Evaluation of wafer curvature during epitaxy growth
磊晶製程 ； 緩衝層 ； 晶圓曲率 ； 幾何非線性 ； 應力集中 ； Epitaxy growth ； buffer layer ； wafer curvature ； geometric nonlinear ； stress concentration
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This research focuses on the curvature variation of GaN on a silicon substrate by the film stress during epitaxy. The film stress is attributed to the lattice mismatch and thermal mismatch between the epitaxial layer and the substrate, depending on the structure of epitaxy. A finite element software ABAQUS is used to build the numerical model to simulate the wafer bowing caused by film stress. By comparing the numerical results with Stoney and another analytical formula of curvature, the effect of nonlinear geometry and the error are obtained. In order to use the formula, the anisotropic material properties were transformed to an effective elastic modulus under biaxial stress condition. The application of the analytical formula for multi-layer films was also discussed. The epitaxy process consists of the heating stage of the silicon substrate, the growth stages of buffer layers and GaN layer, and the cooling stage of the wafer. Through the monitoring of the temperature variation and the curvature variation in the epitaxy process, we can understand the behavior of each stage. The film stresses attributed to lattice mismatch are obtained from back-calculating experimental data under geometrically linear and nonlinear conditions. How to compute the curvature variation caused by thermal mismatch from the heating stage to the cooling stage is discussed. The curvature variation in epitaxy process is verified by the simulation. The stress distribution on the top and bottom of the silicon substrate, and the stress concentration near the wafer edge are also studied. The experimental curvature variation was extended to the prediction for the same epitaxy structure on silicon substrates with different thickness. We expect that the extension can be applied to the slight variation of film thickness.
工程學 > 土木與建築工程