Silicon nitride, a high potential dielectric for 600 V integrated RC-snubber applications

Monolithically integrated RC-snubbers were realized by metal-insulator-semiconductor capacitors on a silicon substrate also serving as a series resistor. These devices provide a promising alternative to passive surface-mounted device components that are commonly used for snubber applications in power electronic circuits. The surface area of the substrate was enlarged with circular trench structures to increase the integration level of the capacitor, and a silicon nitride layer with a thickness of 1.05 mu m was deposited on top of a 20 nm-thin silicon oxide layer as a potential dielectric for applications up to 600 V. With the trench geometry, a capacitance per surface area of 0.6 nF/mm(2) was achieved, which is more than ten times the capacitance of a planar device using the same dielectric layers. However, combining the thick silicon nitride layer with the trench geometry caused an excessive wafer bow of nearly 800 mu m, so deposition and structuring of a surface passivation layer, such as polyimide, was not feasible. Therefore, inert oil had to be used as a surface passivation for high voltage measurements. The silicon nitride dielectric exhibits a leakage current density lower than 0.3 nA/mm(2) at the requested 600 V operating voltage, while dielectric breakdown of the devices is observed at 1050 V. A low deviation in capacitance and series resistance across the wafer and a high yield regarding the high voltage stability is achieved because of the good quality and homogeneity of the silicon nitride dielectric layer.