JP3461398B2 - Dielectric capacitor and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric capacitor, and more particularly to improvement of its ferroelectricity.

FIG. 29 shows a conventional ferroelectric capacitor. A silicon oxide layer 4 is formed on the silicon substrate 2. A lower electrode 6 made of platinum is provided thereon. PZ, which is a ferroelectric layer, is formed on the lower electrode 6.
A T (PbZr _X Ti _1-X O ₃ ) film 8 is provided, and further thereon,
An upper electrode 10 made of platinum is provided. In this way, the lower electrode 6, the PZT film 8 and the upper electrode 10 form a ferroelectric capacitor.

The reason why platinum is used as the lower electrode 6 is as follows. PZ
The T film 8 must be formed on the alignment film. This is because if it is formed on an amorphous film, it will not be oriented and the ferroelectricity will be impaired. On the other hand, the lower electrode 6 is
It must be formed in a state of being insulated from the silicon substrate 2. Therefore, the silicon oxide layer 4 is formed on the silicon substrate 2.
Is formed. This silicon oxide layer 4 is amorphous. In general, a film formed on an amorphous film is a non-oriented film, but platinum has a property of forming an oriented film even on an amorphous film. For this reason, platinum is used as the lower electrode.

[0004]

However, the conventional ferroelectric capacitors as described above have the following problems.

Since platinum easily permeates oxygen, there is a problem that oxygen escapes from the ferroelectric substance (PZT), deterioration over time and repeated polarization inversion deteriorate the ferroelectricity. That is, as shown in FIG. 30, oxygen in the ferroelectric substance may escape from between the columnar crystals of platinum.

Further, such a problem similarly occurs in a capacitor using a dielectric having a high dielectric constant.

It is an object of the present invention to solve the above problems and provide a ferroelectric capacitor or a dielectric capacitor having a high dielectric constant, which is less likely to deteriorate over time and to be repeatedly deteriorated due to repeated polarization inversion.

[0008]

In the present invention, the term "capacitor" refers to a structure in which electrodes are provided on both sides of an insulator, regardless of whether or not it is used for storing electricity. It is a concept including those having this structure.

The dielectric capacitor of the present invention includes a substrate, a lower electrode formed on the substrate via a silicon oxide layer, and having at least an iridium oxide layer and an iridium layer formed thereon, and a lower electrode. A dielectric layer formed of a ferroelectric or a dielectric having a high dielectric constant, and an upper electrode formed on the dielectric layer,
Is equipped with.

Further, according to the present invention, in the dielectric capacitor, the lower electrode is composed of an iridium oxide layer formed by sputtering.

The dielectric capacitor of the present invention is formed on a substrate and a silicon oxide layer on the substrate,
A lower electrode having at least an iridium oxide layer and an alloy layer of platinum and iridium formed thereon, and a dielectric layer formed on the lower electrode and composed of a ferroelectric substance or a dielectric substance having a high dielectric constant. And an upper electrode formed on the dielectric layer.

In the dielectric capacitor of the present invention, the lower electrode has a bonding layer in contact with the silicon oxide layer.

Further, the dielectric capacitor of the present invention comprises a substrate, an iridium layer formed on the substrate via a silicon oxide film, and a platinum thin film on the iridium layer as a conductive thin film having a good crystal orientation. A lower electrode including an iridium oxide layer formed by oxidizing the iridium layer in a state where an alloy layer of iridium is formed, and a ferroelectric or high dielectric constant formed on the conductive thin film of the lower electrode. A dielectric layer formed of a dielectric having a refractive index and an upper electrode formed on the dielectric layer.

Further, the dielectric capacitor of the present invention is formed on the lower electrode, the lower electrode, and formed on the dielectric layer and the dielectric layer composed of a ferroelectric or a dielectric having a high dielectric constant. In the dielectric capacitor provided with the above upper electrode, the lower electrode is formed by oxidizing the iridium layer in a state where an alloy layer of platinum and iridium is formed as a conductive thin film having good crystal orientation on the surface of the iridium layer. It is characterized by being formed.

