Low-pressure CMP for reliable porous low-k/Cu integration

We developed a method of low-pressure CMP for the Cu damascene process on 300-mm wafers in order to prevent porous low-k film from being damaged. A new failure criterion, the time to CMP-induced delamination, was defined and found to be strongly dependent on the Young's modulus of the low-k film. In order to integrate porous low-k films into Cu damascene interconnects (k<2.5), a modulus of more than 8 GPa is required to suppress CMP-induced damage. He-plasma treatment before cap-CVD film deposition was also effective to improve low-k film adhesion. Because the time to delamination is inversely proportional to the polishing pressure, a high-removal-rate process is important even in low-pressure CMP. With a goal of integrating low-k materials (k<2.0) we investigated the feasibility of ultra-low pressure CMP (at 0.8 psi).