SiC Trench Gate Oxide Reliability
# SiC Trench Gate Oxide Field Crowding
A trench MOSFET carves its gate down into the silicon carbide rather than laying it flat on top, and that geometry buys real benefits — higher channel density, lower on-resistance — at the cost of a sharp corner at the bottom of every trench. SiC's own high critical electric field, the same property that makes it such an attractive power-device material in the first place, concentrates intensely at exactly that trench corner, putting more electrical stress on the thin gate oxide there than anywhere else in the device.
Field crowding happens because electric field lines concentrate at any sharp convex corner in a dielectric structure, and SiC's naturally high breakdown field makes that concentration especially severe. Any sharp geometric transition in a field-carrying structure — a convex corner is the textbook case — locally intensifies the electric field well above the average value elsewhere in the structure, the same electrostatic principle that makes lightning rods work by concentrating field at a point. A trench gate's bottom corner is exactly this kind of sharp feature, and because SiC itself supports a critical electric field roughly ten times higher than silicon before the material breaks down, the bulk SiC drift region sitting beneath the trench can sustain field strengths that would already be dangerous to a thin gate oxide — concentrated further at the trench corner, that field can exceed what the oxide was ever designed to block.
A thin shielding layer buried beneath the trench corner is the standard engineering fix, specifically designed to intercept the field before it reaches the vulnerable oxide. A deep, heavily doped P-type implant placed directly below the trench bottom — a buried shield region — locally redistributes the electric field so the highest-stress point moves away from the thin gate oxide and into the bulk semiconductor underneath, which is far better equipped to sustain high field than a thin dielectric layer ever could be. Getting this shield region's depth, doping, and alignment right relative to the trench is a tight process-integration problem in its own right: misaligned or insufficiently deep shielding leaves the gate oxide exposed to exactly the field concentration the structure was supposed to prevent.
Trench corner rounding during fabrication is a second, complementary lever, since a less sharp corner geometrically reduces the field-concentration factor at the source. Etch and anneal process steps specifically tuned to round the trench's sharp bottom corner — rather than leave it geometrically sharp — directly reduce how much field concentration that corner geometry itself creates, independent of whatever shielding structure also sits beneath it. Production SiC trench MOSFET processes typically combine both techniques, buried shielding plus corner rounding, since neither alone fully eliminates the field-crowding risk a sharp trench corner on a high-critical-field material inherently creates.
Fin bending and nanosheet stiction (607, 608) are mechanical collapse risks from suspended silicon geometry. SiC trench gate field crowding is a different kind of geometry-driven failure entirely — not a structure falling over, but a sharp corner concentrating electric field onto a thin dielectric that was never designed to survive it, a reliability problem specific to the trench architecture's own shape rather than anything about the material being mechanically fragile.