Semiconductor device and method for manufacturing the same

摘要

An object is to provide a structure of a transistor which has a channel formation region formed using an oxide semiconductor and a positive threshold voltage value, which enables a so-called normally-on switching element. The transistor includes an oxide semiconductor stack in which at least a first oxide semiconductor layer and a second oxide semiconductor layer with different energy gaps are stacked and a region containing oxygen in excess of its stoichiometric composition ratio is provided.

主权项

1. A semiconductor device comprising:
an oxide semiconductor stack including a first oxide semiconductor layer, a second oxide semiconductor layer in contact with a top surface of the first oxide semiconductor layer, and a third oxide semiconductor layer in contact with a top surface and a side surface of the second oxide semiconductor layer and in contact with a side surface of the first oxide semiconductor layer, wherein the second oxide semiconductor layer has a smaller energy gap than the first oxide semiconductor layer, and the third oxide semiconductor layer has a larger energy gap than the second oxide semiconductor layer; a source electrode layer and a drain electrode layer adjacent to the oxide semiconductor stack; a gate insulating film adjacent to the oxide semiconductor stack; and a gate electrode layer adjacent to the oxide semiconductor stack with the gate insulating film interposed therebetween, wherein, in the oxide semiconductor stack, a region which does not overlap the source electrode layer or the drain electrode layer has a higher oxygen concentration than a region which overlaps the source electrode layer or the drain electrode layer.