In semiconductor manufacturing, the chemical mechanical polishing (or CMP) step is used to planarize, or create a level topography, between each layer of the interconnect structure as the device is built. The polishing slurries used in CMP are key to getting good results, as the tiny particles contained in the slurries provide the abrasives needed to achieve the final surface results. The trick, though, is to keep the working particles in the slurry unchanged during the polishing process, and at the same time, remove any large slurry particle agglomerations which cause uneven planarization conditions that are more likely to cause defects in the device layers. Gel-type particles in the slurry can also easily form during the CMP process, causing defects of their own. Finally, in order to achieve the desired results, both particle and gel defectivity causes must be managed without reducing the slurry flow rate and increasing the pressure drop leave across the filter. Flow rate is a measure of the volume of liquid that passes through the filter in a period of time. Pressure drop is a measure of the pressure required to achieve a given flow rate. Reducing pressure drop can be achieved with innovative media designs and new materials of construction.
CMP filtration media, such as that manufactured by Entegris, has long been used in the CMP process to maintain the desired slurry characteristics. As device geometries shrink, however, so does the abrasive size used in advanced slurries, moving generally towards sub-50 nm particle size, and to single-digit nanometer dimensions for some specific applications. As the size of the abrasive particle decreases, however, the potential for slurry-caused defects increases, and so the CMP filter retention rating has to be lowered to tighter and tighter pore size, along with the filter design (which often now requires multiple layers of media in order to be most effective). However, these CMP filters for the most advanced polishing slurries will typically result in a decrease in the slurry flow rate when using standard media types.
For advanced polishing slurries, Entegris has developed a Nano Melt Blown (NMB) filtration media with improved media porosity that addresses the problems associated with flow rate reductions during filtration. The risk of large particle agglomeration is also reduced with NMB media, as the "shear" effect is greatly reduced. The high particle holding capacity of the NMB media also extends filter life, reducing the overall cost of ownership in the filtration process. The Entegris product can also be used with tighter retention ratings, and enable filtration in bulk/chemical delivery system applications where a higher particle loading capacity is required.
Entegris planargard NMB filter
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