"Low-temperature ECR-PECVD silicon dioxide as gate insulator for polycrystalline silicon thin film transistors"

Silicon dioxide films have been deposited at temperatures below 270 °C in an electron cyclotron resonance (ECR) plasma reactor from O2, SiH4, and He gas mixture. Pinhole density analysis as a function of substrate temperature for different microwave powers was carried out. Films deposited at higher microwave power and at room temperature show defect densities (<7 pinhole/mm2), ensuring low-temperature process integration on large area. From Fourier transform infrared analysis and thermal desorption spectrometry we also evaluated very low hydrogen content if compared to conventional rf-plasma-enhanced chemical-vapor-deposited (PECVD) SiO2 deposited at 350 °C. Electrical properties have been measured in metal-oxide-semiconductor (MOS) capacitors, depositing SiO2 at RT as gate dielectric; breakdown electric fields >10 MV/cm and charge trapping at fields >6 MV/cm have been evaluated. From the study of interface quality in MOS capacitors, we found that even for low annealing temperature (200 °C), it is possible to considerably reduce the interface state density down to 5×1011 cm–2 eV–1. To fully validate the ECR-PECVD silicon dioxide we fabricated polycrystalline silicon thin-film transistors using RT-deposited SiO2 as gate insulator. Different postdeposition thermal treatments have been studied and good device characteristics were obtained even for annealing temperature as low as 200 °C.