Semiconductor device manufacturing: process – Coating of substrate containing semiconductor region or of... – Insulative material deposited upon semiconductive substrate
Reexamination Certificate
1999-05-28
2001-05-29
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating of substrate containing semiconductor region or of...
Insulative material deposited upon semiconductive substrate
C438S789000
Reexamination Certificate
active
06239044
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an apparatus for forming a silicon oxide film and a method of forming a silicon oxide film.
For example, in production of a MOS type semiconductor device, it is required to form a gate oxide film composed of a silicon oxide film on a surface of a silicon semiconductor substrate. In production of a thin film transistor (TFT), it is also required to form a gate oxide film composed of a silicon oxide film on a surface of a silicon layer formed on an insulation substrate. It can safely be said that reliability of the semiconductor devices depends upon these silicon oxide films. The silicon oxide films are therefore constantly required to have high dielectric breakdown durability and long-term reliability.
With a decrease in thickness of a gate oxide film and an increase in diameter of a substrate, an apparatus for forming a silicon oxide film has been being converted from a horizontal-type apparatus in which a process chamber (oxidation chamber) formed of quartz extends in a horizontal direction to a vertical-type apparatus in which a process chamber extends in a vertical direction. The reason therefor is as follows. Not only the vertical-type apparatus for forming a silicon oxide film can easily cope with an increase in a diameter of a substrate as compared with the horizontal-type apparatus, but also the vertical-type apparatus can serve to decrease formation of a layer of silicon oxide (to be referred to as “natural oxide” hereinafter) caused by atmosphere taken into the process chamber of the vertical-type apparatus during transfer of silicon semiconductor substrates into the process chamber. However, even the use of the vertical-type apparatus for forming a silicon oxide film results in the formation of a natural oxide having a thickness of approximately 2 nm on the surface of the silicon semiconductor substrate. The natural oxide contains a large amount of impurities derived from atmosphere, and the presence of the natural oxide is not at all negligible when a gate oxide is decreased in thickness. There have been therefore proposed methods for preventing the formation of the natural oxide to the lowest level possible, such as (1) a method in which a nitrogen gas atmosphere is formed in a substrate transfer portion provided in a vertical-type apparatus by flowing a large volume of nitrogen gas (nitrogen gas purge method), and (2) a method in which a substrate transfer portion is vacuumed and then nitrogen gas or the like is introduced into the substrate transfer portion to discharge atmosphere (vacuum loadlock method).
Thereafter, in a state where an inert gas atmosphere is formed in the process chamber (oxidation chamber), silicon semiconductor substrates are brought into the process chamber (oxidation chamber). Then, an atmosphere of the process chamber (oxidation chamber) is replaced with an oxidative atmosphere and the silicon semiconductor substrates are thermally oxidized to form gate oxide films. For the formation of the gate oxide film, there is generally employed a method in which high-purity water vapor is introduced into the process chamber maintained at a high temperature to thermally oxidize the surface of the silicon semiconductor substrate (wet oxidation method). In this method, a gate oxide film having high electric reliability can be obtained as compared with a method in which the surface of the silicon semiconductor substrate is oxidized with high-purity dry oxygen gas (dry oxidation method). Included in the above wet oxidation method is a pyrogenic oxidation method (also called “hydrogen gas combustion oxidation method or wet oxidation”) in which hydrogen gas is mixed with oxygen gas at a high temperature and is combusted and the so-generated water vapor is used. The pyrogenic oxidation method is widely used. In the pyrogenic oxidation method, generally, oxygen gas is supplied into a combustion chamber which is disposed outside the process chamber (oxidation chamber) and which interior is maintained at 700 to 900° C., and then hydrogen gas is supplied into the combustion chamber to combust the hydrogen gas at a high temperature. The so-obtained water vapor is used as oxidizing species.
FIG. 21
shows a schematic view of a vertical-type apparatus for forming a silicon oxide film by the pyrogenic oxidation method. The vertical-type apparatus comprises a double-tubular structured process chamber
10
made of quartz and held perpendicularly, a water vapor inlet port
12
for introducing water vapor and the like into the process chamber
10
, a gas exhaust portion
13
for exhausting the gas from the process chamber
10
, a heater
14
for maintaining the interior of the process chamber
10
at a predetermined ambient temperature through a cylindrical heat equalizer tube
16
made of SiC, a substrate transfer portion
20
, a gas introducing portion
21
for introducing nitrogen gas into the substrate transfer portion
20
, a gas exhaust portion
22
for exhausting the gas from the substrate transfer portion
20
, a shutter
15
for partitioning the process chamber
10
and the substrate transfer portion
20
, and an elevator unit
23
for bringing silicon semiconductor substrates into and out of the process chamber
10
.
A base portion
26
is attached to the elevator unit
23
, and a heat insulation member
25
is disposed on the base portion
26
. Further, onto the heat insulation member
25
is attached a substrate receiving member
24
made of quartz or SiC for receiving silicon semiconductor substrates therein. A sealing member
27
formed of, for example, an “O-ring” is attached to a marginal portion of the upper surface of the base portion
26
, and when the substrate receiving member
24
is brought into the process chamber
10
, the lower portion of the process chamber
10
is sealed with the base portion
26
(see FIG.
22
). The base portion
26
is structured so as to flow coolant inside.
The heat insulation member
25
is also called a heat-retaining cylinder or a heat barrier, and generally, it is a hollow and cylindrical member having its top and bottom surfaces closed and being formed of quartz, and it has a structure in which the hollow portion is filled with glass fiber. Further, a piping
17
for flowing coolant is disposed outside the process chamber
10
and near the heat insulation member
25
. In the above structure, damage of the sealing member
27
caused by radiation heat directly conducted to the base portion
26
in the process chamber
10
, can be prevented and malfunction of the elevator unit
23
can be reliably prevented.
Hydrogen gas supplied to a combustion chamber
30
is mixed with oxygen gas at a high temperature and combusted in the combustion chamber
30
to generate water vapor. The water vapor is introduced into the process chamber
10
through a piping
31
, a gas flow passage
11
and a water vapor inlet port
12
. The gas flow passage
11
corresponds to a space between an inner wall and an outer wall of the double-tubular structured process chamber
10
.
A conventional method of forming a silicon oxide film with a conventional apparatus having the above structure will be outlined with reference to
FIGS. 23
to
25
hereinafter. [Step-
10
]
First, nitrogen gas is introduced into the process chamber
10
through a piping
32
, the combustion chamber
30
, the piping
31
, the gas flow passage
11
and the water vapor inlet port
12
to form a nitrogen atmosphere in the process chamber
10
, and the ambient temperature in the process chamber
10
is maintained at 700 to 750° C. with the heater
14
through the heat equalizer tube
16
. The purpose in maintaining the ambient temperature in the process chamber
10
at the above temperature range is to decrease thermal shock which silicone semiconductor substrates
50
suffer when the silicon semiconductor substrates
50
are transferred into the process chamber
10
. In this state, the shutter
15
is kept closed. The substrate transfer portion
20
is in a state where it is
Kashiwagi Akihide
Kataoka Toyotaka
Suzuki Toshihiko
Dang Phuc T.
Kananen Ronald P.
Nelms David
Rader Fishman & Grauer
Sony Corporation
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