M. Bassler

Intrinsic SiC/SiO2 Interface States

The energy distribution of electron states at SiC/SiO 2 interfaces produced by oxidation of various (3C, 4H, 6H) SiC polytypes is studied by electrical analysis techniques and internal photoemission spectroscopy. A similar distribution of interface traps over the SiC bandgap is observed for different polytypes indicating a common nature of interfacial defects. Carbon clusters at the SiC/SiO 2 interface and near-interfacial defects in the SiO 2 are proposed to be responsible for the dominant portion of interface traps, while contributions caused by dopant-related defects and dangling bonds at the SiC surface are not observed.

“Carbon cluster model” for electronic states at SiCSiO2 interfaces

Abstract The electronic properties of the SiC SiO 2 interface are studied for a series of SiC polytypes (3C, 4H, 6H) using various electrical methods and internal photoemission spectroscopy. The energy distribution of states at SiC SiO 2 interfaces is found to be similar for all the investigated polytypes. The lowest density of states measured at SiC SiO 2 interfaces is at least one order of magnitude higher than the density of states at Si SiO 2 interfaces. We have strong indications that this enhancement is caused by residual carbon (graphite-like films, carbon clusters) bonded at the SiC SiO 2 interface. We propose a “carbon cluster model”, which qualitatively describes the electrical properties of (3C, 4H, 6H)-SiC MOS structures.

Degradation of 6H-SiC MOS capacitors operated at high temperatures

Abstract 6HSiC MOS capacitors were operated at temperatures above 600K under negative bias. Enhancement of energetically shallow and deep interface states at n/p-type SiC SiO 2 structures and of a fixed charge are observed, which can partially be passivated by a hydrogen treatment. The generation and passivation of the fixed charge is explained in the framework of the “negative-bias-temperature instability” originally proposed for Si-based MOS capacitors.

Charge trapping and interface state generation in 6H-SiC MOS structures

Abstract Comparative studies of the oxide charge trapping and interface state generation in n-6HSiC SiO 2 and Si SiO 2 structures were performed using electron/hole photo-injection. The thermal oxide on SiC was found to have a comparable density of electron traps and even lower density of hole traps than that one on Si. In contrast to the Si SiO 2 system, the electron injection in the oxide on 6HSiC produces a large density of deep acceptor interface states, which are stable in the temperature range below 300 °C.

Traps at the SiC/SiO 2 -Interface

The density of interface states Dit at SiC/SiO 2 interfaces of different SiC polytypes (4H-, 6H- and 15R-SiC) is monitored and the origin of these states is discussed. The hydrogenation behavior of interface states in the temperature range from 250°C to 1000°C is studied by C-V and G-V investigations. The strong increase of Dit close to the 4H-SiC conduction band is attributed to defects located in the oxide (so-called “Near Interface Traps”).

Oxidation of 6H silicon carbide in carbon containing atmosphere

The effect of different oxidizing ambients on the SiC/SiO2 interface has been investigated. We studied the dry oxidation of 6H silicon carbide in O2 with different partial pressures of CO2 as well as in pure CO2 and CO. The density of states at the interface Dit characterized by admittance spectroscopy was found to be correlated with the partial pressure of CO2. We propose that the CO2 partial pressure prevents the outdiffusion of the CO2 which results from the oxidation of SiC leading to a higher Dit with increasing CO2 partial pressure in the oxidizing ambient (Dit (dry O2)=6.3×1010 cm−2 eV−1, Dit(100% CO2)=9.4×1011 cm−2 eV−1).

Long-time constant-capacitance DLTS investigations of 6H SiC/MOS structures : comparison of dry and wet oxidation

Abstract A long-time constant-capacitance deep level transient spectroscopy (LT-CC-DLTS) method has been established to investigate the energy distribution D it and the capture-cross-section σ n/p of states at the interface of 6H SiC/MOS structures. A comparison of dry and wet oxidation (1120°C) reveals a change in the distribution of interface states and a different magnitude of capture-cross-sections indicating that the interface states consist of at least two types of defects.