Ion implanter electron shower having enhanced secondary electron emission

摘要

A plasma-enhanced electron shower (62) for an ion implantation system (10) is provided, including a target (64) provided with a chamber (84) at least partially defined by a replaceable graphite liner (82). A filament assembly (67) attached to the target generates and directs a supply of primary electrons toward a surface (118) provided by the graphite liner, which is biased to a low negative voltage of up to -10V (approximately -6V) to insure that secondary electrons emitted therefrom as a result of impacting primary electrons have a uniform low energy. The filament assembly (67) includes a filament (68) for thermionically emitting primary electrons; a biased (-300V) filament electrode (70) for focusing the emitted primary electrons, and a grounded extraction aperture (72) for extracting the focused primary electrons toward the graphite surface (118). A gas nozzle (77) attached to the target (64) introduces into the chamber a supply of gas molecules to be ionized by the primary electrons. The direction of the nozzle is set with respect to the filament assembly (67) to maximize the ionization rate of the gas molecules.