Semiconductor device and method for producing the same

A method for producing a semiconductor device including a substrate and a thin film transistor supported by the substrate, the thin film transistor including a semiconductor layer, a gate electrode, a gate insulating layer formed between the gate electrode and the semiconductor layer, and a source electrode and a drain electrode that are electrically connected to the semiconductor layer, the semiconductor layer having a stacked layer structure including a first oxide semiconductor layer and a second oxide semiconductor layer,

• the production method comprising:
• Step (A) of forming a first oxide semiconductor film including In, Ga, Zn, and Sn and being amorphous;
• Step (B) of forming, on the first oxide semiconductor film, a second oxide semiconductor film including In, Ga, Zn, and Sn, having a lower mobility than the first oxide semiconductor film, and being amorphous;
• and
• Step (C) of patterning stacked semiconductor films including the first oxide semiconductor film and the second oxide semiconductor film to form, respectively from the first oxide semiconductor film and the second oxide semiconductor film, the first oxide semiconductor layer and the second oxide semiconductor layer,
• wherein a Sn atomic ratio R1 relative to all metal elements in the first oxide semiconductor layer and a Sn atomic ratio R2 relative to all metal elements in the second oxide semiconductor layer satisfy
• 0.8×R1≤R2≤1.2×R1.