Growth of nodular defects during film deposition

Defects in films created by dust or particles are usually called nodules. A simple geometric model is often used to explain their shape, but their size is not well described. Here we analyze how the growth and dimensions of the nodule depend on the surface reaction probabilities of gaseous precursors which determine the conformality of film deposition. The shape of nodules obtained from calibrated particles is investigated. Hydrogenated amorphous silicon deposited by plasma-enhanced chemical-vapor deposition and chromium layers deposited by sputtering have been used to study the effects of conformality. We demonstrate a satisfactory model based on a modification of a simple geometric growth approach by comparisons of calculations with scanning electron microscopy measurements. Furthermore, a 2D analytical simulation using two precursors and their respective loss and sticking probabilities has been carried out. The computed nodule diameters are in excellent agreement with the measured ones. These observations lead us to infer the presence of an interface between the nodule and the film in specific conditions.