Electrical damage induced by reactive ion-beam etching of lead-zirconate-titanate thin films

Abstract

Ion-beam etching of sputtered Pb(Zrx,Ti1−x)O3 (PZT) thin films with x equal to 0.54 grown on Pt∕TiOx∕SiO2∕Si substrates has been performed using pure Ar gas and a varying CHF3∕Ar gas mixing ratio. The etch rate dependence on the process parameters (gas composition, current density, and acceleration voltage) has been investigated. PZT etch rate under 40% CHF3 in Ar can reach 100nm∕min with an acceleration voltage of 900 V and a current density of 0.7mA∕cm2 (in comparison to 35nm∕min in pure Ar). A selectivity ratio of 8 has been obtained between PZT and photoresist (1.3 in pure Ar). We have evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases less under a gas mixture than under a pure argon beam, and that the preferential etching observed at the grain boundaries under a pure argon beam disappears when we increase the proportion of CHF3 in the gas mixture. For some etching parameters (current density, acceleration voltage, and gas mixing ratio), we have observed electrical damage. C(V) and hysteresis loops P(E) measurements before and after etching have demonstrated these degradations. We have noted a large decrease of the permittivity after the etching process, independently of the current density and the acceleration voltage. The ferroelectric damage was illustrated by a large increase of the average coercive field after etching in pure argon. The presence of CHF3 in the plasma partially reduces the damage.