Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
2000-05-10
2004-08-17
Fahmy, Wael (Department: 2814)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S250000, C438S253000, C438S393000, C438S396000, C438S240000
Reexamination Certificate
active
06777248
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a ferroelectric element such as an FeRAM utilizing a non-volatile property of a ferroelectric material, a semiconductor device using the ferroelectric element, and a method of manufacturing the ferroelectric element. The present invention also relates to a high dielectric element such as a DRAM utilizing a high dielectric constant and a low leakage current density, a semiconductor device using the high dielectric element, and a method of manufacturing the high dielectric element.
BACKGROUND OF THE INVENTION
As a semiconductor memory, there is a DRAM (Dynamic Random Access Memory) having the ability of rewriting data at a high speed. DRAMs have been produced which have a large capacity of 16 M bits to 64 M bits in response to the progress of these technologies for realizing a higher density and a higher integration. Such large capacity also requires a technology for achieving finer geometries for circuit components, particularly, finer geometries for capacitors for storing information. For achieving finer geometries for capacitors, it is required to provide a thin dielectric film, to select a material having a high dielectric constant, and to change the structure of the capacitor composed of upper and lower electrodes and a dielectric material from two-dimensional to three-dimensional. With respect to a high dielectric material, it is known that BST (Ba/Sr)TiO
3
having a simple lattice perovskite crystal structure exhibits a dielectric constant (&egr;) larger than that of SiO
2
/Si
3
N
4
. An example of the use of such a high dielectric material has been reported in International Electron Device Meeting Technical Digest (IEDM Tech. Dig.), p. 823, 1991.
A non-volatile memory FeRAM (Ferroelectric Random Access Memory) using a ferroelectric material as a capacitor material has a characteristic capable of storing data in the OFF state of a power supply because it utilizes two residual polarization states which are different in polarity. The FeRAM has a feature in terms of rewriting data at a speed which is very high, such as the order of &mgr;s or less, and therefore, it is expected to provide an ideal memory in the next generation. In the case of such a FeRAM, it is also required to provide a thin ferroelectric film for achieving a large capacity. Incidentally, a semiconductor memory intended to suppress reactivity between a ferroelectric material and a metal electrode has been disclosed in Japanese Patent Application Laid-open No. 5-190797, in which PZT (lead zirconate titanate) is used as a ferroelectric material and a silicon nitride (SiNx) film operating as a diffusion preventive layer is formed around the ferroelectric material.
SUMMARY OF THE INVENTION
The above-described technologies, however, have failed to examine the suppression of the leakage current density accompanied by thinning of a dielectric material essentially to be performed for increasing the degree of integration. A memory using the above-described BST has the object of lowering an operational voltage along with higher integration. For lowering the operational voltage of a memory, it is required to ensure a sufficient capacitance at a small voltage. To increase such a capacitance, it has been proposed to select a material having a high dielectric constant, to increase the electrode area, and to make the high dielectric material thin. A thin film made of BST having a polycrystalline structure, however, has a problem in terms of withstand voltage characteristic because such a polycrystalline film allows leakage current to easily flow through grain boundaries of the crystals. For this reason, in the case of using the BST thin film as a capacitor, it is difficult to apply a sufficient operational voltage thereto.
In the above described ferroelectric capacitor, in which a silicon nitride film is formed around the PZT film, the silicon nitride film acts as a diffusion preventive layer capable of preventing thermal diffusion from elements of PZT, thereby maintaining a desirable stoichiometric composition of the ferroelectric material necessary for ferroelectric characteristics. The silicon nitride layer in the above-described ferroelectric capacitor, however, has a problem. Since the silicon nitride film has a dielectric constant as small as 7, it must be formed to an ultra-thin thickness of 30 Å or less for suppressing a lowering of the total capacitance of the ferroelectric capacitor having a size of 4 &mgr;m
2
. Further, in the case of a higher integration in the order of 1 G bits, the area of the capacitor becomes as small as 0.1 &mgr;m
2
. In this case, it becomes apparent on the basis of simple calculation that the silicon nitride layer must be formed to a further ultra-thin thickness of 1 Å or less.
Additionally, in the thinning process used in the prior technologies, if a metal is as an electrode, there occurs a problem that a transition layer is formed by diffusion of an element at an interface between a dielectric thin film and the metal electrode, to thereby reduce spontaneous polarization (Pr), to increase field reversing (Ec), and to give rise to film fatigue.
To solve the above-described problems, the present invention has been made, and an object of the present invention is to provide a high dielectric layer containing insulating particles, which is capable of suppressing leakage current flow through grain boundaries of crystals and which can be thinned to such an extent as to meet a requirement of high integration; a high dielectric element in which the high dielectric thin film is sandwiched between upper and lower electrodes; a semiconductor device using the high dielectric element; and a method of manufacturing the high dielectric element.
Another object of the present invention is to solve the above-described problems and to provide a ferroelectric layer containing insulating particles, which is capable of suppressing leakage current flow through grain boundaries of crystals and which can be thinned to such an extent as to meet a requirement of high integration; a ferroelectric element in which the ferroelectric thin film is sandwiched between upper and lower electrodes; a semiconductor device using the ferroelectric element; and a method of manufacturing the ferroelectric element.
A further object of the present invention is to provide a high dielectric element or a ferroelectric element including the above mentioned high dielectric thin film or the above mentioned ferroelectric thin film having a thickness of 200 Å or more, wherein the element can be supplied with an operation voltage of 2 V for operating a semiconductor memory.
A further object of the present invention is to provide a high dielectric element in which a conductive oxide is used as an electrode which is in contact with the above mentioned high dielectric thin film to suppress formation of a transition layer, and a method of manufacturing the high dielectric element.
A further object of the present invention is to provide a ferroelectric element in which a conductive oxide is used as an electrode which is in contact with the above mentioned ferroelectric thin film to suppress formation of a transition layer, and a method of manufacturing the ferroelectric element.
To achieve the above objects, according to the present invention, there is provided a ferroelectric element including an upper electrode, a ferroelectric thin film, and a lower electrode, wherein the ferroelectric layer contains insulating particles having a resistance of 10
6
&OHgr; or more.
According to the present invention, there is provided a high dielectric element including an upper electrode, a high dielectric thin film, and a lower electrode, wherein the high dielectric layer contains insulating particles having a resistance of 10
6
&OHgr; or more.
The insulating particles have particle sizes each being in a range of 50 Å or less.
The ferroelectric thin film may be made of a material selected from the group consisting of a material expressed by (Pb
1−x
A
x
)(Zr
1−y
Ti
y
)O
Higashiyama Kazutoshi
Nabatame Toshihide
Oishi Tomoji
Suzuki Takaaki
Antonelli Terry Stout & Kraus LLP
Fahmy Wael
Hitachi , Ltd.
Rao Shrinivas H.
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