Double shield for electron and ion beam columns

Details Double shield for electron and ion beam columns Double shield for electron and ion beam columns

1998-03-31

2001-10-02

Nguyen, Kiet T. (Department: 2881)

Radiant energy

Radiation controlling means

Shields

C250S505100

Reexamination Certificate

active

06297512

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to electron and ion beam columns, and, more particularly, to shielding of such columns from electromagnetic (EMI, RFI) interference.
2. Description of Related Art
Electron and ion beam columns use electrical lenses and scan coils, together with mechanical shields, to focus the electrons or ions in the column. In the areas of the column which the beam passes that are not in close proximity to a lense or a coil, the beam is subject to external electrical interference such as EMI, RFI, etc. Also subject to interference are the column control signals.
In addition, the control of these beams is becoming increasingly more stringent as geometries of integrated circuits are becoming smaller. For example, one use for an ion beam is to open a vertical connection in an integrated circuit by removing a vertical conductive region. With IC geometries used today and prior art ion beam systems, the beam must be accurate to within about 0.2 micrometers (&mgr;m) and must hold this accuracy during the entire operation which takes over 20 minutes. Typically, electron/ion beam system manufacturers do not guarantee image drift for as long as 20 minutes.
Therefore, it can be appreciated that preventing unwanted electrical noise from interfering with an electron or ion beam is highly desirable.
SUMMARY OF THE INVENTION
In accordance with the present invention, a double shield for an electron or ion beam has a metallic column enclosing a major portion of the beam and forming at least a portion of a vacuum retaining structure. The metallic column provides a first shield for the beam. A second shield is provided for the beam separate from the metallic column, the second shield and the metallic shield forming a double shield for the beam over a major portion of the metallic column.


REFERENCES:
patent: 4508967 (1985-04-01), Boissel et al.
patent: 4701623 (1987-10-01), Beasley
patent: 5029249 (1991-07-01), Ohtaka
patent: 5082995 (1992-01-01), Paterson et al.
patent: 5376792 (1994-12-01), Schamber et al.

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