JPH0624222B2 - Method of manufacturing thin film capacitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a thin film capacitor used in a microelectronic circuit.

(Prior Art) With the development of integrated circuit technology, electronic circuits are becoming smaller and smaller, and it is becoming more important to make capacitors, which are circuit elements essential for various electronic circuits, smaller. Thin film capacitors using dielectric thin films are used by being formed on the same substrate as active elements such as transistors, but miniaturization of thin film capacitors has been delayed due to rapid miniaturization of active elements. , Has become a major factor preventing further high integration. This is because the dielectric thin film materials used conventionally are limited to materials with a dielectric constant of at most 10 such as SiO ₂ and Si ₃ N ₄ , and in order to miniaturize thin film capacitors. It is necessary to develop a dielectric thin film with a large dielectric constant. BaTiO _3, SrTiO _3, PbTiO ₃ is a perovskite type oxide represented by the chemical formula ABO _3, PbZrO ₃
And ilmenite type oxide LlNbO ₃ or Bi ₄ Ti ₃ O ₁₂
It is known that oxides belonging to ferroelectrics such as, etc. have the above-mentioned single composition and mutual solid solution composition, and have a dielectric constant of 100 to 10,000 in single crystals or ceramics, and are widely used in ceramic capacitors. It is used. Thinning these materials is extremely effective for miniaturizing the above-mentioned thin film capacitor, and research has been conducted for quite some time. Among them, examples in which relatively good characteristics are obtained are Proceedings of thw IEEE Vol. 59, No. 10, 1440-1447.
There is a paper published on the page, BaTiO ₃ thin films sputtered and heat-treated from 16 (created at room temperature) to 1900
A dielectric constant of (1200 ° C heat treatment) is obtained.

(Problems to be Solved by the Invention) However, BaTiO3 conventionally produced as described above is used.
The high dielectric constant thin films such as A and B are all formed on the lower electrode made of a noble metal material such as platinum, palladium, and gold because a high temperature is required for forming the high dielectric constant thin films.
Such electrodes of noble metal materials are not compatible with various kinds of integrated circuits most of which are currently manufactured using a silicon substrate. Therefore, it is not possible to apply the above-mentioned conventional high dielectric constant thin film to integrated circuits. It is impossible. The reasons why the noble metal materials are not compatible with integrated circuits include that they act as impurities to cause malfunction of silicon transistors, and that fine processing techniques for these noble metals have not been established.

The electrode material widely used in silicon integrated circuits is polycrystalline silicon or a low resistance silicon layer in which a part of the silicon substrate itself is highly doped with impurities. Hereinafter, these are collectively called a silicon electrode. Since a fine processing technique has been established for silicon electrodes and is already widely used, if a good high-inductivity thin film can be formed on silicon electrodes, it can be used for capacitors for integrated circuits.
However, in the prior art, for example, IBM
Of Research and Development (IBM Journa
l of Research and Development) November 1969 686-695
687-68 in the paper on SrTiO ₃ films on page
The description on page 8 reports that when a thin film of a high dielectric constant material is formed on silicon, a layer equivalent to about 100 Å silicon dioxide (SiO ₂ ) is formed at the interface. Since this interface layer is a layer having a low dielectric constant, the effective dielectric constant of the high dielectric constant thin film formed on silicon was greatly reduced as a result, and the advantage of using a high dielectric constant material was almost lost. . Another example of a similar report is the Journal of Vacuum Science and Technology (J
ournal of Vacuum Science and Technology) Volume 16 Issue 2
It can be found in the description on page 316 in the paper on BaTiO ₃ published on pages 315-318.

The present invention, when forming a thin film of a high dielectric constant material belonging to a ferroelectric material typified by BaTiO ₃ and SrTiO ₃ on a silicon electrode, makes it possible to extremely reduce the influence of a low dielectric constant layer generated at the interface. The purpose is to realize a small-sized thin film capacitor that can be applied to an integrated circuit.

(Means for Solving the Problem) In order to solve the above-mentioned problems, a method of manufacturing a thin film capacitor according to the present invention is directed to BaTiO 3 on a lower electrode made of silicon.
₃ , SrTiO ₃ , PbTiO ₃ , PbZrO ₃ , LiNb
A high dielectric constant dielectric thin film consisting of one composition selected from O ₃ and Bi ₄ Ti ₃ O ₁₂ or a solid solution was prepared at a substrate temperature of 300 ° C to 500 ° C, and then at a temperature of 550 ° C to 650 ° C or less. It is characterized in that it is formed by performing heat treatment and then forming an upper electrode.

Hereinafter, the present invention will be described in detail based on examples.

Example An SrTiO ₃ thin film of 50 to 500 nm was prepared by RF magnetron sputtering on a silicon substrate having a low resistance layer formed by doping phosphorus (P) as an impurity at a high concentration. While changing the substrate temperature during fabrication,
Heat treatment was performed at various temperatures. Aluminum (Al) was formed as the upper electrode, and the effective dielectric constant and leakage current were evaluated.

