JP2552185B

PURPOSE:To improve the optical efficiency for extracting an ion beam by constituting an ion gun grid with an insulator and a conductor, providing multiple holes penetrating them, and setting the ratio between the diameter of the hole and the thickness of the insulator and the thickness of the conductor to specific values respectively. CONSTITUTION:An ion gun grid 1 is constituted of a conductor metal foil 2 and an insulator ceramic plate 3, and the foil 2 and the plate 3 are integrally connected. Multiple holes 4 penetrating the foil 2 and the plate 3 are formed on the grid 1. The ratio D/L between the diameter D of the hole 4 and the thickness L of the plate 3 is set to 1.0+ or -0.2, and the thickness L of the plate 3 is set to 100-200mum. When D/L is set to 0.8-1.2 in particular, no ion collides with the foil 2, and an ion beam can be efficiently extracted. When the thickness L of the foil 2 is set to the above value, the directivity of the ion beam can be improved together with the above aspect ratio.