010]

However, when the PZT thin film 38 is formed by the MOCVD method described above, there are the following problems.

In the MOCVD method, the above-mentioned thermal decomposition and oxidation reaction are performed at a relatively low molecular level. Accordingly, cracks may occur due to deposition fluctuation (ie, agglomeration) during the crystallization of the non-complexed composite oxide or a difference in the thermal expansion coefficient between the PZT crystal and the base such as a silicon oxide film. The quality of the thin film was not good. In particular, when the film thickness was several hundred nm or less, a uniform film could not be obtained.

PZT having such a crystal structure defect
The thin film 38 has been problematic in electrical, optical and mechanical properties.

On the other hand, the sol-gel method has been conceived as a film forming technique in order to overcome the above-mentioned disadvantages of the MOCVD method which is a dry method, but has the following problems. Had a point.

In the sol-gel method, an adjusted sol solution is applied to a substrate and then fired to form a film. Therefore, the substrate surface is flattened regardless of the shape of the base. Specifically, even when a step exists in the underlying silicon oxide film, the PZT thin film 40 formed as shown in FIG.
Has a flat surface.

Since the PZT thin film 40 is not uniform in thickness, the ferroelectricity of the PZT thin film, for example, remanent polarization and polarization reversal, is not uniform, and it has been difficult to use the PZT thin film in a semiconductor device.

Accordingly, the present invention is to solve the above problems and to provide a manufacturing method capable of forming a composite oxide thin film excellent in film quality and obtaining a uniform film thickness irrespective of the shape of a base. With the goal.

[0017]

In the method for producing a composite oxide thin film according to the first aspect, a hydrolysis / polycondensation reaction is caused in a gas phase on a plurality of alkoxide solutions having a desired metal component, After generating the precursor material, the precursor material is deposited on the upper surface of the substrate.

[0018]

In the method for producing a composite oxide according to the first aspect, a plurality of alkoxides having a desired metal component are sent to a reaction chamber.
Into the reaction chamber separately from the alkoxide.
Hydrolysis and in the gas phase by feeding the upper surface of the substrate
A polycondensation reaction is caused to generate a precursor substance.

Accordingly, a high molecular precursor substance can be obtained.

Further, the precursor substance is deposited on the upper surface of the substrate.

Therefore, the precursor material is uniformly deposited regardless of the shape of the base.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a method of manufacturing a composite oxide thin film according to one embodiment of the present invention, a case where a PZT thin film as a composite oxide thin film is formed on the upper surface of a silicon thermal oxide film provided on a silicon substrate will be described below. I do.

It is manufactured using a CVD apparatus 2 schematically shown in FIG. As shown in FIG. 2, a substrate 6 having a silicon oxide film 4 provided on the upper surface of the substrate is prepared. This substrate 6
Is set in the CVD apparatus 2 as shown in FIG.

Next, a lead isoalkoxide solution 7, which is a lead alkoxide, kept at a constant temperature in a thermostat 15,
Using a tetrapropoxytitanium solution 9 which is an alkoxide of titanium and a tetraisopropoxyzirconium solution 11 which is an alkoxide of zirconium as a source material, the solution is fed into the reaction chamber 8 with an argon gas while heating.
At the same time, steam is generated by the steam generator 10 and sent to the reaction chamber 8. At this time, the valves 12, 14,
Using P.16, the composition ratio of Pb, Zr and Ti is Pb: Zr: Ti = 1: 0.58:
The flow rate of each source material is adjusted to be 0.48. In addition, the flow rate of each argon gas is set to MFC (Mass Flow Control).
ler) 18, 20, 22 respectively. Further, the amount of water vapor is adjusted by the controller 24 so as to be 5 to 70% of the total amount of converted oxides of the source material.

On the other hand, a Rotary Pump (PR) 42 provides a pressure of 1 to 10 Torr. In the reaction chamber 8 which has been reduced in pressure to a certain degree, each source material which has flowed in as a gas undergoes a hydropolycondensation reaction together with water vapor to generate a precursor substance in the gas phase. Thereafter, a precursor substance is deposited on the substrate heated to 650 ° C. by the IR lamp 26, and a crystalline PZT thin film 28 is formed.

The PZT thin film 28 formed as described above had a uniform and uniform film quality with a thickness of 100 nm.

Further, in the method of forming a PZT thin film as described above, it is possible to suppress the reactivity with the base during the manufacturing process by the sol-gel method, for example, the diffusion of lead into the silicon oxide film.

In the above-described embodiment, the PZT crystal is deposited after the oxide film is formed on the upper surface of the silicon substrate as the upper surface of the substrate. However, the PZT crystal can be deposited on another base. For example, a PZT crystal may be directly deposited on a silicon substrate. Further, a PZT crystal may be deposited after a platinum layer is further provided on the oxide film on the silicon substrate.

[0029]

According to the method for producing a composite oxide according to the first aspect, a plurality of alkoxides having a desired metal component are reacted.
Into the chamber, and separate the steam from the alkoxide.
Hydrolysis and polycondensation reactions occur in the gas phase by being sent to the upper surface of the substrate in the reaction chamber to generate a precursor substance.

Therefore, since a high molecular weight precursor substance can be obtained, a composite oxide thin film having uniformly high-quality crystals can be formed.

Further, the precursor substance is deposited on the upper surface of the substrate.

Therefore, the precursor material is uniformly deposited regardless of the shape of the underlayer, and a composite oxide thin film having a uniform thickness can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of a CVD apparatus used for a method of manufacturing a composite oxide thin film according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view of a substrate set in a CVD apparatus.

FIG. 3 is a schematic view of a CVD apparatus used for manufacturing a composite oxide thin film by a conventional MOCVD method.

FIG. 4 is a schematic cross-sectional view showing a conventional method for producing a composite oxide thin film by a sol-gel method.

FIG. 5 is a schematic cross-sectional view showing a defect of a method for producing a composite oxide thin film by a sol-gel method.

[Explanation of symbols]

 8 reaction chamber 6 substrate 28 PZT thin film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/316 C23C 16/40

Claims (1)

(57) [Claims] 1. A method for producing a composite oxide thin film in a semiconductor device, comprising the steps of: placing a plurality of alkoxides having a desired metal component in a reaction chamber.
And reacting steam separately from the alkoxide
A hydrolysis / polycondensation reaction is caused in the gas phase by sending the precursor material to the upper surface of the chamber to generate a precursor material. Then, the precursor material is deposited on the upper surface of the substrate. A method for producing a composite oxide thin film, comprising thermally decomposing.