Particle adhesion and removal mechanisms in post-CMP cleaning processes

Chemical mechanical polishing (CMP) is considered as the paradigm shift that enabled optical photolithography to continue down to 0.12 mum. Currently, the polishing physics is not well defined though it is known that the nature of the process makes particle removal after CMP difficult and necessary. It is important to understand the particle adhesion mechanisms resulting from the polishing process and the effect of the adhering force on particle removal in post-CMP cleaning processes. In this paper, strong particle adhesion is shown to be caused by chemical reactions (after initial hydrogen bonding) that take place in the presence of moisture and long aging time. In particle removal using brush cleaning, contact between the particle and the brush is essential to the removal of submicron particles. In noncontact mode, 0.1-mum particle can hardly be removed when the brush is more than 1 mumaway from the particle. While in full contact mode, removal is possible for a 0.1-mum particle at the investigated brush rotational speeds. The experimental data shows that high removal efficiency (low number of defects) is possible with a high brush pressure and a short cleaning time.