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

Abstract

Ion-beam etching of sputtered Pb͑Zr x ,Ti 1−x ͒O 3 ͑PZT͒ thin films with x equal to 0.54 grown on Pt/ TiO x / SiO 2 / Si substrates has been performed using pure Ar gas and a varying CHF 3 / Ar gas mixing ratio. The etch rate dependence on the process parameters ͑gas composition, current density, and acceleration voltage͒ has been investigated. PZT etch rate under 40% CHF 3 in Ar can reach 100 nm/ min with an acceleration voltage of 900 V and a current density of 0.7 mA/ cm 2 ͑in comparison to 35 nm/ min in pure Ar͒. A selectivity ratio of 8 has been obtained between PZT and photoresist ͑1.3 in pure Ar͒. 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 CHF 3 in the gas mixture. For some etching parameters ͑current density, acceleration voltage, and gas mixing ratio͒, we have observed electrical damage. C͑V͒ and hysteresis loops P͑E͒ 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 CHF 3 in the plasma partially reduces the damage.

Etching characteristics and plasma-induced damage of Ba0.65Sr0.35TiO3 thin films etched in CF4/Ar/O2 plasma

“…In order to accomplish the integration of these devices, the etching process for BST films must be developed. Several techniques have been used for etching BST films: wet chemical etching, reactive ion etching (RIE), magnetically enhanced reactive ion etching (MERIE), inductively coupled plasma (ICP) etching, electron cyclotron resonance (ECR) etching, helicon wave plasma (HWP) etching, and reactive ionbeam etching (RIBE) [4][5][6][7][8]. Among those technologies, MERIE system has shown high etch rate and good selectivity performance for etching BST films because of the presence of relatively intensive magnetic field and the high density plasma at low pressure.…”

Characterization and reliability studies towards piezoelectrically actuated RF-MEMS switches

“…The positively charged defects, in particular oxygen vacancies, are the most probable ones induced during the ion milling process [139,[141][142][143][144]. We speculate that the positively charged defects initiate the dielectric breakdown.…”

“…Jung et al detect the generation of H -O dipoles due to hydrogen reduction during plasma exposure [136]. 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].…”

“…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].…”

“…To understand the difference between these two kinds of PZT capacitors in the RVS and TDDB measurements, it is necessary to know the difference between their PZT layers. The damaged PZT layer is assumed to be caused by structural defects generated by the ion bombardments [139,[141][142][143][144]. Only the PZT in overetched capacitors is directly bombarded by the energetic ions.…”