Abrading – Abrading process
Reexamination Certificate
2000-02-03
2003-05-20
Banks, Derris H. (Department: 3723)
Abrading
Abrading process
C451S444000
Reexamination Certificate
active
06565419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a particle removing method for removing particles (dust) from a stage that holds a planar workpiece such as a semiconductor wafer, and a cleaning plate used according to the method.
2. Description of the Related Art
For processing or machining a planar workpiece (plate-like piece), normally, the plate-like piece is held on a stage having a flat placement surface. For example, during an electronic part manufacturing process for processing or machining a semiconductor wafer, the semiconductor wafer is locked or held on the stage according to a suction method by electrostatic force or vacuum suction method. The semiconductor wafer is held or locked on the stage during such processes as follows: a lithography process using a step-and-repeat photolithography system with demagnification or an electron-beam lithography system; a film handling process using a sputtering system, a deposition system, a chemical vapor deposition (CVD) system, and an etching system; an electric testing process for testing dies (chips) delineated on a semiconductor wafer using a prover and a tester; and a process for optically inspecting patterns drawn on a semiconductor wafer. Moreover, for manufacturing a panel for a liquid crystal display or plasma display, a glass substrate is locked or held on a stage in order to carry out various kinds of processing including patterning. A stage for holding a semiconductor wafer during the lithography process will be taken for instance in order to proceed to a further description. The present invention is not limited to this sort of stage. The present invention can be applied to any stage as long as the stage holds a planar workpiece (plate-like piece) for precise processing or machining.
FIG. 1
shows the basic structure of a wafer stage employed during the lithography process or the like. In
FIG. 1
, a stage
1
holds and locks a semiconductor wafer on the top thereof, and is placed on a Y-direction movable base
2
. The Y-direction movable base
2
is supported to be movable in a Y direction along movement grooves bored in an X-direction movable base
3
. The Y-direction movable base
2
moves in the Y direction when driven by a DC servomotor
5
. The X-direction movable base
3
is supported to be movable in an X direction along movement grooves bored in a base
4
, and moves in the X direction when driven by a DC servomotor
6
. Owing to this mechanism, the stage
1
is movable in the two, X and Y, directions. In practice, the stage
1
is movable in Z directions or vertical directions. A laser interferometer or the like for precisely measuring a magnitude of movement is included in the stage but is omitted herein.
For holding and locking a placed semiconductor wafer, a vacuum suction method or a suction method by electrostatic force is adopted.
FIG. 2
shows the schematic structure of a vacuum suction mechanism included in the wafer stage. As shown in
FIG. 2
, a plurality of holes is bored in the top of the stage
1
and communicating with a connection port via an air path
11
formed inside the stage
1
. The connection port is linked to a vacuum pump
15
by way of a hose
12
and an air valve
13
. After a semiconductor wafer
100
is placed on the top of the stage
1
, the air valve
13
is turned to select the vacuum pump
15
. This causes the vacuum pump
15
to operate (the vacuum pump is connected to a vacuum chamber). The interior of the air path
11
is depressurized accordingly. The semiconductor wafer
10
is then sucked onto the top of the stage
1
and locked. For collecting the semiconductor wafer
100
from the stage
1
, the air valve
13
is turned to select an exhaust path
14
. Outside air is introduced into the air path
11
. Consequently, the semiconductor wafer is freed from the vacuum suction mechanism. Thereafter, a vertical movement pin, which is not shown, formed on the stage
1
is moved upward. With the semiconductor wafer
100
thus moved upward, a wafer transportation mechanism receives the semiconductor wafer. For placing the semiconductor wafer
100
on the top of the stage
1
, the vertical movement pin is moved upward. In this state, the wafer transportation mechanism places the semiconductor wafer
100
on the vertical movement pin. After the wafer transportation mechanism withdraws, the vertical movement pin is moved downward. Consequently, the semiconductor wafer
100
is placed on the stage.
The foregoing vacuum suction mechanism is widely adopted as a suction mechanism for wafer stages. However, in a system in which a semiconductor wafer and a stage are held in a vacuum (depressurized) environment, such as an electron-beam lithography system, the vacuum suction mechanism is unusable. A suction mechanism utilizing static electricity is adopted.
Semiconductor devices have been considerably downsized in recent years. The occurrence of microscopic particles (dust) during a semiconductor manufacturing process greatly affects a yield of semiconductor devices. In general, the semiconductor manufacturing process is carried out in a very clean environment, or more particularly, in a clean room. Especially a lithography process for manufacturing semiconductor devices is required to achieve highly precise processing and is therefore carried out in a clean room of the highest level of cleanness. However, even when the processing is carried out in such an environment, it is impossible to perfectly prevent occurrence of particles. A decrease in the yield caused by adhesion of particles onto the top of a semiconductor wafer has been discussed mainly in the past. A method of removing particles from the air circulated within a clean room using a filter or the like has been adopted in the past. The standard stipulating the degree of cleanness of a clean room describes the number of particles existing in the air.
However, particles not floating in the air but adhering to the surface of a stage may be scattered into the air during placement or collection of a semiconductor wafer. It is highly possible that the particles may adhere to the surface of another semiconductor wafer and become a factor of the decrease in the yield. It is relatively small particles that may be scattered into the air during placement or collection of a semiconductor wafer. Such particles are scattered into the air during collection of a semiconductor wafer, and a semiconductor wafer to be exposed next is then supplied immediately thereafter. There is therefore a high possibility that the scattered particles may adhere to the surface of the next semiconductor wafer. This greatly affects the yield.
Moreover, relatively large particles are less likely to scatter than small particles. However, when a semiconductor wafer is placed on the surface of a stage to which the large particles adhere, if the semiconductor wafer is duly sucked, the flatness of the semiconductor wafer deteriorates due to the particles. FIG.
3
A and
FIG. 3B
show this condition. When the semiconductor wafer
100
is placed on the stage
1
having a particle
21
and is sucked as shown in
FIG. 3A
, the part of the semiconductor wafer lying on the particle
21
is higher than the other part thereof. This leads to deteriorated flatness. Besides, the semiconductor wafer
100
is deformed around the particle
21
during suction. If the particle is small enough, the deterioration in the flatness of the semiconductor wafer or the deformation thereof is negligible. For this reason, almost no measures have been taken to remove particles adhering to the surface of a stage.
However, semiconductor devices have been getting smaller in recent years. A numerical aperture (NA) offered by the step-and-repeat photolithography system with demagnification has reached 0.5 or more. Since a depth of focus is very small (shallow), even a small decrease in the flatness causes trouble. Moreover, the electron-beam lithography system offers a larger depth of focus than the step-and-repeat photolithography system with demagnification. T
Ishida Kazushi
Nishio Naoki
Takigawa Yukio
Yano Ei
Advantest Corporation
Banks Derris H.
Christie Parker & Hale LLP
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