Semiconductor device and manufacturing method thereof

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

• forming a gate electrode over a substrate by a first photolithography process;
• forming a gate insulating layer over the gate electrode;
• forming a semiconductor layer including a first oxide semiconductor over the gate insulating layer;
• forming a source electrode and a drain electrode over the semiconductor layer by a second photolithography process;
• forming a layer including a second oxide semiconductor having a higher insulating property than the semiconductor layer over the source electrode and the drain electrode;
• forming a contact hole by selectively removing a portion of the layer that overlaps with the drain electrode and forming a groove portion by removing a portion of the layer, the semiconductor layer, and the gate insulating layer, by a third photolithography process;
• and
• forming a pixel electrode over the layer by a fourth photolithography process.

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

• forming a gate electrode over a substrate;
• forming a gate insulating layer over the gate electrode;
• forming a semiconductor layer including a first oxide semiconductor over the gate insulating layer;
• forming a source electrode and a drain electrode over the semiconductor layer;
• forming a layer including a second oxide semiconductor having a higher insulating property than the semiconductor layer over the source electrode and the drain electrode;
• forming a contact hole by selectively removing a portion of the layer that overlaps with the drain electrode;
• and
• forming a pixel electrode over the layer.