Influence of the Gas Phase on the Water Vapor Barrier Properties of SiO_x Films Deposited from RF and Dual‐Mode Plasmas

Abstract

The influence of different gas phase species and the positive ion density on the water vapor barrier performance of SiO x thin films is investigated in this study. A reactor equipped with a remote 2.45 GHz slot antenna plasma source and a 13.56 MHz-biased substrate holder was used to deposit films from gas mixtures of oxygen and HMDSO. Besides determining the WVTR of films, different excited gas phase species were monitored by means of OES and the positive ion density in pure oxygen was measured by LP. The dependencies of the positive ion density and of the actinometric trends of species on the oxygen flow rate as well as on the power input by RF and MW source were investigated. Both gas-phase diagnosis techniques reveal a higher excitation of the gas-phase in dual mode than in pure RF plasma. Production of atomic species seems to be enhanced under such conditions, which however leads to enhanced oxidation of HMDSO and its fragments by atomic oxygen. Hence, at oxygen flow rates above 200 sccm, enough atomic oxygen seems to be obtained so that the film growth mechanism is dominated by homogeneous combustion reactions, overriding the beneficial effect of the substrate self bias. Thus, a complete loss of the water vapor diffusion barrier is observed. Apart from these defective deposits, typical films revealed low WTVR for the entire variation range in RF mode and below 200 sccm of oxygen flow also in dual mode. Here, a decrease of the WVTR with RF power (i.e. DC self bias) and the oxygen flow rate was obtained, while WVTR could be reduced to 0.1 g Á m À2 Á d À1 corresponding to a barrier improvement by a factor of 150 if compared to uncoated substrate polymers.

Characterization of the Chemical Kinetics in an O2/HMDSO RF Plasma for Material Processing

“…Application of the source to the treatment of PET results in the deposition of a highly inorganic SiO 2 film, with very low water contact angle of a few tens of degrees, when oxygen-to-HMDSO ratio is larger than 7. Preliminary measurements of the water vapour transmission rate show a decrease from 23 of untreated PET to 5.5 g/m 2 /day at an O 2 /HMDSO ratio of 7.5, which appears encouraging even if not yet comparable with results reported in the literature [17,19]. Chemical kinetics in the gas phase of O 2 /HMDSO plasmas largely controls the deposited film composition and characteristics.…”

Silicon Oxide Permeation Barrier Coating and Plasma Sterilization of PET Bottles and Foils

“…Plasma deposited silicon oxide films are found to increase the permeation barrier of packaging materials and are accepted by the consumer due to its transparency. The deposition of these films is established using various reactor geometries and silicon sources, e.g., silane, hexamethyldisiloxane (HMDSO), or tetraethoxysilane (TEOS) 7–13. Considering the barrier properties of deposited films, the influence of the coating composition and structural phenomena like coating defects seem to be the major topics to have to be analyzed 14–17.…”

Oxygen permeation, mechanical and structural properties of multilayer diffusion barrier coatings on polypropylene

“…Deposition experiments were conducted in a cylindrical stainless steel PECVD apparatus which has been described in more detail in previous works [10,11]. The PP substrate samples were placed on the powered electrode, which was capacitively coupled to a 13.56 MHz RF generator via a matching network.…”