Dick Scholten

Electrical Impact of the Aluminum P-Implant Annealing on Lateral MOSFET Transistors on 4H-SiC N-Epi

In this work we investigate the effect of the aluminum p-well implant annealing process on the electrical properties of lateral 4H-SiC MOSFET transistors. The interface trap concentration was measured by quasi-static capacitive voltage (QSCV) and negative bias stress measurements on MOSFETs. We found that higher annealing temperatures significantly reduce the trap density in the lower bandgap, and as a consequence the threshold voltage drift of the transistor after negative stress is reduced.

Effect of Shallow n-Doping on Field Effect Mobility in p-Doped Channels of 4H-SiC MOS Field Effect Transistors

A high inversion channel mobility is a key parameter of normally off Silicon-Carbide MOS field effect power transistors. The mobility is limited by scattering centers at the interface between the semiconductor and the gate-oxide. In this work we investigate the mobility of lateral normally-off MOSFETs with different p-doping concentrations in the channel. Additionally the effect of a shallow counter n-doping at the interface on the mobility was determined and, finally, the properties of interface traps with the charge pumping method were examined. A lower p-doping in the cannel reduces the threshold voltage and increases the mobility simultaneously. A shallow counter n-doping shows a similar effect, but differences in the behavior of the charge pumping current can be observed, indicating that the nitrogen has a significant effect on the electrical properties of the interface, too.

Trench-MOSFETs on 4H-SiC

This paper introduces n-channel normally-off Trench-MOSFETs on 4H-SiC featuring a blocking voltage of 600 V and 1200 V. The Trench-MOSFETs exhibit a specific room temperature on-state resistance RDS,on of 1.5 mΩ cm² and 2.7 mΩ cm², respectively. It is shown that a further reduction of the RDS,on by approximately 25 % can be achieved using square-shaped or hexagonal unit cells instead of stripe-shaped unit cells. The Trench-MOSFET switching characteristics using a double pulse setup with a switching current Isw of 100 A and a switching voltage Vsw of 450 V is presented and discussed. The short turn-off and turn-on times in the range of several ten nanoseconds yield large maximum disw/dt and dvsw/dt values, which enable highly efficient power conversion with low switching losses.

Influence of Annealing, Oxidation and Doping on Conduction-Band near Interface Traps in 4H-SiC Characterized by Low Temperature Conductance Measurements

Current power MOSFET devices on Silicon Carbide show a limited inversion channel mobility, which can be a result of the expected very high density of interface states near the conduction band . In the current work, the effect of the post implantation annealing temperature, the thermal oxidation and the nitrogen doping of the n-epi layer on the density of these interface traps is investigated using capacity-conductance measurements. Instead of the usage of very high frequencies as used in , in this investigation the measurements were performed in liquid nitrogen to decrease the recharging times of the interface traps.Due to the different processing the samples showed a wide spreading of the inversion channel mobility. The conductance measurements show a characteristic peak caused by the conduction band near interface traps especially for the low temperature measurements. But these traps could not be correlated to the mobility. Instead, a correlation to the nitrogen doping of the epi layer could be observed.

Influence of Post-Implantation Annealing Temperature on MOSFET Performance and Oxide Reliability

In the present work, we studied the influence of the post-implantation annealing temperature on the performance and oxide reliability of lateral 4H-SiC MOSFETs. The maximum field effect mobility of the MOSFETs at 25°C decreases from 22.4cm2/Vs to 17.2cm2/Vs by increasing annealing temperature from 1600°C to 1800°C. Respectively, the measured meantime to failure is about one order of magnitude higher for the 1700°C annealed sample at an applied field of 8.5MV/cm compared to the 1600°C and 1800°C annealed samples.