Horizontal Versus Vertical Annealing of Silicon Wafers at High Temperatures

The gravitational induced shear stresses in 200 mm silicon wafers supported in verticaltype or horizontal-type furnace 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 τM was chosen. The computed maximum values of τM demonstrate that the gravitational induced stress for vertical processing is approximately one order of magnitude less than the gravitational induced stress for horizontal processing. The experimental results obtained from processing of 200mm wafers with different oxygen concentration in horizontal and vertical boats at 1200°C are in an excellent agreement with the theoretical simulations.