Fluid handling – Systems – Multi-way valve unit
Reexamination Certificate
1996-11-12
2001-01-23
Fox, John (Department: 3753)
Fluid handling
Systems
Multi-way valve unit
C137S375000, C251S363000
Reexamination Certificate
active
06176265
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a pick-up tool for releasably holding an article such as a semiconductor wafer by using vacuum suction, and more particularly relates to a valve unit which is suitable for use in such a pick-up tool.
BACKGROUND OF THE INVENTION
Semiconductor devices are most often made by chemically and physically processing silicon wafers, and pick-up tools using vacuum suction are often used for handling the silicon wafers, instead of more conventional pincers. Such pick-up tools are required to be resistant to various chemicals and high temperatures which are used to etch or otherwise process the silicon wafers, and to be free from electrostatic charges because electrostatic charges can damage the silicon wafers. Examples of such pick-up tools are disclosed in Japanese patent publication (kokoku) No. 3-50672, and Japanese patent publication (kokoku) No. 5-75554.
A pick-up tool is equipped with a valve unit for controlling the vacuum suction, and the valve unit also must meet the above-mentioned requirements which are associated with the handling of silicon wafers. The valve unit typically includes a valve main body having a valve seat defined therein, and a valve member which is slidably received in the valve seat so that a passage defined inside the valve main body may be selectively opened and closed as required by turning or otherwise moving the valve member in relation with the valve seat. The valve member must be closely fitted in the valve seat so that a required fluid-tightness may be obtained, and it is essential that the valve main body has a sufficient rigidity not to deform and to maintain the fluid-tightness under substantial external forces. The material for the valve unit must be also capable of withstanding various chemical substances, moisture and temperatures of up to 250° C.
The requirements for the material of the valve unit can thus be summarized as given in the following.
(1) The material should be electroconductive so as to avoid electrostatic charging of the valve unit components which could cause damages to the silicon wafers and lead to deposition of foreign matters.
(2) The material should be resistant to chemical substances which are used for chemically processing and washing the silicon wafers, and should not release any metallic ions when subjected to such chemical substances.
(3) The material should be self-lubricating so that smooth operation may be ensured and emission of particles may be avoided even after long use.
One of the most preferred materials for such valve units as well as such article pick-up tools is fluoride resins such as tetrafluoroethylene. Fluoride resins can meet most of the required properties, but are relatively readily deformable. Therefore, when subjected to significant external forces, a valve unit made of a fluoride resin may not be able to operate smoothly or may lose fluid-tightness. In particular, the screws used for securing a fluoride resin member may become loose in time due to the combined effect of repeated application of fluid pressure and the lack of the mechanical strength of the fluoride resin material. Loosening of the screws, which are typically made of metal or alloy, is also a cause of the rusting of the screws because it increases the chance of exposing the screws to various chemical substances. Additionally, fluoride resins are less immune to electrostatic charging than other resin materials, and the article pick-up tool could become undesirably electrically charged as it is handled by hand.
Fluoride resins such as tetrafluoroethylene are also known to be unsuitable for injection molding and extruding, and are therefore not suited to be molded into complicated shapes.
BRIEF SUMMARY OF THE INVENTION
In view of such problems of the prior art, a primary object of the present invention is to provide a valve unit which is both mechanically and chemically stable.
A second object of the present invention is to provide a valve unit which is suitable for use in extreme environments which arise in the processing of semiconductor wafers.
A third object of the present invention is to provide a valve unit which is economical to manufacture, and reliable in use.
A fourth object of the present invention is to provide a valve unit which is suitable for use in a pick-up tool for handing semiconductor wafers.
According to the present invention, these and other objects are accomplished by providing a valve unit, comprising: a valve main body having a communication passage, and a valve seat defined in an intermediate part of the communication passage; a valve member received in the valve seat for selective communication of the communication passage; and a valve case which is injection molded around the valve main body; the valve member being provided with a valve stem extending out of the valve main body and the valve case.
Thus, the valve main body may be made of a material suitable for the operation of the valve member while the valve case may be made of a material suitable for ensuring a required mechanical strength of the valve unit. For instance, the valve main body may be made of a resin material having a self-lubricating property, and the valve case may be made of a resin material which is resistant to deformation. Also, the valve case may be made of a material suited to be molded into a desired complicated shape. This is particularly advantageous when the valve case is provided with a passage communicating with the communication passage of the valve main body for external communication.
In applications where the electrostatic charging of the valve body may become a problem, for instance in semiconductor wafer pick-up tools, the valve case may be made of a relatively electroconductive resin material. According to a preferred embodiment for such an application, the valve case is made of polyether-etherketone resin material mixed with carbon fibers while the valve main body is made of tetrafluoroethylene resin material.
Because the injection molding process can achieve a highly close attachment between the valve main body and the valve case, the leakage of fluid can be avoided. If the valve main body is provided with a plurality of grooves or projections for restraining relative deformation between the main body and the valve case, an even closer attachment between the two parts can be achieve. In particular, the valve main body can be favorably reinforced by the valve case so that the valve seat defined in the valve main body can be maintained even under significant external forces, and the satisfactory operation of the valve unit can be ensured at all times.
According to a preferred embodiment of the present invention which is suited to be installed in semiconductor wafer pick-up tools, the valve main body comprises a cylindrical member, the communication passage consisting of a longitudinal passage passed longitudinally through the cylindrical member, the valve seat being defined by a valve guide hole passed laterally across the cylindrical member. Typically, the valve member is slidably or rotatably received in the valve guide hole, and a valve stem extends out of the valve case coaxially with the valve guide hole. To achieve a close contact between the valve case and the valve main body, and to favorably reinforce the valve main body against deformation, an annular groove may be defined in a surface part of the valve main body surrounding the valve guide hole, and a pair of annular grooves may be formed circumferentially around the valve main body on either axial side of the valve guide hole.
According to a particularly preferred embodiment of the present invention, the valve member is slidably received in the valve guide hole, and a compression coil spring is interposed between a bottom end of the valve member and a bottom of the valve guide hole, the valve member being provided with an annular groove for selectively communicating with the communication passage. Furthermore, the valve case may be provided with an upstream passage communicating with one end the commun
Takahashi Kazuo
Takahashi Kiyoshi
Edwards Gary J.
Fox John
MacPherson Alan H.
Skjerven, Morrill, MacPherson, Franklin & Friel LLP
Takahashi Kiyoshi
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