Models of Bifurcation and Gravity Induced Deflection in Wide Band Gap 4H-SiC Semiconductor Wafers

Handling and warpage control of larger and thinner semiconductor wafers can be critical within the large-scale semiconductor manufacturing process. With the development of 8” wide band gap substrates pilot lines, e.g. based on silicon carbide, similar issues may emerge. In particular, the lack of containment of the warpage at early stages in the manufacturing process may evolve into the phenomenon of wafer bifurcation, consisting in an uncontrolled asymmetric warpage. This can occur also for the case of 8” 4H-SiC substrates. In this work, the investigation of the phenomenon of wafer bifurcation has been extended to the case of a 4H-SiC (0001) 8” wafer, metallized with a thin layer of aluminum. For the SiC substrates, we investigated both the spherical and bifurcation regime, through finite element analysis (FEA) methods, by using ANSYS® tools. In particular, the bifurcation has been induced in the wafer by applying a pair of weak forces as perturbations along two perpendicular directions acting normally with respect to the wafer surface. Moreover, the deflection induced by the action of Earth’s gravity on bare SiC 8” thinned wafers has also been considered. Indeed, gravity induced deflection (GID) is a factor that can influence the handling, move and load of wafers in an 8” production line. In the paper, the GID of a 8” SiC plain wafer fixed at two points is compared with the case of the same wafer supported at four points.In this work a preliminary evaluation of the GID and a solution to reduce it is proposed by means of ANSYS simulations tools.