TWI654649B

An ion implanter includes: a beam deflector that deflects an ion beam passing through a previous stage beam path and outputs the beam to pass through a subsequent stage beam path toward a wafer; a beam filter slit that partially shields the beam traveling through the subsequent stage beam path and allows passage of a beam component having a predetermined trajectory toward the wafer; a dose cup that is disposed between the beam deflector and the beam filter slit and measures a part of the beam exiting from the beam deflector as a beam current; and a trajectory limiting mechanism that is disposed between the beam deflector and the dose cup and prevents a beam component having a trajectory deviated from the predetermined trajectory from being incident to a measurement region of the dose cup.