JP2002261252A - Ferroelectric capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferroelectric capacitor having superior characteristics. SOLUTION: The capacitor comprises a silicon oxide layer 4, a lower electrode 12, a ferroelectric layer 8 and an upper electrode 15 on a silicon substrate 2. An alloy layer of the lower electrode 12 can take an adequate lattice constant according to the kind or composition of the ferroelectric layer 8, thereby obtaining a ferroelectric layer 8 which has superior characteristics.

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.

FIG. 13 shows a conventional ferroelectric capacitor. 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 of PZ
A T (PbZrXTi1-XO3) film 8 is provided, and further thereon,
An upper electrode 10 made of platinum is provided. 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.

First, depending on the type and composition of the ferroelectric,
The mismatch between the lattice constant of platinum and the lower electrode was increased, and ferroelectricity was likely to deteriorate.

[0006] Second, since platinum is easily permeable to oxygen,
There has been a problem that the ferroelectricity is reduced due to the escape of oxygen in the ferroelectric (PZT), repeated aging, and repetition of polarization inversion. That is, as shown in FIG. 14, oxygen in the ferroelectric material might escape from between the platinum columnar crystals.

[0007] Such a problem also occurs in a capacitor using a dielectric having a high dielectric constant.

The present invention solves the above-mentioned problems and has excellent ferroelectricity and high dielectricity, and has a ferroelectric capacitor or a high dielectric constant with little deterioration due to aging and repetition of polarization reversal. It is an object to provide a dielectric capacitor.

[0009]

In the present invention, the term "capacitor" refers to a structure in which electrodes are provided on both sides of an insulator, irrespective of whether it is used for accumulating electricity. , Including those having this structure. A first ferroelectric capacitor according to the present invention includes a substrate having a silicon oxide film on the surface, an iridium layer composed of columnar polycrystal formed on the silicon oxide film, and a crystal formed between the columnar polycrystal and the surface. A lower electrode having an iridium oxide layer formed thereon, a ferroelectric layer formed on the lower electrode so as to be in contact with the iridium layer of the lower electrode, and an upper electrode formed on the ferroelectric layer. It is characterized by having. Further, the second ferroelectric capacitor of the present invention comprises a lower electrode, a ferroelectric layer formed on the lower electrode, an iridium layer formed on the ferroelectric layer and made of columnar polycrystal, and And an upper electrode having an iridium oxide layer formed between polycrystals and on the surface. Further, a third ferroelectric capacitor according to the present invention has a lower electrode having an iridium layer made of columnar polycrystal, and an iridium oxide layer formed between the crystals of the columnar polycrystal and on the surface thereof. And a dielectric layer having a high dielectric constant formed in contact with the iridium layer of the lower electrode, and an upper electrode formed on the dielectric layer having a high dielectric constant. Also,
A fourth ferroelectric capacitor according to the present invention comprises: a lower electrode; a dielectric layer having a high dielectric constant formed on the lower electrode; an iridium layer formed of columnar polycrystal; And an upper electrode having an iridium oxide layer formed thereon.

In addition, the following can be considered as other embodiments. That is, the first ferroelectric capacitor and the eleventh dielectric capacitor having a high dielectric constant have a lower electrode having an alloy layer of platinum and iridium, on the lower electrode, in contact with the alloy layer of the lower electrode. And an upper electrode formed on the dielectric layer.

A second ferroelectric capacitor and a twelfth dielectric capacitor having a high dielectric constant are formed on a lower electrode having an iridium layer and on the lower electrode so as to be in contact with the iridium layer of the lower electrode. A dielectric layer, and an upper electrode formed on the dielectric layer.

In a third ferroelectric capacitor and a thirteenth dielectric capacitor having a high dielectric constant, the lower electrode is formed on a silicon oxide layer formed on a substrate. Is characterized in that a bonding layer in contact with the silicon oxide layer is provided below the alloy layer or the iridium layer.

A fourth ferroelectric capacitor uses PbZrTiO ₃ as the ferroelectric layer, uses Pt _Y Ir _1-Y as a lower electrode layer in contact with the ferroelectric layer, and sets Y to 0 to 0.5.
It is characterized by being between.

