Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
2000-04-28
2001-07-24
Mills, Gregory (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S7230ER, C156S345420
Reexamination Certificate
active
06263831
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to treating a semiconductor wafer with a plasma or a glow discharge for dissociating a gas into reactive ionic and neutral species and, in particular, to a downstream etch using gas mixtures containing oxygen.
Plasma etch apparatus can be divided into two broad categories, downstream or remote etching and direct etching. In downstream etching, the semiconductor wafer is not immersed in the glow discharge, as it is in direct etching. The result is a somewhat more gentle treatment of the wafer because high frequency at high power is not coupled through the wafer. In either type of apparatus, it is known in the art to employ an oxygen bearing plasma for removing organic compounds such as photoresist or for oxidizing a semiconductor wafer.
More typically, oxygen is used in combination with other gases due to the highly reactive nature of oxygen. It is known in the art to add nitrogen or water vapor to oxygen in a downstream plasma cleaning chamber. A problem with these additives is that the energy necessary to dissociate a nitrogen molecule or a water molecule is much less than that necessary to dissociate an oxygen molecule. In the discharge zone, the applied energy is absorbed mostly by the water vapor or the nitrogen.
In the prior art, a power supply producing 1500 watts of microwave power was necessary to assure dissociation of the gas mixture. Much of this power is wasted in recombination away from the wafer. Often the reactive ions attack the chamber, or other components, thereby introducing undesirable contamination into the process.
A problem with either nitrogen or water vapor is that the molecules diffuse everywhere, including toward the source of oxygen, thereby contaminating the source. While one could adjust the relative flows of the gases, the mixture would be determined by the diffusion problem rather than by the most effective mixture for cleaning or oxidizing a wafer.
In view of the foregoing, it is therefore an object of the invention to provide apparatus for efficiently dissociating oxygen and an additive gas in a plasma.
Another object of the invention is to provide apparatus for producing reactive ionic and neutral species from a mixture of oxygen and an additive gas, without contaminating the source of oxygen.
A further object of the invention is to provide apparatus for producing an effective amount of reactive ion species and neutral species from a mixture of oxygen and an additive gas at an applied power as low as 50 watts.
SUMMARY OF THE INVENTION
The foregoing objects are achieved in this invention in which it has been found that a constriction or narrowing in the exhaust side of the discharge chamber containing oxygen localizes the oxygen plasma to the region of the constriction and isolates the oxygen plasma from the rest of the system. The constriction is smaller than or the same size as the lines supplying other gases and, at a pressure of 1-3 Torr, a constriction having an inside diameter of four mm. or less effectively isolates the source of oxygen from the rest of the system, thereby enabling mixtures of oxygen and lighter gases to be used in a downstream plasma system.
In one embodiment of the invention, the gases are dissociated separately and then combined in a mixing chamber. In another embodiment, oxygen is dissociated and then a lighter gas is added and the mixture is dissociated. In a preferred embodiment of the invention, the lighter gas is selected from the group consisting of water vapor and nitrogen.
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Dry Plasma Systems, Inc.
Hassanzadeh P.
Mills Gregory
Wille Paul F.
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