Highly reliable high-voltage transistors by use of the SIPOS process

The npn and pnp high-voltage transistors showing high reliabilities have been developed by using semi-insulating polycrystalline-silicon (SIPOS) films for the surface passivation. SIPOS films are chemically vapor-deposited polycrystalline-silicon doped with oxygen or nitrogen atoms. SIPOS films employed for the surface passivation of high-voltage transistors are composed of triple layers, which are oxygen-doped films of 0.5 µm thickness to stabilize the silicon interface, nitrogen-doped films of 0.15 µm thickness to prevent water or sodium ions from reaching the silicon surface and silicon dioxide films to prevent dielectric breakdown. The npn and pnp SIPOS transistors rated at 800 V and 2500 V have been produced in planar-like structures with field-limiting rings. Furthermore, 10 kV SIPOS transistors with multiple rings have been fabricated and found that operation is stable.