Further, in the method for manufacturing a dielectric capacitor of the present invention, a step of forming an iridium layer on a substrate by sputtering, and a step of forming a conductive thin film having good crystal orientation on the surface of the iridium layer and being resistant to oxidation. Oxidizing the iridium layer having the conductive thin film formed on the surface thereof, forming a ferroelectric film or a dielectric film having a high dielectric constant as a dielectric layer on the conductive thin film, the dielectric Forming an upper electrode on the layer.

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

The dielectric capacitor of the present invention has an iridium oxide layer on the lower electrode and an iridium layer formed thereon. Therefore, it is possible to prevent the escape of oxygen from the dielectric layer, and to suppress the secular change in the dielectric characteristics. That is, the iridium oxide layer does not have orientation regardless of whether the underlayer is oriented, but when an iridium layer is further formed on this iridium oxide layer, the iridium layer has orientation. The dielectric layer formed on this upper layer is well oriented, and good characteristics can be obtained with almost no change in the integrated current value.
Further, since iridium is formed on the iridium oxide layer, it is possible to prevent the escape of oxygen and improve the orientation of the ferroelectric layer. Furthermore, since the lead component in the ferroelectric layer does not penetrate to the lower electrode,
Imprint characteristics are improved.

In the dielectric capacitor of the present invention, a conductive layer having a good crystal orientation is provided on the iridium layer, and the dielectric layer is provided on the conductive layer. Therefore, the orientation of the dielectric layer is improved, and the secular change in the dielectric characteristics can be suppressed. That is, the lower electrode is configured to include an iridium oxide layer formed by oxidizing a conductor layer having a good crystal orientation on the iridium layer. Therefore, the good conductor layer on the surface does not react with oxygen and is not oxidized, and only the inter-crystals of the iridium layer are oxidized to close the inter-crystals, and the permeation of oxygen from the dielectric layer can be effectively prevented. Becomes Further, since the surface on which the dielectric layer is formed is a conductor having a good orientation, the dielectric layer formed on this layer is formed with a very good orientation.

[0033]

[0034]

[0035]

[0036]

That is, it is possible to provide a dielectric capacitor having good ferroelectricity and high dielectricity.

[0038]

FIG. 1 shows the composition of a ferroelectric capacitor according to an embodiment of the present invention. A silicon oxide layer 4, a lower electrode 12, a ferroelectric film (ferroelectric layer) 8 and an upper electrode 15 are provided on the silicon substrate 2. Lower electrode 12
Is formed of iridium oxide, and the upper electrode 1
5 is also formed of iridium oxide.

FIG. 2 shows a comparison of the physical properties of platinum and iridium. As is clear from this table, the resistivity of iridium oxide is 49 × 10 ⁻⁶ Ωcm, and there is no problem as an electrode material.

As shown in FIG. 30 of the conventional example, since platinum is a columnar crystal, oxygen in the ferroelectric film 8 is transmitted. In this embodiment, iridium oxide is used as the lower electrode 12.
Used as. Since this iridium oxide layer 12 is not a columnar crystal, it hardly transmits oxygen. Therefore, deficiency of oxygen in the ferroelectric film 8 can be prevented. Upper electrode 1
The same applies to 5. As a result, the ferroelectricity of the ferroelectric film 8 is improved. This point will be described later in detail together with experimental data.

In the above embodiment, since both the lower electrode 12 and the upper electrode 15 are made of iridium oxide, it is possible to reliably prevent the permeation of oxygen. However, a certain degree of effect can be obtained by using only one of them. This point will also be described later.

The ferroelectric capacitor as described above can be used as a non-volatile memory in combination with the transistor 24, for example, as shown in FIG.

FIG. 4 shows a manufacturing process of a ferroelectric capacitor according to an embodiment of the present invention. The surface of the silicon substrate 2 is thermally oxidized to form the silicon oxide layer 4 (FIG. 4A).
Here, the thickness of the silicon oxide layer 4 is 600 nm. Next, using iridium as a target, iridium oxide is formed on the silicon oxide layer 4 by reactive sputtering, and this is used as the lower electrode 12 (FIG. 4).
B). Here, it is formed to a thickness of 200 nm.

