JPH0513706A - Semiconductor device - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to provide a highly reliable capacitor which can secure a sufficient capacitor capacity. In a semiconductor device including a capacitor having a first electrode, two electrodes, and a capacitor insulating film sandwiched between these electrodes, the capacitor insulating film has different forbidden band widths. It is composed of a laminate of more than one kind of metal oxide film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a capacitor structure in a DRAM or the like.

[0002]

2. Description of the Related Art One of semiconductor devices is a DRA for storing information by combining a capacitor and a transistor.
There is M (Dynamic Random Access read write Memory).

In such a device, a capacitor is formed by sandwiching a capacitor insulating film between a semiconductor substrate and a capacitor electrode. Conventionally, a silicon oxide film is used as the capacitor insulating film, but in recent years, with higher integration and larger capacity rapidly, in order to compensate for the decrease in the capacitor capacity due to miniaturization, a dielectric film more than the silicon oxide film is used. A material having a high ratio has been studied, and improvements such as using a laminated film of a silicon nitride film and a silicon oxide film have been attempted.

However, it is necessary to use a material having a higher dielectric constant in order to cope with the future increase in the capacity of the capacitor due to the further miniaturization of the area occupied by the capacitor. From these requirements, it has been considered to use a tantalum oxide film, which is a material having a dielectric constant about 7 times larger than that of a silicon oxide film, as an insulating film.

However, since such a high dielectric material is a compound containing a metal, it generally has a problem that the forbidden band width is small in spite of having a high dielectric constant and the leak current is essentially large. Therefore, the performance as an original insulating film is remarkably deteriorated, the charge holding ability of the capacitor is lowered, and the reliability of the DRAM or the like is impaired.

For example, since the band gap of tantalum oxide is as small as about 4.7 eV, there is a problem that the leak current is large. In order to suppress such leak current, for example, the underlying silicon and tantalum oxide are combined. At the interface,
A method of providing a silicon oxide film or a silicon nitride film having a larger band gap has been proposed.

However, in the limit of film thickness,
The interposition of silicon oxide or silicon nitride having a small dielectric constant leads to a decrease in the capacitance of the capacitor.

As described above, it is extremely difficult to suppress the leak current while securing a sufficient capacitor capacity.

[0009]

As described above, in the conventional capacitor, it is extremely difficult to suppress the leak current while ensuring a sufficient capacitor capacity.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a highly reliable capacitor that can secure a sufficient capacitor capacity in spite of a reduction in occupied area. To do.

[0011]

Therefore, the present invention provides a semiconductor device including a capacitor having a first electrode, a second electrode, and a capacitor insulating film sandwiched between these electrodes. There is provided a semiconductor device characterized in that the insulating film is composed of a laminated body of two or more kinds of metal oxide films having different forbidden band widths.

Further, according to the present invention, in a semiconductor device including a capacitor having a first electrode, a second electrode, and a capacitor insulating film sandwiched between these electrodes, the capacitor insulating film is A first metal oxide film and a second metal oxide film formed on both sides of the first metal oxide film, wherein the forbidden band width of the second metal oxide film is the first metal oxide film. Provided is a semiconductor device having a width greater than a forbidden band width of an oxide film.

[0013]

According to the above structure, the leak current can be suppressed in the capacitor using the metal oxide film as the capacitor insulating film.

Therefore, it is possible to provide a capacitor having an excellent charge retention ability with a sufficient capacitor capacity and a small leak current.

This is due to the following action.

Generally, a material having a higher dielectric constant has a smaller band gap. And the smaller the forbidden band,
A large leak current flows when a voltage is applied, and the performance as an insulator deteriorates.

This is because the height of the energy barrier between the electrode, that is, the conductor and the insulating film becomes small.

However, in the case of a capacitor intended to retain electric charges, it is necessary to have excellent insulation and high capacity at the same time. Therefore, it is desirable to use a material having a high dielectric constant as the material of the insulating film and to make the film thickness as thin as possible.

In order to satisfy such a demand, it is necessary to satisfy the contradictory demands that the permittivity of the film as a whole is large while increasing the energy barrier height between the conductor and the insulating film.

Based on these requirements, consider the case of a tantalum oxide film and a titanium oxide film.

