Amorphous dielectric capacitors on silicon

Details Amorphous dielectric capacitors on silicon Amorphous dielectric capacitors on silicon

1999-04-27

2001-07-03

Bowers, Charles (Department: 2823)

Semiconductor device manufacturing: process

Having magnetic or ferroelectric component

C438S392000, C438S511000

Reexamination Certificate

active

06255122

ABSTRACT:

DESCRIPTION
1. Field of the Invention
The present invention relates to high-capacitance capacitors, and more particular to an amorphous (or low temperature) phase of a high dielectric constant thin film material which can be employed as a dielectric in capacitors formed directly on silicon. Such structures will be useful as capacitors in dynamic random access memory (DRAM) applications, gate dielectrics in transistors and as decoupling capacitors. The present invention also relates to a gate dielectric material, and more particular to an amorphous (or low temperature) phase high dielectric constant thin film material which can be employed as a gate dielectric in a transistor.
2. Background of the Invention
Dielectric materials in high density circuits appear as capacitors in dynamic random access memory (DRAM) applications, gate dielectrics in transistors and as decoupling capacitors. The dielectric materials in these structures are typically silicon dioxide (SiO
2
), silicon nitride (Si
3
N
4
), aluminum oxide (Al
2
O
3
) or any combination thereof. These dielectric materials typically have a dielectric constant of 9.0 or below. As today's generation of circuits become smaller and smaller, the dielectric materials employed therein must be made thinner to satisfy circuit requirements. The use of thin, low dielectric constant materials in today's circuits is undesirable since such materials lead to leaky circuits. Thus, it would be beneficial if the dielectric constant of the dielectric material used in such circuits could be increased.
A variety of high dielectric constant materials such as the crystalline form of perovskite-type oxides including a titanate system material such as barium titanate, strontium titanate, barium strontium titanate (BST), lead titanate, lead zirconate titanate, lead lanthanum zirconate titanate, barium lanthanum titanate, barium zirconium titanate; an aluminate such as lanthanum aluminate and yttrium aluminate; a niobate or tantalate system material such as lead magnesium niobate, lithium niobate, lithium tantalate, potassium niobate, strontium aluminum tantalate and potassium tantalum niobate; a tungsten-bronze system material such as barium strontium niobate, lead barium niobate, barium titanium niobate; and Bi-layered perovskite system material such as strontium bismuth tantalate, bismuth titanate are known in the art. Despite having dielectric constants of about 200 or more, crystalline perovskite-type oxides are deposited at temperatures of about 500° C. or more. At such high temperatures, if deposited directly on silicon, interfacial layers form which may degrade device performance. In addition, grain boundary leakage paths and lowered barrier heights may result which could lead to high device leakage.
In view of the drawbacks with prior art dielectric materials, it would be beneficial if a new dielectric material was developed which could be directly deposited on silicon. This new dielectric material must exhibit low leakage as compared to dielectric materials presently employed in this field and must have a dielectric constant that is about 10 or above.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a thin film dielectric material which can be employed in forming capacitors on silicon or as a gate dielectric material.
Another object of the present invention is to provide a thin film dielectric material which has a dielectric constant higher than conventional dielectric materials such as SiO
2
(∈=4), Si
3
N
4
(∈=7), and Al
2
O
3
(∈=8) and which is compatible with CMOS (complimentary metal oxide semiconductor) processing.
A further object of the present invention is to provide a thin film dielectric material which exhibits good conformity to the electrode material to which it is applied as well as a low leakage current that is on the order of 1 A/cm
2
or less, preferably 1×10
−4
A/cm
2
or less.
These and other objects and advantages are achieved in the present invention by utilizing an amorphous (or low temperature) phase material as a thin film dielectric material. Specifically, one embodiment of the present invention relates to high-capacitance capacitors (on the order of 1 nF/mm
2
or above) formed using thin films of materials which are in the amorphous (or low temperature) phase. Such dielectric materials can be formed directly on top of silicon minimizing the formation of any interfacial layers or grain boundaries which can lead to device degradation.
Another embodiment of the present invention relates to a gate electrode insulator which comprises a thin film of an amorphous (or low temperature) phase material as the gate dielectric material in a transistor.
In the latter stages of CMOS processing and in applications such as BEOL structures and organic FETs, ambient temperatures must be kept low, less than 500° C., thus the novel capacitors and transistors of the present invention use a low temperature deposition and annealing process to stay at or below this temperature. These low temperature processes ensure formation of a dielectric material which is in the amorphous (or low temperature) phase. For example, it has been determined that the low temperature (or amorphous) phase of barium strontium titanate has a dielectric constant of up to about 25 which value is significantly higher than that of the typical dielectrics used in circuit applications. Other perovskite-type oxides such as lead lanthanum titanate can have even greater dielectric constants in their amorphous phase. Capacitors and transistors formed utilizing these particular types of low temperature dielectrics also exhibit low leakage and good conformability.
More specifically, the present invention provides an amorphous thin film dielectric material having a dielectric constant greater than 10 that may be used in fabricating high-capacity capacitors or gate insulators. The term “amorphous” is used herein to denote a material which lacks an ordered crystal structure. This is different from the crystalline phase of the material wherein a highly ordered crystal structure is observed.
In general the structures of the present invention comprise at least an amorphous or low temperature phase dielectric material which is selected from the group consisting of a perovskite-type oxide such as a titanate system material, i.e. barium titanate, strontium titanate, barium strontium titanate, lead titanate, lead zirconate titanate, lead lanthanum zirconate titanate, barium zirconium titanate and barium lanthanum titanate; an aluminate such as lanthanum aluminate and yttrium aluminate; a niobate or tantalate system material such as lead magnesium niobate, lithium niobate, lithium tantalate, potassium niobate, strontium aluminum tantalate and potassium tantalum niobate; a tungsten-bronze system material such as barium strontium niobate, lead barium niobate, and barium titanium niobate; or a Bi-layered perovskite system material such as strontium bismuth tantalate, and bismuth titanate as the dielectric material. The amorphous phase dielectric material of the present invention is formed using low temperature deposition and annealing steps wherein the temperature of both steps is about 450° C. or less.
The capacitor of the present invention is prepared using the following steps:
(a) preparing a bottom semiconducting electrode, said semiconducting electrode being composed of a semiconducting material such as silicon, a silicon containing material, a semiconducting organic or inorganic material;
(b) forming an amorphous (or low temperature) phase high dielectric constant material (∈=10 or above) on top of the bottom semiconducting electrode;
(c) annealing the amorphous dielectric material at a temperature which is effective in improving the quality as well as the dielectric constant of the amorphous dielectric material; and
(d) fabricating a top conductive electrode on said annealed dielectric material.
In an optional embodiment of the present invention, the above described method further c

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