JPS61190074A - Formation of thin oxide film - Google Patents

Abstract

PURPOSE:To form a thin oxide film having good characteristics at a substantially high growing rate at a low temp. by irradiating UV light on a gas consisting of gaseous metallic alkoxide as an effective component to induce a photoexcitation reaction. CONSTITUTION:The metallic alkoxide 10 such as Ta(OCH3)5 sealed into a vessel 1 is held at a prescribed temp. by a heater 11 and a carrier gas 2 which is an inert gas such as Ar is fed therein and is gasified. The generated gas is introduced together with a suitable diluting gas 3 into a reaction chamber 9 of a reactor 4 the inside of which is evacuated to a vacuum by a vacuum pump 8. The UV light is irradiated through a synthetic quartz window 6 by a lamp 5 such as low pressure mercury lamp on the gaseous metallic alkoxide introduced into the chamber 9. The photoexcitation reaction or photodecomposition reaction is induced in the above-mentioned gas by the energy of the UV light and the metallic oxide such as Ta2O5 is formed on the substrate 7 kept at a suitable temp. by a heater 14, by which the thin film is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for forming an oxide thin film used for semiconductor devices, sensors, functional elements such as waveguide elements, and other elements.

<Prior Art> In semiconductor integrated circuits for large-capacity memories, high dielectric films such as Ta205 and Tt02 are being introduced into capacitive parts for the purpose of further miniaturization. Further, Ta2'Os and TL02 films are also being considered for application to optical circuit elements due to their optical properties. Furthermore, thin films of oxides such as Sn02 and ZnO are used in sensors and the like. When forming such an oxide thin film, for example, the following method has been used to form a Ta205 thin film.

(2) A Ta film is formed by sputtering, and then thermally oxidized in an oxygen atmosphere.

(2) A Ta film is formed by sputtering and then anodized.

Ta by 0-reactive sputtering method (mixed gas of Ar and 02)
2Os lII is formed.

(2) Form a Ta2Os film by RF sputtering.

(2) Formed using the oxidation reaction of Ta alkoxide using the low pressure CVD method.

However, when sputtering methods such as those described in (1) to (2) are used, the charged particles cause damage to the substrate, resulting in deterioration of the characteristics of the final device.

Further, thermal oxidation (2) requires a high temperature of 500°C or more. ■
In the anodic oxidation, oxidation is performed in an electrolytic solution, but at this time, negative ions in the solution are also taken into the membrane, making it inevitable that impurities will be mixed in. Another drawback is that it is difficult to obtain a uniform composition in the thickness direction.

In the low-pressure CVO method (2), a good film can be formed at temperatures above 420°C, but at low temperatures (below 420°C), the refractive index drops drastically (normally 2.0 or more becomes 1.5 or less). )
It has been reported that the growth rate decreases as the temperature decreases below 450°C, which is not practical. Furthermore, the high-temperature processes required by methods ① and ③ can cause process-induced defects, reactions between materials, and disturbances in the distribution of impurities on the substrate.

gives undesirable results such as

<Objective> The present invention aims to eliminate the drawbacks of the above-mentioned conventional techniques and to provide a method for forming an oxide thin film that has a sufficiently high growth rate at low temperatures and has good properties.

Structure> The method for forming an oxide thin film of the present invention involves irradiating a gas containing a metal alkoxide gas as an active ingredient introduced into a reaction chamber with ultraviolet light to cause a photoexcitation reaction, thereby forming a metal layer on the substrate surface. It is characterized by producing oxides.

<Example> FIG. 1 is a block diagram of an apparatus used in the implementation method of the present invention.

A metal alkoxide (M (OR) Then, a carrier gas 2 such as an inert gas such as Ar or N is sent into the container 1, and a metal alkoxide gas is introduced into the reaction chamber 9 of the reactor 4 through the introduction pipe 12. At this time, a suitable diluent gas 3 is sent into the introduction pipe 12, mixed with the metal alkoxide gas, and supplied into the reaction chamber 9 which is evacuated by the vacuum pump 8. The reactor 4 has a built-in heater 14, which maintains the substrate 7 placed in the reaction chamber 9 at an appropriate temperature for the purpose of controlling film quality and film growth rate. A lamp 5 such as a low-pressure mercury lamp is placed above the substrate 7 in the reaction chamber 9 , and ultraviolet light is irradiated into the reaction chamber 9 from the lamp 5 through the synthetic quartz window 6 of the reactor 4 . The energy of this ultraviolet light causes a photoexcitation reaction or a photodecomposition reaction in the metal alkoxide gas, and metal oxide is generated on the substrate 7 to form a 1F film. Note that the heater 13 is used to keep the introduction tube 12 warm.

