The understanding of charge injection mechanism at metal/dielectric interface is crucial in many applications. A direct probe of such phenomenon requires a charge measurement method whose spatial resolution is compatible with the characteristic scale of phenomena occurring after injection, like charge trapping, and with the geometry of samples under investigation. In this paper, charge injection at metal/dielectric interface and their motion in silicon nitride layer under tunable electric field are probed at nanoscale using a technique derived from Atomic Force Microscopy. This was achieved by realizing embedded lateral electrode structures and using surface potential measurement by Kelvin Probe Force Microscopy (KPFM) to provide voltage, field and charge profiles close to the metal/dielectric interface during and after biasing the electrodes. The influence of electric field enhancement at the interface due to the electrode geometry was accounted for. Electron and hole mobility was estimated from surface potential profiles obtained under polarization. Charge dynamic was investigated during depolarization steps.
Charge injection and retention in thin dielectric layers remain critical issues due to the great number of failure mechanisms they inflict. Achieving a better understanding and control of charge injection, trapping and transport phenomena in thin dielectric films is of high priority aiming at increasing lifetime and improving reliability of dielectric parts in electronic and electrical devices. Thermal silica is an excellent dielectric but for many of the current technological developments more flexible processes are required for synthesizing high quality dielectric materials such as amorphous silicon oxynitride layers using plasma methods. In this article, the studied dielectric layers are plasma deposited SiOxNy. Independently on the layer thickness, they are structurally identical: optically transparent, having the same refractive index, equal to the one of thermal silica. Influence of the dielectric film thickness on charging phenomena in such layers is investigated at nanoscale using Kelvin Probe Force Microscopy (KPFM) and Conductive Atomic Force Microscopy (C-AFM). The main effect of the dielectric film thickness variation concerns the charge flow in the layer during the charge injection step. According to the SiOxNy layer thickness two distinct trends of the measured surface potential and current are found, thus defining ultrathin (up to 15 nm thickness) and thin (15 nm-150 nm thickness) layers. Nevertheless, analyses of KPFM surface potential measurements associated with results from Finite Element Modelling of the structures show that the dielectric layer thickness has weak influence on the amount of injected charge and on the decay dynamics, meaning that pretty homogeneous layers can be processed. The charge penetration depth in such dielectric layers is evaluated to 10 nm regardless the dielectric thickness.
Charges injection at metal/dielectric interface and their motion in silicon nitride layer is investigated using samples with embedded lateral electrodes and surface potential measurement by Kelvin Probe Force Microscopy (KPFM). Bipolar charge injection was evidenced using this method. From surface potential profile, charge density distribution is extracted by using Poisson's equation. The evolution of the charge density profile with polarization bias and depolarization time was also investigated.
Charges accumulation and injection in dielectric material remains critical because it is related to a lot of applications or issues. A deep understanding of interfaces phenomena is needed, but classical space charges techniques exhibit less resolution than the required one. Atomic Force Microscopy (AFM) because of its sensitivity to electrostatic force and its high resolution (close to nanometer) appears to be the best method to characterize charges at nanoscale. Here, two techniques are investigated and compare: Kelvin Force Microscopy (KFM) and Electrostatic Force Distance Curve (EFDC). KFM is used to measured surface potential modification induced by charges. However vertical localization of charges seems difficult to attempt. EFDC follows electrostatic force as function of tip-surface distance. This technique appears promising because of its high resolution, sensitivity to charges localization and distance dependance.
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