The forbidden band widths of the tantalum oxide film and the titanium oxide film are about 4.6 eV and 3 eV, respectively. On the other hand, the dielectric constant (relative dielectric constant) is about 28 and 80, respectively.

As described above, the titanium oxide film has a smaller forbidden band width than the tantalum oxide film, but has a much higher dielectric constant. Therefore, the capacitor insulating film has a laminated structure of these tantalum oxide film and titanium oxide film, and the leak current is suppressed by arranging the tantalum oxide film having a large forbidden band on the electrode side, particularly on the side where charges are injected. On the other hand, by stacking titanium oxide having a large dielectric constant, the average dielectric constant of the film as a whole can be increased.

Desirably, by sandwiching both sides of the metal oxide film having a small forbidden band with the metal oxide film having a large forbidden band, the leak current is suppressed and the metal oxide film having a large dielectric constant is formed. By stacking, the average dielectric constant of the film as a whole can be increased.

In this way, it is possible to obtain a capacitor having a high capacitance and a high charge retention capability.

[0025]

Embodiments of the present invention will now be described in detail with reference to the drawings.

1A to 1D, a tungsten film 10 serving as a lower electrode (storage node), a capacitor insulating film, and a capacitor insulating film are formed via a titanium silicide film 9 formed on an n + polycrystalline silicon film 8. Tantalum oxide film 11 as a film
/ Titanium oxide film 12 / Tantalum oxide film 13 three-layer laminated film, and a DRAM having a laminated memory cell structure using a capacitor in which a tungsten film 14 is sequentially laminated as an upper electrode.
FIG.

First, as shown in FIG. 1 (a), the specific resistance 10
An element isolation insulating film 2 is formed in a (100) p-type silicon substrate 1 of about Ω · cm by a normal LOCOS method.
Then, a film thickness of 200 to be a gate insulating film is formed by a thermal oxidation method.
nm silicon oxide layer 3 and gate electrode 300 nm
To form a gate insulating film 3 and a gate electrode 4 by photolithography and reactive ion etching. Further, using the gate electrode 4 as a mask, As
Ions are ion-implanted to form a source / drain region composed of the n @-type diffusion layer 5 to form a MOSFET as a switching transistor.

Further, as shown in FIG. 1 (b), a silicon oxide film 6 having a film thickness of about 150 nm is deposited on the entire surface by the CVD method, and then the photolithography method and the reactive ion etching are performed to store the silicon oxide film 6. The di-node contact 7 is formed.

After this, as shown in FIG. 1C, after depositing a second n + polycrystalline silicon film 8 having a film thickness of 80 nm on the entire surface, a photolithography method and a chemical dry etching method (isotropic etching) are used. ), A titanium silicide film 9 is further formed thereon to a thickness of 20 to 30 nm, and a film thickness of 100 is selectively formed on the titanium silicide film 9 by the CVD method.
A capacitor lower electrode made of the first tungsten film 10 having a thickness of nm is formed. After that, the first tantalum oxide film 11 serving as a capacitor insulating film is formed to a thickness of 5 nm, the titanium oxide film 12 is formed to a thickness of 15 nm, and the second tantalum oxide film 13 is formed to a thickness of 5 nm, for example, by the CVD method. Form sequentially.

Finally, as shown in FIG. 1D, after forming a second tungsten film 14 having a film thickness of 100 nm as a capacitor upper electrode on the entire surface, patterning is performed by using a normal photolithography method. Form a memory cell.

The leak current characteristic of the DRAM thus formed is shown by a curve a in FIG. For comparison, a curve b shows a leakage current characteristic when a tantalum oxide film is used as a capacitor insulating film in a single layer structure. Here, the film thickness of both is 2 nm. Here, the value of this film thickness is a value converted into the film thickness when a silicon oxide film is used as the capacitor insulating film.

Also from these comparisons, the DR of the embodiment of the present invention
It can be seen that the AM has significantly reduced leakage.

FIGS. 3A and 3B are comparison diagrams of band structures of the capacitor insulating film of the embodiment of the present invention and the conventional capacitor insulating film.

According to the DRAM thus formed, since the capacitor is configured to have a small leak current, a large capacitor capacity, and a large charge holding amount, a highly reliable DRAM with few malfunctions can be obtained. Obtainable.

