부산대학교 도서관

Bifurcation is a non-linear phenomenon which determines the emergence of an abrupt degeneration in the symmetry of large wafers undergoing the large-scale integration process of the semiconductor industry. Because of the stress induced by the thin films manufactured upon the wafer, the warpage can degenerate and increase asymmetrically, resulting in two main principal and different curvatures. The purpose of processing is to contain the warpage and avoid the phenomenon of bifurcation. However, an understanding of the occurrence of this phenomenon can further be of help in controlling the warpage of thinned wafers having large diameters. In this work we present an extension of a model of bifurcation for the 8” Si, 500 $\mu$m thick, wafers metalized with a 4.5$\mu$m of Al, we developed previously. Indeed, in the present work, we approached the problem of bifurcation using FEA models based on the ANSYS Layered Shell Elements. In particular, we simulated a quarter of wafer and investigated the linear and non-linear behaviour of the whole wafer in the spherical regime and hence in the case of bifurcation. The numerical results obtained are consistent and in agreement with the previous ones and allowed to investigate more precisely the behaviour of the bifurcation around the bifurcation point.