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Germanium is gaining interest in the semiconductor industry as a replacement channel material for high mobility applications. Contamination directly affects the device performance, yield and reliability. Therefore, effective surface preparation is critical for full utilization of the high mobility characteristics of the Ge substrate. Effective surface preparation involves effective removal of metal, native oxide and organic contaminants with minimal consumption of the substrate and minimal increase in the surface roughness. Robust surface passivation characteristics are also required.
Fundamental properties of the Ge substrate were investigated by looking at the correlation between the etch rates and surface roughness. Aqueous solutions containing oxidants such as SC-1 and SC-2 have abnormally high Ge etch rates and increase the surface roughness. Ozonated DI solution (DI-O 3 ) was used to improve the surface roughness equal to that of Si prime wafers.
In this work, metal removal efficiencies were studied by intentional contamination of the Ge surface and subsequent droplet collection and ICP-MS measurement. This wafer scanning analysis (WSA) method coupled with Pourbaix diagrams allowed us to optimize HCl and HBr solutions that were effective in removing native oxide and metal contaminants, including Cu, from the Ge surface without surface roughness degradation and substrate consumption. Organic contamination was removed by ozone oxidation and thermal treatments. Surface passivation characteristics of hydrogen halides (HF, HCl, HBr, HI) on Ge were studied.
Surface passivation characteristics of hydrogen halides (HF, HCl, HBr, HI) on Ge were studied. Surface passivation characteristics improved with increasing atomic number halogen specie with HBr and HI having the most robust passivation. With accurate surface bonding studies with synchrotron radiation XPS studies, electronegativity and steric effects were used to explain the passivation trend. Effective Ge surface cleaning was clearly demonstrated in this study and a fully integrated Ge baseline cleaning process was proposed.