In the above embodiment, the tungsten film 10 as the lower electrode (storage node) is formed on the n + polycrystalline silicon film 8 via the titanium silicide film 9, and the capacitor insulating film is formed thereon. However, compared with the case where the capacitor insulating film is directly formed on the n + polycrystalline silicon film 8, the depletion layer is not formed,
The capacity can be increased. In addition, since the interface between the tantalum oxide film and the tungsten film is stable, no defects occur in the tantalum oxide film due to the reaction of both films, and a large capacity can be maintained.

Further, as shown in FIG. 4, a zirconium oxide (ZrO ₂ ) film 21-titanium oxide film 22-zirconium oxide film 23, which is a capacitor insulating film, is directly formed on the polycrystalline silicon film 8 in the above-described embodiment. A layer structure film may be formed and the polycrystalline silicon film 24 may be used as the upper electrode. Further, polycrystalline silicon may be used as the lower electrode and a metal film such as a tungsten film may be used as the upper electrode. Further, three-layer structure film of zirconium oxide film-titanium oxide film-hafnium oxide film, three-layer structure film of hafnium oxide film-titanium oxide film-hafnium oxide film, hafnium oxide film-titanium oxide film-zirconium oxide film
A layer structure film or the like is also effective. Further, although a tungsten film is used as the upper electrode and the lower electrode of the capacitor,
The material is not necessarily limited to these, and can be appropriately changed within the range of satisfying the conditions of the present invention such as metal or metal alloy.

Furthermore, in the above embodiment, the three-layer film of tantalum oxide film / titanium oxide film / tantalum oxide film was used as the capacitor insulating film, but a two-layer film or a laminated film of four or more layers may be used. . Further, the material of the capacitor insulating film is not limited to the combination of tantalum oxide and titanium oxide, and the tantalum oxide film (TaO ₂ ) and the strontium titanate film (SrTiO ₃ ), the yttrium oxide film (Y ₂ O ₃ ) And lead titanate (PbTiO ₃ )
A combination of the above and the like can be appropriately selected. In addition, in these embodiments, a DRAM having a multilayer capacitor structure is used.
However, it goes without saying that the present invention is also applicable to a DRAM having a trench structure.

..

As described above, according to the capacitor of the present invention, since a laminated film of two or more kinds of metal oxide films having different forbidden band widths is used as a capacitor insulating film, high integration is achieved. Also in the case of conversion, it is possible to reduce the leak current and increase the charge retention ability while maintaining a sufficient capacitor capacity.

[Brief description of drawings]

FIG. 1 is a DRA of a stacked memory cell structure according to an embodiment of the present invention.
Manufacturing process diagram of M

FIG. 2 is a comparative diagram showing leakage currents of a DRAM capacitor according to an embodiment of the present invention and a conventional DRAM capacitor.

FIG. 3 is a comparison diagram of band structures of a capacitor according to an embodiment of the present invention and a capacitor according to a conventional example.

FIG. 4 is a schematic sectional view showing the structure of a DRAM having a stacked memory cell structure according to another embodiment of the present invention.

[Explanation of symbols]

1 p-type silicon substrate 2 element isolation insulating film 3 Gate insulating film 4 gate electrodes 5 n-type diffusion layer 6 Interlayer insulation film 7 Storage node contact 8 n + type polycrystalline silicon layer 9 Titanium silicide film 10 Tungsten film (lower electrode) 11 Tantalum oxide film (capacitor insulating film) 12 Titanium oxide film (capacitor insulating film) 13 Tantalum oxide film (capacitor insulating film) 14 Tungsten film (upper electrode)

Claims (2)

[Claims] 1. A semiconductor device comprising a capacitor having a first electrode, a second electrode, and a capacitor insulating film sandwiched between these electrodes, wherein the capacitor insulating film has different forbidden band widths. A semiconductor device comprising a laminate of two or more kinds of metal oxide films. 2. A semiconductor device comprising a capacitor having a first electrode, a second electrode, and a capacitor insulating film sandwiched between these electrodes, wherein the capacitor insulating film is a first metal oxide film. Membrane and this first
And a second metal oxide film formed on both sides of the metal oxide film, the forbidden band width of the second metal oxide film is larger than the forbidden band width of the first metal oxide film. A semiconductor device characterized by the above.