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Germanium Surface Cleaning with Hydrochloric Acid

BACKGROUND Germanium is gaining interest as a potential substrate with high mobility applications. Therefore effective surface preparation for Ge substrates is becoming important. Effective surface cleaning involves removing metal contaminants with minimal consumption of the substrate and minimal increase in surface roughness. Effect of standard cleaning chemicals on surfaces roughness was investigated in a previous study [1]. It was found that germanium has properties very different from that of silicon because of the water-soluble nature of the native oxide layer. For Si, effective surface cleaning can be achieved by removal of the contaminant trapping native oxide layer by such solutions as SC-1 (NH4OH:H2O2:DI) and SC-2 (HCl:H2O2:DI). But as can be seen in Figure 1, Ge has very high etch rates in SC-1 and SC-2 type mixtures even at room temperatures. Effectiveness of Ge native oxide removal was investigated using different concentrations of HF and HCl solutions without etching the Ge substrate. Also metal removal efficiency from Ge surface was investigated using HCl solutions using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry).