Internal Split Faraday Shield for an Inductively Coupled Plasma Source

Abstract

An inductively coupled plasma source for a focused charged particle beam system includes a conductive shield within the plasma chamber in order to reduce capacitative coupling to the plasma. The internal conductive shield is maintained at substantially the same potential as the plasma source by a biasing electrode or by the plasma. The internal shield allows for a wider variety of cooling methods on the exterior of the plasma chamber.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates to inductively-coupled plasma ion sources for focused beam systems.BACKGROUND OF THE INVENTION[0002]Plasma ion technology is commonly used for semiconductor wafer processing. Ion sources designed to process an entire semiconductor wafer are required to provide a uniform beam of ions over a broad area, such as over a 300 mm wafer. One application of such plasma systems would be to remove photoresist. The plasma produces a reactive species, such as monatomic fluorine or oxygen, that reacts with the photoresist to turn it to ash, which is subsequently removed by the vacuum pump. Because the ashing is performed by a reactive species, rather than by sputtering, the energy of the ions impacting the work piece can be relatively low and the voltage difference between the interior of the plasma chamber and the work piece is generally low.[0003]The requirements for plasma sources used in focused beam systems, such as a scanni...

AI Technical Summary

Benefits of technology

The present invention provides a new structure for a specific task. The technical effects of the invention include improved efficiency, better performance, and reduced costs. These benefits can be achieved by modifying or designing other structures based on the same principles as the invention. Additionally, the patent allows for the creation of equivalent constructions that meet the same requirements as the invention.

Problems solved by technology

The electrical isolation of the high voltage plasma creates several design problems that are difficult to solve in light of other goals for a plasma source design.

For example, it is desirable to place the radio frequency coils that provide power to the plasma as close as possible to the plasma to efficiently transfer power, but having a difference in voltage across a small distance leads to arcing, which can damage the system.

This solution, however, would require maintaining the power supply for the coil at the high plasma potential, which would excessively complicate the power supply design and greatly increase the cost.

When the Faraday shield is located close to the dielectric plasma container, the large electric field caused by the voltage difference between the grounded shield and the plasma being biased to the necessary accelerating voltage (e.g. 30 kV) causes the possibility of a high voltage discharge which could damage the source.

The presence of air trapped between the Faraday shield and the ceramic also causes the potential for arcing in that region.

The introduction of the Faraday shield between the plasma chamber and the antenna also inevitably leads to the antenna being placed further away from the plasma vessel, which can cause complications including arcing from the antenna to the shield and from the shield to the plasma.

Furthermore, Faraday shields may have sharp edges which cause additional high voltage management concerns.

Not only is high voltage management a design challenge for a plasma source for a focused ion beam system, heat management is also a challenge.

The high voltage can also make cooling difficult, which can limit the density of the plasma used.

These conflicting requirements make the design of an ICP source very challenging.

The Faraday shield can complicate the cooling methods.

Fluids in contact with the shield must not erode or oxidize the shield, and the choice of cooling fluid may also be limited by the dielectric concerns associated with the high voltage management at the sharp edges of the Faraday shield.

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