A fifth ferroelectric capacitor is characterized in that, in the fourth aspect, the Y is set between 0.2 and 0.3.

The sixth ferroelectric capacitor uses Bi ₄ Ti ₃ O ₁₂ as a ferroelectric layer, Pt _Y Ir _1-Y as a lower electrode layer in contact with the ferroelectric layer, and sets Y to 0. It is characterized in that it is between eight.

The seventh ferroelectric capacitor and the fourteenth dielectric capacitor having a high dielectric constant include a lower electrode having an alloy layer of two or more conductors having different lattice constants. A ferroelectric layer formed in contact with the alloy layer; and an upper electrode formed on the ferroelectric layer.

According to an eighth ferroelectric capacitor and a fifteenth dielectric capacitor having a high dielectric constant, the alloy layer comprises:
It is characterized by being an alloy layer containing at least iridium.

The ninth ferroelectric capacitor and the sixteenth dielectric capacitor having a high dielectric constant are formed on a lower electrode, a ferroelectric layer formed on the lower electrode, a ferroelectric layer, An upper electrode having an alloy layer of platinum and iridium,
It has.

The tenth ferroelectric capacitor and the seventeenth ferroelectric capacitor
Has a lower electrode, a ferroelectric layer formed on the lower electrode, and an upper electrode formed on the ferroelectric layer and having an iridium layer.

According to an eighteenth method for manufacturing a ferroelectric capacitor and a twenty-third method for manufacturing a dielectric capacitor having a high dielectric constant, an alloy layer of platinum and iridium or an iridium layer is formed on a substrate by sputtering. Forming, forming a dielectric layer so as to be in contact with the alloy layer, and forming an upper electrode on the dielectric layer.

A nineteenth method for manufacturing a ferroelectric capacitor and a twenty-fourth method for manufacturing a dielectric capacitor having a high dielectric constant include a step of forming a silicon oxide layer on a substrate; Forming a bonding layer, forming an alloy layer or iridium layer of platinum and iridium on the titanium layer, forming a lower electrode, forming a dielectric layer on the lower electrode, Forming an upper electrode on the body layer.

A twentieth method of manufacturing a ferroelectric capacitor and a twenty-fifth method of manufacturing a dielectric capacitor having a high dielectric constant include a step of heat-treating the lower electrode at 400 ° C. or higher.

A twenty-first method for manufacturing a ferroelectric capacitor and a twenty-sixth method for manufacturing a dielectric capacitor having a high dielectric constant are characterized in that the heat treatment step also serves as a heat treatment for forming a dielectric layer. And

According to a twenty-second method for manufacturing a ferroelectric capacitor and a twenty-seventh method for manufacturing a dielectric capacitor having a high dielectric constant, the lower electrode is made of an alloy of two or more kinds of metals having different lattice constants, and By changing the ratio, the lattice constant of the alloy is changed to match the lattice constant of the dielectric layer.

The first ferroelectric capacitor and the eleventh dielectric capacitor having a high dielectric constant are characterized by using a lower electrode having an alloy layer of platinum and iridium. Therefore, the lattice constant can be matched by changing the mixture ratio of platinum and iridium according to the type and composition of the ferroelectric or the dielectric having a high dielectric constant. Further, iridium contained in the alloy is more easily oxidized than platinum, and the oxidized iridium can prevent the escape of oxygen in the ferroelectric.

The second ferroelectric capacitor and the twelfth dielectric capacitor having a high dielectric constant are characterized by using a lower electrode having an iridium layer. Therefore, the escape of oxygen in the ferroelectric can be prevented by the oxidized iridium.

The third ferroelectric capacitor and the thirteenth dielectric capacitor having a high dielectric constant are characterized by having a bonding layer in contact with the silicon oxide layer below the lower electrode. Therefore, the adhesion between the ferroelectric layer and the dielectric layer having a high dielectric constant can be improved.

