Papers by Keyword: Scanning Capacitance Microscopy

Abstract: The suitability of scanning probe methods based on atomic force microscopy (AFM) measurements is explored to investigate with high spatial resolution the elementary cell of 4H-SiC power MOSFETs. The two-dimensional (2D) cross-sectional maps demonstrated a high spatial resolution of about 5 nm using the scanning spreading resistance microscopy (SSRM) capabilities. Furthermore, the scanning capacitance microscopy (SCM) capabilities enabled visualizing the fluctuations of charge carrier concentration across the different parts of the MOSFETs elementary cell.

Abstract: This paper presents a macro-and nanoscale electrical investigation of Schottky and metal-oxide junctions with hetero-epitaxial 3C-SiC layers grown on Si. Statistical current-density-voltage (J-V) characterization of Pt/3C-SiC Schottky diodes showed an increase of the reverse leakage current with increasing the devices diameters. Furthermore, C-V and J-V analyses of SiO₂/3C-SiC capacitors revealed non-idealities of the thermal oxide, such as a high trapped positive charge (3×10¹² cm⁻²) and a reduced breakdown field (E_BD=6.5 MV/cm) compared to ideal SiO₂. Nanoscale electrical characterizations by conductive atomic force microscopy (CAFM) and scanning capacitance microscopy (SCM) allowed to shed light on the origin of non-ideal behavior of Schottky and thermal oxide junctions, by correlating the morphological features associated to 3C-SiC crystalline defects with local current transport and carrier density.

Abstract: In this work, the combined effect of a shallow phosphorus (P) pre-implantation and of a nitridation annealing in N₂O on the properties of the SiO₂/4H-SiC interface has been investigated. The peak carrier concentration and depth extension of the electrically active dopants introduced by the nitridation and by the combination of P pre-implantation and nitridation were determined by high resolution scanning capacitance microscopy (SCM). Macroscopic capacitance-voltage (C-V) measurements on metal oxide semiconductor (MOS) capacitors and nanoscale C-V analyses by SCM allowed to quantify the electrical effect of the donors introduced underneath the SiO₂/4H-SiC interface. Phosphorous pre-implantation and subsequent high temperature electrical activation has been shown not only to produce an increased doping in the 4H-SiC surface region but also a better homogeneity of surface potential with respect to the use of N₂O annealing only.

Abstract: Ferroelectric-relaxor behavior on highly epitaxial Barium Zirconium Titanate (Ba (Zr_0.2Ti_0.8)O₃) thin film was investigated using the Piezoresponse Force Microscopy specifically to investigate the onset of relaxor behavior. The surface roughness, microstructure and the grain size of the film were systematically studied. Ferroelectric switching at random localized points were observed at room temperature though it has been previously reported that the phase transition in BZT-20 occurs at 285K. Phase reversal with the reversal of the applied voltage was also seen. Scanning Capacitance Microscope has been employed to interrogate the localized change in the capacitance with change in voltage. The thin film sample showed the presence of ferroelectric nanoregions at room temperature unlike its bulk counterparts which is paraelectric at room temperature.

Abstract: In this paper a comparative study of the impact of N₂O and POCl₃ annealing on the SiO₂/SiC system is presented, combining nanoscale electrical characterization of SiC surface doping by scanning spreading resistance microscopy (SSRM) and scanning capacitance microscopy (SCM) to the conventional capacitance-voltage (C-V) and current-voltage (I-V) measurements on MOS-based devices. A significant reduction of the interface states density (from 1.8×10¹² to 5.7×10¹¹ cm^-2eV^-1) and, correspondingly, an increase in the carrier mobility (from 19 to 108 cm²V^-1s^-1) was found moving from N₂O to POCl₃ annealing. Furthermore, SSRM measurements on bare p⁺-type SiC regions selectively exposed to N₂O and POCl₃ at high temperature provided the direct demonstration of the incorporation of N or P-related donors in the SiC surface, leading to a partial compensation of substrate acceptors during N₂O treatment and to an overcompensation during POCl₃ annealing. Finally, cross-sectional SCM profiles performed on epitaxial n-doped 4H-SiC with 45 nm SiO₂ (subjected to post deposition annealing in the two ambients) allowed to quantify the active donors concentrations associated to P or N incorporation under the gate oxide, showing almost a factor of ten higher doping (4.5×10¹⁸cm^-3 vs 5×10¹⁷cm^-3) in the case of P related donors.

