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The physical and reliability characteristics of strained-Si0.8Ge0.2 MOS capacitor and strained-Si0.7Ge0.3 MOSFET with Hf-based gate dielectrics prepared by atomic layer chemical vapor deposition are investigated. The thickness and composition of the gate dielectrics are measured by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy, respectively. The gate leakage current and interface traps of HfO2/Si1-xGex gate structure are slightly higher as compared to the HfO2/Si MOS devices, which is basically caused by the Ge at the interface. The electrical properties of both HfO2/Si and HfO2/Si1-xGex devices can be improved with increasing PDA temperature up to 800°C, which is due to the thicker interfacial layer grown at the interface, even though crystallization also grows with increasing temperature. However, with higher PDA temperature (>800°C), serious crystallization of HfO2 film causes more bulk traps induced electrical degradation. The electrical stress induced degradation of Si1-xGex substrate is slightly higher as compared to the control Si, due to more traps generations at the HfO2/Si1-xGex interface. For MOSFET, strained-Si1-xGex can effectively improve the drain current for about 20% at saturation and 69% at linear region. The higher gate leakage (Jg∼1.4×10-9A/cm2 at 2 V) and lower breakdown voltage (BD∼3.1 V) of Si0.7Ge0.3 pMOS devices are observed as compared to control Si devices (Jg∼7.9×10-12A/cm2 at 2 V and BD∼7.4 V). After the electrical stress, the degradation of drain current and transconductance and the shift of threshold voltage for Si1-xGex PMOSFET are larger than those for control Si devices, implying Ge induced trap generation at the Hf-silicate/Si1-xGex interface.
Device and Materials Reliability, IEEE Transactions on (Volume:5 , Issue: 2 )
Date of Publication: June 2005