Plastic deformation in 200 mm silicon wafers arising from mechanical loads in vertical-type and horizontal-type furnaces

Slip-free high temperature processing of silicon wafers at temperatures up to 1200 °C still remains an engineering challenge. Therefore, the authors present the physical basis for estimation of gravitational constraints in 200 mm silicon wafers subjected to high temperature processes both in vertical-type and horizontal-type furnaces. The load-induced shear stresses in 200 mm silicon wafers stacked horizontally and vertically were calculated using 3D-FEM analysis of the displacement vector assuming linear elastic behavior of the anisotropic material. For comparison of the two complex loading cases and for relating the effect of gravitational constraints to the mechanical strength of the wafers, the invariant Von Mises shear stress was chosen. Calculation of load-induced stresses and determination of the onset of plastic deformation have shown that for vertical-type boats annealing at temperature >850 °C would lead to slip formation in the bearing area of the wafer whereas for horizontal-type boats largely slip-free processing would be possible up to 1200 °C.