Electric resistance heating devices – Heating devices – Vaporizer
Reexamination Certificate
1999-11-19
2002-10-22
Bueker, Richard (Department: 1763)
Electric resistance heating devices
Heating devices
Vaporizer
C392S394000, C392S399000, C118S724000, C118S726000
Reexamination Certificate
active
06470144
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chemical vapor deposition (CVD) apparatuses, vaporizers for CVD apparatuses, and semiconductor devices, and in particular to a CVD apparatus capable of long-term, reliable production of CVD film with good quality, a vaporizer for a CVD apparatus, and a semiconductor device manufactured thereby.
2. Description of the Background Art
In recent years, there has been a further advancement in the integration of devices such as semiconductor memory. For instance, there has been a rapid advancement in enhancing the integration of a dynamic random access memory, quadrupled in the number of bits in three years. Such integration aims at achieving rapid device operation, reducing device power consumption, reducing device cost, and the like. While semiconductor memory and the like are highly integrated as described above, a capacitor, a component of such devices, is required to store a certain quantity of electric charge. Thus, along with the advancement in the integration of devices, there have also been developed a technique for forming a material for a capacitor's dielectric film into an extremely thin film, a technique for forming a capacitor of a complex, three-dimensional structure to increase the surface area of the capacitor, and other techniques.
Main traditional materials for dielectric film include silicon oxide (SiO
2
) film. Due to its physical properties, however, it is extremely difficult to further reduce currently used silicon oxide film in thickness, and it has been accordingly noted that silicon oxide film is replaced with a material having a higher dielectric constant that silicon oxide film, since using a material having a dielectric constant higher than conventional as a material for a capacitor's dielectric film can increase the density of the electric charge stored in the capacitor. When a material of a high dielectric constant is used as a dielectric film to achieve a storage of electric charge comparable to that achieved by a conventional capacitor, the dielectric film may have a thickness greater than that formed of silicon oxide film. If a dielectric film may have a thickness increased to some extent, the process for forming the dielectric film can be improved in controllability and the dielectric film can thus be enhanced in reliability. That is, there are a multitude of advantages in using a material of a high dielectric constant as a dielectric film material.
Such capacitor's dielectric film is also sought to have small current leakage as an important characteristic thereof. To achieve such small current leakage, in general the dielectric film preferably has an equivalent SiO
2
film thickness of no more than 0.5 nm, and a leakage current density of no more than 2×10
−7
A/cm
2
when a voltage of 1V is applied.
The density of electric charge stored in a capacitor and other properties also significantly depend on the material for the capacitor's electrode, which is required to be highly stable and have good workability.
Furthermore it is also considered to use a material of a lower electrical resistance than conventional as a wiling material in a highly integrated semiconductor device as above to operate the device rapidly.
As such, oxide-type dielectrics including tantalum oxide (Ta
2
O
5
), lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), strontium titanate (ST), barium titanate (BT), and barium strontium titanate ((Ba, Sr) TiO
2
(hereafter referred to as BST)) are considered as possible materials for a capacitor's dielectric film. Furthermore, platinum, ruthenium, iridium and a conductive oxide thereof or SrRuO
3
are considered as possible materials for a capacitor's electrode. Copper is also considered as an alternative wiring material to aluminum, a conventional wiring material.
Generally, in forming a thin film on a capacitor's electrode of a micro-fabricated memory device having fine steps it is preferable to employ a film deposition method through a chemical vapor deposition (CVD) which allows complex geometry to be covered satisfactorily. The CVD is also most advantageous in simplifying the process. In this CVD, an organometallic compound containing a predetermined type of metal is used as a material for a thin film. Vaporizing the material and spraying the vaporized material onto a substrate allows formation of a thin film with a high dielectric constant or capacitor's electrode. However, most materials conventionally used for forming a thin film with a high dielectric constant are disadvantageously not stable nor have good vaporization characteristics.
Under such circumstances, some of the Inventors have invented, as disclosed in Japanese Patent Laying-Open No. 7-268634, a CVD film material with a greatly enhanced vaporization characteristic by dissolving a solid material such as an organometallic compound in an organic solvent called tetrahydrofuran or THF (C
4
H
8
O) to provide a solution thereof. Some of the Inventors have also invented, as disclosed in Japanese Patent Laying-Open No. 8-186103, a CVD apparatus for use with a liquid material that is capable of vaporizing the above-mentioned solution of the material (a liquid material) and supplying it stably to the CVD apparatus's reaction chamber. Furthermore, some of the Inventors have succeeded in using the CVD apparatus disclosed in Japanese Patent Laying-Open No. 8-186103 to form a thin film of a high dielectric constant having good surface morphology and electrical characteristics. Some of the Inventors have also invented, as disclosed in U.S. patent application Ser. No. 09/150,212, a CVD apparatus and CVD process condition allowing stable vaporization of a liquid material in a vaporization chamber.
It has been found, however, that it is difficult to use such CVD apparatus for use with a liquid material for a long term to reliably form thin films of a high dielectric constant with good characteristics. As the Inventors examined the apparatus, it has been found that the problem is caused by a solid component of an organometallic compound or the like that is separated from the liquid material in the CVD apparatus's vaporization chamber. This will be described in detail below with reference to the drawings.
FIG. 8
schematically shows a vaporizer as a vaporizer for use with a CVD apparatus related to the present invention. The vaporizer will now be described with reference to FIG.
8
.
Referring to
FIG. 8
, a vaporizer
121
as the vaporizer includes a body
121
a
of the vaporizer and an upper lid
121
b
of the vaporizer. A rod heater
122
is varied in body
121
a
and upper lid
121
b
. Upper lid
121
b
is provided with a vaporizer inlet
121
c
for supplying into vaporizer
121
a mixture of a liquid material and nitrogen gas as a carrier gas. Inlet
121
c
is connected to a material supply tube
126
a
via a connecting member
121
d
. Material supply tube
126
a
is connected via a connecting member to a material transport tube (not shown) connected to a container holding the liquid material. Body
121
a
is also provided with a vaporizer outlet
101
b
for exhausting a vaporized material. Outlet
101
b
is connected via a transport tube to a reaction chamber for forming a CVD film. Outlet
101
b
and the transport tube connected thereto are provided with a heater
124
.
Herein the material transport tube is typically a narrow tube of stainless steel. Material supply tube
126
a
is a narrow tube, e.g., of polytetrafluoroethylene (PTFE), polyimide. Body
121
a
and upper lid
121
b
are formed of metal, preferably a highly heat-conductive metal, such as aluminum, copper. Inlet
121
c
and outlet
101
b
and connecting member
121
d
may be formed, e.g., of stainless steel.
In such vaporizer
121
, from an end of material supply tube
126
a
that is located internal to vaporizer
121
a liquid material is scattered or sprayed together with a carrier gas and thus supplied into vaporizer
121
. The liquid material in
Horikawa Tsuyoshi
Kawahara Takaaki
Matsuno Shigeru
Sato Takehiko
Tarutani Masayoshi
Bueker Richard
Mitsubishi Denki & Kabushiki Kaisha
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