High Quality Growth of SiO2 at 80° C by Electron Cyclotron Resonance (ECR) for Thin Film Transistors

Silicon dioxide (SiO2) films have been deposited at 80°C in an Electron Cyclotron Resonance (ECR) plasma reactor from a gas phase combination of He, O2 and SiH4. The ECR configuration provides a highly ionised plasma (∼1016 m−3) with low ion energies (∼10eV) that gives efficient dehydrogenation of the growing material whilst minimizing defect creation. The physical characterisation of the material gives a refractive index of 1.46, an etch rate in buffered HF below 3 nm/s and a hydrogen content of less than 2 at.%. Electrical tests reveal a resistivity in excess of 1014Ωcm, an average breakdown strength of 5 MV/cm, and fixed charge and interface state densities of 1011 cm−2 and 1012 eV−1cm−2 respectively. This has been achieved using a O2:SiH4 flow ratio ≍ 2:1.