M metal alkoxide (M (OR) x )
10, for example Ta (OCH3) 5 , T
t(OC2)15)4.

A I (OC2H5)3.5□ (OCH3)4 etc. can be used. Metal alkoxides are generally volatile, and in many cases, the amount of gas necessary for film formation is generated at room temperature or at a slight temperature increase, for example, about 100° C. in the case of Ta(OCH3)S. Furthermore, metal alkoxide exhibits light absorption unique to the ultraviolet region, and has the property of being decomposed into oxides by light energy in a wavelength range that can be easily obtained from a low-pressure mercury lamp or the like. Figure 2, Figure 3, Figure 4
Ta (OCH3) 5 is shown in the figure.

T t (OC2)1 s ) a , S t
The absorption spectrum of (OCH3) 4 is shown. Said substrate 7
A semiconductor such as St, an insulator such as 5j02, or a metal can be used for the material, and there is no dependence on the substrate.

Although an inert gas such as N2 may be used as the diluent gas 3, 02 gas may be used for the purpose of improving stoichiometry and reactivity. It can also be used without dilution.

Using the method of the present invention, Ta(OCRa)S-0
FIG. 5 shows the temperature dependence of the production rate when a Ta2Os film is formed using a mixture of two gases, and FIG. 6 shows the temperature dependence of the refractive index. As is clear from FIGS. 5 and 6, the growth rate of the film is more than four times faster than when grown under the same conditions without irradiation with light, and even when the film is formed at 200"C or less, the growth rate is 2.
Maintains a refractive index of 0 or more.

Using the method of the present invention, ↑t (OC2tl S) 4
FIG. 7 shows the temperature dependence of the formation rate when a TiO2 film is formed using a mixed gas of -N2. As is clear from FIG. 7, the growth rate is greatly increased by light irradiation.

Effects> The present invention has the above-described structure, and allows oxide thin films to be grown sequentially at a sufficient growth rate at low temperatures, without causing radiation damage to the substrate, and without causing a decrease in refractive index. It is possible to form a good oxide thin film with a uniform composition in the film thickness direction.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the apparatus used in the method of carrying out the present invention;
The figure shows the light absorption spectrum of Ta (OCR3) 5, Figure 3 shows the light absorption spectrum of Tj(OC2H5)4, Figure 4 shows the light absorption spectrum of SL (OCH3)4, and Figure 5 shows the light absorption spectrum of the present invention. Figure 6 shows the temperature dependence of the production rate when a Ta205 film is formed using the Ta205 method.
FIG. 7 is a diagram showing the temperature dependence of the refractive index of Ill', and FIG. 7 is a diagram showing the temperature dependence of the production rate when a T602 film is formed by the method of the present invention. 2...-Carrier gas 3-Dilution gas 4-Reactor 5-Lamp 6-Synthetic quartz window 7-Substrate 9-Reaction chamber 10--Metal alkoxide Fig. 6, /, ,xtl)' (ζ−1
) Procedural amendment (Own ship Date of May 30, 1985 Patent Application No. 28808 2, Title of invention Method for forming oxide thin film 3, Relationship with the case of the person making the amendment Patent applicant address Abeno, Osaka City Ward Nagaike-cho 22-22 Name (
504) Sharp Corporation Representative Asahi Saeki Address 5-6-4 Minamisawa, Higashikurume City, Tokyo Address Tarui
Original address: 1-16-7 Nishi-Shinbashi, Minato-ku, Tokyo Name: Japan #
Iso Co., Ltd. Representative Natsube Ishizawa 4, Agent

Claims (1)

[Claims] An oxide thin film characterized in that a gas containing a metal alkoxide gas as an active ingredient introduced into a reaction chamber is irradiated with ultraviolet light to cause a photoexcitation reaction, thereby forming a metal oxide on the surface of a substrate. Formation method.