Preferential Halogen Adsorption on Si, Ge, and SiGe Surfaces for Selective Etching

The continued reduction in semiconductor device dimensionality has motivated the evolution of device architectures from two-dimensional planar to three-dimensional vertical structures. Among them, the Gate-All-Around (GAA) device architecture has been gaining popularity because it allows short channel effects to be controlled by wrapping the device gate around the entire channel, in order to eliminate current leakage. GAA devices are formed by heteroepitaxial growth of alternating Si and SiGe layers, which are patterned and recessed vertically, therefore being exposed laterally. Isotropic and selective etching between Si and SiGe, depending on the channel charge carriers, is then needed for device manufacturing. In this work, using ab initio density-functional theory (DFT), we present an extensive study on halogen adsorption on Si and SiGe systems to address the topic of reverse selectivity. We perform a detailed analysis of the characteristics of the SiGe alloy and subsequently use the molecular precursor chemistry of NF3 to model the interaction and possible etching reactions with Si/SiGe heterojunctions. Differential halogen chemistry interactions with Si and SiGe surfaces are also reported, and the effect of surface and subsurface nitrogen adsorption on Si and SiGe is studied in detail, with the aim of proposing a simple selective etching mechanism that serves to optimize the otherwise complex vertical and recessed patterning of Si and SiGe stacks.