The effect of anisotropy on the deformation and fracture of sapphire wafers subjected to thermal shocks

Residual stresses in silicon-on-sapphire thin film systems

“…The finite element used was the three-dimensional Solid 98 in ANSYS (ANSYS manual) which has 10 nodes and six degrees of freedom at each node. This type (Flinn and Chiang, 1990): (a) coordinate systems in the sapphire crystal and the R-plane, and (b) a sapphire wafer in the R-plane and the coordinate system in the FEA simulations (Vodenitcharova, 2007). of element has both the thermal and structural fields and coupling capability required for the present analysis.…”

“…Thus in our FE analysis, the sapphire substrate considered was also along its R-plane. According to Vodenitcharova et al (2007), sapphire in this orientation could be considered as an orthotropic material, whose crystalline planes related to the X-, Y-and Z-axes are illustrated in Fig. 2.…”

“…The buffer layer was considered to be isotropic due to its amorphous nature. The elastic and thermal properties of silicon layers and sapphire substrate are based on the work of Hull (1999) and Vodenitcharova et al (2007). Table 1 lists the material properties in our FE analysis.…”

“…The mismatch of the lattice parameters and of the thermal expansion properties between thin film layers and substrate materials are the main causes of cross-layer defect development and residual stress generation (Nakamura et al, 2004;Yamamoto et al, 1979). Several methods have been proposed to minimise the residual stresses caused by lattice mismatch (Lau et al, 1979), such as ion implantation and annealing (Hull, 1999;Roulet et al, 1979;Vodenitcharova et al, 2007) of which the former is to introduce further disorder in the crystalline as-deposited structure and the latter is to regrow the crystalline layers.…”

Epitaxial Growth of AlN on (0001) Sapphire: Assessment of HVPE Process by a Design of Experiments Approach

“…It consists in writing a mechanical modeling of the AlN layer + sapphire substrate taking into account the initial compressive misfit strain of −0.7% [47], tensile strain due to island coalescence [48] depending on island size at coalescence and thermal strain due to the misfit in thermal expansion coefficients between materials. The polynomial used for fitting the thermal expansion coefficients of AlN and sapphire normal to c-axis (biaxial stress only) and their respective biaxial modulus come from different sources [49][50][51][52]. The island size at coalescence is used as the adjusting parameter so that the calculated stress fits with the stress deduced from Raman shift [53] or curvature measurements.…”