JPH11289057A - Ferroelectric capacitor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a leak current from increasing between electrodes and electrical short-circuiting by forming a ferroelectric film on a first electrode, burying an insulation film at a recessed part on the surface of the ferroelectric film, and forming a second electrode on the ferroelectric film where the insulation film is buried. SOLUTION: An interlayer insulation film 16 is formed on a semiconductor substrate 10 where a transfer transistor with a gate electrode 12 and a source/ drain diffusion layer 14 is formed, an electrode plug 20 is buried into a contact hole 18 of the insulation film 16, and an adhesive layer 22 is formed on them. Then, a first electrode 32 is formed on the adhesive layer 22, and a ferroelectric film 26 is formed on the first electrode 32. Further, an insulation film 28 is buried into a recessed part on the surface of the ferroelectric film 26, and a second electrode 34 is formed on the ferroelectric film 26 where the insulation film 28 is buried, thus reducing increase in the leak current of a ferroelectric capacitor and electrical short-circuiting.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to SrBi ₂ Ta ₂ O.
_{The present} invention relates to a ferroelectric capacitor using a ferroelectric film such as _nine films and a method for manufacturing the same.

[0002]

2. Description of the Related Art Ferroelectric films have been applied to various fields utilizing their high dielectric constant and polarization reversal characteristics. For example, as a device using the polarization inversion of a ferroelectric film, a capacitor using a ferroelectric film as a dielectric film is formed, and information corresponding to the polarization direction of the ferroelectric film is stored in this capacitor. There is memory.

Conventionally, as a dielectric film of a ferroelectric memory,
PZT (PbZrTiO_Three) Has been widely used
Was. However, in recent years, low power consumption and high reliability
At the request, lower voltage operation is possible and longer service life
SBT (SrBi_TwoTa_TwoO ₉) Is drawing attention.
Although SBT has such excellent characteristics,
Structure of ferroelectric capacitor using PZT
It was difficult to apply. That is, SBT is
Crystallization temperature is 800 ℃ or higher, which is much higher than that of PZT
High and the crystal grains are large,
Electrode material easily enters crystal grain boundaries during processing, etc.
Mechanical short-circuit, increase in leakage current, deterioration of dielectric strength, etc.
Had to bring.

For this reason, in a conventional ferroelectric capacitor using SBT, bismuth oxide is segregated at crystal grain boundaries by adding bismuth excessively in the SBT film,
Thus, the penetration of the electrode material is reduced, and the leakage current is reduced or stabilized.

[0005]

SUMMARY OF THE INVENTION However, SBT
In the conventional ferroelectric capacitor using the above, when heat treatment is performed in an atmosphere containing hydrogen in a later step, bismuth oxide at crystal grain boundaries is reduced to metal bismuth having conductivity, thereby increasing leakage current and increasing electric current. Sometimes resulted in a short circuit.

SUMMARY OF THE INVENTION An object of the present invention is to provide a ferroelectric capacitor capable of performing a stable operation with less increase in leakage current between electrodes and an electrical short, and a method of manufacturing the same.

[0007]

An object of the present invention is to provide a first electrode, a ferroelectric film formed on the first electrode, and an insulating film embedded in a concave portion on the surface of the ferroelectric film. And a second electrode formed on the ferroelectric film in which the insulating film is buried. By configuring the ferroelectric capacitor in this way, the insulating film that fills the concave portion on the surface of the ferroelectric film prevents the electrode material forming the second electrode from entering the ferroelectric film. It is possible to reduce an increase in leakage current and an electric short circuit of the ferroelectric capacitor. Thus, the ferroelectric capacitor can be formed stably, and the reliability can be improved.

In the above-mentioned ferroelectric capacitor, the insulating film may be formed not only on the concave portion on the surface of the ferroelectric film but also on almost the entire area on the ferroelectric film.
In the above ferroelectric capacitor, it is preferable that the ferroelectric film is a SrBi ₂ Ta ₂ O ₉ film.
In the ferroelectric capacitor using the SrBi ₂ Ta ₂ O ₉ film, the electrode material is remarkably penetrated into the ferroelectric film.
This is particularly effective for a ferroelectric capacitor using an SrBi ₂ Ta ₂ O ₉ film.

