Semiconductor device

A method for fabricating a semiconductor device comprising:

• forming a first oxide by a sputtering method using a first target;
• forming a second oxide over the first oxide by the sputtering method using a second target;
• forming a first conductor and a second conductor over the second oxide;
• forming a third oxide over the second oxide, the first conductor, and the second conductor by the sputtering method using a third target;
• forming a fourth oxide over the third oxide by the sputtering method using a fourth target;
• forming an insulator over the fourth oxide;
• and
• forming a third conductor over the insulator,
• wherein the first to fourth targets each comprise two or more kinds of metal elements,
• wherein an atomic ratio of the metal elements in the first target and an atomic ratio of the metal elements in the fourth target are the same or similar to each other, and
• wherein an atomic ratio of the metal elements in the second target and an atomic ratio of the metal elements in the third target are the same or similar to each other.