JP2002134710A - Dielectric capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dielectric capacitor which shows dielectric characteristics of less changes due to aging. SOLUTION: This dielectric capacitor is provided with a substrate, a lower electrode composed of an iridium layer consisting of column-shape crystals formed on an insulated surface of the substrate and an iridium oxide layer, formed among the column-shape crystals by oxidation of the iridium layer, a dielectric layer formed on the lower electrode and composed of a ferrodielectric or a dielectric having a high dielectric constant, and an upper electrode formed on the dielectric layer.

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 an improvement in ferroelectricity.

[0002]

2. Description of the Related Art A conventional ferroelectric capacitor is shown in FIG. A silicon oxide layer 4 is formed on a silicon substrate 2. A lower electrode 6 made of platinum is provided thereon. On the lower electrode 6, a ferroelectric layer P
A ZT (PbZr _X Ti _{1 -X} O ₃ ) film 8 is provided, and an upper electrode 10 made of platinum is further provided thereon. Thus, a ferroelectric capacitor is formed by the lower electrode 6, the PZT film 8, and the upper electrode 10.

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. If formed on an amorphous film, ferroelectricity is impaired because the film is not oriented. On the other hand, the lower electrode 6
It must be formed in a state 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. Generally, a film formed on an amorphous film is a non-oriented film, but platinum has a property of being an oriented film even on an amorphous film. For this reason, platinum is used as the lower electrode.

[0004]

However, the above-mentioned conventional ferroelectric capacitors have the following problems.

[0005] Since platinum easily transmits oxygen, there is a problem in that ferroelectricity is reduced due to escape of oxygen in the ferroelectric (PZT), aging, and repetition of polarization reversal. That is, as shown in FIG. 30, oxygen in the ferroelectric material might escape from between the platinum columnar crystals.

[0006] Such a problem also occurs in a capacitor using a dielectric having a high dielectric constant.

An object of the present invention is to solve the above-mentioned problems and to provide a ferroelectric capacitor or a dielectric capacitor having a high dielectric constant, which causes less deterioration due to aging and repetition of polarization inversion.

[0008]

According to a first aspect of the present invention, there is provided a lower electrode formed on an insulated surface of a substrate and having at least an iridium oxide layer and an iridium layer formed thereon. And a dielectric layer formed on the lower electrode and composed of a ferroelectric or a dielectric having a high dielectric constant, and an upper electrode formed on the dielectric layer. . In a second aspect of the present invention,
A lower electrode formed by an iridium layer formed on a surface insulated on the substrate and an iridium oxide layer formed thereon, formed on the lower electrode,
It is characterized by 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. In a third aspect of the present invention, a substrate;
An iridium layer formed of a columnar crystal formed on a surface insulated on the substrate, and a lower electrode including an iridium oxide layer formed on the columnar crystal by oxidation of the iridium layer; It is characterized by comprising a dielectric layer formed on the lower electrode and made of a ferroelectric or a dielectric having a high dielectric constant, and an upper electrode formed on the dielectric layer. In a fourth aspect of the present invention, a lower electrode,
A dielectric layer formed on the lower electrode and made of a ferroelectric or a dielectric having a high dielectric constant; an iridium layer formed on the dielectric layer and made of columnar crystals; and an oxidation of the iridium layer And an iridium oxide layer formed between the columnar crystals. In the present invention, the term “capacitor” refers to a structure in which electrodes are provided on both sides of an insulator, and is a concept including one having this structure regardless of whether it is used for storing electricity. is there.

Preferably, a lower electrode having at least an iridium oxide layer, a dielectric layer formed on the lower electrode and formed of a ferroelectric or a dielectric having a high dielectric constant, and a dielectric layer formed on the dielectric layer Upper electrode.

[0010] Preferably, the lower electrode is formed of an iridium oxide layer formed by sputtering.

Preferably, a conductor layer having good crystal orientation is formed on the iridium oxide layer to form a lower electrode, and a ferroelectric layer is formed on the conductor layer. It is characterized by.

Preferably, the conductive layer is a platinum layer.

Preferably, the conductive layer is an iridium layer.

Preferably, the conductive layer is an alloy layer of platinum and iridium.

Preferably, the lower electrode is formed on a silicon oxide layer formed on a substrate, and the lower electrode has a bonding layer in contact with the silicon oxide layer. And

Preferably, the lower electrode comprises an iridium layer and an iridium oxide layer formed thereon.