Next, a PZT film is formed as the ferroelectric layer 8 on the lower electrode 12 by the sol-gel method (FIG. 4C). As starting _{materials, Pb (CH 3 COO) 2} · 3H 2 O, Zr (t chromatography
A mixed solution of OC ₄ H ₉ ) 4 and Ti (i-OC ₃ H ₇ ) ₄ was used. After spin-coating this mixed solution, 150 degrees Celsius (the same applies below)
And dry it in a dry air atmosphere at 400 degrees for 3
It was calcined for 0 seconds. After repeating this 5 times, O ₂
Heat treatment was performed at 700 ° C. or higher in the atmosphere. In this way, the 250 nm ferroelectric layer 8 was formed. In addition,
Here, in PbZr _x Ti _1-x O ₃ , x is set to 0.52 (hereinafter referred to as PZT (52 · 48)) to form a PZT film.

Further, iridium oxide is formed on the ferroelectric layer 8 by reactive sputtering, and the upper electrode 1
5 (FIG. 4D). Here, it is formed to a thickness of 200 nm. In this way, a ferroelectric capacitor can be obtained.

In FIG. 5 and FIG. 6, P is used as the ferroelectric film 8.
The fatigue of the remanent polarization Pr when a ferroelectric capacitor is formed using ZT (52/48) is shown. The test was performed by applying a voltage between points a and b in the structure as shown in FIG. Voltages of 5V and -5V as shown in FIG. 7 were applied between the upper electrode 15 and the lower electrode 12 to measure the deterioration of the remanent polarization Pr. The application of voltages of 5 V and -5 V was set as one cycle. The voltage is 500KH
It was applied at a frequency of z.

The vertical axes of FIGS. 5 and 6 are Pr when the initial remanent polarization is Po and the remanent polarization after fatigue is Pr.
It represents the value of / Po. That is, the larger this value is, the more remarkable the deterioration is. The horizontal axis represents how many cycles the voltage of FIG. 7 was applied repeatedly. In the figure,
A curved line 50 is formed when both the upper electrode 15 and the lower electrode 12 are made of iridium oxide, and a curved line 52 is formed when the upper electrode 15 is made of platinum and the lower electrode 12 is made of iridium oxide.
A curved line 54 indicates that when the upper electrode 15 is made of iridium oxide and the lower electrode 12 is made of platinum, the upper electrode 15 and the lower electrode 1
2 is a characteristic change when both are made of platinum.

As is clear from this figure, the upper electrode 1
It is clear that if either 5 or the lower electrode 12 is made of iridium oxide, the deterioration of the remanent polarization Pr is considerably improved. In particular, the upper electrode 15 and the lower electrode 1
It is clear that when both 2 are composed of iridium oxide, deterioration hardly occurs up to 10 ¹⁰ cycles.

By the way, iridium oxide has no orientation regardless of whether the underlayer is oriented. Therefore, the ferroelectric film 8 formed on the iridium oxide
Will not be oriented.

The following test was conducted to verify that iridium oxide has no orientation regardless of the orientation of the underlayer. The characteristics of a ferroelectric capacitor in which iridium oxide was formed as the lower electrode 12 directly on the silicon substrate 2 and a ferroelectric capacitor in which iridium oxide was formed as the lower electrode 12 on the silicon oxide layer 4 were compared. . FIG. 9 shows the hysteresis characteristic.
9A shows the case where the lower electrode 12 is formed on the silicon oxide layer 4, and FIG. 9B shows the case where the iridium oxide is directly formed on the silicon substrate 2 as the lower electrode 12. As is clear from this graph, it is shown that the characteristics of the ferroelectric film 8 are the same regardless of whether the underlayer of iridium oxide is silicon or silicon oxide. This is probably because iridium oxide has no orientation regardless of whether the underlayer is oriented.

