Uniformity and composition of silicon oxide films on 3D geometries by plasma enhanced chemical vapor deposition

Abstract

In a dual source reactor, plasma enhanced chemical vapor deposition of silicon oxide films was conducted in order to study the influence of different plasma operation modes as well as of the various three-dimensional substrates geometries (plate substrates, hollow cylinders, and hollow cuboids) on film uniformity and composition. Deposits were obtained by means of a mixture of oxygen and hexamethyldisiloxane. Both aluminum and polyvinyl chloride (PVC) were used as substrate materials. The reactor used is equipped with a microwave (MW) slot antenna plasma source and a radio frequency (RF) biased substrate holder. Films were characterized by ellipsometry and by Fourier transform infrared spectroscopy. Independent of the substrate material and the plasma operation mode, it was found that an increase of the cylinder height or a decrease of its diameter leads to a reduction of the film thickness at the substrate bottom in its hollow space. This is in contrast to the observation that the organic content decreases for deposits on PVC with increasing cylinder height and diameter. In case of vertically mounted plate substrates, thicker films were achieved with increasing distance from the substrate holder for the MW mode, while for RF mode, it was opposite. With respect to this, the dual mode appears to superpose the two dominating processes, ion flux enhancement by the RF bias towards the substrate holder and pre-excitation of the gas phase by the remote MW source. Here, the most inorganic and scratch resistant films were obtained.