JPH0687492B2 - Thin film capacitor and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a thin film capacitor used in a small electronic circuit.

(Prior Art) With the development of integrated circuit technology, electronic circuits are becoming smaller and smaller, and miniaturization of capacitors, which are circuit elements essential for various electronic circuits, is becoming more important. 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 material or SiO ₂ which has been used conventionally, Si ₃ N ₄ dielectric constant such as is limited to at most 10 or less of the material, a dielectric as a means to reduce the size of the thin film capacitor It is necessary to develop a dielectric thin film with a high rate. BaTiO _3, SrTiO _3, PbZrO ₃ and ilmenite type oxides LiNbO ₃ or Bi ₄ Ti ₃ O strong oxide belonging to the dielectric, such as _12, which is a Berobusukai type oxide represented by the chemical formula ABO _3, the above-described single It is known that the composition and mutual solid solution composition have a dielectric constant of 100 or more and 10000 in a single crystal or ceramic,
Widely used in ceramic capacitors. Thinning of these materials is extremely effective for miniaturization of the above-mentioned thin film capacitor, and research has been conducted for quite some time. Among these, as an example where relatively good characteristics are obtained,
Proceeding of Eye Eee (Pr
There is a paper published in Volume 59, No. 10, pp. 1440-1447, which uses a BaTiO ₃ thin film deposited by sputtering and heat-treated from 16 (prepared at room temperature) to 1900 (12
A dielectric constant of (heat treatment at 00 ° C) is obtained.

The electrode material widely used in the present highly 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 technology has been established for silicon electrodes and is already widely used, if a good high-dielectric-constant 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 Journal of Research and Development (IBM Jour
nal of Research and Development) November 1969 686−
A paper on SrTiO ₃ film on page 695 is published in
A paper on BaTiO ₃ is reported in Journal of Vacuum Science and Technology, Vol. 16, No. 2, pp. 315-318.

(Problems to be Solved by the Invention) As described above, a high film formation temperature is required to obtain a high dielectric constant, but BaTi that is conventionally formed on a silicon electrode
Dielectric thin film such as O ₃ is about 100 Å silicon dioxide (SiO ₂ )
It is reported that a layer equivalent to is formed at the interface. Since this interface layer is a layer having a low dielectric constant, as a result, the effective dielectric constant of the high dielectric constant thin film formed on silicon is greatly reduced. Most of the benefits of using high dielectric constant materials have been compromised.

(Means for Solving the Problems) The present invention relates to a thin film capacitor having a structure in which a conductive layer, a dielectric, and an upper electrode are sequentially formed on a silicon electrode, and a conductive layer is formed on the first layer and the first layer. And a second layer formed on the first layer, wherein the first layer is at least one material selected from ruthenium, ruthenium silicide and ruthenium oxide, and the second layer is selected from high melting point noble metals such as platinum, palladium and rhodium. And a step of oxidizing the first conductive layer at a predetermined temperature.

Example 1 Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a structural diagram of the thin film capacitor of this embodiment. A low resistance layer 2 is formed by heavily doping phosphorus on a part of the surface of the single crystal silicon 1, and a silicon oxide film 3 is formed thereon as an interlayer insulating film. In a part of the silicon oxide film, two contact holes for drawing out the lower electrode through the low resistance layer are formed, one contact hole is filled with the polycrystalline silicon film 4, and the other contact hole is an Al film. Filled with 5. Therefore, the Al film 5 becomes a terminal of the lower electrode. The lower electrode film 4 may fill the contact hole and be partially formed on the silicon oxide film. Conductive layer first layers 6 and second layers 7 are formed on the lower electrode film 4, a BaTiO ₃ film 8 is formed thereon, and Al 9 is formed thereon as an upper electrode.

