JPH0687493B2 - Thin film capacitors - 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 conventionally used dielectric thin film materials are limited to materials with a dielectric constant of at most 10 such as SiO ₂ , Si ₃ N _4, etc. It is necessary to develop a dielectric thin film with a high rate. BaTiO ₃ , which is a perovskite type oxide represented by the chemical formula ABO ₃ , SrTiO ₃ , PbZrO ₃ and ilmenite type oxides such as LiNbO ₃ or Bi ₄ Ti ₃ O ₁₂ are ferroelectric oxides belonging to the above single Composition and mutual solid solution composition, 100 in single crystal or ceramic
It is known to have a dielectric constant as high as 10,000, and is 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, examples in which relatively good characteristics have been obtained are the papers published in Proceedings of the IEEE Vol. 59, No. 10, pp. 1404-1447. There is a sputtered and heat-treated BaTiO ₃ thin film from 16 (created at room temperature) to 1900
A dielectric constant of (heat treated at 1200 ° C) is obtained.

(Problems to be Solved by the Invention) Dielectric thin films such as BaTiO ₃ that have been conventionally produced as described above require high temperature at the time of thin film formation in order to obtain a high dielectric constant. It is formed on the lower electrode made of a high melting point precious metal material. Aluminum, nichrome, copper, etc., which are generally used as electrode materials, cause a significant decrease in the dielectric constant due to evaporation of the electrodes at high temperatures and mutual reaction with the dielectric film. However, even with the high melting point noble metal electrode as described above, the surface of the electrode is roughened by recrystallization in the dielectric film formation at 300 ° C. or higher. The dielectric film formed on such an electrode has a non-uniform film thickness, and when a voltage is applied, the electric field is strongly applied to a portion having a small film thickness, so that there is a problem in insulation characteristics.

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
Of Research and Development (IBM Jo
urnal of Research and Development) November 1969 686
In the paper on SrTiO ₃ film on page −695, 687−68
It is reported in the description on page 8 that when forming a thin film of a high dielectric constant material on silicon, a layer equivalent to about 100 Å of silicon dioxide (SiO ₂ ) is formed at the interface. Since this interface layer has 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.
It can be found in the description on page 316 in the article on BaTiO ₃ published in Vol. 16, No. 2, pp. 315-318.

An object of the present invention is to realize a thin film capacitor having high capacitance density and excellent insulating properties, which can be applied to a silicon integrated circuit, by using a thin film of a high dielectric constant material typified by BaTiO ₃ and SrTiO _3. There is.

(Means for Solving the Problems) The present invention is a thin film capacitor having a structure in which a lower electrode, a dielectric, and an upper electrode are sequentially stacked on a substrate, and the lower electrode for directly depositing the dielectric is rhenium, Rhenium silicide, osmium, osmium oxide, osmium silicide, rhodium oxide, rhodium silicide, iridium oxide, iridium silicide, or rhenium, osmium, rhodium, iridium, and their silicides or oxides It is a thin film capacitor characterized by comprising two or more of them.

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

FIG. 1 is a structural diagram of a thin film capacitor of Example 1, in which a silicon oxide film 2 is formed as an insulating layer on a surface of a silicon substrate 1, a lower electrode 3 is formed on the silicon oxide layer, and a dielectric is formed on the lower electrode. BaTiO ₃ film 4 is formed, and the Al film 5 of the upper electrode is formed thereon.

First, a silicon oxide layer having a thickness of 1 μm was formed on the surface of single crystal silicon by a steam thermal oxidation method. The atmosphere controls the flow ratio of oxygen gas and hydrogen gas to 1: 1 respectively, and the temperature is 1100 ° C.
Thermal oxidation was performed at. The lower electrode was manufactured by DC magnetron sputtering to have a film thickness of 0.5 μm. Re or ReSi ₂
Using a target having the composition, an Ar gas atmosphere or a mixed gas atmosphere of Ar and O ₂ was used at 4 × 10 ⁻³ Torr and a substrate temperature of 100 ° C. For the BaTiO ₃ film, a stoichiometric powder target was used.
A film having a thickness of 0.5 μm was produced by the high frequency magnetron sputtering method. Sputter deposition was performed at 1 × 10 ^-2 Torr and a substrate temperature of 600 ° C. in an Ar—O ₂ mixed gas. 0.5 μm Al for the upper electrode
Was formed by a DC sputtering method. The effective area of this capacitor is 3 × 5 mm ² . Next, the difference in the characteristics of the BaTiO ₃ film when the Pd film which is a high melting point noble metal is used for the lower electrode and when the film of this method is used will be described. Fig. 2 (a)
Is the second of the BaTiO ₃ film when the lower electrode film of this method is used.
FIG. 6B is a histogram of the dielectric breakdown strength of the BaTiO ₃ film when a Pd film having a film thickness of 0.5 μm is used. The dielectric breakdown strength is defined as the electric field strength when a current of 1 × 10 ⁻⁴ A / cm ² flows. The dielectric breakdown strength of the present method is three times or more larger, and the distribution thereof does not vary, showing excellent insulation characteristics.

