Ion beam etching of lead–zirconate–titanate thin films: Correlation between etching parameters and electrical properties evolution

Abstract

Ion beam etching of sputtered Pb(Zr x ,Ti 1Ϫx )O 3 ͑PZT͒ with x equal to 0.54 thin films grown on Pt/Ti/SiO 2 /Si substrates has been performed using pure Ar gas. The etch rate dependence on the process parameters ͑current density, acceleration voltage, gas pressure͒ has been investigated. The PZT etch rate can reach 600 Å/min with acceleration voltage of 1000 V and current density of 1 mA/cm 2 . Selectivity ratios between PZT and masks of various natures ͑photoresist, Pt, Ti͒ have been evaluated to determine a pertinent material for etching mask. According to our etching conditions, titanium seems to be the best candidate. We evaluated the PZT surface damage by contact mode atomic force microscopy. It appears that the roughness increases after ion bombardment, and that the grain boundary zone is preferentially etched. For some etching parameters, we also observed electrical damage. Carrying out C(V) and hysteresis loops P(E) measurements before and after etching have provided evidence of degradation. We noted a large decrease in permittivity after the etching process irrespective of the current density and acceleration voltage. Ferroelectric damage was illustrated by a large increase in the average coercive field. For each of the electrical properties under study, the same behavior has been observed after etching: the increase of damage was obtained as a function of the current density and acceleration voltage. The evolution of electrical properties when the PZT layer is protected by a metallic mask has also been studied. We observed very slight variations in the electrical properties.

Characterization and reliability studies towards piezoelectrically actuated RF-MEMS switches

“…6.1. The top electrode-PZT interface of the overetched capacitor is rougher and more defective than that in the regular capacitor, because of the first ion milling process [144]. These two kinds of MIM PZT capacitors are made on the same wafer, have the same geometry and consist of the same materials.…”

“…As a result, PZT grain boundaries are preferentially etched and the PZT surface roughness increases [144]. The shift of the hysteresis loop indicates the generation of an internal electric field, which may correspond to the charge accumulation or compensation at the top electrode-PZT interface [144]. A damaged layer at the PZT surface (or sidewall) becomes non-ferroelectric due to the ion bombardments.…”

“…This is presumably because the PZT grain boundaries contain more Pb than PZT bulk and the etching rate of Pb oxide is higher than Ti/Zr oxide. As a result, PZT grain boundaries are preferentially etched and the PZT surface roughness increases [144]. The shift of the hysteresis loop indicates the generation of an internal electric field, which may correspond to the charge accumulation or compensation at the top electrode-PZT interface [144].…”

“…PbZr 1-x Ti x O 3 (PZT) is one of the most widely used piezoelectric materials in MEMS because of its excellent piezoelectric properties [134]. It has been reported that PZT properties are influenced by fabrication processing, especially plasma etching [135][136][137][138][139][140][141][142][143][144]. Nowadays, with the decreasing of device feature size, plasma etching (or dry etching) is more widely used than wet etching, because of its an-isotropic and accurate pattern transfer for PZT [145].…”

“…Soyer et al show a surface layer developed during plasma etching which contains fluorine and has poor electrical properties [143]. The PZT damage/degradation caused by the physical effect of ion bombardments can manifest itself by the increase of surface roughness, shift of the hysteresis loop, decrease of permittivity, decrease of remnant polarization, and increase of coercive fields [141,142,144]. Soyer et al study the PZT damage as a function of ion milling parameters [144].…”