If the iridium oxide layer of the lower electrode 12 is not oriented, the orientation of the ferroelectric film 8 formed thereon will be poor. Therefore, if the orientation of the ferroelectric layer 8 is improved while using the iridium oxide layer, the fatigue characteristics of the remanent polarization Pr are further improved.

To this end, a platinum layer may be formed on the iridium oxide layer to form the lower electrode 12. FIG. 10A shows changes in the characteristics in this case. In this graph, the vertical axis represents the magnitude of polarization, and the horizontal axis represents the same voltage application cycle as in FIG. In addition, this graph shows changes in the characteristic amounts Pr, Pmax, P, and N of the hysteresis characteristic shown in FIG. 10B. As is clear from the graph, the deterioration of the characteristics is further improved by providing the platinum layer on the iridium oxide layer. That is, there is almost no deterioration up to 1011 cycles.

Instead of the platinum layer, an iridium layer or a conductor layer having a good orientation such as an alloy of platinum and iridium may be provided (as will be described later, the structure shown in FIG. 27 may be used. Good). In particular, for the alloy of platinum and iridium, the lattice constant can be selected by changing the compounding ratio, and it is easy to match the lattice constant with the ferroelectric layer.

In FIG. 11, PZT (5
2/48) and Pt _x Ir _1-x is used as the lower electrode 12, and the composition ratio x of platinum and iridium is changed,
A graph showing changes in the remanent polarization Pr and the coercive electric field Ec. As is clear from this figure, the remanent polarization Pr is higher when the alloy with iridium is used as the lower electrode 12 than when only platinum is used (when x = 1.0). It is clear that it gives a value. That is, it can be said that the ferroelectricity is improved. In the range of 0% to 50% of platinum, remarkable improvement of the characteristics is obtained, and particularly at a mixing ratio of 20% to 30% with a peak of about 25% of platinum, extremely excellent characteristics are obtained. Therefore, if the above alloy is formed on the iridium oxide layer, the ferroelectric film 8 having excellent characteristics can be obtained.

Even when a conductive layer is formed on the iridium oxide layer and used as an electrode, the upper and lower electrodes 15 and 12 have the iridium oxide layer as in the case of FIGS. 5 and 6. It is preferably formed.

FIGS. 12 and 13 show hysteresis characteristics when the iridium oxide layer and the iridium layer are used for the upper electrode 15 (FIGS. 12A and 13A) and the hysteresis characteristics when only the iridium layer is used for the upper electrode 15. (Fig. 12
B, FIG. 13B). The lower electrode was formed of an iridium oxide layer and an iridium layer in both cases. Both the initial characteristics (FIGS. 12A and 12B) are the same, but the characteristics (FIGS. 13A and 13B) after applying the pulse for 10 ⁸ times (cycles) are clearly
It is better to use the iridium oxide layer and the iridium layer for the upper electrode 15 as well. This also seems to be the effect of preventing the escape of oxygen by the iridium oxide layer.

It should be noted that there is no difference in the secular change characteristics of the remanent polarization Pr and the coercive electric field Ec between the case where platinum is provided on the iridium oxide layer and the case where iridium is provided. However, if a pulse in a fixed direction is continuously applied to the ferroelectric layer 8 or if a polarized state in the fixed direction is maintained for a long time, the polarization characteristic becomes distorted, resulting in a difference in imprint characteristics.

FIG. 14 shows the characteristics of the ferroelectric capacitor when platinum is provided on the iridium oxide layer to form the lower electrode 12. This graph shows that when a voltage different from the polarization direction is applied to the ferroelectric capacitor (ferroelectric film 8) in the polarized state (inversion mode shown in FIG. 15A).
15A and 15B show temporal changes in current (current per unit area) when the same voltage as the polarization direction is applied (non-inversion mode shown in FIG. 15B). It can be seen that a larger current flows in the inversion mode.

This characteristic is utilized when the ferroelectric capacitor is used as a memory. In other words, it is used to judge the magnitude of the integrated value of the current when a voltage is applied by comparing it with the threshold value and read the recorded information. Therefore, the integrated current value in the inversion mode QP decreases (that is, approaches the threshold value) or the integrated current value in the non-inversion mode increases (that is, the threshold value) with the passage of the use period. Approaching) may cause erroneous reading.

