Electricity: electrical systems and devices – Discharging or preventing accumulation of electric charge – By charged gas irradiation
Patent
1993-02-24
1997-04-15
Shoop, Jr., William M.
Electricity: electrical systems and devices
Discharging or preventing accumulation of electric charge
By charged gas irradiation
361230, 361231, H05F 306
Patent
active
056216050
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a neutralizing apparatus used to neutralize a charged body such as a substrate (a wafer) or carrier in manufacturing process of semiconductor devices because the substrate, the carrier or the like is so easily charged and should be kept away from charged condition.
TECHNOLOGICAL BACKGROUND
In conventional manufacture of semiconductor devices, it is well known to perform, for example, transportation of a wafer from one processing room to the other processing room through a dedicated path or directly so as to perform a predetermined sequential processing to the wafer. In this case, there are many opportunity to perform a variety of handling such as grasping, or transportation of the wafer. In particular, instruments and the like contacting the-wafer during handling are generally made of fluorocarbon resin, quartz or the like so as to avoid the wafer from being contaminated by metal. Therefore, when the wafer contacts the instruments, the wafer tends to be positively charged and to be at a high potential because of the electrification rank relationship with respect to the instruments.
The wafer is charged positively or negatively according to electrification rank of the contacting material with respect to the wafer as follows: the wafer is charged within a range from +500 to +3300 [V] when grasping the wafer by a pincette made of fluorocarbon resin, and is charged within a range from +600 to +2000 [V] when mounting the wafer on a stand made of polypropylene. Further, the wafer is charged within a range from +1000 to +1500 [V] when mounting the wafer on a quartz plate by using the pincette made of fluorocarbon resin, and is charged within a range from +500 to +3300 [V] when washing the wafer by extrapure water. Moreover, the wafer is charged within a range -200 to -1000 [V] when spraying gaseous nitrogen on the wafer.
However, if the wafer or the carrier is charged, suspended particles may be adhered to the wafer or the carrier by electrostatic force, or the semiconductor devices, during manufacturing, may be destroyed due to electrostatic discharge.
FIG. 9 illustrates the amount of suspended particles adhered by the electrostatic force to the wafer per surface potential of the wafer. There is shown the result of experiment in which a 5 inch wafer is employed as the wafer, and the wafer is vertically mounted through an insulating stand on a conductive grating. In FIG. 9, the transverse axis shows a potential of the wafer, and the ordinate shows the number of adhering particles. Here, the number of adhering particles means the number of particles adhering to effective area of the wafer (which is 69.4 [cm.sup.2 ] for a 5 inch wafer). It will be appreciated that the number of the adhering particles is converted to the number of particles adhering to the effective area, provided that the wafer is left for five hours in an atmosphere containing ten particles having a particle diameter of 0.5 [.mu.m] or more per unit volume (cubic feet).
Referring to FIG. 9, there is little accumulation of particles due to gravity settling in case the wafer is vertically mounted. Accordingly, no particle adheres to the wafer when the wafer potential is low, i.e., at a range of 0 to 50 [V]. However, the number of the adhering particles is rapidly increased due to the effect of electrostatic force as the wafer potential rises in a range of 300 to 1800 [V].
FIG. 10 illustrates an adhering range of the suspended particles by the electrostatic force with a particle diameter used as a parameter provided that high voltage (1000 [V]) is applied to the wafer W. In this case, a particle concentration is set to 1 [g/cm.sup.3 ]. Further, in FIG. 10, the rectangular closing line shows potential 0, the dotted lines in the closing line show equipotential lines, and the solid lines show lines of electric force.
Referring to FIG. 10, there are little particles adhering to the wafer when particles have a particle diameter of 2 [.mu.m]. As the particle diameter is decreased to 0.5 [.mu.m] or
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Inaba Hitoshi
Ohmi Tadahiro
Ganjoo Peter
Ohmi Tadahiro
Shoop Jr. William M.
Takasago Netsugaku Kogyo Kabushiki kaisha
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