Conveyors: fluid current – Miscellaneous
Reexamination Certificate
1999-12-27
2001-11-13
Ellis, Christopher P. (Department: 3651)
Conveyors: fluid current
Miscellaneous
C406S191000, C406S088000
Reexamination Certificate
active
06315501
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a particle collecting apparatus which is employed in a transfer apparatus for transferring an object to be processed afloat within a transfer passage by means of an air stream, and particularly in an air stream transfer apparatus for transferring semiconductor wafers in a semiconductor manufacturing apparatus.
BACKGROUND ART
In semiconductor manufacturing apparatuses, transfer apparatuses are employed in order to transfer the semiconductor wafers between the processing apparatuses. Standard transfer apparatuses of this type are transfer apparatuses in which the semiconductor wafer cassette jig is loaded on a transfer carriage, and transfer apparatuses in which the semiconductor wafers are transferred one at a time by a robot arm. However, in such transfer apparatuses, the atmosphere of the space in which the semiconductor wafers are processed is not separated from the outside atmosphere, and the atmosphere of this space is not sufficiently clean. Recently, methods have been employed in which the semiconductor wafer cassette jig is placed in a sealed container for transfer; however, the problems of contamination from the container materials and the air tight gaskets and the like has not been solved.
For this reason, air stream transfer apparatuses which transfer semiconductor wafers through a transfer passage by means of an air stream (air bearing) have been experimentally produced, and such air stream transfer apparatuses enable a closed type (closed system) transfer passage, so that it is possible to attain a sufficiently high level of cleanliness in the atmosphere.
However, in the air stream transfer apparatuses, even if the structure is such as to contain no parts which give rise to contamination within the apparatus, so that a clean space may be maintained, there may be cases in which particles which have been brought in from the outside, for example, particles which have been deposited on the semiconductor wafers, are released within the apparatus.
Such particles present a problem in that they are then deposited on other clean semiconductor wafers. Additionally, in concert with the miniaturization and increase in functionality of the semiconductor integrated circuits and the like which are formed on these semiconductor wafers, the situation is such that, increasingly, almost no contamination or deposition of matter can be tolerated, so that this problem is important in view of an increase in the reliability of the semiconductor manufacturing apparatus and in the productivity (yield) of the semiconductor wafers.
The present invention was created in order to solve the problems described above; it has as an object thereof to provide a particle removing apparatus which is capable of preventing the deposition of particles on objects to be processed within a transfer passage.
DISCLOSURE OF THE INVENTION
The air stream transfer apparatus of the present invention is an air stream transfer apparatus for transferring an object to be processed by means of an air stream, characterized in that a transfer face and a transfer passage partition, which are faces to be cleared of dust and which together constitute a transfer passage, are made of an electroconductive material and each have a thin insulating layer on the surface thereof; a planar dust collecting electrode is opposed to an object to be processed; a mechanism is provided for bringing the dust collecting electrode and the faces to be cleared of dust close to each other while jetting air; and a mechanism is provided for applying voltages between the transfer face and the dust collecting electrode and between the transfer passage partition and the dust collecting electrode.
It is preferable that a semiconductor material having a surface resistivity within a range of 5×10
5
−10
8
&OHgr;·cm in the shape of a plate-shaped body or a film be employed as the dust collecting electrode described above.
It is preferable that the distance between the dust collecting electrode described above and the transfer face which is to be cleared of dust, and between the dust collecting electrode and the transfer passage partition which is to be cleared of dust, be less than 2.0 mm. A distance within a range of 0.2-0.5 mm is more preferable.
It is preferable that a circuit be provided which generates an electrical field between the transfer face, the transfer passage partition, and the dust collecting electrode described above, and that a power source apparatus be provided which is capable of selectively switching between a positive and negative applied electrical field.
It is preferable that the amount of air jetted during the removal of particles be made variable, so as to maintain the insulation by adjusting the very small gap between the dust collecting electrode and transfer face and transfer passage partition by means of an air layer.
An air stream transfer apparatus of the present invention is an air stream transfer apparatus for conveying objects to be processed by means of an air stream, characterized in that a transfer face and a transfer passage partition, which are faces to be cleared of dust and which together constitute a transfer passage, are made of an electroconductive material and each has a thin insulating layer on the surface; a mechanism for transferring a pre-charged semiconductive plate-shaped body afloat along the transfer passage is provided, and a semiconductive plate-shaped body is used as the dust collecting electrode.
The particles which enter into the apparatus are affected by various forces, such as gravity, Brownian motion, inertial motion, static electric force, Brownian dispersion, vander Waals forces, and the like, and are deposited on the transfer face and the transfer passage partition. If the particle size is one micrometer or less, it becomes extremely difficult to remove such particles under dry processing conditions while maintaining a highly clean atmosphere. Among methods for such removal while maintaining a highly clean atmosphere, electrostatic force (Coulomb force) is the most powerful; however, experimental results show that such removal is difficult, irrespective of the particle material (good conductors such as metals or the like, semiconductors, non-conductors, or resins).
In order to remove particles using electrostatic force, it is necessary to weaken the force of adhesion in advance and to make the particles easily charged by electrostatic induction.
As a result of experimentation, it has been determined that by employing conductive materials having thin oxide film insulating layers formed thereon, and by applying an electric field to the particles on the surface of the insulating layers, removal by means of electrostatic force is facilitated. In such a case, it is thought that the various forces acting on the particles which are described above are weakened.
Examples of conductive materials having insulating layers formed thereon which are capable of maintaining a highly clean atmosphere include, for example, those in which Al
2
O
3
is formed on the surface of highly pure aluminum or an aluminum alloy material, which avoids heavy metal contamination and involves little release of moisture or other gases, and those in which Cr
2
O
3
is formed in a thickness within a range of 5-10 micrometers on the surface of stainless steel SUS316L. Nitrides are acceptable in place of oxides.
Among insulating materials, those with high dielectric constants are polarized by electric fields and interfere with the release of particles, and further weaken the Coulomb force, so that dielectric substances are not appropriate.
When particles are captured at the dust collecting electrode by electrostatic force, those particles having a resistivity of less than 10
5
&OHgr;·cm lose their charge, and an electrostatic attractive force in the opposite direction acts on these particles by electrostatic induction from the electrical field and they move in the direction of the transfer face and transfer passage partition, and recharging and recapturing is repeated,
Toda Masayuki
Umeda Masaru
Yagai Michio
Dillon, Jr. Joe
Ellis Christopher P.
Kabushiki Kaisha Watanabe Shoko
Knuth Randall J.
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