As the conductive layer, ruthenium oxide as the first layer and platinum as the second layer were sequentially manufactured by the DC magnetron sputtering method. Ar gas atmosphere, 4 × 10 ⁻³ Torr, substrate temperature 100 ° C., and the film thickness of platinum and ruthenium oxide were 1500 Å. A RuO ₂ composition sintered body target was used for the ruthenium oxide film formation.
The BaTiO ₃ film was prepared by a high-frequency magnetron sputtering method with a stoichiometric powder target to a film thickness of 3000 Å. 1 × 10 ^-2 Torr in Ar-O ₂ mixed gas, substrate temperature 600
The film was formed by sputtering at ℃. 5000 Å Al was deposited on the upper electrode by DC sputtering. The effective area of this capacitor is
It is 250 μm ² . Next, platinum of this method as a conductive layer,
When using ruthenium oxide, when using only a platinum film which is a high melting point noble metal, and when not forming a conductive layer, Ba
The difference in the characteristics of the TiO ₃ film will be described. In FIG. 2, (a) is a BaTiO ₃ film when a platinum and ruthenium oxide multilayer film of this method is used, (b) is a platinum film having a film thickness of 3000 Å, and (c) is a film thickness. Sheet resistance 100Ω / c at 3000Å
This is an examination of changes in the dielectric constant depending on the film thickness of the BaTiO ₃ film when a polycrystalline silicon film of m ² is used. When the multilayer film of this method is used, the dielectric constant of the BaTiO ₃ film is constant irrespective of its film thickness, whereas when the platinum film or polycrystalline silicon film is used, the film thickness of the dielectric film is As becomes smaller, the permittivity decreases significantly.

As previously reported, the decrease in the dielectric constant of the polycrystalline silicon film is due to the formation of a silicon oxide layer at the interface between the dielectric and the electrode or the formation of a low dielectric constant layer at the initial stage of the dielectric film growth. In the case of the platinum film of (b), silicidation of platinum was confirmed by X-ray diffraction after forming the dielectric film. This means that silicon reacts with platinum at the time of forming a dielectric film at 600 ° C. and reaches the outermost surface while forming a silicide compound. Therefore, it is considered that silicon exists on the outermost surface of the electrode and the low dielectric constant layer is formed in the same state as in the case of the polycrystalline silicon film. On the other hand, according to the same X-ray diffraction, in the multi-layer film of platinum and ruthenium oxide, platinum remains in the original state without being silicidized even after the dielectric film is formed. That is, it is considered that the diffusion of silicon was suppressed by the ruthenium oxide layer and did not reach the platinum layer, and the formation of the low dielectric constant layer due to the oxidation of silicon as described above did not occur.

For the purpose of improving the adhesion between platinum and ruthenium oxide, the effect of the present invention is impaired even if the structure is such that an adhesion layer such as titanium is inserted between platinum and ruthenium oxide as is generally done. There is no. It was also confirmed that similar results could be obtained by using a high melting point noble metal such as palladium or rhodium instead of platinum.

Example 2 In the thin film capacitor of Example 1, ruthenium silicide was used for the first conductive layer, and the film thickness dependence of the dielectric constant of the BaTiO ₃ film was examined. Ruthenium silicide was deposited by direct current sputtering using a sintered target of Ru / Si = 1/1 composition to a film thickness of 1500Å.

Similar to Example 1, the dielectric constant of the BaTiO ₃ film did not depend on the film thickness, and the original value of about 220 was obtained. However, according to X-ray diffraction after forming the dielectric film, unlike the case of ruthenium oxide,
It was confirmed that platinum was silicided. From this, ruthenium silicide does not have the effect of suppressing diffusion of silicon at least like ruthenium oxide, and silicon reaches the outermost surface of the electrode. It is considered that the film is different from the film formed on the platinum film.

In this example, it was confirmed that similar results were obtained when ruthenium was used instead of ruthenium silicide.

(Example 3) In the thin film capacitor of Example 1, an alloy film made of a high melting point noble metal of platinum, palladium, or rhodium, or a multilayer film was used for the second layer of the conductive layer. Table 1 summarizes the materials used in this example.

Also in this example, as in Example 1, the dielectric constant of the BaTiO ₃ film did not depend on the film thickness, and a value of about 220 was obtained, and formation of the low dielectric constant layer at the interface could be prevented. In addition, it was confirmed by X-ray diffraction that the second melting point noble metal alloy or the multilayer film was not silicided.

