Patent ID: 6346768
Filing Date: 2002-02-12
Classification: H01J

Abstract:
Apparatus for the production of low energy charged article beams comprising: a plasma chamber; means for generating in the plasma chamber a plasma comprising particles of a first polarity and oppositely charged particles of a second polarity; means for restraining particles of the first polarity in the plasma chamber; a first multi-aperture electrode grid contacting the plasma, wherein the first electrode grid is arranged for connection to a first potential source so as to impart to the first electrode grid a first potential of the second polarity; a second multi-aperture electrode grid arranged for connection to a second potential source so as to impart to the second electrode grid a second potential, the second potential being less than the first potential so as to produce between the first and second electrode grids a first acceleration field for accelerating charged particles of the second polarity towards and through the second grid; and a third multiaperture electrode grid arranged for connection to a third potential source so as to impart to the third electrode grid a third potential of the first polarity and to produce between the second and third electrode grids a second acceleration field for accelerating charged particles of the second polarity towards and through the third electrode grid, the grid spacing between the first and second grids being greater at the periphery of the grids than at the centre thereof, the apertures of the first, second and third grids being aligned so that particles emerging from an aperture of the first grid are accelerated through a corresponding aperture of the second grid and then through a corresponding aperture of the third grid in the form of a beamlet, a plurality of beamlets from the third grid forming a beam downstream of the third grid.