Extensive Study of the Correlation between Contact Etch Stop Nitride film Properties and Negative Bias Temperature Instabilities Measured in pMOSFETS

Mobility enhancement by process induced strain in the Si channel has been extensively used since 90nm node to improve transistor drive current. Such technique becomes mandatory to compensate scalability limits of several processes like ultra thin gate oxide growth. The Contact Etch Stop nitride Layer (CESL) is the most commonly used method to get stress induced mobility enhancement. However, the re-engineering of this nitride layer for stress enhancement needs to cover all electrical aspects including reliability characteristics, in particular the Negative Bias Temperature Instabilities (NBTI). In this work, we confirm that pMOS NBTI can be significantly impacted by the nitride CESL properties. A Design Of Experiment methodology allows demonstrating that the NBTI is enhanced by the nitride weight density, linked to hydrogen diffusivity within the film. It is finally shown that the nitride density must be set as low as possible to minimize the NBTI.