The fourth ferroelectric capacitor uses PbZrTiO ₃ as a ferroelectric layer, uses Pt _Y Ir _1-Y as a lower electrode layer in contact with the ferroelectric layer, and sets Y to 0 to 0.5. And between. Therefore, both lattice constants are matched, and excellent ferroelectricity can be obtained.

The fifth ferroelectric capacitor has Y of 0.2
０．３0.3. Therefore, the lattice constants of the two can be more closely matched, and more excellent ferroelectricity can be obtained.

The sixth ferroelectric capacitor uses Bi ₄ Ti ₃ O ₁₂ as a ferroelectric layer, uses Pt _Y Ir _1-Y as a lower electrode layer in contact with the ferroelectric layer, and sets Y to 0. It is between eight. Therefore, both lattice constants are matched, and excellent ferroelectricity can be obtained.

Each of the seventh ferroelectric capacitor and the fourteenth dielectric capacitor having a high dielectric constant has an alloy layer of two or more conductors having different lattice constants on the lower electrode. Therefore, it is easy to match the lattice constant with the dielectric layer by changing the ratio of the alloy.

The eighth ferroelectric capacitor and the fifteenth dielectric capacitor having a high dielectric constant further include iridium in the alloy layer. Therefore, the escape of oxygen from the dielectric layer can be prevented by the oxidized iridium.

The ninth and tenth ferroelectric capacitors and the sixteenth and seventeenth dielectric capacitors having a high dielectric constant each have an upper electrode provided with an alloy layer or an iridium layer of platinum and iridium. Therefore, it is possible to prevent oxygen in the ferroelectric from being released from the upper electrode by the oxidized iridium.

An eighteenth method for manufacturing a ferroelectric capacitor and a twenty-third method for manufacturing a dielectric capacitor having a high dielectric constant include a step of forming a bonding layer in contact with a silicon oxide layer below a lower electrode. I have. Therefore, the adhesion between the ferroelectric layer and the dielectric layer having a high dielectric constant can be improved.

A nineteenth method for manufacturing a ferroelectric capacitor and a twenty-fourth method for manufacturing a dielectric capacitor having a high dielectric constant include forming an alloy layer of platinum and iridium or an iridium layer as a lower electrode, and forming the lower electrode at 700 ° C. A heat treatment step. Therefore, iridium in the iridium layer or the alloy layer is oxidized, and escape of oxygen can be prevented.

According to a twentieth method of manufacturing a ferroelectric capacitor and a twenty-fifth method of manufacturing a dielectric capacitor having a high dielectric constant, heat treatment for forming a dielectric layer is performed together with heat treatment of a lower electrode. Features. Therefore, the process can be simplified and the production can be performed efficiently.

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

[0038]

FIG. 1 shows the structure 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 layer 8, and an upper electrode 10 are provided. The lower electrode 12 is formed of an alloy layer of platinum and iridium.

FIG. 2 compares the physical properties of platinum and iridium. As is clear from this table, the physical properties of iridium are almost equal to those of platinum. Iridium has a lower resistivity than platinum and is a preferred material for electrodes. The lattice constant of platinum is 3.923 angstroms, while the lattice constant of iridium is 3.839.
Angstrom. Therefore, by changing the mixing ratio, the lattice constant of the alloy of platinum and iridium is
It can be set between 3.923 angstroms and 3.839 angstroms. That is, an appropriate lattice constant can be set according to the type and composition of the ferroelectric.

For example, a case where bismuth titanate Bi ₄ Ti ₃ O ₁₂ (hereinafter referred to as BIT) is used as the ferroelectric layer 8 will be described. The lattice constant of BIT is a = 5.45,
b = 5.41 and c = 32.815. On the other hand, platinum or iridium as the lower electrode 12 is oriented in the (111) direction as shown in FIG. Therefore, in order to obtain a c-axis alignment film of BIT, the interatomic distance L of the (111) plane of the lower electrode 12 is set to a = 5.45 or b = 5.41
Must be equal to In this embodiment, the composition ratio of the alloy of platinum and iridium is expressed as x = Pt _X Ir _1- x
By setting it to 0.8, the interatomic distance L of the (111) plane is obtained.
Can be set to 5.43. That is, a BIT film having high ferroelectricity can be formed by matching with the lattice constant of BIT.

