Mechanisms for polycrystalline silicon defect passivation by hydrogenation in an electron cyclotron resonance plasma

An in-line mass spectrometer and Langmuir probes have been employed to examine mechanisms of plasma immersion hydrogen passivation of grain boundary defects in polycrystalline silicon thin film transistors. Relative fluxes of H+ and H+2 as well as total ion current density were measured at the substrate location in an electron cyclotron resonance hydrogen discharge. Measurements were made over a range of operating conditions over which passivation rates have been shown to vary dramatically. Data presented show a strong correlation of both H+ flux and ion bombardment energy with good transistor performance obtained at operating pressures below 1 mTorr. This suggests that discharge operating conditions that promote dissociation of H2 to form H and H+ (which may diffuse more rapidly through solid material than H2), as well as increased sheath voltages and therefore ion energy at the substrate, are important to obtaining acceptable process rates.