Thomas Aichinger

Charge Pumping Measurements on Differently Passivated Lateral 4H-SiC MOSFETs

This paper shows a successful transfer of the charge pumping (CP) method, which is extensively applied on silicon (Si) transistors, to Si carbide (SiC) lateral MOSFETs to characterize the quality of the SiC/SiO2 interface near the conduction and valence band edges. In particular, the constant base technique provides more accuracy and flexibility with respect to the most commonly used constant amplitude technique. Anomalous phenomena previously reported in literature, such as the so-called geometric component, are absent if the measurements are performed on transistors with optimized geometry and if the parameters of the applied CP gate pulses are carefully chosen. Furthermore, interface properties of gate oxides subjected to different postoxidation treatments are compared using this technique and the influence of the measurement parameters and temperature on the resulting CP signal is discussed.

Interface defects in SiC power MOSFETs - An electrically detected magnetic resonance study based on spin dependent recombination

This study presents electrically detected magnetic resonance (EDMR) measurements on a silicon carbide (SiC) MOSFET having the structure of a double-diffused silicon MOSFET (DMOS). The resonance pattern of a SiC DMOS was measured by monitoring the change of the recombination current between the source/body and the drain. The amplitude of the response has a maximum when the device is biased in depletion due to the equal concentrations of electrons and holes at the interface resulting in the most efficient recombination. The measured anisotropic g-tensor has axial symmetry with g∥ = 2.0051(4) (B ‖ c-axis), and g⊥ = 2.0029(4) (B⊥ c-axis) and the pattern shows several hyperfine (HF) peaks. We tentatively identify the observed defect as a silicon vacancy located directly at the interface.

Electrically detected magnetic resonance of carbon dangling bonds at the Si-face 4H-SiC/SiO2 interface

SiC based metal-oxide-semiconductor field-effect transistors (MOSFETs) have gained a significant importance in power electronics applications. However, electrically active defects at the SiC/SiO2 interface degrade the ideal behavior of the devices. The relevant microscopic defects can be identified by electron paramagnetic resonance (EPR) or electrically detected magnetic resonance (EDMR). This helps to decide which changes to the fabrication process will likely lead to further increases of device performance and reliability. EDMR measurements have shown very similar dominant hyperfine (HF) spectra in differently processed MOSFETs although some discrepancies were observed in the measured g-factors. Here, the HF spectra measured of different SiC MOSFETs are compared, and it is argued that the same dominant defect is present in all devices. A comparison of the data with simulated spectra of the C dangling bond (PbC) center and the silicon vacancy (VSi) demonstrates that the PbC center is a more suitable can...

Characterization of MOSFET Interface States Using the Charge Pumping Technique

In this chapter we present two-level Charge Pumping (CP) as an efficient tool for energetic and spatial interface state profiling of lateral metal oxide semiconductor field effect transistors. We study the accessible energy range, discuss the meaning of CP threshold and flat band voltages and investigate contributions of near-interface oxide traps to the CP current. Different CP techniques are introduced and compared to each other. It is shown that the constant base level CP technique has crucial advantages over the more frequently used constant amplitude technique. It is demonstrated how the CP threshold and flat band voltages of differently doped transistor areas can be determined experimentally from the derivatives of constant high and constant base level CP curves. When subjecting the device to non-uniform Hot Carrier (HC) stress, a characteristic degradation peak appears in the CP derivative. It is shown how one can determine the precise location of the HC induced damage through the application of the so-called constant field CP technique. In the constant field technique the stressed transistor junction is pulsed in phase with the gate terminal using a second pulse generator.

Recombination centers in 4H-SiC investigated by electrically detected magnetic resonance and ab initio modeling

Electrically detected magnetic resonance (EDMR) is a powerful technique for the observation and categorization of paramagnetic defects within semiconductors. The interpretation of the recorded EDMR spectra has long proved to be challenging. Here, defect spectra are identified by comparing EDMR measurements with extensive ab initio calculations. The defect identification is based upon the defect symmetry and the form of the hyperfine (HF) structure. A full description is given of how an accurate spectrum can be generated from the theoretical data by considering some thousand individual HF contributions out of some billion possibilities. This approach is illustrated with a defect observed in nitrogen implanted silicon carbide (SiC). Nitrogen implantation is a high energy process that gives rise to a high defect concentration. The majority of these defects are removed during the dopant activation anneal, shifting the interstitial nitrogen to the desired substitutional lattice sites, where they act as shallow...

