Paper PS-ThP34
Effect of High DC Bias on Silicon Oxide Coatings Deposited by Plasma Enhanced Chemical Vapor Deposition

Thursday, November 10, 2016, 6:00 pm, Room Hall D

It is well known that electronic devices such as organic light emitting diode and electronic paper are degenerated by water vapor and oxygen that penetrate from air. Therefore polymer substrates, which are expected to replace glass substrates for their flexibility and light weight but are permeable to water vapor and oxygen, are required to be coated with gas-barrier layers such as Silicon oxide (SiOx). In addition to the high barrier property, it is necessary for practical use to suppress curl of the polymer substrates caused by the coating with high stress.

Plasma enhanced chemical vapor deposition (PECVD) is one of the industrial-scale coating techniques of the SiOx layers with high barrier performance (see, for example, ref. 1). It has been reported that for the deposition of the SiOx layers using PECVD, ion bombardment plays an important role to densify the layers and improve the barrier performance, through experiments in which SiOx layers are deposited with DC bias applied at the substrate [2]. However curl of the polymer substrates tends to be enhanced by a high compressive stress of the SiOx layers caused by a strong ion bombardment and is required to be controlled.

The objective of this study is to explore the possibility of compatible high density and low stress through experiments in which SiOx layers were deposited with a wide range of DC bias. SiOx layers were deposited using a PECVD system. The substrate silicon wafers (4 inch in diameter) were mounted on a 400kHz RF applied electrode (6 inch in diameter). The power was varied to yield DC bias from 0 to -1.2kV. 13.56MHz RF was inductively coupled into the chamber with a planar-coiled RF antenna through a quartz window with an applied power kept at 300W. Hexamethyldisiloxane and oxygen were introduced into the chamber at a pressure of 4Pa.

The density of the SiOx layers examined with a X-ray reflectometer increased with enhancing DC bias from 0 to -360V, and it remained almost constant for higher DC bias. On the other hand, compressive stress measured with a profilometer steeply increased from DC bias of 0 to -200V and then reduced gradually to the highest DC bias investigated, which is in contrast to the above-mentioned constant density for high DC bias. These results suggest that the high bias enables a desirable polymer substrate with a SiOx barrier layer. Detailed analysis of the SiOx layers to comprehend these bias dependent phenomena will be reported at the presentation.

[1] T. Okimoto et al., The 21th International Display Workshops Proceedings, 1448-1451 (2014)

[2] L. Martinu et al., Journal of Vacuum Science & Technology A 12, 1360-1364 (1994)