Chemical Wear of Cu CMP
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Chemical Wear of Cu CMP Hong Liang, University of Alaska Fairbanks; Jean-Michel Martin and Beatrice Vacher, Ecole Centrale de Lyon; and Vlasta Brusic, Cabot Corporation In this work, we used surface analysis techniques, such as a field-emission highresolution analytical TEM, X-ray spectroscopy, and XPS to analyze abrasive particles after polishing. Results showed evidence of copper oxide (Cu2O) in the polished slurry. However, there was no metallic crystalline copper detected. After comparing these data with the results obtained from our electro-chemical experiments, we propose two possible chemical wear mechanisms in Cu CMP.
Introduction Chemical mechanical polishing (CMP) is a synergetic process that undergoes kinetic combination of three different components. Investigation in understanding CMP mechanisms has been focused on slurries, quality and defects on wafers, and pad behavior. Previous studies in effects of abrasive particles on CMP were done by extrapolating and estimating existing data. It was concluded that particles abraded a soft surface layer from wafer surfaces1. The metal (tungsten) CMP mechanisms have been accepted by many researchers as the passivation of a metal surface2 but other researchers have found contradictory results3. These indicate the need for further investigation. The previous studies have been mainly focused on the chemical nature of CMP processes. Therefore, a broader view or aspects should be taken. The interactions between abrasive particles and wafer surfaces during polishing result in changes on the contacted surfaces and in the chemical bonding types. Pioneer work has been done on tribochemical wear 4, 5, 6. An understanding was established that chemical reactivity affects wear significantly. Under stress, chemical reactions proceed differently from those without stress7. Due to synergetic processes, CMP may posses more than one mechanism. In order to understand the effect of mechanical components on CMP, we characterized the reaction products by using the state-of-the-art surface analysis techniques. These techniques were proven being effective providing key information for understanding CMP.
Experimental Copper CMP was performed on a modified bench-type disc-on-pad polisher. The frictional force, displacement, and applied pressure can be measured during polishing. A 2" square copper block was mounted on a self-rotating disk. The polished pad, used as IC1000, was mounted on a 4" rotating disc. Particles with a high pH (~ 10) in the deionized water were used to polish the copper block. The average pressure applied was 5 psi. The disk speed was 20 rpm. During polishing, slurry was collected for analysis. E2.5.1
A field-emission high-resolution analytical TEM and X-ray spectroscopy were used to analyze the abrasive particles after polishing. For comparison, abrasive particles before and after polishing were compared side-by-side. The X-ray photoelectron spectroscopy (XPS) was used for chemical analysis. The TEM and XPS have been used by Varlot et. al. at the Ecole Centrale de
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