Impact of Hot Carrier Degradation and Positive Bias Temperature Stress on Lateral 4H-SiC nMOSFETs

We study the impact of positive bias temperature stress and hot carrier stress on lateral 4H-SiC nMOSFETs. These degradation mechanisms are prominent in silicon based devices where both create oxide as well as interface traps. For SiC MOSFETs only limited information regarding these mechanisms is available. We transfer the charge pumping technique, known from Si MOSFETs, reliably to SiC MOSFETs to learn about the nature of the stress induced defects.

Threshold voltage peculiarities and bias temperature instabilities of SiC MOSFETs

Abstract Silicon carbide (SiC) based metal-oxide semiconductor-field-effect-transistors (MOSFETs) are increasingly entering the high power device market. Besides all the well-known benefits which come along with these new generations of switches, the nature of the wide bandgap material and the different properties of the semiconductor-dielectric interface involve some natural peculiarities in threshold voltage variation and bias-temperature-instability (BTI) which differ from comparable silicon (Si) MOSFET counterparts and which need to be understood and assessed. The target of this paper is to highlight such differences, explain their relation to the semiconductor material, challenge their relevance for the application and define their consequences with regard to datasheet specifications. Most of the new effects can be understood by means of simple physical models and do not compromise the reliability of the device. However, it turns out that the standard test procedures typically used to characterize threshold voltage and threshold voltage drifts for Si devices need to be adapted for SiC MOSFETs. A new measure-stress-measure procedure for BTI evaluation of SiC MOSFETs is proposed which allows distinguishing between reversible threshold voltage hysteresis and more permanent threshold voltage drift (BTI). The measurement pattern is then used to assess the VTH stability of recently launched SiC MOSFET parts. The tested devices differ considerably in BTI drift amplitude and drift variation. The differences are attributed to variations in device processing and device design.

Performance and ruggedness of 1200V SiC — Trench — MOSFET

This paper describes a novel SiC trench MOSFET concept. The device is designed to balance low conduction losses with Si-IGBT like reliability. Basic features of the static and dynamic performance as well as short circuit capability of the 45mΩ/1200 V CoolSiC™ MOSFET are presented. The favorable temperature behavior of the on-state resistance combined with a low sensitivity of the switching energies to temperature simplify the design-in. Long-term gate oxide tests reveal a very low extrinsic failure rate well matching the requirements of industrial applications.

Influence of Oxide Processing on the Defects at the SiC-SiO2 Interface Measured by Electrically Detected Magnetic Resonance

Anneals in nitrogen (N) containing atmosphere have been proven as efficient means of improving the channel mobility of SiC MOSFETs. It has been demonstrated that simultaneously the density of interface traps is reduced. However, this process is not yet fully understood. In this study we show a comparison of MOSFETs annealed in different atmospheres and compare their electrically detected magnetic resonance (EDMR) spectra with electrical parameters. We find hints for the N incorporation not only passivating but also creating or transforming defects.

Impact of Hydrogen on the Bias Temperature Instability

The ability of hydrogen to saturate lattice imperfections, which arise naturally at the silicon–oxide interface due to the structural mismatch of the two materials, has already early motivated to connect H with the bias temperature instability. Consistently, ESR measurements after NBTS observed P b center defects, i.e. previously H passivated interfacial dangling bonds on silicon atoms at the interface, which supports the assumption that H is detached from defect precursors during NBTS. In contrast, theoretical and experimental investigations on the Si–H bond dissociation energy revealed a rather large value, inconsistent with the low-energy nature of conventional NBTI test. We summarize several explanations to this problem and compare these ideas with studies where the amount of H near the interfacial layer is varied through particular process adjustments.