In FIG. 16, the ferroelectric film 8 (upper electrode 15,
Both lower electrodes 12 are formed by providing platinum on the iridium oxide layer), and currents in the inversion and non-inversion modes after applying a pulse in the same direction 3 × 10 ⁹ times are shown. As is clear from this experimental result, the inversion mode Q
The integrated current value at P ⁺ decreases and almost reaches the value equal to the integrated value of the first non-inversion mode QU ⁻ .

FIG. 17 shows the change in the integrated current value in the above case. The horizontal axis is the pulse application cycle (number of times),
The vertical axis represents the integrated current value. As you can see from the graph,
It can be seen that the integrated current value has changed significantly after the number of times exceeds 10 4.

FIG. 18 shows changes in the integrated current value of the ferroelectric film 8 when both the upper electrode 15 and the lower electrode 12 are formed by forming an iridium layer on the iridium oxide layer. As is clear from the graph, the current integrated value hardly changes and good characteristics are selected. That is, it was revealed that the electrode having iridium oxide formed on iridium oxide was superior to the electrode having platinum formed on iridium oxide with respect to the imprint characteristics as described above.

FIG. 19 shows the result of analyzing the content of elements in each layer of the ferroelectric capacitor used in the above experiment. FIG. 19A shows a case where platinum is formed on iridium oxide, and FIG. 19B shows a case where iridium is formed on iridium oxide. The horizontal axis represents the depth from the surface of the upper electrode, and the vertical axis represents the content of each element.

What is apparent from this graph is FIG. 19A.
In this case, the lead (Pb) component in the ferroelectric layer 8 penetrates to the platinum (Pt) of the lower electrode. On the other hand, in the case of FIG. 19B, the lead (Pb) component 8 in the ferroelectric substance hardly penetrates into the lower electrode. This seems to have an influence on the imprint characteristics as described above.

FIG. 20 shows the structure of a ferroelectric capacitor according to another embodiment of the present invention. In this embodiment, a titanium layer (5n) is formed between the lower electrode 12 and the silicon oxide layer 4.
m) is provided as the bonding layer 30. In general, the adhesion between iridium oxide and silicon oxide is not very good. Therefore, the alloy layer may be partly peeled off, and the ferroelectric characteristics may be deteriorated. In particular, this becomes remarkable as the ratio of iridium in the alloy increases. Therefore, in this embodiment, a titanium layer having good adhesion to the silicon oxide layer 4 is provided as the bonding layer 30. This improves the ferroelectric characteristics. Note that the titanium layer may be formed by sputtering.

Although the titanium layer is used as the bonding layer 30 in the above embodiment, any material that improves the bonding property can be used.
It can be anything. For example, a platinum layer may be used.

In each of the above embodiments, the ferroelectric film 8 is made of P
Although ZT is used, any oxide ferroelectric material may be used. For example, Ba ₄ Ti ₃ O ₁₂ may be used.

A capacitor according to another embodiment of the present invention is shown in FIG. In this embodiment, instead of the ferroelectric layer 8, a dielectric layer 90 having a high dielectric constant is used. A lower electrode 12 of iridium oxide was provided on the silicon oxide layer 4, and a high dielectric constant thin film having a perovskite structure of SrTiO ₃ , (Sr, Ba) TiO ₃ was formed thereon as a dielectric layer 90. Also in this case, the improvement of the dielectric property was achieved as in the case of the ferroelectric substance. That is, it has been clarified that what has been described about the ferroelectric layer can be applied to the dielectric layer having a high dielectric constant.

FIG. 22 shows the structure of a ferroelectric capacitor according to another embodiment of the present invention. A silicon oxide layer 4, a lower electrode 12, a ferroelectric film (ferroelectric layer) 8 and an upper electrode 15 are provided on the silicon substrate 2. The lower electrode 12 is formed by the iridium layer 11 and the iridium oxide layer formed thereon. The upper electrode 15 is formed by the iridium layer 7 and the iridium oxide layer 9 formed thereon.