Preferably, the lower electrode is formed by oxidizing the surface of the iridium layer.

Preferably, a conductor layer having good crystal orientation is formed on the iridium oxide layer to form a lower electrode, and a ferroelectric layer is formed on the conductor layer. It is characterized by having.

Preferably, the conductive layer is a platinum layer.

Preferably, the conductive layer is an iridium layer.

Preferably, the conductive layer is an alloy layer of platinum and iridium.

Preferably, the lower electrode is formed on a silicon oxide layer formed on a substrate, and the lower electrode has a bonding layer in contact with the silicon oxide layer. And

Preferably, the semiconductor device includes a lower electrode, a dielectric layer formed on the lower electrode and made of a ferroelectric or a dielectric having a high dielectric constant, and an upper electrode formed on the dielectric layer. In the above dielectric capacitor, the lower electrode is formed by forming a conductive thin film having good crystal orientation on the surface of the iridium layer and then oxidizing the conductive thin film.

Preferably, the conductive thin film is made of platinum.

Preferably, the conductive thin film is made of an alloy of iridium and platinum.

Preferably, a lower electrode, a dielectric layer formed on the lower electrode and formed of a ferroelectric or a dielectric having a high dielectric constant, and at least an iridium oxide layer formed on the dielectric layer Having an upper electrode.

Preferably, the upper electrode is constituted by an iridium oxide layer formed by sputtering.

Preferably, the upper electrode comprises an iridium layer and an iridium oxide layer formed thereon.

Preferably, the upper electrode is formed by oxidizing the surface of an iridium layer.

Preferably, a lower electrode having at least an iridium oxide layer, a dielectric layer formed on the lower electrode and formed of a ferroelectric or a dielectric having a high dielectric constant, and a dielectric layer formed on the dielectric layer And an upper electrode having at least an iridium oxide layer.

The dielectric capacitor according to the first aspect has an iridium oxide layer and iridium on the lower electrode. Therefore, the escape of oxygen from the dielectric layer can be prevented, and the secular change of the dielectric characteristics can be suppressed.
That is, the iridium oxide layer has no orientation regardless of whether or not the underlying layer is oriented.However, when an iridium layer is further provided 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 current integrated value. In addition, since iridium is formed on the iridium oxide layer, the orientation of the ferroelectric layer can be improved while preventing escape of oxygen. Furthermore, since the lead component in the ferroelectric layer does not penetrate into the lower electrode, the imprint characteristics are improved. Further, in the dielectric capacitor according to the second aspect, the lower electrode is composed of an iridium layer formed on the substrate surface via the silicon oxide film and an iridium oxide layer formed thereon. Therefore, since the dielectric layer is formed on the lower electrode, the entire surface of the dielectric layer is in contact with the lower electrode, and transmission of oxygen from the dielectric layer becomes a problem. Then, iridium oxide is formed so as to fill the space between the columnar crystals of iridium. Therefore, transmission of oxygen from the dielectric layer can be prevented very well. For this reason, it is possible to prevent the permeation of oxygen and to provide a dielectric capacitor having excellent remanent polarization characteristics.
4. The dielectric capacitor according to claim 3, wherein a substrate, an iridium layer made of a columnar crystal formed on a surface insulated on the substrate, and an oxidation formed between the columnar crystals due to oxidation of the iridium layer. Since the lower electrode includes the iridium layer, iridium oxide is formed so as to fill the space between the columnar crystals of iridium. Therefore, transmission of oxygen from the dielectric layer can be prevented very well. For this reason, it is possible to prevent the permeation of oxygen, and it is possible to provide a dielectric capacitor having excellent remanent polarization characteristics. In the dielectric capacitor according to the fourth aspect, the upper electrode has an upper electrode composed of an iridium layer made of a columnar crystal and an iridium oxide layer formed between the columnar crystals by oxidizing the iridium layer. Therefore, iridium oxide is formed so as to fill the space between the columnar crystals of iridium. Therefore, transmission of oxygen from the dielectric layer can be prevented very well. For this reason, it is possible to prevent the permeation of oxygen and to provide a dielectric capacitor having excellent remanent polarization characteristics.

