Focused electron and ion beam systems

Details Focused electron and ion beam systems Focused electron and ion beam systems

2002-08-30

2004-07-27

Lee, John R. (Department: 2881)

Radiant energy

Ion generation

Field ionization type

C250S424000, C250S427000, C315S111810, C315S111910

Reexamination Certificate

active

06768120

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates generally to electron and ion beam systems and more particularly to electron and ion beam systems based on plasma ion sources.
Conventional focused electron beam systems (such as the electron microscope) are large in size. They operate with thermionic cathodes and are normally designed for single beam operation with fixed beam spot size and energy. The lifetime and throughput current are limited by the cathode capability.
Accordingly it would be desirable to have a focused electron beam system which has a very compact size, a long lifetime, a small but variable spot size, a high current density, and a beam energy of a few to tens of kV.
A new type of instrument, a Dual Beam FIB (Focused Ion and Electron Beam) system has been developed recently which uses a focused Ga
−
ion beam for high-rate sputtering of material and a scanning electron beam for imaging. The tool can be used in surface treatment for high-resolution imaging in nanomaterial characterization, in TEM sample preparation, and for failure analysis in the semiconductor industry. This system is bulky and uses a liquid metal ion source which leaves a lot of unwanted residues on the target sample.
Accordingly, it would be desirable to have a system which avoids the use of a liquid metal source of Ga
−
ions.
It also would be desirable to have a system that has an accelerator column which is very compact, thus making it moveable and exchangeable.
It further would be desirable to have a system in which the same gun can be used to generate focused electron beams as well as molecular and negative ion beams in addition to positive ion beams.
SUMMARY OF THE INVENTION
The electron beam system of the invention is very compact and has a long lifetime. The system is based on a plasma generator in a plasma ion source with an accelerator column. The electrons are extracted from a plasma cathode in a plasma ion source. An accelerator column following the plasma ion source has a length down to about 1 cm. The total length of the system can be less than 10 cm. The beam spot size is less than 60 nm and can be varied, and the current density can be higher than 7×10
4
A cm
2
. The accelerator column can be designed to produce focused electron beams with energy ranging from a few to tens of kV. The beam can be scanned in both the x and y directions, and the system can be operated with multiple beamlets.
The invention also includes a new type of ion gun. The new focused ion beam system consists of a plasma ion source and an all-electrostatic beam acceleration and focusing column. The ion source is preferably a small (about 1.5 cm diameter) quartz chamber (although it can be larger in size) with the plasma produced by radio-frequency (RF) induction discharge. The RF antenna is preferably a water-cooled copper coil which is wound outside the quartz chamber and connected to an RF supply. There is no weak component in this arrangement and therefore the plasma source should have a very long lifetime. Ions or electrons can be extracted from the ion source.
This type of source can be used to produce positive ion beams with nearly all the elements in the periodic table. This gun can be operated with a wide range of energy and beam spot size to facilitate surface modification purposes. The same gun can be used to produce focused cluster or negative ion beams so as to achieve very low impact energy, to minimize substrate charging problems and to reduce high-voltage holding issues in the accelerator column. It further can be used to produce electron beams. The invention also includes a multi-beam system having several sources of different species and an electron beam source.


REFERENCES:
patent: 4447732 (1984-05-01), Leung et al.
patent: 4793961 (1988-12-01), Ehlers et al.
patent: 5198677 (1993-03-01), Leung et al.
patent: 6094012 (2000-07-01), Leung et al.
patent: 6294862 (2001-09-01), Brailove et al.
patent: 6364995 (2002-04-01), Fairbairn et al.

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