A. Gölz

Long term stability of gate-oxides on n- and p-type silicon carbide studied by charge injection techniques

Abstract A large part of interface states in thermal oxides on n- and p-type 6H-SiC can be passivated by introducing hydrogen to the fabrication process. The oxide trap densities of passivated and unpassivated samples are investigated by charge injection experiments using Fowler Nordheim and photo-injection techniques.

Charge trapping in dry and wet oxides on N‐type 6H–SiC studied by Fowler–Nordheim charge injection

Metal‐oxide‐semiconductor capacitors fabricated by dry and wet oxidation at 1150 °C of n‐type 6H–SiC exhibit a drastic negative charging during Fowler–Nordheim charge injection. This charging strongly depends on the fabrication conditions of the samples. The densities of interface states and oxide charges can be significantly reduced by a postoxidation anneal in Ar for as long as 60 min. A large part of the charge appears to be trapped at the interface. These charges are released from the traps by illumination at photon energies between 2 and 4 eV or by annealing below 300 °C. During charge injection interface states are created near the conduction band edge. Their density is strongly reduced by annealing at 150 °C. For the oxide charging we find capture cross sections in the range of 10−15–10−17 cm−2. In unannealed wet oxidized samples the traps exhibit properties similar to those of water‐related traps in SiO2 on Si.

Effects of Ar and H2 annealing on the electrical properties of oxides on 6H SiC

Abstract We report on the influence of post-oxidation annealing (POA) on the electrical properties of metal-oxide-semiconductor capacitors fabricated on n- and p-type 6H SiC (Si face). All samples were oxidized in dry or wet oxygen at 1150 °C. POA at this temperature reduces the densities of fixed oxide charges and interface states. Negative fixed oxide charges on n-type SiC were found to be located at the SiO2SiC interface. High temperature H2 annealing experiments show that hydrogen plays a critical role in the SiO2SiC system. Oxide defects on p-type SiC, which are believed to result from dopant (Al) incorporation in SiO2, could be passivated by annealing in forming gas.

Characterization of annealed oxides on N-type 6H-SiC by high- and low-frequency CV-measurements

Abstract Electrical properties of Oxides on 6HSiC are extracted from HFCV and QSCV measurements from 24°C to 300°C. Dit values calculated by the Terman and the HF-LF method differ in hight and position with respect to the bandgap. However, both methods result in the same relations for different samples. Negative charge trapping in slow interface states and oxide traps is observed during positive bias stress. The trapping properties of different devices correlate to the initial fixed oxide charge densities.

High-field Fowler - Nordheim stress of n-type silicon carbide metal-oxide-semiconductor capacitors

Fowler - Nordheim electron injections have been carried out in n-type silicon carbide (SiC) metal-oxide-semiconductor (MOS) capacitors. A systematic variation in the temperature and in the average oxide field applied during the stress allowed us to show both a positive charge and electron trapping. The positive charge build-up is shown to emerge above a critical oxide field close to . It decreases with temperature, and can be dissociated into two different exponential time processes. The overall results agree with mechanisms based on impact ionization in the oxide, leading to pair creation and subsequent hole trapping.

Passivation of interface traps in MOS-devices on n- and p-type 6H-SiC

Abstract Interface traps in the SiO2-6H-SiC system can be passivated by a high temperature anneal in hydrogen or moistrous atmosphere. The passivation is very effective for deep donor like traps which are reduced towards the 1011 cm−2 eV−1 range. The electrical properties of n-channel MOSFETs show that the gate oxides contain only a low density of fixed oxide charges in the low 1011 cm−2 range for the passivated and the unpassivated state. It is further demonstrated that deep donor-like interface states hardly affect the electrical properties of n-channel MOSFETs on 6H-SiC.

Fabrication of high-quality oxides on SiC by remote PECVD

Abstract The interface trap density in oxides grown on 6H silicon carbide by remote plasma-enhanced chemical vapor deposition as well as by thermal oxidation is studied. This trap density is found to be drastically reduced by a plasma-assisted PDP (pre-deposition process) in hydrogen. The reduction is stable if a high-temperature annealing step is carried out which excludes a simple passivation by hydrogen.

Electrical properties of oxides on silicon carbide grown by remote plasma chemical vapor deposition annealed in different gas ambients

Abstract Oxides fabricated by a two-step remote plasma enhanced chemical vapor deposition (RPECVD)-process on n- and p-type 6H-SiC are electrically characterized. In contrast to thermal oxidation the semiconductor surface becomes a reactive interface during this process offering various technological possibilities to control chemical reactions. Since the growth rates are 15 times as high as for thermal oxidation this process appears attractive for thick field oxides, too. Oxide qualities comparable to those found for thermally grown ones are achieved. An in-situ plasma, especially for p-type SiC, assisted cleaning step in hydrogen before the deposition is found to play a very critical role concerning the oxide layer quality.

High field and high temperature stress of n-SiC MOS capacitors

Abstract The development of reliable oxides built on SiC has become a very important issue with respect to either passivation processes or metal-oxide-semiconductor (MOS) applications. The aim of this paper is to present a detailed investigation of Fowler-Nordheim electron injections in n-type silicon carbide (SiC) MOS capacitors. A systematic variation in the temperature and in the average oxide field E OX applied during the stress allowed us to evidence both a positive charge and electron trapping. The positive charge build-up is shown to emerge above a threshold field close to 7 MV cm −1 . It decreases with temperature, and can be dissociated into two different exponential time processes. The overall results agree with mechanisms based on impact ionization in the oxide, leading to pair creation and subsequent hole trapping.

The role of oxygen and nitrogen at the SiO2SiC interface

Abstract A method for surface preparation of 6HSiC with different plasma sources (oxygen, and nitreous oxide) to reduce defects in deposited gate oxides is presented. CV- (Capacitance-Voltage) measurements prove that by suitable processing defect densities can be reduced by one order of magnitude down in the range of 10 11 cm −2 . In contrast to silicon nitrogen disturbs the deposition of oxides on SiC. By AES (Auger Electron Spectroscopy) measurements the different behavior of nitrogen at the SiO 2 SiC interface compared to the SiO 2 Si interface is analyzed.