Influence of Dry-Etch Patterning of Top Electrode and SrBi[sub 2]Ta[sub 2]O[sub 9] on the Properties of Ferroelectric Capacitors

Abstract

In this article, we investigate the influence of the dry etch of SrBi 2 Ta 2 O 9 ͑SBT͒ and Pt top electrode ͑TE͒ on the ferroelectric properties of Pt/SBT/Pt capacitors, and we discuss the effect of recovery anneals applied after TE deposition, TE etch, and SBT etch. We have determined that the TE etch step damages the capacitors through a charging effect, which is dependent on the perimeter-to-area ratio. Complete recovery of the electrical damage is provided by an anneal step after TE etch. We have also evidenced a lateral physical damaging of the SBT film after SBT dry etch, which is well correlated with the observed degradation of the remanent polarization P r of the capacitors. A strong further degradation of P r is found when the Pt bottom electrode is significantly etched during the SBT overetch.Ferroelectric SrBi 2 Ta 2 O 9 ͑SBT͒ is attracting attention as a capacitor material used in ferroelectric random access memories ͑Fe-RAMs͒ due to its low switching voltage and good reliability properties. 1 However, the integration of Pt/SBT/Pt capacitors in a memory device implies the use of processes that potentially induce damage to these capacitors. In particular, fine patterning by dry etching of both metal and ferroelectric materials is required for scaled technologies, and the ferroelectric properties need to be preserved during these process steps.Many papers report on the optimization of dry-etch conditions of metal and ferroelectric films to improve parameters such as the etch rate, the selectivity or the slope of the sidewalls. 2-6 Still, few articles deal with the influence of these etch steps on the ferroelectric properties of the capacitors.In this work, we investigate first the influence of the Pt top electrode ͑TE͒ dry etch on the ferroelectric properties of Pt/SBT/Pt capacitors, we discuss the effect of recovery anneals ͑RAs͒ after TE deposition and after TE etch, and second we study the SBT dry-etch effect on the electrical properties of the capacitors. In view of different damage contributions that can or cannot be observed physically, of the effects of main-and overetch, and of the effect of RAs, we then discuss the possible mechanisms taking place at the SBT etch step. Note that our integrated device structure 7 uses prepatterned bottom electrode ͑BE͒ before deposition of the SBT layer, so that there is no possible effect of the BE etch on the capacitor properties. That is the reason why, except for the BE attack during the SBT overetch, no separate evaluation of BE patterning effect is performed. ExperimentalAmorphous 120 nm SBT was deposited by metallorganic chemical vapor deposition ͑MOCVD͒ on a bottom electrode/oxygen barrier stack ͑Pt/IrO 2 /Ir/Ti͑Al͒N/SiO 2 ͒. Ex situ X-ray fluorescence ͑XRF͒ measurements carried out right after deposition showed the following ratios: 2Sr/Ta = 0.8 and 2Bi/Ta = 2.2. The as-deposited layer was crystallized into the right ferroelectric phase by a postanneal step done in oxygen atmosphere at 700°C. No preferential crystalline orientation was detected by X-ray...

Etching Behavior and Damage Rejuvenation of Top Electrode and Bi3.15Nd0.85Ti3O12 Films Applied in Ferroelectric Random Access Memory Devices

“…[13][14][15][16][17] There are some studies on the etching characteristics of PZT and SBT films, including wet etching and dry etching. [18][19][20][21] However, there is no published work on etching damage or its method of recovery or the effect of capacitor size in BNdT-based ferroelectric capacitors.…”