Spectroscopic and Electrical Studies of Hafnium-Based High-k Thin Film Dielectrics on Germanium Surfaces

Abstract

The research discussed here has been carried out in order to advance the basic understanding of the compatibility between germanium surfaces and hafnium-based high κ dielectric materials with a particular emphasis on their potential for microelectronic applications. To this end, spectroscopic studies were carried out to determine the physical and electronic properties of Ge/high-κ structures, and MOS capacitors were fabricated to study their electrical characteristics. Crystallinity, thermal stability, electronic defect levels, and Hf d state degeneracy removal in this material system were studied via x-ray absorption spectroscopy (XAS). The presence of conduction band edge defect states was confirmed by spectroscopic ellipsometry (SE), and medium energy ion spectroscopy (MEIS) was employed to investigate chemical distributions within these structures. Capacitance-voltage (C-V) measurements made on related MOS structures provided valuable insight into the nature of carrier trapping and charged traps in these devices, and lastly, current-voltage (I-V) measurements revealed information about the integrity of these gate materials while in contact with germanium surfaces. While the nitridation of germanium surfaces was shown to mitigate atomic migration and diffusion to a degree during device processing, both hafnia and hafnium nitro-silicate films demonstrated a large degree of physical and chemical instability when in contact with germanium. Moreover, these difficulties were found to be correlated with electrically active defects which make this technology unsuitable for CMOS applications at present.