Pipes and tubular conduits – With flow regulators and/or baffles – Restrictors
Reexamination Certificate
2000-10-30
2003-05-13
Mills, Gregory (Department: 1763)
Pipes and tubular conduits
With flow regulators and/or baffles
Restrictors
C427S008000, C427S248100, C216S059000
Reexamination Certificate
active
06561226
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus and method for semiconductor processing and more particularly, relates to a closed-loop controlled apparatus and method for preventing contamination in a semiconductor process chamber which includes an exhaust vent mounted to the process chamber such that the chamber may be continuously pumped during wafer loading and unloading, the vent is equipped with a reduced cross-sectional area for achieving increased fluid flow rate and a butterfly valve for adjusting the flow rate through the exhaust vent and for detecting when the vent is blocked by contaminating particles.
BACKGROUND OF THE INVENTION
In semiconductor processing, a large portion of the yield losses can be attributed to contaminations by particles and films of various nature. The contaminants may be organic or inorganic particles, films formed of polymeric bases, or other ionic based materials. The particles or films may be generated as byproducts in the reaction of reactant gases, by the surrounding environment, by the processing equipment or by the handling of manufacturing personnel. Some contaminants are particles or films generated from condensed organic vapors, solvent residues, photoresist or metal oxide compounds.
Typical problems and the detrimental effects caused by particle or film contaminants are poor adhesion of deposited layers, poor-formation of LOCOS oxides, or poor etching of the underlying material. The electrical properties and the stability of devices built on the semiconductor substrate may also be seriously affected by ionic based contaminants. The various forms of contaminants therefore not only reduce the product yield but also degrades the reliability of the devices built. For instance, contaminant particles can cause a device to fail by improperly defined patterns, by creating unpredictable surface topography, by inducing leakage current through a insulating layer, or otherwise reducing the device lifetime. It is generally recognized that a particle contaminant that exceeds one-fifth to one-half of a minimum feature size on a device has the potential of causing a fatal defect, i.e. a defect that causes a device to fail completely. A defect of smaller size may also be fatal if it falls in a critical area, for instance, a particle contaminant in the gate oxide layer of a transistor. In modern high density devices, such as a dynamic random access memory chip, the maximum allowable number of particle contaminants per unit area of the device must be reduced accordingly in order to maintain an acceptable yield and reliability.
One of the widely used processing techniques for semiconductor wafers is a low pressure chemical vapor deposition (LPCVD) technique. A LPCVD process can be carried out in an apparatus such as that shown in FIG.
1
. The LPCVD method has been widely used in the deposition of silicon nitride or TEOS oxide films on semiconductor wafers. In the method, a gas containing the structural elements of the film material to be formed is first fed into a chamber, followed by heating the gas mixture to induce a chemical reaction to deposit the desired film on the semiconductor substrate. In a conventional CVD method, a silicon nitride film can be deposited by a chemical reaction between silane (SiH
4
) and ammonia (NH
3
) at 1 ATM and a temperature of 700~900° C., or by a mixture of dichlorosilane (SiCl
2
H
2
) and ammonia at a reduced pressure and a temperature of 700~800° C.
As shown in
FIG. 1
, reactant gases of dichlorosilane
12
and ammonia
14
, each carried by a carrier gas of nitrogen, are fed into the process chamber
18
through the inner tubes
40
. The reaction gases are mixed at the bottom portion of inner tubes
40
. Manifold
16
provides inlets and outlets for the gases and is used as a pedestal support for the inner tubes
40
and the outer tubes
24
. The process chamber
18
is first evacuated by vacuum pump
20
prior to the reaction. A purge gas of nitrogen
22
is then used to fill the process chamber
18
and to drive out any residual gas left from the previous deposition cycle. A cold trap
26
maintained at sub-ambient temperature, e.g., of approximately 12~18° C., is used in the vacuum line to trap particles that cannot be pumped away. The manifold
16
is provided with a pressure sensor
28
which is connected via a conduit
30
to the manifold
16
at a pressure port
32
. A main valve
34
and pressure switches (not shown) are provided in the vacuum evacuation line for controlling the fluid flow. A vent line
48
is connected to the vacuum evacuation line for venting spent reactant gases through control valves
52
and
54
to the exhaust vent
56
.
After the reactant gases of SiCl
2
H
2
and NH
3
are mixed in the inner tube
40
, the gas mixture is flown into the process chamber
18
to deposit silicon nitride films on wafers held in a wafer boat (not shown). It has been observed that during the reaction between SiCl
2
H
2
and NH
3
, a reaction byproduct of NH
4
Cl is frequently produced. The ammonium chloride powder which is in a very fine powdery form causes a defect on the wafer surface known as nitride haze. It is believed that during a nitride deposition process, contaminating powder may be coated inside the conduit between the chamber
18
and the cold trap
26
, inside the conduit between the cold trap
26
and the gate valve
34
, inside the gate valve
34
, and inside the conduit between the gate valve
34
and the automatic pressure controller
20
. The powdery contaminant may then be siphoned back into the process chamber
18
during an unintentional back-flow process. The fine powder of ammonium chloride deposits on top of a wafer surface and forms a haze defect. The nitride haze, once formed, is very difficult to remove from the wafer surface. For instance, a wet scrubbing method by using a brush cannot remove the haze from the wafer surface. The nitride haze acts as an additional insulating layer on top of the silicon wafer and presents processing difficulties in subsequently carried out processes. One of such processing difficulties occurs in the formation of LOCOS oxide insulation. The nitride haze impedes the growth of LOCOS oxide. Similar contaminants have also been observed in a TEOS oxide deposition process with similarly undesirable results.
In an effort to reduce or eliminate the nitride haze problem, a bypass vent pipe has been used to bypass the gate valve and to provide continuous pumping of the chamber during wafer loading and unloading steps. Even though this method reduces somewhat the magnitude of the chamber contamination problem, the small vent tube used for bypassing the gate vale is frequently plugged with the contaminating particles. The cleaning of such tubes becomes a time and labor consuming process during a preventive maintenance procedure. It is therefore desirable to have a bypass vent pipe for use in such application that does not get plugged up and furthermore, it would be desirable to have a vent pipe that is capable of indicating when such blockage occurs so that the vent pipe may be serviced.
It is therefore an object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber that does not have the drawbacks or shortcomings of the conventional apparatus of a vent tube.
It is another object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber that utilizes an exhaust vent for bypassing a gate valve such that the chamber may be continuously pumped during wafer loading and unloading to prevent a back-flow of contaminating particles into the chamber.
It is a further object of the present invention to provide a closed-loop controlled apparatus for preventing contamination to a low pressure chemical vapor deposition chamber by utilizing an exhaust vent equipped with a reduced cross-sectional area such that a fluid flow rate through the area is signif
MacArthur Sylvia R
Mills Gregory
Taiwan Semiconductor Manufacturing Co. Ltd.
Tung & Associates
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