Atomic layer deposited high-κ nanolaminates for silicon surface passivation

Abstract

Nanolaminates comprising of TiO2 or HfO2 sublayers within an Al2O3 matrix are grown with atomic layer deposition. These nanolaminates provide an improved silicon surface passivation compared to conventional Al2O3 films. The physical properties of the nanolaminates can be described with a dynamic growth model that considers initial and steady-state growth rates for the involved metal oxides. This model links the cycle ratios of the different atomic layer deposition precursors to the thickness and the material concentrations of the nanolaminate, which are determined by means of spectroscopic ellipsometry. Effective carrier lifetime measurements show that Al2O3-TiO2 nanolaminates achieve values of up to 6.0 ms at a TiO2 concentration of 0.2%. In Al2O3-HfO2 nanolaminates, a maximum effective carrier lifetime of 5.5 ms is reached at 7% HfO2. Electrical measurements show that the TiO2 incorporation causes strong hysteresis effects, which are linked to the trapping of negative charges and result in an enhanced field effect passivation. For the Al2O3-HfO2 nanolaminates, the capacitance data clearly show a very low density of interface traps (below 5·1010 eV−1·cm−2) and a reduction of the fixed charge density with increasing HfO2 concentration. Due to the low number of recombination centers near the surface, the reduced field effect passivation only had a minor impact on the effective carrier lifetime.