The above object is also achieved by a lower electrode forming step of forming a lower electrode on a base substrate, a ferroelectric film forming step of forming a ferroelectric film on the lower electrode, and a step of forming a ferroelectric film. A method of manufacturing a ferroelectric capacitor, comprising: an insulating film embedding step of embedding an insulating film in a concave portion on the surface; and a step of forming an upper electrode on the ferroelectric film in which the insulating film is embedded. Is also achieved. By manufacturing the ferroelectric capacitor in this manner, the insulating film embedded in the concave portion on the surface of the ferroelectric film prevents the electrode material forming the upper electrode from entering the ferroelectric film. In addition, it is possible to reduce an increase in leakage current and an electric short circuit of the ferroelectric capacitor. Thus, the ferroelectric capacitor can be formed stably, and the reliability can be improved.

In the above method of manufacturing a ferroelectric capacitor, the step of embedding the insulating film includes the step of forming the insulating film on the ferroelectric film and the step of removing the insulating film in a plane. Preferably, the method further includes an insulating film removing step of leaving the insulating film in the concave portion of the ferroelectric film. In the method of manufacturing a ferroelectric capacitor, the insulating film forming step may include forming a conductive film on the ferroelectric film, and replacing the conductive film with the insulating film. It is desirable to have The insulating film can also be formed by replacing a conductive film with an insulating film. For example, after depositing a silicon film, a silicon oxide film can be formed by thermal oxidation.

In the method of manufacturing a ferroelectric capacitor, the step of embedding the insulating film may include a step of forming a conductive film on the ferroelectric film and a step of removing the conductive film in a planar manner. Preferably, the method further includes a conductive film removing step of leaving the conductive film in the concave portion of the ferroelectric film, and a replacing step of replacing the conductive film with the insulating film. After the conductive film is left in the concave portion, the insulating film can be embedded in the concave portion by replacing the conductive film with the insulating film.

In the above method of manufacturing a ferroelectric capacitor, in the insulating film embedding step, the insulating film is embedded in the concave portion of the ferroelectric film, and the insulating film covers almost the entire area on the ferroelectric film. It is desirable to leave it. In the method of manufacturing a ferroelectric capacitor, it is preferable that the ferroelectric film is a SrBi ₂ Ta ₂ O ₉ film. For SrBi ₂ Ta ₂ O ₉ ferroelectric capacitor using the film enters into the ferroelectric film of the electrode material is remarkable, is particularly effective in a ferroelectric capacitor using a SrBi ₂ Ta ₂ O ₉ film .

[0013] Further, the object is to provide a transfer transistor formed on a semiconductor substrate, a lower electrode connected to the transfer transistor, a ferroelectric film formed on the lower electrode, and a ferroelectric film. A ferroelectric capacitor having an insulating film embedded in a concave portion on the surface of the semiconductor device and an upper electrode formed on the ferroelectric film in which the insulating film is embedded. Is also achieved. By configuring the semiconductor memory device in this manner, even when a ferroelectric film having a high crystallization temperature and large crystal grains such as a SrBi ₂ Ta ₂ O ₉ film is used,
A semiconductor memory device having a high-quality ferroelectric capacitor can be configured. Thereby, the reliability and the like of the semiconductor memory device can be improved.

[0014]

[First Embodiment] A ferroelectric capacitor according to a first embodiment of the present invention and a method for fabricating the same will be described with reference to FIGS. FIG. 1 is a schematic sectional view showing the structure of the ferroelectric capacitor according to the present embodiment, FIG. 2 is a graph showing the electrical characteristics of the ferroelectric capacitor according to the present embodiment, and FIGS. It is a process sectional view showing the manufacturing method of the capacitor.

