Abstract
We demonstrated that a flat band voltage (VFB) shift could be controlled in TiN/(LaO or ZrO)/SiO2 stack structures. The VFB shift described in term of metal diffusion into the TiN film and silicate formation in the inserted (LaO or ZrO)/SiO2 interface layer. The metal doping and silicate formation confirmed by using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) line profiling, respectively. The direct work function measurement technique allowed us to make direct estimate of a variety of flat band voltages (VFB). As a function of composition ratio of La or Zr to Ti in the region of a TiN/(LaO or ZrO)/SiO2/Si stack, direct work function modulation driven by La and Zr doping was confirmed with the work functions obtained from the cutoff value of secondary electron emission by auger electron spectroscopy (AES). We also suggested an analytical method to determine the interface dipole via work function depth profiling.
Highlights
In this study, the work function depth profiling technique has been applied to measure the work function of the gate electrodes directly; further, the work function was obtained from the cutoff energy of secondary electron energy distribution induced with the incident low energy (
The advantage of this technique is to measure the work function of a localized area using a focused electron beam and measure an accurate work function of the surface using a low energy electron beam. These results demonstrated the mechanism of the work function changes, which were observed by using the LaO or ZrO as a work function control layer in TiN metal gate stacks
Our previous paper reported[12] that the effective work function (EWF) exponentially decreased as La doping concentration increased in a TiN gate electrode
Summary
The chemical compositions of the TiN/LaO/SiO2/Si-sub stacks were measured via TEM-EDX and TEM, in order to interpret the above-mentioned results. Their Fermi levels (EF) were aligned when both the samples and analyzer were grounded. These results show the direction of the dipole moments. In case of LaO, the EWF was determined using the sum of the dipole and the La doped TiN effect, which reduces the EWF as described in Eq (2)
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