Gas separation: processes – Filtering
Reexamination Certificate
2003-02-20
2004-12-28
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Filtering
C055S312000, C055S385600, C055S481000
Reexamination Certificate
active
06835233
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to fabrication of semiconductor integrated circuits on semiconductor wafer substrates and more particularly, to an apparatus and method for eliminating or reducing particle flux and contamination caused by flow of air between processing chambers of disparate pressures during semiconductor wafer processing.
BACKGROUND OF THE INVENTION
Generally, the process for manufacturing integrated circuits on a silicon wafer substrate typically involves deposition of a thin dielectric or conductive film on the wafer using oxidation or any of a variety of chemical vapor deposition processes; formation of a circuit pattern on a layer of photoresist material by photolithography; placing a photoresist mask layer corresponding to the circuit pattern on the wafer; etching of the circuit pattern in the conductive layer on the wafer; and stripping of the photoresist mask layer from the wafer. Each of these steps provides abundant opportunity for organic, metal and other potential circuit-contaminating particles to accumulate on the wafer surface as well as on the interior surfaces of the process chambers in which the processes are carried out.
As an example, CVD processes include thermal deposition processes, in which a gas is reacted with the heated surface of a semiconductor wafer substrate, as well as plasma-enhanced CVD processes, in which a gas is subjected to electromagnetic energy in order to transform the gas into a more reactive plasma. Forming a plasma can lower the temperature required to deposit a layer on the wafer substrate, to increase the rate of layer deposition, or both. However, in plasma process chambers used to carry out these various CVD processes, materials such as polymers are coated onto the chamber walls and other interior chamber components and surfaces during the processes. These polymer coatings frequently generate particles which inadvertently become dislodged from the surfaces and contaminate the wafers.
In semiconductor production, the quality of the integrated circuits on the semiconductor wafer is directly correlated with the purity of the fabricating processes, which in turn depends upon the cleanliness of the manufacturing environment. Furthermore, technological advances in recent years in the increasing miniaturization of semiconductor circuits necessitate correspondingly stringent control of impurities and contaminants in the plasma process chamber. When the circuits on a wafer are submicron in size, the smallest quantity of contaminants can significantly reduce the yield of the wafers. For instance, the presence of particles during deposition or etching of thin films can cause voids, dislocations, or short-circuits which adversely affect performance and reliability of the devices constructed with the circuits.
Particle and film contamination has been significantly reduced in the semiconductor industry by improving the quality of clean rooms, by using automated equipment designed to handle semiconductor substrates, and by improving techniques used to clean the substrate surfaces. However, as deposit of material on the interior surfaces of the processing chamber remains a problem, various techniques for in-situ cleaning of process chambers have been developed in recent years. Cleaning gases such as nitrogen trifluoride, chlorine trifluoride, hexafluoroethane, sulfur hexafluoride and carbon tetrafluoride and mixtures thereof have been used in various cleaning applications. These gases are introduced into a process chamber at a predetermined temperature and pressure for a desirable length of time to clean the surfaces inside a process chamber. However, these cleaning techniques are not always effective in cleaning or dislodging all the film and particle contaminants coated on the chamber walls. The smallest quantity of contaminants remaining in the chamber after such cleaning processes can cause significant problems in subsequent manufacturing cycles.
FIG. 1
illustrates a typical conventional integrated cluster tool
10
for the local multi-step processing of wafers
30
in the fabrication of integrated circuits on the wafers
30
. The tool
10
includes a pair of loadlock chambers
12
each of which receives a wafer cassette
32
loaded with wafers
30
. A wafer transfer robot
22
, provided inside a central transfer chamber
20
, individually unloads each wafer
30
from one of the loadlock chambers
12
and transfers the wafer
30
first to a wafer orientation chamber
14
and then sequentially to multiple processing chambers
16
. In the processing chambers
16
, a variety of semiconductor fabrication processes, including chemical vapor deposition, physical vapor deposition, ion sputtering and etching, for example, are carried out on each wafer
30
. The processes carried out in the processing chambers
16
are conducted under various pressures, depending upon the particular process parameters required for each process. Accordingly, a vacuum system (not shown) maintains the process chambers
16
typically at a lower pressure than the pressure that is maintained in the wafer transfer chamber
20
. These pressures are typically on the order of about 4-80 mTorr. After processing of each wafer
30
in the process chambers
16
is completed, the wafer transfer robot
22
places each wafer
30
in a cool down chamber
18
, and then, returns the wafer
30
to the cassette
32
in the other cool down chamber
12
. Finally, the cassette
32
is transported to another processing station (not shown) in the facility for further processing of the wafers
30
therein.
During sequential transfer of each wafer
30
from one processing chamber
16
to the next processing chamber
16
in the processing sequence, the wafer transfer robot
22
removes the wafer
30
from one processing chamber
16
, re-positions the wafer
30
in the transfer chamber
20
and then places the wafer
30
in the adjacent processing chamber
16
, respectively. As shown in
FIG. 2
, a wafer transfer gate opening
26
, which is reversibly closed by a gate door
28
, is provided in the chamber wall
24
that divides the transfer chamber interior
21
from the process chamber interior
17
of each process chamber
16
. During processing of each wafer
30
in the process chamber interior
17
, the gate door
28
is closed, as shown in phantom, to sustain partial vacuum pressures inside the process chamber interior
17
while typically maintaining a higher pressure in the transfer chamber interior
21
. Before transfer of the wafer
30
from one processing chamber
16
to the next processing chamber
16
, the gate door
28
is opened to expose the wafer transfer gate opening
26
so that the wafer transfer robot
22
can transfer the wafer
30
from the process chamber interior
17
and back into the transfer chamber interior
21
, prior to transfer of the wafer
30
into the next processing chamber
16
in the processing sequence.
As heretofore noted, during processing of the wafers
30
in each of the process chambers
16
, various polymer and other impurities have a tendency to accumulate on the chamber walls in the process chamber interior
17
. Upon opening of the gate door
28
, the higher-pressure air inside the transfer chamber interior
21
has a tendency to rush into the lower-pressure process chamber interior
17
. The flowing air dislodges particulate impurities from the chamber walls in the process chamber
16
, and these have a tendency to fall on the wafer
30
, potentially contaminating the devices being fabricated on the wafer
30
. Accordingly, a device is needed for slowly equalizing air pressures between chambers of disparate air pressures prior to opening a wafer transfer gate door between the chambers, in order to prevent the rush or flow of air from the higher-pressure chamber to the lower-pressure chamber that would tend to dislodge potential device-contaminating particles from the walls of the lower-pressure chamber.
An object of the present invention is to provide a method and device for gradually equalizing air or
Spitzer Robert H.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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