Iridium is more easily oxidized than platinum. As shown in the table of FIG. 2, platinum does not easily react with oxygen, whereas iridium oxidizes at high temperatures. When this alloy of platinum and iridium is heat-treated, iridium is slightly oxidized. Since this iridium oxide 20 is formed between the columnar crystals of platinum and blocks the passage through which oxygen in the ferroelectric 8 escapes, oxygen deficiency can be prevented (see FIG. 4).

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. 6 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. 6A).
Here, the thickness of the silicon oxide layer 4 was set to 600 nm. Next, using platinum and iridium as targets, an alloy of platinum and iridium is formed on the silicon oxide layer 4 (FIG. 6B). This is the lower electrode 12. 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. 6C). 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 250 nm ferroelectric layer 8 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, an upper electrode 10 is formed on the ferroelectric layer 8 by sputtering using platinum.
D). Thus, a ferroelectric capacitor can be obtained.

In the above embodiment, By the heat treatment for forming the ferroelectric layer 8 (700 degrees or more), the lower electrode 12 is also heat-treated to oxidize iridium. However, this heat treatment may be performed when the lower electrode 12 is formed. It has been found that the improvement of the high-dielectric property, which will be described later, appears significantly when a heat treatment of 400 ° C. or more is performed. Of course, a predetermined effect can be obtained even at a lower temperature. In addition, even without special heat treatment, oxidization of iridium gradually progresses with aging to obtain an effect.

FIG. 7 shows a PZT (52) as the ferroelectric layer 8.
/ 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 as the lower electrode 12 than when only platinum is used (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 0% to 50% of platinum, and particularly excellent characteristics are obtained at a mixing ratio of 20% to 30% with a peak of about 25% of platinum.

FIG. 8 shows the hysteresis characteristics of the ferroelectric capacitor when only platinum is used as the lower electrode 12. FIG. 8B shows that platinum 25 is used as the lower electrode 12.
2 shows the hysteresis characteristics of a ferroelectric capacitor when an alloy containing 75% iridium and 75% iridium is used. Here, the silicon oxide layer is 600 nm, and the lower electrode 12 is 20 nm.
0 nm and PZT were 250 nm. As is clear from a comparison between the two graphs, the case using the alloy (FIG. 8B) shows more excellent characteristics in remanent polarization Pr.

FIG. 9 shows the hysteresis characteristics of the ferroelectric capacitor when only iridium is used as the lower electrode 12. Thus, even when only iridium is used, the remanent polarization Pr and the coercive electric field Ec are improved. This is presumably because iridium is a columnar crystal like platinum, but its surface or between the crystals is oxidized to change into iridium oxide which is not a columnar crystal.

When the alloy of platinum and iridium or iridium is used for the lower electrode and the upper electrode, the reason why the characteristics of the dielectric material is improved is not necessarily clear, but the above-mentioned reasons and the like have a complex influence. Seems to be.

FIG. 10 shows a structure of a ferroelectric capacitor according to another embodiment of the present invention. In this embodiment, a titanium layer is provided as a bonding layer 30 between the lower electrode 12 and the silicon oxide layer 4. Adhesion between iridium and silicon oxide layer 4 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.

FIG. 11 shows a lower electrode 12 made of iridium.
Below shows the hysteresis characteristics when a titanium layer is provided as the bonding layer 30 below. Here, the silicon oxide layer is 6
000 angstroms, bonding layer 5 nm, lower electrode 1
2 was 200 nm, and PZT was 250 nm. As is clear from the figure, the remanent polarization Pr,
Both the coercive electric field Ec are improved.

In the above embodiment, a titanium layer was used as the bonding layer 30, but any material that can improve the bonding property may be used.
Anything is fine. For example, a platinum layer may be used. FIG. 11B shows hysteresis characteristics when a platinum layer (100 nm) is used as a bonding layer. Again,
As is apparent from comparison with FIG. 9, the remanent polarization Pr and the coercive electric field Ec are improved.

