Interface layer in hafnia/Si films as a function of ALD cycles

Abstract

A systematic angle resolved x-ray photoelectron spectroscopy study of the structure of hafnia films grown on silicon with atomic layer deposition (ALD) is presented. The hafnium precursor employed was tetrakis dimethyl amino hafnium with water as the oxidant agent. The number of ALD cycles ranged from 3 to 25. The Hf 4f spectrum shows two components 0.47 eV apart, one associated with hafnia (17.6 eV) and the other (18.1 eV) with a hafnium silicate interface layer. The composition of the interface layer, HfxSi1-xOy, evolves continuously from silicon-rich (x = 0.1 for 3 ALD cycles) to hafnium rich (x = 0.75 for 25 ALD cycles). The binding energy difference between the Hf 4f components associated with the silicate and hafnia changes very little with the silicate composition. The binding energy of the Si4+ component, which is associated with the silicate, varies from 3.25 to 2.85 eV (referenced to the Si0+ component) with the number of ALD cycles. The oxygen stoichiometric coefficient of the silicate is close to the expected value of 2 for all the samples. However, the hafnia shows an excess of oxygen for some of the samples.