Abstract: In this work the field effect mobility measured on lateral n-channel MOSFETs in 4H-SiC with Al implanted body was correlated with the interface trap density measured on MOS capacitors. The test devices were fabricated on samples subjected to different post implantation annealing conditions (i.e. with or without a protective carbon capping layer) and to an identical post-oxidation annealing in N₂O. Despite the improved interfacial morphology, a reduction of the peak mobility (from 40 to 24 cm²V^-1s^-1) was observed using the carbon capping layer. An increase in the density of interface traps was consistently found. Nanoscale measurements of the active dopant concentration in the SiC channel region by cross-sectional scanning capacitance microscopy showed an higher compensation of p-type SiC for the sample processed without the capping layer, which indicates a more efficient incorporation of nitrogen at the SiO₂/SiC interface.

Abstract: This paper reports on the electrical activation and structural analysis of Al implanted 4H-SiC. The evolution of the implant damage during high temperature (1650 – 1700 °C) annealing results in the presence of extended defects and precipitates, whose density and depth distribution in the implanted sheet was accurately studied for two different ion fluences (1.31014 and 1.31015 cm-2) by transmission electron microscopy. Furthermore, the profiles of electrically active Al were determined by scanning capacitance microscopy. Only a limited electrical activation (10%) was measured for both fluences in the samples annealed without a capping layer. The use of a graphite capping layer to protect the surface during annealing showed a beneficial effect, yielding both a reduced surface roughness and an increased electrical activation (20% for the highest fluence and 30% for the lowest one) with respect to samples annealed without the capping layer.

Abstract: This paper reports a detailed study of the electrical activation and the surface morphology of 4H-SiC implanted with different doping ions (P for n-type doping and Al for p-type doping) and annealed at high temperature (1650–1700 °C) under different surface conditions (with or without a graphite capping layer). The combined use of atomic force microscopy (AFM), transmission electron microscopy (TEM), and scanning capacitance microscopy (SCM) allowed to clarify the crucial role played by the implant damage both in evolution of 4H-SiC surface roughness and in the electrical activation of dopants after annealing. The high density of broken bonds by the implant makes surface atoms highly mobile and a peculiar step bunching on the surface is formed during high temperature annealing. This roughness can be minimized by using a capping layer. Furthermore, residual lattice defects or precipitates were found in high dose implanted layers even after high temperature annealing. Those defects adversely affect the electrical activation, especially in the case of Al implantation. Finally, the electrical properties of Ni and Ti/Al alloy contacts on n-type and p-type implanted regions of 4H-SiC were studied. Ohmic behavior was observed for contacts on the P implanted area, whilst high resistivity was obtained in the Al implanted layer. Results showed a correlation of the electrical behavior of contacts with surface morphology, electrical activation and structural defects in ion-implanted, particularly, Al doped layer of 4H-SiC.

Abstract: We studied the evolution of the electrical activation with annealing temperature and time in 4H-SiC implanted with Al ions at room temperature (RT). An accurate comparison between the electrical activation data obtained by FPP and SCM was carried out. The dependence of the electrically active profiles on annealing time was studied during isothermal (Tann=1600 °C) annealings for times ranging from 0 (spike anneal) to 30 min. By performing isochronal (t=30 min) processes at temperatures from 1550 to 1650 °C, the effect of the annealing temperature on the net doping concentration profiles was studied. Moreover, the activation energy (6.30.3 eV) associated to the process was extracted from the Arrhenius plot of the net active dose. Finally, the effect of the different thermal budgets on the roughening of the Al implanted 4H-SiC surface was also investigated in details by atomic force microscopy.