TDDB Reliability Improvement of Low Thermal Budget RMG Stacks

Low thermal budget flows are essential for enabling 3D integration schemes in future CMOS nodes. Novel low thermal budget “reliability anneal” solutions are currently being investigated to cure dielectric defects and improve BTI and TDDB reliability. We report here a TDDB study on pMOS gate stacks with a novel hydrogen radical IL treatment combined with four different HK post-deposition anneals (PDA) at increasing (low) thermal budgets for a complete BTI/TDDB reliability solution. We confirm a clear improvement of the TDDB reliability with a 550°C-lh PDA; a similar improvement is achieved with a 500°C-lh PDA, while a somewhat smaller improvement is observed with a 450°C-lh PDA. A larger improvement at 450°C can be obtained by increasing the PDA duration to 2h, suggesting longer anneals at reduced temperature might possibly match the TDDB reliability of standard high thermal budget gate stacks. We attribute the TDDB improvement observed with the PDA's to strain relaxation in the HK layer upon densification. This reduces the density of stretched Hf-O bonds, which are potential precursors for defect generation eventually inducing breakdown.