Handling: hand and hoist-line implements – Contact lens applicator
Reexamination Certificate
2001-07-27
2002-09-24
Kramer, Dean J. (Department: 3652)
Handling: hand and hoist-line implements
Contact lens applicator
C294S064200, C414S941000
Reexamination Certificate
active
06454327
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a wafer blade for picking up wafers during semiconductor fabrication processes and more particularly, relates to a wafer blade that is equipped with an impact-absorbing bumper along at least two edges of the blade for picking up wafers during semiconductor fabrication processes.
BACKGROUND OF THE INVENTION
Apparatus for polishing thin, flat semi-conductor wafers is well known in the art. Such apparatus normally includes a polishing bead 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 bead is rotated and oscillates the wafer over the polishing surface. The polishing bead is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing bead against the polishing surface can be adjusted as desired. The polishing bead is typically mounted on an elongated pivoting carrier arm, which can move the pressure bead between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure bead 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 bead and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure bead and wafer carried by the pressure bead to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing bead; 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 bead. 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
,
2
and
3
. 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
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. 2
, is in a pick-up position when the robot lowers the blade.
In a conventional chemical mechanical polishing apparatus, a cassette tub pin is used to fix the wafer cassette position inside the tub. The original design by the machine manufacturer is only one single pin for inserting into a cassette tub hole. The single pin is designed to hold the wafer cassette in position during the robot pick-up process of the wafer from the cassette. However, the cassette tub pin can easily fall off from the cassette tub hole and thus cause the wafer cassette position to shift away from its supposed position, i.e. at a 5.5° angle. When this happens, the robot blade
18
, when lowered to pick-up a wafer, as shown in
FIG. 3
, may collide with the wafer
20
and thus either damages the wafer or causes wafer breakage and thus the wafer becomes scrape. It is therefore important in the robot blade pick-up process that the blade does not damage the wafer when the blade accidentally touches or strikes the wafer due to either a mispositioning of the wafer cassette
10
or a misalignment of the robot blade
18
.
It is therefore an object of the present invention to provide a wafer blade for picking up wafers during a semiconductor fabrication process 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 that is equipped with an impact-absorbing bumper along at least two edges of the blade.
It is a further object of the present invention to provide a wafer blade that is equipped with an impact-absorbing bumper along at least two edges of the blade for protecting a wafer that the blade accidentally touches.
It is another further object of the present invention to provide a wafer blade that is equipped with an elastomeric bumper positioned along a periphery of the blade for protecting wafers that the blade accidentally touches.
It is still another object of the present invention to provide a wafer blade that is equipped with an elastomeric O-ring around a periphery of the blade for protecting wafers that the blade accidentally touches.
It
Kramer Dean J.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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