Cleaning and Passivation of Germanium and Silicon Germanium Surfaces

Abstract

Germanium and silicon germanium are promising materials for the development offuture microelectronics as they exhibit higher carrier mobilities and smaller bandgaps which can be advantageous in the creation of faster devices. Before these materials can be integrated into current manufacturing, processes for cleaning, etching and passivation of the surface must be developed. Understanding and controlling these processes is critical as the surface plays a key role in device performance. Additionally, the development of liquid phase processes is important because they offer a simpler and less expensive method compared to in-situ methods. This work studies the effects of semiconductor cleaning and etching solutions on SiGe as well as the passivation of these surfaces. SiGe surfaces were treated in aqueous solutions of HCl, HF, and various combinations to determine the most effective strategy to remove oxides and limit carbon contamination. The most effective etching process is a combined solution of HF and HCl in a ratio of 1:3:300 v/v HF:HCl:H2O. The presence of HF is necessary to remove SiO2. Further cleaning studies were carried out on SiGe surfaces in solutions of (NH4)OH:H2O2:H2O at varying concentrations. The solution selectively etches Ge atoms and enriches the surface in Si atoms which are oxidized in solution. At high concentrations of (NH4)OH and H2O2 the selective etching of Si0:25Ge0:75 and Si0:15Ge0:85 can remove the entire SiGe film. The passivation of these surfaces with (NH4)2S and alkanethiols was studied. (NH4)2S deposits sulfur which reacts preferentially with the Ge atoms. The deposition of alkanethiol self-assembled monolayers (SAMs), particularly 1-eicosanethiol (ET, C20H42S) was studied on Ge with the goal of identifying the source of surface oxidation which occurs during the self-assembly process. Eliminating dissolved oxygen in solution and air exposure after the alkanethiol deposition resulted in the least oxidation as measured by XPS.