Combustion – Process of combustion or burner operation – Heating feed
Reexamination Certificate
2002-09-25
2004-04-27
Basichas, Alfred (Department: 3743)
Combustion
Process of combustion or burner operation
Heating feed
C431S161000, C431S354000
Reexamination Certificate
active
06726468
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to semiconductor manufacturing and, more particularly, to a diffusion furnace used in a diffusion process for forming an oxide film on a semiconductor wafer by thermal oxidation.
Diffusion furnaces have been used to form oxide films on semiconductor substrates. Some diffusion furnaces are configured to mix a dilution gas in an oxidizing gas such as water vapor, and thermally oxidize the mixture to form an oxide film on the semiconductor wafer. Various examples of oxide forming apparatus that employ diffusion furnaces are illustrated in
FIGS. 1-3
.
As shown in
FIG. 1
, a diffusion furnace apparatus
10
includes a torch heater
12
for heating H
2
from line
14
and O
2
from line
16
to a temperature that is higher than the ignition point for H
2
. Water vapor or steam is generated from the H
2
and O
2
in the external torch chamber
20
. A dilution gas is added to the water vapor via a dilution gas line
24
prior to entry into the furnace tube
26
for thermal oxidation to form the oxide film on one or more semiconductor wafers inside the furnace tube
26
. An exhaust
28
is provided for the gas to exit the furnace tube
26
. Because the dilution gas is colder than the steam, the mixing of the colder dilution gas with the steam may cause condensation.
FIG. 2
shows a diffusion furnace apparatus
30
which heats the dilution gas prior to mixing with the steam. For convenience, the same components have the same reference characters in
FIG. 2
as in FIG.
1
. In
FIG. 2
, a heated dilution gas line
34
introduces a heated dilution gas into the steam line prior to entry into the furnace tube
26
. This apparatus
30
, however, requires an additional heater and quartz piece to provide the heated dilution gas.
In another diffusion furnace apparatus
40
shown in
FIG. 3
, the dilution gas
42
is introduced through the H
2
line
14
or the O
2
line
16
. This approach is not desirable for forming thin oxides which require very low gas flow. The need to maintain a very low gas flow will cause the torch flame to be unstable and lead to flame out problems.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to providing a dilution gas in a diffusion furnace apparatus for forming an oxide layer on a semiconductor wafer. In some embodiments, the dilution gas is mixed with steam and the mixture is thermally oxidized to form the oxide film on the semiconductor wafer. The dilution gas is preheated prior to mixing with the steam to avoid condensation problems. The dilution gas is heated by an existing heater in the external torch chamber or combustion chamber used to produce the oxidizing gas such as steam, so that no additional heater is needed. The preheated dilution gas is mixed with the steam at the outlet of the external torch chamber or combustion chamber so as not to cause any disturbance to the stable flame in the chamber. The dilution gas flow desirably is sufficiently low so that it is possible to form a very thin oxide layer with uniform thickness.
An aspect of the present invention is directed to an apparatus for supplying a diluted process gas into a diffusion furnace for forming an oxide layer on a substrate in the diffusion furnace. The apparatus comprises a torch device configured to receive one or more inlet gases supplied by one or more inlet gas lines. The torch device includes a torch heater configured to generate an oxidizing gas by heating the inlet gases in a torch chamber disposed downstream of the torch heater. A dilution gas line is configured to receive a dilution gas. The dilution gas line extends through the torch chamber to permit heating of the dilution gas by the heat in the torch device without mixing the dilution gas and the oxidizing gas in the torch chamber. A mixing region downstream of the torch chamber is configured to receive and mix the oxidizing gas and the heated dilution gas prior to entry into the diffusion furnace.
In some embodiments, the oxidizing gas comprises steam generated from O
2
and H
2
in the torch chamber. The dilution gas is typically Ar or N
2
. The torch heater is configured to produce a flame in the torch chamber to generate the oxidizing gas from the inlet gases. The dilution gas line is configured to produce a dilution gas flow of at most about 20 slm.
Another aspect of the invention is directed to an apparatus for supplying a diluted process gas into a diffusion furnace for forming an oxide layer on a substrate in the diffusion furnace. The apparatus comprises an oxidizing gas chamber configured to receive one or more inlet gases supplied by one or more inlet gas lines, and a mechanism for heating the one or more inlet gases in the oxidizing gas chamber to generate an oxidizing gas. A dilution gas line is configured to receive a dilution gas. The dilution gas line extends through the oxidizing gas chamber to permit heating of the dilution gas by the heat in the oxidizing gas chamber without mixing the dilution gas and the oxidizing gas in the oxidizing gas chamber. A mixing region downstream of the oxidizing gas chamber is configured to receive and mix the oxidizing gas and the heated dilution gas prior to entry into the diffusion furnace.
Another aspect of the present invention is directed to a method of supplying a diluted process gas into a diffusion furnace for forming an oxide layer on a substrate in the diffusion furnace. The method comprises supplying one or more inlet gases into a chamber, and heating the one or more inlet gases in the chamber to generate an oxidizing gas. A dilution gas is flowed through a dilution gas line which extends through the chamber to permit heating of the dilution gas by the heat in the chamber without mixing the dilution gas and the oxidizing gas in the chamber. The oxidizing gas and the heated dilution gas are mixed downstream of the chamber prior to entry into the diffusion furnace.
In some embodiments, heating the one or more inlet gases comprises producing a flame from the O
2
and H
2
to generate the steam. The dilution gas flow rate is sufficiently low so that the dilution gas is heated to a temperature which is substantially equal to a temperature of the oxidizing gas before mixing the oxidizing gas and the heated dilution gas.
Another aspect of the invention is directed to a method of supplying a diluted process gas into a diffusion furnace for forming an oxide layer on a substrate in the diffusion furnace. The method comprises supplying one or more inlet gases into a chamber, and producing a flame in the chamber to heat the one or more inlet gases in the chamber to generate an oxidizing gas. A dilution gas is flowed through a dilution gas line which extends at least partially through the chamber to a location downstream of the flame to permit heating of the dilution gas by the heat in the chamber without mixing the dilution gas and the oxidizing gas at or upstream of the flame. The oxidizing gas and the heated dilution gas are mixed downstream of the flame prior to entry into the diffusion furnace.
REFERENCES:
patent: 5785762 (1998-07-01), Masuda
patent: 6221791 (2001-04-01), Wang et al.
patent: 6276926 (2001-08-01), Chen et al.
patent: 6348397 (2002-02-01), Ide
patent: 6348417 (2002-02-01), Moriyama
patent: 6365519 (2002-04-01), Kraus et al.
patent: 6372663 (2002-04-01), Yeh et al.
patent: 6391116 (2002-05-01), Moriyama
Ibrahim Kader
Joung Joon Ho
Pillai Umasangar V.
Basichas Alfred
SilTerra Malaysia Sdn. Bhd.
Townsend and Townsend / and Crew LLP
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