Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1998-12-30
2001-02-06
Wilczewski, Mary (Department: 2822)
Television
Camera, system and detail
Combined image signal generator and general image signal...
C438S003000, C438S393000, C438S396000
Reexamination Certificate
active
06184927
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to technology about semiconductor memory devices; and, more particularly, to methods for forming ferroelectric capacitors of semiconductor devices which have a diffusion barrier layer preventing the breakdown of a ferroelectric thin film used as a dielectric film of a capacitor in Ferroelectric RAM (FeRAM)
DESCRIPTION OF THE PRIOR ART
As well known, FeRAM includes transistor, bitline, and a ferroelectric capacitor having a ferroelectric thin film. It is necessary to form a diffusion barrier layer for protecting the properties of the ferroelectric thin film in this ferroelectric capacitor since the properties of the ferroelectric thin film may be greatly changed as changing its composition and greatly affected by the thermal treatment conditions of the following processes or the following processes themselves. It is also necessary to cap the ferroelectric film using a diffusion barrier layer in order to decrease edge effect since the edge effect is increased with decreasing the capacitor size particularly in highly integrated FeRAM.
Hereinafter, referring to
FIG. 1
, a method for forming FeRAM according to the prior art and its drawbacks will be illustrated.
First, a film of platinum
12
and a thin film of ferroelectric material
13
are formed, in turn, over a silicon substrate
11
on which predetermined processes are completed and patterned. The film of platinum
12
is a bottom electrode connected to the substrate
11
. A film of TiO
2
16
as a diffusion barrier layer is then deposited and selectively etched to expose the ferroelectric film
13
. Subsequently, an upper electrode
14
is formed so as to contact with the exposed ferroelectric film
13
, thereby completing a FeRAM.
In the processes, when PZT is used as a material of the ferroelectric film, the film of TiO
2
16
can depress the diffusion of a ingredient of PbO or the other ingredients in the film of PZT and minimize the change of the composition of the PZT ferroelectric film, thereby preventing the breakdown of the PZT ferroelectric film. However, when strontium bismuth tantalate (SBT) is used as a material of the ferroelectric film, it results in problems as described below.
The oxygen in the SBT ferroelectric thin film has relatively high binding energy with TiO
2
. Therefore, when the oxygen is activated by a process of thermal treatment, it is diffused to the film of TiO
2
and, thus, transforms the perovskite structure of the SBT ferroelectric film to non-stoichiometry state. The atomic radius of Ti is also smaller than the ingredients of SBT. Therefore, Ti may be entered into the ferroelectric film to result in defects of the ferroelectric film. This may cause deterioration of the electric properties of the ferroelectric capacitor and break the ferroelectric film.
As described above, it is not appropriate to form an excellent film of diffusion barrier for the SBT ferroelectric film using the prior method. Accordingly, it is required to develop a new method for forming a film of diffusion barrier in the ferroelectric capacitor.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a method for forming a ferroelectric capacitor of a semiconductor which has a film of diffusion barrier to prevent the breakdown of a ferroelectric film induced from the out-diffusion of ingredients of the ferroelectric film.
In accordance with one embodiment of the present invention, there is provided a method for forming a ferroelectric capacitor of semiconductor which comprises the steps of: forming a lower electrode connected to a substrate; forming a ferroelectric thin film of SBT on the lower electrode; forming a SBT thin film as a diffusion barrier layer in order to prevent the out-diffusion of the ingredients or dopant of the ferroelectric film; selectively etching the SBT thin film to expose the SBT ferroelectric film; and forming an upper electrode contacted with the exposed SBT ferroelectric film.
In accordance with another embodiment of the present invention, there is provided a method for forming a ferroelectric capacitor of semiconductor which comprises the steps of: forming a lower electrode connected to a substrate; forming a ferroelectric thin film of SBT on the lower electrode; forming a thin film of Bi
2
O
3
as a diffusion barrier layer in order to prevent the out-diffusion of the ingredients or dopant of the ferroelectric film; selectively etching the Bi
2
O
3
thin film to expose the SBT ferroelectric film; and forming an upper electrode contacted with the exposed SBT ferroelectric film.
Using a thin film of SBT or Bi
2
O
3
as a diffusion barrier layer of the SBT ferroelectric capacitor according to the present invention can prevent the breakdown of the ferroelectric film induced from the subsequently proceeded thermal treatment process at high temperature. As a result, the invention can decrease the fatigue of the device and enhance margin in the processes and the reliability of the device.
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patent: 5976928 (1999-11-01), Kirlin et al.
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patent: 4-344384 (1992-11-01), None
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Blakely & Sokoloff, Taylor & Zafman
Goodwin David
Hyundai Electronics Industries Co,. Ltd.
Wilczewski Mary
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