The Effects of Friction and Temperature in the Chemical-Mechanical Planarization Process.

Chemical-mechanical planarization (CMP) represents the preferred technology in which both chemical and mechanical interactions are combined to achieve global planarization/polishing of wafer surfaces (wafer patterns from metal with a selective layer, in this paper). CMP is a complex process of material removal process by friction, which interferes with numerous mechanical and chemical parameters. Compared with chemical parameters, mechanical parameters have a greater influence on the material removal rate ( MRR ). The mechanical parameters manifest by friction force ( F f ) and heat generated by friction in the CMP process. The F f can be estimated by its monitoring in the CMP process, and process temperature is obtained with help of an infrared rays (IR) sensor. Both the F f and the MRR increase by introducing colloidal silica (SiO 2 ) as an abrasive into the selective layer CMP slurry. The calculated wafer non-uniformity ( WNU ) was correlated with the friction coefficient ( COF ). The control of F f and of the slurry stability is important to maintain a good quality of planarization with optimal results, because F f participates in mechanical abrasion, and large F f may generate defects on the wafer surface. Additionally, the temperature generated by the F f increases as the SiO 2 concentration increases. The MRR of the selective layer into the CMP slurry showed a non-linear (Prestonian) behavior, useful not only to improve the planarization level but to improve its non-uniformity due to the various pressure distributions. The evaluation of the F f allowed the calculation of the friction energy ( E f ) to highlight the chemical contribution in selective-layer CMP, from which it derived an empirical model for the material removal amount ( MRA ) and validated by the CMP results. With the addition of abrasive nanoparticles into the CMP slurry, their concentration increased and the MRA of the selective layer improved; F f and MRR can be increased due to the number of chemisorbed active abrasive nanoparticles by the selective layer. Therefore, a single abrasive was considered to better understand the effect of SiO 2 concentration as an abrasive and of the MRR features depending on abrasive nanoparticle concentration. This paper highlights the correlation between friction and temperature of the SiO 2 slurry with CMP results, useful to examine the temperature distribution. All the MRRs depending on E f after planarization with various SiO 2 concentrations had a non-linear characteristic. The obtained results can help in developing a CMP process more effectively.