LOCOS MOS DEVICE FOR ESD PROTECTION AND ITS FORMATION METHOD

摘要

PROBLEM TO BE SOLVED: To obtain a MOS transistor which has a large drain-gate breakdown voltage, and to obtain its manufacturing method. SOLUTION: A MOS transistor which is used in an EDS protective circuit and which comprises a multilayered gate oxide layer is obtained. When a thick gate oxide layer is formed near a drain, the transistor can have a comparatively large drain-gate breakdown voltage. When a thin gate oxide layer is formed near a source, a gate voltage can change over a turning-on/off operation of the transistor at a high changeover speed. A thick part in the multilayer gate oxide layer of the MOS transistor is formed by the selective oxidation (LOCOS) process of silicon, and the thin gate layer is formed in another step. Also a method in which the MOS transistor comprising the EDS protective circuit and the multilayered gate oxide layer is manufactured is obtained.