Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-05-12
2003-08-26
Pert, Evan (Department: 2829)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S311000
Reexamination Certificate
active
06611014
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a semiconductor device having a ferroelectric capacitor and its manufacturing method.
For years, there are known non-volatile ferroelectric memory devices for non-volatile storage of data by using spontaneous polarization of a ferroelectric capacitor. Ferroelectric random access memory is usable without a battery and operable at a high speed. Its development to non-touch cards (radio frequency identification, herein after abbreviated RF-ID) is going to start, and its use in replacement of existing SRAM (static random access amemory), DRAM (dynamic random access memory), flash memory, etc.) and also as memory integrated with logic circuit, is hopefully expected.
A ferroelectric capacitor is typically made by using platinum (Pt) as upper and lower electrodes and a PZT (PbZr
1-x
TiO
x
) film as its ferroelectric film. For fabricating ferroelectric random access memory in an LSI process using a silicon substrate, a surface of the silicon substrate having formed transistors and other elements is covered with an insulating film such as silicon oxide film, and a lower Pt electrode, PZT film and upper Pt electrode are made by patterning, to thereby make the ferroelectric capacitor. Normally, a Ti or Ti
x
O
y
film, for example, is interposed as a base layer of the lower Pt electrode to improve its adherence.
It is known that, with this conventional ferroelectric capacitor, a reducing gas of hydrogen, etc. generated in a Si-LSI process invites deterioration of the ferroelectric property, that is, degradation of spontaneous polarization. As a countermeasure against characteristic deterioration of the ferroelectric capacitor due to reduction by hydrogen, there have been proposed some protection techniques for preventing entry of hydrogen, etc. into the capacitor portion. Heretofore, however, there have been no simple and reliable techniques.
Ferroelectric capacitors involve various problems such as deterioration of the property caused by process damage, which must be removed, in addition to characteristic deterioration due to reduction by hydrogen.
For example, Japanese Patent Laid-Open Publication No. H 8-335673 discloses a method for covering a ferroelectric capacitor with a diffusion inhibiting film to prevent direct contact of the ferroelectric capacitor of PZT or other material and a SiO
2
insulating film and thereby prevent mutual diffusion of elements between them. The publication indicates that TiO
2
, ZrO
2
and Al
2
O
3
, for example, are effective as the diffusion inhibiting film. However, this publication deals with exfoliation of the capacitor ferroelectric film by mutual diffusion, and not the problem of characteristic deterioration of the ferroelectric capacitor by diffusion of hydrogen generated, in the fabricating process.
On the other hand, through recent research, the Inventors have come to realize that the use of the Ti
x
O
y
film as the adhesion layer between the ferroelectric capacitor and the SiO
2
film invites some undesirable problems, including deterioration of the ferroelectric property by diffusion of Ti into the PZT film, for example.
SUMMARY OF THE INVENTTON
It is therefore an object of the invention to provide a semiconductor device having a ferroelectric capacitor with an excellent property and is manufacturing method.
A feature of the invention is that, in semiconductor devices having a ferroelectric capacitor whichi comprises a semiconductor substrate, and a ferroelectric capacitor composed of a lower electrode, ferroelectric film and upper electrode sequentially stacked on the semiconductor substrate via an insulating film, at least one of the upper and lower electrodes forming the, ferroelectric capacitor is covered with a hydrogen barrier film which does not contain titanium.
More specifically, the hydrogen barrier film is formed on the surface of at least one of the position between the lower electrode and the insulating film and the. surface of the upper electrode.
In the present invention, thehydrogen barrier film not containing titanium is preferably a metal oxide film having a hydrogen diffusion constant of 10
−5
cm
2
/s or less. The hydrogen barrier film not containing titanium is required to have a high resistance if it is formed so as not to short-circuit the electrodes above on and under the ferroelectric capacitor. In this case, the metal oxide film preferably has a specific resistance not lower than 1 k&OHgr;cm. By making such a hydrogen barrier film on at least one of the base layer of the lower electrode and the upper surface of the upper electrode, deterioration in property of the ferroelectric film due to reduction by hydrogen is prevented. Additionally, by selecting an appropriate material for the hydrogen barrier film, it functions as an adhesion layer and exfoliation of the capacitor formed on the insulating film is prevented.
In this specification, the “hydrogen barrier film” pertains to a barrier film against diffusion of a reducing gas like fluorine other than hydrogen gas, and it is used because of its function to prevent damage to the ferroelectric film in the fabrication process. Still in this specification, the “ferroelectric capacitor” pertains to a capacitor not only of a type formed independently from a transistor like in ferroelectric random access memory of a one-transistor/one-capacitor type memory cell structure but also of a type formed in the gate portion of a transistor integrally therewith like in a memory cell of a one-transistor type ferroelectric random access memory.
Still in this specification, the “metal oxide” pertains to a oxide not only of a type including a single metal element but also of a type including more than two metal elements.
In the present invention, when the hydrogen barrier film is interposed under the lower electrode, it is made simultaneously with the lower electrode by patterning. In a structure where the ferroelectric film of the ferroelectric capacitor and the lower electrode are formed to lie over a larger area than that of the upper electrode, the hydrogen barrier film is made to extend from the upper surface of the upper electrode to its side surface and then onto the upper surface of the ferroelectric film. Alternatively, if the lower electrode of the ferroelectric capacitor is made to lie over a larger area than those of the upper electrode and the ferroelectric film, the hydrogen barrier film is made to extend from the upper surface of the upper electrode, covering its side surface and further the side surface of the ferroelectric film, onto the upper surface of the lower electrode.
In the present invention, the ferroelectric capacitor may be configured so that at least a part thereof from the lower electrode to the ferroelectric film is buried in a groove formed in the insulating film. In this case, the hydrogen barrier film is buried in the groove so as to cover the bottom and side surfaces of the ferroelectric capacitor. The hydrogen barrier film may be brought into direct contact with the ferroelectric capacitor, or may be buried not to contact directly. In this case, the hydrogen barrier film is preferably formed also on the upper surface of the ferroelectric capacitor.
The present invention is also characterized in that, in a semiconductor device which comprises a semiconductor substrate, a ferroelectric capacitor having a lower electrode, ferroelectric film and upper electrode sequentially stacked on the semiconductor substrate via an insulating film, and an inter-layer insulating film formed to cover the ferroelectric capacitor, the inter-layer insulating film has a multi-layered structure including first and second inter-layer insulating films, and a hydrogen barrier film is buried between the first and second inter-layer insulating films.
That is, the hydrogen barrier film need not be in direct contact with the ferroelectric capacitor. Also when the hydrogen barrier film is buried inside the inter-layer insulating film covering the ferroelectric capacitor, it is possible to prevent diffusion of hydrogen into
Hidaka Osamu
Iwamoto Tsuyoshi
Kanaya Hiroyuki
Kumura Yoshinori
Kunishima Iwao
Banner & Witcoff , Ltd.
Kabushiki Kaisha Toshiba
Pert Evan
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