In the dielectric capacitor of the present invention, a conductive layer having good crystal orientation is provided on the iridium oxide layer, and the dielectric layer is provided on the conductive layer. Therefore, the orientation of the dielectric layer is improved, and the secular change of the dielectric characteristics can be suppressed.

In the dielectric capacitor of the present invention, an iridium layer is provided on an iridium oxide layer, and a dielectric layer is provided on the iridium layer. Therefore, the orientation of the dielectric layer is further improved, and the secular change of the dielectric characteristics can be suppressed.

The dielectric capacitor of the present invention is formed by providing a thin-film conductor having good crystal orientation on the iridium surface and then performing an oxidation treatment. Therefore, the escape of oxygen from the dielectric layer can be prevented, and a dielectric layer having good orientation can be obtained. Therefore, the secular change of the dielectric characteristics can be extremely suppressed.

The dielectric capacitor of the present invention has an iridium oxide layer on the upper electrode. Therefore, the escape of oxygen from the dielectric layer can be prevented, and the secular change of the dielectric characteristics can be suppressed.

The dielectric capacitor of the present invention has an iridium oxide layer on both the upper electrode and the lower electrode.
Therefore, the escape of oxygen from the dielectric layer can be reliably prevented, and the secular change of the dielectric characteristics can be suppressed.

That is, a dielectric capacitor having good ferroelectricity and high dielectric properties can be provided.

[0038]

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

FIG. 2 compares 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 permeates. In this embodiment, iridium oxide is deposited on the lower electrode 12.
Used as Since this iridium oxide layer 12 is not a columnar crystal, it does not easily transmit oxygen. Therefore, the oxygen deficiency of the ferroelectric film 8 can be prevented. Upper electrode 1
The same applies to No. 5. Thereby, the ferroelectricity of the ferroelectric film 8 was 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, the permeation of oxygen can be reliably prevented. However, a certain effect can be obtained by only one of them. This point will also be described later.

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

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

Next, a sol-gel is placed on the lower electrode 12.
A PZT film is formed as the ferroelectric layer 8 by a method.
(FIG. 4C). As a starting material, Pb (CH_ThreeCOO)_Two・ 3H_TwoO, Zr (t ー
OC_FourH₉) _Four, Ti (i-OC_ThreeH₇)_FourWas used. This mixed solution
After spin coating the liquid, 150 degrees (Celsius, the same applies hereinafter)
And dry at 400 degrees in a dry air atmosphere.
Preliminary baking for 0 seconds was performed. After repeating this five times,_Two
A heat treatment of 700 ° C. or more was performed in an atmosphere. like this
Thus, a ferroelectric layer 8 of 250 nm was formed. In addition,
Here, PbZr_xTi_1-xO_ThreeWhere x is 0.52
(Hereinafter referred to as PZT (52 · 48)), forming a PZT film
Has formed.

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

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

The vertical axes in FIGS. 5 and 6 indicate that the initial remanent polarization is Po and the remanent polarization after fatigue is Pr.
/ Po value. In other words, the larger the value, the more significant the deterioration. The horizontal axis indicates how many cycles the voltage of FIG. 7 was repeatedly applied. In the figure,
Curve 50 is when the upper electrode 15 and the lower electrode 12 are both made of iridium oxide, and curve 52 is when the upper electrode 15 is made of platinum and the lower electrode 12 is made of iridium oxide.
Curve 54 shows the case where upper electrode 15 is made of iridium oxide and lower electrode 12 is made of platinum.
2 are characteristic changes when both are made of platinum.

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

Incidentally, iridium oxide has no orientation regardless of whether or not the underlying layer 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 does not have orientation regardless of the orientation of the underlayer. A comparison was made between the characteristics of a ferroelectric capacitor in which iridium oxide was formed directly as the lower electrode 12 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. . FIG. 9 shows the hysteresis characteristics.
FIG. 9A shows a case where the lower electrode 12 is formed on the silicon oxide layer 4, and FIG. 3B shows a case where iridium oxide is formed as the lower electrode 12 directly on the silicon substrate 2. As is clear from this graph, the characteristics of the ferroelectric film 8 are the same regardless of whether the underlying layer of iridium oxide is silicon or silicon oxide. This is presumably because iridium oxide does not have orientation regardless of whether the underlying layer is oriented.

