A new vacuum coating technology deposits metal oxide films like silicon dioxide and zinc oxide on large area substrates. The coatings are uniform and dense and are deposited at high rates compared to reactive sputtering. Potential applications for the process include clear abrasion-resistant coatings, optical coatings, transparent conductive oxides, photovoltaic films and clear barrier coatings. Low deposition temperature especially enables web coating processes.

A new coating technology for large-area substrates employs plasma enhanced chemical vapor deposition (PECVD). While PECVD has been routinely used in semiconductor processing for many decades, it has not been applied to flexible webs or other large-area applications. One problem limiting use of PECVD is that the reactor electrodes are coated along with the substrate. In semiconductor processing, routine etch back cycles are implemented to clean the electrodes. In a roll-to-roll web application this is not possible, and the insulating buildup on the electrode causes process drift. GPI's new patent pending source, termed the Dual Plasma Beam Source™ (Dual PBS™), overcomes the electrode-coating problem and offers a new coating technique to add to the two most common vacuum deposition techniques: evaporation and magnetron sputtering.

The Dual PBS™ combines two linear plasma sources across a mid-frequency alternating current power supply. When the dense plasma beam emanating from the sources is directed onto a moving substrate, a PECVD vapor precursor is efficiently reacted and deposited. Advantageously, the sources operate in the millitorr region so gas phase nucleation is minimal and powder formation does not occur.

The Dual PBS™ is used to deposit SiOx films on 6mm thick polycarbonate (PC) samples and the deposition rates are measured for a range of oxygen / precursor ratios. The figure shows the results for three HMDSO flow conditions. As shown, the deposition rate is over 1000 nm-m/min. This rate is 10 times faster than MS deposition of SiOx. The abrasion resistance of the SiOx coatings are measured with a Taber Abrader™ using CS-10F Type 3 wheels. The resulting haze after 1000 cycles with 500g is less than 2 percent. A leading commercial atmospheric hard coat measured 10 percent haze under the same conditions. These abrasion resistance results demonstrate the high-quality, dense nature of the films deposited by Dual PBS™.

Editor's note: see the complete online paper, including all charts and diagrams, at www.convertingmagazine.com.