An enlarged view of the vicinity of the lower electrode 12 is shown in FIG. Since the iridium layer 11 is a columnar crystal, it transmits oxygen in the ferroelectric film 8. In this example,
An iridium oxide layer 13 is formed on the upper surface of the iridium layer 11. As described above, this iridium oxide layer 1
By 3, the deficiency of oxygen in the ferroelectric film 8 can be prevented. The same applies to the upper electrode 15.

In the above embodiment, since the iridium oxide layer is formed on both the lower electrode 12 and the upper electrode 15, it is possible to obtain a ferroelectric capacitor having excellent characteristics with little secular change. Even if one of the lower electrode 12 and the upper electrode 15 has the above structure, some effects can be obtained. This point will also be described later.

FIG. 24 shows the manufacturing process of this ferroelectric capacitor. The surface of the silicon substrate 2 is thermally oxidized to form the silicon oxide layer 4 (FIG. 24A). Here, the thickness of the silicon oxide layer 4 is 600 nm. Next, using iridium as a target, the iridium layer 11 is formed on the silicon oxide layer 4 (FIG. 24B). Then O
The iridium oxide layer 13 is formed on the surface of the iridium layer 11 by performing heat treatment at 800 ° C. for 1 minute in 2 atmospheres. The iridium layer 11 and the iridium oxide layer 13 are used as the lower electrode 12. Here, the lower electrode was formed to a thickness of 200 nm.

Next, a PZT film is formed as the ferroelectric layer 8 on the lower electrode 12 by the sol-gel method (FIG. 24C). As starting _{materials, Pb (CH 3 COO) 2} · 3H 2 O, Zr
A mixed solution of (t-OC ₄ H9) ₄ and Ti (i-OC ₃ H ₇ ) ₄ was used. After spin-coating this mixed solution, it was dried at 150 degrees Celsius (the same applies hereinafter) and pre-baked at 400 degrees for 30 seconds in a dry air atmosphere. After repeating this 5 times,
Heat treatment was performed at 700 ° C. or higher in an O ₂ atmosphere. In this way, the 250 nm ferroelectric layer 8 was formed. Here, in PbZr _X Ti _1-X O ₃ , x was set to 0.52 (hereinafter referred to as PZT (52 · 48)) to form a PZT film.

Further, the iridium layer 7 is formed on the ferroelectric layer 8 by sputtering. Next, the iridium layer 7 is heat-treated in an O ₂ atmosphere at 800 ° C. for 1 minute.
An iridium oxide layer 9 is formed on the surface of (FIG. 24D).
The iridium layer 7 and the iridium oxide layer 9 are used as the upper electrode 15. Here, the upper electrode 15 is formed to a thickness of 200 nm. In this way, a ferroelectric capacitor can be obtained.

25 and 26 show the fatigue characteristics of the remanent polarization Pr of the ferroelectric capacitor thus obtained. The measurement of this graph was performed by the same method as in FIGS.

The vertical axes of FIGS. 25 and 26 represent Pr when the initial remanent polarization is Po and the remanent polarization after fatigue is Pr.
It represents the value of / Po. The horizontal axis represents how many cycles the voltage of FIG. 7 was applied repeatedly. In the figure,
Curve α is the case where only the lower electrode 12 is manufactured as in the above-described embodiment. Here, the silicon oxide layer 4 is set to 60
0 nm, the lower electrode 12 (the surface of the iridium layer 11 is oxidized) is 200 nm, and the ferroelectric film 8 (PZ
T (52/48)) was set to 250 nm, and the upper electrode was composed of platinum. The curve β is the case where the surface of the iridium layer of the lower electrode 12 was not oxidized (other conditions are the same as the curve α). The curve γ is the case where the lower electrode 12 is made of platinum (other conditions are the same as the curve α).

