Special receptacle or package – Holder for a removable electrical component – Including electrical field – magnetic field – or static...
Reexamination Certificate
2000-01-20
2001-03-06
Sewell, Paul T. (Department: 3728)
Special receptacle or package
Holder for a removable electrical component
Including electrical field, magnetic field, or static...
C206S723000, C206S454000
Reexamination Certificate
active
06196391
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a container for holding articles made of an electrically insulating material and more particularly, relates to a container that is electrostatic discharge-free (ESD-free) for storing articles made of an electrically insulating material for preventing ESD damage.
BACKGROUND OF THE INVENTION
In the semiconductor fabrication process, a square cross-sectional or rectangular cross-sectional container made of a plastic material is frequently used to transport articles. These articles may include silicon wafers, reticles or other substrates used for building IC devices. A reticle is a transparent ceramic substrate that is coated with a metallic layer forming a pattern for an electronic circuit. It is generally used in an imaging step during a photolithographic process wherein a pattern of a circuit is reproduced on the surface of an electronic substrate, i.e., on a wafer surface.
A reticle can be constructed of any suitable transparent ceramic materials. One of the most commonly used material is quartz or silicon dioxide. A quartz reticle can be readily coated with a chrome layer at selective areas to reproduce an electrical circuit. The chrome metal layer may be formed by either a pure chromium or a chromium alloy. During a photolithographic imaging process, a light source is projected from one side of the reticle that is coated with the pattern such that the pattern can be reproduced on the surface of a wafer which is positioned on the opposite side of the reticle. The pattern for the electronic circuit coated on the reticle is frequently laid out in a 5
33
magnification. The true dimensions of the electronic circuit reproduced on the wafer surface can be obtained by suitably adjusting the optical lenses situated between the reticle and the wafer. Metallic coatings other than chrome may also be coated on the surface of the reticle for the circuit lay-out. However, chrome has been found to be an ideal material for its appearance of a brownish tone and its ease of identification by human eyes.
In a semiconductor fabrication facility, static electricity or electrostatic discharge frequently develops on surfaces of articles made of insulating materials when they are touched or rubbed by other insulating materials such as insulating gloves. The electricity is produced based on a triboelectricity theory. The discharge of the static electricity to machines and to human operators can cause damages to semiconductor wafers and process tools. Sometimes, it may even cause injury to a machine operator. In a semiconductor fabrication facility, it is therefore necessary to control ESD by grounding the machines, by controlling the relative humidity, or by building walls and floor coverings with slightly conductive materials such that electrical charges can be routed to ground. When the triboelectricity is suitably controlled, the control of dust and particulate contamination is also enhanced. For instance, the metal racks, pipe lines, cabinets, cables and rails are normally grounded in a facility to an equal potential bar or to a planar ground. The metal pedestals of the raised floor are then connected to the planar ground under the raised floor. To further enhance ESD protection, the metal framework of the clean room wall systems are also connected to the planar ground. Air ionization systems are frequently installed at selected locations in a fabrication facility, to provide additional ESD control.
Despite the elaborate efforts spent in grounding process machines and various facilities, ESD damages still occur in a fabrication facility. A typical example is the occurrence of ESD when an insulating material is shipped or transported in a container made of another insulating material. For instance, when a reticle is transported from a storage facility to a photolithography machine in a container, i.e., a pod, that is normally constructed of a thermoplastic material. Since the reticle itself is an insulating material, i.e., a quartz or other silicon dioxide materials coated with a chrome coating, when the pod is handled by machine operators wearing insulating gloves, the static charge on the pod drastically increases due to friction generated between two insulating articles. Since the pod is not equipped with an anti-electrostatic device, high static electricity cumulates on the surface of the pod. For instance, it has been confirmed that the static electrical field generated on a pod surface increases from 0.1 KV/inch to nearly 15 KV/inch when a polycarbonate pod is rubbed with PVC gloves. Such a high static electricity build-up on the surface of the pod immediately causes an electrostatic discharge between the pod and the reticle contained therein. When ESD occurs between the pod and the reticle, the pattern on the reticle surface is usually damaged to such an extent that it can no longer be used for imaging. Conventional air ionization devices installed at a fabrication facility are not useful for preventing such ESD damages.
Others have proposed techniques for controlling or minimizing ESD damages to reticles carried in plastic containers. For instance, anti-electrostatic-type plastic materials, such as Bayon® has been used for the construction of the pod. However, due to its high cost, this type of anti-electrostatic plastic material cannot be widely utilized in a fabrication facility. Still others have proposed the use of gloves that are made of a conductive material such as Propex® so that the generation of electrostatic discharge can be avoided. The high cost of the Propex® gloves prohibits its broad usage in the processing industry.
In some of the newer models of the reticle pods, the internal moving parts are provided with ESD metal mask shield to eliminate electrostatic discharge. However, there are no provisions for preventing a stepper mask pick-up arm from generating ESD during its movement in picking up a reticle. For instance, one of such stepper mask arm
60
is shown in FIG.
3
. During an attempt of the stepper mask arm
60
in picking up reticle
24
, the bottom surface
26
of the reticle inevitably slides on the tips of pedestals
22
, as shown in FIG.
1
.
Referring initially to
FIG. 1
where it is shown a cross-sectional view of a container equipped with a conventional reticle support system. The container
10
is constructed of a top lid
12
, a bottom lid
14
, a left sidewall
18
and a right sidewall
16
. The front and rear sidewalls (not shown) are constructed of similar materials, i.e., a thermoplastic material such as polycarbonate or polymethylmethacrylate. Pedestals
22
are positioned on the bottom lid
14
of the container for supporting a reticle
24
. The reticle
24
is normally constructed of a transparent ceramic material such as quartz or other types of silicon dioxide. On a surface
26
of the reticle
24
, a pattern
28
is formed by coating the surface with a suitable metallic material. The pattern
28
can be formed by one of many suitable metallic materials. A handle
32
is affixed to the top lid
12
of the container
10
for easy carrying by an operator. The d
2
value for the commercially obtained container is 3.365 cm.
The scratching of the reticle surface
26
during its removal procedure from the pod
10
can cause a serious contamination problem. As shown in
FIG. 2
, a plane view of the reticle
34
with two alignment marks
20
situated in the surface
26
. The position of the pedestals
22
for supporting the reticle
24
are shown in ghost lines. During the reticle removal process, the surface
26
is dragged on the tip of the pedestals
22
and therefore, not only the frictional force may cause scratching of the alignment marks
22
and thus cause misalignment, the frictional force on the surface
26
may also cause particle contamination from the reticle material. Moreover, electrostatic discharge may be generated by the friction between two electrically insulating articles, i.e., between the pedestal
22
and the quartz surface
26
.
It is therefore an object of the pr
Luong Shian
Sewell Paul T.
Taiwan Semiconductor Manufacturing Company Ltd
Tung & Associates
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