High-carbon concentrations at the silicon dioxide–silicon carbide interface identified by electron energy loss spectroscopy

Abstract

High carbon concentrations at distinct regions at thermally-grown SiO2/6H–SiC(0001) interfaces have been detected by electron energy loss spectroscopy (EELS). The thickness of these C-rich regions is estimated to be 10–15 Å. The oxides were grown on n-type 6H–SiC at 1100 °C in a wet O2 ambient for 4 h immediately after cleaning the substrates with the complete RCA process. In contrast, C-rich regions were not detected from EELS analyses of thermally grown SiO2/Si interfaces nor of chemical vapor deposition deposited SiO2/SiC interfaces. Silicon-rich layers within the SiC substrate adjacent to the thermally grown SiO2/SiC interface were also evident. The interface state density Dit in metal–oxide–SiC diodes (with thermally grown SiO2) was approximately 9×1011 cm−2 eV−1 at E−Ev=2.0 eV, which compares well with reported values for SiC metal–oxide–semiconductor (MOS) diodes that have not received a postoxidation anneal. The C-rich regions and the change in SiC stoichiometry may be associated with the higher than desirable Dit’s and the low channel mobilities in SiC-based MOS field effect transistors.

Atomic scale characterization of SiO2/4H-SiC interfaces in MOSFETs devices

“…Going from SiC to SiO 2 across the interface, the C/Si (O/Si) ratio decreases (increases) gradually without any observable enrichment in any of the elements. In particular, no C-rich area is detected in the SiC or in the bulk SiO 2 as it was previously reported [3][4][5][6][7] . From these profiles, a region of continuously varying composition including the three elements (Si, C and O) named transition layer (TL)…”

“…This degradation was related to electrically active defects at the SiC/SiO 2 interface, such as C clusters [3,4] and/or changes in the C/Si ratio across the SiC/SiO 2 interface. They were observed by different transmission and scanning transmission electron microscopy (TEM and STEM, respectively) techniques, such as high resolution transmission electron microscopy (HRTEM), Z-contrast imaging [5,6] and Electron Energy Loss Spectroscopy (EELS) [7].…”

Structural and electronic properties of the transition layer at the SiO2/4H-SiC interface

“…[5][6][7][8][9][10][11] Considerable effort has been devoted to the identification and characterization of interface defects at the SiO 2 /SiC interface. 6,[12][13][14][15][16][17][18][19][20][21] These investigations drew a conclusion that intrinsic oxide defects and excess carbon are the most dominant contributions to interface states. Intrinsic defects in SiO 2 that are independent of the polytype and orientation of SiC substrate, can account for the D it near the bottom of the SiC conduction band gap, so-called near-interface trap (NIT) levels.…”

“…27,30 This may explain the experimentally observed carbon excess at the interface. 14,15 To elucidate the chemical bonding and charge transfer between carbon clusters and the surrounding atoms, we depict the three-dimensional charge-density difference with respect to carbon clusters (see Fig. 3).…”

“…[24][25][26][27][28][29][30] The residual carbon atoms may contribute to the formation of carbon clusters, as observed by atomic force microscopy (AFM) 13 and combined transmission electron microscopy (TEM)/electron energy loss spectroscopy (EELS). 14,15 Much theoretical work has been performed to understand the atomic-scale nature of carbon-related defects at the SiO 2 /SiC interface. Knaup et al studied the oxidation mechanism of 4H-SiC and proposed several possible defects occurring on both the SiC and oxide sides of the interface.…”