IN-SITU ELLIPSOMETRIC STUDY OF THE INFLUENCE OF POWDER FORMATION ON THE INITIAL GROWTH OF GLOW-DISCHARGE A-SIH

Even under standard preparation conditions for amorphous hydrogenated silicon (a-Si:H) by r.f. glow discharge decomposition of silane, powder formation can occur leading to an initial transient behaviour of silane discharges. Phase-modulated real-time in situ ellipsometry is used to study the influence of the discharge behaviour on the initial stage of growth of a-Si:H after ignition and subsequent to intentional discharge interruptions. A clear correlation between the powder-determined time dependences of the discharge parameters pressure and self-bias voltage and of the ellipsometric angles is confirmed. In the discharge regime where this initial transient behaviour due to powder formation is observed, the corresponding DELTA - PSI trajectories can be attributed to the initial growth of less dense material. The time-dependent DELTA signal of the growing film is found to be very sensitive even to minor discharge perturbations. The influence of controlled temporal variations of preparation parameters on the growing a-Si:H film can be simultaneously monitored by real-time in situ ellipsometry. This offers an opportunity for interface optimization in a-Si:H structures.