Spacers Alternatives for INTEGRATION OF (3D) STACKED SBT FeCAPs

Abstract

The thermal and mechanical stability of Ir and Ir\Pt metals spacers deposited on top of Ti(Al)N\Ir\IrO 2 patterned structures has been investigated in pseudo 3D stacked SrBi 2 Ta 2 O 9 (SBT) capacitors. Their stability was compared to standard TEOS spacers. The high compressive stress at the edge of patterned electrodes, as a consequence of the high thermal expansion mismatch between the metals used in the electrode and TEOS, make the system mechanically unstable at the SBT crystallization conditions (700 • C for 1 hour). The mechanical problems could be overcome if the same noble metals used in the electrode are incorporated as spacers. However, thermal stability during the SBT crystallization conditions is still an issue. For the case of Ir, surface oxidation decreases the SBT polarization values. In the case of Ir\Pt, Ir diffuses through Pt and oxidizes, leading to unstable patterned structures and to the oxidation of the Ti(Al)N layer.

Integration of ferroelectric SrBi2Ta2O9-based capacitors in 0.35μm CMOS technology

“…4). The microstructural characteristics of each layer and the thermo-mechanical stability investigations of the integrated BE\SBT\Pt FeCAP's structure have been published elsewhere [5,6]. As a brief summary, we have observed that Ir and Pt layers mainly define the overall stress of the stack [3].…”

“…Further optimization of the sidewall material, e.g. using metal spacers, is currently under investigation [5].…”

Challenges for Integration of Embedded FeRAMs in the sub-180 nm Regime

“…Among them the most challenging is BE lateral oxidation during ferroelectric anneal [10][11], while control of parasitic capacitors (adjacent FeCaps along same Bit Line) can be mastered even at design level.…”