The aim of this research is to develop low temperature gate dielectric/passivation layer for μc-Si and poly-Si based devices and circuits compatible with plastic substrates.
The PECVD silicon oxide films were fabricated from mixture of silane and nitrous oxide at 250 °C, 120 °C and 75 °C. Helium, argon and nitrogen were used as diluent gases to optimize density, stress, uniformity, and electronic properties.
Chemical composition and bonding in the films were studied by FTIR spectroscopy. The absorption peak at 1075-1080 cm-1 observed in the spectrum of each film corresponds to SiO2 stretching mode. No presence of SiH stretching or NH-stretching vibrations was found in the FTIR spectra of the samples.
Film uniformity was varied from 1.44 % to 5.60 % for 3“×3” area. Four wafers were processed at the same time. The deposited films have compressive stress varied from 0.063 GPa to 0.117 GPa. Respective film density is in the range from 1.63 g/cm3 to 1.77 g/cm3.
The electronic properties were studied on MOS capacitors with 200 nm thick SiOx. The dielectric permittivity was in the range between 2.03 and 3.57. The dielectric breakdown at 9 MV/cm was observed for the films deposited at 120 °C. The films deposited at higher temperatures are characterized by lower leakage current density, which was 3.7.10-10 A/cm2 for the sample deposited at 250 °C, 9.10-9 A/cm2 for 120 °C, and 2.2.10-8 A/cm2 for 75 °C at 5 MV/cm.
The a-Si:H based TFTs were fabricated using low temperature oxide as gate dielectric. TFTs demonstrate threshold voltage (3.02 – 4.12 V) and mobility (0.12 – 0.59 cm2/Vs) comparing with those using silicon nitride.