Thermophoretic vacuum wand

Details Thermophoretic vacuum wand Thermophoretic vacuum wand

2000-03-23

2001-05-15

Jeffery, John A. (Department: 3742)

Electric heating

Heating devices

Tool or instrument

C219S228000, C219S521000, C294S064200, C279S003000, C269S021000, C438S795000

Reexamination Certificate

active

06232578

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to tools for grasping objects, and more particularly, to a vacuum wand used to grasp silicon wafers during the manufacture of integrated circuits whereby the amount of particle contaminants that deposit onto the silicon wafer as it is being held is reduced or eliminated.
BACKGROUND OF THE INVENTION
Integrated circuits are manufactured on thin silicon wafers which are circular in shape and typically range in diameter from four to twelve inches. The wafers undergo many different processes during the overall manufacturing cycle, and each process may be performed by a different machine in cleanrooms. It is critically important during the entire cycle that the wafers be kept as clean as possible, and that they be handled as carefully as possible to avoid damaging the integrated circuits thereon. Therefore, wafers must be transported with the utmost care from machine to machine within a clean-room manufacturing facility.
Much of the transporting of wafers during the manufacturing process is performed by automated transporters. Robotic arms remove the wafers from each processing machine and place them in a transportation rack. The rack is moved to the next processing machine where another robotic arm removes the wafers from the rack and places them in the machine. Generally, if all components maintain proper alignment in the wafer-transportation system, the entire cycle can be handled automatically. Sometimes, however, it is necessary for human intervention and, therefore, the manual grasping and transportation of wafers. Vacuum wands are used to manually transfer wafers, masks, and the like.
Current state-of-the-art cleanrooms are designed to exclude particles greater than ~0.2 micron diameter in ambient air. However, as the minimum electronic feature size decreases, so does the critical size of “killer particles.” Since it is estimated that there are about 100 times more 0.05 micron particles than there are 0.2 micron particles in, for example, a Class 100 cleanroom, it is more difficult to prevent such small particles from contaminating sensitive surfaces.
SUMMARY OF THE INVENTION
The invention is directed to an improved vacuum wand device that is particularly suited for transporting articles such as wafers and masks in a cleanroom environment so that potential particle contaminants in the air do not become adhered to the surface of the article. The invention is based in part on the recognition that heating the article will effectively prevent particles in the air from depositing on the article.
Accordingly, in one aspect, the invention is directed to a vacuum apparatus, for grasping objects having a surface to be protected from particle contaminants in an environment containing particle contaminants, that includes:
a housing having a platen with a surface adapted to receive the object;
at least one suction port defined through the platen;
means for applying a negative pressure to at least one suction port; and
means for heating the object.
With prior art vacuum wands, the article, e.g., wafer or mask, that is being held and transported will collect particle contaminants. The invention employs the phenomenon known as thermophoresis in which particles, residing in a gas supporting a temperature gradient, are driven away from warm surfaces toward cooler surfaces. Thermophoresis can counteract particle contamination by diffusive, electrostatic or gravitational deposition. Thermophoresis can significantly reduce (or eliminate) the amount of particle deposition on the surfaces of the heated article.
If portability is important, the wand may be heated with an attached heating element (e.g., thermoelectric heater) that is powered by a rechargeable battery. This arrangement would allow the wand to be used without an attached power cord, although a grounding wire would be desirable.


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Nazaroff, W.W., et al. “Particle Deposition from a Natural Convection Flow onto a Vertical Isothermal Flat Plate”J. Aerosol Sci., vol. 18, No. 4, pp. 445-455.

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