Fluid simulation of the plasma uniformity in pulsed dual frequency inductively coupled plasma

Abstract

As the wafer size increases, pulsed dual frequency inductively coupled plasma sources have been proposed as an effective method to achieve large-area uniform plasmas. A two-dimensional (2D) self-consistent fluid model, combined with an electromagnetic module, has been employed to investigate the influence of the pulse duty cycle and the pulse phase shift on the plasma radial uniformity in an argon discharge. When both antennas are pulsed, the best radial uniformity is obtained at 30%, due to the balance between the positive feedback and diffusion loss. When the duty cycle decreases, the bulk plasma density becomes lower since the power absorption is limited during the shorter active-glow period. As the duty cycle decreases to 10%, the plasma density is characterized by an edge-high profile because of the strong diffusion. When the pulse duty cycle of the outer two-turn coil is fixed at 70%, the plasma density profiles shift from center-high over uniform to edge-high as the pulse duty cycle of the inner coil decreases from 50% to 10%, and the best plasma uniformity appears at 30%. In addition, by adjusting pulse phase shifting of two antennas, the plasma uniformity could also be improved, and the nonuniformity degree decreases from 0.138 for the synchronous pulse to about 0.101 for the asynchronous pulse.