Semiconductor device

A semiconductor device comprising:

• an insulating film comprising silicon;
• an oxide semiconductor film over the insulating film;
• a gate insulating film over the oxide semiconductor film;
• a gate electrode over the gate insulating film;
• a source electrode electrically connected to the oxide semiconductor film;
• and
• a drain electrode electrically connected to the oxide semiconductor film,
• wherein the oxide semiconductor film comprises:
• a first region in contact with the insulating film;
• and
• a second region over the first region,
• wherein a concentration of silicon in the first region is lower than or equal to 1.0 at. %,
• wherein the first region comprises a crystal portion, and
• wherein a c-axis in the crystal portion is aligned in a direction substantially parallel to a normal vector of a surface of the insulating film.

A semiconductor device comprising:

• an insulating film comprising silicon;
• an oxide semiconductor film over the insulating film;
• a gate insulating film over the oxide semiconductor film;
• a gate electrode over the gate insulating film;
• a source electrode electrically connected to the oxide semiconductor film;
• and
• a drain electrode electrically connected to the oxide semiconductor film,
• wherein the oxide semiconductor film comprises:
• a first region in contact with the insulating film;
• and
• a second region over the first region,
• wherein a concentration of silicon in the first region is lower than or equal to 1.0 at. %,
• wherein the first region comprises a crystal portion,
• wherein a c-axis in the crystal portion is aligned in a direction substantially parallel to a normal vector of a surface of the insulating film, and
• wherein a concentration of carbon in the first region is lower than or equal to 1.0×1020 atoms/cm3.

A semiconductor device comprising:

• an insulating film comprising silicon;
• an oxide semiconductor film over the insulating film;
• a gate insulating film over the oxide semiconductor film;
• a gate electrode over the gate insulating film;
• a source electrode electrically connected to the oxide semiconductor film;
• and
• a drain electrode electrically connected to the oxide semiconductor film,
• wherein the oxide semiconductor film comprises:
• a first region in contact with the insulating film;
• and
• a second region over the first region,
• wherein a concentration of silicon in the first region is lower than or equal to 1.0 at. %,
• wherein the first region comprises a crystal portion,
• wherein a c-axis in the crystal portion is aligned in a direction substantially parallel to a normal vector of a surface of the insulating film,
• wherein a concentration of carbon in the first region is lower than or equal to 1.0×1020 atoms/cm3, and
• wherein a thickness of the first region is less than or equal to 5 nm.