Semiconductor device and method for manufacturing semiconductor device

A semiconductor device comprising a plurality of transistors, wherein the plurality of transistors each comprise:

• a first insulator;
• a first oxide over the first insulator;
• a first conductor, a second conductor, and a second oxide over the first oxide, the second oxide being between the first conductor and the second conductor;
• a second insulator over the second oxide;
• and
• a third conductor over the second insulator,
• wherein a top surface the first oxide in a region overlapping with the third conductor is at a lower position than a position of a top surface of the first oxide in a region overlapping with the first conductor,
• wherein the first oxide in the region overlapping with the third conductor comprises a curved surface between a side surface and the top surface of the first oxide, and
• wherein in Id-Vg characteristics of the plurality of transistors, a standard deviation σ of Vsh is less than 60 mV.

A semiconductor device comprising a transistor,

• wherein the transistor comprises:
• a first insulator;
• a first oxide over the first insulator;
• a first conductor, a second conductor, and a second oxide over the first oxide, the second oxide being between the first conductor and the second conductor;
• a second insulator over the second oxide;
• a third conductor over the second insulator;
• and
• a third insulator in contact with a top surface of the first conductor, a top surface of the second conductor, and a part of a side surface of the first oxide,
• wherein in a channel width of the transistor, a length of a bottom surface of the first oxide in a region overlapping with the first conductor is larger than a length of a bottom surface of the first oxide in a region overlapping with the third conductor,
• wherein the first oxide in the region overlapping with the third conductor comprises a curved surface between the side surface and a top surface of the first oxide,
• wherein the first oxide comprises indium, an element M, and zinc,
• wherein the element M is any one of gallium, yttrium, and tin,
• wherein the third insulator comprises an element that is to be an impurity of the first oxide, and
• wherein a concentration ratio of the element to the element M at the side surface of the first oxide in the region overlapping with the third conductor is lower than a concentration ratio of the element to the element M at the side surface of the first oxide in a region overlapping with the first conductor.