Electrochemical passivation of Si and SiGe surfaces

Abstract

Publisher Summary This chapter discusses the structural and electronic properties of electrochemically passivated silicon (Si) surfaces. The chapter describes the in situ techniques of Fourier transform infrared spectroscopy (FTIR), surface photovoltage (SPV), and pulsed photoluminescence (PL), which give information about surface chemical bonds, electronic trap states, and nonradiative recombination centers at the Si surface, respectively. The combination of these methods gives the opportunity to correlate changes in chemical bonds with changes in trapping sites or intrinsic dangling bonds, which act as nonradiative recombination defects. Stroboscopic measurements of PL and SPV signals with laser pulses in the nanosecond range have been developed to minimize the influence of the exciting light on the electrochemical processes. Interface state distributions are obtained by ex situ SPV measurements. The chapter also discusses the electronic states of hydrogenated Si surfaces and their dependence on morphology. Hydrogenation of Si surfaces plays a key role in ultraclean processing of Si and is the initial step for following treatments, like epitaxial growth of semiconductor material on crystalline silicon or thin gate oxide formation. The ideally hydrogenated Si surface is free of electronic states in the forbidden gap. Thus, electronic states at hydrogenated Si surfaces should be related to isolated defects. Chemically and/or electrically active surface sites at hydrogenated Si surfaces can serve as reaction sites for organic molecules. The surface morphology has great influence on the electronic states at hydrogenated Si surfaces. Four types of hydrogenated Si surfaces are distinguished by their basic structural properties: HF-dipped, buffered ammonium fluoride treated, electrochemically hydrogenated, and electrochemically etched-porous silicon. The electronic surface states of hydrogenated Si surfaces are described in this section. The electrochemical hydrogenation that takes place during the so-called current transient is investigated in detail. The chapter discusses the role of local surface reconstruction for passivation and stabilization of hydrogenated Si surfaces.