INCIDENCE ANGLE DISTRIBUTIONS OF IONS BOMBARDING GROUNDED SURFACES INHIGH-DENSITY PLASMA REACTORS

Ion incidence angle distribution on surfaces in plasma etching reactor s determines the shape evolution of via holes and trenches through its effects on the spatial variation of ion fluxes along the walls of the se microscopic features, We describe a novel retarding-field energy an alyzer design that is capable of measuring the energy and the incidenc e angle distributions of ions bombarding grounded surfaces in plasma r eactors with sub-0.5 degrees resolution. Using this analyzer we measur ed the energy and angle distributions of Ar ions incident onto a Si su rface in a low-pressure helicon wave excited Ar plasma. Ion angle dist ributions 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 rando m ion energy in the plasma. Variation of the ion angle distribution wi dth as a function of plasma power and pressure is determined by the de pendence of the sheath potential and the ion temperature on these exte rnally controlled parameters. In low pressure Ar plasmas, the ion angl e distribution broadens with increasing power and shows a maximum as a function of pressure in the range 0.5-4 mTorr. (C) 1998 Elsevier Scie nce Ltd. All rights reserved.