Semiconductor device and method for manufacturing semiconductor device

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

• forming an oxide semiconductor layer over an insulating surface;
• forming a source electrode layer and a drain electrode layer over the oxide semiconductor layer;
• exposing a part of the oxide semiconductor layer to diluted hydrofluoric acid after the formation of the source electrode layer and the drain electrode layer;
• forming an insulating layer over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer;
• and
• forming a gate electrode layer over the insulating layer, the gate electrode layer overlapping with the oxide semiconductor layer,
• wherein a concentration of the diluted hydrofluoric acid is higher than 0.0001% and lower than or equal to 0.25%.

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

• forming a first electrode layer over an insulating surface;
• forming a first insulating layer over the first electrode layer;
• forming an oxide semiconductor layer over the first insulating layer;
• forming a source electrode layer and a drain electrode layer over the oxide semiconductor layer;
• exposing a part of the oxide semiconductor layer to diluted hydrofluoric acid after the formation of the source electrode layer and the drain electrode layer;
• forming a second insulating layer over the oxide semiconductor layer, the source electrode layer, and the drain electrode layer;
• and
• forming a second electrode layer over the second insulating layer, the second electrode layer overlapping with the oxide semiconductor layer,
• wherein a concentration of the diluted hydrofluoric acid is higher than 0.0001% and lower than or equal to 0.25%.