Semiconductor device and method for fabricating the same

摘要

A trench isolation region separating active regions in which MISFETs are formed includes: side insulating films covering the sides of a trench; polycrystalline semiconductor layers of a first conductivity type covering the respective sides of the side insulating films, and a polycrystalline semiconductor layer of a second conductivity type filling a gap between the polycrystalline semiconductor layers of the first conductivity type. Two pn junctions extending along the depth direction of the trench are formed between each of the polycrystalline semiconductor layers of the first conductivity type and the polycrystalline semiconductor layer of the second conductivity type. Upon application of a voltage between the active regions, a depletion layer expands in one of the pn junctions, so that the voltage is also partly applied to the depletion layer. As a result, the concentration of electric field in the side insulating films is relaxed.