Semiconductor device and method of manufacturing the same

A semiconductor device, comprising:

• an active layer formed over a substrate having an insulating surface, said active layer having at least source and drain regions and a channel formation region therebetween;
• a gate insulating film formed on the surface of said active layer;
• and
• a gate electrode on said gate insulating film,
• wherein said active layer comprises needle-shaped or column-shaped crystals arranged in a direction substantially parallel with a length direction of said channel formation region;
• wherein said active layer contains a metal element for promoting crystallization at a concentration of not higher than 1×1018 atoms/cm3;
• and
• wherein S-value expressing electric characteristics is within 80±30 mV/dec for an N-channel type and 80±45 mV/dec for a P-channel type.

A semiconductor device manufactured by a method comprising the steps of:

• forming an amorphous semiconductor film comprising silicon over a substrate having an insulating surface;
• selectively forming a mask insulating film on said amorphous semiconductor film;
• allowing said amorphous semiconductor film to selectively keep a metal element for promoting crystallization;
• transforming at least a part of said amorphous semiconductor film into a crystalline semiconductor film by a first heat treatment;
• removing said mask insulating film;
• forming an active layer made of only said crystalline semiconductor film by patterning;
• forming a gate insulating film on said active layer;
• conducting a second heat treatment in an atmosphere containing a halogen element so that said metal element in said active layer is removed through gettering and a thermal oxidation film is formed at an interface between said active layer and said gate insulating film;
• and
• improving film qualities of said gate insulating film including said thermal oxidation film and a state of said interface by a third heat treatment,
• wherein said active layer comprises at least source and drain regions and a channel region therebetween,
• wherein said active layer comprises needle-shaped or column-shaped crystals arranged in a direction substantially parallel with a length direction of said channel formation region, and
• wherein an s-value of 80±30 mV/dec is obtained in an N-channel type transistor manufactured as said semiconductor device by said method, and an S-value of 80±45 mV/dec is obtained in a P-channel type transistor manufactured as said semiconductor device by said method.