As is clear from this figure, when the surface of the iridium layer 11 is oxidized to form the iridium oxide layer 13, the deterioration of the remanent polarization Pr is considerably improved. It should be noted that iridium (when not oxidized) (curve β) is superior to platinum (curve γ) because iridium is oxidized in other steps without special oxidation treatment. Is considered to be.

Also in this embodiment, it is preferable to provide the bonding layer 30 as described with reference to FIG.

The embodiment of oxidizing the surface of iridium described here is applicable not only to the ferroelectric film but also to the above-mentioned dielectric film having a high dielectric constant, and the same effect can be obtained. .

As described above, by oxidizing the surface of the iridium layer, the escape of oxygen from the ferroelectric film can be prevented, but iridium oxide is formed on the surface and the orientation of the ferroelectric film deteriorates. This can be solved by providing an iridium layer, a platinum layer, an alloy layer thereof, or the like on the iridium oxide layer 13 as described above (see FIG. 10). However, the problem can be solved by forming the lower electrode as follows.

First, as shown in FIG. 27, a platinum layer 80 (thin film conductor) is provided very thinly on the iridium layer 11. Here, it is set to 30 nm. Next, heat treatment is performed in this state. Since the platinum layer 80 on the surface does not react with oxygen,
Not oxidized. Further, since the platinum layer 80 is thinly formed, the crystal grains of the iridium layer 11 therebelow are oxidized, and iridium oxide is formed to prevent the permeation of oxygen. Therefore, it is possible to form the lower electrode 12 capable of preventing the permeation of oxygen while the surface has excellent orientation. As the thin film conductor, any conductor may be used as long as it has good orientation and is hard to oxidize.

The iridium layer 11 obtained by forming the thin film platinum layer 80 and then oxidizing the same is used alone as the lower electrode 1.
It can be used as 2. However, in the embodiment (see FIG. 10) in which the conductive layer having good orientation (iridium layer, platinum layer, etc.) is provided on the iridium oxide layer formed by sputtering to improve the orientation, the conductive layer having good orientation is provided. Can also be used as

FIG. 28B shows iridium oxide (50 nm).
27 shows hysteresis characteristics of the ferroelectric substance 8 when the lower electrode 12 is obtained by providing an iridium layer (200 nm) and a platinum layer (30 nm) having the structure of FIG. Further, in FIG. 28A, an iridium oxide layer (50
(nm) is provided with an iridium layer (200 nm) and subjected to oxidation treatment, the hysteresis characteristics of the ferroelectric substance 8 are shown. As is apparent from the figure, the hysteresis characteristic is superior when the structure shown in FIG. 27 is used.

Further, the embodiment described here can be applied not only to the ferroelectric film but also to the above-mentioned dielectric film having a high dielectric constant, and the same effect can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a composition of a ferroelectric capacitor according to an embodiment of the present invention.

FIG. 2 is a diagram showing physical properties of platinum and iridium.

FIG. 3 is a diagram showing a nonvolatile memory using a ferroelectric capacitor 22.

FIG. 4 is a diagram showing a manufacturing process of a ferroelectric capacitor.

FIG. 5 is a graph showing a secular change in remanent polarization when an electrode material is changed.

FIG. 6 is a graph showing a secular change in remanent polarization when an electrode material is changed.

FIG. 7 is a diagram showing a voltage applied when a fatigue test is performed.

FIG. 8 is a diagram showing a structure for a fatigue test.

FIG. 9 is a graph showing a result of verifying that iridium oxide is not affected by an underlayer.

FIG. 10 is a graph showing changes in remanent polarization Pr when platinum is provided on iridium oxide.

FIG. 11 is a diagram showing changes in remanent polarization Pr and coercive electric field Ec when the mixing ratio of platinum and iridium alloy is changed.

FIG. 12 is a graph comparing the case where an iridium oxide layer is provided on both the lower electrode and the upper electrode with the case where only the lower electrode is provided.

FIG. 13 is a graph comparing a case where an iridium oxide layer is provided on both the lower electrode and the upper electrode with a case where the iridium oxide layer is provided only on the lower electrode.

