Methods for manufacturing semiconductor devices having a non-volatile memory transistor

Abstract

Embodiments include a method for manufacturing a semiconductor device including a plurality of non-volatile memory transistors that include field effect transistors operated at a plurality of different voltage levels. The method includes the following steps: (a) forming a gate insulation layer and a floating gate of a non-volatile memory transistor on a silicon substrate in a memory region (b) forming, on the wafer, a first silicon oxide layer L by a thermal oxidation method and a second silicon oxide layer L by a CVD method; (c) removing the first and the second silicon oxide layers in the first transistor region; and (d) forming a silicon oxide layer L on the wafer by a thermal oxidation method. The silicon oxide layer formed in step (d) compose at least a portion of a gate insulation layer of a first voltage-type transistor and a gate insulation layer of a second voltage-type transistor.