Coplanar amorphous-indium-gallium-zinc-oxide thin film transistor with He plasma treated heavily doped layer

We report thermally stable coplanar amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with heavily doped n+ a-IGZO source/drain regions. Doping is through He plasma treatment in which the resistivity of the a-IGZO decreases from 2.98 Ω cm to 2.79 × 10−3 Ω cm after treatment, and then it increases to 7.92 × 10−2 Ω cm after annealing at 300 °C. From the analysis of X-ray photoelectron spectroscopy, the concentration of oxygen vacancies in He plasma treated n+a-IGZO does not change much after thermal annealing at 300 °C, indicating thermally stable n+ a-IGZO, even for TFTs with channel length L = 4 μm. Field-effect mobility of the coplanar a-IGZO TFTs with He plasma treatment changes from 10.7 to 9.2 cm2/V s after annealing at 300 °C, but the performance of the a-IGZO TFT with Ar or H2 plasma treatment degrades significantly after 300 °C annealing.