Semiconductor device manufacturing: process – Making passive device – Stacked capacitor
Reexamination Certificate
1999-01-25
2001-08-14
Nguyen, Tuan H. (Department: 2813)
Semiconductor device manufacturing: process
Making passive device
Stacked capacitor
C438S003000, C438S240000
Reexamination Certificate
active
06274454
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for fabricating dielectric capacitors, and precisely to a method for fabricating dielectric capacitors usable in ferroelectric nonvolatile memories, etc.
Ferroelectric memories are fast-reloadable nonvolatile ones for which are used high-speed polarization inversion and remanence of ferroelectric thin films. In conventional ferroelectric memories, transistors and ferroelectric capacitors were aligned in the plane direction of a substrate. The ferroelectric capacitor is formed by laminating, on a silicon oxide film, a buffer layer of a titanium metal film having a thickness of 30 nm or so, a lower electrode of, for example, a platinum film having a thickness of 200 nm or so, a ferroelectric film of a PZT [Pb(Zr,Ti)O
3
] film or SBT (SrBi
2
Ta
2
O
3
) film having a thickness of 200 nm or so, and an upper electrode of a platinum film having a thickness of 200 nm or so, in that order.
To increase the information recording density in those memories, transistors and ferroelectric capacitors must be disposed on a substrate in layers, for which the capacitors are so-called stack-type capacitors. In that structure, each transistor is electrically connected with the lower electrode of each ferroelectric capacitor via a silicon plug.
However, reactive ion etching (RIE) of platinum is difficult, and fine working to give capacitors having a lower electrode of platinum is difficult.
Forming a ferroelectric film in capacitor fabrication generally requires heat treatment at high temperatures falling between 600° C. and 800° C., which, however, involves thermal diffusion between a silicon plug and the lower electrode that underlies the film whereby silicon having diffused into the lower electrode is oxidized in the upper layer of the lower electrode to retard the electroconductivity of the lower electrode, or, as the case may be, silicon further diffuses into the ferroelectric film to significantly worsen the capacitor characteristics.
On the other hand, fabricating ordinary MOS memory structures requires forming gas annealing at temperatures falling between 400° C. and 500° C. for transistor recovery, prior to metal wiring operation. However, it is known that such forming gas annealing worsens the characteristics of ferroelectrics such as SBT, etc. In addition, where the lower electrode in capacitors is made of a noble metal except platinum and gold, the noble metal is oxidized through heat treatment for dielectrics. Forming gas annealing after fabrication of ferroelectric capacitors having a lower electrode of a noble metal except platinum and gold much more worsens the dielectric characteristics of the capacitors than those of capacitors where the electrode is made of platinum or the like that is not oxidized at all. This is because the noble metal oxide having formed through the heat treatment for dielectric formation is reduced through the forming gas annealing, thereby bringing about a significant change in the capacitor structure.
SUMMARY OF THE INVENTION
The present invention is to solve the problems with the related art noted above, and its object is to provide a method for fabricating dielectric capacitors. The first embodiment of the invention is a method for fabricating a dielectric capacitor that comprises a lower electrode made of at least one of iridium, palladium, ruthenium and rhodium or containing at least one of those elements, a dielectric film of a ferroelectric or high dielectric substance as formed on the lower electrode, and an upper electrode as formed on the dielectric film, and the method comprises a first heat treatment step for completing the formation of the dielectric film in an oxygen-containing vapor atmosphere followed by a second heat treatment step to be effected in a nitrogen or inert gas atmosphere. The second heat treatment is effected at a temperature not lower than that for the first heat treatment.
In the first embodiment of the method for fabricating the dielectric capacitor, the lower electrode is made of at least one of iridium, palladium, ruthenium and rhodium or contains at least one of those elements. In this, therefore, the lower electrode is etched more easily than platinum electrodes. In addition, in the method, the first heat treatment step for completing the formation of the dielectric film in an oxygen-containing vapor atmosphere is followed by the second heat treatment step to be effected in a nitrogen or inert gas atmosphere at a temperature not lower than that for the first heat treatment. Therefore, in this, even though the lower electrode will be also oxidized in the first heat treatment step, the oxidized part of the lower electrode could be reduced in the second heat treatment step when the oxidation is so minor that it could not be detected in analysis, for example, through X-ray diffractometry.
In the dielectric capacitor thus fabricated in this method, the dielectric film overlies the lower electrode made of or containing the above-mentioned, non-oxidized metal. Therefore, the capacitor has no part to be reduced in the subsequent forming gas annealing, and exhibits stable characteristics. Accordingly, the characteristics of the dielectric capacitor fabricated in this method are prevented from being worsened after forming gas annealing.
The second embodiment of the invention is a method for fabricating a dielectric capacitor that comprises a lower electrode made of at least one of iridium, palladium, ruthenium and rhodium or containing at least one of those elements, a dielectric film of a ferroelectric or high dielectric substance as formed on the lower electrode, and an upper electrode as formed on the dielectric film, and the method comprises a heat treatment step for completing the formation of the dielectric film in an oxygen-containing vapor atmosphere followed by a reduction step for reducing the oxide having been formed in the lower electrode through oxidation in the heat treatment step.
In the second embodiment of the method for fabricating the dielectric capacitor, the lower electrode is etched more easily than platinum electrodes for the same reasons as in the first embodiment noted above. In addition, in the method, the heat treatment step for completing the formation of the dielectric film in an oxygen-containing vapor atmosphere is followed by the reduction step for reducing the oxide having been formed in the lower electrode through oxidation in the heat treatment step. Therefore, in this, the lower electrode will be also oxidized in the heat treatment step but the oxidized part of the lower electrode is reduced in the reduction step, even though the oxidation is promoted to such a high degree that it is detected in analysis, for example, through X-ray diffractometry.
In the dielectric capacitor thus fabricated in this method, the dielectric film overlies the lower electrode made of or containing the above-mentioned, non-oxidized metal. Therefore, the capacitor has no part to be reduced in the subsequent forming gas annealing, and exhibits stable characteristics. Accordingly, the characteristics of the dielectric capacitor fabricated in this method are prevented from being worsened after forming gas annealing.
The third embodiment of the invention is a method for fabricating a dielectric capacitor that comprises a lower electrode made of at least one of iridium, palladium, ruthenium and rhodium or containing at least one of those elements, a dielectric film of a ferroelectric or high dielectric substance as formed on the lower electrode, and an upper electrode as formed on the dielectric film, and the method comprises a first heat treatment step for completing the formation of the dielectric film in an oxygen-containing vapor atmosphere followed by a reduction step for reducing the oxide having been formed in the lower electrode through oxidation in the first heat treatment step and by a second heat treatment step to be effected after the reduction step in a nitrogen or inert gas atmosphere at a temperature not lower than that for the fi
Nguyen Tuan H.
Sonnenschein Nath & Rosenthal
Sony Corporation
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