First, the structure of the ferroelectric capacitor according to the present embodiment will be explained with reference to FIG. FIG.
1 shows an example in which the ferroelectric capacitor according to the present embodiment is used as a capacitor of a semiconductor memory device. A transfer transistor having a gate electrode 12 and a source / drain diffusion layer 14 is formed on a semiconductor substrate 10. An interlayer insulating film 16 is formed on the semiconductor substrate 10 on which the transfer transistor has been formed. Interlayer insulating film 16
The source / drain diffusion layer 14 of the transfer transistor
Is formed. An electrode plug 20 is embedded in the contact hole 18. Interlayer insulating film 16 in which electrode plug 20 is embedded
An adhesive layer 22 made of a Ti (titanium) film is formed thereon. On the adhesive layer 22, a lower electrode 32 made of a Pt (platinum) film is formed. On the lower electrode 32,
Ferroelectric film 2 made of SBT (SrBi ₂ Ta ₂ O ₉ ) film
6 are formed. On the ferroelectric film 26, an upper electrode 34 made of a Pt film is formed. Thus, the lower electrode 32, the ferroelectric film 26, and the upper electrode 34 constitute a ferroelectric capacitor, and the transfer transistor and the ferroelectric capacitor constitute a ferroelectric memory.

In the ferroelectric capacitor according to the present embodiment, the silicon oxide film 28 is buried in the crystal grain boundaries on the upper surface of the ferroelectric film 26, and the surface of the ferroelectric film 26 is substantially flattened. There is a feature. By configuring the ferroelectric capacitor in this way, it is possible to prevent the Pt constituting the upper electrode 34 from entering the crystal grain boundary of the ferroelectric film 26, thereby preventing a problem such as increasing a leak current or causing a short circuit failure. Can be.

FIG. 2 is a graph showing current-voltage characteristics of the ferroelectric capacitor according to the present embodiment and a conventional ferroelectric capacitor. In the figure, a solid line indicates a ferroelectric capacitor according to the present embodiment, and a dotted line indicates a conventional ferroelectric capacitor. As shown in the figure, in the conventional ferroelectric capacitor, the leak current sharply increases with an applied voltage of about 2 V, but in the ferroelectric capacitor according to the present embodiment, the leak current is reduced to 10 ⁻⁶ A even with an applied voltage of about 10 V.
/ Cm ² .

As described above, the silicon oxide film 28 is buried in the crystal grain boundaries on the upper surface of the ferroelectric film 26, and the ferroelectric film 26
Of the upper electrode 34 is prevented from entering the ferroelectric film 26, and the electrical characteristics of the ferroelectric capacitor can be greatly improved. Next, the method for fabricating the semiconductor device according to the present embodiment will be explained with reference to FIGS.

First, an ordinary MOS transistor is placed on a semiconductor substrate 10.
The gate electrode 12 is formed in the same manner as the method of forming the transistor.
And a transfer transistor having the source / drain diffusion layer 14 (FIG. 3A). Next, for example, CVD is performed on the semiconductor substrate 10 on which the transfer transistor is formed.
A silicon oxide film is deposited by a method to form an interlayer insulating film 16.

Subsequently, a contact hole 18 reaching the source / drain diffusion layer 14 is formed in the interlayer insulating film 16 by using ordinary lithography and etching techniques. Thereafter, an electrode plug 20 made of polycrystalline silicon, tungsten, or the like is formed in the contact hole 18 by using a normal electrode plug forming technique (FIG. 3B).

Next, on the interlayer insulating film 16 in which the electrode plugs 20 are buried, a film thickness of about 3
An adhesive layer 22 made of a 0 nm Ti film is formed. The adhesive layer 22 has a role of improving the adhesion between the lower electrode 32 formed thereon and the interlayer insulating film 16. Then, the adhesive layer 2
A Pt film 24 having a thickness of about 180 nm is deposited on the substrate 2 by, for example, a sputtering method. The Pt film 24 is a film that becomes the lower electrode 32 of the ferroelectric capacitor (FIG. 3C).

