Semiconductor device and method for manufacturing semiconductor device

A semiconductor device comprising:

• a first insulating layer;
• a second insulating layer;
• a third insulating layer;
• and
• a transistor comprising:
• a semiconductor layer;
• a first conductive layer;
• a second conductive layer;
• a third conductive layer;
• a fourth insulating layer;
• a fifth insulating layer;
• and
• a sixth insulating layer,
• wherein the first conductive layer, the first insulating layer, the second conductive layer, the fifth insulating layer, the second insulating layer, and the third insulating layer are stacked in this order and overlap with one another,
• wherein the first insulating layer, the second conductive layer, the second insulating layer, and the third insulating layer comprise an opening reaching the first conductive layer,
• wherein the first insulating layer comprises a portion protruding in the opening more than a side surface of the second conductive layer, a side surface of the second insulating layer, and a side surface of the third insulating layer,
• wherein the fifth insulating layer is in contact with a top surface of the second conductive layer and side surfaces including the side surface of the second conductive layer,
• wherein the fourth insulating layer is in contact with a top surface of the first insulating layer in the opening, a side surface of the fifth insulating layer in the opening, and the side surface of the second insulating layer in the opening,
• wherein the semiconductor layer is in contact with a top surface of the first conductive layer in the opening, a side surface of the fourth insulating layer in the opening, and a top surface of the third insulating layer,
• wherein the sixth insulating layer is in contact with a top surface of the semiconductor layer,
• wherein the third conductive layer is placed over the sixth insulating layer to overlap with the opening in a plan view,
• wherein the second conductive layer comprises a first element, and
• wherein the fifth insulating layer comprises an oxide of the first element.

A method for manufacturing a semiconductor device, comprising:

• forming a first conductive layer;
• forming a first insulating film over the first conductive layer;
• forming a second conductive layer over the first insulating film to comprise a region overlapping with the first conductive layer;
• oxidizing a surface of the second conductive layer, thereby forming a first insulating layer on a top surface and a side surface of the second conductive layer;
• forming a second insulating film, a third insulating film, and a third conductive layer in this order over the first insulating film and the first insulating layer;
• partly removing the third conductive layer, the third insulating film, the second insulating film, the first insulating layer, and the second conductive layer, thereby forming a first opening and forming a fourth conductive layer, a second insulating layer, a third insulating layer, a fourth insulating layer, and a fifth conductive layer;
• oxidizing a side surface of the fifth conductive layer exposed in the first opening, thereby forming the fourth insulating layer on the side surface of the fifth conductive layer;
• forming a fourth insulating film in contact with a top surface of the fourth conductive layer, a side surface of the fourth conductive layer in the first opening, a side surface of the second insulating layer in the first opening, a side surface of the third insulating layer in the first opening, a side surface of the fourth insulating layer in the first opening, and a top surface of the first insulating film in the first opening;
• partly removing the fourth insulating film and the first insulating film, thereby forming a second opening reaching the first conductive layer and forming a fifth insulating layer comprising a protruding portion in the second opening and a sixth insulating layer in contact with the side surface of the fourth conductive layer in the second opening, the side surface of the second insulating layer in the second opening, the side surface of the third insulating layer in the second opening, the side surface of the fourth insulating layer in the second opening, and a top surface of the protruding portion in the second opening;
• forming a semiconductor layer in contact with the top surface of the fourth conductive layer, a side surface of the sixth insulating layer in the second opening, and a top surface of the first conductive layer in the second opening;
• forming a seventh insulating layer in contact with a top surface and a side surface of the semiconductor layer, the top surface of the fourth conductive layer, and a top surface of the second insulating layer;
• and
• forming, over the seventh insulating layer, a sixth conductive layer comprising a region overlapping with the semiconductor layer and the sixth insulating layer in a plan view.