PLANARIZATION MECHANISM OF RF-BIASED AL SPUTTERING

The planarization mechanism of Al bias sputtering is clarified by evaluating the effects of the incident angle range of Al deposition and resputtering independently. Although narrowing the range of Al incident angles increases the amount of Al deposited on the via bottom to improve step coverage, the effect is limited due to the self-shadowing effect. When the substrate bias voltage (Ar ion energy) is high, most of the resputtered Al from the via upper peripherals redeposits only on opposite side of via upper peripherals, resulting in void and damage formation in the via. When the substrate bias voltage is reduced, resputtered Al redeposits efficiently inside the vias, and sufficient via filling and surface planarization are achieved. A new deposition method, i.e., the combination of deposition and resputtering by Ar ions both with a range of incident angles, is also proposed. The new method showed sufficient filling effect although little planarization was observed.