When a part of the BaTiO ₃ film was removed by etching and the surface roughness of the lower electrode was measured with a stylus surface profilometer, the average roughness Ra of the film such as rhenium and the Pd film was 50Å and 380Å, respectively.
It was found that the film made of rhenium or the like had better surface flatness. The surface roughness of the lower electrode before forming the BaTiO ₃ film is about 30Å. Therefore, it is considered that the difference in the insulating properties between the two is due to the surface roughness of the lower electrode in the high temperature process of BaTiO ₃ film formation. In this case, the same effect was obtained with rhenium, rhenium oxide, rhenium silicide, or a laminated structure of these as the lower electrode.

Further, in the case of using osmium, rhodium, iridium, and their silicides or oxides instead of rhenium, rhenium oxide, and rhenium silicide of this embodiment, the dielectric breakdown strength of the BaTiO ₃ film formed thereon is The Pd film was more than 3 times larger than that using the Pd film, and excellent insulating properties were obtained. Table 1 summarizes the dielectric breakdown strength of the lower electrode material and the BaTiO ₃ film formed thereon.

(Embodiment 2) FIG. 3 is a structural diagram of a thin film capacitor of Embodiment 2, in which a silicon oxide layer 7 as an insulating layer is formed on the surface of a single crystal silicon substrate 6.
Is formed, a polycrystalline silicon film 8 is formed as a lower electrode on the silicon oxide layer, and a film 9 made of rhenium or the like is formed thereon, a dielectric BaTiO ₃ film 10 is formed on these lower electrodes, and an upper film is formed thereon. The Al film 11 of the electrode is formed.

Polycrystalline silicon film is formed at 300 ℃ by plasma CVD method
A film having a thickness of 0.3 μm was produced. Arsenic ions were implanted into this polycrystalline silicon film at an acceleration voltage of 70 KV in an amount of 2 × 10 ¹⁶ cm ^-2 , and then heat-treated at 900 ° C. for 20 minutes to obtain about 100
The sheet resistance was Ω / □. Other films were formed in the same manner as in Example 1.

In this case, the polycrystalline silicon film is used to improve the adhesion between the silicon oxide of the insulating layer and the lower electrode, but even if a film of rhenium or the like is formed on the polycrystalline silicon film,
As in Example 1, a thin film capacitor having excellent insulating properties was obtained. In the case of rhenium or rhenium oxide, a multilayer film containing metal silicide such as rhenium silicide and rhenium or polycrystalline silicon may be used instead of polycrystalline silicon.

Example 3 FIG. 4 is a structural diagram of a thin film capacitor of Example 3. A low resistance layer 13 is formed by doping phosphorus at a high concentration on a part of the surface of the single crystal silicon 12, and a silicon oxide film 14 is formed thereon as an interlayer insulating film. In a part of the silicon oxide film, two contact holes for leading out the lower electrode through the low resistance layer are formed, one contact hole is filled with the lower electrode film 15, and the other contact hole is the Al film 16 It is filled with. Therefore, Al
The film 16 serves as a terminal of the lower electrode. The lower electrode film may fill the contact hole and a part thereof may be formed on the silicon oxide film. A BaTiO ₃ film 17 is formed on the lower electrode film, and A 18 is formed thereon as an upper electrode.

In this embodiment, the lower electrode film is formed on the single crystal silicon in order to draw the lower electrode through the low resistance layer of the single crystal silicon. However, the insulation characteristics of the thin film capacitor are similar to those of the first embodiment. I confirmed that.

