Estimation methods for the angle of divergence of low energy ion beams

Three estimation methods for the determination of the angle of divergence β for low energy ion beams are described. A Kaufman-type argon ion source of 11 cm beam diameter, 150 to 2000 eV beam energy, and 0.1 to 1 mA/cm2 ion current density is used. The first method is based on the etching morphology of a 12-μm-thick HgCdTe sample that is overlayed by a 3-μm-thick photoresist pattern. The second method makes use of the halfwidth of the ion current density profile measured along the diameter of the ion beam cross-section at different distances z, from the grid. The third method employs a variable angle collimator to profile the ion current density along a diameter of the ion beam cross section; the angle of divergence is then extracted by fitting a mathematical model to the data. The angle of divergence that is obtained by using the above three measurement methods indicates that β decreases from 16° to 4° as the ion beam energy is increased from 150 to 900 eV, respectively.