Effect of nitrogen passivation/pre nitration on interface properties of atomic layer deposited HfO₂

Abstract

Properties and quality of thin films depend on the methods used to deposit it. ALD is a surface dependent process and is one of the best deposition techniques because of the control we have on the deposition. In ALD, quality of initial few layers depends on substrate surface. A well prepared substrate surface reduces problem of nucleation. In this work, we have reported nitrogen passivation/pre nitration of silicon wafer as a surface preparation technique for atomic layer deposition. The results obtained have shown that the nitrogen passivation/pre nitration have profound effect on electrical characteristics. Nitrogen passivation has been done at two different temperatures, 350 and 500 °C. Crystal structures and phase information of deposited HfO₂ thin films were studied in passivated and non passivated cases using GI-X-ray diffraction, elemental composition was investigated by EDX. Capacitance–voltage (C–V), current–voltage (I–V) and conductance–voltage (G–V) measurements were performed. The density of the interface state charges (D_it) was computed from C–V and G–V characteristics. Leakage current has been reduced almost two fold by utilizing this technique indicating change in properties of deposited oxide and its interface with the substrate. Decrease in interface trap charges has also been observed. Density of interface traps has been decreased from 2.87 × 10⁻¹² to 1.57 × 10⁻¹² cm⁻² eV⁻¹. Crystallographic phase of the deposited films are also found different in two different temperatures, 350 and 500 °C of passivation. Crystallographic phase of the deposited films were determined from analysis of measured XRD spectra and are found different in two cases.