Semiconductor device, electronic device, and manufacturing method thereof

A semiconductor device comprising:

• a first semiconductor layer over an insulator, the first semiconductor layer having at least a channel formation region and low-concentration impurity regions;
• a gate insulating film over the first semiconductor layer;
• a gate electrode over the gate insulating film;
• sidewalls being in contact with side surfaces of the gate electrode, end portions of the sidewalls being extended over the first semiconductor layer;
• and
• second semiconductor layers being in contact with and stacked over the first semiconductor layer and being in contact with or covering at least a part of the end portions of the sidewalls, the second semiconductor layers having high-concentration impurity regions,
• wherein the channel formation region overlaps with the gate electrode and the low-concentration impurity regions overlap with the sidewalls.

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

• forming a first semiconductor layer over an insulator;
• forming a gate insulating film and a gate electrode which are stacked over the first semiconductor layer in this order;
• adding an impurity element imparting one conductivity to the first semiconductor layer using the gate electrode as a mask to form low-concentration impurity regions in the first semiconductor layer;
• forming sidewalls which are in contact with side surfaces of the gate electrode and of which end portions are extended over the first semiconductor layer;
• forming a semiconductor film covering the gate electrode, the sidewalls, the end portions of the sidewalls, and the first semiconductor layer;
• etching the semiconductor film using a resist mask to form two second semiconductor layers so that the second semiconductor layers are in contact with and stacked over the first semiconductor layer and are in contact with or cover at least a part of the end portions;
• and
• adding an impurity element imparting the one conductivity to form high-concentration impurity regions in the first semiconductor layer and the second semiconductor layers.

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

• forming a first semiconductor layer over an insulator;
• forming a gate insulating film, a gate electrode, and an insulating layer which are stacked over the first semiconductor layer in this order;
• adding an impurity element imparting one conductivity to the first semiconductor layer using the gate electrode as a mask to form low-concentration impurity regions in the first semiconductor layer;
• forming sidewalls on side surfaces of the gate electrode;
• forming a semiconductor film covering the insulating layer, the sidewalls, and the first semiconductor layer;
• forming a negative resist covering the semiconductor film;
• forming a resist mask by performing light exposure from a rear surface side of the insulator to the negative resist using the gate electrode as a mask;
• etching the semiconductor film using the resist mask;
• patterning the semiconductor film which is etched to form two second semiconductor layers so that the second semiconductor layers are in contact with and stacked over the first semiconductor layer and are in contact with or cover a part of the sidewalls;
• and
• adding an impurity element imparting the one conductivity to form high-concentration impurity regions in at least the second semiconductor layers.