Room-temperature relaxation of stress gradients in copper micro-cantilever beams using inert ion implantations

초록

Reduction of the residual stress and its gradient in a thin film is important for improving the reliability of microelectromechanical systems (MEMS) devices. In this work, we investigate a room-temperature control of the residual stress gradient in a sputtered copper (Cu) film by using inert ion implantations. A Cu micro-cantilever beam array is fabricated by bulk micromachining and used for evaluating the residual stress gradient of the film by measuring tip deflection of the cantilever beams. The as-fabricated Cu cantilever shows upward bending deformation as a consequence of the positive residual stress gradient in the film. To release the residual stress gradient, inert ions, such as helium and xenon ions, are implanted with various doses and energies onto the Cu cantilever before releasing it from the substrate. We found that the residual stress gradient can be effectively controlled by adjusting the implantation conditions. With the advantages of the well-established room-temperature process of the ion implantation technique, the proposed approach could be applied to reduce the residual stress of thin film in the integrated systems of electronic circuits made of metals.