Brushing – scrubbing – and general cleaning – Electrostatic cleaning
Reexamination Certificate
1998-11-20
2001-07-10
Graham, Gary K. (Department: 1744)
Brushing, scrubbing, and general cleaning
Electrostatic cleaning
C134S001000, C134S001300, C134S021000, C134S034000, C134S037000, C134S902000, C438S906000, C361S212000
Reexamination Certificate
active
06256825
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to the field of dust removal during semiconductor processing, more particularly to dust removal in loadlocks.
(2) Description of the Prior Art
The rapid development of the integrated circuit art, particularly the ability to form, with high process yield, many circuits on a single semiconductor wafer, has been due in part to the development of methods for controlling the levels of particulate contamination at all stages of the manufacturing process. While great pains are taken to ensure that no dust enters the process from outside the various processing chambers that are used, there still remains a problem with dust generated within these processing chambers themselves.
Particular attention has been paid in the prior art to dust that is generated as a byproduct of plasma processes. Dust particles, in general, are likely to carry an electrical charge, as witness the effectiveness of electrostatic precipitators. In addition, in a plasma environment, the opportunities for dust particles to acquire charges are even greater. This increases the likelihood that the dust particles will adhere to various exposed surfaces, including the surfaces of semiconductor wafers that are undergoing processing within the plasma environment.
Thus, several patents reflect the development, in the prior art, of methods for removing particulate contamination from semiconductor surfaces in a plasma environment. For example, Cuomo et al. (U.S. Pat. No. 5,298,720 March 1994) teach the design of electrode surfaces in a plasma apparatus to include grooves or tapers in which contaminating particles are preferentially trapped. Su et al. (U.S. Pat. No. 5,410,122 April 1995) remove particles that adhere to a semiconductor surface by inducing electric charges on this surface, to repel the particles away from the surface, and then removing the repelled particles by the application of a force parallel to the surface, such as by flowing gas across the surface.
A major limitation of these, and similar, patents is that they are restricted to the removal of dust resulting from plasma processes. Furthermore, the removal of the dust is performed in the plasma processing chamber itself. This means that modifications have to be made to the processing apparatus thereby introducing the possibility of reducing the efficiency of the process as presently practiced and/or as might be practiced in some new and improved manner in the future.
In the present invention, removal of the dust particles is not performed in the processing chamber, but in the loadlock that feeds or unloads the processing chamber. Such loadlocks are widely used as a buffer between the processing chamber and the atmosphere or another (different) processing chamber. Thus the present invention is not restricted to plasma processes nor is any modification of any processing apparatus required.
SUMMARY OF THE INVENTION
It has been an object of the present invention to provide apparatus and method for removing dust particles during semiconductor processing without having to modify any of the chambers used for such processing.
Another object of the present invention is that such dust removal be possible at a time when the processing chambers are being used, prepared or otherwise engaged.
These objects have been achieved by performing the dust removal function inside loadlocks instead the processing chambers. Dust removal, in a loadlock, is accomplished by first initiating a flow of gas over the wafer surface. Then a negative charge is induced at the surface for a period of time followed by the induction of a positive charge. This causes the charged particles to be repelled away from the surface, at which point they are swept away by the gas. To remove the electrically neutral dust particles, the induced surface charge is switched too rapidly for these particles to follow, so they are briefly repelled from the surface and then swept away by the gas.
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“Particles on Surfaces 1” Cooper et al. pp. 339-349, 1988.*
Strasser et al, “Reduction of Particles Contamination By Controlled Venting and Pumping of Vacuum Loadlocks”, Vac. Sci. Technol. A vol. 8, No. 6, pp. 4092-4097, Nov. 1990.*
Seto et al, “Fine Particulate Contaminant Control by the w/Photoelectron Method Under a Low Pressure Condition”, Nov. 1995.*
Rev. Sci. Instrum, vol. 66, No. 11, pp. 5348-5351.
Ackerman Stephen B.
Graham Gary K.
Saile George O.
Taiwan Semiconductor Manufacturing Company
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