Characterization of fast interface states in nitrogen- and phosphorus-treated 4H-SiC MOS capacitors

Abstract

We investigate 'fast interface states' at semiconductor-dielectric interfaces in SiC MOS capacitors that underwent three different interface passivation processes: two nitrogen-based annealing techniques (NO and nitrogen-plasma) and phosphosilicate glass (PSG). 'Fast interface' states in this case refer to interface states with response times <1 μs typically used in standard admittance based MOS characterization methods. In order to appropriately characterize the density of interface states (D it ) taking into account these fast states, conductance and highlow frequency C-V methods were used from room temperature down to 100 K. Measuring at lower temperature shifts the response of the fast interface states into the accessible measurement frequency range. The key finding of this work is that while fast interface states were detected in the nitrided samples, such states were not observed in PSG-passivated samples. On the other hand, conventional interface states with time constants similar to those found in silicon samples were detected at room temperature in the PSG samples. The capture cross-section of fast interface states is larger than that of conventional interface states and demonstrates a different energy dependence. These results strongly indicate that the significantly lower density of fast states at the PSG-SiC interface is one of the main reasons for higher channel mobility in PSG MOSFETs.

Distribution of interface traps in Au/2% GC‐doped Ca3Co4Ga0.001Ox/n‐Si structures

“…Therefore, D it values obtained by high–low frequency method correspond to different kinds of interface traps. This suggests that there exits interface traps that conductance method fails to detect because these traps are too slow . Obtained D it values are on the order of 10 13 eV −1 cm −2 ; this value is reasonable for Schottky type structures with organic interfacial layer particularly considering some other PVA‐based structures, which have D it values above 10 16 eV −1 cm −2 …”

A method for characterizing near-interface traps in SiC metal–oxide–semiconductor capacitors from conductance–temperature spectroscopy measurements

“…13 The larger peaks are the so-called NI signal and are due to NITs. [12][13][14][15][16] By comparison, the NO grown sample exhibits more peaks than the NO annealed spectra. The dopant signals are still present…”

“…This signal (which sometimes labeled "OX" in G-T spectroscopy measurements) is strongly reduced following nitridation and only contributes a weak background signal to the present measurements. [12][13][14][15] DLTS and TDRC are fundamentally low frequency (<1 kHz) measurements, and they rely on the temperature dependent emission process for interface traps. This is different from the higher frequency temperature-independent release process being probed in this work.…”

“…1,2 Fast traps, sometimes labeled "NI," have been assumed as one of the primary contributors to this problem. 1,[12][13][14] These traps can be observed in the high frequency or low temperature conductance of test MOS capacitors. [12][13][14] When the conventional interface-trap analysis is applied to these defects, the extracted properties are physically unreasonable, leading to questions about their origin.…”

“…1,[12][13][14] These traps can be observed in the high frequency or low temperature conductance of test MOS capacitors. [12][13][14] When the conventional interface-trap analysis is applied to these defects, the extracted properties are physically unreasonable, leading to questions about their origin. Recently, new evidence has suggested that these traps are due to near-interface traps (NITs), rather than conventional interface states.…”