Figure 1 shows the relationship between the effective dielectric constant and film thickness of SrTiO ₃ thin films prepared at various substrate temperatures, evaluated without heat treatment. Curve 1 shows data for a film made at a substrate temperature of 400 ° C, curve 2 shows data for a film made at 600 ° C, and curve 3 shows data for a film made at 700 ° C. The film thickness dependence of the effective permittivity is remarkable in any of the films, and it is clear that the interface of the low permittivity layer depends on the interface as in the conventional technique described above. In particular, the influence of the low dielectric constant layer at the interface is large in the region where the film thickness is small. In addition, at a substrate temperature of 700 ° C, the effective permittivity decreased as a whole, suggesting a significant interface reaction at high temperatures.

Figure 2 shows the relationship between effective permittivity and film thickness after heat treatment of SrTiO ₃ thin films prepared at substrate temperatures of 300 ° C to 600 ° C. Curve 1 shows the data at a heat treatment temperature of 550 ° C to 650 ° C, and curve 2 shows the data at a temperature of 700 ° C to 800 ° C. As is clear from comparison with FIG. 1, heat treatment at 550 ° C. to 650 ° C. increases the effective dielectric constant particularly in the region where the film thickness is small. As can be seen from the data in curve 2, the effective permittivity decreases again at higher heat treatment temperatures. The above results are
Heat treatment at 550 to 650 ° C causes crystallization of the low dielectric constant layer at the interface to increase the effective permittivity, but heat treatment at 700 ° C or higher decreases the effective permittivity due to significant interface reaction. Is interpreted as At the heat treatment temperature of 550 ° C. or lower, the actual dielectric constant equal to or lower than that of the curve 2 was obtained.

FIG. 3 shows the relationship between the leak current when a voltage of 10 V is applied and the substrate temperature at the time of fabrication for a film having a thickness of 100 nm that has been heat-treated at 550 to 650 ° C. A film produced at a substrate temperature of 300 ° C or less causes large strain during heat treatment,
In a severe case, a crack is generated and a leak current becomes large. On the other hand, it is interpreted that a film produced at a substrate temperature of 500 ° C. or higher has a large leak current due to a reaction with silicon during the production. From FIG. 3, it can be seen that the leak current at a practical level (10 ⁻⁹ A / cm ² or less) can be suppressed only in the film formed at the substrate temperature of 300 to 500 ° C.

Comprehensively looking at the above data, as a fabrication method that achieves a high effective dielectric constant of 100 or more as a practically valuable value and a low leakage current at a practically meaningful thin thickness of 100 nm, a 300 ° C The present invention has been made in which a film is formed at a substrate temperature of 500 ° C. or higher and a heat treatment is performed at a temperature of 550 ° C. or higher and 650 ° C. or lower.

The above is the description of the SrTiO ₃ thin film.
O ₃ , PbTiO ₃ , PbZrO ₃ , LiNbO ₃ , Bi ₄ Ti ₃ O ₁₂ and solid solution
(Ba, Sr) TiO ₃ , (Ba, Pb) TiO ₃ , Pb (Zr, Ti) O ₃ the same preparation and evaluation results, the highest effective dielectric constant in the same preparation method as SrTiO ₃ It was confirmed that a low leakage current was obtained. That is, the method for manufacturing a thin film capacitor according to the present invention is effective for a wide range of materials of high dielectric constant oxides belonging to the above-mentioned ferroelectrics. In this example, the RF magnetron sputtering method was used as the method for forming the thin film, but the present invention is the sputtering method,
It goes without saying that all methods of physical vapor deposition methods such as the ion beam sputtering method and the vapor deposition method can be applied.

(Effect of the Invention) As described above, according to the present invention, a high dielectric constant thin film having a high effective dielectric constant and a small leak current can be formed on a lower electrode made of silicon, and therefore a small size suitable for an integrated circuit can be obtained. It is possible to manufacture the thin film capacitor of, and it is possible to contribute to higher integration.

[Brief description of drawings]

Figure 1 shows the relationship between the effective permittivity and film thickness of the SrTiO ₃ film before heat treatment, and Figure 2 shows the effective permittivity after heat treatment of the SrTiO ₃ film prepared at a substrate temperature of 300 to 600 ° C. FIG. 3 is a diagram showing the relationship between the film thickness, and FIG. 3 is a diagram showing the relationship between the substrate temperature and the leak current at the time of manufacturing the SrTiO ₃ film subjected to the heat treatment at 550 to 650 ° C.

Claims (1)

[Claims] 1. A method of manufacturing a thin film capacitor comprising a step of laminating a lower electrode made of silicon, a high dielectric constant dielectric thin film and an upper electrode on a substrate, wherein the high dielectric constant dielectric thin film is made of BaTiO ₃ or SrTiO ₃ . ₃ , PbTiO ₃ , P
One composition selected from bZrO ₃ , LiNbO ₃ , and Bi ₄ Ti ₃ O ₁₂ or a solid solution, which is formed on the lower electrode at a substrate temperature of 300 ° C. or more and 500 ° C. or less and then 5
A method of manufacturing a thin film capacitor, characterized by performing heat treatment at a temperature of 50 ° C. or higher and 650 ° C. or lower, and then forming an upper electrode.