Silicon dioxide deposited by ECR-PECVD for low-temperature Si devices processing

Silicon dioxide films have been deposited at temperatures less than 270 °C in an electron cyclotron resonance (ECR) plasma reactor from a gas phase combination of O₂, SiH₄ and He. The physical characterization of the material was carried out through pinhole density analysis as a function of substrate temperature for different μ-wave power (E_w). Higher E_w at room deposition temperature (RT) shows low defects densities (<7 pinhole/mm²) ensuring low-temperatures process integration on large area. From FTIR analysis and Thermal Desorption Spectroscopy we also evaluated very low hydrogen content if compared to conventional rf-PECVD SiO₂ deposited at 350 °C. Electrical properties have been measured in MOS devices, depositing SiO₂ at RT. No significant charge injection up to fields 6–7 MV/cm and average breakdown electric field >10 MV/cm are observed from ramps I–V. Moreover, from high frequency and quasi-static C–V characteristics we studied interface quality as function of annealing time and annealing temperature in N₂. We found that even for low annealing temperature (200 °C) is possible to reduce considerably the interface state density down to 5 × 10¹¹ cm⁻² eV⁻¹. These results show that a complete low-temperatures process can be achieved for the integration of SiO₂ as gate insulator in polysilicon TFTs on plastic substrates.