Chemical Mechanical Cleaning for Post-CMP Applications: Defects and Metals Results
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Abstract Double-sided brush scrubbing has become a dominant method for post-CMP cleaning applications. Chemicals delivered in-situ with brush scrubbing greatly enhance the cleaning capabilities. In this paper, the effect of dilute HF on reducing particulate defects and trace metal contamination on polished oxide surface is studied using a HF-compatible double-sided scrubber. AFM data on the interaction of dilute HF with oxide / tungsten plug array after tungsten CMP is also presented. Scrubbing with dilute HF is shown to be highly effective is removing slurry agglomerates that strongly adhere to the post-CMP oxide film.
Introduction In recent years chemical mechanical polishing (CMP) has rapidly been adopted for global planarization of silicon wafers during the process of sub-half micron integrated circuit fabrication. CMP is an inherently dirty process in which wafers are exposed to various sources of contamination.' If not successfully removed, defects due to the CMP process can contribute to yield loss in device manufacturing. Therefore, post-CMP cleaning is an integral part of a successful manufacturable planarization process. For many high volume production fabs, the cleaning process of choice is mechanical brush scrubbing using double-sided scrubbers.2' 3"4 CMP related surface contamination primarily consists of particles and trace metals. Mechanical brush scrubbing in aqueous environment using soft PVA (Polyvinyl Alcohol) material is well suited to remove residual slurry particles from polished wafer surface.2 ' 5 Chemicals delivered insitu during brush scrubbing greatly enhance the cleaning capabilities without compromising throughput. 5,6 In this paper, we present data on the effect of dilute HF on oxide and tungsten CMP cleaning. Polishing of oxide layers with silica based slurry may result in different final defect levels depending on the polishing process.' The cleaning strategy has to accommodate these variations and provide acceptable defect levels for all cases. Brush scrubbing with dilute HF is highly effective in removing slurry particles and reducing metallic contamination on polished oxide surfaces.6 As a result of oxide removal and pH change, trace metal and mobile ion concentrations on post-CMP oxide film are significantly reduced. Particles that adhere strongly to the surface of oxide film can be removed by using dilute HF during scrubbing. Experimental data on the optimization of the chemical and mechanical scrubbing process is presented for oxide CMP. Compared to oxide CMP, tungsten CMP presents additional challenges for post-CMP cleaning. Typically, alumina based slurry is used during the W-CMP process. In a neutral pH environment, the surface of alumina particle is positively charged, while the surfaces of Si0 2 film and PVA material are negatively charged. The electrostatic attraction causes alumina particles 137
Mat. Res. Soc. Symp. Proc. Vol. 477 0 1997 Materials Research Society
difficult to remove from wafer surface and difficult to rinse away from the PVA brush. In basic environm
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