Fluid handling – Systems – Dividing into parallel flow paths with recombining
Reexamination Certificate
1999-11-30
2001-10-30
Hepperle, Stephen M. (Department: 3753)
Fluid handling
Systems
Dividing into parallel flow paths with recombining
C126S253000, C431S170000
Reexamination Certificate
active
06308738
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a drafting apparatus, and more particularly, to a drafting apparatus disposed in a furnace to isolate and reduce the burning region.
2. Description of the Related Art
Thermal process is a very important technique in semiconductor fabrication such as annealing, thermal oxidation, and thermal diffusion. Currently, thermal fabrication equipment is categorized into a horizontal type and a vertical type. The operating theory of both types is similar. The follow description is thus taking the horizontal type as a example to introduce.
In
FIG. 1A
, a top view of a horizontal type thermal furnace is shown. The thermal furnace comprises an annealed quartz tube
110
, a 3-zone heating element
120
to heat the quartz tube
110
to a certain temperature, and an air injector
130
to inject air or gas into the quartz tube
110
to be heated. The 3-zone heating element
120
is a heater to heat a front end, a middle part, and a rear end of the quartz tube
110
, respectively, so as to adjust the heat distribution of the quartz tube
110
. A number of wafers
102
, for example, about 100 to 150 wafers, is disposed on an annealed quartz wafer boat
106
to be placed into the quartz tube
110
. By the heat provided by the 3-zone heating element, the quartz tub
110
is heated to a required temperature.
In a wet oxidation process, hydrogen (H
2
) and oxygen (O
2
) flow through two different intakes to the injector
130
. Hydrogen and oxygen mix with each other and are injected into the quartz tube
110
by the injector
130
. While igniting the mixture of hydrogen and oxygen, highly purified water steam is obtained to perform a wet oxidation process on the wafers
102
. The amount of hydrogen is adjustable to avoid that while the oxygen is consumed, the remaining hydrogen causes an explosion in the furnace.
FIG. 1B
schematically illustrates the injector
130
. Using an axis
100
as a reference, the injector
130
has a tilt angle &thgr;
1
for gas injection. Typically, the tilt angle &thgr;
1
is no more than 10°. While hydrogen is ignited, a high temperature oxy-hydrogen flame
132
and water steam are produced as shown in the figure.
As shown in
FIG. 1C
, to avoid the wafers carried aside on the wafer boat having a heat energy different from that of the wafers carried amid on the wafer boat
106
, dummy wafers
104
are disposed aside on the wafer boat
106
instead of wafer products, while wafers
102
are disposed enclosed by the dummy wafers
104
. Therefore, the heat energy is evenly and uniformly distributed to each wafer on the wafer boat
102
. The number of the dummy wafers
104
is typically between 6 to 10 as specifically required.
In the above mentioned furnace, the effective region of the oxy-hydrogen flame
132
is long. In order to provide a substantially equal temperature to each, the wafer boat has to be disposed in a long distance away from the oxy-hydrogen flame
132
, so that the temperatures of front end and the rear end of the wafer boat are substantially the same. In this manner, a large space is required. The amount of wafers to be carried in the wafer boat is limited to seriously affect the throughput of products.
However, the internal furnace temperature is difficult to control at all points, due to the long, effective region of the oxy-hydrogen flame
132
. The front end of the quartz tube
110
has a temperature very much different from the temperature of the rear end of the quartz tube
110
. As a consequence, the uniformity between wafers is reduced and disadvantageous to the subsequent fabrication process.
In addition, the effective region of the oxy-hydrogen flame
132
is not isolated from the wafers. The high temperature water steam is reacted with the wafers without being drafted. Thus, the reaction regions above the wafers are not uniform to affect the quality of the thermal process.
To solve the problem, an external ignition apparatus is developed. While the external ignition apparatus ignites, a high temperature wafer steam is lead into the quartz tube
110
. However, since the ignition apparatus is disposed externally, once the hydrogen explodes, the operators are directly in danger. In addition, while cleaning the furnace, the external ignition apparatus has to be detached first and installed after the cleaning process. The above described procedures are both time and labor consuming. Thus, it is not very applicable in terms of safety and efficiency.
In summary, the disadvantages of the conventional thermal process comprises:
1. The utility space is highly reduced to reduce the throughput of products, so that the fabrication cost is increased.
2. The uniformity of the heat region above the wafers is compromised, due to the long expanse of the oxy-hydrogen flame.
3. Alternatively, an external ignition apparatus is used to replace the oxy-hydrogen flaming system. The external ignition apparatus causes a great problem in safety for operators. Furthermore, the efficiency is poor.
4. The water steam flows in random direction, so that the reaction regions above the wafers are non-uniform to cause a quality problem of thermal process.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a drafting apparatus in a furnace to replace the conventional arrangement of dummy wafers. The utility space is effectively reduced, the throughput is enhanced. The furnace is thus more competitive in commerce. As used herein, the term “Drafting Apparatus” should be construed to mean “air flow apparatus”. In this regard, a “Drafting Apparatus” is merely a device that operates to alter or redirect the airflow in a space (e.g., a furnace).
It is another object of the invention to provide a drafting apparatus within a furnace to reduce the possibility of endangering human beings while operating.
It is yet another object of the invention to provide a drafting apparatus in a furnace. The water steam is drafted into a uniform flow, so that the reaction regions above the wafers are uniform to improve the quality of thermal process. To achieve these objects and advantages, and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention is directed towards a drafting apparatus in a furnace. A buffer board having a plurality of gas intakes is disposed in a front end of the drafting apparatus. A laminar flow board having a plurality of gas outtakes is disposed in a rear end of the drafting apparatus. A drafting region is enclosed by the drafting apparatus. The drafting region comprises at least one drafting board to draft and redirect the gas flow. A laminar flow is then obtained to flow through the outtakes on the laminar board.
The invention further provide a furnace for performing a thermal treatment. The furnace comprises a drafting apparatus as described above. Therefore, the furnace can be designed with a reduced dimension. The wafer boat can carry more wafers to perform the thermal treatment than the conventional furnace.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 3420267 (1969-01-01), Veazey
patent: 3737283 (1973-06-01), Nikles
patent: 5106453 (1992-04-01), Benko et al.
patent: 5212116 (1993-05-01), Yu
patent: 5248253 (1993-09-01), Philipossian et al.
patent: 5647945 (1997-07-01), Matsuse et al.
patent: 1904538 (1970-08-01), None
Chen Tony
Chu Eric
Liu Tien-Jui
Hepperle Stephen M.
Thomas Kayden Horstemeyer & Risley
United Microelectronics Corp.
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