Plasma immersion ion implantation for materials modification and semiconductor processing: Carbon nitride films and poly-Si TFTs hydrogenation

This paper provides a review of the recent research on plasma immersion ion implantation (PIII) for materials modification and semiconductor processing performed by the Plasma Science group at Northeastern University. The results from two PIII experiments: thin carbon films modification by nitrogen implantation and the hydrogenation of polycrystalline silicon (poly-Si) thin film transistors (TFTs) for defect passivation are presented. For the nitrogen implanted carbon films (CN _x), low energy PIII (∼ 2 keV) formed covalent carbon-nitrogen bonds in the carbon films and reduced the interfacial tension between the films and the substrate which suggest an improvement in adhesion. Conventional ion beam (IB) nitrogen implantation produced CN _x films with less nitrogen to carbon ratio {[N]}/{[C]} and significant surface damage. In the hydrogenation of poly-Si TFTs experiment, a high hydrogenation efficiency was achieved by low energy (1 keV) and high dose rate (∼ 10 ¹⁶/cm ² s) implantation using an inductively coupled plasma (ICP) source. Significant improvement in the device parameters (e.g., leakage current, effective mobility, threshold voltage, and subthreshold slope) was achieved in a fraction of the time needed by other hydrogenation methods.