If the iridium oxide layer of the lower electrode 12 is not oriented, the orientation of the ferroelectric film 8 formed thereon is also deteriorated. 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.

For this purpose, the lower electrode 12 may be formed by forming a platinum layer on the iridium oxide layer. FIG. 10A shows a change in characteristics in such a 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. Also,
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 characteristics is further improved by providing the platinum layer on the iridium oxide layer. In other words, deterioration hardly occurred until 10 ¹¹ cycles.

Note that, instead of the platinum layer, an iridium layer or a conductor layer having good orientation such as an alloy of platinum and iridium may be provided. Good). In particular, for an 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.

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

In the case where a conductive layer is formed on the iridium oxide layer and used as an electrode, the upper and lower electrodes 15 and 12 may be provided with the iridium oxide layer in the same manner as in FIGS. Preferably, it is formed.

FIGS. 12 and 13 show hysteresis characteristics when an iridium oxide layer and an iridium layer are used for the upper electrode 15 (FIGS. 12A and 13A), and 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. Although the initial characteristics (FIGS. 12A and 12B) do not change, the characteristics (FIGS. 13A and 13B) after applying the pulse for 108 times (cycles) are clearly
It is better to use an iridium oxide layer and an iridium layer also for the upper electrode 15. This is also considered to be the effect of preventing the escape of oxygen by the iridium oxide layer.

It should be noted that there was no difference in the aging characteristics of the residual polarization Pr and the coercive electric field Ec between the case where platinum was provided on the iridium oxide layer and the case where iridium was provided. However, when a pulse in a fixed direction is continuously applied to the ferroelectric layer 8 or the polarization state in the fixed direction is maintained for a long time, a difference occurs in the imprint characteristic in which the polarization characteristic is destabilized.

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 a case where a voltage different from the polarization direction is applied to a ferroelectric capacitor (ferroelectric film 8) in a polarized state (inversion mode shown in FIG. 15A).
15 shows the temporal change of the 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 used when a ferroelectric capacitor is used as a memory. That is, the integrated value of the current when the voltage is applied is compared with the threshold value to determine the magnitude, and is used to read the recorded information. Therefore, as the usage period elapses, the current integral value in the case of the inversion mode QP decreases (ie, approaches the threshold value), or the current integral value in the non-inversion mode increases (ie, the threshold value increases) ), Erroneous reading may occur.

FIG. 16 shows the ferroelectric film 8 (the upper electrode 15,
The current in the inversion and non-inversion modes after applying a pulse in the same direction 3 × 10 ⁹ times when the lower electrode 12 is formed by providing platinum on the iridium oxide layer). As is clear from the experimental results, the inversion mode Q
The integrated value of the current at the time of P + decreases and almost approaches the integrated value of the first non-inverting mode QU-.

FIG. 17 shows the change in the current integrated value in the above case.
Is shown. The horizontal axis is the pulse application cycle (number),
The vertical axis is the current integrated value. As you can see from the graph,
10 ^FourThe current integrated value changes greatly from around
You can see that it is doing.

FIG. 18 shows the change in the current integral of the ferroelectric film 8 when both the upper electrode 15 and the lower electrode 12 are formed by providing an iridium layer on the iridium oxide layer. As is clear from the graph, the current integral value hardly changed, and good characteristics were selected. That is, with respect to the above imprint characteristics, it was clarified that the electrode formed with iridium on iridium oxide was superior to the electrode formed with platinum on iridium oxide.

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 shows the depth from the surface of the upper electrode, and the vertical axis shows the content of each element.

It is clear from this graph that FIG.
In the case of (1), the lead (Pb) component in the ferroelectric layer 8 has penetrated to the platinum (Pt) of the lower electrode. On the other hand, in the case of FIG. 19B, the lead (Pb) component of 8 in the ferroelectric hardly permeates the lower electrode. This seems to affect 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 provided between the lower electrode 12 and the silicon oxide layer 4.
m) is provided as the bonding layer 30. Generally, the adhesion between iridium oxide and silicon oxide is not very good. For this reason, the alloy layer may be partially peeled off, and the ferroelectric properties may be degraded. This is particularly noticeable 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. Thereby, the ferroelectric characteristics are improved. Note that the titanium layer may be formed by sputtering.

In the above embodiment, a titanium layer was used as the bonding layer 30. However, any material that can improve the bonding property may be used.
Anything is fine. 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 may be used. For example, Ba ₄ Ti ₃ O ₁₂ may be used.

