Method of forming a perovskite structure semiconductor...

Details Method of forming a perovskite structure semiconductor... Method of forming a perovskite structure semiconductor...

1999-01-20

2001-02-27

Wojciechowicz, Edward (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Field effect device

Having insulated electrode

C257S310000, C257S532000

Reexamination Certificate

active

06194753

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a capacitor, and more particularly, to an improved structure and method of making a semiconductor memory cell capacitor using a high dielectric film of Perovskite structure.
BACKGROUND ART
With memory chips becoming increasingly integrated, a memory cell and the cell surface area thereof in which a capacitor is to be formed are becoming smaller. Subsequently, as a proper method for securing a Dynamic Random Access Memory (hereinafter, “DRAM”) with a 25 fF (pico Farad)/Cell capacitance in such a small portion of a cell, several studies are being conducted for fabricating a thinner NO (nitrogen-oxygen) dielectric film into three-dimensional capacitor structures, such as a cylinder type capacitor, a fin type capacitor, a trench type capacitor, and applying Ta
2
O
5
(&egr;r=24) having a high dielectric constant (&egr;r) or a Perovskite structure material such as (Ba
0.5
,Sr
0.5
)TiO
3
(&egr;r<300) (hereinafter, “BSTO”) or Pb(La,Zr)TiO
3
(hereinafter, “PLZT”) to the dielectric film for forming a capacitor.
When used as a Perovskite type dielectric material, BSTO or PLZT exhibits a high dielectric constant due to the displacement occurring between the Ti and O atomic surfaces, and tends to exhibit ferroelectric properties. In recent studies, two directions have been investigated in applying a Perovskite structure BSTO or PLZT having a high dielectric constant to a capacitor dielectric film for a DRAM or Ferroelectric Random Access Memory (hereinafter, “FRAM”).
One proposal is to form an electrode layer such as YBa
2
Cu
3
O
7-x
(hereinafter, “YBCO”) or La
1-x
Sr
x
Co
1
O
3
(x=0.5) (hereinafter, “LSCO”) on a substrate composed of a mono-crystalline, such as MgO or STO, which exhibits a proper lattice matching with BSTO or PLZT. High dielectric constant films of Perovskite structure are consecutively formed thereon into an epitaxial structure, which is comparable in bulk physical properties with a dielectric film having no grain boundaries.
The other proposal is to form a poly-crystalline high dielectric film on a lower side electrode layer composed of Pt/Ti/SiO
2
or RuO
2
/SiO
2
. The structure is focused on improving the dielectric and electrical properties of the dielectric film. The deposition conditions, such as temperature and oxygen partial pressure, are regulated instead of regulating a crystalline orientation direction thereof in relation with the lower side electrode.
According to an article in J. Appl. Phys., Vol. 76, No. 5, Sep. 1, 1994, whose disclosure is incorporated by reference, (001)-phase-oriented high dielectric film of a Perovskite structure has no grain boundaries therein exhibits a higher dielectric constant than those of a poly-crystalline structure, which results from the epitaxial structure. Since a (001)-phase orientation denotes a higher dielectric constant than those of other phase orientations, excellent electric properties and flat surfaced film are secured. Even with such excellent properties of the epitaxial structure, application thereof encounters difficulties in manufacturing memory chips adopting an epitaxial structure, and the properties are still under study.
Studies continue on a poly-crystalline high dielectric film which is applicable to memory chips. Leading examples for electrode layer materials being employed in a poly-crystalline structure are metallic electrode layers of Pt/Ti/SiO
2
and conductive oxide films, such as RuO
x
, RuO
2
/Ru. In recent years, Perovskite conductive oxide films, such as SRU(SrRuO
3
), are being considered as lower side electrode layer materials.
An article in Journal of Electronic Materials, Vol. 23, No. 1, 1994, whose disclosure is incorporated herein by reference, reveals that a Pt-related electrode causes electrical short circuits in a capacitor due to hillock generation during a high temperature process thereof and causes grain growth therein which produces difficulties in chip fabrication. Further, RuO
2
or SRO enables formation of a high dielectric film with improved properties. In a poly-crystalline structure, as described above, a high dielectric film is deposited at a temperature below 650° C., according to a report in Extended Abstracts of the 1991 International Conference on Solid State Devices and Materials, Yokohama, 1991, pp. 195-197.
However, the high dielectric film deposited on a substrate at such a low temperature has a tendency towards a certain crystal phase depending on the deposition conditions. Further, it is difficult to regulate the crystal phase therein, and there may occur an incomplete crystal formation therein. The dielectric film deposited thereon is composed of both a plurality of smaller grains and subsequently increased grain boundaries. An unstable phase may be formed therein resulting from boundary segregation between grains.
As described in Extended Abstracts of the 1994 International Conference on Solid State Devices and Materials, Yokohama, 1994, pp. 682-684, a BSTO (100) phase is preferred on a RuO
2
(110) phase, and a PZT(Pb(Zr,Ti)O
3
) (100) phase is known to be formed preferentially on a Pt (111) phase within a certain deposition temperature. However, both phases are known to cause disadvantages such as a difficulty in forming a complete (001) phase Perovskite dielectric film and the generation of growth of other phases.
Further, although the upper surface of the high dielectric film is generally flat, the film itself has random crystal phases instead of predetermined ones, and interfaces are formed therebetween devoid of electrode layers or lattice matchings. Hence, interfaces having larger surface energy, as in high angle grain boundaries, are formed.
Therefore, there are several disadvantages with regard to the above-described dielectric film. Trapped charges occur along the interface between the electrode layer and grain boundaries within the high dielectric film. Thus the leakage current is increased while the TDDB (time-dependent direct breakdown) is decreased. Moreover, the high dielectric film, which is formed on an electrode layer and has a random poly-crystalline structure, exhibits a lower dielectric constant than that of an epitaxial structure or a poly-crystalline structure with a single phase orientation.
DISCLOSURE OF THE INVENTION
An advantage of the present invention is in decreasing leakage current.
Another advantage of the present invention is in improving the TDDB.
The present invention is achieved in part by a semiconductor device comprising: a first electrode including a first conductive oxide film of a Perovskite structure; a second electrode including a second conductive oxide film of a Perovskite structure; and a first Perovskite dielectric film formed between the first and second electrodes.
The above advantages, objects and others are achieved in part by a capacitor structure having a substrate, an insulation film formed on the substrate and having a contact hole so that a portion of the substrate surface is exposed therethrough, a first electrode formed on a portion of the substrate including the contact hole and having a conductive plug, an anti-oxide film formed on the conductive plug, a Perovskite structure conductive seed layer formed on the anti-oxide film, a Perovskite structure high dielectric film formed on the first electrode, and a Perovskite structure second electrode formed on the high dielectric film.
Additionally, a capacitor structure according to a second embodiment of the present invention includes a substrate, a first insulation film formed thereon and having a contact hole exposing a portion of a surface of the substrate therethrough, a first electrode formed on the first insulation film including the contact hole and having a conductive plug, an anti-oxide film formed thereon and a Perovskite structure high dielectric film formed thereon, first side wall spacers formed on each side of the first electrode, a Perovskite structure first dielectric film deposited on the first insulation film including the first electrode and the first side wall spacers so

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