Ronny Kern

Performance of a 650V SiC Diode with Reduced Chip Thickness

A significant performance gain of 650V SiC diodes is possible by reducing the wafer thickness from the standard thickness of 350 µm to < 150 µm. Not only the differential resistance of the diodes but also the Rth benefit from this chip thickness reduction. As consequence a further chip size reduction with accompanying capacitive charge reduction leads to a device with improved efficiency in PFC applications under both high load and low load conditions.

Investigations on Surge Current Capability of SiC Schottky Diodes by Implementation of New Pad Metallizations

In this paper we describe how a merged pn Schottky diode (MPS diode) is capable to drive surge current levels far beyond the normal current of the diode and how to improve the device in order to achieve even higher surge current levels. For a sine half wave of 10 µs an 8A MPS diode (size: 2.52mm2) with conventional Al pad metallization shows surge current levels of greater than 500A, using Cu it can be increased to ~900A. For 10ms pulse length a different behaviour was observed, here diodes with Al pad metallization show a higher surge current level (80A) compared to Cu pad metallization (~ 40A). The root cause for this negative result at longer pulse time is based in a chemical interaction between Cu and the Schottky metal (Ti). Additionally, an outlook is given how Cu can contribute to improved surge current capability also at longer pulse lengths.

SiC Epitaxial Growth in a 7x100mm/3x150mm Horizontal Hot-Wall Batch Reactor

We present results on the homo-epitaxial growth on the Si face of 100 mm and 150 mm (0001)-oriented (4° off-orientation) 4H SiC wafers utilizing the horizontal hot-wall batch reactor Probus-SiCTM from Tokyo Electron Limited. Standard epitaxial growth processes show very high levels of intra-wafer, intra-run wafer-to-wafer, and run-to-run uniformities in the layer thickness as well as in the n-type doping concentration. N-type background doping levels less that 5e13 /cm3 have been reached. AFM measurements reveal a surface roughness of 0.2nm (rms). The density of epitaxy related defects such as triangular defects, carrots, and ingrown particles due to downfall are very low, as confirmed by high blocking yields.

Alternative Highly Homogenous Drift Layer Doping for 650 V SiC Devices

A new method for homogenous drift layer doping is introduced. Instead of in-situ doping during epitaxial growth a subsequent high energy ion implant step is used to dope the drift layer of 650V MPS (Merged-PN-Schottky) diodes. In order to avoid multiple implant steps with various energies for emulating a box-like doping profile, a novel “energy filter” membrane is used to transform the monochromatic ion beam to a beam with a continuous energy spectrum suited for box-like doping. The electrical characteristics of the diodes manufactured by this means show a very homogenous blocking behavior on wafer level, however the expected improved homogeneity in differential resistance of the wafers could not be confirmed by wafer level measurements. More work is needed to understand this discrepancy between experiment and theory.