The characteristics of RF bias-sputtered Al films are clarified. A negative substrate bias voltage, VDC, produced by RF biasing, strongly influences not only the planarization effect but also film characteristics such as hillock and void growth, and Ar content.
Films deposited at VDc lower than -150 V. are significantly degraded due to the formation of two kinds of voids grown during annealing. One type is a blister-like voids, while the others are large and irregular. These are produced when Ar is released from the films during heat treatment. as evidenced by the fact that the amount of Ar released from the films rapidly increases when VDC is lower than -150 V.
Although biasing strongly effects Al films resulting in the formation of an almost complete (111) texture. the effect degrades as VDC exceeds -200 V. Thus, Al bias sputtering requires a high resputtering rate and a VDC higher than -150 V to achieve appropriate planarization with suitable film characteristics.