Wafer processing method

A wafer processing method for processing a back side of a wafer having a plurality of devices on a front side thereof, the plurality of devices being separated from each other by a plurality of crossing division lines formed on the front side of the wafer, the wafer processing method comprising:

• a wafer providing step of placing a thermoplastic polymer sheet on an upper surface of a substrate for supporting the wafer, and placing the wafer on an upper surface of the thermoplastic polymer sheet in a condition where the back side of the wafer is exposed upward;
• a thermocompression bonding step of setting the wafer placed through the polymer sheet on the substrate in an enclosed environment after performing the wafer providing step, next evacuating the enclosed environment, and next heating the polymer sheet as applying a pressure to the wafer, thereby uniting the wafer through the polymer sheet to the substrate by thermocompression bonding;
• a back processing step of processing the back side of the wafer after performing the thermocompression bonding step;
• and
• a separating step of separating the wafer from the polymer sheet after performing the back processing step.