Behaviour of total surface charge in SiO 2–Si system under short-pulsed ultraviolet irradiation cycles characterised by surface photo voltage technique

Abstract

Effects of time-accumulated ultraviolet (UV) irradiation and surface treatment on thermally oxidized p-type silicon wafers were investigated by using the surface photo voltage (SPV) technique via the direct measurement of the total surface charge, Q SC. The rise and fall times of Q sc curves, as a function of accumulated UV irradiation, depended on the thermal oxide thickness. A simple model was proposed to explain the time-varying characteristics of Q sc based on the UV-induced bond breaking of SiOH and SiH, and photoemission of bulk electrons to wafer surface where O 2 − charges were formed. While these mechanisms resulted in charge variations and hence in Q sc, these could be removed by rinsing the silicon wafers in de-ionized water followed by spin-dry or blow-dry by an ionizer fan. Empirical parameters were used in the model simulations and curve-fitting of Q SC. The simulated results suggested that initial changes in the characteristic behaviour of Q sc were mainly due to the net changes in the positive and negative charges, but subsequently were dominated by the accumulation of O 2 − during the UV irradiation.