Low temperature glass-thin-films for use in power applications

A novel approach on wafer-level passivation of power devices using a thin, hermetic borosilicate glass layer as passivation or dielectric layer is presented here. The technology will be benchmarked to those conventional technologies. The glass layer is deposited at low temperatures (T <; 100°C) using a plasma-enhanced e-beam deposition and can be structured by a lift-off process using a standard photo resist process for masking. The process flow is fully compatible with standard CMOS post processing and is integrated in a state-of-the-art production environment. The borosilicate thin-films yield breakdown voltages as high as 250 V/μm and a typical specific resistance of 1E17 Ohm/cm at room temperature, a value which is very close to the specific resistance of bulk borosilicate glass. The coefficient of thermal expansion of the borosilicate thin-film (~3 ppm/K) is matched to silicon and enables systems to be reliable at high temperatures or in temperature cycling. Microstructured glass films were tested under extreme conditions e.g. up to temperatures as high as 650 °C as well as long-term temperature-humidity storage (85°C, 85% for 8000h). We demonstrate the use of borosilicate thin-films as inter-dielectric layers in wafer-level redistribution, replacing standard polymers such as BCB or PI as a drop-in solution. Process parameters and reliability results are discussed.