Thereafter, a ferroelectric film 26 made of an SBT film is formed on the Pt film (FIG. 4A). For example, an SBT film having a thickness of about 240 nm is formed by a spin-on method. SBT film is MOCVD (metal organic chemical vapor deposition)
It may be formed by a method, a laser ablation method, a sputtering method, or the like. Then, for example, at 800 ° C. in an oxygen atmosphere,
A heat treatment is performed for 60 minutes to crystallize the deposited SBT film. The crystallized SBT film has large crystal grains, as shown in FIG.
The surface morphology decreases as shown in FIG. Also,
At the interface between the Pt film 24 and the ferroelectric film 26, the ferroelectric film 2
Pt enters the crystal interface of No. 6.

Subsequently, a silicon oxide film 28 having a thickness of about 100 nm is formed on the ferroelectric film 26 thus formed, for example, by the CVD method (FIG. 4C). It is desirable that the thickness of the silicon oxide film 28 be sufficient to bury the surface irregularities of the ferroelectric film 24. Thereafter, for example, CMP (Chemical Mechanical Polishing)
5), the silicon oxide film 28 is planarly removed until the ferroelectric film 26 is exposed, and the silicon oxide film 28 is left only in the concave portions on the surface of the ferroelectric film 26, that is, in the crystal grain boundaries (FIG. 5). (A)). Thereby, the ferroelectric film 26
Becomes almost flat.

Next, a Pt film 30 having a thickness of about 180 nm is deposited on the ferroelectric film 26 by, for example, a sputtering method (FIG. 5B). The Pt film 30 is a film that becomes the upper electrode 34 of the ferroelectric capacitor. At this time, the ferroelectric film 2
Since the silicon oxide film 28 is buried in the crystal grain boundaries of the SBT film No. 6, the Pt film 30 does not enter the ferroelectric film 26 during deposition or subsequent heat treatment.

Subsequently, the Pt film 30, the ferroelectric film 26, the P
The t film 24 and the adhesive layer 22 are patterned, and the lower electrode 32 made of the Pt film 24 and the ferroelectric film 2 made of the SBT film
6. A ferroelectric capacitor having the upper electrode 34 made of the Pt film 30 is formed (FIG. 5C). in this way,
According to the present embodiment, the silicon oxide film 28 is buried in the crystal grain boundaries on the upper surface of the ferroelectric film 26, and the surface of the ferroelectric film 26 is substantially flattened.
It is possible to prevent the constituent material of the upper electrode 34 from entering the ferroelectric film 26 at the interface therewith. Thereby, the electrical characteristics of the ferroelectric capacitor can be significantly improved.

[Second Embodiment] The method for fabricating a ferroelectric capacitor according to a second embodiment of the present invention will be explained with reference to FIG. The same components as those of the ferroelectric capacitor according to the first embodiment and the method of manufacturing the same are denoted by the same reference numerals, and description thereof will be simplified or omitted. FIG. 6 is a process sectional view illustrating the method for manufacturing the ferroelectric capacitor according to the present embodiment.

In the present embodiment, another method of manufacturing the ferroelectric capacitor according to the first embodiment shown in FIG. 1 will be described. First, the ferroelectric film 26 is formed in the same manner as in the method for manufacturing the ferroelectric capacitor according to the first embodiment shown in, for example, FIGS. 3A to 4B. Next, a silicon film 36 is deposited on the ferroelectric film 26 by, for example, a CVD method (FIG. 6A).

Subsequently, the silicon film 36 is planarly removed by, eg, CMP until the ferroelectric film 26 is exposed, and the silicon film 36 is left only in the concave portion of the ferroelectric film 26 (FIG. 6 ( b)). Thereafter, the silicon film 36 embedded in the concave portion of the ferroelectric film by, for example, a thermal oxidation method.
Is oxidized to replace the silicon film 36 with the silicon oxide film 28.

Next, for example, FIGS. 5B and 5C
A ferroelectric capacitor including the lower electrode 32, the ferroelectric film 26, and the upper electrode 34 is formed in the same manner as in the method of manufacturing the semiconductor device according to the first embodiment shown in FIG. As described above, according to the present embodiment, the silicon oxide film 28 can be embedded in the crystal grain boundaries of the ferroelectric film 26 also by oxidizing the silicon film 36 after embedding it. Thereby, the electrical characteristics of the ferroelectric capacitor can be significantly improved.

