Simulation and Analysis of GaN Wafer Bowing on Sapphire Substrate

During the process of heteroepitaxial growth, if the lattice constant of the growing film differs from that of the substrate, the wafer surface bows, regardless of whether the lattice mismatch occurs or not. As the growth in large-scale wafers speeds up, bowing effects are becoming more and more important. Wafer bowing has a direct impact on the yield in modern mass-production compound semiconductor industries. By using finite element analysis software, the bowing deformation of the GaN wafer on sapphire substrate can be studied. This paper summarizes the causes of bowing deformation, builds the mathematical model, and deduces the relation equation of the wafer bowing. The results show that epitaxial wafer bowing has a linear relationship with the square of the diameter of the substrate but has little relationship with the thickness of the substrate. Moreover, the relation equation of the wafer bowing is also simplified finally.

The MOCVD growth process can be divided into four phases: a reactant input phase, a reactant mixing phase, an immediate boundary layer phase above the substrate, and the growth phase on the substrate surface itself. Growth complications that can occur in these phases include gas phase reactions during reactant mixing, reactant diffusion and/or pyrolysis in the boundary layer above the substrate, and thermodynamic or kinetic rejection of species from the substrate. The worst effects can be reduced or eliminated by providing appropriate equipment design and process conditions.


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