Semiconductor device and method for manufacturing semiconductor device

A semiconductor device comprising:

• a first conductor;
• a first insulator over the first conductor;
• a first oxide over the first insulator;
• a second oxide over the first oxide;
• a second conductor and a third conductor over the second oxide, wherein the second conductor and the third conductor are separate from each other;
• a third oxide over the first insulator, the second oxide, the second conductor, and the third conductor;
• a second insulator over the third oxide;
• a fourth conductor at least part of which overlaps with the second oxide and which is over the second insulator;
• and
• a third insulator over the first insulator, the second insulator, and the fourth conductor,
• the second oxide comprising:
• a first region comprising an element M wherein M is one or more of Al, Ga, Si, B, Y, Ti, Fe, Ni, Ge, Zr, Mo, La, Ce, Nd, Hf, Ta, W, Mg, V, Be, and Cu;
• and
• a second region comprising one or both of In and Zn,
• wherein the first region and the second region are mixed to form a mosaic pattern,
• wherein the third oxide comprises In, Zn, and the element M,
• wherein the third oxide has a higher atomic ratio of the element M to In than the second oxide, and
• wherein side surfaces of the first oxide and the second oxide are covered with the third oxide.

A method for manufacturing a semiconductor device, comprising the steps of:

• forming a first conductor;
• forming a first insulator over the first conductor;
• performing first heat treatment after the first insulator is formed;
• forming a first oxide over the first insulator;
• forming a second oxide over the first oxide at a substrate temperature of higher than or equal to 100° C. and lower than 140° C. with a proportion of an oxygen gas of higher than or equal to 0% and lower than or equal to 30%;
• forming a second conductor and a third conductor over the second oxide so that the second conductor and the third conductor are separate from each other;
• forming a third oxide over the first insulator, the second oxide, the second conductor, and the third conductor at a substrate temperature of higher than or equal to room temperature and lower than 200° C. with a proportion of an oxygen gas of higher than or equal to 70% to cover the first oxide and the second oxide;
• forming a second insulator over the third oxide;
• performing second heat treatment after the second insulator is formed;
• forming a fourth conductor over the second insulator;
• performing third heat treatment after the fourth conductor is formed;
• etching part of the fourth conductor selectively after the third heat treatment to form a fifth conductor at least part of which overlaps with the second oxide;
• and
• forming a third insulator over the first insulator, the second insulator, and the fifth conductor.

A semiconductor device comprising:

• a first conductor;
• a first insulator over the first conductor;
• a first oxide over the first insulator;
• a second oxide over the first oxide;
• a second conductor and a third conductor over the second oxide, wherein the second conductor and the third conductor are separate from each other;
• a third oxide over the first insulator, the second oxide, the second conductor, and the third conductor;
• a second insulator over the third oxide;
• a fourth conductor at least part of which overlaps with the second oxide and which is over the second insulator;
• and
• a third insulator over the first insulator, the second insulator, and the fourth conductor,
• wherein side surfaces of the first oxide and the second oxide are covered with the third oxide,
• wherein part of the third oxide is in contact with a top surface of the first insulator,
• wherein part of the third insulator is in contact with the top surface of the first insulator,
• wherein one side end portion of the second conductor is substantially aligned with one side end portion of the first oxide and one side end portion of the second oxide, and
• wherein one side end portion of the third conductor is substantially aligned with the other side end portion of the first oxide and the other side end portion of the second oxide.