Next, the difference in the dielectric constant of the BaTiO ₃ film when the polycrystalline silicon film is used for the lower electrode and when the film of the present invention is used will be described. Polycrystalline silicon film is a material that is generally used as an electrode film of current silicon LSI. Figure 5 shows BaTi
The relationship between the dielectric constant and the film thickness of the O ₃ film was investigated, and the results are obtained when the film of the present invention is used (a) and when the polycrystalline silicon film (b) is used. When the film of the present invention is used, the dielectric constant of the BaTiO ₃ film does not depend on the film thickness and is constant at about 240, whereas the dielectric constant of the BaTiO ₃ film when the polycrystalline silicon film is used. Depends on the film thickness, and the dielectric constant decreases as the film thickness decreases. This is considered to be because, as described in the prior art, a low dielectric constant silicon oxide film was formed at the interface between BaTiO ₃ and polycrystalline silicon, and the apparent dielectric constant of the BaTiO ₃ film was lowered.

Further, as in the second embodiment, the lower electrode may have a two-layer structure in which a film of rhenium or the like and polycrystalline silicon thereunder are provided. In this case, the polycrystalline silicon film has an effect of improving the adhesion between the film of rhenium or the like and the single crystal silicon or the silicon oxide. Furthermore, a planarization technique for filling the contact hole with a polycrystalline silicon film has been established, and it has a great advantage to be used as a part of the lower electrode.

By using a film made of rhenium, osmium, rhodium, iridium, and one or more of their silicides or oxides for the lower electrode as shown in this embodiment,
A thin film capacitor having a constant high dielectric constant can be manufactured on a silicon electrode without depending on the film thickness of the dielectric film.

(Effects of the Invention) As described above, the present invention provides iridium which does not cause surface roughness on a lower electrode of a thin film capacitor due to high temperature process,
By using a film of osmium, rhodium, iridium, and their silicides or oxides, it is possible to provide a high dielectric constant thin film capacitor having excellent insulating characteristics. Moreover, unlike the conventional silicon electrode, since a silicon oxide layer having a low dielectric constant is not formed at the interface with the dielectric, a thin film capacitor having a constant high dielectric constant does not depend on the thickness of the dielectric film. It can be fabricated on silicon.

[Brief description of drawings]

FIG. 1 is a sectional side view of a thin film capacitor showing an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are histogram diagrams of dielectric breakdown strength, and FIGS. 3 and 4 are thin film capacitors showing the embodiment. Fig. 5 is a sectional side view of Fig. 5, and Fig. 5 is a diagram showing the relationship between the dielectric constant and the film thickness of the BaTiO ₃ film. 1, 6, 12 are single crystal silicon substrates, 2, 7, 14 are silicon oxides, ₃ , 9, 15 are lower electrodes, 4, 10, 17 are BaTiO ₃ ,
5, 11, 16, and 18 are Al, 8 is polycrystal silicon, and 13 is a low resistance layer of single crystal silicon.

Claims (4)

[Claims] 1. In a thin film capacitor having a structure in which a lower electrode, a dielectric and an upper electrode are sequentially formed on a substrate, the lower electrode for directly depositing the dielectric is made of rhenium or rhenium silicide. Alternatively, a thin film capacitor comprising a laminated body of two or more materials selected from rhenium, rhenium oxide, and rhenium silicide. 2. In a thin film capacitor having a structure in which a lower electrode, a dielectric and an upper electrode are sequentially laminated on a substrate, the lower electrode for directly depositing the dielectric is made of osmium, osmium oxide and osmium silicide. A thin film capacitor comprising one or more selected materials. 3. In a thin film capacitor having a structure in which a lower electrode, a dielectric and an upper electrode are sequentially formed on a substrate, the lower electrode for directly depositing the dielectric is either rhodium oxide or rhodium silicide. A thin film capacitor, which is made of or consisting of a laminate of two or more materials selected from rhodium, rhodium oxide, and rhodium silicide. 4. In a thin film capacitor having a structure in which a lower electrode, a dielectric and an upper electrode are sequentially formed on a substrate, the lower electrode on which the dielectric is directly formed is either iridium oxide or iridium silicide. Consists of or
Alternatively, a thin film capacitor comprising a laminated body of two or more materials selected from iridium, iridium oxide, and iridium silicide.