Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
1998-12-30
2001-02-20
Bowers, Charles (Department: 2813)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S240000, C438S396000, C438S253000
Reexamination Certificate
active
06190924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for forming semiconductor devices; and, more particularly, to methods for forming ferroelectric capacitors applied to ferroelectric random access memory (FeRAM) as a non-volatile memory element and highly integrated post-generation Dynamic RAM (DRAM) using a thin film of strontium bismuth tantalate (SBT) as a ferroelectric film.
DESCRIPTION OF THE PRIOR ART
The operation property such as refresh property of semiconductor has been considered as a primary thing in pursuit of high integration of semiconductor memory devices such as DRAM. Therefore, in order to obtain suitable operation properties, various researches and developments have been made on the technology for obtaining sufficient static capacitance of capacitors.
The materials such as strontium bismuth tantalate (SBT) and Pb
x
Zr
1-y
Ti
y
O
3
(PZT) have been considered as ferroelectric materials of capacitors in FeRAM as non-volatile memory elements and lately post-generation semiconductor memory devices.
FIG. 1
among the appended drawings is a section view of the ferroelectric capacitor fabricated according to the prior art using SBT as the material of ferroelectric layer.
As shown in
FIG. 1
, when the ferroelectric capacitor
15
is fabricated using a SBT thin film
11
as a ferroelectric layer over substrate
10
, the SBT thin film
11
is formed and crystallized by the processes of deposition and post thermal treatment at a high temperature of 800° C. in order to obtain better ferroelectric properties. In the drawing, the reference number
10
represents a substrate,
12
represents a bottom electrode and
13
represents an upper electrode, respectively.
The crystallization process is necessary since the SBT thin film
11
can possess suitable ferroelectric properties such as high dielectric constant and remanent polarization in the state of polycrystalline. However, the crystalline grain boundaries in the polycrystalline of the SBT thin film
11
provide conductive paths of leakage current.
Therefore, there is a drawback that the grain boundaries result in dielectric loss due to leakage current, and thus deteriorate the properties of the ferroelectric capacitors.
Various methods such as using various electrodes and adding dopants have been tried in order to decrease such leakage current. However, these methods are not satisfactory.
There is also another drawback that in the process of thermal treatment for crystallization at high temperature, Bi is evaporated at the surface of the SBT thin film
11
to change the composition of the ferroelectric material, and deteriorating the properties of the ferroelectric.
Accordingly, the other methods of ferroelectric capacitors are required in order to decrease leakage current without sacrificing good properties of polycrystalline.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a method for fabricating a ferroelectric capacitor without the dielectric loss due to leakage current or with the decreased dielectric loss.
In accordance with an embodiment of the present invention, there is provided a method for fabricating a ferroelectric capacitor which comprises the steps of: forming a bottom electrode over a substrate on which a predetermined lower structure is formed; forming a thin film of polycrystalline strontium bismuth tantalate (SBT) over the entire structure; forming an amorphous thin film of SBT on the polycrystalline film of SBT; and forming an upper electrode on the amorphous film of SBT.
The present invention is directed to a technology by which an amorphous thin film of SBT containing excess bismuth is thinly formed between the upper electrode of the ferroelectric capacitor and the polycrystalline thin film of SBT. Though the amorphous thin film of SBT is lower in dielectric constant than the polycrystalline thin film of SBT so as not to have the properties of ferroelectric, it does not have crystalline grain boundary and thus does not form the path for transferring material. Therefore, it can block the path of leakage current. The amorphous thin film is not required too thick for obtaining this effect and thus, it does not mostly affect the deterioration of the ferroelectric properties such as the decrease of dielectric constant. It also results in the complement of bismuth lost in the processes of deposition and thermal treatment for crystallization of the ferroelectric film of SBT at a high temperature.
REFERENCES:
patent: 5426075 (1995-06-01), Perino et al.
patent: 5519566 (1996-05-01), Perino et al.
patent: 5566046 (1996-10-01), Kulwicki
patent: 5614018 (1997-03-01), Azuma et al.
patent: 5650646 (1997-07-01), Summerfelt
patent: 5757061 (1998-05-01), Satoh et al.
patent: 6033920 (2000-03-01), Shimada et al.
patent: 9-260516 (1996-03-01), None
patent: 9-36309 (1997-02-01), None
patent: 9-142844 (1997-03-01), None
patent: 9-186376 (1997-07-01), None
Blakely & Sokoloff, Taylor & Zafman
Bowers Charles
Huynh Yennhu B.
Hyundai Electronics Industries Co,. Ltd.
LandOfFree
Apparatus and method to form ferroelectric capacitors having... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method to form ferroelectric capacitors having..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method to form ferroelectric capacitors having... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2608343