[Modified Embodiment] The present invention is not limited to the above embodiment, and various modifications are possible. For example, in the first and second embodiments, the silicon oxide film 28 is removed until the ferroelectric film 26 is exposed, and the silicon oxide film 28 is left only at the crystal grain boundaries on the upper surface of the ferroelectric film 26. However, it is not necessary to remove the ferroelectric film 26 until it is exposed.

That is, the effect of the present invention of preventing the constituent material of the upper electrode from entering the ferroelectric film 26 can be achieved by embedding the insulating film in the crystal grain boundaries of the ferroelectric film 26. For example, as shown in FIG. 7A, the removal of the silicon oxide film 28 is stopped when the silicon oxide film 28 remains thin on the upper surface of the ferroelectric film 26, and the ferroelectric capacitor is formed in this state. Good (Fig. 7
(B)). However, in this case, the ferroelectric capacitor and the paraelectric capacitor are connected in series, and the total storage capacity is reduced. Therefore, the thickness of the silicon oxide film 28 remaining depends on the device structure and the required thickness. It is desirable to make appropriate adjustments according to the characteristics to be performed.

In the first and second embodiments, the silicon oxide film is used to fill the crystal grain boundaries on the upper surface of the ferroelectric film 26. However, another insulating film may be used. For example, a silicon oxide film or a silicon nitride film containing phosphorus or boron may be used. These insulating films are formed by CVD.
In addition to the method, the film may be formed by another film forming method such as a spin coating method and a sputtering method.

In the second embodiment, the silicon film 36 is left at the crystal grain boundaries of the ferroelectric film 26 and then thermally oxidized to form the silicon oxide film 28.
After the silicon oxide film 28 is oxidized into the silicon oxide film 28, the silicon oxide film 28 may be left only at the crystal grain boundaries of the ferroelectric film 26 in the same manner as in the first embodiment. In the first and second embodiments, an example in which the present invention is applied to a semiconductor memory device using a ferroelectric capacitor is described. However, the present invention is similarly applied to other semiconductor devices using a ferroelectric capacitor. be able to.

In the above embodiment, the case where the SBT film is used as the ferroelectric film has been described. However, the present invention can be widely applied to prevent the electrode material from entering the crystal grain boundaries of the ferroelectric film. Can be. Therefore, SBT
The invention can be applied not only to a film but also to a capacitor using another ferroelectric film.

[0035]

As described above, according to the present invention, the first electrode, the ferroelectric film formed on the first electrode, and the insulating film embedded in the concave portion on the surface of the ferroelectric film And a second electrode formed on the ferroelectric film in which the insulating film is buried, so that the ferroelectric capacitor is formed. Can be prevented from entering the ferroelectric film. As a result, it is possible to reduce an increase in leak current and an electric short circuit of the ferroelectric capacitor. Further, the ferroelectric capacitor can be formed stably, and the reliability can be improved.

A lower electrode forming step of forming a lower electrode on the underlying substrate; a ferroelectric film forming step of forming a ferroelectric film on the lower electrode; and an insulating film formed in a concave portion on the surface of the ferroelectric film. A ferroelectric capacitor is manufactured by an insulating film embedding step of embedding the insulating film and a step of forming an upper electrode on the ferroelectric film in which the insulating film is embedded. The film can prevent the electrode material constituting the upper electrode from entering the ferroelectric film. As a result, it is possible to reduce an increase in leak current and an electric short circuit of the ferroelectric capacitor. Also,
The ferroelectric capacitor can be formed stably, and the reliability can be improved.

