An ion source and a polishing system using the ion source are disclosed. The ion source includes a discharge chamber, an electron emitter, a cathode, a screen grid, an accelerator grid, and a screen electrode. The discharge chamber is configured for accommodating discharge gas. The electron emitter is disposed in the discharge chamber. The cathode, the screen grid, the accelerator grid, and the accelerator grid are separately aligned in the discharge chamber in an ascending order with respect to the respective distance thereof from the electron emitter. The electron emitter, the cathode, the screen grid, the accelerator grid, and the accelerator grid are powered in order of descending voltages. The screen electrode defines an adjustable orifice to permit adjustment of an ion-beam ejecting area associated with the orifice. The polishing system further employs a movable stage and control and monitor components, in addition to the ion source.
