Material or article handling – Device for emptying portable receptacle – Nongravity type
Reexamination Certificate
2001-08-10
2003-05-13
Bratlie, Steven A. (Department: 3652)
Material or article handling
Device for emptying portable receptacle
Nongravity type
C414S225010, C414S941000, C294S064200
Reexamination Certificate
active
06561744
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to an apparatus for picking up wafers from a water tank and a method for using the apparatus and more particularly, relates to an improved wafer blade for picking up wafers immersed in a water tank that does not have the problem of having a wafer sticking to the backside of the wafer blade due to capillary reaction of water and a method for using the improved wafer blade.
BACKGROUND OF THE INVENTION
Apparatus for polishing thin, flat semi-conduct or wafers is well known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is “planarized” or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
The CMP method can be used to provide a planner surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An outer layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing, a metal oxide layer can be formed and removed repeatedly.
During a CMP process, a large volume of a slurry composition is dispensed. The slurry composition and the pressure applied between the wafer surface and the polishing pad determine the rate of polishing or material removal from the wafer surface. The chemistry of the slurry composition plays an important role in the polishing rate of the CMP process. For instance, when polishing oxide films, the rate of removal is twice as fast in a slurry that has a pH of 11 than with a slurry that has a pH of 7. The hardness of the polishing particles contained in the slurry composition should be about the same as the hardness of the film to be removed to avoid damaging the film. A slurry composition typically consists of an abrasive component, i.e, hard particles and components that chemically react with the surface of the substrate. For instance, a typical oxide polishing slurry composition consists of a colloidal suspension of oxide particles with an average size of 30 nm suspended in an alkali solution at a pH larger than 10. A polishing rate of about 120 nm/min can be achieved by using this slurry composition. Other abrasive components such as ceria suspensions may also be used for glass polishing where large amounts of silicon oxide must be removed. Ceria suspensions act as both the mechanical and the chemical agent in the slurry for achieving high polishing rates, i.e, larger than 500 nm/min. While ceria particles in the slurry composition remove silicon oxide at a higher rate than do silica, silica is still preferred because smoother surfaces can be produced. Other abrasive components, such as alumina(Al
3
O
2
) may also be used in the slurry composition.
When a wafer surface is planarized by a CMP process, the wafer may have to be transferred between various CMP process stations before the planarization can be completed. During the transfer of the wafer between various CMP stations, the wafers are stored in a wafer storage cassette in a vertical position and the whole cassette is then positioned in a water tank such that the wafers are immersed in water to prevent the slurry solution left on the wafer surface from drying or solidifying. This is an important process step since if the wafers are not stored immersed in water, the solidified particles on the wafer surface becomes a contaminated source and may cause serious scratching of the wafer surface during the subsequent CMP operation.
A cassette tub is normally used for holding at least one wafer cassette, i.e. holding four wafer cassettes, in a tilted position for accessing by a robot blade, as shown in
FIGS. 1 and 2
. A wafer cassette
10
is positioned in a cassette tub
12
at a tilt angle of about 5.5° as measured from the horizontal plane, i.e. the bottom wall
14
of the tub. A robot arm
16
operating a robot blade
18
is used to pick-up wafers
20
that are stored in the wafer cassette
10
. The wafers
20
are positioned in slots (not shown) formed on the interior sidewall of the wafer cassette
10
. For instance, the robot blade
18
, shown in
FIG. 1
, is in a pick-up position when the robot lowers the blade.
A typical construction of the conventional robot blade
18
is shown in
FIGS. 3A and 3B
.
FIG. 3A
is a plane view of the front side
12
, i.e, the wafer pick-up side of the wafer blade
18
, while
FIG. 3B
is a plane view of the backside
14
of the wafer blade
18
. As shown in
FIG. 3A
, the wafer blade
18
is constructed in a generally elongated rectangular shape that has a first thickness of about 2 mm, or in a range between about 1.5 mm and about 3 mm, with a recessed vacuum port
22
that is covered with an elastomeric material layer
24
on top. The recessed vacuum port has an opening
26
that is in fluid communication with a vacuum passageway
28
, shown in FIG.
3
B. The vacuum passageway
28
is further in fluid communication with a vacuum inlet
30
which is connected to an external vacuum source (not shown).
In the configuration shown for the conventional wafer blade of
FIGS. 3A and 3B
, the surface
32
of the backside
14
of robot blade
18
is a smooth metal surface (such as a surface of aluminum) such that when the wafer blade
18
reaches into a wafer cassette
10
which is immersed in water to pick up a wafer
20
, the backside
14
of the blade can easily stick to another wafer
20
that is situated behind the wafer to be picked up by a capillary reaction of water entrapped between the wafer
20
and the smooth backside surface
32
. This is shown in FIG.
2
. When such wafer pick-up occurs on the backside of the wafer blade
18
, the wafer
20
that is picked up on the backside may fall off the wafer blade
18
as the blade leaves the wafer cassette, i.e. or the water tank, and thus causing the wafer
20
to break or to be seriously damaged.
It is therefore an object of the present invention to provide a wafer blade for picking up wafers that are immersed in a water tank that does not have the drawbacks or shortcomings of the conventional wafer blades.
It is another object of the present invention to provide a wafer blade for picking
Bratlie Steven A.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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