Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
1999-09-20
2002-05-28
Loke, Steven (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S303000, C257S306000, C257S309000, C257S310000, C257S741000, C438S003000, C438S244000, C438S253000, C438S387000, C438S396000, C438S239000, C438S240000, C365S065000, C365S087000, C365S001000, C365S145000
Reexamination Certificate
active
06396092
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a semiconductor device and a fabrication method thereof, and particularly to a semiconductor device which has a capacitor using a high-dielectric-constant or ferroelectric material thin film as a capacitor dielectric film and exhibiting a reduced leakage current, a large capacitance and a high residual polarization, and which is suitable for a memory of a large-scale integrated circuit (LSI), and a fabrication method thereof.
BACKGROUND ART
A semiconductor memory, typically a dynamic random access memory (DRAM) has a problem associated with the increased area and complicated structure of a capacitor along with a higher level of integration. To cope with such a problem, examination has been made to use, as a capacitor dielectric film, a high-dielectric-constant or ferroelectric material having a significantly large specific dielectric constant as compared with a prior art capacitor using silicon oxide or silicon nitride. In particular, it has been examined to apply the capacitor dielectric film using the high-dielectric-constant or ferroelectric material to a semiconductor device requiring a large capacitance with a reduced area, such as a large-scale DRAM in which the density of integration is in the order of gigabit. Further, since the high-dielectric-constant or ferroelectric material has a spontaneous polarization, the direction of which can be reversed by an external electric field applied thereto, an attempt has been made to form a non-volatile memory by making use of such a characteristic of the high-dielectric-constant or ferroelectric material. A prior art memory using the high-dielectric-constant or ferroelectric material has been described, for example, in Japanese Patent Laid-open No. Sho 63-201998.
The high-dielectric-constant or ferroelectric thin film used for the above memory is generally made from a composite metal oxide type high-dielectric-constant or ferroelectric material such as lead titanate zirconate (Pb(Zr, Ti)O
3
) (hereinafter, referred to as “PZT”), or barium strontium titanate ((Ba, Sr)TiO
3
) (hereinafter, referred to as “BST”).
A lower electrode (storage electrode) is generally made from a noble metal excellent in oxidation resistance, such as platinum, iridium or ruthenium for suppressing deterioration thereof due to heating at a crystallization temperature of 500° C. or more upon formation of the high-dielectric-constant or ferroelectric film. On the other hand, an upper electrode (plate electrode), which is usually formed after film formation of a composite metal oxide, is generally made from the same material as that of the lower electrode for enhancing an electrical symmetry, and to avoid reaction with the high-dielectric-constant or ferroelectric film at a heat-treatment step performed after formation of a capacitor, the upper electrode is often made from a noble metal such as platinum (for example, described in the specification of U.S. Pat. No. 5,005,102).
In the fabrication process for the above memory, however, since the process has a processing step carried out in a hydrogen atmosphere such as a step of forming an interlayer insulating film, if the electrode is made from an electrode material acting as a strong catalyst to reduction such as platinum, the oxide type high-dielectric-constant or ferroelectric material is reduced. This causes a significant deterioration in characteristics, such as the increase in leakage current or disappearance of the hysteresis characteristic.
For this reason, a process not to generate hydrogen has been selected at the sacrifice of the characteristic of an interlayer insulating film to some extent. However, it may be of course desirable to use a technique of forming an insulating film being good in coverage and resistance against etching. Further, even at the step of forming an interconnection after formation of a capacitor, hydrogen may be used, and to increase the degree of freedom in selection of the process, the capacitor using a high-dielectric-constant or ferroelectric film is required to be improved in terms of the resistance against hydrogen heat-treatment.
To be more specific, as described above, after formation of a high-dielectric-constant or ferroelectric film, the capacitor is subjected to treatment in a reducing atmosphere for forming an interconnection layer and an insulating film. Further, a through-hole formed for electrical connection between a peripheral circuit and an interconnection layer is generally formed into a shape in which a ratio of the depth to the size of the opening, that is, a so-called aspect ratio is large, and accordingly, tungsten or the like is formed by a CVD process in such a manner as to bury the through-hole. The CVD process is also performed in a reducing atmosphere.
It is known that the capacitor suffers a serious damage when being subjected to the above-described treatment in a reducing atmosphere. For example, in Material Research Society Symposium Proceedings Vol. 310, pp. 151-156 (1993), it was reported that when a SiO
2
film is formed by CVD, PZT as a high-dielectric-constant or ferroelectric material loses its ferroelectricity and increases the leakage current. Further, in the memory fabrication process, the memory is finally subjected to hydrogen heat-treatment (hydrogen annealing) for ensuring the reliabilities of a metal interconnection layer and a transistor formed in a layer under the capacitor. It is known that like the above step of forming an interlayer insulating film, the hydrogen annealing exerts an effect on the capacitor characteristics. For example, in the eighth International Symposium on Integrated Ferroelectrics, 11C (1996), it was reported that in the case of using SrBi
2
Ta
2
O
3
(hereinafter, referred to as SBT) as a high-dielectric-constant or ferroelectric material, when being subjected to treatment in a hydrogen atmosphere, the capacitor is peeled, or if not peeled, it causes significant deterioration in leakage current characteristic.
Disclosure of Invention
(Solving Means)
To solve the above-described problems, according to the present invention, there is provided a high-dielectric-constant or ferroelectric capacitor including an upper electrode formed of a conductive film of iridium oxide or ruthenium oxide, characterized in that lead, bismuth or barium is added to iridium oxide or ruthenium oxide for reducing the catalytic action of iridium or ruthenium which is not oxidized and remains.
It was examined what kind of material should be used as an upper electrode for a high-dielectric-constant or ferroelectric capacitor capable of keeping its characteristics after the step in a hydrogen atmosphere. A double-layer film of platinum and titanium was formed as a lower electrode on a silicon substrate on which a thermally oxidized film was formed. A lead titanate zirconate thin film having a thickness of 100 nm was formed on the electrode by a sol-gel process. The sol used was obtained by reaction of lead acetate, titanium isopropoxide, and zirconium isopropoxide in methoxy ethanol. To obtain a perovskite type structure upon crystallization, 10% of lead oxide was excessively added thereto. The lead titanate zirconate thin film was subjected to rapid thermal annealing in an oxygen atmosphere at 650° C. for 2 minutes, to crystallize lead titanate zirconate. An upper electrode having a size of 100 &mgr;m×100 &mgr;m was formed on the lead titanate zirconate thin film by a lift-off process. The capacitor with upper electrode thus obtained was heat-treated in a hydrogen atmosphere at 300° C., and was examined in terms of the presence or absence of deterioration of the characteristics. To be more specific, four kinds of the capacitors including the upper electrodes made from platinum, iridium oxide, stacked layer of platinum and iridium oxide, and gold were examined. A ratio of the spontaneous polarization value after hydrogen heat-treatment to that before hydrogen heat-treatment for each capacitor was shown in Table 1.
As is apparent from Table 1, the deterioration of the characteristi
Fujisaki Yoshihisa
Kushida Keiko
Miki Hiroshi
Takatani Shinichiro
Torii Kazuyoshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Kange Dongee
Loke Steven
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