Long-Term Stability of SiNx Thin-Film Barriers Deposited by Low Temperature PECVD for OLED

Abstract

Silicon nitride thin film barriers for organic light emitting diode with stress and water vapor transmission rate related to a function of NH3/SiH4 gas flow rate were deposited by plasma enhanced chemical vapor deposition at 85°C. To evaluate the changes of the film properties before and after the storage in high temperature and humidity, the samples were stored in a chamber at 85°C and 85% relative humidity for up to 240 hrs. Both the stress and the refractive index decreased with increasing NH3/SiH4 gas flow ratio. The values varied significantly with higher NH3/SiH4 gas flow ratios. The refractive index of the SiNx barrier with NH3/SiH4 ratio of 3.2 decreased to 1.44, which is a similar value to SiOx film. FTIR analysis showed that the Si-N and N-H bonds reacted with water vapor/oxygen and formed thermodynamically more stable Si-O or Si-OH bonds. The in-depth composition analysis by Auger electron spectorscopy showed that the oxidation rate for the NH3/SiH4 gas ratios of 0.8 and 3.2 were 0.88 and 6.63 Å/hr, respectively. Cross-section transmission electron microscopy confirmed the calculated oxidation rates of the SiNx barrier layers.