Department: Electrical & Computer Engineering
Faculty Advisor(s): Andrew Kummel

Primary Student
Name: Maximillian Samuel Clemons
Email: msclemon@ucsd.edu
Phone: 858-534-3498
Grad Year: 2016

Silicon-Germanium is expected to be used in the future CMOS technology due to tunability of its carrier mobility and band gap by variation in Ge content and tensile/compressive stresses. In contrast to Si, SiGe native oxide is a combination of SiOx and GeOx, which has low interface quality and stability in comparison with SiO2. Scaling SiGe devices is crucial in its future application and ALD growth of high-k oxides with small equivalent oxide thickness (EOT) such as Al2O3, HfO2 and TiO2 on SiGe is favorable. The present study determines the effect of the ex-situ sulfur passivation (via (NH4)2S dip) and in-situ NH3 plasma nitridation, prior to ALD, on high-k oxide/SiGe interfaces in terms of oxide leakage and interface and near-interface trap density. MOS capacitors fabricated by Al2O3 and HfO2 ALD at 120C and 300C, have been compared by capacitance-voltage (C-V) and current-voltage (I-V) measurements. Compared to HF clean, both ex-situ S-passivation and in-situ plasma nitridation led to smaller gate leakage current for Al2O3. In addition, both methods resulted in surface stability in air up to an hour, which extends the wafer queue time prior to low interfacial defect density ALD oxide deposition. Lower Al2O3/SiGe interface trap density (Dit) relative to HF-treated samples was achieved by ex-situ S-passivation at low ALD temperatures (120 C) and by in-situ NH3 plasma at high ALD temperatures (300 C). Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) measurements on SiGe(001) with 0.8nm thick Al2O3 showed that (NH4)2S clean significantly reduces the amount of GeOx at the in Al2O3/SiGe(001) interface, compared to HF clean. Similarly NH3 plasma at 300 C largely reduced the GeOx and GeON components at the interface and selectively terminated the Al2O3/SiGe interface with Si3N4 and SiON. The universality of the two SiGe passivation techniques was demonstrated by fabrication of HfO2/SiGe MOSCAPs.

Industry Application Area(s)
Electronics/Photonics | Materials | Semiconductor

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