Further, a transfer transistor formed on a semiconductor substrate, a lower electrode connected to the transfer transistor, a ferroelectric film formed on the lower electrode, and a recess embedded in a surface of the ferroelectric film. A semiconductor memory device is composed of a ferroelectric capacitor having an insulating film formed and an upper electrode formed on a ferroelectric film in which the insulating film is buried, so that a crystal like a SrBi ₂ Ta ₂ O ₉ film is formed. Even when a ferroelectric film having a high activation temperature and large crystal grains is used, a semiconductor memory device having a high-quality ferroelectric capacitor can be configured. Thereby, the reliability and the like of the semiconductor memory device can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a graph showing electric characteristics of the ferroelectric capacitor according to the first embodiment of the present invention.

FIG. 3 is a process sectional view (part 1) illustrating the method for manufacturing the ferroelectric capacitor according to the first embodiment of the present invention.

FIG. 4 is a process sectional view (part 2) illustrating the method for manufacturing the ferroelectric capacitor according to the first embodiment of the present invention.

FIG. 5 is a process sectional view (part 3) illustrating the method for manufacturing the ferroelectric capacitor according to the first embodiment of the present invention.

FIG. 6 is a process sectional view illustrating the method for manufacturing the ferroelectric capacitor according to the second embodiment of the present invention.

FIG. 7 is a process cross-sectional view illustrating a structure and a manufacturing method of a ferroelectric capacitor according to a modification of the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Semiconductor substrate 12 ... Gate electrode 14 ... Source / drain diffusion layer 16 ... Interlayer insulating film 18 ... Contact hole 20 ... Electrode plug 22 ... Adhesive layer 24 ... Pt film 26 ... Ferroelectric film 28 ... Silicon oxide film 30 ... Pt Film 32: Lower electrode 34: Upper electrode 36: Silicon film

Claims (10)

[Claims] A first electrode; a ferroelectric film formed on the first electrode; an insulating film embedded in a concave portion on a surface of the ferroelectric film; And a second electrode formed on the ferroelectric film. 2. The ferroelectric capacitor according to claim 1, wherein the insulating film is formed over substantially the entire area of the ferroelectric film. 3. The ferroelectric capacitor according to claim 1, wherein the ferroelectric film is a SrBi ₂ Ta ₂ O ₉ film. 4. A lower electrode forming step of forming a lower electrode on a base substrate; a ferroelectric film forming step of forming a ferroelectric film on the lower electrode; A method for manufacturing a ferroelectric capacitor, comprising: an insulating film embedding step of embedding an insulating film; and a step of forming an upper electrode on the ferroelectric film in which the insulating film is embedded. 5. The method for manufacturing a ferroelectric capacitor according to claim 4, wherein the step of embedding the insulating film comprises: an insulating film forming step of forming the insulating film on the ferroelectric film; And removing the insulating film in the concave portion of the ferroelectric film to remove the insulating film. 6. The method for manufacturing a ferroelectric capacitor according to claim 5, wherein the insulating film forming step includes: a conductive film forming step of forming a conductive film on the ferroelectric film; A method of manufacturing a ferroelectric capacitor, the method including: replacing a film with a film. 7. The method of manufacturing a ferroelectric capacitor according to claim 4, wherein the step of embedding the insulating film includes: a step of forming a conductive film on the ferroelectric film; A conductive film removing step of removing the conductive film in the concave portion of the ferroelectric film, and a replacing step of replacing the conductive film with the insulating film. Manufacturing method. 8. The method of manufacturing a ferroelectric capacitor according to claim 4, wherein in the step of embedding the insulating film, the insulating film is embedded in the recess of the ferroelectric film. A ferroelectric capacitor, wherein the ferroelectric film is left almost all over the ferroelectric film. 9. The ferroelectric capacitor manufacturing method according to claim 4, wherein said ferroelectric film is an SrBi ₂ Ta ₂ O ₉ film. Method for manufacturing a body capacitor. 10. A transfer transistor formed on a semiconductor substrate, a lower electrode connected to the transfer transistor, a ferroelectric film formed on the lower electrode, and a concave portion on a surface of the ferroelectric film. And a ferroelectric capacitor having an upper electrode formed on the ferroelectric film in which the insulating film is embedded.