Measuring plastic deformation of silicon as a result of thermal oxidation
K.V. Sweers (TU Delft - Mechanical Engineering)
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Abstract
Thermal oxidation in silicon microelectromechanical systems (MEMS) induces stress in the oxide film and silicon. Such residual stresses are usually unwanted, as it can influence performance or damage components. It can also cause unwanted plastic deformation in silicon, as was observed in previous research. Currentmeasurement methods inMEMSare not able to distinguish plastic and elastic strain as a result of thermal oxidation. This thesis presents a novel method to distinguish elastic and plastic strain in silicon beams, by removing the oxide layer to show the plastic strain. A lever mechanism is used as a mechanical amplifier. The plasticity model developed by Alexander and Haassen (AH) is
used in a numerical model to predict the elastic and plastic strain. Experiments in epitaxially grown silicon show significantly less plastic strain than predicted by the model. We conclude that the AH model is not valid for epitaxially grown silicon with low or zero initial dislocations. As significant plastic deformation was observed in FZ silicon samples in previous research by P.R. Kuppens, it is
concluded that epitaxially grown silicon is the better choice when plastic deformation is to be avoided.