SEMICONDUCTOR DEVICE AND METHOD FOR MANUFACTURING THE SAME

摘要

A semiconductor device and its manufacturing method are provided to prevent increase of a leak current between wells and degradation of mobility by using a nitride layer covering the whole surface of a sidewall of a first trench. A first trench(28) of a predetermined depth is formed on a predetermined region of a silicon substrate(5). A nitride layer(27) is formed to cover the whole surface of a sidewall of the first trench. The nitride layer in a lower portion of the first trench and in the proximity thereof is removed to expose the silicon substrate by keeping the nitride layer of an upper portion of the trench. The exposed silicon substrate is thermally-oxidized to form a thermal oxide layer(26) on the lower portion. The thermal oxide layer of the substrate side is wider than a lower end of the nitride layer.