Semiconductor device and manufacturing method thereof

A semiconductor device comprising:

• a first insulator over a substrate;
• a first oxide over the first insulator;
• a second oxide in contact with at least a portion of a top surface of the first oxide;
• a second insulator over the second oxide;
• a first conductor over the second insulator;
• a second conductor over the first conductor;
• a third insulator over the second conductor;
• a fourth insulator in contact with side surfaces of the second insulator, the first conductor, the second conductor, and the third insulator;
• and
• a fifth insulator in contact with a top surface of the second oxide and a side surface of the fourth insulator,
• wherein the third insulator comprises aluminum oxide or hafnium oxide,
• wherein the fourth insulator comprises aluminum oxide or hafnium oxide,
• wherein a thickness of the fourth insulator is greater than or equal to 1 nm and smaller than or equal to 20 nm, and
• wherein a top surface of the fourth insulator is substantially aligned with a top surface of the third insulator.