Planar heater and semiconductor heat treatment apparatus provided with the heater

A plane heater comprising a carbon wire heating element arranged and sealed two-dimensionally inside a silica glass plate-like member and an earth electrode arranged and sealed two-dimensionally inside the silica glass plate-like member above said carbon wire heating element, wherein

• said carbon wire heating element is accommodated in a groove formed at a bottom face of a silica glass plate-like member and said earth electrode is accommodated in a recess formed at a top face of said silica glass plate-like member, and other silica glass plate-like members are fused to the top face and bottom face of said silica glass plate-like member to seal said carbon wire heating element and said earth electrode inside the silica glass plate-like member, and
• a plurality of projections are formed inside said recess and a plurality of through holes are formed in said earth electrode at predetermined intervals, and the projections formed inside said recess are inserted through the through holes of said earth electrode.