Low flow rate moisture supply process

Details Low flow rate moisture supply process Low flow rate moisture supply process

1998-12-09

2002-01-01

Langel, Wayne (Department: 1754)

Compositions

Gaseous compositions

C423S580100, C438S584000, C438S590000, C438S800000

Reexamination Certificate

active

06334962

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an improvement of a low flow rate moisture feeding system for use especially in the production of semiconductors by the low moisture oxidation technique. More particularly, the present invention relates to the accurately controlled generation and supply of moisture in very small quantities.
BACKGROUND OF THE INVENTION
In the manufacture of semiconductor elements, the conventional so-called dry oxygen (O
2
) oxidation technique for coating silicon oxide film by thermal oxidation is now largely replaced by the moisture oxidation technique, which is also called the wet oxygen oxidation method. That is because the silicon oxidation film formed by the moisture oxidation technique is superior to that obtained by the dry oxygen oxidation technique in properties such as insulation strength and masking effect.
Oxide film coating by the aforesaid moisture oxidation technique uses a mixed gas with a moisture content (H
2
O/O
2
) of, generally, approximately 20 to 30 percent. The amount of moisture to be mixed into oxygen is approximately 200 to 2000 cubic centimeters in terms of the standard state (“sccm”). That is, a relatively large quantity of moisture is fed from the reactor for the generation of moisture to the semiconductor manufacturing facilities.
FIG. 6
shows an example of the apparatus for the generation of moisture used in the moisture oxidation technique in current practice. In
FIG. 6
, H
2
represents hydrogen; O
2
, oxygen; N
2
, nitrogen gas for purging the system; MFC
1
to MFC
5
, mass controllers; V
1
to V
5
, valves; T
1
to T
6
, thermocouples for measuring the temperature; CV
1
to CV
5
, check valves; F
1
to F
3
, filters; H
0
and H
1
, gas preheater coils; Mx
1
, oxygen-hydrogen mixer; Mx
2
, oxygen-moisture mixer;
1
, the reactor for the generation of moisture; and SM, processing equipment such as semiconductor manufacturing facilities.
As shown in
FIG. 7
, the aforesaid reactor
1
for the generation of moisture comprises reactor structural components
2
and
3
provided with a gas supply joint
4
and a moisture gas take-out joint
5
, a reflector
9
on the inlet side provide inside the reactor
1
and opposite gas feed passage
4
a
of the reactor structural component
2
, a reflector
12
on the outlet side provided inside the reactor
1
and opposite a moisture gas outlet passage
5
a
of the reactor structural component
3
, a filter
10
provided in the middle of the reactor
1
, and a platinum-coated catalyst layer
13
provided on the inside wall of the reactor structural component
3
.
The platinum-coated catalyst layer
13
, which is formed on the inside wall surface of the reactor structural component
3
, is of a double layer construction, having a barrier coat
13
a
with a platinum coat
13
b
formed thereupon. The barrier coat
13
a
is formed of a nitride such as TiN, on which the platinum coat
13
b
is fixed by a vapor deposition technique or an ion coating technique.
Hydrogen and oxygen are fed into the reactor
1
through the gas feed passage
4
a
, diffused by gas diffusion means
8
comprising the inlet reflector unit
9
, the filter
10
, and the outlet reflector unit
12
, and then come into contact with the platinum-coated catalyst layer
13
. Upon coming into contact with the platinum-coated catalyst layer
13
, hydrogen and oxygen are enhanced in reactivity by catalytic action and come to be in what is called the radicalized state. Radicalized, hydrogen and oxygen instantaneously react with each other at a temperature lower than the ignition point to produce moisture (i.e., water) without undergoing combustion at a high temperature.
The flow rates of hydrogen and oxygen which are fed into the reactor
1
are set properly to, for example, 1000 sccm : 600 sccm or so. Generally, a 20 percent oxygen rich material gas mixture of oxygen and hydrogen is sent into the reactor. The gas supply pressure of oxygen and hydrogen is set to 1.0 to 3.0 kg/cm
2
to produce approximately 1000 sccm of moisture. The reactor
1
for the generation of
It is noted that the mass flow controllers MFC
1
to MFC
5
are generally constituted so that the flowing gas reaches a set flow rate as soon as possible. That is, the flow rate of the flowing oxygen or hydrogen gas rises to a set level within approximately one second after the start of the feeding of the gas.
The moisture generator illustrated in
FIG. 6
can produce over approximately 1000 sccm of high-purity water. The amount of moisture to be generated and supplied can be controlled relatively easily with high precision by regulating the feeding of oxygen and hydrogen. Thus, the generator is excellent in practical usefulness. However, that moisture generator has problems yet to be solved. Of these, the foremost problem is the control of the flow rate of moisture when it is to be generated in very small quantities.
In recent years, what is called the low moisture oxidation technique is being put to wide practical application in the silicon oxide film coating by moisture oxidation. This low moisture oxidation is practiced using the mixture gas of oxygen and water with a moisture content of 1000 ppm −2 percent.
The moisture generator illustrated in
FIG. 6
, too, is required to regulate the generation of moisture at a very low rate, that is, one to 50 sccm, with high precision. With the moisture generator outlined in
FIG. 6
, a variety of inconveniences arise and it is virtually impossible to control the generation of moisture at such a low rate, which will be described later.
Shown in
FIG. 8
is a testing apparatus developed to test the response characteristics or responsiveness of the reactor
1
for the generation of moisture. Experiments were conducted using this testing apparatus and the response characteristics of the reactor
1
for the generation of moisture were determined with the production of moisture kept at very low levels.
In
FIG. 8
, MFC
1
to MFC
3
indicate mass flow controllers; V
1
to V
6
, valves; SV, a suction-regulating valve; E, a quadrupole mass spectrometer (Q-mass spectrometer); P, a vacuum pump (rotary pump); D, a turbo molecular pump; and R, a moisture-collecting reservoir. Moisture is condensed at room temperature, and the condensed moisture is collected. The mass flow controllers MFC
1
to MFC
3
are moisture is 114 mm in outside diameter, approximately 31 mm in thickness, and 86 cm
3
in interior space with 99 cm
2
in a platinum-coated catalyst layer area. Though very small in size as shown, this reactor can turn out over 1000 sccm of moisture.
On the outlet side of the reactor is provided the aforementioned oxygen-moisture mixer Mx
2
where the moisture as generated can be mixed with oxygen in any desired ratio and diluted.
FIG. 6
illustrates an operation in which a 20 percent oxygen rich material gas mixture is fed into the reactor
1
. The reactor
1
can also be operated with a hydrogen-rich material gas mixture. In such an arrangement, a hydrogen-moisture mixer Mx
1
is provide instead of the oxygen-moisture mixer Mx
2
as necessary.
The aforesaid gas preheater coils H
0
and H
1
are for heating the material gas mixture or oxygen respectively at not higher than approximately 200° C. The reactor
1
is also provided with a heater and, as necessary, a cooler so that if the reaction heat pushes up the temperature in the reactor in operation to over 500° C. (which rarely happens), the cooler will be activated to bring down the temperature below 500° C. In addition, the mixture in the mixer Mx
2
provided near the outlet of the reactor is constantly maintained at approximately 120° C. to prevent water from condensing on the pipe wall. A heater is provided as necessary.
Prior to starting up the reactor
1
for the generation of moisture, such equipment as the mass flow controllers MFC
1
to MFC
5
and temperature controllers first are prepared for operation, and the valves V
2
and V
5
are opened, and the valves V
1
, V
3
, and V
4
are closed to purge the system with nitrogen gas. Then the valves V
2

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