Semiconductor device and method for manufacturing the same

A semiconductor device comprising:

• a first insulating layer including aluminum and oxygen;
• an oxide semiconductor layer over the first insulating layer;
• a gate insulating layer over the oxide semiconductor layer;
• a gate electrode over the gate insulating layer;
• a second insulating layer in direct contact with a top surface of the gate electrode, a first side surface of the gate electrode and a second side surface of the gate electrode, the second insulating layer containing aluminum and oxygen;
• a third insulating layer over the gate electrode, the third insulating layer containing silicon, oxygen and nitrogen;
• a fourth insulating layer over the second insulating layer and the third insulating layer, the fourth insulating layer containing aluminum and oxygen;
• a source electrode electrically connected to the oxide semiconductor layer;
• and
• a drain electrode electrically connected to the oxide semiconductor layer,
• wherein a distance between the gate electrode and a contact region in which the oxide semiconductor layer is in direct contact with the source electrode is greater than or equal to 1 nm and less than or equal to 30 nm,
• wherein the third insulating layer is in direct contact with a side surface of the second insulating layer.