Patent ID: 8147705

Claim:
A method of operating an ion source which comprises a plasma chamber into which an ion source gas is introduced, and which is used for internally producing a plasma, an extraction electrode system which is disposed in a vicinity of an opening portion of said plasma chamber, which extracts an ion beam from the plasma, and which has one or more electrodes, an insulating member for electrically insulating a plasma electrode from said plasma chamber, said plasma electrode being an electrode which is closest to the plasma among said electrodes constituting said extraction electrode system, and a plurality of magnets form a cusp magnetic field in a vicinity of an inner wall of said plasma chamber and are placed only outside of said plasma chamber in opposition to an outer wall of said plasma chamber, said method comprising: supplying a control signal configured to switchingly and selectively supply either boron trifluoride (BF 3 ) or phosphine (PH 3 ) as the ion source gas into the plasma chamber, when the ion beam is to be extracted by using a gas containing boron trifluoride (BF 3 ) as the ion source gas, setting a bias voltage of said plasma electrode with respect to said plasma chamber to be positive so as to increase a ratio of B + in the ion beam with respect to all other ions present in the ion beam, and when the ion beam is to be extracted by using a gas containing phosphine (PH 3 ) as the ion source gas, setting the bias voltage of said plasma electrode with respect to said plasma chamber to be negative so as to increase a ratio of PHx + in the ion beam with respect to all other ions present in the ion beam, wherein x is an integer and 0≦x≦3, wherein when the gas containing phosphine (PH 3 ) is used as the ion source gas, the bias voltage is set in a range of −30[V]≦V B <0, where V B is the bias voltage.