Cleaning and liquid contact with solids – Processes – Including use of vacuum – suction – or inert atmosphere
Reexamination Certificate
2000-01-20
2002-03-19
El-Arini, Zeinab (Department: 1746)
Cleaning and liquid contact with solids
Processes
Including use of vacuum, suction, or inert atmosphere
C134S025100, C134S025400, C134S030000, C015S300100, C015S302000, C015S303000
Reexamination Certificate
active
06358328
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method and an apparatus for cleaning a wafer container and more particularly, relates to a method for dry cleaning a wafer container that is equipped with a bottom mounting plate covered with contaminating particles by first mounting the container in an enclosure and then blowing an inert gas or air on the bottom mounting plate and simultaneously withdraw by vacuum the inert gas or air that contains contaminating particles.
BACKGROUND OF THE INVENTION
In the recent development of semiconductor fabrication technology, the continuous miniaturization in device fabricated demands more stringent requirements in the fabrication environment and contamination control. When the feature size was in the 2 &mgr;m range, a cleanliness class of 100-1000 (which means the number of particles at sizes larger than 0.5 &mgr;m per cubic foot) was sufficient. However, when the feature size is reduced to 0.25 &mgr;m, a cleanliness class of 0.1 is required. It has been recognized that an inert mini-environment may be the only solution to future fabrication technologies when the device size is reduced further. In order to eliminate micro-contamination and to reduce native oxide growth on silicon surfaces, the wafer processing and the loading/unloading procedures of a process tool must be enclosed in an extremely high cleanliness mini-environment that is constantly flushed with ultrapure nitrogen that contains no oxygen and moisture.
Different approaches in modern clean room design have been pursued in recent years with the advent of the ULSI technology. One is the utilization of a tunnel concept in which a corridor separates the process area from the service area in order to achieve a higher level of air cleanliness. Under the concept, the majority of equipment maintenance functions are conducted in low-classified service areas, while the wafers are handled and processed in more costly high-classified process tunnels. For instance, in a process for 16M and 64M DRAM products, the requirement of contamination control in a process environment is so stringent that the control of the enclosure of the process environment for each process tool must be considered. This stringent requirement creates a new mini-environment concept. Within the enclosure of the mini-environment of a process tool, an extremely high cleanliness class of 0.1 (which means the number of particles at sizes larger than 0.1 &mgr;m per cubic foot) is maintained, in contrast to a cleanliness class of 1000 for the overall production clean room area In order to maintain the high cleanliness class inside the process tool, the loading and unloading sections of the process tool must be handled automatically by an input/output device known as a SMIF (standard mechanical interface) apparatus. A cassette of wafer can be transported into the process tool by a SMIF pod situated on top of a SMIF apparatus.
A conventional SMIF apparatus consists of a robotic transfer system or a robotic arm which is normally configured for gripping the top of a cassette from a platform on which the cassette is placed (inside a pod). The robotic arm, sometimes is replaced by a gripper assembly, is capable of transporting the cassette into the process tool and place it on a platform vertically such that the cassette is oriented horizontally. At the beginning of the process, an operator positions a SMIF pod on top of a SMIF arm port which contains a cassette for holding a large number of wafers in an upright position. The SMIF arm port then descends into the SMIF apparatus for the robotic arm to transport the cassette into the process tool. The SMIF system is therefore capable of automatically utilizing clean isolation technology to maintain a high class clean room effectiveness near wafers and processing equipment. The operation of the robotic arm or the gripper is controlled by an ancillary computer (not shown) or by the process tool. The cassette carries wafers or other substrates that are being processed.
Referring initially to
FIGS. 1A and 1B
, wherein the top view of a SMIF arm port
10
is shown in
FIG. 1A
while a bottom view of a SMIF pod
20
is shown in FIG.
1
B. In the bottom view of the SMIF pod
20
, a bottom mounting plate
22
is used for matching to the SMIF arm port
10
on its top surface
12
. At the beginning of a wafer loading process, an operator positions SMIF pod
22
on top of the SMIF arm port
10
. The mating process for the two surfaces
12
,
22
is carried out by human hands and therefore, friction between the two surfaces
12
,
22
cannot be avoided. To accomplish the mating process, the locating pins
14
on the SMIF arm port surface pod
12
must penetrate the apertures
24
on the bottom mounting plate
18
. A mechanical locking device
16
located on the top plate surface
12
of the SMIF arm port
10
must further be aligned with the pod lock alignment hole
26
on the bottom mounting plate
18
of SMIF pod
20
. During the mating operation of the two surfaces
12
and
22
, frictional forces between the surfaces generates particles in between the surfaces. The most likely areas that cumulate particles are areas close to the locating pins
14
and close to the pod lock
16
. For instances, the shaded areas
28
shown in
FIG. 1A
illustrate typical locations where particles contaminations occur.
While SMIF pods are normally cleaned in a wet cleaning process by utilizing deionized water or other cleaning solvents periodically during a preventive maintenance procedure. The wet cleaning is only used to clean the wafer cassette positioned inside the SMIF pod and the interior surfaces in the pod. Due to the presence of mechanical components in the SMIF arm port
10
and on the SMIF pod bottom mounting plate
20
, i.e., the pod lock
16
which is fabricated of metal, the SMIF arm port
10
and the bottom mounting plate
20
of the SMIF pod can not be cleaned in a wet cleaning process in order to prevent corrosion and other deteriorating effects caused by the cleaning solvent.
Presently, the surfaces on the SMIF arm port
10
and on the bottom mounting plate
20
of the SMIF pod can only be cleaned by manually wiping the surfaces with a dustless cleaning cloth, or with a dustless cleaning cloth wetted with isopropyl alcohol. However, the surface wiping method does not thoroughly clean the particles on the SMIF arm port or on the bottom mounting plate.
While other cleaning methods for the SMIF arm port and for the bottom mounting plate have been proposed, none of them is effective in correcting the particle contamination problem. For instance, others have proposed the use of adhesive tape to remove particles from the surfaces. However, residual adhesive from an adhesive tape left on the surfaces may cause more severe contamination problem. A rolling brush has also been used to remove particles from the bottom mounting plate of a SMIF pod, however, the brush generates electrostatic electricity which leads to further accumulation of particles.
It is therefore an object of the present invention to provide a method for cleaning a wafer container that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for cleaning the bottom mounting plate of a wafer container that does not require a wet cleaning process.
It is a further object of the present invention to provide a method for cleaning the bottom mounting plate of a wafer container that can be carried out either with or without wafers in the container.
It is still another object of the present invention to provide a method for cleaning the bottom mounting plate of a SMIF pod that can be easily carried out without causing a fabrication yield loss.
It is another further object of the present invention to provide a method for cleaning the bottom mounting plate of a SMIF pod that can be easily carried out by mounting the pod in an enclosure.
It is yet another object of the present invention to provide a method for cleaning the bottom mounting
Kuan Suan-Jun
Lee Ching-Ling
Liao Kuo-Hung
Yang Huai-Tei
El-Arini Zeinab
Taiwan SEmiconductor Manufacturing Company, Ltd.
Tung & Associates
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