(Example 4) As in Example 2, after ruthenium silicide was deposited on the first layer of the conductive layer by 1500 Å by the DC sputtering method, the ruthenium silicide film was oxidized by heat treatment at 500 ° C in an oxygen gas atmosphere. Then, platinum, BaTiO ₃ , and Al were formed in the same manner as in Example 1.

As in Examples 1 and 2, the BaTiO ₃ film had a dielectric constant of about 220 regardless of the film thickness. According to X-ray diffraction after forming the dielectric film, platinum is not silicidized, which is different from the result of Example 2. That is, although the film obtained by oxidizing ruthenium silicide contains a large amount of silicon,
It suppresses the diffusion of silicon into platinum. The temperature for oxidizing the ruthenium silicide film needs to be 400 ° C. or higher. The sheet resistance of the ruthenium silicide film depends on the oxidation temperature and is about 10Ω / □ from 400 ℃ to 600 ℃.
It starts to increase from 630 ℃, and when oxidized at temperatures higher than 700 ℃, it increases remarkably and reaches 100Ω / □ or more. In a thin film capacitor, the smaller the resistance of the electrode, the better. Therefore, the oxidation treatment temperature of ruthenium silicide is preferably 400 ° C or higher and 700 ° C or lower.

The ruthenium-silicon oxide film produced in this example is characterized in that it has better adhesion to the silicon electrode than the ruthenium oxide film produced in Example 1. For example, a film thickness of 1500 is formed on a silicon substrate as in the present embodiment.
Even if an oxide film made of ruthenium-silicon of Å was formed and a BaTiO ₃ film of 2 μm was sputter-deposited on the oxide film, the film was not peeled off, but the film thickness was 1500 Å on the silicon electrode as in Example 1. On top of sputter deposited ruthenium oxide film
When BaTiO ₃ with a film thickness of 3500Å or more was deposited, the entire surface was peeled between the ruthenium oxide and the silicon electrode.

Further, even if a ruthenium film was used instead of the ruthenium silicide film of this example, the effect of improving the adhesion was similarly obtained.

In the above examples, the BaTiO ₃ film was explained.
_{SrTiO 3, PbTiO 3, PbZrO 3} , LiNbO 3, Bi 3 Ti 4 O 12 and solid solutions _{(Ba, Sr) TiO 3,} (Ba, Pb) TiO 3, Pb (Zr, Ti) same manufacturing also O _3, As a result of the evaluation, the original dielectric constant of the dielectric film was obtained regardless of the film thickness.

(Effect of the invention) As described above, according to the present invention, in a thin film capacitor formed on a silicon electrode, a film made of ruthenium oxide, ruthenium silicide, or ruthenium and a high melting point noble metal film are provided between the silicon electrode and the dielectric film. By forming such a conductive layer, it is possible to prevent the formation of the low dielectric constant layer and provide a high dielectric constant thin film capacitor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional side view of a thin film capacitor of Example 1 of the present invention, and FIG. 2 is a diagram showing a relationship between a film thickness of a BaTiO ₃ film and a dielectric constant. In the figure, 1 ... Single crystal silicon substrate, 2 ... Low resistance layer of single crystal silicon, 3 ... Silicon oxide, 4 ... Polycrystalline silicon film, 5, 9 ... Al, 6 ... Conductive layer first layer, 7 ... Conductive layer The second layer,
8 ... BaTiO ₃ film.

Claims (2)

[Claims] 1. In a thin film capacitor having a structure in which a conductive layer, a dielectric and an upper electrode are sequentially formed on a silicon electrode, the conductive layer is a first layer formed on the silicon electrode and a second layer formed thereon. And a first layer of ruthenium,
A thin film capacitor comprising at least one material selected from ruthenium silicide and ruthenium oxide, and the second layer comprising at least one material selected from high melting point noble metals such as platinum, palladium and rhodium. 2. After forming ruthenium or ruthenium silicide on the first layer of the conductive layer on the silicon electrode, 400 ° C.
The conductive layer first layer is partially or wholly oxidized by heat treatment in an oxygen atmosphere of 700 ° C. or lower, and then the conductive layer second layer is made of at least one or more refractory precious metals such as platinum, palladium, and rhodium. A method of manufacturing a thin film capacitor, which comprises forming a material, and then sequentially forming a dielectric and an upper electrode thereon.