Method of forming conductive film and capacitor

Details Method of forming conductive film and capacitor Method of forming conductive film and capacitor

1999-09-30

2001-10-02

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Making passive device

Stacked capacitor

C257S306000

Reexamination Certificate

active

06297122

ABSTRACT:

BACKGROUND OF THE INVENTION
As the scale of semiconductor integrated circuits which are typified by a DRAM becomes larger and the miniaturization of ICs progresses, the device area becomes smaller generation by generation. For a DRAM each of its memory cells is comprised of a single transistor and a single capacitor, the reduction in device area decreases the area of the capacitor that stores information, thereby lowering the information memory capability.
For semiconductor memory devices like DRAMs, various attempts have been made to secure a sufficient capacitance of each capacitor in order to prevent the information memory capability from being impaired by the large scale integration and miniaturization.
One of the attempts is to use a material which has a higher dielectric constant than the conventional oxide SiO
2
/SiN film. Materials with a high dielectric constant include strontium titanate (SrTiO
3
) and strontium barium titanate ((Ba, Sr)TiO
3
) (BST).
Studies are also being made on the use of a thin film of a functional material of a ferroelectric substance such as Pb(Zr
1-x
, Ti
x
)O
3
(PZT) or SrBi
2
Ta
2
O
9
(SBT), and people have begun to propose devices with very new functions, such as an FRAM (Ferroelectric Random Access read write Memory).
In using those dielectric substances in capacitors of semiconductor memory devices, it is typical to use noble metals like Pt, Ru and Ir or their oxides as the upper and lower electrodes that sandwich the capacitor insulating film.
The reason for the above is that BST, PZT and SBT are oxides and the lower electrode is exposed to an oxygen environment at the time of forming those films, so that it is essential to prevent oxidization of the surface of the lower electrode.
It has recently been reported that the characteristic of a capacitor is improved by using a conductive perovskite oxide film like an SrRuO
3
film as the capacitor electrode. That is, the use of this type of a capacitor can dramatically improve the reliability of capacitors in a DRAM or FRAM.
In adapting a capacitor whose capacitor insulating film is formed of a high dielectric substance or ferroelectric substance in a semiconductor memory device of a large scale integration like a DRAM or FRAM, CVD is used as a scheme of forming the capacitor electrode as well as a scheme of forming the capacitor insulating film for the following reason.
Attempts to provide larger integration and further miniaturization of semiconductor memory devices like a DRAM will continue in the future and it is essential to form capacitors into a three-dimensional structure in order to secure the necessary amount of signals for the operation of such a semiconductor memory device. CVD which can be expected to provide an excellent step coverage is therefore effective in making such a design.
The formation of a conductive perovskite oxide thin film by CVD is disclosed in Jpn. Pat. Appln. KOKAI Publication No. Hei 9-27602. This method forms a (Ba
1-x
Sr
x
)RuO
3
film by CVD using Ba(THD)
2
, Sr(THD)
2
and Ru(Cp)
2
as raw materials where THD is C
11
H
19
O
2
(2,2,6,6-tetramethyl-3,5-heptanedionato) and Cp is C
5
H
5
.
A perovskite oxide has a conductivity only in the vicinity of the stoichiometric composition, and its electric conductivity gets lower as the composition deviates from the stoichiometric composition. As the composition of SrRuO
3
deviates from Sr/Ru=1, for example, the electric conductivity will not be seen. When Sr/Ru>1 at which the composition approaches SrO, particularly, this tendency becomes prominent.
BRIEF SUMMARY OF THE INVENTION
The present inventors discovered that the conventional method of forming a conductive perovskite oxide film (Jpn. Pat. Appln. KOKAI Publication No. Hei 9-27602) had the following problems.
When (Ba
1-x
Sr
x
)RuO
3
is formed by this method, problems arise, such that the composition does not becomes uniform (particularly, the composition becomes non-uniform in the widthwise direction), and the composition and the non-uniformity of the composition vary depending on the type of the substrate that serves as a base.
In particular, in a case of using the aforementioned conductive perovskite oxide film as the lower electrode of a DRAM capacitor which uses a capacitor insulating film with a high dielectric constant like a Ba
0.5
Sr
0.5
TiO
3
film, the base for the lower electrode is comprised of a plurality of materials so that the uniformity of the composition gets poorer.
As mentioned above, a perovskite oxide has a conductivity only in the vicinity of the stoichiometric composition, and its electric conductivity gets lower as the composition deviates from the stoichiometric composition. The present inventors found out that such a phenomenon would lead to the following problem.
If a perovskite oxide film is used as the lower electrode of a capacitor, the aforementioned phenomenon leads to the formation of a layer with no electric conductivity in part of the perovskite oxide film, and, in the worst case, results in the formation of a high-resistance perovskite oxide film which cannot be used as the lower electrode. It is therefore difficult to adapt the conventional method of forming a perovskite oxide film to capacitors of a semiconductor memory device like a DRAM.
Accordingly, it is an object of the present invention to provide a method of forming a conductive film of ARuO
3
(A being a substance containing at least one of elements Ca, Sr and Ba) and a method of forming a capacitor uses ARuO
3
as an electrode material, which methods can reduce the non-uniformity of composition.
To achieve this object, according to one aspect of this invention, there is provided a conductive film forming method comprising the steps of preparing a substrate; and forming a conductive film of ARuO
3
(A being a substance containing at least one of elements Ca, Sr and Ba) on the substrate by CVD using a &bgr; diketone complex of Ru as Ru materials.
The following are some of more specific modes of the conductive film embodying this invention.
(1) A THD compound (=C
11
H
19
O
2
) is used as the &bgr; diketone complex.
(2) SrRuO
3
is used as AruO
3
(=Ca
x
Ba
y
Sr
1-x-y
RuO (0≦×≦1, 0≦y≦1)).
(3) The &bgr; diketone complex dissolved in a liquid is used.
(4) As the A material, the &bgr; diketone complex of A is used. It is preferable that the &bgr; diketone complex of the A material be the same as the &bgr; diketone complex of the Ru material.
(5) After a plurality of regions of different materials are formed on the same surface of the substrate, the conductive film is formed on those regions.
According to another aspect of this invention, there is provided a capacitor forming method comprising the steps of forming a lower electrode on a substrate; forming a capacitor insulating film of Ba
x
Sr
1-x
TiO
3
(0≦×≦1) on the lower electrode; and forming an upper electrode on the capacitor insulating film, as at least one of the lower electrode and the upper electrode, a conductive film of ARuO
3
(A being a substance containing at least one of elements Ca, Sr and Ba) being formed by CVD using a &bgr; diketone complex of Ru as an Ru material.
According to a further aspect of this invention, there is provided a capacitor forming method comprising the steps of a preparing a semiconductor substrate having a conductive region; forming a first insulating film on the semiconductor substrate; forming a first opening in the first insulating film and burying inside the first opening with a connecting member which electrically connects to the conductive region; forming a lower electrode, which electrically connects to the connecting member, on the first insulating film; forming a capacitor insulating film of Ba
x
Sr
1-x
TiO
3
(0≦×≦1) on the lower electrode; and forming an upper electrode on the capacitor insulating film, as at least one of the lower electrode and the upper electrode, a conductive film of ARuO
3
(A being a substance containing at least one of elements Ca, Sr and Ba) being formed by CVD using a &bgr;

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