The substrate bias voltage is applied to improvement of the directionality and energy of arriving particle to the substrate surface. It can modify the arrival characteristics of these particles such as direction and kinetic energy. As the direction and kinetic energy are controlled, greater penetration into high aspect ratio structures could be reached. On the other hand, collision of the particles which have sufficient energy with the deposited film could cause re-sputtering of the deposited layer. As a result, angular distribution of the deposited material could be increased and not only density of the deposited thin film will be increased, but also uniformity of the deposited layer on the substrate with 3D structures could be improved. In addition, applying the substrate bias voltage can change the crystallographic orientation of the deposited films and causes improvement of the film adhesion to the substrate.
RF substrate bias is appropriate if substrate is non-conductive. Applying DC voltage to non-conductive substrate causes the substrate charged due to collision of the charged particles. That could disturb the deposited thin film.
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