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저주파 잡음 측정을 이용한 High-k 절연막 MOSFET 소자의 신뢰성에 관한 연구

저주파 잡음 측정을 이용한 High-k 절연막 MOSFET 소자의 신뢰성에 관한 연구
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This thesis describes the reliability study of MOSFETs with high-k dielectrics using low-frequency noise measurements. For La-incorporated high-k dielectrics, the oxide breakdown characteristics are verified using low-frequency noise measurements. For SiGe channel p-MOSFETs with high-k dielectrics, the oxide breakdown, the negative bias temperature instability (NBTI), and hot carrier instability (HCI) are observed using low-frequency noise and charge pumping measurements. The n-MOSFET with La-incorporated high-k dielectrics is measured before and after channel oxide breakdown. Low frequency noise (LFN) after channel soft oxide breakdown (SBD) of n-MOSFETs with a HfLaSiO gate dielectric and TaN metal gate shows a Lorentzian-like spectrum, which is not observed in HfSiO gate dielectric devices after channel SBD. This is related to the spatial location of the SBD spot. Because the La weakens atomic bonding in the interface layer, the SBD spot is generated close to the Si/SiO2 interface. This is verified using the time domain analysis. The reliability of SiGe channel p-MOSFETs with high-k dielectrics is studied. Si0.75Ge0.25 p-MOSFETs with HfSiO gate dielectrics show the higher breakdown voltage than the Si channel p-MOSFETs in TZDB measurements. At the first instant after TZDB, the increase of hole current is larger than the increase of electron current in Si0.75Ge0.25 p-MOSFETs, which is opposite to the Si channel p-MOSFETs. This supports that the breakdown in Si0.75Ge0.25 p-MOSFETs are occurred at interfacial layer (IL) and that in Si p-MOSFETs are occurred at bulk layer. These characteristics are also observed in BD measurements. Low-frequency noise (LFN) after BD of Si0.75Ge0.25 p-MOSFETs shows a small Lorentzian hump and that of Si p-MOSFETs shows an only increase for all measured frequency. This is evidence that the IL of Si0.75Ge0.25 p-MOSFETs is more fragile than that of Si p-MOSFETs because of the Ge induced trap generation.Finally, the NBTI and HCI of SiGe channel p-MOSFETs are studied. The short gate-length devices are more degraded by NBTI in respect of the threshold voltage shift (ΔVth) than the long gate-length devices in Si0.75Ge0.25 channel p-MOSFETs. This supports that the short gate-length devices contain more fragile bond than the long gate-length devices do. Under channel hot carrier (CHC) stress, the drain currents are severely degraded and the kink effect in subthreshold region is observed in Si0.75Ge0.25 channel p-MOSFETs.
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