Silicon nitride PECVD at low temperature: film properties and plasma analysis

Summary form only given. Recently there has been growing interest in the development of materials and processes at low temperatures compatible with transparent plastics for use in more rugged and flexible flat panel displays. Silicon nitride is a commonly used dielectric in thin film transistors (TFTs), the active switching element for each pixel in a display. We used plasma enhanced chemical vapor deposition (PECVD) at temperatures <150/spl deg/C with SiH/sub 4/, N/sub 2/ and He to deposit silicon nitride. Process analysis was done using in-situ mass spectroscopy and optical emission spectroscopy. Nitrogen instead of NH/sub 3/ was used to inhibit hydrogen incorporation which has been found to increase as temperature decreases in PECVD materials. Our films had an atomic hydrogen concentration near 20% at 50/spl deg/C vs. 30% in films deposited with NH/sub 3/. He dilution was used to engineer the distribution of hydrogen to obtain equal amounts bonded to Si and N, a physical property that has been associated with good quality films deposited at high temperatures. We found that increasing N/sub 2/:SiH/sub 4/ flow rate ratio from 50 to 150 resulted in a decrease in N atom incorporation relative to Si atoms in the films from N/Si=1.37 to 1.27. To examine the possibility of an increasing Si incorporation causing an apparent decrease in N atom fraction, we obtained the silane consumption fraction from mass spectrometry as a function of N/sub 2//SiH/sub 4/ flow rate ratio. The silane consumption fraction decreased from 97% at N/sub 2/ /SiH/sub 4/=50 to 93% at N/sub 2//SiH/sub 4/=150, which means increased Si incorporation as N/sub 2/ flow is increased is unlikely. Optical emission was used to observe nitrogen excited states, and detailed correlations between emission intensities, gas phase species distribution, and Si/N ratio in the deposited films will be reported.