| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 98 === Gadolinium (Gd) cap layer on the Hf-based high-k dielectric is proposed to reduce effective work function (EWF) and threshold voltage (VTH) of TaC metal gate. However, Gd could diffuse through Hf-based layer into substrate to cause unwanted damages, thus, needing a post NH3 nitridation to suppress these unwanted damages and decrease gate leakage current. Besides, even a NH3 nitridation could improve devices’ performances; however, the nitrogen atoms incorporated in the gate stack via the NH3 plasma treatment could also diffuse into the Gd-cap layer, thus blocking the Gd ions at the top of the Hf-based high-k/metal-gate, which then generate bulk charges to degrade the device’s positive bias temperature instability (PBTI) significantly. We identify the diffusion of nitrogen in the Gd cap layer, as well as the location of trap defects in the Hf-based high-k/metal-gate with secondary ion mass spectrometry (SIMS), flicker noise, and charge pumping measurements.
Furthermore, we report the optimism channel stack thickness ratio by controlling strained SiGe and Si cap layer thickness to overcome Ge diffusion and confine carriers in strain SiGe layer without formation of a significant parasitic channel at the interface. By optimizing the channel thickness ratio, we achieved higher performance and better reliability Hf-based high-k/metal gate SiGe pMOSFET compared to gate stack on Si channels. Moreover, a post deposition annealing (PDA) including oxygen ion after high-k dielectric deposition was used to improve reliability of the Hf-based high-k/metal gate device. Experiment results showed that the oxygen PDA didn’t degrade the drive current and effective oxide thickness of the Hf-based gate devices. In addition, reliability issues such as PBTI, NBTI and time dependent dielectric breakdown (TDDB) were also improved by the oxygen PDA significantly.
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