Decoupled Plasma Nitridation (DPN) and Postnitridation Annealing (PNA) Treatment for Metal Boundary Effect Reduction

A decoupled plasma nitridation (DPN)/postnitridation annealing (PNA) process scheme to reduce the metal boundary effect (MBE) was experimentally demonstrated using a 28-nm high- <tex-math notation="LaTeX">k </tex-math> first/gate last process platform. Through extensive physical and electrical characterization, it was found that the main reason for the MBE effect could be the lateral diffusion of aluminum through the HK layer. The DPN/PNA treatment process was found to improve the nitrogen distribution in the HK layer and enhance its diffusion barrier properties. Consequently, the MBE-induced <tex-math notation="LaTeX">Vₜ </tex-math> shift was successfully suppressed in pFETs that were particularly susceptible to the MBE effect. Additionally, the proposed solution led to an increased static noise margin (SNM) of a specially designed tightly spaced SRAM. This outcome not only validates the effectiveness of the proposed approach, but also demonstrates its value for future SRAM scaling in advanced nodes.