FIG. 21 shows a capacitor according to another embodiment of the present invention. In this embodiment, a dielectric layer 90 having a high dielectric constant is used instead of the ferroelectric layer 8. 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 and (Sr, Ba) TiO ₃ was formed thereon as the dielectric layer 90. In this case, as in the case of the ferroelectric, the dielectric property was improved. That is, it has been clarified that what has been described about the ferroelectric layer can be applied to a dielectric layer having a high dielectric constant.

FIG. 22 shows a structure of a ferroelectric capacitor according to another embodiment of the present invention. On a silicon substrate 2, a silicon oxide layer 4, a lower electrode 12, a ferroelectric film (ferroelectric layer) 8, and an upper electrode 15 are provided. 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.

FIG. 23 is an enlarged view showing the vicinity of the lower electrode 12. Since the iridium layer 11 is a columnar crystal, oxygen in the ferroelectric film 8 permeates. 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
3, the oxygen deficiency of 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, a ferroelectric capacitor having excellent characteristics with little aging can be obtained. Note that some effects can be obtained even if one of the lower electrode 12 and the upper electrode 15 has the above-described structure. This point will also be described later.

FIG. 24 shows a manufacturing process of this ferroelectric capacitor. The surface of the silicon substrate 2 is thermally oxidized to form a silicon oxide layer 4 (FIG. 24A). Here, the thickness of the silicon oxide layer 4 was set to 600 nm. Next, using iridium as a target, an iridium layer 11 is formed on the silicon oxide layer 4 (FIG. 24B). Next, O
Heat treatment is performed at 800 ° C. for 1 minute in _two atmospheres to form an iridium oxide layer 13 on the surface of the iridium layer 11. 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 sol-gel is placed on the lower electrode 12.
A PZT film is formed as the ferroelectric layer 8 by a method.
(FIG. 24C). As a starting material, Pb (CH_ThreeCOO)_Two・ 3H_TwoO, Zr
(t-OC_FourH ₉)_Four, Ti (i-OC_ThreeH₇)_FourWas used. This mix
After spin-coating the mixed solution, 150 degrees Celsius
And dry at 400 degrees in a dry air atmosphere.
For 30 seconds. After repeating this five times,
O_TwoA heat treatment of 700 ° C. or more was performed in an atmosphere. this
Thus, the ferroelectric layer 8 having a thickness of 250 nm was formed. What
Oh, here, PbZr_XTi_1-XO_ThreeIn x, 0.52
(Hereinafter referred to as PZT (52 · 48)), and the PZT film
Is formed.

Further, the iridium layer 7 is formed on the ferroelectric layer 8 by sputtering. Next, a heat treatment is performed at 800 ° C. for 1 minute in an O ₂ atmosphere to obtain an iridium layer 7.
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 was formed to a thickness of 200 nm. Thus, a ferroelectric capacitor can be obtained.

FIGS. 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 indicate that the initial remanent polarization is Po and the remanent polarization after fatigue is Pr.
/ Po value. The horizontal axis indicates how many cycles the voltage of FIG. 7 was repeatedly applied. In the figure,
The curve α is a case where only the lower electrode 12 is manufactured as in the above embodiment. Here, the silicon oxide layer 4 is
0 nm, the lower electrode 12 (the oxidized surface of the iridium layer 11) was 200 nm, and the ferroelectric film 8 (PZ
T (52/48)) was 250 nm, and the upper electrode was made of platinum. A curve β is a case where the surface of the iridium layer of the lower electrode 12 is not oxidized (other conditions are the same as the curve α). A curve γ is a case where the lower electrode 12 is formed of platinum (other conditions are the same as the curve α).

As is apparent 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. The reason that iridium (when not oxidized) (curve β) is superior to platinum (curve γ) is that iridium is oxidized in other steps without special oxidation treatment. It is considered to be.

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 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. .

As described above, by oxidizing the surface of the iridium layer, the escape of oxygen from the ferroelectric film can be prevented. However, iridium oxide is formed on the surface, and the orientation of the ferroelectric film deteriorates. As described above, 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 (see FIG. 10). However, the problem can be solved also by forming the lower electrode as follows.

