<p>A mass separation type ion implanter performing ion implantation by irradiating a substrate with a mass separated ion beam. In the ion implanter (10) having a separation split (20) for receiving an ion beam (1) from a mass separation electromagnet (17) and passing desired ions selectively, the separation split (20) has a variable gap profile for passing the ion beam (1). The ion implanter (10) is disposed between an extraction electrode system (15) and the mass separation electromagnet (17), and forms a gap for passing the ion beam (1). The ion implanter has a variable slit (30) arranged to vary the profile of the gap such that the ion beam (1) extracted from an ion source (12) is blocked partially. The ion implanter (10) may comprise any one or both of the separation split (20) and the variable slit (30).</p>
