SEMICONDUCTOR DEVICE HAVING MOS TRANSISTOR WITH BURIED IMPURITY REGION, MANUFACTURING METHOD THEREOF, AND METHOD OF EVALUATING FABRICATION PROCESSES OF SEMICONDUCTOR DEVICE

摘要

PURPOSE: A semiconductor device, a manufacturing method thereof, and a method of evaluating fabrication processes of the semiconductor device are provided to restrain the current between a source and a drain in an MOS(Metal Oxide Semiconductor) transistor form leaking into a semiconductor layer and to improve a surge breakdown voltage by arranging properly the transistor and forming a buried impurity region under a second impurity region in the transistor. CONSTITUTION: A semiconductor device includes an MOS transistor(103). The MOS transistor includes a second impurity region, a third impurity region, a source region, and a buried impurity region. The second impurity region(7) is formed in a semiconductor layer(2) within a trench isolation layer. The third impurity region(6) is between a first impurity region(3) and the second impurity region in the semiconductor layer. The source region(5) is formed in the third impurity region. The buried impurity region(4) is formed at an interface between the semiconductor layer and a semiconductor substrate(1) under the second impurity region.