In the above embodiment, matching of lattice constants was achieved by using an alloy of platinum and iridium. However, by using conductors having different lattice constants, the lattice constants can be similarly matched.

In each of the above embodiments, the lower electrode 12 is formed of one layer of alloy or the like, but may be formed of two or more layers. In this case, if an alloy layer of platinum and iridium or an iridium layer is used as a layer in contact with the ferroelectric layer 8, a good ferroelectric layer 8 can be obtained by matching lattice constants. Also, by oxidation of iridium,
The effect of preventing the escape of oxygen from the ferroelectric layer 8 can be obtained if any of the layers is the above alloy layer or iridium layer. However, a higher effect can be obtained by providing an alloy layer or an iridium layer so as to be in contact with the ferroelectric layer 8.

Further, the effect of the escape of oxygen due to the oxidation of iridium can be obtained even when the upper electrode 10 is made of the above-mentioned alloy layer or iridium layer. If both the upper and lower electrodes 10 and 12 are made of an alloy layer or an iridium layer, a greater effect can be obtained.

FIG. 12 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. On the silicon oxide layer 4, a lower electrode 12 made of an alloy of platinum and iridium (only iridium may be used as described above)
Was formed thereon, 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.

[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 crystal planes of platinum and iridium.

FIG. 4 is a diagram showing a structure in which iridium oxide prevents escape of oxygen in an alloy of platinum and iridium.

FIG. 5 is a diagram showing a nonvolatile memory using a ferroelectric capacitor 22.

FIG. 6 is a diagram showing a manufacturing process of the ferroelectric capacitor.

FIG. 7 is a diagram showing changes in residual polarization Pr and coercive electric field Ec when the mixing ratio of platinum and iridium of the lower electrode 12 is changed.

FIG. 8 is a diagram comparing hysteresis characteristics when using only platinum as the lower electrode and when using an alloy of platinum and iridium as the lower electrode.

FIG. 9 is a diagram showing a hysteresis characteristic when only iridium is used as a lower electrode.

FIG. 10 shows that between a lower electrode 12 and a silicon oxide layer 4
FIG. 4 is a diagram illustrating an example in which a bonding layer 30 is provided.

FIG. 11 is a diagram showing hysteresis characteristics when an iridium layer and a platinum layer are used as the bonding layer 30.

FIG. 12 is a diagram showing an embodiment of a dielectric capacitor having a high dielectric constant.

FIG. 13 is a diagram showing a structure of a conventional ferroelectric capacitor.

FIG. 14 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 10. . . Upper electrode 12. . . Lower electrode 90. . . Dielectric layer having high dielectric constant

Claims (4)

[Claims] A substrate having a silicon oxide film on a surface thereof; an iridium layer made of columnar polycrystal formed on the silicon oxide film; and an iridium oxide layer formed between crystals of the columnar polycrystal and on the surface. A ferroelectric capacitor comprising: a lower electrode having: a ferroelectric layer formed on the lower electrode so as to be in contact with the iridium layer of the lower electrode; and an upper electrode formed on the ferroelectric layer. . 2. A lower electrode, a ferroelectric layer formed on the lower electrode, an iridium layer formed on the ferroelectric layer and formed of columnar polycrystal, and formed between and on the surface of the columnar polycrystal. And a top electrode having an iridium oxide layer formed thereon. 3. A lower electrode having an iridium layer composed of a columnar polycrystal and an iridium oxide layer formed between the crystals of the columnar polycrystal and on the surface thereof, the lower electrode being in contact with the iridium layer of the lower electrode. Having a high dielectric constant, a dielectric layer having a high dielectric constant, and an upper electrode formed on the dielectric layer having a high dielectric constant. 4. A lower electrode, a dielectric layer having a high dielectric constant formed on the lower electrode, an iridium layer made of columnar polycrystal, and an iridium oxide layer formed between the crystals of the columnar polycrystal and on the surface thereof And a top electrode having a high dielectric constant.