First, as shown in FIG. 27, a very thin platinum layer 80 (thin film conductor) is provided on the iridium layer 11. Here, the thickness was 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 formed thin, the space between the crystals of the iridium layer 11 thereunder is oxidized, and iridium oxide is formed to prevent the permeation of oxygen. Therefore, it is possible to form the lower electrode 12 that can prevent the transmission of oxygen while maintaining the surface with excellent orientation. As the thin film conductor, any conductor may be used as long as it has good orientation and is hardly oxidized.

The iridium layer 11 oxidized after forming such a thin-film platinum layer 80 can be used alone as the lower electrode 1
2 can be used. However, in the embodiment (see FIG. 10) in which a conductive layer with good orientation (such as an iridium layer or a platinum layer) is provided on the iridium oxide layer formed by sputtering to improve the orientation, the conductive layer with good orientation is used. Can also be used.

FIG. 28B shows iridium oxide (50 nm).
27 shows the hysteresis characteristics of the ferroelectric 8 when the lower electrode 12 is provided with an iridium layer (200 nm) and a platinum layer (30 nm) having the structure shown in FIG. FIG. 28A shows an iridium oxide layer (50
9 shows a hysteresis characteristic of the ferroelectric 8 when an iridium layer (200 nm) is provided on the upper surface of the ferroelectric material 8 and oxidized. As is clear from the drawing, the case of using the structure of FIG. 27 has better hysteresis characteristics.

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 the drawings]

FIG. 1 is a diagram showing a composition of a ferroelectric capacitor according to one 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 the ferroelectric capacitor.

FIG. 5 is a graph showing the secular change of remanent polarization when the electrode material is changed.

FIG. 6 is a graph showing the secular change of remanent polarization when the electrode material is changed.

FIG. 7 is a diagram showing voltages applied when performing a fatigue test.

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 a change in residual 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 an alloy of platinum and iridium 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 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. 14 is a graph showing a temporal change of a current generated when a voltage is applied to a ferroelectric.

FIG. 15 is a diagram showing a voltage application direction in the graph of FIG. 14;

FIG. 16 is a graph showing a state in which the characteristics of FIG. 14 have changed due to 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 a cause of a difference in imprint characteristics.

FIG. 20 is a view showing an embodiment 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 embodiment.

FIG. 23 is a diagram showing a mechanism for preventing escape of oxygen by an iridium oxide layer.

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

FIG. 25 is a diagram showing a change in remanent polarization over time.

FIG. 26 is a diagram showing a comparison of aging of remanent polarization.

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

FIG. 28 is a graph showing a comparison of effects obtained when the electrode shown in FIG. 27 is used.

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

FIG. 30 is a diagram showing a state in which oxygen escapes from a lower electrode 6 made of platinum.

[Explanation of symbols]

 2. . . Silicon substrate 4. . . 7. silicon oxide layer . . Ferroelectric layer 12. . . Lower electrode 15. . . Upper electrode 90. . . Dielectric layer having high dielectric constant

Claims (4)

[Claims] A lower electrode formed on an insulated surface of the substrate and having at least an iridium oxide layer and an iridium layer formed thereon; a lower electrode formed on the lower electrode; A dielectric capacitor comprising: a dielectric layer made of a dielectric or a dielectric having a high dielectric constant; and an upper electrode formed on the dielectric layer. 2. A lower electrode comprising a substrate, an iridium layer formed on a surface insulated on the substrate and an iridium oxide layer formed thereon, and a lower electrode formed on the lower electrode. A dielectric capacitor comprising: a dielectric layer made of a ferroelectric or a dielectric having a high dielectric constant; and an upper electrode formed on the dielectric layer. 3. A substrate, an iridium layer made of columnar crystals formed on a surface insulated on the substrate, and an iridium oxide layer formed on the columnar crystals by oxidizing the iridium layer. Comprising a lower electrode configured, a dielectric layer formed on the lower electrode and formed of a ferroelectric or a dielectric having a high dielectric constant, and an upper electrode formed on the dielectric layer Dielectric capacitor. 4. A lower electrode, a dielectric layer formed on the lower electrode and formed of a ferroelectric or a dielectric having a high dielectric constant, and iridium formed on the dielectric layer and formed of columnar crystals. Layer, by oxidation of the iridium layer,
A dielectric capacitor comprising an upper electrode composed of the iridium oxide layer formed between the columnar crystals.