Fraunhofer Institute for Microstructure of Materials and Systems IMWSTime-of-Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) can be used to detect dopant elements in semiconductors. While Dynamic Secondary Ion Mass Spectrometry (DSIMS), which is also common, has a higher detection sensitivity than ToF-SIMS, it has a significantly lower spatial resolution. ToF-SIMS may therefore be the most suitable method for characterizing structured samples.
An interesting example is the investigation of dopings in the immediate vicinity of gate trenches in vertical or semi-vertical devices based on gallium nitride (GaN). Vertical GaN devices are promising for high power applications such as power supplies, electric vehicles and renewable energy systems. Therefore, GaN-on-Si semi-vertical trench MOSFETs are being intensively investigated as an intermediate step towards vertical transistors. Trench MOSFETs are a special type of metal-oxide-semiconductor field-effect transistor (MOSFET) that use a trench structure to improve performance and efficiency. In particular, the magnesium concentration of the p-GaN layer (in the gate trench area) is of interest and influences the most important device parameters.
To investigate the influence of processes (such as trench etching or dielectric deposition) on local distributions of the dopant concentration in these transistors, a high spatial resolution is necessary, which can be achieved with ToF-SIMS. A team from Fraunhofer IMWS, in collaboration with researchers from the Interuniversity Microelectronics Centre (imec) in Leuven, Belgium, investigated the capabilities of this method and presented their results in the paper “Doping investigation of structured GaN devices by highly lateral resolved TOF-SIMS”, which was published in the journal “Power Electronic Devices and Components.”
ToF-SIMS provides necessary detection sensitivity and spatial resolution for 3D doping analysis of GaN trench MOSFETs
It has been shown that the detection sensitivity and spatial resolution of the ToF-SIMS method is suitable for three-dimensional detection of the distribution of the dopant elements with a spatial resolution in the range of 100 nm. Since the measurement results are influenced by the topography of the actual 3D structure of the devices under investigation, scanning electron microscopy measurements of the actual gate trench structures were used to correct the 3-dimensional ToF-SIMS data retrospectively for topography.
Using the correction applied, it was demonstrated that there are no significant changes in the magnesium and silicon doping levels near the gate trench sidewalls as a result of process steps such as trench etching or dielectric layer deposition. The results demonstrate the potential of this analytical method for the characterization and process control of GaN power electronics.
(July 24, 2026)