In situ endpoint detection by pad temperature in chemical-mechanical polishing of copper overlay
As the number of metal levels and the wafer size increase, the global planarity and effective removal of metal overlay across the wafer becomes more crucial. Chemical-mechanical polishing (CMP) has been recognized essential to achieve this goal. Accurate in situ endpoint detection and monitoring method significantly improves the yield and throughput. Previous methods have been proposed, which either require the rearrangement of the machine set-up, or can only be implanted on certain types of machines. In this study, a model for pad temperature capable of predicting the endpoint of CMP in situ is established based on the total consumed kinematic energy between wafer and pad. Limited assumptions of thermal and kinematic conditions are made. The model of temperature rise uses the integral of the relative polishing speed and is verified by on-line measurement. Since the coefficient of friction between the pad and dielectric layer is distinguishably lower than that between the pad and the metal layer, the pad temperature increases milder than polishing the metal layer. In use of the proposed regression method applied to the measured temperature rise, the endpoint of the process can be detected.
The exothermic reaction and temperature measurement for tungsten CMP technology and its application on endpoint detection
A novel in-situ endpoint detection method used pad temperature measurement to control the polishing tungsten and barrier metal Ti/TiN is proposed. The metal chemical-mechanical polishing (CMP) process includes chemical reaction. It is an exothermic process as the polishing slurry reacts on tungsten and Ti/TiN films. Therefore, the pad temperature increases as tungsten and barrier metal films are polished, but will drop dramatically when metal layers are polished and touch the oxide layer. A non-contact thermal sensor system was installed on our CMP tool to measure the pad temperature. From the in-situ pad temperature curve, the endpoint can be detected clearly and the polishing process stops at the oxide layer. This method can also be used to study the reactions between the pad temperature curve and the effects of CMP process conditions such as down force, platen speed as well as polishing performance such as removal rate and uniformity.
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