Incidence angle distributions of ions bombarding grounded surfaces in high density plasma reactors

Ion incidence angle distribution on surfaces in plasma etching reactors determines the shape evolution of via holes and trenches through its effects on the spatial variation of ion fluxes along the walls of these microscopic features. We describe a novel retarding-field energy analyzer design that is capable of measuring the energy and the incidence angle distributions of ions bombarding grounded surfaces in plasma reactors with sub-0.5° resolution. Using this analyzer we measured the energy and angle distributions of Ar ions incident onto a Si surface in a low-pressure helicon wave excited Ar plasma. Ion angle distributions are approximately Gaussian. In absence of collisions in the sheath, the width of the ion angle distribution function is determined by the ratio of the directed energy gained in the sheath to the random ion energy in the plasma. Variation of the ion angle distribution width as a function of plasma power and pressure is determined by the dependence of the sheath potential and the ion temperature on these externally controlled parameters. In low pressure Ar plasmas, the ion angle distribution broadens with increasing power and shows a maximum as a function of pressure in the range 0.5-4mTorr.