Department of Chemical and Biological Engineering and ‡Department of Chemistry and Geochemistry, Colorado School of Mines , Golden, Colorado 80401, United States.
Langmuir. 2013 Oct 22;29(42):12915-23. doi: 10.1021/la402631p. Epub 2013 Oct 10.
Chemical mechanical polishing (CMP) is an essential technology used in the semiconductor industry to polish and planarize a variety of materials for the fabrication of microelectronic devices (e.g., computer chips). During the high shear (1,000,000 s(-1)) CMP process, it is hypothesized that individual slurry particles are driven together to form large agglomerates (≥0.5 μm), triggering a shear thickening effect. These shear-induced agglomerates are believed to cause defects during polishing. In this study, we examined the shear thickening of a 25 wt % fumed silica slurry with 0.17 M added KCl using in situ small-angle light scattering during rheological characterization (rheo-SALS). The salt-adjusted slurry displays a ~3-fold increase in viscosity at a critical shear rate of 20,000 s(-1) during a stepped shear rate ramp from 100 to 25,000 s(-1). As the shear rate is reduced back to 100 s(-1), the slurry displays irreversible thickening behavior with a final viscosity that is 100-times greater than the initial viscosity. Corresponding rheo-SALS images indicate the formation of micrometer scale structures (2-3 μm) that directly correlate with the discontinuous and irreversible shear thickening behavior of the fumed silica slurry; these micrometer scale structures are 10-times the nominal particle diameter (0.2 μm). The scattering patterns from the 25 wt % slurry were corroborated through rheo-SALS examination of 27 and 29 wt % slurries (C(KCl) = 0.1 M). All slurries, regardless of ionic strength and solids loading, display scattering patterns that are directly associated with the observed thickening behavior. Scattering was only observable during and after thickening (i.e., no scattering was detected in the absence of thickening). This work serves as the first in situ observation of micrometer scale structures within the fumed silica CMP slurry while under shear.
化学机械抛光（CMP）是半导体行业中用于抛光和平面化各种材料以制造微电子器件（例如计算机芯片）的关键技术。在高剪切（1,000,000 s(-1)）CMP 过程中，假设单个浆料颗粒被驱动在一起形成大的团聚体（≥0.5 μm），引发剪切增稠效应。这些剪切诱导的团聚体被认为会在抛光过程中造成缺陷。在这项研究中，我们使用原位小角光散射（rheo-SALS）在流变特性表征期间检查了添加 0.17 M KCl 的 25 wt % 烟硅石浆料的剪切增稠。在从 100 到 25,000 s(-1)的逐步剪切速率斜坡中，盐调整后的浆料在临界剪切速率 20,000 s(-1)下显示出粘度增加约 3 倍。当剪切速率降低回 100 s(-1)时，浆料显示出不可逆的增稠行为，最终粘度比初始粘度大 100 倍。相应的 rheo-SALS 图像表明形成了与烟硅石浆料的不连续和不可逆剪切增稠行为直接相关的微米级结构（2-3 μm）；这些微米级结构是标称粒径（0.2 μm）的 10 倍。通过对 27 和 29 wt %浆料（C(KCl) = 0.1 M）的 rheo-SALS 检查，验证了 25 wt %浆料的散射图案。所有浆料，无论离子强度和固体装载量如何，都显示出与观察到的增稠行为直接相关的散射图案。只有在增稠期间和之后才能观察到散射（即在没有增稠的情况下未检测到散射）。这项工作是在剪切下首次原位观察烟硅石 CMP 浆料中的微米级结构。
