The Mechanism of Haze and Defectivity Reduction in a New Generation of High Performance Silicon Final Polishing Slurries
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1249-E03-03
The Mechanism of Haze and Defectivity Reduction in a New Generation of High Performance Silicon Final Polishing Slurries Michael L. White, Richard. Romine, Lamon Jones and William Ackerman Cabot Microelectronics Corp. 870 N. Commons Dr. Aurora, Il 60504
Abstract The mechanism of haze reduction during silicon polishing using a new generation of additives has been explored. These additives are thought to decrease haze by adsorbing to the wafer surface and increasing the activation energy of the reaction between the silanolates on the silica particle surface with the surface silicon. This leads to greater selectivity between the peaks and valleys resulting in a net decrease in surface roughness. Silicon substrates have been polished with high pH, silica based slurries for many years. There have been numerous reports of using water soluble polymers to improve the surface quality of polished silicon wafers.5-8 However, the introduction of ever-smaller features for advanced IC devices is driving the demand for slurries that result in improved surface quality. In this study, we will discuss a novel approach for reducing the particle defects and haze on silicon wafers. Such slurries can polish silicon surfaces to haze values below 0.030 ppm while maintaining removal rates of over 900 Å/min. This can enable a reduction in polishing time vs. commercially prevalent slurries and lead to lower slurry usage that can translate directly into a lower cost per wafer while yielding wafers with a superior surface finish.
Introduction 1-4
Experimental 8” diameter, p- boron doped, (100) silicon wafers were obtained from Silicon Valley Microelectronics. Wafers were polished on an IPEC Planar 472 at various down forces, table speeds and slurry flow rates. Removal rates were determined by weight differences to the nearest 0.00001g. The surface finish was analyzed with a Veeco D5000 AFM using a 5x5 µm spot size and a Wyko Veeco NT3300 white light interferometer. pH was measured with an Accumet Ap61 meter. Formulations were prepared by mixing colloidal silica under high shear with the appropriate chemical additives. Haze and defectivity (DCO and DCN) were measured via a KLA-Tencor SP1 TBI. Viscosities were determined using an Ubbelohde capillary viscometer held in a constant temperature bath at 25 oC. Haze is a measure of the light scattered off of a surface. Lower roughness translates into less scattered light and a lower haze. Residual particles scatter light and also increase haze. Typical haze values are less than 0.1 ppm in the narrow normal channel for a highly polished, reflective surface. It is possible to add certain agents that adsorb to the silicon wafer to form a steric barrier which requires energy for the particles to penetrate and therefore reduces the removal rate. We believe that the removal mechanism for polishing silicon wafers with silica involves the interfacial nucleophilic attack of the silanolates on the silicon atoms on
Discussion
the surface of the wafer. Evidence includes a correlation between the
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