Experimental evidences of charge transition levels in ZrO2 and at the Si: ZrO2 interface by deep level transient spectroscopy

Abstract

The native defects in zirconium oxide (ZrO2) and defects at the ZrO2/Si interface lead to threshold voltage shifts, Fermi level pinning, and various other reliability concerns. It is necessary to recognize the origin of these defects and to quantify them. A large number of theoretical reports deal with oxygen vacancy related defect states in the ZrO2 films; however, the large band gap limits the experimental assessments. In this study, we have deployed Deep Level Transient Spectroscopy to study the deep level defects present in high-κ ZrO2 gate dielectrics and at the Si:ZrO2 interface. The band alignment of the Al/ZrO2/Si stack was derived from Ultraviolet Photo electron Spectroscopy measurement to find the exact locations of trap levels. Five deep levels were observed in the band gap of ZrO2; these are related to different charge states of oxygen vacancies. The activation energies of these trap states are in the range of 1.16–1.84 eV from the ZrO2 conduction band. The capture cross-section of these states was also measured and found to be quite low (10−21 cm2). The small value of capture cross-sections is attributed to tunneling events occurring between the energy levels of the bulk and interface. This study would aid in the understanding of numerous fascinating facts witnessed in ZrO2, such as resistive switching, threshold voltage instabilities, and leakage current problems associated with oxygen vacancy related traps.