Heating – Work chamber having heating means – Having means by which work is progressed or moved mechanically
Reexamination Certificate
2001-07-30
2002-08-20
Lu, Jiping (Department: 3749)
Heating
Work chamber having heating means
Having means by which work is progressed or moved mechanically
C432S241000, C118S715000
Reexamination Certificate
active
06435865
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and a method for positioning gas injectors in a vertical furnace and more particularly, relates to an apparatus and a method for positioning a plurality of gas injectors in a mounting ring in a vertical furnace wherein the gas injectors may be self-positioned without mis-installation.
BACKGROUND OF THE INVENTION
In connection with processes used to manufacture semiconductor devices, such as integrated circuits, numerous process steps are carried out in a controlled environment at elevated temperatures. Such processes includes oxidation, diffusion, chemical vapor deposition and annealing. In order to realize elevated processing temperatures, semiconductor wafers are processed in an evacuated chamber, typically in a form of a quartz tube which is housed within a semiconductor furnace.
The most common type of semiconductor furnace is of the so-called “hot wall ” electric type which facilitates batch processing of semiconductor wafers. Furthermore, hot wall electric furnaces exhibit excellent temperature stability and precise temperature control. Modern hot wall diffusion furnaces are capable of controlling temperatures over the range of 300°-1200° C. to an accuracy of 0.5° or −0.5° C. Hot wall furnaces were initially designed as horizontal diffusion furnaces, however, more recently, vertical furnaces have gained favor because they present a number of advantages over their horizontal predecessors. These advantages include: elimination of cantilever or soft-landing since the wafers are held in a quartz boat which does not touch the process tube walls; wafers can be loaded and unloaded automatically; and, the clean room footprint of the system is somewhat smaller than that of the conventional horizontal configuration.
Vertical semiconductor furnaces of the type mentioned above employ a quartz tube which typically has a polysilicon coating when used for a deposition or annealing process. The polysilicon deposition reduces the power loss due to quartz reflection or radiation, and reduces the degradation of a boat occasioned by wet etching. Because semiconductor furnaces are subjected to high rates of usage and their components are exposed to harsh operating environments, periodic maintenance must be performed on various furnace components, including the quartz tube assembly.
In a vertical furnace, a plurality of gas injectors for flowing into the furnace a variety of process gases is also provided. The gas injectors are normally formed of quartz tubes and are positioned in a mounting ring at a bottom of the furnace. The gas injectors are normally formed in a “L” shape such that the horizontal portion of the “L” sits in a slot opening provided in the mounting ring while the vertical portion of the “L” stands perpendicularly to the mounting ring with a number of nozzle openings provided in the quartz tube for flowing a process gas therethrough. Several different process gases may be required for a single process. For instance, in a chemical vapor deposition process for forming silicon oxide, at least three gas injectors for feeding the three different gases are provided in the vertical furnace. During SiO
2
deposition, a first gas injector may be used for feeding silane gas into the chamber cavity, a second gas injector may be used for feeding N
2
O gas into the chamber cavity, while a third gas injector may be used to feed a carrier or a dilution gas of N
2
into the chamber cavity.
In a typical chemical vapor deposition process conducted in a vertical furnace, as many as 172 wafers may be stacked in a wafer boat and positioned in the chamber cavity. In order to accommodate a large wafer boat that carries as many as 172 wafers, a substantially tall furnace tube must be utilized. For instance, a vertical furnace tube as long as 150 cm may be necessary to allow the processing of a large number of wafers. During the furnace process, the positioning of the various gas injectors in the furnace cavity is therefore important not only from a quality point-of-view, but also from a process repeatability point-of-view. In order to carry out a consistent deposition process, the position of each gas injector for the particular process gas must be exactly the same during each batch of wafer processing. For instance, in SiO
2
deposition, the length of the plurality of gas injectors may range between about 60 cm and about 150 cm. A repeatable process can only be achieved by locating the plurality of gas injectors at exactly the same location each time the process is repeated on a different batch of wafers. The positioning, or the ability to self-positioning the plurality of gas injectors in a vertical furnace is therefore very important.
It is therefore an object of the present invention to provide a vertical furnace that is equipped with a plurality of gas injectors for processing wafers in the furnace cavity that does not have the drawbacks or shortcomings of the conventional vertical furnace.
It is another object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers that is capable of producing repeatable results.
It is a further object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a plurality of quartz gas injectors in “L” configuration is utilized.
It is another further object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a plurality of quartz gas injectors in “L” configuration each equipped with a stopper mounted on a horizontal portion of the injector is utilized.
It is still another object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a mounting ring which has a plurality of slot openings each with a different dimension for mounting the plurality of gas injectors is provided.
It is yet another object of the present invention to provide a vertical furnace that is equipped with self-positioning gas injectors for processing wafers wherein a plurality of slot openings of varying dimensions is provided in a mounting ring for the self-positioning of a plurality of gas injectors each equipped with a stopper mounted on the injector at a different location.
It is still another further object of the present invention to provide a method for mounting a plurality of gas injectors in a vertical furnace for processing wafers by first mounting a stopper to the plurality of gas injectors at a different position for each process gas such that the gas injectors are installed in the mounting ring at the same location repeatedly.
SUMMARY OF THE INVENTION
In accordance with the present invention, an apparatus and a method for positioning gas injectors in a vertical furnace with repeatable results such that the same gas injector is always installed at the same location are provided.
In a preferred embodiment, a vertical furnace that is equipped with self-positioning gas injectors for processing wafers is provided which includes a cylindrical-shaped tube that has a sealed top and an open bottom, the open bottom is sealable by an end cap; a cavity formed inside the cylindrical-shaped tube that has a size sufficient for a wafer carrier to be positioned therein; a mounting ring for positioning inside the cavity juxtaposed to the open bottom, the mounting ring has a substantially rectangular cross-section, a width in the radial direction, a thickness in the vertical direction, and a plurality of slot openings each opens to an outer periphery of the ring and each has a different depth cut into the width of the ring; and a plurality of gas injectors each formed in an “L” shape with a vertical portion and a horizontal portion in fluid communication with each, each of the horizontal portions has an inlet end and is provided with a stopper mounted on a bottom surface at a different location fo
Cho Guey-Shyung
Tseng Heng-Yi
Lu Jiping
Taiwan Semiconductor Manufacturing Co. Ltd.
Tung & Associates
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