PURPOSE:To form a graded magnetic field by providing an auxiliary yoke, which has a cylindrical portion, in a cylindrical hole of a cylindrical permanent magnet. CONSTITUTION:An ion source for semiconductor manufacture has an operation chamber 1 and a processing chamber 6. A microwave is introduced through a ceramic window 2. A pair of drawing-out electrodes 4, 4 are provided to an exit 5. Reactive gas is poured in through an inlet 11. A cylindrical permanent magnet 12a is provided to the outside circumference of the operation chamber 1. An auxiliary yoke 16 is provided to the end part 13 of the permanent magnet 12a in such a manner that a cylindrical portion 15 of the auxiliary yoke 16 is inserted into a cylindrical hole 14. Because the cylindrical portion 15 of the yoke 16 is put into the cylindrical hole 14 of the permanent magnet 12a, a graded cyclotron resonance magnetic field is formed in the operation chamber 1. The magnetic field can be regulated by changing the insertion length of the cylindrical portion 15.
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