FIG. 14 is a graph showing a change over time in current generated when a voltage is applied to a ferroelectric.

15 is a diagram showing a voltage application direction in the graph of FIG.

16 is a graph showing a state in which the characteristics of FIG. 14 are changed by the imprint characteristics.

FIG. 17 is a graph showing imprint characteristics.

FIG. 18 is a graph showing imprint characteristics.

FIG. 19 is a diagram for explaining the cause of a difference in imprint characteristics.

FIG. 20 is a diagram showing an example in which a bonding layer 30 is provided.

FIG. 21 is a diagram showing an example in which a dielectric 90 having a high dielectric constant is used.

FIG. 22 is a diagram showing a structure of a ferroelectric capacitor according to another example.

FIG. 23 is a diagram showing a mechanism by which an iridium oxide layer prevents the escape of oxygen.

FIG. 24 is a diagram showing a manufacturing process of the ferroelectric capacitor of FIG. 22.

FIG. 25 is a diagram showing a comparison of secular changes in remanent polarization.

FIG. 26 is a diagram comparing and showing changes over time in remanent polarization.

FIG. 27 is a diagram showing an example in which thin film platinum is provided on the surface of iridium to perform oxidation.

FIG. 28 is a graph showing a comparison of the effects when the electrodes of FIG. 27 are used.

FIG. 29 is a diagram showing a structure of a conventional ferroelectric capacitor.

FIG. 30 is a diagram showing a state where oxygen is released from the lower electrode 6 by platinum.

[Explanation of symbols]

2. ． ． Silicon substrate 4. ． ． Silicon oxide layer 8. ． ． Ferroelectric layer 12. ． ． Lower electrode 15. ． ． Upper electrode 90. ． ． Dielectric layer with high dielectric constant

Claims (7)

(57) [Claims] 1. A substrate, a lower electrode formed on the substrate via a silicon oxide layer, having at least an iridium oxide layer and an iridium layer formed thereon, and formed on the lower electrode, A dielectric capacitor comprising: a dielectric layer composed of a ferroelectric or a dielectric having a high dielectric constant; and an upper electrode formed on the dielectric layer. 2. The dielectric capacitor according to claim 1, wherein the lower electrode is composed of an iridium oxide layer formed by sputtering. 3. A substrate, a lower electrode formed on the substrate via a silicon oxide layer, and having at least an iridium oxide layer and an alloy layer of platinum and iridium formed thereon, and an upper electrode. A dielectric capacitor comprising: a dielectric layer formed of a ferroelectric substance or a dielectric substance having a high dielectric constant; and an upper electrode formed on the dielectric layer. 4. The dielectric capacitor according to claim 1, 2, or 3, wherein the lower electrode has a bonding layer in contact with the silicon oxide layer. 5. A substrate, an iridium layer formed on the substrate via a silicon oxide film, and an alloy layer of platinum and iridium as a conductive thin film having good crystal orientation on the iridium layer. A lower electrode including an iridium oxide layer formed by oxidizing the iridium layer in a state, and formed on the conductive thin film of the lower electrode by a ferroelectric substance or a dielectric substance having a high dielectric constant. And a top electrode formed on the dielectric layer. 6. A lower electrode, a dielectric layer formed on the lower electrode and made of a ferroelectric substance or a dielectric substance having a high dielectric constant, and an upper electrode formed on the dielectric layer. In the dielectric capacitor, the lower electrode is formed by oxidizing the iridium layer in a state where an alloy layer of platinum and iridium is formed as a conductive thin film having good crystal orientation on the surface of the iridium layer. And dielectric capacitors. 7. A step of forming an iridium layer on a substrate by sputtering, a step of forming a conductive thin film having good crystal orientation on the surface of the iridium layer and being resistant to oxidation, and the conductive thin film formed on the surface Oxidizing the iridium layer, forming a ferroelectric film or a dielectric film having a high dielectric constant as a dielectric layer on the conductive thin film, forming an upper electrode on the dielectric layer, A method for manufacturing a dielectric capacitor comprising: